UW News

August 15, 2011

Younger siblings of children with autism have one in five chance of autism diagnosis

News and Information

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Parents of a child with an autism spectrum disorder face a 19 percent chance of having additional children diagnosed with the disorder, according to a new study co-authored by the UW Autism Center. The previous estimate of the recurrence risk for autism in younger siblings was 3 to 10 percent.

The study, published online Aug. 15 in the journal Pediatrics, highlights the importance of carefully monitoring the early development of younger siblings of children with autism spectrum disorders. With early intervention, autism symptoms can be attenuated, or perhaps even prevented.

“Almost one in five later-born siblings of children with autism spectrum disorders will receive a similar diagnosis, so we need to be active rather than passive in assessing risk factors and identifying developmental concerns in these children from young ages,” said Wendy Stone, co-author and director of the UW Autism Center.

“We need to make sure that families and professionals are aware of developmental norms in social and communicative domains, so that concerns can be addressed early,” Stone said. “Intervention is more cost-effective and has a bigger impact when provided at young ages, when the brain is undergoing rapid development and organization.”

The study involved 664 infants who were enrolled from ages as young as 6 months, which is before autism symptoms typically appear. The infants development was followed until age 36 months. It is the largest study so far of younger siblings of children with autism and used the latest and most comprehensive diagnostic criteria.

The data, compiled from the multi-institution High Risk Baby Siblings Research Consortium, also show

–       If infants have more than one sibling with autism, their risk of developing an autism spectrum disorder increased to more than 32 percent.

–       Male infants who have an older sibling with autism spectrum disorder had an almost three times greater risk than female infants (26 percent compared with 9 percent).

–       The severity of the older siblings symptoms did not affect the risk for autism in later-born children, nor did the parents characteristics such as age, socio-economic status or ethnicity.

“It’s important to recognize that these are estimates that are averaged across all of the families. So, for some families, the risk will be greater than 18.7 percent, and for other families it would be less than 18.7 percent,” Sally Ozonoff, lead author and professor of psychiatry and behavioral sciences at the MIND Institute at the University of California, Davis, said in a news release. “At the present time, unfortunately, we do not know how to estimate an individual family’s actual risk.”

UW is one of the 21 institutions in the U.S., Canada, Israel and the United Kingdom participating in the High Risk Baby Siblings Research Consortium, a partnership between the National Institutes of Health and the advocacy group Autism Speaks.