We found that ADHD risk was associated with common variants located in genes significantly expressed in the brain, especially the frontal cortex. We also observed an enrichment of ADHD risk variants in genes expressed in major cell types of the brain, including both excitatory and inhibitory neurons and in midbrain dopaminergic neurons. The findings for frontal cortex and dopamine neurons fit well with the motor, reward and executive function deficits associated with ADHD; the frontal cortex is involved in executive functions including attention and working memory63, and midbrain dopaminergic neurons are essential for controlling key functions, such as voluntary movement64 and reward processing65. This interpretation is further supported by our ADHD-PGS analyses in PNC, which revealed that common ADHD risk variants impair several domains of cognitive abilities.
