passionless Droning about autism

Archive for the ‘Some Jerk On The Internet’ Category

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

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

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

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

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


Hello friends –

One of the more beautiful and terrifying concepts I’ve come across in the last year or so is the idea of ‘developmental programming’, or sometimes fetal programming, or as I imagine it will eventually be recognized, the realization of subtle change is still change, and subtle change during critical timeframes can amplify into meaningful outcomes.  The underlying hypothesis is that environmental influences during early life, gestation, infancy, or even childhood, have the capacity to permanently influence physiological and behavioral state into adulthood.  The available evidence implicates the potential for developmental programming to be involved with an assortment of conditions that on the whole, you’d rather not have than have, including the spectrum sized set of disorders grouped as ‘metabolic syndrome’ that incorporates several risk factors for cardiovascular disorders, obesity, type II diabetes.  There is also less pronounced evidence for some autoimmune disorders, and perhaps, autism. 

Here is the most concise explanation of developmental programming I’ve seen so far, from Developmental Programming of Energy Balance and Its Hypothalamic Regulation

The concepts of nutritional programming, fetal programming, fetal origins of adult disease, developmental origins of health and disease, developmental induction, and developmental programming were all conceived to explain the same phenomenon: a detrimental environment during a critical period of development has persistent effects, whereas the same environmental stimulus outside that critical period induces only reversible changes.

I am absolutely in love with the importance of time dependent effects, a sort of combo pack of why the dose doesn’t always make the poison, and the importance of understanding subtle interactions in developing systems. 

The area of developmental programming that has a ton of research in the human field and animal models is the link between metabolic syndrome and a differently structured uterine and/or early postnatal environment.  A nice review from 2007, Developmental programming of obesity in mammals (full paper) has this:

Converging lines of evidence from epidemiological studies and animal models now indicate that the origins of obesity and related metabolic disorders lie not only in the interaction between genes and traditional adult risk factors, such as unbalanced diet and physical inactivity, but also in the interplay between genes and the embryonic, fetal and early postnatal environment. Whilst studies in man initially focused on the relationship between low birth weight and risk of adult obesity and metabolic syndrome, evidence is also growing to suggest that increased birth weight and/or adiposity at birth can also lead to increased risk for childhood and adult obesity. Hence, there appears to be increased risk of obesity at both ends of the birth weight spectrum.

And

Childhood and adult obesity are amongst the cardiovascular risk factors now considered to be ‘programmed’ by early life and, perhaps counter-intuitively, babies subjected either to early life nutritional deprivation or to an early environment over-rich in nutrients appear to be at risk. Supportive evidence includes the observation of a ‘U-shaped’ curve which relates birthweight to risk of adult obesity (Curhan et al. 1996).

[Check out that example of a hormetic dose curveTotally sweet!]

The list of papers supporting a link between abnormal gestational or birth parameters and subsequent obesity in the offspring is very, very voluminous.   The satellite level high view of the research starts with Dutch mothers during a time of famine, and the observations that these children were much more likely to be obese at nineteen in Obesity in young men after famine exposure in utero and early infancy.  Later, infants in England were found to have birth weight positively correspond to adult weight in Birth weight, weight at 1 y of age, and body composition in older men: findings from the Hertfordshire Cohort Study (full paper).  A study with twin pairs, Birth weight and body composition in young women: a prospective twin study  had similar findings, but with the additional coolness factor of being able to detect differences between genetically identical twins who happened to be born at different weights.  There are studies on infants that are born light but then ‘catch up’are consistently more likely to be obese, a review of which can be found in Rapid infancy weight gain and subsequent obesity: systematic reviews and hopeful suggestions.  Startlingly, Weight Gain in the First Week of Life and Overweight in Adulthood observed that formula fed babies who gained considerable weight during the first eight days after birth were more likely to be obese as adults, similar to other findings implicating formula fed babies with adult obesity.

Therearealsoconservativelya bazillionanimalmodelsthattellusthatthestudiesin humans are accurate.

