Archive for the ‘Impending Doom’ Category
The Fairytale of a Static Rate of Autism Part 5 – The Prevalence Jackpot Versus The Prevalence Hookup, Futilely Struggling To Making Sense Out of Static, And How Journey Autism Flavors Our Path Of Moving Forward
Posted April 17, 2013on:
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.
Piling Up Small Changes, The Selective Skepticism Of Replacing One Fallacy With Another, And The Seductive Lure of Hubris Versus The Dispassionate Rules Of Nature
Posted September 28, 2012on:
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.
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.
A Sense Of Relief After (Some Of) Your Phantoms Are Observed By Others, A Distillation of Humbling Complex Early Life Neuroimmune Literature: “Microglia in the developing brain: a potential target with lifetime effects”, and The Need For Dispassionate Analysis
Posted June 15, 2012on:
Hello friends –
I have a confession to make. The fact that a lot of very smart people have ignored or flat out laughed at my arguments bothers me sometimes. I have applied non-trivial, not to be rebated time and effort to put forth what I considered to be logical views, scientifically defendable and important ideas; and yet people I knew were otherwise rational, and in some cases, very intelligent, just hadn’t seemed to get what I was saying. Often this was within the context of a discussion argument of vaccination, but my larger concern, that of a non-imaginary, non-trivial increase in children with autism in the past decades, also usually falls on deaf ears. If “environmental changes” incorporate the chemical milieu of our mother’s wombs, the microbial world our infants are born into, or the ocean of synthetic chemicals we all swim through every day, we have no rational conclusion but that our environment has changed a lot in the past few decades. Considered within the context of the reality based model where the events of early life can be disproportionally amplified through the lifetime of an organism, clinging to the idea that there has been a stable incidence of autism seems dangerously naïve, at most charitable.
And yet, for the most part, many or most of the people who are alarmed are crackpots. There were times I questioned myself. Am I missing something? Am I chasing phantoms? Why aren’t any of these other smart people as worried as I am?
A while ago I got a copy of Microglia in the developing brain: A potential target with lifetime effects (Harry et all), a paper that tells me that if nothing else, I have some good company in pondering the potential for disturbances in early life to uniquely affect developmental outcome, in this instance through alterations to the neuroimmune system. If I am incorrect about the validity of a developmental programming model with lifetime effects, lots of prolific researchers are wrong about the same thing in the same way. Harry is a very thorough (and terrifying) review of the relevant literature. Here is the abstract:
Microglia are a heterogenous group of monocyte-derived cells serving multiple roles within the brain, many of which are associated with immune and macrophage like properties. These cells are known to serve a critical role during brain injury and to maintain homeostasis; yet, their defined roles during development have yet to be elucidated. Microglial actions appear to influence events associated with neuronal proliferation and differentiation during development, as well as, contribute to processes associated with the removal of dying neurons or cellular debris and management of synaptic connections. These long-lived cells display changes during injury and with aging that are critical to the maintenance of the neuronal environment over the lifespan of the organism. These processes may be altered by changes in the colonization of the brain or by inflammatory events during development. This review addresses the role of microglia during brain development, both structurally and functionally, as well as the inherent vulnerability of the developing nervous system. A framework is presented considering microglia as a critical nervous system-specific cell that can influence multiple aspects of brain development (e.g., vascularization, synaptogenesis, and myelination) and have a long term impact on the functional vulnerability of the nervous system to a subsequent insult, whether environmental, physical, age-related, or disease-related.
The body of Microglia in the developing brain: A potential target with lifetime effects has tons of great stuff. From the Introduction
The evidence of microglia activation in the developing brain of patients with neurodevelopmental disorders(e.g., autism) and linkage to human disease processes that have a developmental basis (schizophrenia) have raised questions as to whether developmental neuroinflammation actively contributes to the disease process. While much of the available data represent associative rather than causative factors, it raises interesting questions regarding the role of these ‘‘immune-type’’ cells during normal brain development and changes that may occur with developmental disorders. Within the area of developmental neurotoxicology, the potential for environmental factors or pharmacological agents to directly alter microglia function presents a new set of questions regarding the impact on brain development.
There is a short section on what is known about the colonization of the brain by microglia, it is a busy, busy environment, and while we are just scratching the surface, microglia seem to be involved in scads of uber-critical operations, many of which pop up in the autism literature. It is just being confirmed that microglia constitute a distinct developmental path that diverges as an embryo, two papers from 2007 and 2010 are referenced as reasons we now believe microglia are a population of cells that migrate into the CNS before birth and are not replaced from the periphery in adulthood. From there, the beautiful complexity is in full effect; as the microglia develop and populate the brain there are specific spatial and morphological conditions, microglia are first evident at thirteen weeks after conception, and do not reach a stable pattern until after birth. In fact, it appears that microglia aren’t done finishing their distribution in the CNS until the postnatal period, “With birth, and during the first few postpartum weeks, microglia disseminate throughout all parts of the brain, occupying defined spatial territories without significant overlap (Rezaie and Male, 2003) suggesting a defined area of surveillance for each cell.”
It occurred to me to wonder if there are differences in microglia settlement patterns in males and females in human infants, as has been observed in other models? Could a spatially or temporally different number of micoglia, or different developmental profiles of microglia based on sex be a participant in the most consistent finding in the autism world, a rigid 4:1 male/female ratio?
