Issue: October 2011
October 01, 2011
2 min read

Diagnoses of autism higher than thought in siblings with ASD

Ozonoff S. Pediatrics. 2011; doi: 10.1542/peds.2010-2825.

Issue: October 2011
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The largest prospective study of autism spectrum disorder and sibling recurrence has demonstrated that the risk of a younger sibling developing autism if an older sibling has been diagnosed is actually around 19%, and even higher for male infants.

Sally Ozonoff, PhD, who is a professor of psychiatry and behavioral sciences at University of California, Davis’ MIND Institute, and colleagues looked at 664 infants who were part of the Baby Siblings Research Consortium, which is an international network supported by Autism Speaks that pools data from individually funded research sites.

The infants’ average age at enrollment was 8 months, with two-thirds recruited prior to aged 6 months. The researchers followed the participants’ development until 36 months, when they were tested for autism, using the autism diagnostic tool called Autism Diagnostic Observation Schedule (ADOS) and the Mullen Scales of Early Learning, which measures nonverbal cognitive, language and motor skills.

Of the 664 participants, 132 infants met the criteria for an autism spectrum disorder. Fifty-four received a diagnosis of autistic disorder and 78 received a diagnosis of Pervasive Developmental Delay Not Otherwise Specified, which is considered a milder form of autism.

About 26% of male infants versus 9% of female infants were diagnosed with an autism spectrum disorder. The overall rate of autism spectrum outcomes for all study participants was 18.7%, which is much higher than previous studies that estimated between 3% and 10%. There was a significant difference in the recurrence rate based on whether the child had one sibling or more than one sibling with autism. In families with one older child with autism, or simplex families, the rate of incidence was 20.1%. Only 37 of the study participants had more than one sibling with autism. But for those families, called multiplex families, the recurrence rate was 32.2%.

In a press release, Ozonoff said that the study has significant family-planning and genetic-counseling implications. “Parents often ask what their risk of having another child with ASD is and, until now, we were really not sure of the answer,” she said.

The study also highlights the critical importance of routine surveillance and rapid referral for treatment of infant siblings of children with autism. Ozonoff said that it is of paramount importance that primary care professionals monitor these children's development closely and refer them for early intervention immediately when concerns arise.

“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.”

Disclosures: The authors reported no relevant financial disclosures.

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