Air pollution and genetics combine to increase risk of autism

Exposure to air pollution appears to increase the risk for autism among people who carry a genetic disposition for the neurodevelopmental disorder, according to newly published research led by scientists at the Keck School of Medicine of the University of Southern California (USC).

"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," said the study's first author, Heather E. Volk, Ph.D., M.P.H.

Heather Volk is assistant professor of research in preventive medicine and pediatrics at the Keck School of Medicine of USC and principal investigator at The Saban Research Institute of Children's Hospital Los Angeles.

The study, "Autism spectrum disorder: Interaction of air pollution with the MET receptor tyrosine kinase gene," is scheduled to appear in the January 2014 edition of Epidemiology.

Autism spectrum disorder (ASD) is a lifelong neurodevelopmental disability characterized by problems with social interaction, communication and repetitive behaviors.

The Centers for Disease Control and Prevention estimates that one in 88 children in the United States has an ASD.

ASD is highly heritable, suggesting that genetics are an important contributing factor, but many questions about its causes remain. There currently is no cure for the disorder.

"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," said Daniel B. Campbell, Ph.D.

David Campbell is assistant professor of psychiatry and the behavioral sciences at the Keck School of Medicine of USC and the study's senior author.

"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."

Independent studies by Volk and Campbell have previously reported associations between autism and air pollution exposure and between autism and a variant in the MET gene.

The current study suggests that air pollution exposure and the genetic variant interact to augment the risk of ASD.

Campbell and Volk's team studied 408 children between 2 and 5 years of age from the Childhood Autism Risks From Genetics and the Environment Study, a population-based, case-control study of preschool children from California.

Of those, 252 met the criteria for autism or autism spectrum disorder. 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.

Campbell and Volk continue to study the interaction of air pollution exposure and the MET genotype in mothers during pregnancy.

Autism Risk: Exposure to high pollution levels during pregnancy

Women in the U.S. exposed to high levels of air pollution while pregnant were up to twice as likely to have a child with autism as women who lived in areas with low pollution, according to a new study from Harvard School of Public Health (HSPH).

It is the first large national study to examine links between autism and air pollution across the U.S.

Andrea Roberts

"Our findings raise concerns since, depending on the pollutant, 20% to 60% of the women in our study lived in areas where risk of autism was elevated," said lead author Andrea Roberts, research associate in the HSPH Department of Social and Behavioral Sciences.

The study appeared online June 18, 2013 in Environmental Health Perspectives.

Exposure to diesel particulates, lead, manganese, mercury, methylene chloride and other pollutants are known to affect brain function and to affect the developing baby.

Two previous studies found associations between exposure to air pollution during pregnancy and autism in children, but those studies looked at data in just three locations in the U.S.

The researchers examined data from Nurses' Health Study II, a long-term study based at Brigham and Women's Hospital involving 116,430 nurses that began in 1989.

Among that group, the authors studied 325 women who had a child with autism and 22,000 women who had a child without the disorder.

They looked at associations between autism and levels of pollutants at the time and place of birth. They used air pollution data from the U.S. Environmental Protection Agency to estimate women's exposure to pollutants while pregnant.

They also adjusted for the influence of factors such as income, education, and smoking during pregnancy.

The results showed that women who lived in the 20% of locations with the highest levels of diesel particulates or mercury in the air were twice as likely to have a child with autism as those who lived in the 20% of areas with the lowest levels.

Other types of air pollution—lead, manganese, methylene chloride, and combined metal exposure—were associated with higher autism risk as well.

Women who lived in the 20% of locations with the highest levels of these pollutants were about 50% more likely to have a child with autism than those who lived in the 20% of areas with the lowest concentrations.

Most pollutants were associated with autism more strongly in boys than girls. However, since there were few girls with autism in the study, the authors said this finding should be examined further.

Marc Weisskopf

Senior author Marc Weisskopf, associate professor of environmental and occupational epidemiology at HSPH, said, "Our results suggest that new studies should begin the process of measuring metals and other pollutants in the blood of pregnant women or newborn children to provide stronger evidence that specific pollutants increase risk of autism. A better understanding of this can help to develop interventions to reduce pregnant women's exposure to these pollutants."