Children born within just one-fifth of a mile of a highway appear twice as likely to have autism, according to a team of researchers from Children’s Hospital Los Angeles, the Keck School of Medicine of the University of Southern California (USC) and the UC Davis MIND Institute.
There has been a 57 percent jump in autism diagnoses between 2002 and 2006, according to the federal Centers for Disease Control and Prevention. The current study supports the idea that environmental factors, along with a strong genetic risk, may offer a clue into this increase.
Although there is little scientific data regarding any links between environmental pollutants and autism, other studies have revealed that a mother’s exposure to air pollution during pregnancy is associated with physical and developmental problems in the fetus. Air pollution exposure during a baby’s first few months of life has also been linked to delayed cognitive development.
Data from autistic children, as well as controls, were taken from the Childhood Autism Risks from Genetics and the Environment (CHARGE) study, a population-based case-control study of preschool children, who were between the ages of 24 and 60 months at the beginning of the research.
The children lived in and around Los Angeles, Sacramento and San Francisco. Population-based controls were from the state of California’s birth files, and these were frequency-matched to the autism cases by age, gender and general geographic location. Each family was evaluated in person, and all of the participating children were assessed; autism evaluation was accomplished with well-established procedures.
Researchers pinpointed the locations where the children’s mothers’ lived during the first, second and third pregnancy trimesters as well as the location at the time of birth and the proximity of these homes to a major road or highway. The fetuses’ gestational ages were confirmed through ultrasound and prenatal records.
Lead author Heather Volk, Ph.D., and her colleagues discovered that if a child was born within 309 meters (just over 1,000 feet) of a highway there was an associated twofold increase in the risk for autism. This link was not affected by adjustment for child ethnicity or gender, level of education in the home, prenatal smoking or maternal age.
In toxicological and human studies, it has been shown that traffic-related air pollutants trigger inflammation and oxidative stress. New evidence that oxidative stress and inflammation are implicated in the development 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. It is highly likely that most of them operate in conjunction with other exposures and/or with genes,” said co-author Irva Hertz-Picciotto, Ph.D., chief of the division of environmental and occupational health in the Department of Public Health Sciences at UC Davis.
The paper appears online in the journal Environmental Health Perspectives.
Source: University of California