SNCA and Parkinson disease: The mean (±SD) plasma concentration of α-synuclein was significantly higher in the control group (127 ± 8.3 ng/ml) than for PD (100.2 ± 3.2 ng/ml; p = 0.015) and MSA (98.6 ± 3.1 ng/ml; p = 0.024) patients (Fig. 7a).