Wednesday, January 28, 2015

More Differences Than Similarities Are Found in Autistic Siblings

Most siblings with a diagnosis of autism do not share the same genetic risk factors for the disorder and are as distinct in their behaviors as any brothers and sisters, scientists reported on Monday in a study that came as a surprise to many doctors, if not to parents. The researchers focused their analysis on about 100 genetic glitches linked to the development of autism. They found that about 30 percent of the 85 sibling pairs in the study shared the same mutation, and about 70 percent did not. The sibling pairs who shared a genetic glitch were more similar to each other, in their habits and social skills, than those pairs whose genetic risks were different, the study found. The report is the latest twist in a genetic plot that seems only to thicken. In recent years, scientists have isolated gene mutations that steeply raise the risk of autism. But those glitches account for only a tiny fraction of cases, and the number of them continues to increase — to about 100 now, and counting. Scientists have not been able to tell a coherent story about causation. It could be that common variants — that is, gene variations that many people carry, which cause no apparent problems — increase the dormant possibility for the disorder, in some combinations. The finding drives home the exasperating diversity of autism, even in the most closely related individuals. And it suggests that scientists will need to analyze tens of thousands of people, perhaps more, to tell any meaningful story about its biological basis.

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