Having one child with autism is a well-known risk factor for having another one with the same disorder, but whether and how a sibling’s gender influences this risk has remained largely unknown.

Now new research led by scientists at Harvard Medical School has for the first time successfully quantified the likelihood that a family who has one child with autism would have another one with the same disorder based on the siblings’ gender.

Overall, the results, published Sept. 25 in JAMA Pediatrics, reveal that having an older female child diagnosed with autism spelled elevated risk for younger siblings and that the risk was highest among younger male siblings. They also affirm past research findings that having one child with autism or an autism spectrum disorder (ASD) portends higher risk for subsequent children, that the disorder is somewhat rare—slightly more than 1.2 percent of children in the study were affected—and that boys have a notably higher overall risk than girls.

The findings can arm physicians and genetic counselors with information useful in counseling families and clarifying the risk for younger siblings in families who already have one child with autism.

“Our results give us a fair degree of confidence to gauge the risk of autism recurrence in families affected by it based on a child’s gender,” said study first author Nathan Palmer, instructor in biomedical informatics at HMS. “It is important to be able to provide worried parents who have one child with the condition some sense of what they can expect with their next child. That information is critical given how much better we’ve become at screening for the disease earlier and earlier in life.”

Continue reading article in Harvard Medical School News