SLC6A4 and Parkinson disease: Using 11C-DASB, which binds selectively to the serotonin transporter (SERT), a membrane protein that facilitates the reuptake of serotonin back into the presynaptic terminal, patients were found to exhibit increases in putaminal SERT expression by 46–172 and 106–285% of the mean binding values calculated for healthy controls and non-transplanted advanced PD patients respectively (Fig. 1) [37, 39].