Researchers seeking the roots of autism have linked the disorder to chemicals in air pollution and, in a separate study, found that language difficulties of the disorder may be due to a problem in brain wiring.
Researchers from Harvard Universitys School of Public Health found that pregnant women exposed to high levels of diesel particulates or mercury were twice as likely to have an autistic child than peers in low-pollution areas. The findings, published Tuesday in Environmental Health Perspectives, are from the largest U.S. study to examine the ties between air pollution and autism.
One in 50 U.S. children is diagnosed with autism or a related disorder, according to the Centers for Disease Control and Prevention. Children with autism may be unresponsive to people, become indifferent to social activity and have communication difficulties.
A separate study from Stanford University and published in Proceedings of the National Academy of Sciences is the first to suggest that weak connections between brain regions for speaking and reward may be why.
The cause of autism isnt known, though genetic factors are thought to be important, according to the National Institutes of Health.
The link to air pollution was initially made in 2006 and met with skepticism, said Marc Weisskopf, an author of todays study.
The Harvard researchers used data from the Nurses Health Study 2, a long-term study involving more than 116,000 nurses, begun in 1989. Within that group, the scientists looked at 325 women who had a child with autism and 22,000 women who had children without the disorder.
Using data from the Environmental Protection Agency, researchers estimated the womens exposure to toxins, a method that Weisskopf said is imperfect. His study is large enough to suggest follow-up studies with more precise methods of detecting chemicals in the air, he said.
In the language study, brain imaging determined that the connections between brain regions for language and reward were stronger in children who dont have the disorder than in those diagnosed with it, said Daniel Abrams, a postdoctoral research fellow at Stanford University in California. Thats important because communication problems are key diagnostic criteria for autism.
Typical infants listen to human speech and engage with sounds to develop early language skills and emotional understanding as well as to bond with their parents, the authors wrote.
The researchers looked at how the speech part of the brain was connected to other regions. Those with autism had weaker connections between the temporal lobe, where speech is controlled, and the dopamine reward pathway that elicits pleasurable feelings, the study found.