Dopaminergic synaptic pathway genes (Dopamine receptor D2 (DRD2) [13, 14], Catechol-o-methyltransferase (COMT) [15, 16], Solute carrier family 3 member 6 (SLC6A3) [17], and others) are currently linked to ADHD [18]. Here, COMT is linked to attention deficit-hyperactivity disorder.