If environmental factors can lead to autism, why does only one
of my twin boys have autism? Today’s question came in response
to my last blog post. In it, I explained that when scientists
talk about the “environmental factors” that increase the risk of
a disorder, they’re referring to pretty much any influence
beyond genetics. In the case of autism, the clearest evidence of
environmental influence seems to surround very early events such
as conception, pregnancy and birth. Those with the strongest
link include parental age at time of conception (both mom and
dad), maternal nutrition or illness during pregnancy, and
certain birth complications. The commenter’s question is a great
one that scientists are actively exploring. The short answer is
that inherited genes (DNA) and environmental factors seem to
interact to influence whether an infant goes on to develop
autism. So if the commenter’s twins are fraternal (meaning they
share about half their DNA), the difference in their genetic
makeup might explain why on