Siblings Face High Recurrence Risk for Autism

August 15, 2011— -- One month before William and Carissa Hawn's second son was born, their first son, Logan, then 3, was diagnosed with autism.

"Logan was our first experience with autism," said William Hawn, 34, of Modesto, Calif.

But when their second son, Aaron, was born, his pediatrician told the Hawns there was a 10 percent chance that he too would develop autism.

Earlier studies are consistent with Aaron's pediatrician. Infants who have siblings with autism have a 3 to 10 percent increased risk for autism, a higher chance than the 1 percent risk among the general population.

But a new study published Monday in the journal Pediatrics now suggests the risk is higher than previously thought. The study, considered the largest autism study to follow infants for sibling recurrence, found that infants with an older autistic sibling have a near 19 percent risk that they too will develop the disorder.

"We were surprised and distressed to see how high the recurrence risk is," said Sally Ozonoff, professor of psychiatry and behavioral science at the MIND Institute at University of California Davis.

Researchers from 12 different sites across the U.S. and Canada followed 664 infants with at least one older sibling diagnosed with autism. Within three years, nearly 19 percent of the infants were diagnosed with autism. Thirty-two percent of those infants who had more than one sibling with autism were also diagnosed with the disorder. And the risk of autism nearly doubled for male infants, the study found.

Logan, now 4, has undergone almost a year and a half of applied behavior analysis.

"The progress he's made has been undescribable," said Hawn.

Hawn said Logan would have probably progressed further by this point if he had been diagnosed earlier.

"With Logan we were late in the game in some ways," said Hawn.