SNCA and Parkinson disease: After a mean follow-up of 3.5 ± 2.1 years, PD patients with baseline pS129-α-synuclein > 8.5 fg/mL were at higher risk of motor symptom progression of at least 3 points in the MDS-UPDRS part III scores than those with pS129-α-synuclein < 8.5 fg/mL (p = 0.03, log rank test).