SLC6A3 and attention deficit-hyperactivity disorder: The vast majority of animal models, in which the mechanisms and etiology of attention-deficit hyperactivity disorder (ADHD) are investigated experimentally, such as the spontaneously hypertensive rat (Sagvolden 2000), the dopamine transporter knockout mouse (Gainetdinov and Caron 2001), and others (Davids et al. 2003), are based on the analysis of genetic predispositions.