Autism Among Siblings Much Higher than Thought

Autism diagnoses may be genetically related

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) Autism runs in families. This understanding has been known in the medical field for some time.  But the chances of an autism diagnosis among siblings are much higher than doctors previously estimated.

Younger siblings of a child with autism have a nearly one in five chance of being diagnosed with the disorder themselves, and the risk is significantly higher for boys.

"Siblings of autistic children should be closely monitored for symptoms."

Researchers at the University of California Davis Medical Center's MIND Institute found that 18.7 percent of children who had a sibling with autism also received an autism diagnosis by their third birthday. For children with more than one autistic sibling, the odds were even higher (32 percent). Male siblings of autistic children had a 26 percent occurrence of developing autism themselves.

Sally Ozonoff, lead author, and her team followed 664 children between infancy and 36 months of age, at which time they were tested for autism. At that age, 132 of these children with an autistic sibling met the criteria for autism spectrum disorder, which affects the ability to think, communicate, learn and interact socially.

This is the largest investigation of autism spectrum disorder and sibling recurrence to date. Previously, the risk of siblings developing autism was estimated at between three and 10 percent.

"Parents often ask what their risk of having another child with ASD is and, until now, we were really not sure of the answer," Ozonoff said. She added that the surprisingly high risk rate illustrates the important need to closely monitor siblings so that early intervention can ensure the best possible outcomes for those children.

Results will be published in the September issue of the journal Pediatrics.

Photo: UC Davis MIND Institute researcher Sally Ozonoff with infant Cooper Stuart and his mother, Laurisa Stuart, during an evaluation for autism.

Reviewed by: 
Review Date: 
August 26, 2011
Last Updated:
August 28, 2011