GDNF and Parkinson disease: The independent variables were sex, age, LED, MDS-UPDRS-I, MDS-UPDRS II, MDS-UPDRS III, MDS-UPDRS IV, H-Ystage, NMSS total score, MoCA total score, RLS, PDSS total score, ESS total score, age of onset of motor symptoms, GDNF, RBD, and the motor forms of Parkinson's disease.