Speaking towards the extremely low replacement rates for microglia in adulthood, the authors wonder aloud on the possible effects of perturbations of the process of microglial colonization.
The slow turn-over rate for mature microglia raises an issue related to changes that may occur in this critical neural cell population. While this has not been a primary issue of investigation there is limited data suggesting that microglia maintain a history of previous events. Thus, if this history alters the appropriate functioning of microglia then the effects could be long lasting. Additionally, a simple change in the number of microglia colonizing the brain during development, either too many or too few, could have a significant impact not on only the establishment of the nervous system network but also on critical cell specific processes later in life.
Perhaps coincidentally (*cough*), we have abundant evidence of an altered microglial state and population in the autism population; while we do not know that these findings are the result of a disturbance during development, it is an increasingly biologically plausible mechanism, and thus far, I’ve yet to see other mechanisms given much thought, excepting the chance of an ongoing, undetected infection.
There is a brief section concerning the changes found in adult microglial populations in terms of density, form, and gene expression in different areas of the brain, “With further investigation into the heterogeneity of microglia one would assume that a significant number of factors, both cell membrane and secreted, will be found to be differentially expressed across the various subpopulations.” Nice.
There is a section of the paper on microglial phenotypes, there are a lot of unknowns and the transformation microglia undergo between functional states is even more nebulously understood during brain development. “It is now becoming evident that in the developing brain, many of the standards for microglia morphology/activation may require readdressing.” We haven’t even figured out what they’re doing in the adult brain!
There is a really cool reference for a study that shows altered microglial function dependent on the age of the organism.
In the adult rodent, ischemia can induce microglia to display either a more ramified and bushy appearance or an amoeboid morphology depending on the level of damage and distance from the infarct site(s). In the immature rodent, ischemia-induced changes in capillary flow or, presumably, altered CNS vascularization can retain the microglia in an amoeboid phenotype for longer and delay the normal ramification process (Masuda et al., 2011).
One way of looking at this would be to say that we should exercise extreme caution in trying to translate our nascent understanding of how mature microglia react when speculating on how immature microglia will act. To follow up on just how little we know, there is a long discussion about the shortcomings of a the term ‘activated’ microglia with some details on chemical profiles of broadly generalized ‘classically inflammatory, ‘alternatively activated’, ‘anti-inflammatory’, and ‘tissue repair’ phenotypes.
Next up is a dizzyingly list of brain development functions that microglia are known, or suspected to participate in. Without getting too deep in the weeds, of particular interest to the autism realm, that list includes neurogenesis and differentiation in the cortex [related: Courchesne, me], cell maturation via cytokine generation, axon survival and proliferation [related: Wolff, me], programmed cell death of Purkinje cells, clearance of ‘early postnatal hippocampul neurons’, and the ‘significant contribution to synaptic stripping or remodeling events’, i.e., pruning (Paolicelli / fractaltine), and even experience dependent microglia / neuron interactions. Taking all of this (and more) into consideration, the authors conclude “Thus, one can propose that alterations in microglia functioning during synapse formation and maturation of the brain can have significant long-term effects on the final established neural circuitry. “ Ouch.
Next up is a summary of many of the animal studies on microglial participation in brain formation, there is a lot there. Interestingly (and particularly inconvenient) is the finding that a lot of the functional actions of microglia during development appear to operate after birth. “Overall, the data suggest that microglial actions may be most critical during postnatal brain maturation rather than during embryonic stages of development.” Doh!
Early life STRESS gets some attention, and for once there is some good news if you look at it the right way. There is something about a very cool study from Schwarz (et all / Staci Bilbo!) involving drug challenge that peered deep into the underlying mechanisms of an environmental enrichment model; animals given a preferential handling treatment were found by two metrics to have differential microglia response in adulthood with (biologically plausible) observations, increased mRNA levels for IL-10 production, and decreased DNA methylation; i.e., less restriction on the gene that produces IL-10, and more messenger RNA around to pass off the production orders [totally beautiful!]. There is more including thyroid disruption (though in a way that I found surprising), and the observations of time dependent effects on immue disturbances. (super inconvenient)
There is so much data that keeps piling on that the authors end up with “Overall, the existing data suggest a critical regulatory role for microglia in brain development that is much expanded from initial considerations of microglia in the context of their standard, immune mediated responses.”
A terrifying concept that I haven’t found time to dedicate a post towards is microglia priming, which gets some attention in Harry.
There is a significant amount of evidence regarding what is often termed ‘‘priming’’ and ‘‘preconditioning’’ events that serve to either exacerbate or provide neuroprotection from a secondary insult, respectively. In these states, the constitutive level of proinflammatory mediators would not be altered; however, upon subsequent challenge, an exaggerated response would be induced. The phenomena of priming represent a phenotypic shift of the cells toward a more sensitized state. . . Exactly how long this primed state will last has not been determined; however, data from microglia suggest that it can extend over an expanded period of time. Preconditioning can also represent changes that would occur not only over the short term but may be long lasting.”
I happen to think that microglia priming is going to be a very important cog in the machinery for this journey when all is said and done; the evidence to support a preconditioning system is strong, and in parallel, the things we see different in autism (and elsewhere) is consistent with a different set of operations of microglia, AND we also have evidence the disturbances that would invoke microglial change are subtle but real risk factors for autism.
