Study finds mom's age, health may play larger role in autism

CHICAGO — Most of the risk of autism has been blamed by experts on inherited genes. Now one of the largest studies of twins and autism shifts the focus to the womb, suggesting that the mother's age and health may play a larger role than thought.

The new research doesn't solve the mystery of what causes autism. Most scientists think faulty genes and outside factors are both at work. And since autism spectrum disorders include a wide range of conditions, from mild to severe, it's unlikely there's a single cause for all of them.

Conditions during pregnancy may trigger autism where there's a genetic vulnerability, said Dr. Gary Goldstein of the Kennedy Krieger Institute in Baltimore, who was not involved in the new research.

"We've identified lots of vulnerability genes, but not everybody who has them gets autism," Goldstein said.

The new twins study, published today by Archives of General Psychiatry, used rigorous methods to diagnose autism spectrum disorders, including direct observation of the children.

Using California health records, it's the largest study to do that and the first to consider a large sample of twins drawn from a general population, said lead author Dr. Joachim Hallmayer of Stanford University in Palo Alto, Calif.

Children with autism can have trouble communicating and interacting socially. They may have poor eye contact and engage in repetitive behavior such as rocking or hand-flapping. One in 100 children have autism disorders, according to U.S. government estimates.

The new study included 192 sets of twins where at least one of the twins was affected with autism.

Some of the twins were identical and some were non-identical, or fraternal, twins.

The researchers used DNA testing to determine which twins were identical and which were fraternal. That was important because identical twins come from one fertilized egg and have identical genetic makeups. Fraternal twins, from two fertilized eggs, share no more genetic material than any other siblings.

The new study found, as expected, high rates of shared autism disorders for identical twins: 77 percent of male twin pairs and 50 percent for female pairs had autism in both twins.

Surprisingly, it also found fairly high rates of fraternal twins both having autism spectrum disorders: 31 percent rate for male fraternal twins and 36 percent for female fraternal twins.