[T]he CDC now reports that autism spectrum disorders (ASD), comprising autism, unspecified pervasive developmental delay (PDD-NOS) and Asperger disorder, have risen from one case for every 88 children in 2008 to one in 68 as of 2010. This represents an increase of about 30%.Saunders has more at the link. Another question that probably concerns most readers is whether that 30% increase in cases in just two years means that autism is actually occurring more frequently or whether the frequency is about the same but parents are becoming much more aware and thus having their children checked more diligently.
I spoke with a colleague who specializes in developmental pediatrics, who expressed a lack of surprise at these numbers. They continue a trend that has already been demonstrated in numerous prior epidemiological studies, though the exact cause continues to elude us. This study doesn’t say anything about what’s actually causing these increases.
What this new report tells us is “how much” and “who.” Breaking down the numbers, we see that white children are more likely to carry an ASD diagnosis than black or Hispanic children, and that there is a great deal of variation throughout the country. (The study used data collected from 11 states to extrapolate rates for the US as a whole.) Boys are much more likely to be affected than girls, and nearly half of diagnosed patients had at least average intelligence.
Of course, what we would most like to know is what’s responsible for the rise in autism. It’s very frustrating to see these data and have little explanation for them. For all the pseudoscience and controversy, one of the few things we can know with certainty is that vaccines aren’t responsible.
Whatever the cause of autism, emerging evidence points to it happening early in development. In the other big news of the week, a new study in the New England Journal of Medicine reports evidence of brain abnormalities in autistic patients that likely began before birth. Comparing postmortem tissue samples from children with ASD against tissues from unaffected children, researchers found disorganization in nerve cells in the former group, a change that likely started prenatally.
At least some of this is probably related to genetics. Beyond that, however, the “why” of autism remains unclear. What is encouraging, according to one of the study’s authors, is that the disorganization was only found in certain areas of the brain, indicating that therapy may help mitigate the effects of ASD.
I don't know the answer, but if it's the former then wouldn't it make sense to think that the cause is environmental rather than genetic?