The PPMI study also includes a prodromal arm (P-PPMI) in which subjects with RBD, anosmia or a mutation (LRRK2, GBA or SNCA), will be assessed and followed in the same way as PD subjects, allowing for a seamless examination of the prediagnostic and early disease stages of PD. Here, LRRK2 is linked to Parkinson disease.