What comes next is a type of greatest hits mashup of very cool papers on developmental programming in the CNS.
Galic et al.(2008) examined age related vulnerabilities to LPS in rats to determine critical age periods. Postnatal injection of LPS did not induce permanent changes in microglia or hippocampal levels of IL-1b or TNFa; however, when LPS was given during the critical postnatal periods, PND 7 and 14, an increased sensitivity to drug induced seizures was observed in 8-week-old rats. This was accompanied by elevated cytokine release and enhanced neuronal degeneration within the hippocampus after limbic seizures. This persistent increase in seizure susceptibility occurred only with LPS injection at postnatal day 7 or 14 and not with injections during the first day of life or at PND 20. Similar long-lasting effects were observed for pentylenetetrazol-induced seizures when PND 11 or 16 rat pups were subjected to LPS and hyperthermic seizures (Auvin et al., 2009). These results again highlight this early postnatal period as a ‘‘critical window’’ of development vulnerable to long-lasting modification of microglia function by specific stimuli. Work by Bilbo and co-workers demonstrated LPS-induced deficits in fear conditioning and a water maze task following infection of PND 4 rats with Escherichia coli. In the young adult, an injection of LPS induced an exaggerated IL-1b response and memory deficits in rats neonatally exposed to infection (Bilbo et al., 2005). Consistent with the earlier work by Galic et al. (2008), an age dependency for vulnerability was detected with E. coli-induced infection at PND 30 not showing an increased sensitivity to LPS in later life (Bilbo et al., 2006).
In particular, Galic 2008, or Postnatal Inflammation Increases Seizure Susceptibility in Adult Rats (full paper) was a very formative paper for me; it was elegant in design and showed alarming differences in outcome from a single immune challenge experience, if it occurred during a critical developmental timeframe. If you haven’t read it, you should.
This paper has a nice way of distilling the complexity of the literature in a readable way.
One hypothesis for developmental sensitivity is the heterogeneous roles for inflammatory factors and pro-inflammatory cytokines during development, including their timing-, region and situation-specific neurotrophic properties. Many of the proinflammatory cytokines are lower at birth with a subsequent rapid elevation occurring during the first few weeks of life. In an examination of the developing mouse cortex between PND 5 and 11, mRNA levels for TNFa, IL-1b, and TNFp75 receptor remained relatively constant while a significant increase in mRNA levels of CR3, macrophage-1 antigen (MAC-1), IL-1a, IL-1 receptor 1 (IL- )R1, TNFp55 receptor (TNFp55R), IL-6, and gp130 occurred (Fig. 2). This data suggests that an upregulation of interleukins and cytokine receptors may contribute to enhanced cytokine signaling during normal cortical development.
One hypothesis put forward using a model reliant on postnatal exposure to LPS suggests that these types of exposure may ‘‘reprogram’’ neuroimmune responses such that adult stress results in hyperactivation of the hypothalamic pituitary adrenal (HPA) axis (Mouihate et al., 2010) and corticosterone changes (Bilbo and Schwarz, 2009).While limited, the available data suggest that events occurring during development, especially postnatal development, have the potential to cause long term alterations in the phenotype of microglia and that this can be done in a region specific manner.
In what could, conceivably, be a coincidence, our available information on the autism brain also shows region specific changes in microglia populations, microglial activation profiles, and oxidative stress. I do not believe the findings reviewed in Microglia in the developing brain: A potential target with lifetime effects will be meaningless artifacts; the likelihood that our observations of an altered neuroimmune state in autism are not, at least, participatory has become vanishingly small.
Can these findings inform us on the incidence question? I was lurking on a thread on Respectful Insolence a while ago, and someone gave what I thought was a very succinct way of thinking about the changes that our species has encountered the past few decades; it went something like “we have replaced infection with inflammation”. That’s a pretty neat way of looking at how things have gotten different for humanity, at least lots of us, and especially those of us in the first world. We used to get sick and die early; now we live longer, but oftentimes alongside chronic disorders that share a common underlying biological tether point, inflammation.
Any dispassionate analysis of the available data can tell us that we have, indeed, replaced infection with inflammation; we suffer from less death and misery from infection, but more metabolic disorder, more diabetes, more hypertension, more asthma and autoimmune conditions than previous generations. We have largely replaced good fatty acids with poor ones in our diet. All of these conditions are characterized by altered immune biomarkers, including an increase in proinflammatory cytokines. Those are the facts that no one can deny; we have replaced infection with inflammation.
But when we look to the findings of Microglia in the developing brain: A potential target with lifetime effects, it becomes clear that our newfound knowledge of microglial function and crosstalk with the immune system raises some very troubling possibilities.
Lately it has been quite in vogue among a lot of the online posting about autism to at least mention environmental factors which could participate in developmental trajectory leading to autism; that’s a big step, an important and long overdue acknowledgement. If you pay close attention, you will notice that 99% of these admissions are handcuffed to the word “prenatal”. This is likely an attempt to deflect precise questions about the robustness of our evaluation of the vaccine schedule, but the big question, the incidence question, still hinges on fulcrum of the genetic versus environmental ratio ; that is a problem for the purveyors of the fairytale because the prenatal environment of our fetuses, the chemical milieu of their development, is qualitatively different compared to generations past. That chemical soup is their environment; and that environment has unquestionably changed in the past decades as we have replaced infection with inflammation.
