SLC6A3 and Parkinson disease: An exponential decline of tracer uptake in PD has been reported (Nandhagopal et al., 2009, Nandhagopal et al., 2011) for radiotracers of presynaptic dopaminergic integrity, including methylphenidate (MP), a PET marker for the membrane dopamine transporter (DAT) as also targeted in DAT SPECT.