As is often the case, a single well-publicized autism-related study has become a nine days wonder.
Recently, a study looked at 192 California twins to determine whether the rate of autism in identical twins is far higher than that in fraternal twins (as would be expected if autism is a mostly genetic disorder). This particular study, published in the Archives of General Psychiatry, found fewer identical twins share autism than expected - and a higher number of fraternal twins share autism. The study is unusual in this finding, since prior studies have found precisely the opposite.
Based on this study, of course, many autism groups are announcing that the idea of "autism as a genetic disorder" has been debunked. Now, they say, we KNOW that it's all in the environment. What's more, they say, we're finally overturning the holy grail of genetics - the belief that all autism is inherited.
This morning, an NPR interview with Martha Herbert of Harvard seemed to be leaning in the direction of saying something like "since we now know autism is not a largely genetic disorder, we should be looking again at pesticides, plastics and flame retardants as the cause of an epidemic."
I don't believe any of this holds much water.
First of all, virtually no one has been saying "all autism is inherited." The CDC, NIH and other mainstream organizations have long supported the idea that autism is linked both to genetics and environment - and they have been saying so for years.
Secondly, "genetics" does not necessarily mean "inherited DNA." In fact, studies have been coming out for years that say many cases of autism are linked to spontaneous mutations - meaning genetic differences that occur in an individual which are not inherited from a parent.
Thirdly, it seems extraordinary to me that twins who gestated in the same womb, were born under the same circumstances, raised in the same home, ate the same foods, were exposed to the same lawn and pet chemicals, drank from the same bottles, went to the same schools, underwent the same vaccinations and were fed the same cough medicines could be said to have been raised under different "environmental" circumstances. In fact, though, every single environmental "culprit" pointed to by Herbert (or anyone else, including those who believe that vaccines are to blame for an autism epidemic) would be the same for children of the same age raised by the same parents in the same household, unless some outstanding circumstance took one child into a new setting or exposed one child to something unique (eg, twins separated at birth).
Fourth, it is unclear why this particular study's findings were different from those of prior studies. It will be interesting to learn more about this. So far, so far as I know the study has not been replicated. Earlier studies, of which there have been quite a few, seem to suggest that autism is an extremely heritable disorder.
Herbert also made an interesting point on the radio. Asked whether autism is truly on the rise, she responded that a very significant number of new autism diagnoses could NOT be attributed to changes in diagnostic procedure, awareness, new diagnostic criteria, etc. I found this to be an interesting statement since, so far as I know, there is no general agreement on the percentage of "real" as opposed to "apparent" rise in autism spectrum disorders.
More significant, with the new diagnostic criteria (the DSM 5) coming out in two years, the autism spectrum will once again be redefined. According to one preliminary study, a very large percentage of those children now diagnosed with PDD-NOS (which accounts for more than 50% of children with an ASD diagnosis) will no longer quality for an autism spectrum label, but will likely receive a different, non-autism label. I will be fascinated to see whether the world will hail a sudden decline in autism spectrum incidence as of May, 2013.