In all RBD patients and 11 PD patients the presynaptic density of nigrostriatal terminals was visualized and quantified by SPECT and the dopamine transporter tracer N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)tropane ([123I]FP-CIT). Here, SLC6A3 is linked to Parkinson disease.