The Year in Review from Autism Speaks’ Chief Science Officer
When I was a college student starting to explore autism research, one of the first studies I read provided strong evidence that autism was mostly a genetic condition. That study, by Michael Rutter and Susan Folstein, looked at 21 pairs of twins, at least one of each pair being affected by autism. It compared identical twins, who share all of their genetic makeup, with fraternal twins, who share around half their genes. It found that when one identical twin had autism, so did the other 83 percent of the time. By contrast, this was true of only 10 percent of the fraternal twins. For the next three decades, it was taken as fact that the causes of autism were almost completely genetic.