In this study, the discriminative ability of 123I-FP-Cit SPECT was high in the first phase of symptomatic and untreated idiopathic parkinsonian disease against healthy individuals in the same age since PD, MSA, and PSP patients all had significantly lower DAT uptake compared to HCs both at baseline and at the followup. This evidence concerns the gene SLC6A3 and multiple system atrophy.