Archive for the ‘Some Jerk On The Internet’ Category
The Fairytale of a Static Rate of Autism Part 5 – The Prevalence Jackpot Versus The Prevalence Hookup, Futilely Struggling To Making Sense Out of Static, And How Journey Autism Flavors Our Path Of Moving Forward
Posted on: April 17, 2013
Hello friends –
There used to be a poker room about twenty miles from my home; it sat above a run down greyhound racing track and smelled like an old shoe on the best day. But they had poker. They hosted an accumulating jackpot hand, usually worth a couple of thousand dollars, sometimes quite a lot more, which you could win if you got a royal flush in the current suit; i.e., if the suit was hearts, and you wound up with 10-J-Q-K-A hearts, you’d win the Jackpot. This could lead to some unusual cost/reward analysis scenarios.
Let’s say you sit down to play and buy in for a hundred dollars. Then, three hands later, you look at your two hole cards and you have 10-J hearts. Not really a great hand, but if the board winds up showing Q-K-A hearts somewhere in the next five cards, you win fifteen thousand dollars (or whatever the Jackpot had accumulated to). Almost everyone folds, but before you get a chance to see the next three cards for the two measly dollars you put up as a blind, an aggressive, serial over-better to your right raises to fifteen dollars. You are in a tough spot, you know the guy bets like crazy anytime he thinks he can steal a pot, but you still are losing to anyone with a queen. If you had 10-J spades, or clubs, or mixed, or (nearly) whatever else, this is easy; you dump your shitty cards. But with your two royal heart cards, you *could* win the jackpot; your odds still totally suck, even if you were getting paid off a thousand to one you still didn’t have the ‘right’ odds to make the call, but if you inhabit a place where losing fifteen dollars won’t kill you, but winning fifteen thousand would definitely be a game changer, the magnitude of the potential winnings must be part of your decision making process.
I called the raise a few times, but never hit the jackpot. Or even came close.
I keep coming back to the idea of incorporating the scale of potential outcomes when I think about the non event of the hilarious prevalence numbers that came out a while, one in fifty with ‘autism’. Nobody outside of Journey Autism fucking cared and the responses were depressingly predictable; the media and the Internet skeptics went ‘full awareness’, and found nothing of any alarm in these numbers, the Internet vaccine crazies went ‘full autism’, and assumed the numbers were solely comprised of individuals who would need 24×7 assistance for forever. It was all a big joke. Haha.
I don’t know how large the real increase in autism is (the older parental age data tells us unambiguously that some of the increase is non-imaginary), but I do know that as our best efforts at figuring this thing out has left us skipping from one in two hundred and fifty, to one in a fifty in eight short years. To my eye, this means a real increase of fifty percent (or more!) could easily be hiding in the static and we’d never know. Most everyone doesn’t seem to care, that is the way of the Prevalence Hookup, quickly embracing whatever prevalence numbers come out, coupling until a set of newer, bigger, even more ‘greater awareness’ numbers come along.
But my thoughts continue to be formed by concept of a sort of missed jackpot opportunity when I see a sense of complacency about our ever growing autism population; it isn’t that I don’t believe that diagnostic changes and the watering down of what a diagnosis means in terms of life skills aren’t affecting rates, those factors are clearly at play, but the ramifications of just “some” of the increase being real seems like a big, big, big deal to me. When your population of interest is every child, a small real increase means a lot of individual children are affected. Sure, it is, possible that older parental age is the only recent development that is affecting rates upward, with all of the rest being diagnostics, but I find little comfort in this notion. If the soft social scientists are wrong, even a little, and there is a true increase in incidence, we may come to regret the solace provided by our collective bobbleheading at the mantra of ‘greater awareness’, for it enabled us to waste a great amount of precious time.
The thing is, it doesn’t really cost us that fucking much to apply more resources to the unimportant, nagging question on the neurodevelopment of a generation of infants. In 2006, Bush signed the ‘Combating Autism Act’, a bill included a billion of dollars for ‘research, surveillance, and treatment’. That’s two hundred million a year. Last year, The Avengers, a stupid and shitty movie, made over a billion dollars. Now, I know there are other funding sources for research, surveillance, and treatment, but there were also a lot of other stupid movies.
I believe that this prioritization is the equivalent of folding 10-J hearts to a dinky four dollar raise; the knowledge we could gain from a relatively small outlay is worth a lot. We shouldn’t be worrying about the cost, we should be considering the payoff; the question we are trying to understand, “are today’s infants neurobiologically different than infants of the last generation?” has a difficult to understate payoff. We shouldn’t be embracing reasons to stop playing, we should chomping at the bit to see the next three cards. This is an easy call.
And yet, there was a collective yawn when the CDC announced 2%.
Funny enough, it was just a few years ago that the UK NHS study of adults found a prevalence of 1%, a finding which was heralded as remarkably strong evidence that autism rates are stable (at the time, 1% was the general value for US children. Oh well.). For some reason, the robustness of the NHS adult findings didn’t cause anyone to exclaim that there is a sort of epidemic-lite, what with US kids having autism as twice the rate as NHS adults. It was a classic case of doublethink; US kids have autism at 2%, England adults have autism at 1%, and autism rates are stable. (Believing that any of the numbers have validity might be closer to triplethink!)
A while ago I saw an interview with Fombonne on the SFARI site that contained the unsurprising byline: ‘Eric Fombonne says that the new CDC report does not necessarily mean that prevalence is increasing’. [Note: This was BEFORE the 2% numbers were reported!] Anyway, he made some interesting points about the messiness of the autism data showing how silly the state by state numbers are; Utah has four times the cases that Alabama does, and utilized different diagnostic methods. In the text of the interview, he reveals Utah also had very low levels of MR (~ 13% instead of ~ 28%), AND had a creepy low male to female ratio. Either there is something really weird going on in Utah, or the ‘numbers’ from Utah and Alabama are not measuring the same thing. It could also be that the numbers are measuring some of the same thing, and there are a couple of weird things going on in Utah (heh). But the bigger point should be that we shouldn’t expect to get a decent understanding of autism rates at a national level by clumping together Alabama numbers, Utah numbers, and whatever other numbers, shaking up them up, and averaging them out. Maybe the headline ought to read, ‘Pretty much somewhere between half a percent, and two percent of children might have something a psychologist, or a doctor, or both, have something called autism, the manifestations and lifelong impact of which vary considerably individually and regionally’, or maybe ‘Autism Rates: Your guess is as good as ours!’.
I don’t trust any set of numbers more than an educated stab in the dark.
[Note: for a slightly different take on ADDM numbers, you can see this interview on SFARI, where Walter Zahorodny reports that detailed analysis of NJ data indicates a likely real increase in rates. Doh!]
I began to wonder; if almost nobody really seems worried about an ‘epidemic lite’, if no almost no one is alarmed that the confidence intervals in our data could incorporate huge numbers of actual people, why am I so concerned? Is my version of the precautionary principle overly cautious? I don’t know the answer to these questions, but I think that part of the answer lies within my journey autism, watching my son’s challenges (and triumphs) unfold, and the knowledge that whatever we find about autism incidence, he will be reliant on other people for his survival for his entire life. That is the gift autism has given him; it doesn’t mean he can’t be happy, it doesn’t mean he can’t experience love, but so far, we cannot detect that autism has provided him anything other than near debilitating OCD, an imperfect sense of dangerous situations, and a lifelong requirement of the kindness and capabilities of others.
I am filled with a pervasive and soul crushing sadness at the possibility of one ‘extra’ child having the same challenges because of changes we have collectively made to the environment, and that is the heart of the semantic dance over how much of the increase is real. That is the Jackpot.
But, your mileage may vary. I know that there are some parents and people out there who have challenges as heavy as my son’s, and they don’t share my sense of panic over the issue. A lot of people credit their autism with benefits. I won’t discount their experiences. Part of the reason we don’t see eye to eye may be that we look at the same question, but see different risks, and different payoffs.
– pD
Piling Up Small Changes, The Selective Skepticism Of Replacing One Fallacy With Another, And The Seductive Lure of Hubris Versus The Dispassionate Rules Of Nature
Posted on: September 28, 2012
Hello friends –
We keep on finding things that seem to very gently alter developmental trajectory towards (or away from) an eventual diagnosis of autism; a genetic variant here or there, an environmental exposure, or one of our very many experiments in cultural engineering. When these nudges are founded on genetic variances, they are often referred to as “low penetrance” risk factors; here is a snipet from the wiki definition for “Penetrance”
An allele with low penetrance will only sometimes produce the symptom or trait with which it has been associated at a detectable level.
I would argue, and have previously on this blog, that there isn’t a good reason that the descriptive of low penetrance should be relegated solely to genetic inputs. The ‘non-genetic’ factors we seem to have associated with autism risk, or protection, seem to inherit the same quality of a low grade impact; the risk of an autism diagnosis isn’t altered by too much, but instead, just a little.
There are a great number of examples of environmental impacts that seem to follow a low penetrance model of effect; maternal obesity, paternal age, cesarean section, maternal asthma, maternal folate ingestion [protective!], maternal use of anti-depressants (or being depressed?), low birth weight, and some perhaps some drugs given during pregnancy.
[Please, please note: I’m not “blaming the mother” here, but we do not have the luxury of invoking Bettleheim as a mechanism for avoiding evident truths. A dispassionate analysis of the data mandates we accept that the prenatal environment is critical.
If you think that some percentage of the autism ‘epidemic’ is real, you should realize that this issue is too important to be scuttled by emotional hotspots. You cannot blame yourself for things that were unknown to you during your pregnancy. If, instead, you don’t think autism rates have changed, none of the above impacts can be meaningful. Finally, if you believe that autism is more gift than disorder, then you aren’t getting blamed for anything anyways.]
Unfortunately, a mixture of subtle changes makes for a messy situation for our researchers for a few reasons; environmental studies contain a difficult to contend with set of confounders; knowing what to measure, when to measure it, and the often times necessary evil of usage of self reporting, computer models, or other proxies for exposure measurements. Making things even worse, it is biologically plausible, indeed, mandatory, that low penetrant effects operate with each other. What we will eventually need to be working on, for example, is determining the specific genetic dispositions that act in concert with a low birth weight and with gestational anti-depressant exposure to perturb neurodevelopment toward autism. That’s a tough thing to do.
Throwing this kind of disparate data into a blender at study time looks to be largely beyond our current capacities; researchers are struggling to identify single gene-environment interactions, for example, MET-C/pollutants, or the terrifying notion of RORA demythlation/endocrine disruptors interacting together. Looking at more, or a handful, as is likely necessary, is a long ways off.
I’ve been thinking about the intersection of these two things lately; our relative inability to evaluate for several, subtle, interacting forces, with the growing evidence that a great many mysterious conditions, including autism, seem to be governed by lots of small things occurring differently. I am left with the idea that are woefully unready to understand the participating factors in any particular case of autism, with similar reservations regarding our ability to know how much, if any, of the autism ‘epidemic’ is real.
A few weeks ago, there was an Op-Ed in the New York Times that speculated on the link between an in-utero environment characterized by increased inflammation and an eventual diagnosis of autism. I was largely in agreement with Moises Velasquez-Manoff on a the basic premise of his argument; especially regarding the state of the science on the immune findings in the autism realm, the use of helminths, not so much. A very widely read response by Emily Willingham accused the author of the piece of invoking a naturalist theory of the past:
Whether he means to or not, Velasquez-Manoff then echoes one of the favorite refrains of the anti-vaccine movement, that back when the world was a beautiful place of dirty, worm-infested children, clean water, 100% breastfeeding, and no television, it was a place where the immune system could do its work peacefully and with presumably Zen-like calm, weeding out the weak among us and leaving behind the strong.
I don’t think that the NYT article did anything of the sort, the author merely stated that there seem to be fewer signs of immune dysregulation and autoimmune conditions in some types of living conditions.
Then, a few weeks later, a widely publicized metadata study on organic eating came out. Again, the skeptics were ready to pummel the bruised body of the naturalistic fallacy, in this case, Stephen Novella at SBM:
Environmental claims for organic farming are complex and controversial – I will just say that such claims largely fall prey to the naturalistic and false dichotomy fallacies.
Stephen Novella’s version here is terse, but I think it is fair to say that in this context, the idea is that that if something is labeled as ‘natural’, that it then must be somehow superior to a ‘non-natural’ alternative, is a fair characterization of a naturalistic fallacy.
[The masochist could read through a few comments on that thread to see my take on the organic/non organic study; but the TL;DR version is, the study could have just as easily been titled, “Evaluations of Organic Eating Insufficiently Powered Or Designed To Know More Than The Most Primitive Endpoints, At Best”. Here is an NPR transcript where the presenter is a little more up front in that the state of the science is that health benefits have not been evaluated for.
But what I should point out here is that the studies of people were very limited. They were short-term and, like, narrowly focused. So they would look at pregnant women, for instance, and say, are pregnant women eating organic, are their children – did their children have left eczema or allergic conditions? So these are sort of narrowly focused studies. They were short-term, and there weren’t very many of them.
One of the few human studies in this metadata analysis involved a dietary intervention of one apple. What we have is a lack of evaluation, as opposed to a lack of findings, a familiar situation.]
Even so, it must be stated: The naturalistic fallacy(ies), as presented by the skeptics, and as believed by some fraction of grape-nut-eating-tarot-card-flipping people out there, is bogus. Things weren’t better way back then. Just because something is ‘natural’ doesn’t mean it is better, or without unknown consequences. Washing your hands is good, but antibiotics are also good, and work better when necessary. Breastfeeding is good, but it doesn’t keep your infant from getting cholera. Vaccines work. Modern agriculture is feeding a lot more of us than we used to be able to feed, and the hard truth be told, it is policies and habits that are leaving lots of people hungry. I don’t know if eating a organic diet is better for you or not, but I do know that I do like supermarkets.
But.
Our history is littered with the discarded arguments of people just as smart as us using rudimentary tools to understand complicated systems, declaring a lack of effect and throwing a contemptuous look over their shoulder at the rubes who long for the hilariously outdated solutions of yesteryear. We shouldn’t be concerned with the fact that the naturalistic fallacy is intellectually bankrupt; we should be concerned with the fact that our incredibly stupid species is changing our environment with reckless abandon on the assumption that we are smart enough to understand what we are doing. If the naturalistic fallacy is bad, the perfection-of-progess fallacy is almost as bad, with bonus negative points of being invoked by people who should know better.
How many examples do we need of our previous hubris until we realize that we are just barely less dumb now than we were then?
First we thought lead was safe as a pesticide, in paint, and as a gasoline additive. Then, we figured out it was only safe for paint and gasoline; then just in gasoline. Now, we know that any amount of measurable levels of lead are associated with cognitive effects. Any individual reader of this column was very likely an adult in 2002, and at that time, the state of our knowledge didn’t tell us that any amount of lead was less safe than no amount of lead. Ten goddamn years ago, the FDA thought there was a level of lead that in the bloodstream that did not affect cognitive function in children.
We have been performing increasingly optional cesarean sections for decades before starting to figure out that they are associated with adverse health effects for the lifespan. Only within the past few years have we discovered that this procedure is associated with altered microbiomes, obesity, and asthma.
We have been so successful at distributing products with based on plastic that over 90% of every human on the planet has detectable levels of component chemicals in their bloodstream. Only now that we have insured that nearly every human has been touched, we consistently find associations with metabolic and reproductive changes.
After near thirty years, the recommendations over administering Tylenol to infants was changed. In the 1980s we saw Reyes syndrome, made the association with aspirin, failed to observe any acute differences in infants given Tylenol, and pulled the trigger on global recommendation to replace aspirin with acetaminophen. It took decades before we were clever enough realize that eliminating Reyes might not have been the only thing we did, because we were too stupid to realize that effects do not have to be immediately obvious in order to have profound outcomes.
Human bodies were forged through the crucible of evolution, thousands of generations of adaptation, to be ready to start reproducing by the teens, and we have decided to start putting that process of for a decade, or two.
All of these examples are founded of the specificity of our analytical abilities, or rather a relative lack of specificity. We weren’t clever enough to understand to look for associations, so they remained invisible to us. A question never asked is never answered. Even worse, some of these are discrete events, disturbances orders of magnitude more simplistic to analyze compared to ‘eating organic’.
A lot of the skeptical sites will utilize the idea that humans are ‘pattern seekers’, especially when it comes to people reporting temporal associations with development of autistic behaviors and vaccination. I kind of like the idea of the pattern seeking human in general; the biggest pattern we seem to be seeing is the one that tells us that our current state of knowledge gives us enough information to understand what we are doing, a type of uber-pattern.
The idea that we have a decent understanding the effect of ingesting increased pesticide residue, a finding included in the organic metadata study, is a joke. The idea that we have the faintest clue of the outcomes of replacing infection with inflammation, a practice we have embraced with great enthusiasm, is a total fucking joke. We have barely bothered to look. Do not believe anyone who tells you otherwise.
