US research links autism to pollution levels
According to experts at Harvard University, the research — the findings of which are published in the journal Environmental Health Perspectives — is the first large national study to examine links between the prevalence of pollution and the development of the disorder.
“Our findings raise concerns,” said lead author Andrea Roberts, a research associate in the Harvard School of Public Health department of social and behavioural sciences.
“Depending on the pollutant, 20% to 60% of the women in our study lived in areas where risk of autism was elevated,” she said.
The data came from a survey of 116,430 nurses that began in 1989.
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 in pregnancy.
The analysis found that women who lived in areas 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% more likely to have a child with autism.
Researchers said the findings suggest 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.
Meanwhile, some children with autism have weak brain connections in regions that link speech with emotional rewards, possibly signalling a new pathway in treatment, other researchers said.
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 speech may be linked to faulty circuitry in the brain’s reward centres.
Vinod Menon, senior author of the study and professor of psychiatry and behavioural sciences at Stanford University, said: “Weak brain connectivity may impede children with autism from experiencing speech as pleasurable.”
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 children with autism 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 weaker connections meant worse communication abilities. 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.
