Exposure to air pollution when combined with a particular genetic disorder can increase the risk of autism, according to a new study conducted by scientists at the Keck School of Medicine of the University of Southern California, or USC.

According to the study, titled “Autism spectrum disorder: Interaction of air pollution with the MET receptor tyrosine kinase gene,” autism spectrum disorder, or ASD, is highly heritable, and there currently is no cure for the disorder. According to the scientists, the mesenchymal-epithelial transition, or MET, gene variant has been associated with autism in multiple studies. It controls expression of MET protein in both the brain and the immune system, and predicts altered brain structure and function.

“Our research shows that children with both the risk genotype and exposure to high air pollutant levels were at increased risk of autism spectrum disorder compared to those without the risk genotype and lower air pollution exposure,” Heather E. Volk of USC and the lead author of the study, said in a statement.

The study, which is scheduled to be released in the January 2014 edition of Epidemiology, said that ASD is a lifelong neurodevelopmental disability, characterized by problems with social interaction, communication and repetitive behaviors. According to a recent estimate by the Centers for Disease Control and Prevention, one in 88 children in the U.S. has ASD.

“Although gene-environment interactions are widely believed to contribute to autism risk, this is the first demonstration of a specific interaction between a well-established genetic risk factor and an environmental factor that independently contribute to autism risk,” Daniel B. Campbell of USC and the study's senior author, said. “It will be important to replicate this finding and to determine the mechanisms by which these genetic and environmental factors interact to increase the risk for autism.”

The researchers, led by Campbell and Volk, examined 408 children between two and five years of age from the Childhood Autism Risks From Genetics and the Environment Study, a population-based, case-control study of pre-school children from California.

Out of those children, 252 met the criteria for autism or ASD. While exposure to air pollution was determined based on where the children and their mothers had lived in the past, local traffic-related sources, and regional air quality measures, the MET genotype was determined through blood sampling.

Campbell and Volk are currently studying the interaction of air pollution exposure and the MET genotype in mothers during pregnancy.