This is what bothers me so much about a casual wielding of the naturalistic fallacy; it is so frequently a feint from critical questions. The discordance with reality of the naturalist fallacy has been established. It is great how much less suffering there is now, compared to then, but let’s not rest on our laurels. Am I the only one worried about how wrong we are here, now?
I don’t know if eating less pesticide is better than eating more pesticide, and I also can’t be sure that a lifestyle characterized by increased inflammation is a risk factor for developmental differences. I do know that the rules implemented by the natural world have no care for our hubris. Those same rules have violated our once pristine knowledge so dispassionately and with such regularity that I can find no pleasure in hurling the accusation of the naturalistic fallacy at anyone. Instead, the idea fills me with a sense of honorable mention at best; we are more capable than last century, last generation, last year, but we remain at the mercy of machinations which hold no regard for such incremental progress in knowledge in the face of unprecedented changes to our environment.
– pD
Additional Findings of an Altered NeuroImmune Environment In Autism with Intriguing Questions Raised – Microglia in the Cerebral Cortex in Autism
Posted on: April 17, 2012
Hello friends –
A study with a beautifully terse title, Microglia in the Cerebral Cortex in Autism landed in my inbox the other day. It adds to the growing literature showing perturbations in neuroimmune system in the autism population, this time by measuring the number of microglia in different parts of the brain. Here is the abstract:
We immunocytochemically identified microglia in fronto-insular (FI) and visual cortex (VC) in autopsy brains of well-phenotyped subjects with autism and matched controls, and stereologically quantified the microglial densities. Densities were determined blind to phenotype using an optical fractionator probe. In FI, individuals with autism had significantly more microglia compared to controls (p = 0.02). One such subject had a microglial density in FI within the control range and was also an outlier behaviorally with respect to other subjects with autism. In VC, microglial densities were also significantly greater in individuals with autism versus controls (p = 0.0002). Since we observed increased densities of microglia in two functionally and anatomically disparate cortical areas, we suggest that these immune cells are probably denser throughout cerebral cortex in brains of people with autism.
[Note: You don’t see p-values of .0002 too often!] This paper is at a high level largely similar to another recent paper, Microglial Activation and Increased Microglial Density Observed in the Dorsolateral Prefrontal Cortex in Autism (discussed on this blog, here). The authors were clever here, they intentionally used two very anatomically different, and spatially separated parts of the brain to evaluate for microglia population differences, a sort of bonus slice to learn more about the population of microglia in the brain.
The specific measurement technique in use, staining for specific antibodies, does not give us information regarding the activated/non activated state of the microglia, a determination which must be made with evaluations of morphology, though several other studies have measured this directly, and many more provide indirect evidence of a chronic state of activation of microglia. Not only did the author s report an increase in population density in the autism group, the number of microglia was also positively correlated between sites; i.e., a patient with more microglia in the visual cortex was also more likely to have more microglia in the fronto-insular.
These findings demonstrate that, at the time of death, there were significantly higher microglial densities in the subjects with autism compared to the control subjects, and that this change in microglial density is widespread throughout the cerebral cortex in autism. The microglial densities in FI and VC in the same subject were significantly correlated (both measures were available in 10 controls and 8 autistic subjects for a total of 18 subjects) with Pearson’s r2 = 0.4285, p = 0.0024 (Fig. 6). This indicates that the elevation in density is consistent between these areas, and probably throughout the cortex, in both subjects with autism and controls.
Also of interest, in the control group microglia densities tended to decrease with age, but this change was not seen in the autism population.
There is some discussion about a big problem in the autism research world, a very real and meaningful dearth of available tissue samples, this study shared five patients with Morgan, and one from Vargas. [Note: Sign up to help. Morbid but necessary.]
The authors went on to ask the exact same question I had, “How and when does the increased density of autistic microglial arrays arise, and how is it maintained?” Unfortunately, while there aren’t any good answers, I was still a little disappointed with the analysis. There is a quick rundown of a variety of neuroimmune and peripheral immune findings in autism, and some thoughts on ‘sickness behavior’ with the implicit interconnectedness of the immune state and behaviors, and some discussion on some of the many animal models of maternal immune activation in autism.
In an stroke of amazing serendipity, the authors wonder aloud towards the possibility of a type of distracted worker effect of microglia on neural networks, sort of a bank shot on the autism paradox I struggled with in my previous post when I said,
Are increased neuron number and altered white matter tracts the result of microglia not performing the expected maintenance of the brain? Are the findings from Courchesne and Wolff the opportunity costs of having a microglia activated during decisive developmental timeframes?
The authors of Microglia in the Cerebral Cortex in Autism state
In contrast, microglia can also phagocytize synapses and whole neurons, thus disrupting neural circuits. For example,when the axons of motor neurons are cut, the microglia strip them of their synapses (Blinzinger and Kreutzberg 1968; Cullheim and Thams 2007; Graeber et al. 1993). Another example of the disruption of circuitry arises from the direct phagocytosis of neurons. Neurons communicate with microglia by emitting fractalkine*, which appears to inhibit their phagocytosis by microglia. Deleting the gene for the microglial fractalkine receptor (Cx3cr1) in a mouse model of Alzheimer’s disease has the effect of preventing the microglial destruction and phagocytosis of layer 3 neurons that was observed in these mice in vivo with 2-photon microscopy (Furhmann* et al. 2010). In particular, Cx3cr1 knockout mice have greater numbers of dendritic spines in CA1 neurons, have decreased frequency sEPSCs and had seizure patterns which indicate that deficient fractalkine signaling* reduces microglia-mediated synaptic pruning, leading to abnormal brain development, immature connectivity, and a delay in brain circuitry in the hippocampus (Paolicelli* et al. 2011). In summary, the increased density of microglia in people with autism could be protective against other aspects of this condition, and that a possible side-effect of this protective response might involve alterations in neuronal circuitry.
Oh hell yeah. (* concepts and papers discussed on this blog, here)
Going back to the big dollar question, How and when does the increased density of autistic microglial arrays arise, and how is it maintained?”, the possibility of an ongoing infection was raised as a one option, “The increase of microglial densities in individuals with autism could be a function of neuroprotection in response to harmful microorganisms.” Vargas had a dedicated section towards a failure to find agents of the peripheral immune system that are consistent with infiltration from the peripheral immune system commonly observed during acute infection, I do not think other papers have looked for that per se, but will cede to someone with better data. (?) There was a very weird paper from Italy that pointed to a possible polyomavirus transmission from the father in the autism group, though this study was not referenced in Microglia in the Cerebral Cortex in Autism. [Note: I showed my wife this paper, and she told me, “Good job with the autism gametes.” Nice.] Could a virus cause autism, is a nice discussion on this that includes blog and personal favorites, Fatemi, Patterson, and Persico discussing the possibilities and limitations of the study. Great stuff!
While I must admit the possibility that the chronically activated microglia in autism are working on purpose, the irony gods mandate that I wonder aloud if certain segments of the autism Some-Jerk-On-The-Internet population will cling to the possibility that autism is caused by a disease in order to disavow a causative role for neuroinflammation? Those are some tough choices.
There is a discussion on the myriad of ways that microglia could directly participate in autism pathogenesis, starting the discussion off right to the point, “By contrast, there are diseases that arise from intrinsic defects in the microglia themselves which can cause stereotypic behavioral dysfunctions.” There is a short discussion of Nasu-Hakola disease, something I’d never heard of, which has evidence of an increase in cytokines as a result of genetically driven microglial deficiencies, and shows striking behavioral manifestations.
The possibility of some areas of the brain being more susceptible to alterations than others is there too, “Thus, while changes in microglial density appear to be widespread in brains of autistic individuals, some areas may be more vulnerable than others to its effects.” Considering this idea alongside the extremely heterogeneous set of symptoms assigned to autism, a curious question to ponder becomes; if neuroinflammation is a participatory process in the behavioral manifestation of autism, could some of the variability in autistic behaviors be explained by spatially specific gradients of microglial activity? Going further, considering the still largely mysterious migration of microglia into the brain during development, could the temporal origin of microglial activation in autism be a determinant in the eventual behavioral manifestations? These are tricky questions, and I don’t think that our current methodological capacities are sufficient to start thinking about forming a model for analysis.
One concept I was surprised to not receive attention was a developmental programming model, where animal studies tell us that if something happens during critical developmental timeframes, the effect can propagate into adulthood. In fact, one study, Enduring consequences of early-life infection on glial and neural cell genesis within cognitive regions of the brain (Bland et all) exposed four day old animals to e-coli, which found, among other things, “significantly more microglia in the adult DG of early-infected rats”, something seemingly of considerable salience to the current findings, especially considering the known risk factors of early infections as autism risk factors. In Bland, no external agent other than an infection during early life was necessary; this is the essence of the developmental programming model, even after the infection was long since cleared, patterns of physiology were imprinted, the animals recovered from e-coli but were changed from the experience. This my biggest issue with the possibility of an as of yet undefined, and continued evidence free pathogen or process that is causing the immune abnormalities we see in autism, it mandates we ignore existing biologically plausible models that fit well within known risk factors for autism. Why?
Another area this paper was curiously silent on is the data regarding differences in males and females in the timeframes of microglial migration into the brain, something I’d like to learn much more about soon. As an example, Sex differences in microglial colonization of the developing rat brain [yet another by blog favorite, Staci Bilbo] reported “the number and morphology of microglia throughout development is dependent upon the sex and age of the individual, as well as the brain region of interest” among other findings broadly consistent with a beautiful complexity. This is interesting fodder for a discussion concerning possibly the most persistent finding in autism, a very high male to female ratio that has a series of possible explanations [somewhat discussed on this blog, here].
So we know more, but still have only increased our knowledge incrementally. It is increasingly likely that an increased number of microglia in many areas of the brain is characteristic of autism, but the whys, hows, whens, wheres, and whoms still hold many mysteries. The more things change, the more they stay the same.
– pD
Extremely Long Overdue Clinical Findings “Impaired Carbohydrate Digestion and Transport and Mucosal Dysbiosis in the Intestines of Children with Autism and Gastrointestinal Disturbances”, and The Swan Song Of A Tragically Overused Autism Canard
Posted on: January 9, 2012
Hello friends –
My son was a ‘gut kid’. The irony is, for a while, because we were first time parents, we didn’t even know. My son was flagged for evaluation for autism around a year of age and we met with the autism center people several times between his first and third birthdays, with his official diagnosis coming just after he turned three. My wife came home from one of the early meetings convinced that his evaluators didn’t know the first thing about our son, autism, or anything else, and that in fact, they might be insane.
‘Do you know what those idiots asked me today?’
‘What?’
‘What his shits look like. My kid can’t talk and they want to ask me about his diapers!’
‘Who fucking cares?‘
We wound up caring, a lot. It turns out, this wasn’t a stupid question, it just seemed like one to us. The answer to their question was that our son was having at least four or six very messy diapers a day, his stools were never firm logs that look like they came from an spherical filter, but always, always more liquid than solid, and frequently contained chunks of identifiable food. But from our viewpoint, within the context of a child who was not speaking, hurting himself, and never looked at anyone, the idea that we should be worrying about his shit was the stupidest thing we’d ever heard.
But. When we started paying attention, starting reading, and started meeting more people with children with autism, our incredulity waned. We tried GF/CF and probiotics. We paid for lab tests to analyze the bacterial populations in his intestines. We experienced a life saving miracle with anti-fungal agents wherein my son essentially stopped hurting himself over the course of weeks after persistently banging his head dozens of times a day for six months. For nearly a year we removed all complex carbohydrates from our son’s diet, an intervention that makes GFCF feel like a Sunday afternoon after college but before kids and autism. We saw changes in our son based on how his GI tract was performing. For our son, for us, we knew that by some mechanism, what got put in his mouth, and what happened along the way was tightly coupled with how our son felt and behaved.
This is why my vision with spots of rage when I see the ideas of GI and dietary involvement with autism mocked by pseudo-skeptics so rampantly on the Internet. I cannot stand the thought of a single child continuing to suffer the way I watched my son suffer because they were told that there was no basis of GI interaction in autism. That thought hurts.
Those biases stated, we are now, finally, starting to see research indicating that in some cases of autism, there are very real, non imaginary differences in GI function.
A few months ago, Impaired Carbohydrate Digestion and Transport and Mucosal Dysbiosis in the Intestines of Children with Autism and Gastrointestinal Disturbances was published [full, dense, but very cool paper available online]. Here is the abstract.
Gastrointestinal disturbances are commonly reported in children with autism, complicate clinical management, and may contribute to behavioral impairment. Reports of deficiencies in disaccharidase enzymatic activity and of beneficial responses to probiotic and dietary therapies led us to survey gene expression and the mucoepithelial microbiota in intestinal biopsies from children with autism and gastrointestinal disease and children with gastrointestinal disease alone. Ileal transcripts encoding disaccharidases and hexose transporters were deficient in children with autism, indicating impairment of the primary pathway for carbohydrate digestion and transport in enterocytes. Deficient expression of these enzymes and transporters was associated with expression of the intestinal transcription factor, CDX2. Metagenomic analysis of intestinal bacteria revealed compositional dysbiosis manifest as decreases in Bacteroidetes, increases in the ratio of Firmicutes to Bacteroidetes, and increases in Betaproteobacteria. Expression levels of disaccharidases and transporters were associated with the abundance of affected bacterial phylotypes. These results indicate a relationship between human intestinal gene expression and bacterial community structure and may provide insights into the pathophysiology of gastrointestinal disturbances in children with autism.
I’ll admit it. From the outside, from the don’t-have-a-kid-with-autism-and-GI-problems perspective, that is some dense and seemingly bland stuff. Essentially children with GI distress and children with GI distress and autism were compared and it was found that there were distinctly qualitative differences regarding the GI function in the groups. This is validation of what a lot of us have been saying for a long time, that the GI problems our kids were experiencing weren’t coincidental to the autism, but somehow related.
For anyone who has been paying attention to the details of the autism-gut debate, these are dynamite findings. These observations are the death knell for the overused, oversimplified notion that the GI connection to autism was a function of some kids having autism, some kids having GI distress, and that therefore, some kids with autism also have GI distress. This research tells us that the reality is not so simple.
This study is the view from the microscope as opposed to the telescope, and took care not to study just anyone with an autism diagnosis, but those with an autism diagnosis and GI distress, problems so severe that invasive procedures to obtain tissue samples from the GI tract was warranted. This is a critically important facet of the study design in my opinion, a lot of the negative findings in this arena have been epidemiological, and cast the widest possible net, capturing everyone with autism and comparing them with a sample of everyone else. This is a great strength of the paper; for too long everyone has acknowledged the heterogeneous nature of autism, but few studies have tried to understand differences at a phenotype level. This paper is different.
As evidence of the non-random population, the autism patient group had a regression incidence of over eighty percent, and nearly as many of the children in both groups were reported to have food allergies.
The details of the findings in the paper get deep pretty fast, but at a high level there were differences found in proteins involved with the digestion of carbohydrates and changes in bacterial populations between the groups, with some differences found with regard to specific locations in the intestine. Based on these findings, the authors speculate that alterations in carbohydrate processing could result in abnormal bacterial populations by way of altered microbial food availability in parts of the gut.
Based on these findings, we propose a model whereby deficiencies in disaccharidases and hexose transporters alter the milieu of carbohydrates in the distal small intestine (ileum) and proximal large intestine (cecum), resulting in the supply of additional growth substrates for bacteria. These changes manifest in significant and specific compositional changes in the microbiota of AUT-GI children (see Figure 7A–C).
The authors discuss a potential feedback loop of effects of intestinal microbes and nutritional processing, and of the known and potential effects of altered bacterial populations.
Additionally, intestinal microbes can influence the expression of disaccharidases and transporters [59] through the influence of pathogen-associated molecular patterns (PAMPs) and butyrate (a byproduct of bacterial fermentation) on CDX2 expression and activity [60], [61], [62], [63]. In this regard, the observation that CDX2 was decreased in AUT-GI children with increased levels of Betaproteobacteria may be important.
Whatever the underlying mechanisms, reduced capacity for digestion and transport of carbohydrates can have profound effects. Within the intestine, malabsorbed carbohydrates can lead to osmotic diarrhea [64]; non-absorbed sugars may also serve as substrates for intestinal microflora that produce fatty acids and gases (methane, hydrogen, and carbon dioxide), promoting additional GI symptoms such as bloating and flatulence [65].
This is very similar to the underlying theory of the Specific Carbohydrate Diet, impaired carbohydrate digestion promotes bacterial imbalances in the intestine by altered food availability, leading to gastrointestinal distress.
Because of the varied nature of the protein imbalances found and absence of the common alleles associated with such conditions, the authors report that it is unlikely that the underlying cause of the imbalances is genetically based.
In our study, 93.3% of AUT-GI children had decreased mRNA levels for at least one of the three disaccharidases (SI, MGAM, or LCT). In addition, we found decreased levels of mRNA for two important hexose transporters, SGLT1 and GLUT2. Congenital defects in these enzymes and transporters are extremely rare [40], [41], and even the common variant for adult-type hypolactasia was not responsible for reduced LCT expression in AUT-GI children in this cohort. Therefore, it is unlikely that the combined deficiency of disaccharidases (maldigestion) and transporters (malabsorption) are indicative of a primary malabsorption resulting from multiple congenital or acquired defects in each of these genes.