Our previous analysis tells us that invoking inflammation outside the brain modifies microglial function inside the wall of the blood brain barrier; good or bad, no honest evaluation of the literature can argue against a lack of effect. What happens outside the brain affects what happens inside the brain. If, however, microglia are active participants in brain formation, as a swath of recent research indicates, can this fact give us insight into the incidence question?
Is a state of increased inflammation the pathway between maternal asthma, depression, stress, and obesity being associated with increased risk of autistic offspring? Have we replaced infection with inflammation plus?
What could be more lethal to the fairytale of a static tale of autism than a positive relationship between a lifestyle characterized by increased inflammation and the chances of having a baby with autism?
Are we totally fucked?
We cannot know the answers unless we have the courage to ask the difficult questions with methods powerful enough to provide good data, and it won’t be easy. The static rate of autism fairytale is a comforting notion; it expunges responsibility for the coronal mass ejection sized change to our fetuses developing environment, and while hiding behind the utterly frail findings of social soft scientists, we can happily place tin foil hats and accusations of scientific illiteracy on anyone who might be worried that our abilities have outstripped our wisdom. That is a terrible, cowardly way to approach the incidence question, what we should be doing is exactly the opposite, ridiculing the epidemic sized error bars in prevalence studies and demanding more answers from the hard scientists. Eventually we will get there and it will be a critical mass of information from studies like Harry that will propel decision makers to abandon the fairytale for a course regulated by dispassionate analysis.
Low Penetrance Environmental Impacts, Gene Environmental Interactions, and the Depressingly Bad Jokes that Infiltrate Autism Discussions
Posted January 8, 2011on:
Hello friends –
There’s been something at the back of my mind for a while now regarding the potential for environmental influences to participate in autism, and indeed, a true rise in the number of children that have developmental problems that I’ve been struggling with articulating elegantly. The right course came to me while reading threads where the recent autism risk as proximity to highways paper was discussed. I’m actually not too big on the paper, it is very preliminary, uses some terms that are kind of confusing, and at very best, should be used as a guide for more targeted studies. For anyone who didn’t see it when it came out, essentially it reported a small increase of risk of having a baby with autism as the pregnant mother lived closer to some types of highways.
What I liked about this study is that at the core, there was a twinge of a biologically plausible mechanism, specifically, exposure to pollutants during development and consequent interference with neural development. Examples given in the text including possible endocrine disrupting effects of some types of automotive exhaust, and studies showing altered glutamate expression and associated plasticity defects resulting from pollutants.
What I didn’t like about the study is that it didn’t include any biomarkers and seemed relatively soft on the definitional terms. It was essentially a GIS placement and association lookup; lots of data and easy to find phantoms. A methodologically similar study by Bearman was released a few months previously; purporting to assign a very specific percentage of autism increase (16%) to the spatial proximity of other parents with children with autism, with the idea being that those chatty parents convinced their close neighbors to get their child diagnosed, while those people who more than 500 meters from a child with autism, and therefore don’t talk to as many people, failed to get their child diagnosed. I came down pretty hard on Bearman and don’t see much difference to apply less skepticism here. I will note, however, with no small amount of amusement, that when Bearman was discussed, no one seemed too concerned about the lack of control for urbanicity in the ‘skeptical’ realm. Big surprise.
The skeptics took the freeway paper apart, or in some instances, took apart a reporter or blogger who was spinning the findings as stronger than they were. I was more or less in agreement with the skeptics ideas on this one; this paper certainly was not sufficiently strong to make any conclusive statements and as usual, some headlines got it way wrong.
On the other hand, according to my underlying principles of subtle change still being meaningful, the humbling complexity of poking around with systems like embryonic development, and the difficult to overstate gulf between what we know and what we think we know about the effects of our reckless introduction of a galaxy of sythentic chemicals into the environment our infants are born into, this study fit in pretty nicely; at the very least as a reason to perform bioinformatic analysis of pregnant women to test for biomarkers of exhaust exposure and cognitive outcomes a few years down the ‘road’.
It didn’t take long before the gross over simplifications started rolling in though; i.e., ‘If this study is valid, we should have seen the rise in autism when the Interstate program was initiated in the 1950’s!’ [cue laugh track], or ‘I guess I have genes that made me live near an Interstate’. [cue whoot whoot track] It occurred to me that the Interstate jokes are a good illustration of what is largely wrong with nearly every single discussion on environmental participation you stumble into on the Internet. On one hand, the notion that unless an environmental study has sufficient power to prove a causal relationship for autism, or indeed, can be shown to be unable to account for all autism cases, it is safe to be mocked, or for the more academically minded, accused of being the result of data dredging. Similarly, anything showing a glimmer of plausibility that isn’t a genetic finding can lends itself towards showing how worthless the genetic angle is. These are useful cards to play if your goal is to bash environmental causation theories (and thereby, vaccination causation theories), or if your goal is to bash genetic theories; but ultimately are wastes of time if we want to understand a condition with the murky history and multifaceted manifestations of autism. The crux of what really bothered me about both sides of the Internet joke is that they each ignore meaningful information that can be offered from the other side. It is worse than dumb, it is wasteful.
