Autism Link of the day - Gender of older sibling

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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.

Researchers analyzed de-identified health insurance records of more than 1.5 million U.S. families with two children between the ages of 4 and 18, tracking patterns of recurrence among siblings over a year or longer. Of the more than 3.1 million children in the study, some 39,000, or about 1.2 percent—2 percent of boys and 0.5 percent of girls—received a diagnosis of autism or an ASD.
The results confirm previous research showing that, overall, boys have a higher risk of autism and related disorders than girls.
The results, however, also reveal a curious pattern of recurrence based on gender: Siblings born after a female child with autism or a related disorder had a higher risk than siblings born after a male child with autism. Male children were, overall, more susceptible to autism than females. In other words, boys with older female siblings with autism had the highest risk for autism themselves, while female siblings with older brothers with autism had the lowest risk.
For every 100 boys with an older female sibling with autism, 17 received a diagnosis of autism or a related disorder. Male children with older male siblings with ASD had a 13 percent risk of an ASD diagnosis, followed by younger female siblings with older male siblings with ASD (7.6 percent). The lowest risk—4 percent—was observed among younger female siblings who had an older brother with autism or an ASD.

Even for the group at highest risk—males with an older female sibling with autism—the odds are still about five to one that the child will be unaffected," Palmer said. "What we have provided here is context for families who already have children with autism or another similar disorder and need a clearer perspective on recurrence risk."