Harvard Mental Health Letter

Autism spectrum disorders revisited

Several studies raise new questions about cause and prevention.

The conventional wisdom has always been that the autism spectrum disorders (ASDs) develop mostly because of genetic rather than environmental factors. Indeed, the ASDs are usually considered among the most "heritable" psychiatric disorders, with studies in twins suggesting that genetic factors account for at least 90% of the risk of developing an ASD — much more than the genetic risk of depression, anxiety, or other psychiatric conditions.

Now the largest population study in twins so far has turned the accepted wisdom on its head by suggesting that environmental factors may be more important in the development of ASDs than previously realized. Several other studies have identified possible environmental culprits: the use of selective serotonin reuptake inhibitors (SSRIs) or lack of folic acid early in pregnancy, and a variety of complications near or shortly after giving birth. All of the studies need to be replicated by independent teams — and it's clear that genetic risk still matters — but leading researchers are rethinking what causes ASDs and how to prevent them.

To continue reading this article, you must login.
  • Research health conditions
  • Check your symptoms
  • Prepare for a doctor's visit or test
  • Find the best treatments and procedures for you
  • Explore options for better nutrition and exercise
Learn more about the many benefits and features of joining Harvard Health Online »