SLC6A3 and Parkinson disease: Investigations into the laterality of striatal DAT binding using 123I-FP-CIT SPECT showed PSP patients typically exhibit less lateralized DAT loss compared to early-stage PD patients (Hoehn-Yahr stage 1) but not later stages, suggesting asymmetry measurements may have less discriminatory power in later stages of PD relative to PSP [111].