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Autism Spectrum Disorders Health Center

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Risk of Autism Recurrence Higher Than Thought

Study Finds About 19% Risk of Autism in Younger Siblings of Children With the Disorder

Autism Sibling Risk: Study Details

The researchers evaluated infants who were enrolled in an international network known as the Baby Siblings Research Consortium. All 664 infants had an older sibling with an autism spectrum disorder.

The infants were followed from about 8 months of age until 36 months. The children were evaluated many times during the three years.

At the 36-month mark, the children were classified as having an autism spectrum disorder or not.

At the end of the follow-up, 132 children were diagnosed with an autism spectrum disorder. Of the 132, about 41% were diagnosed with autism and 59% were diagnosed with other conditions on the spectrum, such as Asperger's syndrome.

It is impossible, Ozonoff says, to estimate an individual family's risk.

"Remember that overall, over 80% of those babies didn't have autism," she says. "The general population risk is under 1%."

Autism Sibling Risk: Perspective

The new estimates are very sound, says Laura Schreibman, PhD, director of the Autism Intervention Research Program at the University of California, San Diego. She reviewed the study findings but was not involved in the research.

The design of the study, which followed the infants forward, ensures more accuracy than looking backward, she says. "The fact that they could look ahead meant they could be certain about how the diagnoses were obtained." The group included children from 12 locations and was ethnically diverse. Both of these factors reduce bias.

"Families need to know this is an estimate," she says. "It doesn't reflect what will happen to an individual family."

"This new study provides a more definitive estimate of the recurrence of autism in younger siblings," says Alycia Halladay, PhD, director for environmental research for Autism Speaks. Autism Speaks supports the Baby Siblings Research Consortium. Autism Speaks, the National Institutes of Health, and other organizations supported the study.

For parents who have an older child with autism, the new information should motivate them to be sure the younger child has close monitoring, she says. That should be done as early as six months, she tells WebMD.

Genetic counselors can use the information to help parents interpret the findings, says Karin Dent, president of the National Society of Genetic Counselors and assistant professor of pediatrics at the University of Utah, Salt Lake City.

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