Study Shows That Environmental Factors Contribute to Higher Autism Risk

By AnnElise Hatjakes, M.A.

A study lead by Jane and Michael Hoffman and Associate Professor Molly Losh, Ph.D gave some insight into the complex causes of autism.  The study, which will be published in an upcoming issue of the journal Psychological Medicine, revealed that genetic predisposition is not the only cause of autism.  “Environmental factors like low birth weight may play a role either independently or in interaction with autism risk genes,” Losh said in a university press release.  Losh had been studying the causes of autism in general, and had an opportunity to collaborate with experts at the Karolinska Institute to explore environmental risk factors in a large sample of twins. 


In an e-mail interview, Losh explained that the causes of autism are widely misunderstood.  “Early on in the 1950s and 60s, autism was believed incorrectly to be caused by parenting styles,” Losh said.  “This harmful myth led to much anguish for families of individuals with autism. The biggest myth of our current age is that vaccines cause autism. This has been studied carefully and clearly refuted by research.” 


Her study of data on more than 3,700 pairs of identical twins yielded interesting results.  In analyzing discordant twins (twin pairs in which only one twin was affected by ASD) wherein one baby was more than 14 ounces, or at least 15 percent heavier at birth than the other, the researchers found the risk for autism rose 13 percent for every 3.5 ounce drop in birth weight.  Losh, who is the director of Northwestern University’s Neurodevelopmental Disabilities Laboratory, said in the university’s press release that prenatal and perinatal environmental factors may be an especially important factor in the development of autism. 


The researchers noted that their findings may not apply to children who are not part of a multiple-birth pregnancy.  When asked what this research means for women who plan to become pregnant, Losh said, “Because our findings were from a twin sample, we need to be careful about generalizing to the overall population, as prenatal characteristics can differ for twins and singletons. That said, our results certainly point to the importance of the prenatal period as a sensitive time when brain development can be impacted by many environmental factors.”  Losh added that good prenatal care is very important. 


In regards to where this research will be positioned in the scientific community, Losh explained that the investigation into the exact causes of autism are ongoing.  “I think the scientific community is certainly coming to the conclusion that autism can result from complex interactions between genetic and environmental factors,” Losh said.  “Which genes and what types of environmental risks are active areas of investigation. Our study points to birth weight as one important environmental risk, and may help to guide future investigations of sensitive periods.” 


Losh is currently investigating heritable features in autism that can be used in gene-finding studies.  “We continue to consider how environmental risk might interact with genetic etiology,” Losh said.