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In recent years, rates of autism have been on the rise in the U.S. Between 2012 and 2014 alone, rates jumped 30 percent. The increase has largely been attributed to changes in diagnostic criteria for autism.
“Many children that we used to call intellectually disabled and many more with social deficits are now recognized as being on the autism spectrum,” said Kathy Katz, a pediatric psychologist at Georgetown University Medical Center in Washington, DC.
But some experts suggest that environmental exposures may also be contributing to the climbing rates. In California alone, autism diagnoses were up 600 percent between 1990 and 2001. Yet researchers found that only about one-third of the rise could be explained by changing diagnoses or kids being diagnosed at increasingly younger ages.
Earlier this year, scientists examining more than two million births in Sweden reported that inherited genes make up about 50 percent of a child’s autism risk, while environmental factors make up the other half.
It’s tempting to tie the increase in prevalence to environmental factors, said Halladay, but it’s hard to know for sure what’s going on, since some environmental risks have increased over the past few decades while others have decreased.
“Use of pesticides has gone up, so has autism. But air quality has also improved, and we know that air pollution plays a role in autism spectrum disorder risk,” she said.
Some studies are starting to look how environmental exposures may act differently in people whose genetics make them more susceptible. Earlier this year, researchers showed that people with a gene variant associated with autism and high exposure to air pollution had an increased risk of autism over people with the same gene variant but lower exposure to air pollution.
Next, Shelton hopes to look for autism risk from pesticide exposure among mothers with certain genetic variations.
“We need to know if some moms are at higher risk than others and what that risk is. Knowing who is most vulnerable is key to understanding how to better protect them,” she said.