Environmental Exposures and Autism
Where birth defects increased, so did diagnoses of the developmental disorder, study showed
By Amy Norton
THURSDAY, March 13, 2014 (HealthDay News) -- A large U.S. study suggests environmental pollution might be contributing to autism risk, although the specific culprit toxins remain unknown.
Researchers analyzed medical records and found a correlation between U.S. counties' autism rates and their rates of genital birth defects in boys, which could be a sign of some common environmental contributors.
However, the findings, which were reported March 13 in the journal PLoS Computational Biology, do not prove that any particular environmental exposure directly raises the risk for the developmental disorder, experts said.
There's no "smoking gun," said Alycia Halladay, senior director of environmental and clinical sciences for the advocacy group Autism Speaks.
"This study was not designed to figure out what the [environmental] factors are," said Halladay, who was not involved in the research.
Still, she said, experts believe autism arises from a combination of genetic vulnerability and any number of environmental exposures. Some suspects include infections such as flu during pregnancy, certain prescription drugs taken during pregnancy and environmental toxins.
These latest findings support the "scientific agreement that it's a mix of genes and environment," Halladay said.
The lead researcher on the study agreed. "Both genes and environment are important," said Andrey Rzhetsky, a professor of genetic medicine at the University of Chicago.
The task ahead, Rzhetsky said, is to figure out which environmental exposures matter.
Autism refers to a collection of disorders, usually diagnosed during childhood, that affect language and social skills.
For the study, Rzhetsky's team analyzed nearly 100 million U.S. health insurance claims for a county-by-county look at rates of autism and intellectual disability. They also examined rates of genital malformations in boys -- such as micropenis, undescended testicles and hypospadias (in which the urethral opening is on the underside of the penis).
Those genital malformations were used as an indicator of parents' exposure to environmental pollutants, Rzhetsky said. The exact causes of those birth defects are not clear, but some studies have suggested that certain environmental toxins -- including pesticides and lead -- might play a role, he said.
In this study, county rates of genital birth defects ranged from none to just over 2 percent. Overall, the researchers found, for every 1 percent increase in those birth defects, the rate of autism rose by close to 300 percent.
Even accounting for county demographics, a strong link existed between rates of genital defects and autism, Rzhetsky said.
But the reasons for the correlation aren't clear. Genes could play some role, Rzhetsky said, and so could environmental factors other than pollutants.
Halladay said endocrine disruptors -- chemicals found in plastics, food cans and other everyday products -- have been linked to genital birth defects. But so far, researchers haven't found a connection to autism risk.