Little sibs of children with ASD have greater risk of Autism

In Pediatrics Professor Sally Ozonoff and her colleagues of the Baby Siblings Research Consortium have reported data indicating a substantially higher risk for Autism among siblings than had been previously found. Based on data from studies in the 1980s, estimates of the risk of Autism in a child given that an older sibling had Autism were in the range of 3 to 5%, the Consortium found that the risk may be as great as four times higher than that, perhaps as high as 20%.

The researchers in the Consortium used very careful methods in which they found 664 later-born, biological siblings of a child with Autism when that younger sibling was, on average, about 8 months old. They followed the development of the siblings and assessed whether they had the symptoms of Autism when they were 36 months old. They found almost 19% had scores above the cut-off for Autism. The risk for Autism was even greater for boys and when more than one older sibling had Autism.

As Professor Ozonoff told Alan Zarembo Los Angeles Times, “Parents are concerned — could this happen again?” What are the implications for parents? If someone has a child with Autism, she or he is already aware of the importance of early recognition, and it’s important for parents and other caregivers to remind people in the medical community to screen for Autism among very young children.

Parents can be advocates for early screening. Professor Ozonoff and others have preliminary evidence indicating that some early indicator behaviors can be picked up during the 6-12 month age period. Check out the resources available from places such as Autism Speaks, too.

Eminent researchers in the study of Autism who conduct other types of studies have been reported as noting the strength of the study. Laura Schreibman, who directs the Autism Intervention Research Program at the University of California at San Diego has studied interventions for Autism since the 1960s, told WebMD that she found the methods sound because, “The fact that they could look ahead meant they could be certain about how the diagnoses were obtained.”

In a bigger perspective, these results seem to weigh on the side of a genetic explanation for Autism, in contrast to, for example, Professor Hallmayer’s recent work on shared environment. It’ll be fascinating to see how the people who really understand those issues interpret these data and other data like them, if they spin them at all. (By the way, there were 6 half-sibs in the study; the authors reported that the results did not differ when they included or excluded them, so they kept the half-sibs in the final analysis.)


Objective: The recurrence risk of autism spectrum disorders (ASD) is estimated to be between 3% and 10%, but previous research was limited by small sample sizes and biases related to ascertainment, reporting, and stoppage factors. This study used prospective methods to obtain an updated estimate of sibling recurrence risk for ASD.

Methods: A prospective longitudinal study of infants at risk for ASD was conducted by a multisite international network, the Baby Siblings Research Consortium. Infants (n = 664) with an older biological sibling with ASD were followed from early in life to 36 months, when they were classified as having or not having ASD. An ASD classification required surpassing the cutoff of the Autism Diagnostic Observation Schedule and receiving a clinical diagnosis from an expert clinician.

Results: A total of 18.7% of the infants developed ASD. Infant gender and the presence of >1 older affected sibling were significant predictors of ASD outcome, and there was an almost threefold increase in risk for male subjects and an additional twofold increase in risk if there was >1 older affected sibling. The age of the infant at study enrollment, the gender and functioning level of the infant’s older sibling, and other demographic factors did not predict ASD outcome.

Conclusions: The sibling recurrence rate of ASD is higher than suggested by previous estimates. The size of the current sample and prospective nature of data collection minimized many limitations of previous studies of sibling recurrence. Clinical implications, including genetic counseling, are discussed.

Ozonoff, S., Young, G. S., Carter, A., Messinger, D., Yirmiya, N., Zwaigenbaum L., … Stone, W. L. (2011). Recurrence risk for autism spectrum disorders: A baby siblings research consortium study. Pediatrics. Advance online publication retrieved from

UC Davis M.I.N.D. Institute, where Professor Ozonoff works, has a press release.

Autism Speaks, which helped support the research, has a blog post about the study on its Web site.

Alan Zarembo Los Angeles Times story Children with autistic sibling face greater risk, study finds

Kathleen Doheny wrote Risk of Autism Recurrence Higher Than Thought: Study Finds About 19% Risk of Autism in Younger Siblings of Children With the Disorder for WebMD.

Follow this story on Goggle news.

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