One recently published investigation quantified saliva and serum samples of total α-synuclein, nitrotyrosinated proteins (3-NT-proteins), and the correlation between α-synuclein and 3-NT-proteins, in 45 PD patients and 30 healthy volunteers using ELISA (BlueGene Biotech Co., Ltd., Shanghai, China) [42]. Here, SNCA is linked to Parkinson disease.