Autism risk in siblings is double previous estimates

The risk of a family with one autistic child having another child with autism is double what was previously thought, according to a new study.

The findings, published in the journal Pediatrics, are of average risks, scientists say: They will vary according to the family’s specifics.

“I have seen families with five kids with autism,” said Dr. Fred Volkmar, a child psychiatrist and autism expert at Yale University. Volkmar was not part of the study, published Monday.

Scientists have long known that autism runs in families. Still, most previous estimates of the risk of recurrence ranged from 3% to 10%.

The new study of autism risk, conducted at 12 sites in the United States and Canada, followed 664 infants with at least one older brother or sister who had the disorder. It shows a 19% chance a sibling will have autism and an even higher risk -- 32% -- when two children in the family have some form of autism.

When are subsequent children in a family probably not at risk?

Up to 15% of autism cases have been linked to specific genetic mutations. If one of those mutations is present in both an autistic child and a parent, the risk to the next child is considerably higher than the rate found in the study. But if the mutation occurs only in the autistic child and not in a parent, that means it arose spontaneously, and future siblings are probably in the clear.