There are a couple of ideas presented on what might be causing the altered disaccharide transporter levels, with food composition intake, immune or hormonal irregularities, and bacterial populations and their associated fermentation byproducts listed as possible candidates. This study did not attempt to determine if any of these things were actually responsible, but an upcoming paper will also detail qualitative differences in expression of genes involved with inflammation in the autism group.
Regarding bacterial populations found, there were several differences identified by bacterial classification and location as well as some associations with onset of autistic behaviors and GI distress.
Pyrosequencing analysis of mucoepithelial bacteria revealed significant multicomponent dysbiosis in AUT-GI children, including decreased levels of Bacteroidetes, an increase in the Firmicute/Bacteroidete ratio, increased cumulative levels of Firmicutes and Proteobacteria, and increased levels of bacteria in the class Betaproteobacteria.
Stratification of AUT-GI children based on the timing of GI symptom development relative to autism onset revealed that the levels of Clostridiales and cumulative levels of Lachnospiraceae and Ruminococcaceae were significantly higher in AUT-GI children for whom GI symptoms developed before or at the same time as the onset of autism symptoms compared to AUT-GI children for whom GI symptoms developed after the onset of autism and compared to Control-GI children. However, we cannot discern whether changes in Clostridiales occurred before the onset of autism in this subgroup. We can only conclude that increased levels of Clostridiales members in biopsies taken after the development of both GI symptoms and autism are associated with the timing of GI onset relative to autism onset in this cohort. Although the reason for this association remains unclear, this finding may suggest that the timing of GI onset relative to autism is an important variable to consider in the design of future prospective studies investigating the microbiota of children with autism.
I am in love with the appreciation of the subtlety on display at the end, it may not be sufficient to simply categorize by GI and non GI autism, but also by the temporal relationship to onset of behavioral symptoms. It makes for a messy outlook going forward, but one based on pragmatism as far as coming to valid conclusions.
As is appropriate, the authors end with an admission that we are still largely groping in the dusk about how the microbiome interacts with our tightly coupled systems, but give a variety of reasons to believe that what we do know makes system wide effects reasonable and a relationship with autism plausible.
Metabolic interactions between intestinal microflora and their hosts are only beginning to be understood. Nonetheless, there is already abundant evidence that microflora can have system-wide effects [76], [77], [78], [79], [80], [81], [82], [83] and influence immune responses, brain development and behavior [24], [25], [26], [84], [85].
No kidding!
It should be noted that this paper is a child of a 2010 IMFAR abstract, Intestinal Inflammation, Impaired Carbohydrate Metabolism and Transport, and Microbial Dysbiosis in Autism. If I understand correctly, another paper is being prepared regarding the findings of intestinal inflammation that will be complimentary to Impaired Carbohydrate Digestion and Transport and Mucosal Dysbiosis in the Intestines of Children with Autism and Gastrointestinal Disturbances. I’ll try to post something when it is published.
This study was small, with only twenty two participants, largely as a result of the difficulty in obtaining tissue specimens. While this does give us cause for caution, it is important to note that this research does not exist in a vacuum, but rather, as a much larger set of research that tell us that the relationship between GI complaints and autism is more than the inceptions of DAN doctors. Previously, Gastrointestinal abnormalities in children with autistic disorder, performed similar biochemistry and reported broadly consistent carbohydrate digestion problems, ‘Low intestinal carbohydrate digestive enzyme activity was reported in 21 children (58.3%), although there was no abnormality found in pancreatic function.’ Several other papers analyzing fecal samples have reported altered bacterial populations, including Low relative abundances of the mucolytic bacterium Akkermansia muciniphila and Bifidobacterium spp. in feces of children with autism, Gastrointestinal flora and gastrointestinal status in children with autism–comparisons to typical children and correlation with autism severity, Fecal lactoferrin and Clostridium spp. in stools of autistic children, and Pyrosequencing study of fecal microflora of autistic and control children, among others.
If the findings from this latest paper are spurious finding based on sample size problems, a lot of other studies are coincidentally finding the same type of thing in the wrong way. Does anyone think that is likely?
I entered the autism world and online autism debate from a place of seeing with my own eyes the failures of a toddlers GI function and the difficult to overstate changes in that toddler alongside improvements in his GI health. On one of the first autism blogs on which I participated I got into a discussion (argument?) with a blogger who I came to respect very much, but has since moved on. I described the fact that my son had six or more diarrhea stools, a day, every day, for months on end, and that when we added dietary changes, probiotics, and later antifungal agents, the changes to his GI function were profound and impossible to misinterpret. He told me something along the lines that humans were susceptible to illusions and sleight of hand, and I thought, ‘as if not knowing the difference between diarrhea and a log was along the lines of figuring out where the jack of spades went!’. I couldn’t believe, could not fucking believe, someone would try to convince me that I had imagined my sons problems, and associated recovery. This wasn’t a sugar pill study where I was asked if my child acted more or less hyperactive, this was a matter of asking myself, ‘How many diarrhea diapers did I change today? Six? Or Zero?’ [Repeat once a day for 180 days.]
I doubt this is necessary, but just in case, I will go on the record to state that it is easy, very easy, to tell the difference between a condition of chronic diarrhea and normal GI function. There might not be a more simpleminded determination to make on Planet Earth or indeed, our perceptible universe. This is a situation that is susceptible to placebo effects only in the most elaborate imaginations of people who have never experienced chronic GI problems.
From that time on, with nearly zero exceptions, I have become a little less shocked, but a little more saddened by the doublethink style skepticism applied to GI distress and autism in nearly every single conversation I have ever seen on the Internet. I’ve put some time thinking toward this, why so many otherwise intelligent people house such extreme hostility on a relationship between GI function and autism. I believe that the Wakefield / MMR autism debacle is at the heart of this disconnect; his ill fated and now retracted paper that launched a thousand Internet scribbles has seemingly forever tied GI complaints and autism to bad science.
It doesn’t have to be this way. As a community, the vaccine wars and kissing cousin prevalence question has done a lot to fracture us, and very little to unite us. That is a sad statement, and nothing makes it more unfortunate than the fact that it does not have to be this way. Wakefield can be wrong about the MMR and there can still be very real differences in GI function in some cases of autism. We can respectfully disagree about how well our existing prevalence studies inform us on the incidence of autism without also needing to accept a world view where every child with autism has raging bowel problems.
We should have the intellectual honesty to admit that there is nothing inherently dangerous about acknowledging what the data tells us; GI function seems to be abnormal in a subset of children with autism, and the underlying features of that GI distress are qualitatively different than what is found in ‘normal’ children.
– pD
Seeing Patterns or Chasing Phantoms, or Is There A Biologically Plausible Developmental Programming Pathway Toward Impaired Synaptic Pruning In Autism?
Posted on: December 26, 2011
Hello friends –
Lately I’ve found myself reading papers and knowing and owning several of the references; tragically I can’t tell if I’m reading the right research and am onto something, or I am chasing phantoms and my web of pubmed alerts and reading interests are funneling my reference list into a narrowing echo chamber of sorts. With that warning in mind, we can proceed to poking around several papers, only some of which mention autism per se. Along the way, we will see evidence supporting the possibility of a biologically plausible mechanism of developmental programming of the neuroimmune environment, a sequence of events that may lead to impaired synaptic pruning in (some cases of?) autism.
By now, everyone has seen/read/heard about one form or another of the ‘a massive asteroid is going to destroy the world’ story. One of the common survival strategies from an asteroid strike involves altering the path of the asteroid so that it misses the Earth. The thoughtful analysis of this problem allows for the physics based reality of the problem, moving an asteroid out of an extinction based trajectory involves just a little work when the asteroid is ten thousand gazillion miles away, but a lot more work when it is only a gazillion miles away. Upon careful evaluation living organisms display similar behavior, relatively minor disturbances in early life can alter the developmental trajectory, while that same disturbance later in life is unable to materially affect the organism beyond a transient effect. The accumulated evidence that early life experiences can shape the adult outcome is nearly impossible to dispute with any remaining intellectual honesty, the question is instead, is how large is the effect in autism?
This analogy adequately symbolizes one of the more beautiful and terrifying concepts I’ve come across researching autism, that of ‘developmental programming’, which I blogged some about here, but essentially is the idea that there are critical timeframes during which environmental impacts can have long term persistent effects on a wide range of outcomes. The most robustly replicated findings involve changes to metabolic profiles in response to abnormal prenatal nutritional environments, but there is also evidence of various other effects, including neurological, and reputable speculation, that autism, may in fact, be in part, a disorder of developmental programming.
Secondarily, there has long been speculation of problems in the removal of ‘excess’ synapses, i.e., ‘synaptic pruning’ in the autism population. This culling of synapses begins in fetal life continuing throughout adolescence and the repeated observations of increased head circumference during infancy as a risk factor for autism has resulted in the idea that altered synaptic pruning maybe involved in autism.
In the last month or so several rather serendipitously themed papers have been published with tantalizing clues about some of the finer grained mechanisms of synaptic pruning, the possibility of impaired synaptic pruning in the autism population, and a known risk factor for autism that models a developmental programming event sequence that may tie them together.
First off, we have Synaptic pruning by microglia is necessary for normal brain development, (Paolicelli et all) with a very straightforward title, that has this dynamite in the abstract: (snipped for length)
These findings link microglia surveillance to synaptic maturation and suggest that deficits in microglia function may contribute to synaptic abnormalities seen in some neurodevelopmental disorders.
This paper is short, but pretty cool, and very nice from a new territory perspective. It also speaks directly towards one of the increasingly hilarious obfuscations you will sometimes see raised in online discussions about immunological findings in autism, namely, that we can’t know if the state of chronic inflammation in the CNS observed in autism is harmful or beneficial. [hint: It might not be causative, but it isn’t beneficial.]
Here’s is a snippet from the Introduction:
Time-lapse imaging has shown that microglia processes are highly motile even in the uninjured brain and that they make frequent, but transient contact with synapses. This and other observations have led to the hypothesis that microglia monitor synaptic function and are involved in synapse maturation or elimination. Moreover, neurons during this period up-regulate the expression of the chemokine fractalkine, Cx3cl1, whose receptor in the central nervous system is exclusively expressed by microglia and is essential for microglia migration. If, in fact, microglia are involved in scavenging synapses, then this activity is likely to be particularly important during synaptic maturation when synaptic turnover is highest.
Nice. A time dependent participation by microglia in the critical process of optimization of neuron numbers, a process we are still very much groping our way in the dark towards untangling. The researchers focused in on a particular molecular target, a chemical messenger of the immune system, fractalkine, and found that without fractalkine, the process of synaptic turnover was impaired.
A couple of tests were performed, first immunohistochemistry (i.e., exceedingly clever manipulation of antibodies to determine the presence or absence of proteins in very specific locations) which demonstrated that microglia were, in fact, ‘engulfing synaptic material’ in animals during periods of synaptic maturation.
Secondly, so called ‘knock out mice’ (i.e., genetically engineered mice constructed without the ability to make a specific protein, in this case, fractalkine) were used evaluate for changes in synaptic form and function based on a lack of fractalkine. Changes in dendritic spine density were observed in the knock out mice group, with much higher densities in a very specific type of neuron during the second and third postnatal week of life. The authors indicate this is a key timeframe in synaptic pruning, and state their findings are “suggesting a transient deficient synaptic pruning in Cx3cr1 knockout mice “. The effect of not having fractalkine on spine density was time dependent as shown below.
Several other measurements were taken, including synaptic firing frequencies, which also implicated an increased surface area for synapses on dendritic spines, consistent with impaired pruning. Time dependent effects on synaptic efficiency and seizure susceptibility were also found, which the led the authors to conclude that the findings were “consistent with a delay in brain circuit development at the whole animal level.”
For additional evidence of fractalkine participation in synaptic maintenance, we can look to the opposite direction, where researchers evaluating neuron loss in an Alzheimers model reported “Knockout of the microglial chemokine receptor Cx3cr1, which is critical in neuron-microglia communication, prevented neuron loss”. Taken together, the conclusion that fractalkine processing is involved with neuron maintenance is highly likely, and correspondingly, highly unlikely to be a set of spurious findings.
There’s a couple paragraphs on potential mechanisms by which fractalkine could be interacting with microglia to achieve this effect, with the authors claiming that their data and other data generally supports a model wherein microglia were not effectively recruited to appropriate locations in the brain due to a lack of fractalkine, or, a ‘transient reduction in microglia surveillance.’
The conclusion is a good layman level wrap up that speaks toward the Interconnectedness of the brain and the immune system:
In conclusion, we show that microglia engulf and eliminate synapses during development. In mice lacking Cx3cr1, a chemokine receptor expressed by microglia in the brain, microglia numbers were transiently reduced in the developing brain and synaptic pruning was delayed. Deficient synaptic pruning resulted in an excess of dendritic spines and immature synapses and was associated with a persistence of electrophysiological and pharmacological hallmarks of immature brain circuitry. Genetic variation in Cx3cr1 along with environmental pathogens that impact microglia function may contribute to susceptibility to developmental disorders associated with altered synapse number. Understanding microglia-mediated synaptic pruning is likely to lead to a better understanding of synaptic homeostasis and an appreciation of interactions between the brain and immune system
That’s all pretty cool, but there was precious little discussion of autism, except in the general sense of a ‘developmental disorder associated with altered synapse number’. [But the references do speak to autism, the first reference provided, Dendritic Spines in Fragile X Mice displays a significant relationship to autism, and it describes how another flavor of knock out mice, this time designed to mimic Fragile-X, exhibit a ‘developmental delay in the downregulation of spine turnover and in the transition from immature to mature spine subtypes.’ Go figure!]
The other reason Paolicelli is of particular interest to the autism discussion is one of the major players in this study, the microglia (i.e., the resident immune cells of the CNS), have been found to be ‘chronically activated’ in the autism brain by direct measurement in two studies (here, and here, [and by me, here]), and tons of other studies have shown indirect evidence of an ongoing state of immunological alertness in the autism brain.
Considering this is a brand new paper, I do not believe that there are any studies illuminating the results of a state of chronic activation of microglia on the process of synaptic pruning per se. I will, however, go on the record that such an effect is very, very likely, and the logical leap is microscopically small that there will be some detrimental impact to such a state. The inverse argument, a scenario wherein there could be a state of chronic microglial activation that does not interfere with microglia participation in the synaptic pruning requires logical acrobatics worthy of Cirque Du Soleil. I am open to evidence, however.
So, from Paolicelli, we know that a ‘transient reduction in microglial surveillance’ induced by a reduction in the ability to production fractalkine can result in a condition ‘consistent with a delay in brain circuit development at the whole animal level’.
Next up, we have a paper that was all over the JerkNet in the days and weeks following its release, Neuron number and size in prefrontal cortex of children with autism. This is a cool study, and likely a very important paper, but I must say that a lot of the online commentary exhibits an irrational exuberance towards one part of the findings. Here is part of the abstract.
Children with autism had 67% more neurons in the PFC (mean, 1.94 billion; 95% CI, 1.57-2.31) compared with control children (1.16 billion; 95% CI, 0.90-1.42; P = .002), including 79% more in DL-PFC (1.57 billion; 95% CI, 1.20-1.94 in autism cases vs 0.88 billion; 95% CI, 0.66-1.10 in controls; P = .003) and 29% more in M-PFC (0.36 billion; 95% CI, 0.33-0.40 in autism cases vs 0.28 billion; 95% CI, 0.23-0.34 in controls; P = .009). Brain weight in the autistic cases differed from normative mean weight for age by a mean of 17.6% (95% CI, 10.2%-25.0%; P = .001), while brains in controls differed by a mean of 0.2% (95% CI, -8.7% to 9.1%; P = .96). Plots of counts by weight showed autistic children had both greater total prefrontal neuron counts and brain weight for age than control children. [PFC == prefrontal cortex]
Essentially the authors used a variety of mechanisms to measure neuron number in a specific area of the brain, the prefrontal cortex, and found large variations (increases) in the autism group. The prefrontal cortex is thought to be involved in ‘planning complex coginitive behaviors’, and ‘moderating correct social behavior’, among others, so this was a smart place to look.
The implicit hype on the internet is that this firmly indicates a ‘prenatal cause’ to autism, but if you read the paper, read what Courchense has said, and read recent literature, you know that the simplicity of this as a singular prenatal cause of autism is long broad strokes, and short on appreciation of the subtlety that textures reality.
A link @ LBRB sent me to the team at The Thinking Person’s Guide To Autism, who had a very nice transcription of a talk given by Courchesne at IMFAR 2011. Here is a snipet that started my wheels turning.
What we see in autism is either an excess proliferation, producing an overabundance of neuron numbers, or the excess might be due to a reduced ability to undergo naturally occurring cell death. Or it could be both. We don’t know which and our data don’t speak to that, although our data do suggest that it’s probably both.
