SLC6A3 and attention deficit-hyperactivity disorder: For ADHD, molecular studies have concentrated on genes encoding proteins involved in the dopaminergic pathway, with special interest in the dopamine receptor DRD4 (11p15.5) [MIM: 126452] [13] and dopamine transporter DAT1 (or SLC6A3, 5p15.3) [MIM: 126455] [14].