A genome-wide analysis based on 232,964 cases and 494,162 control for eight mental disorders including ADHD suggested that polygenic risk sites of interest were enriched in genes previously associated with neuroticism, cognitive ability, and nocturnal sleep phenotypes, and CACNA1I is one of the genes associated with cognitive ability (Cross-Disorder Group of the Psychiatric Genomics Consortium, 2019). This evidence concerns the gene CACNA1I and attention deficit-hyperactivity disorder.