Functional variants of the human TPH2 gene have been associated with ADHD in numerous studies (Manor et al., 2008; McKinney et al., 2008; Sheehan et al., 2005; Walitza et al., 2005), and Tph2‐/‐ mice are characterized by increased impulsivity (Lesch & Merschdorf, 2000; Sachs et al., 2013), which is a core symptom of ADHD. The gene discussed is TPH2; the disease is attention deficit-hyperactivity disorder.