SLC6A2 and attention deficit-hyperactivity disorder: Results from a meta-analysis of childhood and adolescent ADHD indicated significant associations between several common variants, namely DAT1, DRD4 VNTRs, and SNPs in the ADRA2A, catechol-O-methyltransferase (COMT), and noradrenaline transporter (SLC6A2) genes, and MPH responsiveness (Myer et al., 2018).