Stepping away from the environmental end for a moment, I think it is safe to say that everyone is beginning to realize that the hunt for high impact genetic changes that can explain more than a tiny fraction of our autism cases is an abject failure. While there are some genetic changes, like Fragile X, that confer extremely high risk of autism, the absolute number of people with such changes is relatively simple to determine, and they comprise a vanishingly small subset of the children with autism. What we do seem to be finding is that there are lots of genetic changes that confer a small risk of having autism, the so called, low penetrance genetic changes. The idea here is that if you have many, (maybe as many as a dozen or more) low penetrance genes, the cumulative effects build up until a physiological end point is reached wherein autistic behaviors manifest. I actually like the idea behind low penetrance genes a lot; it makes a lot of our finings of genetics make sense, and I absolutely believe in a strong genetic participation in autism.
Remember, at the end of the day, genes are nothing more than blueprints for building proteins. Most genetic alterations don’t involve complete additions, or removals, of proteins, but rather, creation of a little less, or a little more of a protein, or perhaps, creation of proteins that are just a tiny bit different than ‘normal’, sort of like autism itself. While the environment these proteins enter, or are regulated into entering, starts influencing the eventual biological outcome in the most immediate sense imaginable, the end points of genetics, these proteins and their precise structures are indisputably important in what is happening in everything our bodies do; including, in some instances, have autism.
Consider the tightly orchestrated formation of the microscopic chasms between neurons, the process of synaptogenesis. Dozens (or hundreds) of chemicals dance together in order to form the structures in our brains that exchange chemical messengers, neurotransmitters, that literally form the foundation of neuron to neuron communication, and thus, cognition; the physical constructs of thought. It is a biological cauldron that we are just beginning to comprehend, the mind formingly intricate, time dependent interplay of a chemical deck of cards orders of magnitude more complicated than sequencing the genome.
The evidence for altered synapses, and modified synaptic function in autism, and most (all?) other developmental disorders is impossible for an intellectually honest observer to deny. Some of the most commonly found genetic alterations in people with autism involve genes known to participate in the formation, maintenance, or functioning of synapses. For example, neurexin , shank, and neuroligin, are some well known, or at least, well reported reported genes intimately attached to synapse function also found associated with autism, and our list should also include calcium expression and adhesion genes (and many, many others). Each of these genes or processes contribute to the synapse in subtle, but different ways, at different times, and yet we can see that interferences anywhere down the functional class of chemicals is associated with autism. Yet, very few people, (I’ve read of none), have been found to have a neurixin allele, a shank allele, and a neruoligin mutation. And there are some people who have the same mutations, but do not exhibit autistic behavior. There are also a great many people that have no known mutations in any of these genes, and still, receive an autism diagnosis. What does this tell us?
It should tell us that while there are lots of genetic ways that synapse function can be altered in such a way that autistic behaviors bubble up to the diagnosis endpoint, but more importantly, the critical question need not necessarily revolve around what genes you have, but rather, is synapse function manipulated? Furthermore, we should be able to conclude that simply having a single modifier (i.e., one shank mutation) go wrong isn’t a guarantee of an autism diagnosis, and thus; the participation of individual mutations is real, but small. [I would also argue that it is likely that there are a great number of as of yet, undetected genetic misprints that contribute in the same real, but subtle ways.]
Another more accessible example of a low penetrance gene is the MET gene, which produces a protein known to interact with a lot of important processes involved in autism, including brain formation, immune system functioning, and intestinal repair. There have been a lot of high quality studies on the MET mutations in the past few years including those that report higher incidences of MET mutations in children with autism and gastrointestinal problems, higher findings of MET alleles in autism, association to communication phenotypes and MET expression, replication of above studies, evidence of interaction with other genes known to be associated with autism, decreased expression in post mortem brain tissue, and animal studies showing differential, time dependent expression of MET. (and many, many others).
The kicker towards this discussion, howeever, is that the changes to the MET gene are really, very, very common. Nearly one half of everyone has the low MET production gene, but even still, many more people with autism have it. So, while it is clearly implicated, other changes are obviously necessary for that particular genetic change to result in autism. What we are learning about the systems affected by MET, or lots of the genes implicated in autism, is that very subtle changes towards critical processes are sufficient to modify the course of development. Somewhat counter intuitively, I would argue that the implication of this is compelling evidence (or terrifying news) for those of us with worries about the possibility of an environmentally driven increase in the number of people with an autism diagnosis; indeed, it argues that just like genetics, we must admit the reality that if genes can be low penetrance, so too, then, can environmental impacts.
For example, back to brain formation. We know that the neurexin proteins participate in forming our synapses. But we have evidence that hypo
thyroidism can lead to structural changes during development, and we also know that there is increasing evidence that endocrine disruptors can interferre with thyroid metabolism, or for that matter, a wide range of findings on endocrine disruptors and cognitive function. Or if we look to pesticides, we have evidence that developmental exposure to diazonon can modify neurotransmitter function, with similar findings are available for other classes of pesticides. Similarly with heavy metals.
