UCSF, Stanford Study Finds Autism Triggered By Environment, Not Just Genes
SAN FRANCISCO (CBS / AP) -- What causes autism? Scientists still don't have an answer, but a new study by UCSF's Institute for Human Genetics and Stanford University suggest that conditions in a mom's womb may trigger the developmental disorder.
Heredity is considered a major factor that triggers autism spectrum disorders, but scientists have long wondered what roles - if any - environmental factors play.
"Autism had been thought to be the most heritable of all neurodevelopmental disorders, with a few small twin studies suggesting a 90 percent link," said UCSF geneticist Neil Risch, one of the authors of the study. "It turns out the genetic component still plays an important role, but in our study, it was overshadowed by the environmental factors."
For the study, published in the July 4 issue of Archives of General Psychiatry, scientists used California health records to identify 192 pairs of twins - fraternal or identical - where at least one was affected by autism.
Using diagnostic techniques that included directly observing the children, the scientists found 77 percent of male identical twins and 50 percent of female identical pairs both had autism. Those findings weren't too surprising, consdering identical twins share the same genes.
But what surprised researchers were the high rates of autism spectrum disorders they found in pairs of fraternal twins: 31 percent rate for males and 36 percent for females.
"Our work suggests that the role of environmental factors has been underestimated," said Dr. Joachim Hallmayer, an associate professor of psychiatry and behavioral science at Stanford University, and another of the study's authors. "It doesn't mean that genes don't play a role, but they may not play as big a role as thought."
What exactly those environmental factors are, Hallmayer said, is the "multimillion dollar question," but he noted that the disorder's manifestation in very young children indicates a cause early in life and possibly during pregnancy.
Those factors could include stress, diet, infections, and a mother's age, experts said.
And according to another new study published in the same journal, what medication mom is taking.
That study showed mothers who took antidepressants during the year before birth - particularly in the first three months of pregnancy - were more likely to give birth to autistic children. Specifically, 6.7 percent of women taking antidepressants gave birth to a child with an autism spectrum disorder, compared to 3.3 percent of women who weren't taking antidepressants.
Should expecting mom's stop taking their antidepressants?
It's too early to advise pregnant women against antidepressants because untreated depression can be harmful to mother and baby, said this study's author, Dr. Lisa Croen, director of the California-based Autism Research Program at Kaiser Permanente.
One out of every 110 children has an autism spectrum disorder (ASD), according to the Centers For Disease Control (CDC). People with an ASD may experience challenges with social interaction, communication, intelligence, or behavior.
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