Younger siblings of autism patients need extra surveillance

August 18, 2011

Family history is more important than previously thought in autism spectrum disorder, and pediatricians should consider early intervention for infant siblings of children with autism if any concerns arise about their development, according to new research. The largest prospective investigation of autism spectrum disorder and sibling recurrence to date uncovered surprisingly high occurrence of autism, especially when more than 1 older sibling had the disorder.

Family history is more important than previously thought in autism spectrum disorder (ASD), and pediatricians should consider early intervention for infant siblings of children with autism if any concerns arise about their development, according to new research.

The study, based on data from Autism Speaks’ High Risk Baby Siblings Research Consortium (BSRC) and led by investigators from the University of California, Davis, MIND Institute, found a significantly higher rate of development of autism (19%) in younger siblings of children with ASD. This rate shot up to more than 32% for the risk of a third sibling developing ASD if 2 others already were diagnosed with the disorder. Infant boys with an older sibling with ASD had almost a 3 times greater risk than infant girls (26% vs 9%, respectively).

"There is no previous study that identified a risk of recurrence that is this high," said Sally Ozonoff, PhD, professor of psychiatry and behavioral sciences at the MIND Institute and the study's lead investigator. The study, which evaluated 664 infants from 6 months to 36 months after birth at 12 US and Canadian sites, also is the largest prospective investigation of autism spectrum disorder and sibling recurrence to date.

The Autism Diagnostic Observation Schedule (ADOS) and the Mullen Scales of Early Learning were used in testing study subjects. A total of 132 infants met the criteria for an autism spectrum disorder, 54 receiving a diagnosis of autistic disorder and 78 receiving a diagnosis of pervasive developmental delay not otherwise specified.

In practice guidelines published by the American Academy of Pediatrics in 2007, reaffirmed in 2010, being a younger sibling of a child with autism is considered a risk factor requiring special developmental evaluation, which was underscored by the new data.

"This study shows that the younger siblings of children with autism spectrum disorders need to be tracked very carefully, and this may require more than the normal surveillance that a pediatrician might typically do," Ozonoff said. "This should include very explicitly and regularly checking in with parents on whether developmental milestones are being reached."

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