Study Points to Environmental Factors of Autism
Living near a freeway may be associated with increased risk of autism, according to a study published by a team of researchers from the Keck School of Medicine of USC, Children’s Hospital Los Angeles and the University of California at Davis MIND Institute.
The paper will appear online in the journal Environmental Health Perspectives.
“Children born to mothers living within 309 meters of a freeway appeared to be twice as likely to have autism,” said Heather Volk, the study’s first author.
Volk holds a joint appointment at the Community, Health Outcomes & Intervention Research Program at The Saban Research Institute of Children’s Hospital Los Angeles, the Zilkha Neurogenetic Institute and the Department of Preventive Medicine at USC.
Autism is a developmental disorder that has long been ascribed to genetic factors. While changes in diagnostic criteria and increased awareness have been thought to contribute to the rising incidence of the disorder, these factors alone cannot explain the dramatic increase in the number of children affected.
The Centers for Disease Control and Prevention reported a 57 percent increase between 2002 and 2006. This study supported the theory that environmental factors, in conjunction with a strong genetic risk, may be one possible explanation for the increase.
In addition, while little is known about the role of environmental pollutants on autism, air pollution exposure during pregnancy has been seen to have physical and developmental effects on the fetus in other studies. Exposure to air pollution during the first months of life also has been linked to cognitive developmental delay.
According to the study’s authors, this study is the first to link autism risk with exposure to vehicular pollutants, though direct measurements of pollutants were not made.
Data from children with autism and typically developing children, who served as controls, were drawn from the Childhood Autism Risks From Genetics and the Environment study, a population-based case-control study of preschool children.
Children were between the ages of 24 and 60 months at the start of the study and lived in communities around Los Angeles, San Francisco and Sacramento.
Population-based controls were recruited from state of California birth files and frequently matched to the autism cases by age, gender and broad geographic area. Each participating family was evaluated in person. All children were assessed for autism using well-validated instruments.
The study examined the locations where the children’s families lived during the first, second and third trimesters of the mothers’ pregnancies and at the time of the baby’s birth and looked at the proximity of these homes to a major road or freeway. The participants’ gestational ages were determined using ultrasound measurements and prenatal records.
Volk and her colleagues found that living within 309 meters of a freeway (or just over 1,000 feet) at birth was associated with a two-fold increase in autism risk. This association was not altered by adjustment for child gender or ethnicity, maximum education in the home, maternal age or prenatal smoking. The researchers found no consistent pattern of association of autism with proximity to a major road.
Traffic-related air pollutants have been observed to induce inflammation and oxidative stress in toxicological and human studies. The emerging evidence that oxidative stress and inflammation are involved in the pathogenesis of autism supports the findings of this study.
“We expect to find many, perhaps dozens, of environmental factors over the next few years, with each of them probably contributing to a fraction of autism cases,”
said Irva Hertz-Picciotto, chief of the division of environmental and occupational health in the Department of Public Health Sciences at UC Davis and the study’s principal investigator. “It is highly likely that most of them operate in conjunction with other exposures and/or with genes.”
Volk’s co-authors on the study include Rob McConnell from the Department of Preventive Medicine at USC, Irva Hertz-Picciotto and Lora Delwiche from the University of California at Davis, and Fred Lurmann of Sonoma Technology Inc.
The study was supported by grants from the National Institute of Environmental Health Sciences, the Environmental Protection Agency, the MIND Institute, the Southern California Environmental Health Sciences Center, Autism Speaks, and the Las Madrinas Endowment for Autism Research, Interventions and Outcomes.
An interview with Volk can be seen at http://www.myfoxla.com/dpp/health/living-near-freeways-linked-autism-risk-20101216