By screening the genomes of hundreds of people with autism and analyzing the effect of newly identified mutations in cultured neurons, researchers have clarified the disorder’s complex link to a gene called SHANK2.
Functional mutations in SHANK2 crop up about twice as often in individuals with autism as in typical controls, according to a study published 9 February in PLoS Genetics.
The SHANK2 protein buttresses the synapse, or junction between neurons. The new findings add to already robust evidence from genetic studies and animal models that synaptic proteins — notably SHANK3, neurexins and neuroligins — are important in autism, the researchers say.
But a more surprising finding helps to explain why not everyone who has a SHANK2 mutation has autism. The three individuals with autism known to carry SHANK2 deletions also carry rare deletions or duplications — so-called copy number variations, or CNVs — in an autism-linked segment of chromosome 15. This supports the idea that autism arises not from a single genetic glitch, but from multiple hits to the genome.
“I think many people are still thinking about the genome like the old black-and-white movies from the 1950s: The good guy was in white, the bad guy was in black, and everybody knew what was going on,” says lead investigator Thomas Bourgeron, professor of genetics at the University of Paris Diderot.
But studies like this show that a ‘bad’ genetic glitch isn’t necessarily the only bad guy.
“When we find a single mutation in a patient with autism, we can’t say that we’re done,” Bourgeron says. “We still have to work on the whole genome of these patients to understand exactly what’s going on.”
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