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August 15, 2019
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ADHD, hypomanic symptoms appear to share genetic factors

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Researchers found overlap between ADHD and hypomanic symptoms across childhood and adolescence, which appears to reflect a genetic link between these phenotypes, according to findings from a Swedish twin cohort study published in JAMA Psychiatry.

“High comorbidity rates between bipolar disorder, ADHD and their symptoms have been recorded and associated with worse outcomes than when these symptoms and disorders occur alone (eg, higher rates of suicide attempts),” Georgina M. Hosang, PhD, from the Centre for Psychiatry, Queen Mary, University of London, told Healio Psychiatry. “In order to develop more effective prevention and intervention programs for the ADHD-bipolar disorder comorbidity it is crucial that we establish its origins.”

Hosang and colleagues examined data from 13,532 Swedish twin pairs from a prospective, longitudinal study to determine the extent to which genetic and environmental risk factors from ADHD traits were associated with hypomanic symptoms across childhood and adolescence.

The researchers evaluated hypomania when twins were aged 15 years using the parent-rated Child Mania Rating Scale (CMRS) and at age 18 years using the parent-rated Mood Disorders Questionnaire. They also evaluated ADHD symptoms at age 9 and 12 years using the Autism-Tics, ADHD, and Other Comorbidities Inventory (A-TAC), at age 15 years using the Strengths and Difficulties Questionnaire hyperactivity subscale, and at age 18 years using the ADHD DSM-IV subscale of the Adult Behavior Checklist.

Analysis revealed associations between ADHD and hypomanic symptoms among 3,784 twin pairs aged 15 years (beta = 0.3; 95% CI, 0.24-0.34) and 3,013 pairs aged 18 years (beta = 0.19; 95% CI, 0.16-0.22). In addition, these associations were stronger between hypomania and hyperactivity-impulsivity compared with inattention.

At age 15 years, 21% to 22% of the variance in hypomania was associated with genetic factors shared with ADHD, and at age 18 years, 13% to 29% of the genetic risk factors for hypomania were tied to ADHD. Again, Hosang and colleagues reported higher estimates for symptoms of hyperactivity-impulsivity (10% to 25%) compared with inattention (6% to 16%).

In addition, genetic factors unique to hypomanic symptoms during adolescence were tied to 25% to 42% of its variance, which may indicate some etiologic difference between these forms of psychopathology, according to the researchers.

“Our results highlight the need for early identification and recognition of symptoms of ADHD and hypomania in youth given their significant overlap and association with worse outcomes than when these symptoms occur alone,” Hosang told Healio Psychiatry. “Given that a significant proportion of the variance for hypomania was explained by genetic influences distinct from ADHD indicates that these two symptom groups are not an extension of one another. Thus, they should be both assessed and treated.”

Furthermore, many children previously diagnosed with bipolar disorder may now meet criteria for the new diagnostic category disruptive mood dysregulation disorder (DMDD), which captures children with chronic irritability with significant impairment in function, Lauren V. Moran, MD, of McLean Hospital, and colleagues explained in a related editorial.

“Regardless of the complexities of diagnosis, it is clear that youth with comorbid ADHD and hypomania, bipolar disorder, or DMDD have a more severe course than patients with ADHD without such comorbidity,” they wrote. “Societal concerns about psychotropic medication use in children only increase the need for randomized clinical trials ... to identify optimal treatments for these disorders.” – by Savannah Demko

Disclosures: Hosang reports no relevant financial disclosure. Please see the study for all other authors’ relevant financial disclosures. Moran reports grants from the NIMH. Please see the editorial for all other authors’ relevant financial disclosures.