[11C]3‐amino‐4‐(2‐dimethylaminomethyl‐phenylsulfaryl)‐benzonitrile ([11C]DASB) is a positron emission tomography (PET) tracer that binds to the serotonin transporter (SERT) and can quantify regional serotoninergic projection terminal density,12, 13, 14 providing an opportunity to examine rostral serotoninergic projection system terminal integrity in patients with MSA compared with PD. The gene discussed is SLC6A4; the disease is Parkinson disease.