The skeptics would claim with some legitimacy that there are significant dose dependency problems to be addressed before we should start pointing to every experimental slice of evidence of potential harm and claiming that the sky is falling. But. What if, in fact, we need only perturb the process of brain development a little bit, and with a little help from other, low penetrance genes or other exposures, developmental trajectories begin to alter? This would seem to be precisely what we are learning from the genetic angle; it isn’t one big thing incorrectly designed, it is lots of small things. And while our genetic code has, for the most part, remained stable; our environment today is vastly overpopulated with chemicals capable of minor, but real, effects when compared to yesteryears past.
The search for a single environmental impact with the ability to explain a significant portion of autism diagnosis is as futile as the hunt based on genetics. This makes for a far messier landscape, but also one that fits my terrifying, over arching principle of the Fairytale of a static (or near static) rate of autism, that our uncontrolled experiment of introducing synthetic chemicals into our environment coupled with widespread social changes with real physiological impacts, a set of experiments absolutely unprecedented in the history of living things on planet Earth, that changes to our offspring are unavoidable. To suggest otherwise, strikes me as either the height of arrogance, or the depths of ignorance.
Going back to the freeway study for a minute, I ran into a paper while writing this piece that involves pollutants, interaction with the MET gene, gene x environment interactions, and low penetrance impacts that I think has salience towards this discussion.
Here is the abstract:
Gene by environment interactions (G × E) are thought to underlie neurodevelopmental disorder, etiology, neurodegenerative disorders, including the multiple forms of autism spectrum disorder. However, there is limited biological information, indicating an interaction between specific genes and environmental components. The present study focuses on a major component of airborne pollutants, polycyclic aromatic hydrocarbons (PAHs), such as benzo(a)pyrene [B(a)P], which negatively impacts cognitive development in children who have been exposed in utero. In our study, prenatal exposure of Cpr(lox/lox) timed-pregnant dams to B(a)P (0, 150, 300, and 600 μg/kg body weight via oral gavage) on embryonic day (E14-E17) consistent with our susceptibility-exposure paradigm was combined with the analysis of a replicated autism risk gene, the receptor tyrosine kinase, Met. The results demonstrate a dose-dependent increase in B(a)P metabolite generation in B(a)P-exposed Cpr(lox/lox) offspring. Additionally, a sustained persistence of hydroxy metabolites during the onset of synapse formation was noted, corresponding to the peak of Met expression. Prenatal B(a)P exposure also downregulated Met RNA and protein levels and dysregulated normal temporal patterns of expression during synaptogenesis (!). Consistent with these data, transcriptional cell-based assays demonstrated that B(a)P exposure directly reduces human MET promoter activity. Furthermore, a functional readout of in utero B(a)P exposure showed a robust reduction in novel object discrimination in B(a)P-exposed Cpr(lox/lox) offspring. These results confirm the notion that common pollutants, such as the PAH B(a)P, can have a direct negative impact on the regulated developmental expression of an autism risk gene with associated negative behavioral learning and memory outcomes.
I have to say, finding this paper was a bit of tragic humor for me; it was published in December 2010, with zero fanfare from the press, as opposed to the confounder heavy, Residential Proximity to Freeways and Autism in the CHARGE study, study, which had a thousand similar articles in Google News. But here we find a superb example of what gets bandied around a lot when in quick passing but rarely with any meat behind the discussion; a real life, experimentally sound version of a gene environment interaction that integrates biologically plausible mechanisms that is able to describe what is observed physiologically in autism with dose responses. Beautiful. But, it gets even better. It just so happens, the classifications of agents in use in this study, polycyclic aromatic hydrocarbons, are generated, in some instances, by car exhaust. In fact, in Detection of polycyclic aromatic hydrocarbon exposure from automobile exhaust fumes using urinary 1-hydroxypyrene level as an index, the authors conclude in part that “Automobile exhaust fume exposed subjects have a higher risk to be exposed to PAHs than the non-exposed subjects”. Go figure.
Whatever the problems with the freeway CHARGE study, they pale in comparison to the problems that the notion that because we didn’t observe increases in autism when the Interstate system was constructed, the findings must be spurious. Similarly, genetic predisposition is an indisputable fact; and knowing which genes are implicated in autism can help us intelligently target environmental factors that might be changing our infants.
Hello friends –
I ran into a few abstracts, read a few papers, and tried to get my way through one really dense paper in the past few weeks that got me thinking about this post. It’s all shook up, like pasta primavera in my head, but hopefully something cogent will come out the other end. (?)
Of the metabolic conditions known to be associated with having a child with autism, hypothyroidism is one that I keep on running into by way of the pubmed alert grapevine. By way of example, we have two studies that looked for autoimmune conditions in family members which found hypothyroidism to be one of many autoimmune diseases as a risk factor for autism, including, Familial clustering of autoimmune disorders and evaluation of medical risk factors in autism, and Increased prevalence of familial autoimmunity in probands with pervasive developmental disorders. This shouldn’t be too surprising, we know that, for example, perinatal hypothyroidism is a leading cause of mental retardation, with similar findings for the condition during pregnancy. It turns out, it appears that rates of hypothyroidism are slightly increasing, though at this time, the increases are of relatively small proportions, and as such, may be artifacts unrelated to an actual increase in classically recognized hypothyroidism. In any case, I think it is safe to say that interference with thyroid metabolism is something to be avoided at all costs when possible.
