ABSTRACT: IMPORTANCE:We observed a significant correlation between cerebrospinal fluid (CSF) levels of tau proteins and ?-synuclein, but not ?-amyloid 1-42 (A?1-42), and lower concentration of CSF biomarkers, as compared with healthy controls, in a cohort of entirely untreated patients with Parkinson disease (PD) at the earliest stage of the disease studied so far. OBJECTIVE:To evaluate the baseline characteristics and relationship to clinical features of CSF biomarkers (A?1-42, total tau [T-tau], tau phosphorylated at threonine 181 [P-tau181], and ?-synuclein) in drug-naive patients with early PD and demographically matched healthy controls enrolled in the Parkinson's Progression Markers Initiative (PPMI) study. DESIGN, SETTING, AND PARTICIPANTS:Cross-sectional study of the initial 102 research volunteers (63 patients with PD and 39 healthy controls) of the PPMI cohort. MAIN OUTCOMES AND MEASURES:The CSF biomarkers were measured by INNO-BIA AlzBio3 immunoassay (A?1-42, T-tau, and P-tau181; Innogenetics Inc) or by enzyme-linked immunosorbent assay (?-synuclein). Clinical features including diagnosis, demographic characteristics, motor, neuropsychiatric, and cognitive assessments, and DaTscan were systematically assessed according to the PPMI study protocol. RESULTS:Slightly, but significantly, lower levels of A?1-42, T-tau, P-tau181, ?-synuclein, and T-tau/A?1-42 were seen in subjects with PD compared with healthy controls but with a marked overlap between groups. Using multivariate regression analysis, we found that lower A?1-42 and P-tau181 levels were associated with PD diagnosis and that decreased CSF T-tau and ?-synuclein were associated with increased motor severity. Notably, when we classified patients with PD by their motor phenotypes, lower CSF A?1-42 and P-tau181 concentrations were associated with the postural instability-gait disturbance-dominant phenotype but not with the tremor-dominant or intermediate phenotype. Finally, we found a significant correlation of the levels of ?-synuclein with the levels of T-tau and P-tau181. CONCLUSIONS AND RELEVANCE:In this first report of CSF biomarkers in PPMI study subjects,we found that measures of CSF A?1-42, T-tau, P-tau181, and ?-synuclein have prognostic and diagnostic potential in early-stage PD. Further investigations using the entire PPMI cohort will test the predictive performance of CSF biomarkers for PD progression