SLC6A3 and Parkinson disease: Accordingly, PET tracers are developed to observe the activity of the dopamine transporter (DAT) in early stage of PD, such as 11C-CFT, which is a biomarker of the presynaptic dopaminergic system with high sensitivity (Kazumata et al., 1998; Ilgin et al., 1999; Wang et al., 2013).