Using such radiotracers, studies have shown lower striatal DAT binding, indicative of more dopamine denervation (Scherfler et al., 2007), in PD patients with cognitive impairments compared with those without (Chung et al., 2018; Ekman et al., 2012; Schrag et al., 2017). This evidence concerns the gene SLC6A3 and Cognitive impairment.