ScienceDaily (July 11, 2012) — Researchers at Emory University School of Medicine have identified five rare mutations in a single gene that appear to increase the chances that a boy will develop an autism spectrum disorder (ASD).
Mutations in the AFF2 gene, and other genes like it on the X chromosome, may explain why autism spectrum disorders affect four times as many boys as girls.
The mutations in AFF2 appeared in 2.5 percent (5 out of 202) boys with an ASD. Mutations in X chromosome genes only affect boys, who have one X chromosome. Girls have a second copy of the gene that can compensate.
The results were published July 5 in the journal Human Molecular Genetics.
"Our data suggest that AFF2 could be one of the major X-linked risk factors for ASD's," says senior author Michael Zwick, PhD, assistant professor of human genetics at Emory University School of Medicine.
The finding bolsters a growing consensus among geneticists that rare variants in many different genes contribute significantly to risk for autism spectrum disorders.
The mutations in the AFF2 gene probably do not cause ASDs all by themselves, Zwick says.
"We do not think that the variants we have identified are monogenic causes of autism," he says. "Our data does support the idea that this is an autism susceptibility gene."
In some situations, mutations in a single gene are enough by themselves to lead to a neurodevelopmental disorder with autistic features, such as fragile X syndrome or tuberous sclerosis complex. But these types of mutations are thought to account for a small number of ASD cases.
Recent large-scale genetic studies of autism spectrum disorders have identified several "rare variants" that sharply increase ASD risk. Scientists believe rare variants could explain up to 15 or 20 percent of ASD cases. However, until now no single variant has been found in more than one percent of ASD cases.
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