A new study suggests that, at least in mice, the most important factor causing autism is likely an individual's genes.
Scientists have long been stumped by what causes autism, with many suggesting that toxin and pollution exposure and certain medications taken by pregnant mothers could play a role in causing autism.
But University of California, San Francisco pediatric neurologist Elliott Sherr says that his study suggests that may not be the case, saying "genetics is a strong, if not the strongest component to this."
In the study, published Monday in the journal PLOS One, Sherr was able to pinpoint several places on the mouse genome that may be linked to autistic behavior. Autistic mice, he says, spend more time with inanimate objects than other mice and will ignore other mice in its cage. Sherr says some of the same places on the genome correspond with human genes.
"We've looked in those regions in humans and can suggest that there's an overlap in the genetics of the two," he says. "I would make the leap [that genetics and autism in humans] are linked because there is independent evidence in humans that genetics plays a role. That, with the mice data, is what is compelling. The two together is pretty strong."
His team is working to pinpoint specific genes that may be involved in causing autism in mice.
"We don't know the individual genes yet – we know a series of locations in the genome and we're working on hunting down how many and which genes are involved," Sherr says.
Over the past several years, autism diagnoses in children have greatly increased. Depending on who you ask, that increase suggests that autism has an environmental component or, as the Centers for Disease Control has said, doctors are just getting better at diagnosing the disorder.
A high-profile study published in 1998 in the journal Lancet suggested that childhood vaccines designed to protect against measles, mumps and rubella could be one cause of autism. Since then, the vaccine link has become widely accepted as a major contributor, despite numerous reports undermining that study. In 2010, that Lancet study was fully retracted, and Sherr's study suggests that genetics may play the most important role in autism development.
Last year, Thomas Frieden, director of the CDC, told reporters that autism is a "complex condition with many unanswered questions," but added that "doctors are getting better at diagnosing autism."
Sherr agrees. He says that his study suggests that environmental variables play a "modifying role" in causing autism as opposed to being a "major driver."
"Some of the increase is a naming issue. People are now calling autism what used to be considered intellectual disability," he says. "The primary diagnosis can easily shift without the patients being any different."