More differences than similarities found in siblings with autism

Benedict Carey

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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.

Scientists analyzed genetic material from 85 families, using a technology called whole-genome sequencing. Unlike other approaches, which illuminate a sample of a person’s genetic material, the whole-genome technique maps out the entire voluminous recipe, every biological typo, every misplaced comma or transposed letter. Each of the families had two children with a diagnosis of autism.

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 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.

Experts said the report, in the journal Nature Medicine, would most likely encourage changes in clinical practice. Some hospitals analyze the genetic profile of the eldest affected sibling to try to understand an infant, or to advise parents of the odds of having another child with the same disorder. That approach is not informative in most cases, the study authors said.

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