IL6 and Parkinson disease: A total of 103 studies (9192 PD patients, 5661 controls) assessed the performance of Aβ42, p-tau, t-tau, t-α-syn, p-α-syn, o-α-syn, NFL, Zn, YKL-40, CRP, IL-6, Cu, Fe, Mn, arginine, DJ-1, and citrulline in distinguishing PD patients from controls.