The New York Times Sunday Review had an article this week linking autism with the hygiene hypothesis. Written by Moises Velasquez-Manoff, the piece is part of the Times' opinion coverage, not reported news. It was also one of those sort of stories that comes across as highly persuasive ... until you start looking at the details. About halfway through reading it yesterday, it occurred to me that Velasquez-Manoff was making a lot of big statements—"perhaps 1/3 of autism, and very likely more, looks like a type of inflammatory disease", for example—without citing the sources to back those statements up.
That's easy to do when you're writing a relatively short article summarizing the contents of a much bigger book, as Velasquez-Manoff seems to be doing here. But the problems go deeper than that, according to biologist and science writer Emily Willingham. In a must-read blog post, she goes through the NYT piece and points out many flaws in argument and detail. The main problem, though, is a pretty simple one: Moises Velasquez-Manoff presents what seems to be a largely speculative hypothesis as sure-fire truth. To make that case as persuasive as it is, he leaves out lots of evidence that doesn't match up with his thesis.
First, he appears to describe autism as a “parallel epidemic” with autoimmune diseases, even though a careful review of the literature shows that there likely isn’t an “epidemic” of autism. I'm also having trouble finding any data to confirm an epidemic of autoimmune diseases (he provides no sourcing), although I find that incidence rates in general seem to go up with improvements in diagnostic tools, a scenario that is common with application of new technologies in many diseases and disorders. Without that parallel or even confirmation of either "epidemic," his carefully constructed, fragile “if that, then this” scenario suffers from that point on.
...Velasquez-Manoff then asks, “What has happened to the modern immune system?” and goes on to assert that the concepts underlying the “hygiene hypothesis” also underlie autism and correlations between autism and maternal autoimmune disorders or asthma. An “evolutionary answer,” he says, is that we are no longer sufficiently riddled with parasites and microbes (we actually still have our microbes), so our immune system, twiddling its presumably heroic thumbs, casts its roving eye elsewhere--i.e., on ourselves. See, people who still live with parasites, he says, “don’t suffer from inflammatory diseases as much as we do” (italics mine). “We,” I assume, being the clean people of the western world. No sources given, and that assertion does not dovetail with, for example, what we know about asthma rates in Latin America (really high) versus Western Europe (not so high), although in places where things like leprosy, parasitic worm infections that include river blindness, and nasty bacterial eye infections are high, type 1 diabetes is low. Raise your hand if you're willing to make that tradeoff. And then he says, “Autism also follows this pattern” and “seems to be less prevalent in the developing world.”
... when you’re dealing with intestinal parasites and their friends, you and your government may not really have the time to go around carefully diagnosing developmental disorders. I suffered through his unsourced dismissal of epidemiologists who say as much, and I just about had a coronary when he cited “at least one (unnamed) Western doctor” (the best kind, you know) who had found autism was “nearly nonexistent” in a Cambodian population “rife with parasites and acute infections.” Um… if, as Velasquez-Manoff seems to argue, maternal infection sets the stage for maternal immune dysfunction and presumably autism, how is it that a population rife with acute infections evades autism? He doesn’t ever name the “Western doctor,” but autism does exist in Cambodia, and while we’re at it, here are a few other things Cambodian children must endure because they’ve got this great “evolutionary”-based existence that 'protects' them against autism.
Willingham's basic point: There is an atmosphere of desperation and panic surrounding autism, which has lead some parents to try a range of risky interventions in the hopes of "curing" it. Given that, maybe it's irresponsible to claim that a hypothetical factor in autism is the absolute cause. Especially when the proposed treatment—intentional infection with parasitic whipworms—comes with its own downsides, including growth retardation in children, anemia, and even rectal prolapse.