Part of me hates the deterministic nature of these findings, it’s really just an extension of the fatalism of genetic assignment, but on the other hand, the data is the data.  I must admit, I am in love with the underlying evolutionary cleverness of the thrifty phenotype end of the U curve on display; a fetus or neonate that is deprived of nutrients, or perhaps, some types of nutrients, programs itself for an environment in which food is scarce, handling calories differently at a very fine grained metabolic level.  From a survival standpoint this modification is most definitely the smart move; all inbound indicators are signaling to the fetus that calorie acquisition is going to be tough on the outside, and as a result, the physiology is tweaked so that baby is ready to make the absolute most of any available nutrients.  If that child, however, is raised in a world with plentiful calories, if not always, beneficial calories, they tend to store fat more readily than a baby/child/adult that did not receive the same messages in utero.  Neat.

Like lots of things I seem to be running into, our observations of what is happening seem to be more advanced than our understanding of how it is happening.  The ideas of developmental programming have been around for a while, but we are still very much in the learning phase regarding mechanism of action, a very thorough review that I ran into can be found here:  Mechanisms of developmental programming of the metabolic syndrome and related disorders.   (full paper). 

Another example of programming a bit closer to home to the autism world has been in the news lately, namely the replication of findings that children who grow up around farm animals, or in some cases, pets, are less likely to suffer from allergies and /or asthma than children who grow up without that exposure.  These findings are also very robust, and appear to implicate similar critical developmental timeframes including the gestational environment, infancy, and toddlerhood. 

Here is an example of the kind of thing in this area,  Farming environment and prevalence of atopy at age 31: prospective birth cohort study in Finland

Cross-sectional studies have shown an association between the farming environment and a decreased risk of atopic sensitization, mainly related to contact with farm animals in the childhood. Objective Investigate the association of a farming environment, especially farm animal contact, during infancy, with atopic sensitization and allergic diseases at the age of 31. Methods In a prospective birth cohort study, 5509 subjects born in northern Finland in 1966 were followed up at the age of 31. Prenatal exposure to the farming environment was documented before or at birth. At age 31, information on health status and childhood exposure to pets was collected by a questionnaire and skin prick tests were performed. Results Being born to a family having farm animals decreased the risk of atopic sensitization [odds ratio (OR) 0.67; 95% confidence interval (CI) 0.56-0.80], atopic eczema ever (OR 0.77; 95% CI 0.66-0.91), doctor-diagnosed asthma ever (OR 0.74; 95% CI 0.55-1.00), allergic rhinitis at age 31 (OR 0.87; 95% CI 0.73-1.03) and allergic conjunctivitis (OR 0.86; 95% CI 0.72-1.02) at age 31. There was a suggestion that the reduced risk of allergic sensitization was particularly evident among the subjects whose mothers worked with farm animals during pregnancy, and that the reduced risk of the above diseases by farm animal exposure was largely explained by the reduced risk of atopy. Having cats and dogs in childhood revealed similar associations as farm animals with atopic sensitization. Conclusion and Clinical Relevance Contact with farm animals in early childhood reduces the risk of atopic sensitization, doctor-diagnosed asthma and allergic diseases at age 31.

That is one hell of a long running study and the findings are consistent with a wealth of similar studies across populations, including Exposure to environmental microorganisms and childhood asthma, and Effect of animal contact and microbial exposures on the prevalence of atopy and asthma in urban vs rural children in India.  These findings are part and parcel with the Hygiene Hypothesis, the idea that a relative reduction in ‘training’ of the immune system can lead to disturbances in normal immune system development and consequent development of autoimmune disorders.   (Here’s a nice review of the evidentiary backing for the Hygiene Hypothesis) From a clinical viewpoint, there are reasons to suspect this is a biologically plausible pathway; in Environmental exposure to endotoxin and its relation to asthma in school-age children the researchers reported an inverse relationship between the amount of endotoxin (i.e., a bacterial fingerprint that is recognized by the immune system) and the immune  response, stating, “Cytokine production by leukocytes (production of tumor necrosis factor alpha, interferon-gamma, interleukin-10, and interleukin-12) was inversely related to the endotoxin level in the bedding, indicating a marked down-regulation of immune responses in exposed children.”  We can also see immunomodulatory effects of farm or rural living in the cytokine profiles of breast milk between two populations, as reported in Immune regulatory cytokines in the milk of lactating women from farming and urban environments, which found much higher concentrations of TGF-Beta1, a critical immune modulator, in breastmilk and collustrum of ‘farm mothers’.  The concentration of TGF-Beta1 in breastmilk had already been implicated in infant development of atopic disease in Transforming growth factor-beta in breast milk: a potential regulator of atopic disease at an early age

