Study: Autism May Be Influenced By Environmental Factors
Study name: "Genetic heritability and shared environmental factors among twin pairs with autism," Hallmayer et al., 2011, Archives of General Psychiatry, Volume 68 (11), p. 1099 -1102.
What was found? By conducting a twin study that compared the similarity (concordance) of identical (MZ) twins and fraternal (DZ) twins for autism (a strict clinical definition) and autism spectrum disorders (ASD), this study reported that environmental factors -- specifically those that make twins similar -- are a major cause of autism. Genetic influences, although significant, were of less importance than the environment factors.
Why is this study influential? For the last three decades, the message from twin studies has been that autism is a genetic disorder. This new study, the largest twin study to date that uses the most modern diagnostic methods, fundamentally alters our thinking about the causes of autism and autism spectrum disorders (ASD) by suggesting that research should be directed to potential pre-, peri-, and postnatal environmental risk factors. The results also support genetic influences and genomic research, but the overall message is that environmental risks for autism may be hugely important even after accounting for DNA.
What's the take-home message? Expect to hear a lot more about potential environmental contributions to be a risk for autism, including factors that affect the maternal fetal environment, such as exposure to toxins, use of prescription drugs (including antidepressants), and infections. Because many of these reports will be preliminary (and many more studies will be required to investigate these issues fully), pregnant women will have to sort through the uncertain implications with their practitioners to make decisions that best suit their lives (for example, whether to continue with or abandon antidepressant use).