Though the worldwide prevalence of autism spectrum disorder (ASD) is increasing, the reasons for this trend have not been determined.
“Although we have learned a lot more about ASD in recent years, for most cases, it is not known precisely what genes or environmental insults are working together to produce ASD behaviors,” Janie F. Shelton, PhD, MPH, of the Medical University of Vienna, Austria, told Psychiatry Advisor. However, findings of several recent studies point to prenatal exposure to environmental neurotoxins as a potential factor.
One compelling model of autism development was first described in 2003 by John Rubenstein, MD, PhD, and Michael Merzinich, PhD, of the University of California at San Francisco.1
“This model proposes an early imbalance in the brain’s development which may skew it towards excitation and away from inhibition,” Shelton said. Because some neurotoxic pesticides have that exact effect, Shelton and her former colleagues at the Davis, Sacramento, and Los Angeles campuses of the University of California wanted to investigate whether a mother’s exposure to these compounds during pregnancy increases her child’s risk of ASD.
Last year, they examined data from the Childhood Autism Risks from Genetics and Environment (CHARGE) study, and found that approximately one-third of the mothers lived under a mile away from a site where agricultural pesticides had been applied, and proximity to organophosphates during pregnancy was linked with a 60% higher risk of ASD.2
“This was more pronounced in the second trimester, for a specific organophosphate called chlorpyrifos, where mothers living in close proximity were 3.3 times more likely to have a child with ASD as compared to mothers living further away,” noted Shelton. The association was not limited to agricultural pesticides: compounds commonly used in indoor insecticides and bug repellants were also linked with an increased risk of ASD.