COMT and attention deficit-hyperactivity disorder: In adult patients with ADHD, Contini et al. (2012, 2013) found no associations with DRD4, COMT, serotonin receptor 1B (HTR1B), tryptophan hydroxylase (TPH2), dopamine β-hydroxylase (DBH), 5HTT, and synaptosomal-associated protein 25 (SNAP25) genes, only with DAT1 (Contini et al., 2012; see review Contini et al., 2013).