(DAVIS, Calif.) -- Infants who have siblings with autism have a three to 10 percent increased risk for autism -- a higher chance than the one percent risk among the general population. But a new study published Monday in the journal Pediatrics now suggests the risk is higher than previously thought.
The study, considered the largest autism study to follow infants for sibling recurrence, found that infants with an older autistic sibling have a near 19 percent risk that they too will develop the disorder.
"We were surprised and distressed to see how high the recurrence risk is," said Sally Ozonoff, professor of psychiatry and behavioral science at the MIND Institute at University of California Davis.
Researchers from 12 different sites across the U.S. and Canada followed 664 infants with at least one older sibling diagnosed with autism. Within three years, nearly 19 percent of the infants were diagnosed with autism. Thirty-two percent of those infants who had more than one sibling with autism were also diagnosed with the disorder.
And the risk of autism nearly doubled for male infants, the study found.
Since there are several risk factors for autism that could include genetic markers, an individual family's risk differs, Ozonoff said.
In fact, many parents overestimate the recurrence risk. Ozonoff said that in her clinic, many parents predict as high as 50 percent likelihood that their subsequent child will have autism.
"For parents, it's awareness and a more accurate estimate," said Ozonoff.
These findings could help parents who may be considering another child understand their overall quantifiable risk of autism recurrence. But these findings do not mean that every family is at the higher spectrum of risk, Ozonoff said.
Ozonoff said the findings could also change the way pediatricians examine infants with familial risk for autism.
"These children need careful monitoring and special surveillance [more] than what would be done at a well child visit," said Ozonoff.
A closer look at infants at higher risk could lead to earlier detection of autism symptoms, Ozonoff said.
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