Past research has associated the DAT1 30 bp polymorphism 5-R allele with impulsivity (Paloyelis et al., 2010), ADHD (Asherson et al., 2007; Simpson et al., 2010), and addiction (Guindalini et al., 2006; O’Gara et al., 2007; Smirnova et al., 2011), possibly through the modulation of dopaminergic processes. Here, SLC6A3 is linked to attention deficit-hyperactivity disorder.