UPSIT score (HR = 0.36, P = 0.001), mean signal (HR = 0.44, P = 0.001), and asymmetry index of the putamen (HR = 0.35, P < 0.001) on DAT imaging, CSF p-tau/α-syn (HR = 4.27, P = 0.001), and p-tau (HR = 0.52, P = 0.05), and DDRGK1 rs55785911 genotype (HRAG = 0.45, P = 0.016; HRAA = 0.89, P = 0.66) were found to be final predictors of MCI in PD-RBD patients. Here, DDRGK1 is linked to Parkinson disease.