The evidence supporting developmental programming in these instances is very problematic to overcome, clearly there are mechanisms by which the events of very early life can cause persistent changes to physiology into adulthood; be they changes ‘designed’ to be adaptive, or disturbed trajectories of usually tightly regulated systems that find inappropriate targets in an environment different than what our ancestors evolved in.  I’d note that none of what is above invalidates any findings of genetic involvement with cardiovascular problems, obesity, or asthma, but it should serve as a portrait of how genetic recipes are only part of the process. 

So, what about autism?  This is, admittedly, where things get a bit more speculative, there isn’t the same type of epidemiological evidence in the autism arena as what we see above.  Part of this discrepancy is an artifact of the fuzzy nature of autism, a bazillion different conditions each with their own personalized manifestation, a much more daunting set of variables to detangle compared with measuring BMI, triglyceride levels or asthma.  Those caveats in place, there is still room to discuss some potential examples wherein early life experiences might be participating in ‘programming’ some of what we see in autism. 

A nice review paper that speaks directly towards a developmental programming model that involves autism is Early life programming and neurodevelopmental disorders that includes as an author, Tom Insel, head of the National Institute of Mental Health, and generally, one of the good guys.   This is part of the abstract.

Although the hypothesized mechanisms have evolved, a central notion remains: early life is a period of unique sensitivity during which experience confers enduring effects. The mechanisms for these effects remain almost as much a mystery today as they were a century ago (Insel and Cuthbert 2009). Recent studies suggest that maternal diet can program offspring growth and metabolic pathways, altering lifelong susceptibility to diabetes and obesity. If maternal psychosocial experience has similar programming effects on the developing offspring, one might expect a comparable contribution to neurodevelopmental disorders, including affective disorders, schizophrenia, autism and eating disorders. Due to their early onset, prevalence and chronicity, some of these disorders, such as depression and schizophrenia, are among the highest causes of disability worldwide (World Health Organization, 2002). Consideration of the early life programming and transcriptional regulation in adult exposures supports a critical need to understand epigenetic mechanisms as a critical determinant in disease predisposition.

 

A concise explanation of the concept of developmental programming and the need for more finely detailed understandings of the likely epigenetic underpinnings.  Also included is a discussion of things like maternal stress during gestation, childhood environmental enrichment (or more specifically, ‘de-enriched’ or otherwise, terrible situations), and prenatal infection models.  Nice.  

What about specifics for the autism arena?  One environmental event that most everyone agrees can increase risk of an autism diagnosis is an immune challenge in the gestational period.  The animal models are robust and have been replicatedacross laboratories and epidemiological data supports an association.  A lot of groups have been studying the effects of maternal immune activation in animal models the past few years, what we can see are some striking parallel veins to what is observed in autism that involve the concept of developmental programming. 

One paper, with a title I love, is  Neonatal programming of innate immune function.  Here is a snipet of the abstract from the first paper:

There is now much evidence to suggest that perinatal challenges to an animal’s immune system will result in changes in adult rat behavior, physiology, and molecular pathways following a single inflammatory event during development caused by the bacterial endotoxin lipopolysaccharide (LPS). In particular, it is now apparent that neonatal LPS administration can influence the adult neuroimmune response to a second LPS challenge through hypothalamic-pituitary-adrenal axis modifications, some of which are caused by alterations in peripheral prostaglandin synthesis. These pronounced changes are accompanied by a variety of alterations in a number of disparate aspects of endocrine physiology, with significant implications for the health and well-being of the adult animal.

Another very cool, and very dense, paper with a salient title and content by the same group is  Early Life Activation of Toll-Like Receptor 4 Reprograms Neural Anti-Inflammatory Pathways (full paper) which reports that a single early life immune challenge results in persistently altered response to immune stimulants into adulthood, with differential responses in the CNS compared to the periphery.  Especially interesting in this paper is that the researchers have dug down a layer into the biochemical changes affected by early life immune challenge and found that alterations to HPA-Axis metabolites are responsible for the changes. 

