Michael White examines our still limited understanding of it:
How strong is the genetic basis for autism, anyway? Could it be that researchers are searching for genetic causes that don’t exist? Actually, no. That there is a substantial genetic contribution to autism is well-established, but it has been difficult to pin down just how large it is. Previous studies have estimated the heritability of autism to be as high as 90 percent, or as low as 38 percent. A large study published this week in the Journal of the American Medical Association by researchers at the Karolinska Instutet in Sweden have come up with the most precise estimate yet for the heritability of autism: 54 percent.
The scientists looked at autism diagnoses in a population of more than two million Swedish children born between 1982 and 2006. By looking at rates of autism diagnosis among relatives—specifically identical twins, fraternal twins, full siblings, half siblings, and cousins—the researchers determined that, at least among Swedish families, “genetic and nongenetic influences on the risk for [autism spectrum disorders] and autistic disorder were similarly important.” Strikingly, they found that shared family environmental influences “have only a negligible effect on [autism spectrum disorder] etiology”; only non-shared, individual-specific environmental influences were significant. Just what those influences are remains unknown.
The Dish 