Recently, we and others have identified rare, functionally penetrant, mutations in DAT in subjects with attention-deficit/hyperactivity disorder and juvenile dystonia (Mazei-Robison et al. 2008; Kurian et al. 2009), compelling a better understanding of the impact of DAT mutations and altered DAT regulatory mechanisms in vivo. The gene discussed is SLC6A3; the disease is attention deficit-hyperactivity disorder.