* Antidepressants during pregnancy increase risk
* Both genes, environment play a role
By Julie Steenhuysen
CHICAGO, July 4 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 on 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, suggesting 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.
And the risk was even greater -- a threefold increase --
when the drug was taken in the first trimester of pregnancy.
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
"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.
The Stanford study involved 54 pairs of identical twins,
who share 100 percent of the same genes, and 138 pairs of
fraternal twins, who share half of the same genes.
In each pair, at least one of the twins had been diagnosed
The researchers found the chances of both children having
autism spectrum disorder was higher among identical twins than
among fraternal twins. But fraternal twins were much more
likely to develop autism than studies of children in families
where a sibling has autism.
According to the study, environmental factors common to
twins explain about 55 percent of the cases of autism, and
while genetic factors still play a role, it is much lower than
seen in other studies of twins and autism.
"Environmental factors play a bigger role than previously
thought," said Dr. Joachim Hallmayer of Stanford University
School of Medicine in California, who led the study.
Recent studies have suggested genetics played the biggest
role in autism, but his findings suggest something different,
he said in a telephone interview.
"We have to study both the genetics and the environment,"
Hallmayer said. "If we look only at one side, I don't think
that will lead us to the right answer."
COULD IT BE ANTIDEPRESSANTS?
In a separate study in the same journal, a team led by Lisa
Croen, director of the Autism Research Program at the Kaiser
Permanente Division of Research in Oakland, California, looked
to see whether antidepressants known as selective serotonin
reuptake inhibitors, or SSRIs, contributed to autism risk.
The team studied nearly 300 children with autism and 1,500
randomly selected children and then checked their mothers'
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
"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)