Finally, our evidence shows that across time, there’s a prolonged period of apoptosis, removal and remodeling of circuits. In order to get back to where neuron numbers are supposed to be, it takes a very long time for the autistic brain. In the normal developing brain, this takes just a few months. In autism, it’s a couple of decades.
[Note how well this fits within the model described by Paolicelli, i.e., “consistent with a delay in brain circuit development at the whole animal level”. ]
I would highly recommend anyone who has read this far to go read the entire post @ TPGTA sometime.
As far as synaptic pruning goes, here is the associated segment of the paper:
Apoptotic mechanisms during the third trimester and early postnatal life normally remove subplate neurons, which comprise about half the neurons produced in the second trimester. A failure of that key early developmental process could also create a pathological excess of cortical neurons. A failure of subplate apoptosis might additionally indicate abnormal development of the subplate itself. The subplate plays a critical role in the maturation of layer 4 inhibitory functioning as well as in the early stages of thalamocortical and corticocortical connectivity development.inhibitory functioning and defects of functional and structural connectivity are characteristic of autism, but the causes have remained elusive.
Nearly half of the neurons in the area studied are expected to be removed through pruning, a process that extends well after birth. That is something that you didn’t see referenced in too many places trumpeting this study as ‘proof’ that autism was caused by disturbances in the prenatal environment. I’m not coming down on the prenatal environment as a critical timeframe for autism pathogensesis, just the difficult to defend underlying notion that this is the only time the environment should be evaluated, or the idea that if something is initiated prenatally other timeframes are therefore, unimportant.
So, I’d read that microglia were actively involved in proper synaptic pruning, contingent on utilization of fractalkine, and then read that impaired synaptic apoptotic mechanisms could be participating in autism, with a consequence of an over abundance of neurons.
Then, I got myself a copy of Microglia and Memory: Modulation by Early-Life Infection, which is another study in a growing body of evidence that immune challenges early in life can have unpredictable physiological consequences. (This is another very cool paper with Staci Bilbo as an author, whom I think is seriously onto something.) This study, in particular, focused on interactions microglia and formation of memories. Here is the abstract:
The proinflammatory cytokine interleukin-1ß (IL-1ß) is critical for normal hippocampus (HP)-dependent cognition, whereas high levels can disrupt memory and are implicated in neurodegeneration. However, the cellular source of IL-1ß during learning has not been shown, and little is known about the risk factors leading to cytokine dysregulation within the HP. We have reported that neonatal bacterial infection in rats leads to marked HP-dependent memory deficits in adulthood. However, deficits are only observed if unmasked by a subsequent immune challenge [lipopolysaccharide (LPS)] around the time of learning. These data implicate a long-term change within the immune system that, upon activation with the “second hit,” LPS, acutely impacts the neural processes underlying memory. Indeed, inhibiting brain IL-1ß before the LPS challenge prevents memory impairment in neonatally infected (NI) rats. We aimed to determine the cellular source of IL-1ß during normal learning and thereby lend insight into the mechanism by which this cytokine is enduringly altered by early-life infection. We show for the first time that CD11b+ enriched cells are the source of IL-1ß during normal HP-dependent learning. CD11b+ cells from NI rats are functionally sensitized within the adult HP and produce exaggerated IL-1ß ex vivo compared with controls. However, an exaggerated IL-1ß response in vivo requires LPS before learning. Moreover, preventing microglial activation during learning prevents memory impairment in NI rats, even following an LPS challenge. Thus, early-life events can significantly modulate normal learning-dependent cytokine activity within the HP, via a specific, enduring impact on brain microglial function.
Briefly, the authors infected rats four days after birth with e-coli, and then challenged them with LPS in adulthood to simulate the immune system to evaluate if memory formation was affected. As further evidence of an immune mediated effect, prevention of microglial activation in adulthood was sufficient to attenuate the effect. Clearly the effect on memory formation was based on the immune system. (Note: Most of the studies I’ve read would indicate [i.e., educated guess] that a four day old rat is brain developmentally similar to the third trimester of a human fetus.) While a terrifying and beautiful expression of developmental programming in its own right, there isn’t much to speak towards synaptic pruning in this paper, except maybe, potentially, one part of their findings.
In our study, CX3CL1 did not differ by group, whereas its receptor was decreased basally in NI rats, implicating a change at the level of microglia.
This is where things get either highly coincidental, or connected. CX3CL1 is another name for fractalkine, i.e., animals that were infected in early life had decreased expression of the receptor for fractalkine compared to placebo animals, i.e., fractalkine is the same chemical messenger found to be integral in the process of synaptic pruning in Synaptic pruning by microglia is necessary for normal brain development! From a functionality standpoint, having less receptor is very similar to having less fractalkine; as the animals in Microglial Cx3cr1 knockout prevents neuron loss in a mouse model of Alzheimer’s disease tell us.
If, if synaptic apoptotic processes are impaired in autism, perhaps this is one mechanism of action. The timeline would involve a prenatal immune challenge, which causes a persistent decrease fractalkine receptor expression, which in turn, causes a consequent impairment in synaptic pruning through interference in microglial targeting. There is near universal agreement that immune disturbances in utero are capable of altering developmental trajectory undesirably, and here, in an animal model, we have evidence that infections are capable of reducing availability of receptors of ligands known to play a critical role in synaptic pruning, the absence of which leads to conditions which are “consistent with a delay in brain circuit development at the whole animal level”.
Only time, and more research, will tell if this is a pattern, a phantom, or a little of both.
– pD
The Interconnectedness of the Brain, Behavior, and Immunology and the Difficult to Overstate Flaccidity of The Correlation Is Not Causation Argument
Posted on: May 12, 2011
Hello friends –
I’ve gotten into a lot of discussions online about the vaccines and autism; generally with very poor, if not nonexistent, evidence of having changed any opinions, but relatively strong evidence ( p > .001) that persisting in making my arguments can get you called ‘an antivaccine loon’, ‘idiot’, someone who engages in ‘Gish Gallop’, or the worst insult I’ve received so far, ‘anti-science’. While I am really torn on the vaccine issue, I am certain that both peripheries of this debate are at least somewhat wrong in the conclusions that they’ve drawn from the available evidence. I do believe that lots of parents have witnessed a very real change in their children post vaccination, and I also don’t believe for a single second that vaccines are the cause of an epidemic of autism. It’s a mess and I’ve been poking around the Internet almost five years into journey autism and from my eyes, it hasn’t improved any in the past half decade. This is very sad.
That being said, while I do think we need to have a rational and dispassionate discussion about what our existing vaccine studies can and cannot tell us about autism, I’m really concerned about the fact that the vaccine wars seem to have inoculated otherwise intelligent people from any semblance of intellectual curiosity regarding the immunological findings in the autism realm. That’s a problem, because there are lots of things other than vaccines that can modify the immune response, various environmental agents and cultural changes that are relatively new, and ignoring immunological findings in autism because they happen to intersect with the function of vaccination is a huge, massive, supernova sized disservice to what history will view us poorly on, refusing to perform honest evaluation due to fear and the comfort of willful ignorance.
Here, in this post, I will make the case that this lack of curiosity on immunological findings in autism is either born of a lack of understanding on how much we know about the ties between the immune system and the brain, or alternatively, originates from a deep seated desire to avoid honest interactions. This isn’t to make the case that vaccines can cause autism, or even that the immunological disturbances observed in autism are causative, but rather that an obstinate refusal to consider these as possibilities is the sign of someone who cannot, or will not accept, the biological plausibility of immunologically driven behaviors despite a constellation of evidence.
One of the things that jumps out to me why the autism population might be a subgroup of the population susceptible to changes as a result of immune dysfunction (and thus, potentially adversely affected as a result of vaccination), is the sheer volume of evidence we now have available to us indicating an altered immune response, and indeed, an ongoing state of inflammation within the brain in the autism population, and most strikingly, repeated observations of a correlation between the degree of immune dysregulation as a propensity of an inflammatory state, and the severity of autism behaviors. Again and again we’ve seen that as markers indicative of an inflammatory state increase, so too, do severity of autism behaviors. Not only that, but there are instances wherein the decrease of components known to regulate the immune response decrease, autistic behaviors are more severe. Subtle shifts in either the start or the resolution of the immune response seems to affect autistic behavior severity in the same way. I know coincidences happen all the time, but that doesn’t mean that everything is a coincidence.
We also have a large number of studies that tell us that in vitro, similar levels of stimulation with a variety of agents cause exaggerated or dysregulated production of immune markers in the autism population.
A large percentage of the time that I mention these findings, usually within discussions with an origin in vaccination, someone decides to educate me on one of the most rudimentary scientific axioms:
Correlation does not equal causation.
It must be stated, the above statement is absolutely true. Unfortunately for the people for whom this accurate, but simplistic catchphrase comprises the entirety of their argument, it completely ignores a wealth of research that tells us in very unambiguous terms that there is incontrovertible evidence that crosstalk between the immune system and central nervous system can modify behavior. The research indicating a relationship between immune dysregulation and autism does not exist in a vacuum, but rather, is only a tiny fragment of evidence, mostly accumulated within the last few years, that tells us that the paradigm of the past decades, that of the brain as a immune privileged organ without communication to the immune system, is as antiquated as refrigerator moms and a one in ten thousand prevalence.
From a common sense, why didn’t I think of that standpoint, the best example of the interaction between the brain and the immune response is the old standard, just plain old getting sick. You live in the dirty world, you pick up a pathogen, you get sick, and suddenly you get lethargic and you start to run a fever. But is it the pathogen itself that is actually making you feel like staying in bed all day?
What is being learned is that it is not necessarily the microbial invader that is causing you to get tired and feel sore, but rather, that your decreased energy levels are centrally mediated through your brain, and the triggers for your brain to start a fever include molecules our bodies use for a wide range of communications, including immune based messaging, cytokines. Some of the most common cytokines in the research to follow include IL-6, IL-1B, and TNF-Alpha; so called ‘pro-inflammatory’ cytokines. Researchers have been plugging away at just how the immune response is capable of modifying behaviors, i.e., inducing, sickness behavior for a while now, at least in terms of autism research. From 1998, we have Molecular basis of sickness behavior:
Peripheral and central injections of lipopolysaccharide (LPS), a cytokine inducer, and recombinant proinflammatory cytokines such as interleukin-1 beta (IL-1 beta) induce sickness behavior in the form of reduced food intake and decreased social activities. Mechanisms of the behavioral effects of cytokines have been the subject of much investigation during the last 3 years. At the behavioral level, the profound depressing effects of cytokines on behavior are the expression of a highly organized motivational state. At the molecular level, sickness behavior is mediated by an inducible brain cytokine compartment that is activated by peripheral cytokines via neural afferent pathways. Centrally produced cytokines act on brain cytokine receptors that are similar to those characterized on peripheral immune and nonimmune cells, as demonstrated by pharmacologic experiments using cytokine receptor antagonists, neutralizing antibodies to specific subtypes of cytokine receptors, and gene targeting techniques. Evidence exists that different components of sickness behavior are mediated by different cytokines and that the relative importance of these cytokines is not the same in the peripheral and central cytokine compartments.
The first sentence in this abstract references a practice that is extremely common in studying the immune system, intentionally invoking a robust immune response by exposing either animals, or cells in vitro, to the components that comprise the cell wall of certain types of bacteria; lipopolysaccharide, or LPS. LPS could be considered a sort of bacterial fingerprint, a pattern that our immune systems, and the immune system of almost everything, has evolved to recognize, and correspondingly initiates an immune response.
Because this is a conversation that frequently has an origin in vaccination, essentially the act of faking an infection, it is salient to remember that the animals or cell cultures aren’t really getting sick when exposed to LPS; there is no pathology associated with whatever type of bacteria might be housed within a cell membrane containing LPS. Usually, when the body is exposed to a gram negative bacteria, and the consequent LPS exposure, there are also effects of the bacteria that interact with the organism, but by only incorporating the alert signal for a bacterial invader, we can gain insight into the effect of the immune response itself; there isn’t anything else to cause any changes. This means that similarly to LPS administration, straight administration of these pro-inflammatory cytokines are similar to the result of getting sick with a pathogen, at least as far as the immune response is concerned.
In the above instance, administration of LPS, or simply cytokines, had been shown to be capable of causing reduced food intake and ‘decreased social activities’.
Later in 1998, Central administration of rat IL-6 induces HPA activation and fever but not sickness behavior in rats (full version), was published wherein the authors report that central administration (i.e., directly into the CNS), of cytokines in isolation (IL-6) or in combination (IL-6 + IL-1B) were capable of inducing altered HPA activation, fevers, and sickness behaviors. Effects of peripheral administration of recombinant human interleukin-1 beta on feeding behavior of the rat was published a few years later, and observed that peripheral administration (i.e., not the CNS) of IL-1B could affect how much a rat ate, with sucrose ingestion being consistently altered during periods of sickness.
Jumping ahead a few years, a review paper Expression and regulation of interleukin-1 receptors in the brain. Role in cytokines-induced sickness behavior reviewed how cytokines participate in sickness behavior, Interleukin-6 and leptin mediate lipopolysaccharide-induced fever and sickness behavior examined the interactions of IL-6 and leptin in sickness behavior, and Behavioral and physiological effects of a single injection of rat interferon-alpha on male Sprague-Dawley rats: a long-term evaluation reported “these data suggest that a single IFN-alpha exposure may elicit long-term behavioral disruptions”.
Much more recently, Sickness-related odor communication signals as determinants of social behavior in rat: a role for inflammatory processes more elegantly found that behavior was modified by LPS exposure, and that this effect was neutralized by concurrent administration of the anti-inflammatory cytokine, IL-10. Similarly, Inhibition of peripheral TNF can block the malaise associated with CNS inflammatory diseases observed another distinct means by which interfering with the immune response could attenuate the effect of faux sickness, in part, concluding, “Thus behavioral changes induced by CNS lesions may result from peripheral expression of cytokines that can be targeted with drugs which do not need to cross the blood-brain barrier to be efficacious.” In other words, what is happening in the periphery, outside of the protective boundaries of the blood brain barrier, can none the less manipulate behaviors that are controlled by the brain.
There are tons, tons more studies like this, but the point should be clear by now; it is accepted that you can achieve some of the same behaviors the come alongside illness, such as fever and lethargy, without the presence of an actual bacteria or virus; all you need is for your brain to think that you are sick.
While it must be acknowledged that the behavioral disturbances observed in autism are a lot different than feeling the need to watch TV all day, these types of studies were among the first clues that the traditional view of the CNS as a separate entity within the gated community of the blood brain barrier needed revision.
Measuring how much sugar water a rat drank is great stuff, but the reality is that we have conservatively a gazillion studies telling us that disorders that manifest behaviorally have strong, strong ties to the immune system; and once we begin to understand the vast scope of these findings, the utter frailty of “correlation does not equal causation” becomes painfully clear to the intellectually honest observer.
The big problem I found myself with in crafting this posting was that the sheer volume of studies available really makes a complete illustration of the literature impossible; I started looking and pubmed nearly puked trying to return to me a listing of all of the things I wanted to summarize. So here is some of the best of the best; to keep things interesting, I thought I’d only include findings from 2007 or later as a mechanism to show just how nascent our understanding of the connections between the brain and the immune system really are.
Initially, we can start with a condition that nearly everyone agrees is diagnosed based on behavior, depression. It turns out, the number of findings establishing a link between immune system markers and depression is wide and deep.
Here’s a great one, Elevated macrophage migration inhibitory factor (MIF) is associated with depressive symptoms, blunted cortisol reactivity to acute stress, and lowered morning cortisol, which reports, that MIF can modify HPA axis function and is tied to depression; a particularly compelling finding considering well documented alterations in HPA axis metabolites in autism, and the fact that increased MIF has also been found in the autism population, and as levels increased, so too did autism severity.
Here is part of the abstract for Inflammation and Its Discontents: The Role of Cytokines in the Pathophysiology of Major Depression (full paper)
Patients with major depression have been found to exhibit increased peripheral blood inflammatory biomarkers, including inflammatory cytokines, which have been shown to access the brain and interact with virtually every pathophysiologic domain known to be involved in depression, including neurotransmitter metabolism, neuroendocrine function, and neural plasticity. Indeed, activation of inflammatory pathways within the brain is believed to contribute to a confluence of decreased neurotrophic support and altered glutamate release/reuptake, as well as oxidative stress, leading to excitotoxicity and loss of glial elements, consistent with neuropathologic findings that characterize depressive disorders.
Somewhere along the way, researchers discovered that some anti-depressants can exert anti-inflammatory effects, for examples of these findings we could look to Fluoxetine and citalopram exhibit potent antiinflammatory activity in human and murine models of rheumatoid arthritis and inhibit toll-like receptors, or Plasma cytokine profiles in depressed patients who fail to respond to selective serotonin reuptake inhibitor therapy, which concludes in part, “Suppression of proinflammatory cytokines does not occur in depressed patients who fail to respond to SSRIs and is necessary for clinical recovery”.
