Autism not just hereditary, study suggests

CHICAGO -- Environmental factors may play a greater role in autism than previously thought, tipping the scale away from a strict focus on genetics, two studies released Monday suggest.

In one, a team at Stanford University compared cases of autism in identical and fraternal twins and found that fraternal twins, who share only half of the same genes, have unusually high rates of autism. That suggests that factors other than genetics may be triggering the disease.

In another, researchers at health insurer Kaiser Permanente found mothers of children with autism were twice as likely to have been prescribed a common antidepressant during the year before their pregnancy than mothers of healthy children.

The findings, released in the Archives of General Psychiatry, suggest that something in the birth environment -- drugs, chemicals or infections -- may be triggering autism in children who are already genetically predisposed to develop the disease.

"It has been well-established that genetic factors contribute to risk for autism," Clara Lajonchere, a study co-author and vice president of clinical programs for Autism Speaks, said in a statement. "We now have strong evidence that, on top of genetic heritability, a shared prenatal environment may have a greater than previously realized role in the development of autism."

Autism is a spectrum of disorders ranging from a profound inability to communicate and mental retardation to relatively mild symptoms, such as with Asperger's syndrome.

It affects one in every 150 children born today in the United States, or about 1 percent of the population.