The observed genetic correlations with educational outcomes and other phenotypes suggest a strong genetic component to the epidemiological correlates of ADHD. The significant positive genetic correlation of ADHD with major depressive disorder and depressive symptoms supports previous findings suggesting a positive genetic overlap between those phenotypes24,42, as well as the broader genetic overlap of psychiatric disorders23,24. Positive genetic correlations between ADHD and health risk behaviors such as smoking and obesity are consistent with the observed increase in those behaviors among individuals with ADHD105–108 and are indicative of a shared genetic basis for these traits. We also observe a positive genetic correlation of ADHD with insomnia, consistent with reports of sleep disturbances in ADHD109, but this relationship does not appear to generalize to other sleep-related phenotypes.
