A research study published in the journal Pediatrics suggests that nearly 1 in 5 children who have an older sibling with autism will also develop the disorder at a rate much higher than previously thought. Earlier estimates put the risk at between 3 and 10%, but a new study found a substantially higher risk rate of 18.7%, on average.
Researchers in the U.S., Canada and Israel followed 664 infants from 12 US and Canadian sites who had at least one older brother or sister with an autism spectrum disorder. Overall, 132 infants or approximately 19% received an autism diagnosis by their third birthday.
The highest rates were in infants who had at least two older siblings with autism – 32% also developed the disorder. Boys were nearly three times as likely to develop autism as girls, with a recurrence rate of 26.2% versus 9.1%.
The study’s lead author Sally Ozonoff, a psychiatry and behavioral sciences professor with the Mind Institute at the University of California at Davis, noted that 80% of siblings studied did not develop autism, and that the prevalence rate was an “average.” According to Ozonoff, “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 per cent, and for other families it would be less than 18 per cent.” “At the present time, unfortunately, we do not know how to estimate an individual family’s actual risk.”
The study has important implications for both parents and professionals. Families and primary care professionals should be especially observant with infants whose older siblings have been diagnosed with an autism spectrum disorder. Early identification and intervention are critically important to outcome. Ozonoff and her colleagues comment, “The red flags identified should be followed by immediate referral for infant intervention rather than adopting a 'wait-and-see' attitude because early specialized intervention is considered best practice for ASD and may represent the best hope for reducing symptoms and overall disability in high-risk infants who are developing ASD."
Ozonoff S, et al. Recurrence risk for autism spectrum disorders: a baby siblings research consortium study. Pediatrics 2011; DOI: 10.1542/peds.2010-2825.