DRD4 and attention deficit-hyperactivity disorder: reported significant associations for DAT1, DRD4, DRD5, 5HTT, HTR1B, and SNAP25, but also significant heterogeneity for the associations between ADHD and DAT1, DRD4, DRD5, DBH, ADRA2A, 5HTT, TPH2, MAOA, and SNAP25 (88).