Autism spectrum disorders now affect 1% of the population of the developed world, with 40 out of 10,000 children afflicted by classic autism, and the number keeps rising. Until recently scientists suspected that as much as 90% of autism cases could be explained by genetic factors. But a new study of 192 pairs of twins published in the Archives of General Psychiatry suggests that environmental exposure to some pesticides, medications, or infections, particularly in the womb, may be at least as important as genes in some cases.

autism, environmental exposure, chemical exposure, pesticide exposure, prenatal exposure, autism spectrum disorders, autism research, Archives of General Psychiatry

The interplay between genetic factors and environmental factors seems complex, but studying fraternal twins, who share 50% of their genes, and identical twins, who share 100% of their genes, allowed scientists to narrow down which factors were at play in situations where one twin had autism and the other was either unaffected by autism or had some form of the disorder, often the milder autism spectrum disorder Asperger’s Syndrome. What the researchers found was that “environmental factors common to twins explain about 55 percent of the liability to autism. Although genetic factors also play an important role, they are of substantially lower magnitude than estimates from prior twin studies of autism.”

So how can expecting mothers lower their child’s risk of environmental factors that could cause or trigger autism?

The researchers found that pesticide and plastic chemical exposure, as well as exposure to medications such as popular SSRI anti-depressants or several medications used to control epilepsy or gastric ulcers were factors in development of the disorder.

The list of offending substances is likely to grow longer in the coming months. As a recent study suggested that all plastics may leak harmful chemicals, pregnant women might also want to avoid plastics as much as possible while pregnant and use glass baby bottles. Women can also reduce their exposure to pesticides by eating organic foods as much as possible and avoiding pesticide exposure around the home or from agricultural farms. Prenatal vitamins were also listed as an important factor in the first few months before and after conceiving, so it would seem that for now, the best defense against autism is good prenatal care under the supervision of an informed physician and careful monitoring of environmental exposure to chemicals.