SLC6A3 and attention deficit-hyperactivity disorder: Dopamine transporter (DAT) knockout (KO) mice represent one of the earliest genetic mouse models for ADHD and recapitulate several ADHD-like symptoms, including spontaneous hyperactivity (Gainetdinov & Caron, 2001), impaired learning and memory, and increased impulsivity (Yamashita et al, 2013).