Gene profile may differ in siblings with autism

By Sheryl Ubelacker, The Canadian Press

TORONTO - As if autism wasn't already enough of a puzzle, researchers have discovered that even siblings affected by the disorder often don't share the same genetic mutations that appear to underlie their symptoms.

In a Canadian-led international study of 85 families with two children affected by autism spectrum disorder (ASD), researchers found that almost 70 per cent of the sibling pairs carried different genetic mutations related to the neurodevelopmental condition.

The scientists made the discovery after analyzing the DNA of both parents and children in a family, using whole genome sequencing.

The technique reads every one of the six billion letters that comprise an individual's genetic code, including those that make up more than 20,000 of a person's genes. Mutations are like typos in the massive encyclopedic tome that is human DNA.

"When we looked at the data, we were really surprised to see that when we could find mutations in genes that are known to be involved in autism, more often than not the siblings were carrying different mutations in different genes," said principal investigator Stephen Scherer, director of the Centre for Applied Genomics at Toronto's Hospital for Sick Children.

"I would have expected that more than one sibling would have carried the same sets of mutations because they both have autism."

Autism is a spectrum of related disorders with symptoms that can vary dramatically from one child to the next, although each will have problems with social skills, empathy, communication and inflexible behaviour. Two children with the same diagnosis say Asperger's syndrome may have very different abilities and behavioural traits.

Even in families with two siblings carrying the same genetic mutation, "in one case they'll be high-functioning and in the other low-functioning," he said.

While the genome results initially came as a surprise, Scherer said that on reflection they made sense: scientists have identified more than 100 genes that are implicated in autism spectrum disorder and they believe there are likely hundreds more.

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Gene profile may differ in siblings with autism