In Investigating the inflammatory phenotype of major depression: focus on cytokines and polyunsaturated fatty acids, the authors report that, “The findings of this study provide further support for the view that major depression is associated with a pro-inflammatory phenotype which at least partially persists when patients become normothymic.” A nice review of the evidence of immunological participation in depression can be found in The concept of depression as a dysfunction of the immune system (full paper).
Moving forward, we can look to schizophrenia, we have similar findings, including Serum levels of IL-6, IL-10 and TNF-a in patients with bipolar disorder and schizophrenia: differences in pro- and anti-inflammatory balance, which observed an imbalanced baseline cytokine profile in the schizophrenic group; findings very similar in form with An activated set point of T-cell and monocyte inflammatory networks in recent-onset schizophrenia patients involves both pro- and anti-inflammatory forces. Similarly, the findings from Dysregulation of chemo-cytokine production in schizophrenic patients versus healthy controls, (full paper) which states, in part:
Growing evidence suggests that specific cytokines and chemokines play a role in signalling the brain to produce neurochemical, neuroendocrine, neuroimmune and behavioural changes. A relationship between inflammation and schizophrenia was supported by abnormal cytokines production, abnormal concentrations of cytokines and cytokine receptors in the blood and cerebrospinal fluid in schizophrenia
Their findings include differentially increased and decreased production of chemokines and cytokines as a result of LPS stimulations in the case group. Of particular note, a similarly dysregulated immune profile of cytokine and chemokine generation has been found in the autism population in several studies.
We also have several trials of immunomodulatory drugs in the schizophrenic arena that further implicate the immune system in pathology, including Adjuvant aspirin therapy reduces symptoms of schizophrenia spectrum disorders: results from a randomized, double-blind, placebo-controlled trial, a ‘gold standard’ trial which found that, “Aspirin given as adjuvant therapy to regular antipsychotic treatment reduces the symptoms of schizophrenia spectrum disorders. The reduction is more pronounced in those with the more altered immune function. Inflammation may constitute a potential new target for antipsychotic drug development”. A similar clinical trial, Celecoxib as adjunctive therapy in schizophrenia: a double-blind, randomized and placebo-controlled trial , another gold standard trial, which also had findings in the same vein, “Although both protocols significantly decreased the score of the positive, negative and general psychopathological symptoms over the trial period, the combination of risperidone and celecoxib showed a significant superiority over risperidone alone in the treatment of positive symptoms, general psychopathology symptoms as well as PANSS total scores.” [Celecoxib is a cox-2 inhibitor; i.e., anti-inflammatory, i.e., immunomodulatory]
What about bi-polar disorder? More of the same, including, The activation of monocyte and T cell networks in patients with bipolar disorder, or Elevation of cerebrospinal fluid interleukin-1ß in bipolar disorder, which reports, in part, “Our findings show an altered brain cytokine profile associated with the manifestation of recent manic/hypomanic episodes in patients with bipolar disorder. Although the causality remains to be established, these findings may suggest a pathophysiological role for IL-1ß in bipolar disorder.”. These studies were published in April and March, 2011, respectively.
Brain tissue from persons with bi-polar disorder also showed increased levels of excitotoxicity and neuroinflammation in Increased excitotoxicity and neuroinflammatory markers in postmortem frontal cortex from bipolar disorder patients (full version), and authors report differential cytokine profiles depending on state of mania, depression, or remission in Comparison of cytokine levels in depressed, manic and euthymic patients with bipolar disorder.
Another disorder based solely around behavior, Tourette syndrome, has increasingly unsurprising findings. Polymorphisms of interleukin 1 gene IL1RN are associated with Tourette syndrome reports “The odds ratio for developing Tourette syndrome in individuals with the IL1RN( *)1 allele, compared with IL1RN( *)2, was 7.65.” (!!!) , and Elevated expression of MCP-1, IL-2 and PTPR-N in basal ganglia of Tourette syndrome cases is yet another example of observations of CNS based immune participation in a disorder that is diagnosed by behavior.
There are also some reviews that perform a cross talk of sorts between disorders; i.e., The mononuclear phagocyte system and its cytokine inflammatory networks in schizophrenia and bipolar disorder, or Immune system to brain signaling: Neuropsychopharmacological implications, published in May 2011, which has this abstract:
There has been an explosion in our knowledge of the pathways and mechanisms by which the immune system can influence the brain and behavior. In the context of inflammation, pro-inflammatory cytokines can access the central nervous system and interact with a cytokine network in the brain to influence virtually every aspect of brain function relevant to behavior including neurotransmitter metabolism, neuroendocrine function, synaptic plasticity, and neurocircuits that regulate mood, motor activity, motivation, anxiety and alarm. Behavioral consequences of these effects of the immune system on the brain include depression, anxiety, fatigue, psychomotor slowing, anorexia, cognitive dysfunction and sleep impairment; symptoms that overlap with those which characterize neuropsychiatric disorders, especially depression. Pathways that appear to be especially important in immune system effects on the brain include the cytokine signaling molecules, p38 mitogen-activated protein kinase and nuclear factor kappa B; indoleamine 2,3 dioxygenase and its downstream metabolites, kynurenine, quinolinic acid and kynurenic acid; the neurotransmitters, serotonin, dopamine and glutamate; and neurocircuits involving the basal ganglia and anterior cingulate cortex. A series of vulnerability factors including aging and obesity as well as chronic stress also appears to interact with immune to brain signaling to exacerbate immunologic contributions to neuropsychiatric disease. The elucidation of the mechanisms by which the immune system influences behavior yields a host of targets for potential therapeutic development as well as informing strategies for the prevention of neuropsychiatric disease in at risk populations.
All of the conditions above, depression, schizophrenia, bi-polar, and tourettes are diagnosed behaviorally; it is only in the last few years that the medical dimension of these disorders were even understood to exist. None of the studies that I referenced above are more than five years old; the idea that behavioral disorders were so closely entangled with the immune system is very, very new. It should be noted that I intentionally left out disorders that also have reams of evidence of immune participation, but which are more degenerative in nature; i.e., Alzheimer’s, ALS, Parkinson’s. When discussing autism, I also left out studies involving aberrant presence of auto-antibodies, of which there are many.
One of the things that I have learned in trying to refine my thought processes during my time on the Internet is that rarely does a single study tell us much about a condition; but the converse also holds true, if we have many studies with different methodologies or measurement end points, but they all reach similar conclusions, then the likely-hood that the findings are accurate is much, much greater. All of the studies I have listed above tell us something similar; that the immune system is clearly, unmistakably playing a part in a lot of conditions classically considered neurological and diagnosed behaviorally. It isn’t enough to nitpick flaws in a single one of the studies in order for ‘correlation does not equal causation’ to make meaningful headway into the implications of these studies; instead, all of the studies above, and lots more, have to be wrong in the same way if we would like to return to a place where we can keep our heads in the sand, hoping for coincidences and bleating out catchphrases in the face of clinical findings. That isn’t going to happen. Given this reality, we should not and cannot ignore the growing evidence of immune abnormalities in the autism population, no matter how inconvenient following that trail of evidence might become.
-pD
Hello friends –
I have decidedly mixed feelings on the genetic side of autism research; clearly genetics plays a part, but it does appear that autism has largely mirrored other complicated conditions in that what we thought we were getting when we cracked the genetic code has, for all practical purposes, failed to materialize. To what extent our genetic makeup really plays a part in autism more than any other condition that is currently mystifying us, I don’t think we can say with much certainty; unless you want to count some.
To my mind, one particularly bright spot in the gene realm is the associations of the MET-C allele and an increased risk of an autism diagnosis. At first glance, MET doesn’t seem like a big deal; lots of people have the MET-C mutation, in fact, nearly half of everyone has it. But people with autism have it just a little more frequently, an observation that has been replicated many times. But what is exciting is not only that the MET-C findings are robust, but they can also affect a lot of implicated systems in autism in biologically relevant ways. From an ideological standpoint, the fissure in the autism community about research priorities regarding genetics versus environment, the MET-C studies are a superb example of just how much useful knowledge there is by starting at the genome and working upwards, and finding once we get there that the reality involves lots more than just genes. There is something for everyone!
Getting to the big picture where we can appreciate the beautiful complexity takes a little bit of digging, but it’s worth the effort.
Every now and again you’ll see a period piece about the forties, fifties or sixties, and you’ll get a glimpse of the female operator, someone who would take a call and literally connect two parties together; the gatekeeper. The operator’s actions were binary; either she connected the lines and the call went through, or she didn’t, and nothing happened. Of course, one operator couldn’t connect you to any other phone, but participated in groupings of phones with some logical or functional structure. Ultimately, the operators were the enabler of communication, physically putting two entities into contact to perform whatever business they had with each other.
Within our bodies, tyrosine kinases are enzymes responsible transferring phosphate to proteins; a chemical exchange critical towards a great number of cellular functions, and in a sense, the tyrosine kinases act as cellular operators, helping implement a physical swap of chemicals that ultimately set in motion a great number of processes. Some very rudimentary cellular functions are initiated by the tyrosine kinases; for example, cell division, which is why mutated kinases can lead to the generation of tumors; i.e., the signaling for cell division gets turned on, and never gets turned off. Inhibiting tyrosine kinases is the mechanism of action for some drugs that target cancer.
The MET gene is responsible for creating the MET receptor tyrosine kinase. This particular receptor is involved in lots of processes that are of great interest to autism; the MET receptor is expressed heavily during embryogenesis in the brain, has immune modulating capacities, and is associated with wound healing, and is particularly implicated in repair of the gastro-intestinal track.
Kinases don’t just fire away, shuttling phosphates around any old time, they must be activated by a triggering molecule, or a ligand. There is only one known ligand for the MET receptor; hepatocyte growth factor, or HGF (also sometimes referred to as HGF/SF, or hepatocyte growth factor/scatter factor). We’ll get to why we bother worrying about HGF a little later on, but it is important to keep in mind that without HGF, the functions affected by the MET-C receptor, early brain development, immune modulating, and wound repair cannot be achieved.
So what about autism, and why is it a beautiful illustration of complexity? Walking our way through the MET findings in autism is a rewarding task; it is one of the few instances I’ve seen where the glimpses of relevance gleaned from straight genetic studies have been incrementally built upon to achieve a much grander understanding of autism. This is the kind of thing that I think a lot of people who dismiss the utility of genetic studies are missing; genetics are only the first piece of the puzzle, it doesn’t only implicate genes, it tells us about the processes and the proteins disturbed in autism; and with that knowledge, we can perform targeted analysis for environmental participants.
The first clues about MET involvement with autism came in 2006, when A genetic variant that disrupts MET transcription is associated with autism (full paper) was published. The abstract is longish, but here is a snipet:
MET signaling participates in neocortical and cerebellar growth and maturation, immune function, and gastrointestinal repair, consistent with reported medical complications in some children with autism. Here, we show genetic association (P = 0.0005) of a common C allele in the promoter region of the MET gene in 204 autism families. The allelic association at this MET variant was confirmed in a replication sample of 539 autism families (P = 0.001) and in the combined sample (P = 0.000005). Multiplex families, in which more than one child has autism, exhibited the strongest allelic association (P = 0.000007).
I appreciate the pleiotropic nature of what we are seeing here, a gene that is involved with brain growth and maturation, immune function, and GI repair. The association in ‘multiplex’ (i.e., families with more than one child with autism) was very, very strong. Even still, this was a pretty short paper, and it was all genetics. Coolness factor: 3.
Neater studies were on the horizon shortly thereafter, a year later, some of the same group looked for expression of MET in post mortem brain tissue and found significantly decreased levels of MET protein in Disruption of cerebral cortex MET signaling in autism spectrum disorder.
MET protein levels were significantly decreased in ASD cases compared with control subjects. This was accompanied in ASD brains by increased messenger RNA expression for proteins involved in regulating MET signaling activity. Analyses of coexpression of MET and HGF demonstrated a positive correlation in control subjects that was disrupted in ASD cases.
This is a nice follow up; lots of times a genetic study might suggest a hit, but we really don’t even know how such a genetic change might manifest physiologically, like having a jigsaw puzzle of solid black and finding two pieces that fit together. In those instances, we can’t really go looking for different levels of the protein, so there you are. In this case, the authors found an allele worth investigating, and then went looking to see if relevant proteins were altered in the population, and in the CNS no less! Not only that, but they also looked at the initiating end of the process, the ligand, HGF, and found abnormalities. Good stuff. Unfortunately, I haven’t found myself a copy of this paper yet, but the fact that other proteins in the pathway were altered is another line of evidence that something is amiss. I’ve begun to appreciate the fact that I have spent a long time under appreciating the interconnectedness of biological systems; you aren’t going to have a disturbance in one system without altering the way upstream, and downstream processes are working; so the fact that we see other proteins, those related to MET functions, modified, makes beautiful sense. Coolness factor: 5.
Likely because of the mixed findings of skewed proteins in the MET pathway (?), the next study in line is, Genetic Evidence Implicating Multiple Genes in the MET Receptor Tyrosine Kinase Pathway in Autism Spectrum Disorder (full paper available). Here’s the abstract:
A functional promoter variant of the gene encoding the MET receptor tyrosine kinase alters SP1 and SUB1 transcription factor binding, and is associated with autism spectrum disorder (ASD). Recent analyses of postmortem cerebral cortex from ASD patients revealed altered expression of MET protein and three transcripts encoding proteins that regulate MET signaling, hepatocyte growth factor (HGF), urokinase plasminogen activator receptor (PLAUR) and plasminogen activator inhibitor-1 (SERPINE1). To address potential risk conferred by multiple genes in the MET signaling pathway, we screened all exons and 5′ promoter regions for variants in the five genes encoding proteins that regulate MET expression and activity. Identified variants were genotyped in 664 families (2,712 individuals including 1,228 with ASD) and 312 unrelated controls. Replicating our initial findings, family-based association test (FBAT) analyses demonstrated that the MET promoter variant rs1858830 C allele was associated with ASD in 101 new families (P=0.033). Two other genes in the MET signaling pathway also may confer risk. A haplotype of the SERPINE1 gene exhibited significant association. In addition, the PLAUR promoter variant rs344781 T allele was associated with ASD by both FBAT (P=0.006) and case-control analyses (P=0.007). The PLAUR promoter rs344781 relative risk was 1.93 (95% Confidence Interval [CI]: 1.12−3.31) for genotype TT and 2.42 (95% CI: 1.38−4.25) for genotype CT compared to genotype CC. Gene-gene interaction analyses suggested a significant interaction between MET and PLAUR. These data further support our hypothesis that genetic susceptibility impacting multiple components of the MET signaling pathway contributes to ASD risk.
We’ve got two new genes added to the mix, PLAUR and SERPINE. The juicy part here is that the authors didn’t look for these variants at random, but performed a targeted search; they knew that the proteins encoded by these genes interact with either MET receptor function or HGF, and they also had found altered expression of these genes in the CNS study. From the Introduction:
The hepatocyte growth factor (HGF) gene encodes the activating ligand for the MET receptor. HGF is translated as an inactive precursor protein that requires cleavage for efficient binding to the MET receptor [Lokker et al 1992]. The activating cleavage of HGF is achieved most efficiently by the enzyme plasminogen activator (urokinase-type; uPA; gene symbol: PLAU) under conditions in which uPA binds to its receptor, the urokinase plasminogen activator receptor (uPAR; gene symbol: PLAUR). Activating cleavage of HGF can be suppressed by the plasminogen activator inhibitor-1 (PAI-1; gene symbol: SERPINE1). Together, these proteins regulate the activity of MET receptor tyrosine kinase signaling, and our recent microarray analyses of postmortem temporal lobe of individuals with ASD indicate that disrupted MET signaling may be common to ASD pathophysiology [Campbell et al 2007]. For example, we found that there is increased expression of the HGF, PLAUR and SERPINE1 transcripts in ASD in postmortem cerebral cortex. The observation of disrupted expression suggests a general dysfunction of MET signaling in the cerebral cortex of individuals with ASD.
The proteins encoded by PLAUR and SERPINE were also found increased in the expression study; a finding further supported by the genetic study here. The really grand slice here is that the SERPINE protein suppresses cleavage of HGF; essentially another way MET function can be affected, from a disturbance upstream of HGF binding. In other words, more SERPINE (possibly as a result of a ‘promoter allele’) would result in less MET receptor activation because the SERPINE interferes with the cleavage of HGF, and thus, another pathway to reduced MET activation. In a finding that seems 20/20 with hindsight, a functional promoter of the SERPINE gene was found to increase autism risk; i.e., if you have more SERPINE, you get less functional HGF, and therefore less triggering of the MET receptor. This is cool and begins a portrait of the complexity; it shows how the effect of reduced MET functionality can come from multiple drivers; the reduced MET allele, or, the promoter SERPINE allele, and what’s more, having both is an even bigger risk; the authors are describing a synergy of low penetrance genes.
