This study aims to elucidate the preclinical pathophysiology and delineate the disease trajectories of Parkinson’s disease (PD) and related disorders by continuing and extending Japan Parkinson’s Progressive Marker’s Initiative (J-PPMI), a prospective cohort study on REM sleep behavioral disorder launched in 2014. It also aims to identify biomarkers available for early diagnosis by conducting multi-omics studies using plasma and cerebrospinal fluid samples accumulated in J-PPMI. Furthermore, a validation cohort will be established by recruiting new participants to confirm the achievements of these studies.