DRD4 and attention deficit-hyperactivity disorder: In particular, common single nucleotide polymorphisms (SNPs) harboured in the Adhesion G-protein-coupled receptor L3 (ADGRL3, also known as Latrophilin 3 or LPHN3; markers rs2345039, rs6551665, and rs1947274), the Synaptosomal-associated protein of molecular weight 25 kDa (SNAP25), the Fibroblast growth factor 1 (FGF1), the Solute carrier family 6 (neurotransmitter transporter, noradrenalin) member 2 (SLC6A2), and the Dopamine receptor D4 (DRD4) genes predispose one to ADHD [6,13], as confirmed by worldwide replications [2,3,6,14,15,16,17,18,19,20,21].