We refined ADHD’s genetic architecture by estimating that around 7.3K (s.d. = 324) common variants can explain 90% of the h2SNP. This is a higher estimate than reported based on the 2019 ADHD GWAS (5.6K, s.d. = 400)45, but the current estimate is based on a better fit to the causal mixture model (AIC = 80 vs. AIC = 31 in Hindley et al.45). ADHD is often comorbid with other psychiatric disorders46, with 12–16% of cases also diagnosed with ASD16,47,48 and around 40% with depression49, which is also reflected in the genetic correlations reported here and previously14. Strikingly, when assessing both concordant and discordant allelic directions, over 90% of ADHD risk variants also seem to influence SCZ and MDD, and 84% influence ASD. This extensive sharing with SCZ, MDD, and ASD is at the same level as observed for SCZ and bipolar disorder36, which are among the most genetically correlated mental disorders50. Notably, for both MDD and ASD, around 75% of the variants shared with ADHD demonstrated concordant direction of association. The large sharing of variants influencing ADHD and other