From the discussion section of the paper:
Beyond genetic susceptibility, the functional integrity of the MET signaling system also is sensitive to environmental factors. This concept is supported by bioinformatics analyses that identified PLAUR, SERPINE1 and HGF as genes active in immune response regulation, sensitive to environmental exposures, and within chromosomal regions previously implicated in ASD linkage studies [Herbert et al 2006]. Moreover, a recent cell biological study shows that chemically diverse toxicants reduce the expression of MET in oligodendrocyte progenitor cells, a result that is interpreted as the convergence of toxicant effects on oxidative status and the MET-regulating Fyn/c-Cbl pathway
Here are links to the Hebert paper, Autism and environmental genomics, and the Li paper, Chemically Diverse Toxicants Converge on Fyn and c-Cbl to Disrupt Precursor Cell Function. What is neat here is that we are starting to be able to see a pathway of genes, and resultant proteins, that can effect disparate systems. I believe that there is a subset of acupuncture, acupressure that relies on more knuckles than needles, and while the science on accu* based therapies isn’t very good, it does occur to me that in a sense, our lattice work of HGF-PLAUR-SERPINE proteins that participate in the MET-C process are pressure points in a delicate system, push a little bit and things will bend down the line accordingly. It also exemplifies why I am offended by highly negative attitudes on genetic studies held by people who believe in a non trivial, environmentally mediated increase in the rates of autism; we are approaching a nearly impossible to overturn reality that genes we know to be associated with autism are particularly sensitive to interference from environmental agents, and participate in immune function. That is important information. Coolness factor 8. First glimpse of beauty factor: 10.
Next up we have Dynamic gene and protein expression patterns of the autism-associated Met receptor tyrosine kinase in the developing mouse forebrain (full paper).
The establishment of appropriate neural circuitry depends upon the coordination of multiple developmental events across space and time. These events include proliferation, migration, differentiation, and survival – all of which can be mediated by hepatocyte growth factor (HGF) signaling through the Met receptor tyrosine kinase. We previously found a functional promoter variant of the MET gene to be associated with autism spectrum disorder, suggesting that forebrain circuits governing social and emotional function may be especially vulnerable to developmental disruptions in HGF/Met signaling. However, little is known about the spatiotemporal distribution of Met expression in the forebrain during the development of such circuits. To advance our understanding of the neurodevelopmental influences of Met activation, we employed complementary Western blotting, in situ hybridization and immunohistochemistry to comprehensively map Met transcript and protein expression throughout perinatal and postnatal development of the mouse forebrain. Our studies reveal complex and dynamic spatiotemporal patterns of expression during this period. Spatially, Met transcript is localized primarily to specific populations of projection neurons within the neocortex and in structures of the limbic system, including the amygdala, hippocampus and septum. Met protein appears to be principally located in axon tracts. Temporally, peak expression of transcript and protein occurs during the second postnatal week. This period is characterized by extensive neurite outgrowth and synaptogenesis, supporting a role for the receptor in these processes. Collectively, these data suggest that Met signaling may be necessary for the appropriate wiring of forebrain circuits with particular relevance to social and emotional dimensions of behavior.
Coooooool. Here we touch on the complexity of brain formation, all the little things that need to go exactly right, and how MET might play a role in that incredibly complicated dance. Even better, a mouse model is used to gain an understanding of where and when peak expression of MET proteins occur, a period of significant changes to neural structures and the formation of synapses, the physical structures that enable thought. This is a dense paper, too dense to get deeply into blockquoting for this posting, but there are some parts that deserve notice, namely, documentation of spatially localized MET expression in brain areas associated with social behaviors and some fine grained information on the specific parts of synapse formation that utilize MET. Coolness factor: 8. Complexity Factor: 12.
Here is a paper that a lot of people that play skeptics on the Internet ought to hate, Distinct genetic risk based on association of MET in families with co-occurring autism and gastrointestinal conditions. (full paper)
In the entire 214-family sample, the MET rs1858830 C allele was associated with both autism spectrum disorder and gastrointestinal conditions. Stratification by the presence of gastrointestinal conditions revealed that the MET C allele was associated with both autism spectrum disorder and gastrointestinal conditions in 118 families containing at least 1 child with co-occurring autism spectrum disorder and gastrointestinal conditions. In contrast, there was no association of the MET polymorphism with autism spectrum disorder in the 96 families lacking a child with co-occurring autism spectrum disorder and gastrointestinal conditions. chi(2) analyses of MET rs1858830 genotypes indicated over-representation of the C allele in individuals with co-occurring autism spectrum disorder and gastrointestinal conditions compared with non-autism spectrum disorder siblings, parents, and unrelated controls.
There is a lot of caution in this paper, but the nice part is that there are biologically plausible mechanisms by which a reduction in MET could snowball into problems in the gastro-intestinal track.
In the gastrointestinal system, MET signaling modulates intestinal epithelial cell proliferation, and thus acts as a critical factor in intestinal wound healing. For example, activation of MET signaling via application of exogenous hepatocyte growth factor has been shown to reduce the effects of experimentally induced colitis, inflammatory bowel disease, and diarrhea.
Pushing on the other end of the balloon, increasing MET signaling, has been shown to help GI problems; no less than evidence that a genetic change associated with autism has biologically plausible mechanisms by which GI problems would be more prevalent. In fact, unless our findings of MET alleles are in error, or our clinical findings of the effects of HGF are spurious, it is absolutely expected. There is also a section with the startlingly simple, and simultaneously great idea of why findings like these might be useful markers for phenotypic categorization in studies in the future; i.e., to discern the prevalence of GI problems in autism, it might, for example, make sense to design that study to take presence or absence of MET alleles into consideration. Nice. Coolness Factor: 7. Insidiousness factor: 9.
Here’s another one that found associations with MET and social behavior, and GI disturbances again. Association of MET with social and communication phenotypes in individuals with autism spectrum disorder
Autism is a complex neurodevelopmental disorder diagnosed by impairments in social interaction, communication, and behavioral flexibility. Autism is highly heritable, but it is not known whether a genetic risk factor contributes to all three core domains of the disorder or autism results from the confluence of multiple genetic risk factors for each domain. We and others reported previously association of variants in the gene encoding the MET receptor tyrosine kinase in five independent samples. We further described enriched association of the MET promoter variant rs1858830 C allele in families with co-occurring autism and gastrointestinal conditions. To test the contribution of this functional MET promoter variant to the domains of autism, we analyzed its association with quantitative scores derived from three instruments used to diagnose and describe autism phenotypes: the Autism Diagnostic Interview-Revised (ADI-R), the Autism Diagnostic Observation Schedule (ADOS), and both the parent and the teacher report forms of the Social Responsiveness Scale (SRS). In 748 individuals from 367 families, the transmission of the MET C allele from parent to child was consistently associated with both social and communication phenotypes of autism. Stratification by gastrointestinal conditions revealed a similar pattern of association with both social and communication phenotypes in 242 individuals with autism from 118 families with co-occurring gastrointestinal conditions, but a lack of association with any domain in 181 individuals from 96 families with ASD and no co-occurring gastrointestinal condition. These data indicate that the MET C allele influences at least two of the three domains of the autism triad.
Really sort of plain, but very nice to see the GI component validated in another data set. Coolness factor 5.
Then a few months ago, Prenatal polycyclic aromatic hydrocarbon exposure leads to behavioral deficits and downregulation of receptor tyrosine kinase, MET was released, an uber cool showcase of the autism bigfoot, the often regaled, only very rarely documented, gene/environment interaction.
Gene by environment interactions (G × E) are thought to underlie neurodevelopmental disorder, etiology, neurodegenerative disorders, including the multiple forms of autism spectrum disorder. However, there is limited biological information, indicating an interaction between specific genes and environmental components. The present study focuses on a major component of airborne pollutants, polycyclic aromatic hydrocarbons (PAHs), such as benzo(a)pyrene [B(a)P], which negatively impacts cognitive development in children who have been exposed in utero. In our study, prenatal exposure of Cpr(lox/lox) timed-pregnant dams to B(a)P (0, 150, 300, and 600 μg/kg body weight via oral gavage) on embryonic day (E14-E17) consistent with our susceptibility-exposure paradigm was combined with the analysis of a replicated autism risk gene, the receptor tyrosine kinase, Met. The results demonstrate a dose-dependent increase in B(a)P metabolite generation in B(a)P-exposed Cpr(lox/lox) offspring. Additionally, a sustained persistence of hydroxy metabolites during the onset of synapse formation was noted, corresponding to the peak of Met expression. Prenatal B(a)P exposure also downregulated Met RNA and protein levels and dysregulated normal temporal patterns of expression during synaptogenesis. Consistent with these data, transcriptional cell-based assays demonstrated that B(a)P exposure directly reduces human MET promoter activity. Furthermore, a functional readout of in utero B(a)P exposure showed a robust reduction in novel object discrimination in B(a)P-exposed Cpr(lox/lox) offspring. These results confirm the notion that common pollutants, such as the PAH B(a)P, can have a direct negative impact on the regulated developmental expression of an autism risk gene with associated negative behavioral learning and memory outcomes.
Oh snap. A common pollutant (well, common in the last few decades anyways), is shown to interact with MET in a dose dependent fashion to reduce protein expression in the brain during embryonic development and cause ‘a robust reduction in novel object discrimination’. (Ouch) This is an example of just what we mentioned above, referenced Herbert, concerning the possibility of MET as a gene sensitive to ‘environmental exposures’. Indeed. From the discussions section:
The results from the present study demonstrate that the transcription and developmental expression patterns of a replicated ASD risk gene, MET, are highly sensitive to a common PAH pollutant. In utero exposure to B(a)P produces an oxidative milieu of B(a)P metabolites in offspring during a key postnatal period of synapse development, providing evidence that environmental exposure creates a sustained cerebral cortical burden that likely contributes to an increased oxidative load. Oxidative stressors in the form of metabolites would be expected to negatively impact gene expression (Kerzee and Ramos 2000) and, more specifically, receptor tyrosine kinase function, including Met (Li et al. 2007). These data suggest that B(a)P-induced exposure would impact the expression of key neurodevelopmental genes, including Met. Additionally, the predominance of the 3-OH and 9-OH metabolites places a sustained burden in the brain because of the potential for further oxidization to form B(a)P quinones (McCallister et al. 2008, Hood et al. 2000, Brown et al. 2007) which undergo redox cycling to generate reactive oxygen species (Kerzee and Ramos 2000, Bolton et al., 2000).
And
In conclusion, specific developmental events such as glutamatergic excitatory synapse formation and maturation may be particularly vulnerable to G x E effects that impact regulatory and signaling proteins involved in this process. While we do not suggest that the current study reflects specific defects related to a complex clinical condition such as the ASDs, current molecular, behavioral and functional imaging data are converging on the concept that the ASDs are a manifestation of altered local and long-distance cortical connectivity (Geschwind et al. 2007, Bill and Geschwind 2009, Geschwind and Levitt, 2007, Levitt and Campbell 2009). Also, Met and other related signaling components of this receptor tyrosine kinase pathway have been implicated in both syndromic and idiopathic disorders where the ASDs are diagnosed at a high rate. In combination with risk alleles in key genes, the in utero exposure to PAHs such as B(a)P, which results in both a reduction in absolute levels and the mistiming of peak Met expression, could drive the system toward a pathophysiological threshold that neither genetic risk nor environmental factors could produce individually. The present study focused on the neocortex, but given the highly restricted spatial and temporal expression of Met in mouse limbic circuits associated with social-emotional development and cognition (Judson et al. 2009), it is likely that perturbations occur throughout these key circuits, including in the hippocampus.
Really cool stuff; particularly the finding that developmental, in utero exposure was capable of driving abnormal protein expression well after birth. This is the best of both sides of the genetics versus environment conundrum; the kind of finding that sheds light on how environmental pollutants could be participating in increasing the number of children with autism by interacting with genetically susceptible children. But what I love about this is that it is the death knell of the fairytale of a static rate, or near static rate of autism, just having the genes or the exposure isn’t enough; instead, the interaction of alleles and timed exposure ‘could drive the system toward a pathophysiolical threshold that neither genetic risk nor environmental factors could produce individually’. I think there are some more findings coming from this group soon that might be exciting, or terrifying, depending on how you see it. (or both). Coolness factor: 99.
So what have we learned and just how cool is it?
1) The MET receptor enables some types of cellular signaling that have relevance to the autism community including synapse formation, immune modulation, and gastro intestinal function. The ligand, or trigger of the MET receptor is HGF.
2) Certain alleles of the MET gene that result in decreased expression are more common in children with autism than people without autism.
3) Consistent with findings of increased prevalence of MET alleles, MET protein expression was found to be decreased in brain tissue from people with autism. Other, related proteins, HGF, PLAUR, and SERPINE were also found to be disturbed.
4) Following up on the differential findings of SERPINE and PLAUR, genetic studies found gene to gene interactions between the MET allele and alleles involved with production of SERPINE and PLAUR. Some of the proteins in question are known to be particularly vulnerable to environmental interference.
5) Animal models tell us that MET is heavily expressed in many areas of the mammalian brain during prenatal and postnatal development, and we gain insight into the spatial and temporal expression of MET during the intricate dance of brain formation.
6) Two studies add evidence that the one function of decreased MET expression, GI disturbances, are indeed found with greater consistency within children with autism and the MET allele. This should be a relatively unsurprising finding considering what we know about MET and children with autism.
7) Finally, a portrait of genetic / environmental interactions capable of disturbing physiology and behavior in ways consistent with findings in autism is rendered using an agent that is the product of the automobile age and already associated with decreased cognitive skills for groups with the highest gestational exposure.
It should be noted that this is just a slice of the MET papers out there in the autism realm; they all shared one or more authors, I picked them because they seem to show a nice progression of knowledge, and incremental approach towards learning more. There is a lof more to learn, in particular, I think that the immune modulating effects of reduced expression would be an interesting subject, but one that will have to wait for another posting.
– pD
Adventures in Expected Findings, Fascinating Complexity, Feedback Loops and Tragic Hypocrisy – ‘Mitochondrial Dysfunction In Autism’
Posted on: December 31, 2010
Hello friends –
The mitochondria discussion in the autism community reminds me a lot about the political discussion in the United States; I know it is important, but it is just so hard for me to care enough to get involved; it mandates walking the plank into an environment dripping in hypocrisy, where highly complicated problems are reduced to black and white meme friendly soundbytes, and discussions that seem a lot more like billboards on different sides of the road than people wanting to discuss anything. It started with the case of Hannah Poling, the little girl who experienced a dramatic and sudden developmental regression following her vaccinations at age 18 months, a case wherein the federal government conceded that vaccines through likely interaction with a pre-existing defect in mitochondrial function were likely the cause of her developmental trajectory and ‘autism like features’.
On some parts of the Internet, you’d think that every single child with an autism diagnosis experienced a drastic, overnight regression in development that Hannah Poling did; despite abundant, clear as the day common sense evidence that the onset of autism is gradual in the overwhelming majority of instances. For the most part, I don’t think it was a spin job. I just don’t think they get it. Although, I must admit, I do believe that there are a very small, but real, minority of parents who have witnessed similar things with their children. Hannah Poling is not unique.
On the other hand, lots of other places you could find people whose online existence is part and parcel with the notion that our real autism rates are static, that the inclusion of less severe children was burgeoning our observed rates of increases, and yet, found the intellectual dishonesty to question if Hannah Poling had autism or not, as if suddenly, in this one particular instance, a diagnostic report of having ‘features of autism’ as opposed to ‘autism’ was meaningful. As if that fucking mattered.
On the one side there is the failure to recognize any semblance of nuance, of complexity, and on the other, a startling hypocrisy and lack of curiosity.
A few weeks ago (maybe a few months ago, by the time I finally get this post published, at my rate), a paper came out that reported, among other things, children with autism were more likely to have mitochondrial dysfunction, mtDNA overreplication, and mtDNA deletions than typically developing children. That paper, of course, is Mitochondrial Disorder In Autism, a new winner in the field of simple to understand, straightforward titles. The good news is that Mitochondrial Disorder In Autism is another portrait of beautiful and humbling complexity with something to offer an open mind. Maddeningly, my real world email address received an embargo copy of the paper, which is somehow protected from copy paste operations, meaning most parts from that paper here will be manually transcribed, or more likely, paraphrased.
This is a cool paper, it sheds light on the possible participation of a widely observed phenomena in autism, increased oxidative stress, gives us additional evidence that the broader incidence of mitochondrial dysfunction is significantly very higher in the autism population, and an possible illustration of a feedback loop.
Very briefly paraphrased (damn you, embargo copy!), the authors used samples of peripheral cells of the immune system, lymphocytes, to test for mitochondrial dysfunction. This is a big step, it allowed the researchers to bypass the traditional method of muscle biopsy, which is both invasive and painful. It is reminiscent of using lymphoblastoid cells as proxies for neural cells in genetic expressions studies; the type of small, incremental data that can get lost in the headline, but has potentially broad applications.
In Mitochondrial Dysfunction in Autism, according to the authors, lymphocytes were considered sufficient surrogates because they are power hungry and derive a significant portion of their energy needs from oxidative phosphorylation; i.e, mitochondrial function. It was small study, ten children with autism and ten controls; I’m not clear why such a small sample was used, perhaps the laboratory time and/or dollar requirements involved with detecting mitochondrial dysfunction, even in peripheral cells, mandated that such small numbers be used. (?) Perhaps funding could not be obtained for a larger study without some preliminary results, and as is mentioned several times in the text, these findings should be replicated if and when possible.
