P4HB and Parkinson disease: We performed multiple logistic regression analysis and identified a panel of four proteins PDIA1, PDIA3, MANF, and clusterin, which together with two confounders age and gender, provided the greatest discrimination of PD patients from the non-PD control group, with an accuracy measured by an area under the curve (AUC) of 0.64, calculated from the receiver operating characteristic (ROC) curve (sensitivity 66%, specificity 57%) (Fig. 2a).