Autism risks for siblings are higher than thought

Kathleen Lanese
Kathleen Lanese of Kings Park, N.Y., poses with her two autistic sons Brendan, 14, right and Kevin, 10 at her sister-in-law's home on Thursday, Aug. 11, 2011, in Oyster Bay, N.Y. Lanese says having one son with autism didn't make her think twice about trying to have another child, even though she knew there was a chance the second would be affected, too.
AP Photo/Kathy Kmonicek

A new study suggests that nearly 20 percent of children who have an autistic older brother or sister will develop the disorder too. That's a rate much higher than previously thought.

Researchers at the University of California at Davis followed 664 infants in the U.S. and Canada who had at least one older sibling with autism. About 19 percent, or 132 infants, ended up with an autism diagnosis as well by their third birthday.

Lead researcher Sally Ozonoff, who's with the UC Davis Mind Institute, says "We were all a bit surprised and taken aback about how high it is."

The highest rates were in infants who had at least two older siblings with autism -- that was 32 percent. Also, boys with autistic older siblings had a 26 percent chance of being diagnosed themselves versus 9 percent of girls. Autism is known to be more common in boys.

The study is in Monday's Pediatrics online.

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