SNCA and Parkinson disease: Consequently, an increase of the total α-synuclein/oligomeric α-synuclein ratio was observed in PD patients (0.35 ± 0.18 ng/mL) compared to HC subjects (0.19 ± 0.08 ng/mL), but no correlation between the total α-synuclein levels and disease severity (p-value > 0.05) was found.