Shared genetics of ADHD, cannabis use disorder and cannabis use and prediction of cannabis use disorder in ADHD

Cannabis use disorder (CUD) and cannabis use (CU) are prevalent conditions co-occurring with attention-deficit hyperactivity disorder (ADHD). Here we report results from a cross-disorder genome-wide association study of ADHD and CUD or CU. We identified 36 concordant genome-wide significant loci for ADHD–CUD and ten loci for ADHD–CU. DRD2 was identified as an ADHD–CUD risk gene. ADHD–CUD risk genes showed high expression across brain tissues and brain developmental stages, which was not observed for ADHD–CU genes. ADHD–CUD and ADHD–CU showed similar genetic correlations with substance use, whereas they differed for substance-use disorders. Individuals with ADHD–CUD had increased polygenic scores (PGS) for psychiatric disorders compared with those with ADHD without CUD and increased burden of rare deleterious variants. Stratification of individuals with ADHD by their CUD PGS revealed an absolute risk of 22% for comorbid CUD in the highest CUD-PGS bin—much higher than 1.6% risk among controls. Sex-specific differences were substantial with an approximately 10% higher CUD risk among men in the highest CUD-PGS bin. In this study, the authors use a combination of genetic methodologies to investigate the genetic associations between attention-deficit/hyperactivity disorder, cannabis use disorder and cannabis use.