One possibility is that female ADHD is qualitatively different from male ADHD. Although the majority of twin studies have not detected any quantitative or qualitative sex differences in ADHD heritability 9, 10, 11, 12, this does not necessarily imply that the same genetic variants are involved in ADHD etiology in both sexes. If ADHD in clinically diagnosed male individuals is distinct from ADHD in diagnosed female individuals, this could yield differences in prevalence. Sex-based genetic heterogeneity in common variants has been shown for several complex human traits (e.g., blood pressure, waist-hip ratio) 13, 14. Here, we assessed the genome-wide autosomal genetic correlation of ADHD in male and female individuals to determine whether genetic heterogeneity from common variation contributes to the observed biased prevalence.
