Age of Autism

July 15, 2011
By Mark Blaxill

For over two decades now, so-called “autism experts” have been claiming that autism is more than 90% caused by genes. The influence of these claims on autism policy and research funding is hard to overstate. But few realize that the basis of these claims hangs on a fragile evidence base: two small twin studies–one from Great Britain, the other from Scandinavia–that reported high rates of concordance for autism among identical twins and no concordance at all among fraternal twins. Last week, the largest and most rigorous twin study ever conducted, the California Autism Twin Study (CATS) reported contradictory new evidence that struck a devastating blow to these claims. The CATS identical twins had lower and the fraternal twins higher concordance rates than past studies, a striking finding that suggests that instead of being highly heritable, the vast majority of autism cases stem from environmental causes.