Researchers at the University of California, Davis, MIND Institute, found 19 percent of younger siblings of children with autism spectrum disorder developed autism -- a rate significantly higher than that of the general population -- and if there were two children with autism spectrum disorder in the family, the risk of the third sibling developing autism spectrum disorder increased to more than 32 percent.
The study found that the risk of an autism spectrum disorder diagnosis for male infants who had an older sibling with autism spectrum disorder was almost three times greater than the risk for female infants.
The study did not find any increase in risk associated with the gender of the older sibling, severity of the older sibling's symptoms, or other parent characteristics such as parental age, socioeconomic status or race/ethnicity.
"By pulling together data from many investigators who are studying infant siblings of children with autism, these results offer a more accurate estimate of the recurrence rate for autism in siblings," Geraldine Dawson, chief science officer Autism Speaks, says in a statement. "Surprisingly, the rate is much higher than previous estimates. This points to the important need for closely monitoring and screening siblings so that they can be offered intervention as early as possible to ensure the best possible outcome."
The findings are scheduled to be published in the September issue of the journal Pediatrics.