Two types of changes to mtDNA were evaluated for, the ratio of the total number of mtDNA to nuclear DNA (i.e., ‘normal DNA’), and the presence of deletions of parts of mtDNA. These changes are a lot different than what we normally think of in genetic studies, and here’s my short story (barely longer than my understanding) of how.
Each mitochondria has a variable number of mtDNA copies, usually estimated at between 2 and 10. The understanding on what a relatively higher, or lower number of copies of mtDNA means for an organism is ongoing and nascent; for example, findings of associations with lower mtDNA levels in elderly women and cognitive decline, or finding that mtDNA copy number associate positively with fertility, both of which were published in 2010 (there are, conservatively, a brazillion other studies with a broad range of topics). Highly salient for our purposes, however, are findings cited by this article, Oxidative Stress-related Alteration of the Copy Number of Mitochondrial DNA in Human Leukocytes, which reports that cells experiencing oxidative stress had increased number of mtDNA copies. In Mitochonddrial Dysfunction in Autism the authors report an increase in the number of mtDNA copies in the autism group.
Secondarily, the authors also looked for differences in mtDNA structure, but again in this instance, not in the way that we frequently think about genetic studies; they were not looking for an A replaced G mutation that exists in every gene, in every cell, in the individual, but rather, different structural components that were indicative of damage within the copies of mtDNA. Thus, it wasn’t so much a case of a blueprint gone wrong, as much of case by case differences in mtDNA; potentially the result of exposure to reactive oxygen species during replication.
Changes in both copy number of mtDNA (increased), and structure (mostly deletions) were observed in the autism group.
Up and above changes to mtDNA, several biomarkers of direct and indirect mitochondrial dysfunction were measured, including lactacte to pyruvate ratios, (which have been observed abnormal previously in autism and speculated to be resultant from mitochondrial problems), mitochondrial consumption of oxygen, and hydrogen peroxide production, a known signal for some types of mitochondrial dysfunction. Several of the biomarker findings were indicative of problems in mitochondrial function in the autism group, including impaired oxygen consumption, increased hydrogen peroxide production, and as noted by other researchers, higher pyruvate levels, with a consequent decreased lactate to pyruvate ratio compared to controls.
These findings were described by the authors like this:
Thus, lymphocytic mitochondria in autism not only had a lower oxidative phosphorylation capacity, but also contributed to the overall increased cellular oxidative stress.
In plainer English, not only was the ability to produce energy reduced, but the propensity to create damaging byproducts, i.e., oxidative stress, i.e., ROS was increased. Talk about a double whammy! There have been a lot of studies of increased oxidative stress in the autism population, one of the first was Oxidative stress in autism: increased lipid peroxidation and reduced serum levels of ceruloplasmin and transferrin–the antioxidant proteins, with other titles including, Metabolic biomarkers of increased oxidative stress and impaired methylation capacity in children with autism, Oxidative stress in autism, Brain Region-Specific Changes in Oxidative Stress and Neurotrophin Levels in Autism Spectrum Disorders (ASD) and many, many others. Could mitochondrial dysfunction be the cause of increased oxidative stress in autism? Could oxidative stress by the cause of mitochondrial dysfunction in autism? Could both be occurring?
Oxidative stress deserves a free standing post (or a few), but at a high level refers to the creation of damaging particles, called reactive oxygen species by our bodies during the course of many biological operations; including generating energy (i.e., the function of mitochondria). The graceful management of these particles is essential for normal functioning; too little containment and there can be damage to cellular structures like cell membranes, or DNA. You can measure these types of damage, and a wide swath of studies in the autism realm have found that on average, children with autism exhibit a state of increased oxidative stress when compared to children without that diagnosis. A great variety of conditions other than autism, but which you’d still generally rather not have, are also characterized by increased oxidative stress, as are things that you can’t really help having, like getting old.
(It should be noted, however, that in an illustration of humbling complexity, we are now learning that containing free radicals by all means possible may also not necessarily be a good idea; our bodies utilize these chemicals as signals for a variety of things that aren’t immediately obvious. For example, there is preliminary evidence that too much antioxidants can cancel out, the benefits of exercise; our bodies were using the effects of exercise as a signal to build more muscle, likewise, we have evidence that oxidative stress plays a part in apotosis, or programmed cell death, and interfering with that may not be a good idea; in fact, it could, participate in carcinogenisis. There is no free lunch.)
Mitochondrial Dysfunction in Autism speculates that oxidative stress and mitochondrial dysfunction could be linked, either by increased oxidative stress leading to problems in mtDNA replication (i.e., the observed mtDNA problems are a result of aggressive attempts at repair, repair to damage induced by the presence of reactive species), or by deficiencies in the ability to remove ROS; i.e., decreased glutathione levels as observed by James. This really speaks towards the possibility of a feedback loop, something leads to an increase in oxidative stress that cannot be successfully managed, which causes mitochondrial damage, which leads to problems in mtDNA replication, which in turn, leads to dysfunction, and increased oxidative stress. Again, from the paper:
Differences in mtDNA parameters between control children and those with autism could stem from either higher oxidative stress or inadequate removal of these harmful species. The increased reactive oxygen species production observed in this exploratory study is consistent with the higher ratio of oxidized NADH to reduced glutathione in lymphoblastoid cells and mitochondria from children with ASD, supporting the concept that these cells from children with autism present higher oxidative stress. Increased reactive oxygen species production induced by mitochondrial dysfunction could elicit chronic oxidative stress that enhances mtDNA replication and possibly mtDNA repair.
Collectively, these results suggest that cumulative damage and oxidative stress over time may (through reduced capacity to generate functional mitochondria) influence the onset or severity of autism and its comorbid symptoms.
(My emphasis). More on why a little later.
There is a lengthy section of the paper regarding the limitations of the study, including a relatively small sample set, racial differences between the participants, and the possibility that the number of evaluations made could impact the strength of some associations. Detangling the arrow of causality is not possible from this paper, and likely involves different pathways in different patients. None the less, it is additional confirmation of something gone awry in the power processing centers of cells in people with autism.
This is a pretty small study, from a number of subjects perspective, and the pilot nature of the study is somewhat of a problem in trying to determine how much caution we must use when attempting to generalize the findings to a larger population. However, on the other hand, if we look towards earlier findings, some of which were linked above, the reports in Giulivi should not really be that surprising. In fact, we should have been amazed if they hadn’t observed mitochondrial problems.
Here is why:
We have voluminous observations of a state of increased oxidative stress in the autism population; Chauhan 2004, Zoroglu 2004, James 2004, Ming 2005, Yao 2006, James 2009, Sajdel-Sulkowska 2009, Al-Mosalem 2009, De Felice 2009, Krajcovicová-Kudlácková M 2009, El-Ansari 2010, Mostafa 2010, Youn 2010, Meguid 2010, and Sajdel-Sulkowska 2010, all are clinical trials that reported either increased levels of oxidative stress markers, decreased levels of detoxification markers, or both, in the autism group. There is no way, absolutely no way that children with autism have less oxidative stress, or the same oxidative stress than children without that diagnosis, barring some mechanism by which all of the above studies are wrong in exactly the same direction. There is just too much evidence to support an association, and as far as I know, (?) no evidence to counter balance that association. [Please note that the above studies are for biomarker based studies only, I left out several genetic studies with similar end game conclusions; i.e., alleles known to be associated with increased oxidative stress and/or mitochondrial function are also associated with an autism diagnosis.]
We also have just a large body of clinical evidence that tells us that as oxidative stress and mitochondrial function are closely linked, as oxidative stress increases, so too do problems with mitochondrial function and/or replication; Richter 1998, Beckman 1998, Lu 1999, Lee 2000, Wei 2001, Lee 2002, Liu 2003, Liu 2005, Min Shen 2008 are useful examples. Unless all of these studies, and many more, are incorrect in the same way, and the underlying physical foundations of why oxidative stress would lead to mitochondrial function are also incorrect, we must conclude that a state of increased oxidative stress, as observed repeatedly in autism, leads to a degradation of mitochondrial function.
It turns out, there also a growing body of evidence linking oxidative stress and/or mitochondrial dysfunction to other conditions with a neurological basis (Rezin 2009), such as schizophrenia, (Prabakaran 2004, Wood, 2009, Martins-de-Souza 2010, Verge 2010, Bitanihirwe 2011) or bi-polar disorder (Andreazza 2010, Clay 2010, Kato 2006, Kaikuchi 2005). Here is the abstract for Oxidative stress in psychiatric disorders: evidence base and therapeutic implications:
Oxidative stress has been implicated in the pathogenesis of diverse disease states, and may be a common pathogenic mechanism underlying many major psychiatric disorders, as the brain has comparatively greater vulnerability to oxidative damage. This review aims to examine the current evidence for the role of oxidative stress in psychiatric disorders, and its academic and clinical implications. A literature search was conducted using the Medline, Pubmed, PsycINFO, CINAHL PLUS, BIOSIS Preview, and Cochrane databases, with a time-frame extending to September 2007. The broadest data for oxidative stress mechanisms have been derived from studies conducted in schizophrenia, where evidence is available from different areas of oxidative research, including oxidative marker assays, psychopharmacology studies, and clinical trials of antioxidants. For bipolar disorder and depression, a solid foundation for oxidative stress hypotheses has been provided by biochemical, genetic, pharmacological, preclinical therapeutic studies and one clinical trial. Oxidative pathophysiology in anxiety disorders is strongly supported by animal models, and also by human biochemical data. Pilot studies have suggested efficacy of N-acetylcysteine in cocaine dependence, while early evidence is accumulating for oxidative mechanisms in autism and attention deficit hyperactivity disorder. In conclusion, multi-dimensional data support the role of oxidative stress in diverse psychiatric disorders. These data not only suggest that oxidative mechanisms may form unifying common pathogenic pathways in psychiatric disorders, but also introduce new targets for the development of therapeutic interventions.
(my emphasis)
Given all of this, one might consider casting an extremely skeptical eye towards the argument that the observations in Mitochondrial Dysfunction in Autism are insufficiently powered to reach any conclusions about an association; at this point, I think it is fair to say that what should have been surprising finding would have been a lack of mitochondrial dysfunction in autism. We need to rethink some foundational ideas about the relationship between oxidative stress, mitochondrial function, other neurological disorders, and/or assume that a dozen studies are all incorrect in the same way before the small number of participants and other limitations of this study should cause us to cast too much doubt on the findings. The findings in Mitochondrial Dysfunction in Autism are not due to random chance.
All that being said, there are still lots of questions; the most intriguing ones I’ve seen raised in other discussions on this paper would include, Is the mitochondrial dysfunction physiologically significant? and secondly, What has caused so many children with autism to exhibit these physiological differences?
I’ll admit it, early on in my online/autism persona lifetime, I’d have viewed the first question as largely deserving of a healthy dose of (hilariously delivered) sarcasm. But the reality is that this is a more difficult question to answer than it would seem on the surface. The reasons I’ve seen posited that this might be valid sound pretty good at first glance, i.e., the brain is the most prolific user of energy in the body, and problem with energy creation there are pretty simple to equate to cognitive problems. And this might be what is happening, I don’t believe we have enough information reach any conclusions. I will note, however, with no small amount of amusement, that the online ‘skeptical’ community had no problem with this exact argument in discussing what happened to Hannah Poling, as long as it was exceptionally rare.
Specifically speaking towards the problems of physiological significance, we haven’t any direct evidence one way or the other that the mitochondrial dysfunction observed in muscle biopsy or lymphocytes is present in the CNS of people with autism, and this is an important distinction; it is known that there are large differences in mitochondrial need and function between tissue type, and it is almost always dangerous to assume that because you see something outside the privileges of the blood brain barrier, that you will see the same thing within it. Therefore, we should remember that it is possible that the brains are unaffected, while the peripheral cells are.
However, we do have some indirect evidence to suggest that there are mitochondrial function problems in the CNS in the autism population. Based on studies that have measured oxidative stress levels in the brain, specifically Brain Region-Specific Changes in Oxidative Stress and Neurotrophin Levels in Autism Spectrum Disorders (ASD) we have preliminary evidence that areas of the brain are affected by high levels of oxidative stress. Furthermore, we have a multitude of studies regarding an ongoing immune response in the brain in autism, and we know that the immune response can generate oxidative stress, and indeed, interact with some of the results of oxidative stress, potentially participating in a feedback loop.
In short, we know that inflammation, oxidative stress, and mitochondrial function are closely linked; considering the fact that we have evidence of two of these processes being altered in the CNS in autism, barring an unforeseen mechanism by which this association is not in place in the brain, an exceedingly unlikely situation given our observations in other cognitive domains, it seems probable that some degree of mitochondrial dysfunction occurs in the brain as well as the periphery. If this is sufficient to cause autism will require more studies; some evaluations correlating behavioral severity and / or multiple evaluations over time would be good starting points. as well, of course, as direct CNS evaluation.
The second question, towards relevance of these findings, the reason such a large percentage of children with autism appear to have characteristics of mitochondrial dysfunction is even more difficult to detangle. The potential of a feedback loop existing between oxidative stress and mitochondrial function was problematic enough, but it seems likely there could be other participants, for example, the immune system. There are repeated observations of an exaggerated immune response, from genetic predispositions to known toll like receptor promoters, circulating levels of endogenous factors associated with a vigorous immune response, baseline levels of cytokines and chemokines, and cytokine values resulting from direct toll like receptor activation. Is the over active inflammatory response observed in autism causing the mitochondrial dysfunction through an increase in oxidative stress? Is the increased oxidative stress causing an ongoing inflammatory response? Studies evaluating for a relationship between these parameters would help to answer these questions.
For a real world example of why such a relationship might be possible, we can take a look at a paper that landed in my inbox around the same time that Mitochondrial Dysfunction in Autism did, Dopaminergic neuronal injury in the adult rat brain following neonatal exposure to lipopolysaccharide and the silent neurotoxicity. This paper is another that shows some very difficult to predict outcomes as a response to an early life immune challenge. Here is the abstract:
Our previous studies have shown that neonatal exposure to lipopolysaccharide (LPS) resulted in motor dysfunction and dopaminergic neuronal injury in the juvenile rat brain. To further examine whether neonatal LPS exposure has persisting effects in adult rats, motor behaviors were examined from postnatal day 7 (P7) to P70 and brain injury was determined in P70 rats following an intracerebral injection of LPS (1 mg/kg) in P5 Sprague–Dawley male rats. Although neonatal LPS exposure resulted in hyperactivity in locomotion and stereotyped tasks, and other disturbances of motor behaviors, the impaired motor functions were spontaneously recovered by P70. On the other hand, neonatal LPS-induced injury to the dopaminergic system such as the loss of dendrites and reduced tyrosine hydroxylase immunoreactivity in the substantia nigra persisted in P70 rats. Neonatal LPS exposure also resulted in sustained inflammatory responses in the P70 rat brain, as indicated by an increased number of activated microglia and elevation of interleukin-1b and interleukin-6 content in the rat brain. In addition, when challenged with methamphetamine (METH, 0.5 mg/kg) subcutaneously, rats with neonatal LPS exposure had significantly increased responses in METH-induced locomotion and stereotypy behaviors as compared to those without LPS exposure. These results indicate that although neonatal LPS-induced neurobehavioral impairment is spontaneously recoverable, the LPS exposure-induced persistent injury to the dopaminergic system and the chronic inflammation may represent the existence of silent neurotoxicity. Our data further suggest that the compromised dendritic mitochondrial function might contribute, at least partially, to the silent neurotoxicity.
(my emphasis)
Briefly, the researchers challenged the animals with an immune stimulator shortly after birth, and then went on to observe chronic microglial activation and inhibited mitochondrial function into adulthood. Behavioral problems included hyperactivity and stereotyped tasks (though these behaviors appeared to reverse in adulthood. Subsequent challenge with methamphetamine in adulthood resulted in increased locomotive and stereotyped behaviors in the treatment group.
Check that out! These animals never actually got sick, their immune system had only been fooled into thinking that it was under pathogen attack, and yet, still showed chronic activation of the neuroimmune system and impaired mitochondrial function in dendrites into adulthood! ). In a sense, it might be appropriate to say, then, that the behaviors were not a state of stasis. Talk about an inconvenient finding.
There is also the possibility that exposure to chemicals, such as pesticides, may be able to cause mitochondrial dysfunction.
