SLC6A3 and Parkinson disease: Furthermore, the presence of RBD in PD patients has shown to be a predictor of motor progression in patients with both low α-synuclein CSF levels and reduced striatal DAT [123I]FP-CIT uptake, and a predictor of cognitive decline in patients with low CSF levels of both α-synuclein and low amyloid-β42 [91].