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By On December 10th, 2018

Siblings of children with ADHD or autism may be at heightened risk for both disorders

The hereditary risk of conditions like autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD) has long been established. Families with a child with ASD are typically notified that siblings or other close members of a family may have an increased risk for the disorder. Similarly, siblings of children with ADHD are more likely to develop symptoms of the condition.

However, a new study published in JAMA Pediatrics suggests there may be a surprising amount of crossover in the hereditary risk for these disorders.

As researchers from the Department of Psychiatry and Behavioral Sciences at the UC David MIND Institute explained, their new research shows that later-born siblings of children with either ASD or ADHD face an elevated risk for both conditions.

This is particularly surprising, as the two conditions share relatively little in common.

ADHD is characterized by difficulty focusing, impulse control, and increased activity. Meanwhile, ASD typically presents through issues with social interaction and an increased interest or focus on repetitive behaviors.

“We’ve known for a long time that younger siblings of children with autism are at higher-than-average risk for autism, but the field didn’t have adequate data to tell whether they were at increased risk for ADHD,” said lead researcher Meghan Miller. “Despite the fact that autism and ADHD appear very different in their descriptions, this work highlights the overlapping risk; younger siblings of children with ASD are at elevated risk of both ADHD and autism, and younger siblings of children with ADHD are at elevated risk not only for ADHD, but also for autism.”

The findings come from an analysis of medical records from 730 later-born siblings of children diagnosed with ADHD, 158 later-born siblings of children with ASD, and 14,287 later-born siblings of children with no known mental health issues.

Miller noted that the study only included families who had at least one child after their child was diagnosed.

“Evaluating recurrence risk in samples that include only families who have had an additional child after a diagnosed child is important because recurrence may be underestimated if researchers include families who decided to stop having children after a child was diagnosed with ASD or ADHD,” explained Miller.

Based on their findings, Miller’s team claims that later-born siblings of children with ASD were 30 times more likely to be diagnosed with ASD and 3.7 times more likely to be diagnosed with ADHD compared to siblings of non-diagnosed children. Similarly, siblings of children with ADHD were 13 times more likely to be diagnosed with ADHD and 4.4 times more likely to be diagnosed with ASD.

While the findings may lead to improved screening and identification of these conditions in younger children, Miller said there are still significant issues with diagnosing attention-deficit hyperactivity disorder in young children.

“There are reliable screening measures and practices for the diagnosis of autism in very young children,” Miller said. “Unfortunately, we don’t have any clinical standards or adequate tools for screening for ADHD at such young ages. We are currently working on identifying early markers of autism and ADHD in infants and toddlers who have an older diagnosed sibling, since these younger siblings are at elevated risk for ASD and ADHD.”

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