SLC6A3 and Parkinson disease: Molecular neuroimaging studies (SPECT or PET) have previously demonstrated that radioligands with high affinity to the dopaminergic system (dopamine transporter-DAT, DOPA decarboxylase activity, and vesicular monoamine transporters) estimate the dopamine cell loss and may be used as a surrogate marker of PD, in the prodromal, pre-motor, preclinical phase [6].