Environment, not just genetics, at play in autism

The team studied nearly 300 children with autism and 1,500 randomly selected children and then checked their mothers' medical records.

They found mothers of the children with autism were twice as likely to have taken an antidepressant in the year before delivery than children in the control group.

And the effect was strongest -- three times higher -- when the drugs were taken in the first trimester of pregnancy.

"Our results suggest a possible, albeit small, risk to the unborn child associated with in utero exposure to SSRIs," Croen said in a statement.

But she said this risk must be balanced with the risk to the mother of having untreated depression.

The team cautioned that the SSRI study was preliminary and said much more work was needed to understand the link between antidepressants and autism.

"There are real risks to not being treated for a serious illness like depression. You have to weigh the options," said Dr. Thomas Insel, director of the National Institute of Mental Health.

"A threefold increase in risk is not insignificant. It is worth taking that into account with other factors," Insel said in a telephone interview.

Insel, whose agency funded the twins study, said it is not yet clear what environmental factors may be triggering autism.

"It could be a range of things from infection to chemical exposures. We simply don't know."

What is becoming clear, he said, is that the exposure is likely occurring before childbirth.

"From all the studies that so far have concluded, that is where the evidence seems to be going," he said.

(Editing by Doina Chiacu)

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