Tinkering around with the HPA-Axis, an entangled neuroendicrine system that touches on stress response, immune function, mood, and more can have a lot of disparate effects.  It turns out, there is evidence that early life immune challenges can also modify behaviors in a way consistent with altered stress responses.

For example, the very recently published Peripheral immune challenge with viral mimic during early postnatal period robustly enhances anxiety-like behavior in young adult rats has a short, but to the point abstract:

Inflammatory factors associated with immune challenge during early brain development are now firmly implicated in the etiologies of schizophrenia, autism and mood disorders later in life. In rodent models, maternal injections of inflammagens have been used to induce behavioral, anatomical and biochemical changes in offspring that are congruent with those found in human diseases. Here, we studied whether inflammatory challenge during the early postnatal period can also elicit behavioral alterations in adults. At postnatal day 14, rats were intraperitoneally injected with a viral mimic, polyinosinic:polycytidylic acid (PIC). Two months later, these rats displayed remarkably robust and consistent anxiety-like behaviors as evaluated by the open field/defensive-withdrawal test. These results demonstrate that the window of vulnerability to inflammatory challenge in rodents extends into the postnatal period and offers a means to study the early sequelae of events surrounding immune challenge to the developing brain.

The methodology is very similar to what we see in a lot of animal models of early life immune activation, convince a young animals immune system that they are under microbial attack by mimicking either bacterial or viral invaders, and then measure behaviors, or physiology, later in life. This study could be seen as a complement to a much earlier (2005) paper, Early life immune challenge–effects on behavioural indices of adult rat fear and anxiety, which used a different immune stimulant (bacterial fingerprint/LPS versus viral fingerprint/Poly:IC), but which found generally consistent results.

There are more, for example, Early-Life Programming of Later-Life Brain and Behavior: A Critical Role for the Immune System (full paper), which reviews animal study evidence that early life immune challenges can have lifelong effects.  Here is part of the Introduction:

Thus, the purpose of this review is to: (1) summarize the evidence that infections occurring during the perinatal period can produce effects on brain and subsequent behavior that endure throughout an organism’s life span, and (2) discuss the potential role of cytokines and glia in these long-term changes. Cytokines are produced within the brain during normal brain development, but are expressed at much higher levels during the course of an immune response. In contrast to overt neural damage, we present data indicating that increased cytokine exposure during key periods of brain development may also act as a “vulnerability” factor for later-life pathology, by sensitizing the underlying neural substrates and altering the way that the brain responds to a subsequent immune challenge in adulthood. In turn, this altered immune response has significant and enduring consequences for behavior, including social, cognitive, and affective abilities. We discuss the evidence that one mechanism responsible for enduring cytokine changes is chronic activation of brain microglia, the primary immunocompetent cells of the CNS.

Check that out!  We have several papers showing, indeed, a ‘chronic activation of brain microglia’ in the autism population; one way, it seems, to achieve this, is ‘increased cytokine exposure during key periods of brain development’.  (Ouch!) 

Is developmental programming the mechanism by which gestational immune activation raises the risk of autism?  I don’t think we can answer that question with any authority yet, but the logical jumps to arrive at that conclusion are small, and  are supported by a great deal of evidence.  No doubt, we’ll be learning more about this in the years to come.

Ultimately, I think what all of this means is that, as usual, there is another layer of complexity thrown into the mix.  As far as autism goes, it seems likely that at least some of our children are manifesting behaviors consistent with autism as a result of things that happened to them very, very early in their life.  Figuring out if this is happening, how it is happening, and to which individuals, is a daunting, very difficult task; but at least we are approaching a level of knowledge to allow for such an endeavor.

This posting focused on the bad stuff, but the inverse is just as meaningful, having a ‘normal’ gestational period as far as nutrients go, programs you towards a more healthy weight, and being born to a mother exposed to a variety of microbial agents, as the overwhelming majority of mothers were for most of human existence, programs you away from asthma.  But from a broader standpoint, from a ‘every human on the planet’ view, I think we must begin to recognize that everyone is being programmed, in some ways for good, in others, for not so good.  Curiosity and thoughtful analysis is our way to illuminate the beautiful and dispassionate gears that propel the machinations of nature; developmental programming is one of the cogs in the natural world, hopefully, one day, we will acquire the wisdom to refine the program for our benefit, but in the meantime, it is still exciting to witness the discovery of the inner workings.

          pD


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