Kathleen Lanese of Kings Park, N.Y., poses with her two autistic sons Brendan, 14, right and Kevin, 10 at her sister-in-law’s home on Thursday, Aug. 11, 2011, in Oyster Bay, N.Y. Lanese says having one son with autism didn’t make her think twice about trying to have another child, even though she knew there was a chance the second would be affected, too. (AP Photo/Kathy Kmonicek)A new study suggests nearly one in five children with an autistic older sibling will develop the disorder too – a rate much higher than previously thought.
Researchers followed 664 infants who had at least one older brother or sister with autism. Overall, 132 infants or about 19 percent ended up with an autism diagnosis, too, by their third birthdays. Previous smaller or less diverse studies reported a prevalence of between 3 percent and 14 percent.
“We were all a bit surprised and taken aback about how high it is,” said lead author Sally Ozonoff, a psychiatry and behavioral sciences professor with the Mind Institute at the University of California at Davis.
The highest rates were in infants who had at least two older siblings with autism – 32 percent of them also developed autism. Also, among boys with autistic siblings – 26 percent developed autism versus 9 percent of girls. Autism is already known to be more common in boys.
The study involved 12 U.S. and Canadian sites and was published online Monday in Pediatrics. Earlier studies were more local or involved fewer sites.