GBA1 and Parkinsonism: In addition to enrolling a cohort of de novo PD patients, the Parkinson Progression Markers Initiative (PPMI) study also enrolled individuals without a diagnosis of PD but who are considered at-risk for PD based on the presence of one of the following characteristics: genetic profile (i.e., carriers of Leucine-rich repeat kinase 2 (LRRK2) G2019S or glucocerebrosidase (GBA) gene mutations), hyposmia, or a diagnosis of RBD.