So after having read about that, this paper showed up in my inbox a while ago:
Thyroid hormones have long been known to play important roles in the development and functions of the central nervous system, however, the precise molecular mechanisms that regulate thyroid hormone-responsive gene expression are not well understood. The present study investigated the role of DNA methylaion and histone acetylation in the effects of perinatal hypothyroidism on regulation of reelin and brain-derived neurotrophic factor (BDNF) gene expression in rat hippocampus. The findings indicated that the activities of DNA methyltransferase (DNMT), methylated reelin and BDNF genes were up-regulated, whereas, the activities of histone acetylases (HAT), the levels of global acetylated histone 3 (H3) and global acetylated histone 4 (H4), and acetylated H3, acetylated H4 at reelin promoter and at BDNF gene promoter for exon II were down-regulated in the hippocampus at the developmental stage of the hypothyroid animals. These results suggest that epigenetic modification of chromatin might underlie the mechanisms of hypothyroidism-induced down-regulation of reelin and BDNF gene expression in developmental rat hippocampus
This gets interesting for autism because reelin, and bdnf levels have been found to be decreased in several studies in the autism population, with direct measurements, genetic expression, mouse knockout based models of autism , and genomic alterations all being implicated. There have been some negative genetic studies, but considering that it isn’t always the genes you have, but the genes you use, our other available evidence certainly points to BDNF and reelin involvement with some percentage of children with autism, and the association is such that a reduction in reelin or BDNF is a risk factor for developing autism. It would seem that the paper above might give some insight into the lower level details of the effects of hypothyroidism and subsequent developmental trajectories; modifications of reelin expression; through epigentic mechanisms, no less!. That’s pretty cool!
Then, I got my hands on a review paper that tries to go into detail as to the functional mechanism by which reelin deficiency could contribute to ASD, Neuroendocrine pathways altered in autism. Special role of reelin. It is a review that touches on a variety of ways that reelin contributes to neurodevelopment that have findings in the autism realm, including neuronal targeting and migration during brain formation, interactions with the serotonin and GABA systems, testosterone, and oxytocin. In short, there are plenty of ways that decreased reelin expression can impact development in ways that mirror our some of our observations in autism.
Of the many things that convince me that we are doomed, the proliferation of chemical compounds whose interactions within our bodies we scarcely understand is among them. In my readings on endocrine disruptors, one thing I found that seemed to be worrying lots of researchers was that some classes of these chemicals are capable of interfering with thyroid metabolism, and in some cases interfering with development of cells known to be associated with autism. Terrifyingly enough, since I read those papers, several others have come out, including Polybrominated Diphenylether (PBDE) Flame Retardants and Thyroid Hormone during Pregnancy and Mini-review: polybrominated diphenyl ether (PBDE) flame retardants as potential autism risk factors. At this point, it is important to point out that, as far as I know, there have not been any studies showing that non occupational exposure to PDBEs or other environmental pollutants can lead to classically defined hypothyroidism, at least none that I know of. (?) Be that as it may, I think it is realistic to assume any interference in thyroid metabolism is a bad thing, and while finding people in the outlier regions of hypo (or hyper) thyroidism gives us information on extreme environments, it would take someone with a lot of misplaced faith to assume that we can safely disturb thyroid metabolism just a little bit, and everything will come out in the wash.
I’ve had the argument made to me in the past that environmental pollutant driven increases in autism lacked biological plausible mechanisms; this argument is almost always made within a context of trying to defend the concept of a static rate of autism. While the papers I’ve linked to above do not provide conclusive proof that our changing environment is causing more children to be born with autism, they do provide increasing evidence of a pathway from pollutants to ASD, and indeed, the lack of biological plausibility becomes an increasingly flacid foundation on which to assume that our observations of an increased rate of autism are illusory. Unfortunately, in my opinion, the focus on vaccines has contributed to the mindset that a static rate of autism (or nowadays, maybe a tiny increase), must be protected at all costs, including some ideas on the application of a precautionary principle that seem outright insane to me (or at least, the exact opposite of what I would consider to be a precautionary path).
One thing is for certain, the number of child bearing women in developing countries with measurable concentrations of chemicals known to interferre with thyroid metabolism nears 100% in the industrialized nation as we eat , drink, breathe and bathe in the microscopic remnants of packaging materials, deteriorating carpet fibers, and baby clothes that are made to be fire resistant. This is an environment unambiguously different than that encountered by any other generation of infants in the history of mankind. To believe that we can modify our environment so drastically without having an impact seems incredibly naive to me, or on some days, just plain old stupid.
Unequal distributions of scary chemicals and (possible) implications for autism clusters, a static rate of autism, and why some of us may be more doomed than others
Posted March 12, 2010on:
Hello friends –
Recently there have been a few studies that tackled the issue of apparent autism clusters in California, The spatial structure of autism in California, 1993-2001, and Geographic distribution of autism in California: A retrospective birth cohort analysis. A nice overview and some discussion of these papers can be found at LBRB, here, and here. One of the arguments we see made there is that the rates of autism diagnosis are, in fact, a reflection of the available services in an area, as opposed to an actual difference in the number of children with autism; essentially that an undiagnosed child with autism who lives far from a center of autism services will not get a diagnosis, but a child born relatively close to such services, will be appropriately diagnosed. We are measuring diagnosis, as opposed to autism. I have no doubt that there is some validity to this, but have many doubts that we can, or should, assign all of our observed increases in autism as consequences of this type of artifact.
