Imaging studies indicate reduced volumes in dopaminergic brain regions such as the basal ganglia, caudate, and putamen (Nakao et al., 2011; Hart et al., 2013; Roman-Urrestarazu et al., 2016; Hoogman et al., 2017) and polymorphisms in genes encoding DAT, D4, D5, and forkhead box protein P2, which regulates dopamine and neurodevelopment, are associated with the development of ADHD (Demontis et al., 2019; Faraone and Larsson, 2019). Here, SLC6A3 is linked to attention deficit-hyperactivity disorder.