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Later-born siblings of children with autism, ADHD at higher risk for both

Siblings born to a family after children with autism spectrum disorder or ADHD were more likely to be diagnosed with the same disorder as well as the other disorder, study findings reported.

Although sibling recurrence risk is a common way to measure shared genetic contributions, multiple confounders can obscure recurrence risk estimates for familial disorders, Meghan Miller, PhD, from the department of psychiatry and behavioral sciences, University of California Davis Health System, and colleagues explained in their study, published in JAMA Psychiatry.

“The most important confounder, and the one addressed herein, is that these estimates are often based on the total number of siblings within a family rather than being limited to later-born siblings and can therefore be influenced by reproductive stoppage. That is, if families decide to have fewer children after a child develops ADHD or ASD, risk is underestimated,” Miller and colleagues wrote. “This limitation can be addressed by examining sibling recurrence in families who have had at least one child after the diagnosis of ADHD or ASD in an older child.”

Using data extracted from medical records of two large, U.S. health care systems, the researchers compared estimates of recurrence risk and cross-aggregation in 15,175 later-born siblings of children with ADHD or ASD with later-born siblings of children without these diagnoses. The two data sets included one with children seen from 1995 to 2013 and one with children born between 1998 and May 17, 2010. The investigators measured diagnoses of ASD or ADHD in the later-born siblings.

Analysis showed that compared with later-born siblings of children without either disorder, later-born siblings of children with ASD were about 30 times more likely to be diagnosed with ASD (OR = 30.38; 95% CI, 17.73-52.06). The ASD-risk siblings were more than 3.5 times more likely to be diagnosed with ADHD compared with the no-known-risk siblings (OR = 3.7; 95% CI, 1.67-8.21).

In addition, compared with later-born siblings of children without either disorder, later-born siblings of children with ADHD were about 13 times more likely to be diagnosed with ADHD (OR = 13.05; 95% CI, 9.86-17.27). The ADHD-risk siblings were also more than four times more likely to be diagnosed with autism than the no-known-risk siblings (OR = 4.35; 95% CI, 2.43-7.79).

After examining the prevalence of either ASD or ADHD among risk groups, Miller and colleagues found that there was a greater likelihood of either outcome for both groups, but there was no difference in the odds of having either diagnosis between ASD-risk and ADHD-risk siblings. This could indicate similar degrees of liability in both elevated risk groups, according to the findings.

“Overall, the results of this study enhance etiologic and clinical understanding. Clinically, later-born siblings of children with ASD and ADHD appear to be at elevated risk within and across diagnostic categories and thus should be monitored for both disorders,” the researchers concluded. “Practitioners may wish to share such information with families given the potential relevance of monitoring social communication, attention and behavior regulation skills in later-born siblings of children with ASD or ADHD.” – by Savannah Demko

Disclosure: The authors report no relevant financial disclosures.