In the preclinical LRRK2 PD group, 28 percent (5/18) of the participants have normal DAT-SPECT scans and 72 percent (13/18) have abnormal DAT-SPECT scans grade 2 with an almost normal, symmetrical tracer uptake with a discrete reduction in one or both putamina. This evidence concerns the gene SLC6A3 and Parkinson disease.