Finally, during the time it took me to put this post together, several other reviews of Mitochondrial Dysfunction in Autism landed online in places that purport to be bound by objective and dispassionate evaluation of the science of autism; Respectful Insolencence, LBRB, and Science2.0 all had posts (probably others too). [The masochists out there that go through the discussion threads will note that several of the thoughts in this posting were experimented with in responses to these threads, ideas which were largely, or entirely, ignored.] If you were to read these other reviews (I would recommend that you do), you might come away with the impression that Mitochondrial Dysfunction in Autism consisted of nothing more than criteria for selecting participants and limitations of the study. The calls for caution in running wild with these findings are there, and I largely agree with this sense of caution, as is the admission that this is an area that should be studied more intently, but nowhere was there any acknowledgement of the consistency between these findings and the repeated observations of increased oxidative stress in autism and the biological reality that oxidative stress is linked with mitochondria function, nowhere was there any mention of the fact that the findings were in alignment with deficiencies in detoxification pathways as observed multiple times in autism, nowhere was there anything regarding our voluminous evidence of impaired mitochondrial function in a veritable spectrum of cognitive disorders. Did the online skeptical community get a different copy of the paper that I did? Perhaps, were they unaware of the repeated reports of increased oxidative stress in autism, and the incontrovertible evidence of an association between oxidative stress and mitochondrial dysfunction? Is there a chance that their pubmed results regarding mitochondria and disorders like schizophrenia or bi-polar disorder are different than mine?
I am afraid that this is what the vaccine wars and wrangling over the meaning of neurodiversity have done to us; the skeptical community absolutely went “all in” on the premise that the Hannah Poling concession was founded on a very, very rare biological condition. They have sunk one hundred and ten percent of their credibility behind the notion that thimerosal based studies and MMR based studies are sufficient to answer the question of if vaccines can cause autism, or if we must, features of autism. And now, with converging evidence from several directions pointing towards a confluence of mitochondria impairment and oxidative stress in autism and other neurological conditions, speaking towards the meat of Mitochondrial Dysfunction in Autism is more than just eating crow, it is akin to blaspheming, for if diagnosable mitochondrial disorder affects a meaningful fraction of children with autism, and mitochondrial dysfunction a much larger percentage, the foundations behind the meme of the vaccine question as one that needs no further evaluations begins to fall apart. That is a legitmately scary proposition, but one that is going to have to be reckoned with sooner or later; the only difference is that the more time passes, the greater the credibility strain on the mainstream medical establishment when, eventually, it is admitted, that we need to come up with good ways to generate quality information on vaccinated and unvaccinated populations.
Similarly there is remakarble opposition in some quarters to the idea of imparied detoxificiation pathways, or indeed, a state of increased oxidative stress in some of the same places. I think the underlying reason for this is that some of these early findings were used by some DAN doctors to promote things like chelation, almost certainly the wrong treatment for the overwhelming majority of children on whom it was performed; and in a well intentioned zeal to discount some of these practioners, as well as the outrage over statements by some (i.e., ‘toxic children’), the reality of the situation; that our children are more likely to have increased oxidative stress, do have less glutiathione, became acceptable facts to bypass in the rush to hurl insults or wax poetic. We can acknowlege that children with autism have these conditions while simultaneously expressing concern, or outrage, at the notion that this makes them poisonous; but ignoring the physiological reality of our findings does nothing to help anyone. The data is the data.
This is all too bad. In fact, it is worse than too bad; there is no reason, absolutely no reason that a discussion on mitochondrial impairment must focus exclusively on the vaccine question, in fact, just the opposite. There are lots of ways to achieve an endpoint of mitochondrial dysfunction, and lots of things besides vaccines that can be problematic for people with this problem. (including, of course, actual infection!) But we have become so polarized, so reliant on hearing the same soundbyte laden diatribes, that any sense of nuance on the question immediately labels on as ‘anti vaccine’, ‘anti science’ (even worse!), or for that matter, ‘pro-vaccine’ or shill. The questions raised by Mitochondrial Dysfunction in Autism are important and aren’t going to go away, no matter how inconvenient the follow up findings may be.
– pD
The Beautiful, Dispassionate, and Humbling Complexity of Environmental Enrichment, Butterfly Wings, and How the Granularity of Our Filters Control What We Think We Know
Posted on: November 5, 2010
- In: Autism | BDNF | Brain | Epigenetics | Epigenome | Intriguing | Mr. Rat | Some Jerk On The Internet
- 4 Comments
Hello friends –
I’ve been planning to write something about the idea of environmental enrichment for a while now but other stuff kept on popping up. At a broad level, researchers are finding that the type of external stimulation an animal is raised or housed in can have dizzyingly unpredictable effects on a range of physiological and behavioral endpoints, many of which are of great interest to the autism community. This is a tough area to dance through in the autism world; the available literature has shades of refrigerator mothers, and TV based causation; yet, the underlying idea of environmental enrichment, that the external environment can affect a person in a very physical way, is something known to the autism community in concrete ways. What’s more, much of our data in the environmental enrichment realm is nothing less than compelling. It is exciting to know that we are beginning to have insight into the molecular mechanisms by which the environment can affect the body and brain, and with that insight, just maybe the wisdom to help our children and help ourselves.
From the biomarker side, a couple of neat studies would include Environmental enrichment reduces Abeta levels and amyloid deposition in transgenic mice, wherein striking reductions in amyloid proteins were found in knockout mice housed in a stimulating environment compared to those in standard housing. Or the very recently published, Complex environment experience rescues impaired neurogenesis, enhances synaptic plasticity, and attenuates neuropathology in familial Alzheimer’s disease-linked APPswe/PS1DeltaE9 mice which hits a lot of keywords with parallels to the autism research world. There are many, many others including hits like Altered plasticity in hippocampal CA1, but not dentate gyrus, following long-term environmental enrichment, or hilariously named, soundbyte laden, Hippocampal epigenetic modification at the brain-derived neurotrophic factor gene induced by an enriched environment. The lower level details of these studies and their many ancestors are beyond the scope of what I have time for now, but clearly anything that can be affecting synaptic plasticity, BDNF expression, and neurogenesis should be of interest to the autism community.
If we turn to measurements that go beyond frozen slices of tissue (but do not necessary exclude them), our data regarding behavioral differences in EE housed animals is also robust. For example, we could look at Environmental enrichment delays the onset of memory deficits and reduces neuropathological hallmarks in a mouse model of Alzheimer-like neurodegeneration, which found that EE housed mice performed significantly better at memory tasks that other mice housed in non stimulatory environments. Environmental-enrichment-related variations in behavioral, biochemical, and physiologic responses of sprague-dawley and long evans rats concludes by saying, The data support the claim that environmental enrichment may render animals more resilient to challenges. Ouch. Forgetting chronic diseases such as Alzheimer’s or Parkinson’s, which get a lot of attention in the EE world, even things like traumatic brain injury or lack of oxygen to the brain seem to show benefits from a stimulating environment, as we can see from studies like Environmental Enrichment Influences BDNF and NR1 Levels in the Hippocampus and Restores Cognitive Impairment in Chronic Cerebral Hypoperfused Rats or Empirical comparison of typical and atypical environmental enrichment paradigms on functional and histological outcome after experimental traumatic brain injury. The flip side, a ‘de-enriched’ environment has findings along the lines of what you might expect; i.e., Environmental impoverishment and aging alter object recognition, spatial learning, and dentate gyrus astrocytes. Ouch.
So what is, exactly, an enriched environment? The methods section from Environmental enrichment reduces Abeta levels and amyloid deposition in transgenic mice says this:
Animal experiments were conducted in accordance with institutional and NIH guidelines. Male offspring of transgenic breeding pairs APPswe × PS1 were separated from their mother at 3 weeks of age (after weaning), genotyped, and housed four males to a cage. Enriched environment was composed of large cages running wheels, colored tunnels, toys, and chewable material. For 1 month, mice were exposed to enriched environment every day for 3 hr and were returned to their original cages for the remaining 21 hr. After 1 month of daily enrichment, mice were introduced to the enriched environment three times a week for an additional 4 months. Mice were sacrificed at age of 6months. Following weaning, a control group of animals was maintained for 5 months in standard housing conditions.
Lets consider the implications of these findings. Reducing amyloid buildup has been a holy grail of the pharmaceutical companies for a long time now, though it is possible that this plan of attack was based on bad assumptions. Tens of millions of dollars (or hundreds of millions) have been thrown at synthetic ways to reduce or eliminate the buildup of amyloid plaque in mice, rats, and recently, people with mixed to poor results. Even if it turns out that amyloid isn’t causing Alzheimer’s, that doesn’t do anything to change the fact that these researchers were able to make very significant changes to biological systems by setting their rats up in a rat mansion with rat delivered food and a rat tennis court for a few hours a day. Despite the mixed findings as of late on the effect of brain training in order to stave off dementia, I think most of us have known someone, or Kevin Baconed one degree out to know someone who has seemingly either degenerated with a stagnant environment, or kept on trucking through old age with a more active lifestyle. Is their environment participating?
So what about autism? The most extreme and tragic parallels can be seen in studies of children from orphanages, notably in Romania, where children were raised in absolutely destitute surroundings. A recent study is entitled Stereotypies in children with a history of early institutional care with these findings:
RESULTS: At the baseline assessment prior to placement in foster care (average age of 22 months), more than 60% of children in institutional care exhibited stereotypies. Follow-up assessments at 30 months, 42 months, and 54 months indicated that being placed in families significantly reduced stereotypies, and with earlier and longer placements, reductions became larger. For children in the foster care group, but not in the care as usual group, stereotypies were significantly associated with lower outcomes on measures of language and cognition.
CONCLUSIONS: Stereotypies are prevalent in children with a history of institutional care. A foster care intervention appears to have a beneficial/moderating role on reducing stereotypies, underscoring the need for early placement in home-based care for abandoned children. Children who continue to exhibit stereotypies after foster care placement are significantly more impaired on outcomes of language and cognition than children without stereotypies and thus may be a target for further assessments or interventions.
Another study that looks specifically towards autistic like behaviors in children raised in orphanages is Early adolescent outcomes of institutionally deprived and non-deprived adoptees. III. Quasi-autism.
BACKGROUND: Some young children reared in profoundly depriving institutions have been found to show autistic-like patterns, but the developmental significance of these features is unknown.
METHODS: A randomly selected, age-stratified, sample of 144 children who had experienced an institutional upbringing in Romania and who were adopted by UK families was studied at 4, 6, and 11 years, and compared with a non-institutionalised sample of 52 domestic adoptees. Twenty-eight children, all from Romanian institutions, for whom the possibility of quasi-autism had been raised, were assessed using the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule (ADOS) at the age of 12 years.
RESULTS: Sixteen children were found to have a quasi-autistic pattern; a rate of 9.2% in the Romanian institution-reared adoptees with an IQ of at least 50 as compared with 0% in the domestic adoptees. There were a further 12 children with some autistic-like features, but for whom the quasi-autism designation was not confirmed. The follow-up of the children showed that a quarter of the children lost their autistic-like features by 11. Disinhibited attachment and poor peer relationships were also present in over half of the children with quasi-autism.
CONCLUSIONS: The findings at age 11/12 years confirmed the reality and clinical significance of the quasi-autistic patterns seen in over 1 in 10 of the children who experienced profound institutional deprivation. Although there were important similarities with ‘ordinary’ autism, the dissimilarities suggest a different meaning.
Similarly depressing findings can be found in places like Institutional rearing and psychiatric disorders in Romanian preschool children, or Placement in foster care enhances quality of attachment among young institutionalized children. There is a gripping This American Life about a child adopted from Romania. Please be sure your head is in the right place before listening to part II, which describes a family trying to decide of their very severely autistic son should be placed in residential care. I ran into this episode on accident one day in the car when I was already feeling bleak and walked out the other end pretty fucked up for a few days; those guys are really good and the narrative can hit very close to home for some.
Calling up images from the dark(er) days of autism and Bettleheim we have an array of studies on the effect of maternal separation and subsequent physiological and behavioral effects that have parallels in autism findings. For example, here is an abstract from Behavioural and neurochemical consequences of early weaning in rodents
Among all mammalian species, pups are highly dependent on their mother not only for nutrition, but also for physical interaction. Therefore, disruption of the mother-pup interaction changes the physiology and behaviour of pups. We review how maternal separation in the early developmental period brings about changes in the behaviour and neuronal systems of the offspring of rats and mice. Early weaning in mice results in adulthood a persistent increase in anxiety-like and aggressive behaviour. The early-weaned mice also show higher hypothalamic-pituitary-adrenal activity in response to novelty stress. Neurochemically, the early-weaned male mice, but not female mice, show precocious myelination in the amygdala, decreased brain-derived neurotrophic factor protein levels in the hippocampus and prefrontal cortex, and reduced bromodeoxyuridine immunoreactivity in the dentate gyrus. Because higher corticosterone levels are persistently observed up to 48 h when the mice are weaned on postnatal day 14, the exposure of the developing brain to higher corticosterone levels may be one of the effects of early weaning. These results suggest that deprivation of the mother-infant interaction during the late lactating period results in behavioural and neurochemical changes in adulthood and that these stress responses are sexually dimorphic (i.e. the male is more vulnerable to early weaning stress).
The rapidfire analysis tells us that altered HPA-Axis activity, BDNF levels, and anxiety all have parallels in autism, along with perhaps the most consistent finding in animal studies that have interest to autism, the problems of being born male and consequent risk factors from nearly everything. This is a review paper, but there are a gazillion others with titles like Maternal separation disrupts dendritic morphology of neurons in prefrontal cortex, hippocampus, and nucleus accumbens in male rat offspring, Short- and long-term consequences of different early environmental conditions on central immunoreactive oxytocin and arginine vasopressin levels in male rats, or Prolonged maternal separation decreases granule cell number in the dentate gyrus of 3-week-old male rats.
Though I’m pretty sure that this should be clear to everyone, just to be sure, I’m not proposing a refrigerator mother theory of autism. But the data is the data and the logical opposite of an enriched environment is also born out.
So what? Well, this reminded me of the “Rat Park” studies an Internet friend told me about, wherein researchers seemed to find that animals dosed with opiates for several weeks would voluntarily wean themselves from the drugs if moved to much larger enclosures where they had access to either drugged water or plain water. The startling thing about the Rat Park studies isn’t so much what was learned about opiate addiction, so much as the broader implications that the existing studies on drug addiction might not be studying the right thing; that instead of testing the effects on opiate availability on rodents, they were testing the effects of opiate availability on chronically depressed rodents. Following through, it occurs to me that in addition to the bazillion other problems we have moving from rodent to human with anything other than a hopeful educated guess, we must grudgingly admit that the condition the animals were housed in may be affecting a lot of findings. As if we didn’t have enough confounders already!
But more importantly, these types of findings are beautiful portraits of complexity, the dispassionate hand of nature and the dangers of thinking you understand.
There are so many instances where we have found that as we gain the ability to make more detailed observations, we learn that our existing conclusions were crude facsimiles of reality, and oftentimes, conclusions that had been formed on dangerously unsound foundations. By way of example, exposure to lead and consequent effects on neurodevelopment. At one point, lead was used as a pesticide, eventually we figured out that wasn’t such a good idea, but it should be fine in paint and gasoline. Then we removed it from paint. Then gasoline. And just a few years back, the ‘safe’ level of lead was deemed to be zero; and even the tiniest increases in lead were associated with developmental problems. Of course, this was always the reality, but it was not until we applied filters of sufficient sophistication that our observations were adequately powered to understand the reality. Are our studies of any number of factors clever enough to discern the changes we’d like to understand when we realize that subtle changes are still changes?
It gets thornier for the autism community in particular. One thing a lot of our kids aren’t very good at are “complex environmental interactions”, in fact, a lot of our kids are flat out terrible at them. After a couple of weeks/months/years of soul crushing experiences trying new things out with kid autism, some parents might start to think to themselves that a trip to the zoo, or the museum, or the movie theater or even the super market just isn’t worth it. The result, while not necessarily an abject environment can start to resemble a single square mile of ocean, indistinguishable from the sea for backwards or forwards; the real world equivalent of a DVD set on repeat play. I speak from experience, a rule in our household when one of the parents had to leave the other home for a weekend with kid autism was ‘survive, don’t thrive’. If that meant a trip to the same lake, spinning the same DVD, and a meal of the same food, but a relatively meltdown free weekend, that was OK.
We survived, but did we spite ourselves in the process? Were we reinforcing at a neurochemical level some of the causes of the very behaviors that were causing us to retreat to the middle of the ocean? We are starting to learn that this might be somewhat of a self fulfilling prophecy; taking a child who already does very poorly in new environments and run him or her through the same things over and over could be exacerbating their ability to handle new environments in a physiological way. The data is the data.
That being said, there is an upside, a big one; the flip side is that parents have a chance to make real and salient changes in their child by the least controversial methods possible; gentle but repeated exposure to new things. For some of us, this means a lot of shitty days and late night drinks to get through to the other side. That’s OK. It’s worth it. Steel yourself for a meltdown and turn off the goddamned TV, take kid autism to the zoo, or the bounce house playground, or art festival, or a ‘non-autism’ friends house. A lot of our children might need a helping hand, a gentle push, or a well meaning shove into the world, but someone has to do it, and the world isn’t going to get any less complicated while we wait. When it works out, and you have even a single new experience your child enjoys, that is an enriched environment for you, and enriched environments aren’t just for rats and kids.
– pD
