SLC6A3 and Parkinson disease: Although DAT imaging is used clinically as a sensitive measure of presynaptic dopaminergic neurodegeneration in PD,56 57 the radioligand (123I)-ioflupane used in the PPMI cohort has also been suggested to have a modest affinity for the serotonin transporter.58 The degree to which DAT imaging reflects solely dopaminergic function is therefore uncertain.