The appearance of parkinsonism was significantly more frequent in patients from groups 1 and 2 that had abnormal DAT SPECT data, compared with patients from group 3 that had normal DAT SPECT data (group 1 vs group 3: p < 0.001; group 2 vs group 3: p < 0.001). Here, SLC6A3 is linked to Parkinson disease.