A new study is among the first to clearly demonstrate the kind of gene-environment interactions that experts suspect are behind many if not most cases of autism.
The researchers looked at children who had autism and carried gene changes associated with increased risk for the disorder. Within this group, those whose mothers had infections or fever during pregnancy were significantly more likely to be severely impaired by social-communication challenges and repetitive or restricted behaviors.
The report appears in the Journal of Developmental and Behavioral Pediatrics.
“It's increasingly understood that autism is caused by the interaction of genetic and environmental factors, but identifying how genes and environment interact is incredibly challenging,” comments developmental pediatrician Paul Wang, Autism Speaks head of medical research. “This study is a breakthrough because it shows how certain genes interact with maternal infection.” Dr. Wang was not involved in the study.
Multiple earlier studies have identified maternal infection as one of the prenatal factors that increase autism risk. Animal studies have shown that the inflammation produced by the infection can affect the developing brain. But clearly, most women who have an infection during pregnancy do not have a child with autism. Similarly, many of the gene changes associated with autism are also carried by people who don’t develop the disorder.
In their new study, researchers with the University of Washington-Seattle looked at nearly 2,000 children diagnosed with autism who had at least one genetic “copy number variation” known to increase autism risk. Copy number variations involve deletions or duplications of entire segments of DNA.
They also collected information on the children’s symptom severity and their mother’s health during pregnancy through extensive parent interviews and questionnaires.
They found significantly more-severe autism symptoms among the children whose mothers reported either infection or fever during pregnancy. In particular, these children tended to have greater problems with social-communication and repetitive/restricted behaviors
“The important take-home message is that genes don’t act in a vacuum,” says study leader Raphael Bernier. Dr. Bernier is clinical director of the Seattle Children’s Autism Center and a researcher at the University of Washington. “It’s important for us to explore the early factors involved in moving from genotype to phenotype, or genetic predisposition to autism behaviors,” he says.
Dr. Bernier calls for further research exploring how the gene changes examined in his team’s study interact with the “environment” of the womb when a mother has an infection. “It will be important to identify how these genes may relate to the immune system,” he says.
Adds Dr. Wang, “Studies such as this are helping us understand why infections during pregnancy are associated with autism. Ultimately, they may allow us to take steps to prevent the associated harm to early brain development.”
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