SNCA and Parkinson disease: Salivary concentration, as well as saliva and serum ratios of α-synuclein and 3-NT-proteins are similar in PD patients (α-synuclein in saliva, 361.9 ± 89 pg/mL) and the control group (α-synuclein in saliva, 372.1 ± 91pg/mL).