WASHINGTON: Pregnant women who were exposed to high levels of air pollution were twice as likely to have a child with autism as women who lived in low pollution areas, a United States study said on Tuesday.
According to experts at Harvard University, the research is the first large national study to examine links between the prevalence of pollution and the development of the developmental disorder.
The findings are published in the journal Environmental Health Perspectives.
“Our findings raise concerns,” said lead author Andrea Roberts, a research associate in the Harvard School of Public Health Department of Social and Behavioral Sciences.
“Depending on the pollutant, 20 percent to 60 percent of the women in our study lived in areas where risk of autism was elevated,” she said.
The data came from a large survey of 116,430 nurses that began in 1989.
For the analysis, researchers isolated 325 women who had a child with autism and 22,000 women who had a child without the disorder.
To estimate exposure to pollutants while pregnant, they used air pollution data from the Environmental Protection Agency, and adjusted for factors like income, education, and smoking during pregnancy.
The analysis found that women who lived in 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 areas with the lowest levels.
When the pollutants included lead, manganese, methylene chloride and combined metal exposure, women in areas with the highest levels of these pollutants were about 50 percent more likely to have a child with autism.
Autism is a brain disorder that affects as many as one in 88 in the United States, and about one in 100 in Britain.
Researchers said the findings suggest that metals and other pollutants should be regularly measured in the blood of pregnant women to give a better understanding of whether certain pollutants increase autism risk.
Researchers also said some children with autism have weak brain connections in regions that link speech with emotional rewards, possibly signaling a new pathway in treatment.
The study in the Proceedings of the National Academy of Sciences is the first to suggest that the reason why children with autism display an insensitivity to human speech may be linked to faulty circuitry in the brain’s reward centers.
“Weak brain connectivity may impede children with autism from experiencing speech as pleasurable,” said Vinod Menon, senior author of the study and professor of psychiatry and behavioral sciences at Stanford University.
Researchers took magnetic resonance imaging brain scans of 20 children with a high-functioning type of autism; they had normal range IQs and could speak and read, but had a hard time in conversation or understanding emotional cues.
By comparing the scans to those of 19 children without autism, they found that the brains of youngsters with autism showed poor connections to brain regions that release dopamine in response to rewards.
On the left side of the brain, the autistic children showed weak connections to the nucleus accumbens and the ventral tegmental area.
And on the right side, in the voice-selective cortex where vocal cues and pitch are detected, there was a weak connection to the amygdala, which processes emotional cues.
Researchers also found that weaker connections meant worse communication abilities.
“The human voice is a very important sound; it not only conveys meaning but also provides critical emotional information to a child,” said lead author Daniel Abrams, a postdoctoral scholar in psychiatry at Stanford.
“We are the first to show that this insensitivity may originate from impaired reward circuitry in the brain.”
The findings also give weight to the theory that people with autism have a deficit in social motivation that explains their inattention to voices and words, rather than a sensory deficit that prevents them from hearing words.