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Gene May Be Risk Factor for Autism

By Cheryl Simon Silver

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Researchers studying families with autism have pinpointed a gene that may increase susceptibility to autism in a broad population. Most rare genetic mutations associated with autism have been identified in single families.

Joseph D. Buxbaum and colleagues at Mount Sinai School of Medicine in New York conducted genetic screening of 411 families with members who have autism. The sample included 2,000 people, of whom 720 are afflicted with the disorder.

The researchers report their findings in this month’s American Journal of Psychiatry.

Previous research had demonstrated an association between a gene located on chromosome 2 and autism. This chromosome is known to be associated with deficits in language development—a hallmark of autism. This time, researchers looked for a gene on a specific part of the chromosome, zeroing in on the gene known as SLC25A12.

Buxbaum and his colleagues confirmed that the gene occurs with greater frequency in autistic individuals and in members of their family than in families without the disorder.

The gene increases risk for the disease but carrying the gene doesn’t necessarily mean that an individual will develop the disease, Buxbaum says, noting that more than one gene is involved in autism. But individuals with the gene have twice the risk for developing the disorder as individuals without it.

Now that one gene is identified, Buxbaum says, it is likely to be easier to find the next gene.

Most researchers estimate that there are five to ten genes that interact to produce autism, a complex, largely genetic disorder. One gene by itself might have little effect, but several in combination may increase a child’s risk enough to warrant early and aggressive “interventions” such as training that facilitates language and play skills and appropriate behaviors.

For instance, if doctors know a child is 300 times more likely to develop autism than a child in the rest of the population, intervention could begin even before there is a firm diagnosis.

Symptoms of autism often appear by age three, and the disorder occurs more often in boys than in girls. Autistic children often are unable to communicate normally, either verbally or through nonverbal cues, and seldom have normal social interactions with others, including their families.

Buxbaum describes the disorder as “the most highly genetic of the psychiatric disorders.” It affects approximately one in 1,000 children; some data suggest that the incidence is growing, although no one is sure why. A second child born to a family that already has an autistic child is 50 to 100 times more likely also to be autistic than a child with no family history of autism.

The gene affects the molecule ATP, which produces energy required for cell function. The variation leads the cell to produce too much ATP, possibly compromising normal cell operation.

Buxbaum, Joseph D., et al. Linkage and Association of the Mitochondrial Aspartate/Glutamate Carrier SLC25A12 Gene with Autism. American Journal of Psychiatry, 161, 662-669. April 2004.

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