GBA1 and Parkinson disease: Further studies are required to determine if such readouts are altered at different stages of PD progression, in particular prodromal vs. early stage PD, to determine if these readouts represent potential PD biomarkers in at-risk (asymptomatic/prodromal) individuals, and the extent to which PBMCs or monocytes from subjects harboring GBA or LRRK2 mutations display similar or different immune traits as those in subjects with iPD.