SNCA and Parkinson disease: As both total and phosphorylated α-synuclein levels were increased in the PD group, the pS129-α-synuclein/total α-synuclein ratio cut-off of 0.22 had a 90.8% sensitivity and 58.3% specificity for distinguishing between patients with PD and controls (AUC 0.74; Figure 2).