There have been several other studies that looked at things like mercury emissions, or airborne pollutants, or Superfund sites and autism rates at larger scales. However, on a macro level, these types of studies have, so far, been unable to design around a feature of reality; the likelihood that things like Superfund sites or airborne pollution are situated in relative proximity to an urban center, and as such, autism diagnosis services. In effect, the argument that these observations are diagnostic only is the same; without a controlling factor for diagnostic availability, we can not assume that other parameters are actually responsible. And again, I have no doubt that this is a force that contributes to the findings of these studies.
At the end of the day, I’m just not satisfied with a God of the Gaps explanation; what we seem to be seeing is just too goddamned important to explain away with the spongy soft and ultimately unmeasurable forces of greater awareness et all. (The Fairytale, 20##).
Anyways, the other day pubmed alerted me to the publication of this interesting study:
BACKGROUND: Levels of brominated flame retardants are increasing in US populations, yet little data are available on body burdens of these and other persistent hormonally active agents (HAAs) in school-aged children. Exposures to such chemicals may affect a number of health outcomes related to development and reproductive function. OBJECTIVE: Determine the distribution of biomarkers of polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and organo-chlorinated pesticides (OCPs), such as DDT/DDE, in children, and their variation by key descriptor variables. METHODS: Ethnically diverse cohorts of girls 6-8y old at baseline are being followed for growth and pubertal development in a multi-site, longitudinal study. Nearly 600 serum samples from the California and Ohio sites were analyzed for lipids, 36 PCB congeners, 11 PBDE congeners, and 9 OCPs. The biomarker distributions were examined and geometric means compared for selected analytes across categories of age, race, site, body mass index (BMI), parental education, maternal age at delivery, and breast feeding in adjusted models. RESULTS: Six PBDE congeners were detected among greater than 70% of samples, with BDE-47 having the highest concentration (median 42.2, range 4.9-855ng/g lipid). Girls in California had adjusted geometric mean (GM) PBDE levels significantly higher than girls in Ohio. Furthermore, Blacks had significantly higher adjusted GMs of all six PBDE congeners than Whites, and Hispanics had intermediate values. GMs tended to be lower among more obese girls, while other variables were not strongly associated. In contrast, GMs of the six PCB congeners most frequently detected were significantly lower among Blacks and Hispanics than Whites. PCBs and the three pesticides most frequently detected were also consistently lower among girls with high BMI, who were not breast-fed, whose mothers were younger, or whose care-givers (usually parents) were less educated. Girls in California had higher GMs than in Ohio for the pesticides and most PCB congeners, but the opposite for CB-99 and -118. CONCLUSIONS: Several of these potential HAAs were detected in nearly all of these young girls, some at relatively high levels, with variation by geographic location and other demographic factors that may reflect exposure pathways. The higher PBDE levels in California likely reflect differences in fire regulation and safety codes, with potential policy implications.
The environmental impact argument usually focuses on vaccines, or in some instances, similarly widespread environmental pollutants (i.e., mercury emissions); external forces which tend to operate more or less evenly across large geographic swaths, and also largely independent of things like culture or race. But with this paper we can observe the counter-intuitive opposite, chemicals that have achieved widespread distribution in society and the environment, seem to be bioaccumulating differentially according to factors such as geography, race, body type, and education levels. The paper here mentions fire regulation as a possible factor in state by state differences, but taking things a bit further, it can quickly be seen how socio-economic factors might play a role in why we might observe different levels of chemicals. It takes a lot of crazy chemistry to make a baby onesie not catch on fire, but at a high level, it involves dousing the material with a bunch of exotic chemicals. Politically correct or not the facts on the ground are that the well to do white woman has baby showers where she gets a bewildering array of freshly minted, ‘extra safe’ baby clothes more often than, say, the not so well to do Latina woman. We have already established a connection between having older parents and a diagnosis of autism, it would seem, there is also a correlation between having older parents and your bodies burden of these molecular mimics; and again, white women tend to have babies at later stages in life than their Black or Latina counterparts; especially the ones that happen to be residing near the trendy autism diagnosis hubs (i.e., the wealthier white women). The ability for these types of chemicals to cause a variety of difficult to predict developmental trajectories is too long, and terrifying to go into detail in this post; for purposes of this discussion, it is sufficient to understand that we have a growing body of evidence that endocrine disrupting compounds can have wide ranging effects; including epigenetic changes, changes in immune profiles, altered behaviors and neuroanatomical structures known to be abnormal in autism.
I found the finding of BDE-47 particularly intriguing, considering it was used as a primer for immunological response measurement by Ashwood, who found in vitro differences in immune responses in the autism population (an exaggerated innate immune response was observed).
Of course, this study does not present sufficient evidence for us to draw conclusions about the geographic distribution of autism rates in the two California studies above; but it should give us enough to pause before we take the comforting road out and assume that our observation are the result of diagnostic artifact alone; such assumptions feel good (except for the guilt), but ultimately require that we ignore our growing knowledge of how unpredictable endocrine disruptors affect the body, and how much more we have to learn.