The DAT-1 40 bp VNTR polymorphism has been found to be associated with violent delinquency [14], externalizing problem behavior [13, 21], neuropsychiatric disorders such as Tourette syndrome [22], ADHD [23, 24], schizophrenia [25], psychoactive substance abuse [26, 27] and reward sensitivity [28]. Here, SLC6A3 is linked to attention deficit-hyperactivity disorder.