Several summers ago I spent six weeks in another country, doing research in collaboration with autism researchers there. We traveled around by subway, train, and cab, visiting multiple schools with autistic children. Some were regular schools that had an autism unit; others were boarding schools for special-needs children or for children with autism specifically. We worked with the higher-functioning kids with autism (who had at least some language) and with younger mental-age-matched kids without autism (because mental retardation is very common in autistic kids – up to 74% although I read something non-peer-reviewed on the Internet that claims as low as 50% – to compare autistic and non-autistic kids on cognitive stuff you need to equate them on mental age, not chronological age).
We did a variety of tasks with the kids, involving stuff like sorting cards, or hearing stories and answering questions, or pushing buttons in response to pictures of faces on a computer screen. One of the weirder tasks, which was something for our collaborators, not for me and my prof, involved measuring kids’ heads with a measuring tape. I thought it seemed kind of an odd approach at the time – most of what I was involved in was heavily cognitive. And so I’ve been surprised to see that line of research actually panning out.
Here’s a recent instance of it (citation below). Researchers found that, very clearly, children with autism had larger head circumferences. What I thought was interesting was that head circumference above the 75th percentile was “associated with more impaired adaptive behaviors and with less impairment in IQ measures and motor and verbal language development.”
So something strongly associated with autism was also associated with less mental retardation (but mental retardation is strongly associated with autism). There’s some interesting stuff in there… I’m tempted to hypothesize beyond the data, but I’m not going to.
Larger head circumference was also associated with allergy/immune disorders in the kids and their first-degree relatives. The researchers speculate that this relates to immune dysfunctions that themselves cause or are associated with increased cell cycle progression (cannot dredge what that means up out of my brain) and/or decreased apoptosis (deliberate, clean cell death).
At the time of my first couple years in grad school, it was being speculated that for the quarter or so of autistic kids who have a noticeable period of skill loss (coincidentally around the time of the MMR shot, which has led to a whole lot of bad crap) lose their skills around the time that the brain undergoes a major reorganization in which unnecessarily neuronal connections are “pruned” or cut back.
So: Maybe immune dysfunction leads to lack of cell death in pruning and maybe outside of it too, and thus autism and larger head circumference?
That and a dollar will get you one-quarter of a latte, or almost a small iced tea, or a tiny little bit of the funding necessary to gain actual knowledge, or a fair bit of annoyance from someone more educated who already knows why you’re wrong. Speculation is tasty and rampant, but actual knowledge comes from eliminating the untrue theories with evidence, and hammering on the true ones until we decide there’s not much point in continuing to do so.
Sacco, R., et al. (2007) Clinical, Morphological, and Biochemical Correlates of Head Circumference in Autism. Biol Psychiatry.