Children with a particular gene variant who are exposed to air pollution appear to be at a higher risk of developing autism, according to researchers from the Keck School of Medicine at the University of Southern California (USC).
Drawing on results of previous studies that have shown associations between air pollution and autism, and between autism and the MET gene, the researchers say their new study reveals that the combination of these factors increases the risk of autism.
The study will be published in the January 2014 edition of Epidemiology.
Autism spectrum disorder (ASD) is a lifelong neurodevelopmental disorder that leads to problems with social interactions, communication and repetitive behavior.
The Centers for Disease Control and Prevention (CDC) states that more children than ever before are being diagnosed with ASD, estimating that one in 88 children are affected.
Exploring genetic and environmental effects
There is currently no cure for ASD, and there are still many unanswered questions about what causes it, but the researchers say that "genetics are an important contributing factor."
Daniel B. Campbell, assistant professor of psychiatry and behavioral sciences at the Keck School of Medicine of USC and the study's senior author, explains:
"The MET gene variant has been associated with autism in multiple studies, controls expression of MET protein in both the brain and the immune system and predicts altered brain structure and function. 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."
Exposure to air pollution appears to increase the risk of autism among children with the MET gene variant.
The research identified 408 children, aged between 2 and 5 years, from the Childhood Autism Risks From Genetics and the Environment Study, a population-based, case-control study of preschool children from California.
Of these, 252 kids met the criteria for autism or ASD.
Air pollution exposure was determined based on the past residences of the children and their mothers, local traffic-related sources and regional air quality measures. MET genotype was determined through blood sampling.
Heather E. Volk, first author on the study and assistant professor of research in preventive medicine and pediatrics at USC and principal investigator at the Saban Research Institute of Children's Hospital Los Angeles, confirms the link:
"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."
Prof. Daniel Campbell concludes:
"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."
Previous research from the Harvard School of Public Health has shown a link between air pollution and autism.
The researchers are continuing to study the interaction of air pollution exposure and the MET genotype in women during pregnancy.