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Objective: Urate is a potent antioxidant, and high plasma urate has been associated with lower incidence of Parkinson's disease (PD) in epidemiological studies. We tested the hypothesis that high concentrations of plasma urate are associated with low incidence of PD.Methods: We performed observational and genetic analyses using plasma urate and the urate SLC2A9 rs7442295 and ABCG2 rs2231142 genotype in >102,000 individuals from the CGPS (Copenhagen General Population Study). Information on PD and mortality was from national patient and death registries. Incidences of PD were calculated using Cox regression, Fine and Gray competing-risks regression, and instrumental variable analyses.Results: In total, 398 individuals were diagnosed with PD, of which 285 were incident cases. The multivariable adjusted hazard ratio for PD was 0.56 (95% confidence interval [CI], 0.41-0.77) for the highest versus the lowest tertile of plasma urate (p for trend across 3 groups, 8 × 10-5 ). Each one-allele increase in the combined allele score was associated with 19μmol/l (95% CI, 18.5-19.9) higher plasma urate. In observational analyses, a 50μmol/l higher plasma urate was associated with a hazard ratio of 0.85 (0.77-0.92) for PD; in instrumental variable analyses, 50μmol/l higher plasma urate was associated with an odds ratio of 1.20 (0.85-1.71) for PD.Interpretation: High plasma urate was associated with lower risk of PD in observational analyses; however, in instrumental variable analysis, high plasma urate was not associated with low risk of PD. Thus, our data do not support a causal relationship between high plasma urate and low risk of PD. Ann Neurol 2018;84:178-190. [ABSTRACT FROM AUTHOR]