Test-retest results of clinical DAT-SPECT radioligands 123I-beta-CIT and 123I-FP-CIT showed measurement variability in PD patients of 7.4–16.8 % in STR and 12.2% in striatal subdivisions [32–34], with corresponding ICCs of 0.59–1.00 [33, 34]. Here, SLC6A3 is linked to Parkinson disease.