An important autism study out of Sweden has concluded that environment is as much a cause of autism as genetics.
The researchers said their study is the first to find that genetics and environment are equally responsible for autism. Previous studies have suggested genetics are mostly responsible for the disorder, they said.
Researchers at the Karolinska Institute in Stockholm, King's College London and Mount Sinai School of Medicine's Seaver Autism Center in New York carried out the study, which they described as the largest of its kind. They tracked more than 14,000 autistic Swedish children over a 24-year period, from 1982 to 2006.
"We were surprised by our findings as we did not expect the importance of environmental factors in autism to be so strong," said Avi Reichenberg, a Mount Sinai Seaver professor and researcher on the study.
The study did not determine which environmental factors contribute to autism, though it said candidates include such things as infections acquired in utero and complications at birth.
"It's now clear that we need much more research to focus on identifying what these environmental factors are," said Reichenberg, noting that recent studies have tended to focus on genes. "In the same way that there are multiple genetic factors to consider, there will likely be many different environmental factors contributing to the development of autism," he added.
The study reaffirmed a strong genetic link with autism: it found that children with autistic siblings are ten times more likely to be diagnosed. In addition, cousins of those with autism had the disorder at twice the rate of the general public.
The new report was published in the Journal of the American Medical Association. The researchers presented their findings at the Pediatric Academic Societies annual meeting in Vancouver over the weekend.