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Siblings with autism rarely share genetic mutations

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The findings may affect how we predict a couple's chance of having a second child with autism spectrum disorder

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The majority of siblings with autism spectrum disorder don't share genetic mutations associated with the disorder, reports a new study published today in Nature Medicine. Children who do share genetic mutations, however, also tend to display the same types of symptoms. The findings suggests that the condition may be related to different factors, even in siblings. And figuring out what those factors are for each individual child, the researchers say, may be important for diagnosis — as well as management.

autism may be related to different factors, even in siblings.

"We anticipated that, more often than not, there would be shared inheritance" in siblings, Stephen Scherer, a geneticist at the University of Toronto and a co-author of the study, told The New York Times. "That wasn't the case."

Approximately 1 in 68 children have some form of autism spectrum disorder, and the disorder is five times more common in boys. There's no cure for autism, and taking care of a child with autism spectrum disorder can be costly. The CDC estimates that parents spend about $17,000 more per year when caring for a child with autism than they do for a child without it, and a large chunk of that cost goes toward services like therapy, education, and caregiver time. That's why figuring out the best way to manage a child's autism is essential; the right health management strategy can make things a lot easier for everyone involved.

In the study, researchers sequenced the genomes of 170 people with autism spectrum disorder. Each of the participants belonged to families in which two children have autism. They found that close to 70 percent of the siblings didn't share common autism-associated mutations. In those cases, the siblings also tended to display different symptoms, whereas children that did share genetic mutations were more likely to share symptoms, like habits and social skills. The study's results are also important for families with one sibling because it means that assessing a couple's risk of having another child with autism isn't as clear cut.

This means that assessing a couple's risk of having another child with autism isn't as clear cut

"This study makes us step back and realize we're not necessarily going to get as much predictive value out of genetic mapping as we thought, "Helen Tager-Flusberg, a developmental neuroscientist at Boston University who didn't participate in the study, told The New York Times.

Given the results, doctors may want to complete full assessments of each child's genome "when determining the role of genetic factors in risk- or health-management strategies," the researchers write; relying on the oldest sibling's genome might not be enough. The size of the study was small, however, so it's possible that a bigger sample of siblings might alter the results. Moreover, the researchers only focused on the analysis of 100 previously identified genetic mutations. If other important mutations are identified later on, that may affect the results. The researchers now hope to look into a much larger number of families. Should the study hold up, it will serve as another example of autism's genetic complexity.