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Gene Variants Hold New Clues to Autism

Researchers Identify Gene Mutations That May Raise Risk of Autism Spectrum Disorders
By
WebMD Health News
Reviewed by Louise Chang, MD

April 28, 2009 -- Rare genetic mutations are known to increase the risk of autism and autism spectrum disorders (ASD). Now, researchers have identified new and common gene mutations -- also called gene variants -- that also boost the risk of the developmental disorders that affect an estimated one in 150 U.S. children.

"What we mean by common is that the risk variant is present in about 65% of children diagnosed with autism spectrum disorder," says Hakon Hakonarson, MD, PhD, director of genomics research at The Children's Hospital of Philadelphia and the lead author of two of three studies on the topic published online today.

Based on the new research, which included mostly children with an autism diagnosis -- rather than one of the less severe disorders on the autism spectrum -- the newly identified gene variants for autism could account for about 15% of autism diagnoses, Hakonarson estimates. Having the variant does not automatically mean a person will develop autism, he says, as other genetic and environmental factors are thought to come into play; even so, the 15% estimate is substantial, he says.

Just as importantly, the newly identified gene variants found to boost autism risk are involved in facilitating communication between brain cells -- making more credible the suggestions from other autism experts that autism or ASDs are due to abnormal connections between brain cells early in development, Hakonarson says.

Hakonarson's study, a cooperative effort among numerous institutions and co-authored by respected autism researchers nationwide, is published online today in the journal Nature, along with two other studies uncovering more clues to autism -- one also published in Nature and the other in Annals of Human Genetics.

Gene Variant Study

For the first of two studies, Hakonarson and his colleagues conducted a genome-wide association study on 780 families, including 3,101 participants with affected children, and then a second group of 1,204 people with autism or ASD and 6,491 in a comparison group. A genome-wide study involves the scanning of markers across the complete set of the DNA (or genomes) obtained from many people to find genetic variations associated with specific diseases.

"When we looked to see if any particular regions of the genome looked different, only one region came up," Hakonarson tells WebMD. It was in the region of chromosome 5 involving the genes that facilitate cell-to-cell communication -- CDH9 and CDH10. These genes carry codes to produce crucial neuronal cell-adhesion molecules, Hakonarson says. "They sit on the surface of nerve cells and facilitate and create cell-to-cell communication."

No other common gene variants have been identified and replicated in independent studies with the same scientific rigidity, Hakonarson says.

With the new discovery, the hope is to identify children having these variants at birth or even in utero so intervention can begin early, Hakonarson says. Eventually, he says, the goal would be to create specific treatments to correct the gene variant.

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