MONDAY, Aug. 15 (HealthDay News) -- Younger siblings of a child with an autism spectrum disorder have a nearly one in five chance of being diagnosed with autism, much higher than previous estimates, a new study finds.
The researchers found that 18.7 percent of children who had a sibling with autism also went on to receive an autism diagnosis by their third birthday, and the risk was significantly higher for boys and those with more than one autistic sibling.
"Those of us working in the field knew the rate was a lot higher than the previously published rate, but I don't think we expected it to be this high, " said lead study author Sally Ozonoff, a professor and vice chair for research in the department of psychiatry and behavioral sciences at the University of California Davis Medical Center's MIND Institute.
Previous research has estimated that about 3 percent to 10 percent of younger siblings of kids with an autism spectrum disorder (ASD) will also be diagnosed with the condition.
The study, said to be the largest study of its kind to date, is published online Aug. 15 and in the September print issue of Pediatrics.
About 1 in 110, or less than 1 percent, of the general population of children born today has an autism spectrum disorder, which is characterized by problems with social interaction, verbal and nonverbal communication and restricted interests and behaviors. The overwhelming majority are boys, and genetics are known to play a strong role in autism's development.
For the study, a team from the Baby Siblings Research Consortium, an international network studying the earliest signs of ASD in infants with an affected sibling, tracked 664 younger siblings of autistic kids from an average of 8 months old until age 3. The children were examined and assessed several times during the study period.
They found that 132 children -- includ
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