Risk of Autism in Younger Siblings Substantially Higher Than Previous Estimates

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August 15, 2011
Study highlights importance of routine surveillance, rapid referral for infant siblings of children with ASD

August 15, 2011 (Baltimore, MD)—A new study published today in the journal Pediatrics (Epub ahead of print) found that the risk that an infant sibling of an older child with an autism spectrum disorder (ASD) will also develop the condition, known as recurrence risk, is substantially higher than previously thought. The study found that the average risk of recurrence is 18.7 percent, much higher than the previous estimates of 3 to 10 percent. Researchers from Kennedy Krieger Institute took part in the international, multi-site study, which is the largest prospective investigation of ASD sibling recurrence to date.

Participants included 664 infants, all of whom had at least one older biological sibling with ASD. The children were followed from infancy to 36 months. While the overall average risk of recurrence was 18.7 percent for all study participants, researchers also found the following:

  • Male infants had a recurrence risk of 26 percent, nearly three times higher than females.
  • When infant study participants had more than one older sibling with autism, the recurrence rate was 32.2 percent.
  • In families with only one older child with autism, the rate of incidence was 13.5 percent.

"The study has important implications for families, as younger siblings of a child with ASD need to be screened carefully and from an early age," said Rebecca Landa, PhD, CCC-SLP, a study author and director of Kennedy Krieger's Center for Autism and Related Disorders. "If parents are concerned, they should not take a wait and see attitude. Professionals should work actively with parents to monitor specific developmental milestones and make a plan for intervention as needed."

This study supports the American Academy of Pediatrics' 2007 practice guidelines specifying that being a younger sibling of a child with autism is a risk factor requiring special developmental evaluation. Because the new findings illustrate a greater risk than previously estimated, these infants may require developmental screenings that are more frequent and intensive than pediatricians can typically provide.

The accuracy of the findings is supported by this study's large sample size, gold standard diagnostic methods, diverse geographic sample, and young age of enrollment. The new study also controlled for stoppage, the tendency of parents to limit reproduction after the birth of a child with a disability, by studying only families with later-born siblings.

In 2001, Kennedy Krieger's Dr. Rebecca Landa was the first researcher to receive funding from the National Institutes of Health to launch an innovative study of baby siblings of autism. Still ongoing today, the research was ground-breaking in its identification of the earliest signs of autism, and subsequently sparked Dr. Landa's development and research of an early intervention model which was shown to stimulate significant improvements in toddlers with autism. With the discovery that it was possible to identify warning signs for autism in some children by their first birthday, Dr. Landa and her team recently turned their attention to the development of an early intervention protocol for one-year-olds.

Study of infant siblings has now grown to involve dozens of researchers, all collaborators through the Baby Siblings Research Consortium supported by Autism Speaks. The participants in the current study were enrolled in separate studies at individual-funded research sites, such as Kennedy Krieger, but through this international network the data is pooled to facilitate research with infants at high risk of developing autism.

Other authors of the current study include Sally Ozonoff, Gregory Young and Sally Rogers of the UC Davis MIND Institute; Alice S. Carter of University of Massachusetts, Boston; Daniel Messinger of University of Miami; Nurit Yirmiya of Hebrew University of Jerusalem; Lonnie Zwaigenbaum of University of Alberta, Canada; Susan E. Bryson of Dalhousie University, Halifax, Nova Scotia; Leslie Carver and Karen Dobkins of UC San Diego; John Constantino of Washington University, St Louis; Ted Hutman and Marian Sigman of UCLA; Jana Iverson of University of Pittsburgh; and Wendy Stone, University of Washington, Seattle.

Support for this study was provided by grants from the National Institutes of Health, United States-Israel Binational Science Foundation, Canadian Institute for Health Research and Autism Speaks.

About Autism

Autism spectrum disorders (ASD) is the nation's fastest growing developmental disorder, with current incidence rates estimated at 1 in 110 children. This year more children will be diagnosed with autism than AIDS, diabetes and cancer combined, yet profound gaps remain in our understanding of both the causes and cures of the disorder. Continued research and education about developmental disruptions in individuals with ASD is crucial, as early detection and intervention can lead to improved outcomes in individuals with ASD.

About the Kennedy Krieger Institute

Internationally recognized for improving the lives of children and adolescents with disorders and injuries of the brain and spinal cord, the Kennedy Krieger Institute in Baltimore, MD serves more than 16,000 individuals each year through inpatient and outpatient clinics, home and community services and school-based programs. Kennedy Krieger provides a wide range of services for children with developmental concerns mild to severe, and is home to a team of investigators who are contributing to the understanding of how disorders develop while pioneering new interventions and earlier diagnosis. For more information on Kennedy Krieger Institute, visit Kennedy Krieger Institute.

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