Vivacqua et al. quantified the levels of oligomeric α-synuclein and total α-synuclein, as well as the total α-synuclein/oligomeric α-synuclein ratio in the saliva samples of 100 PD patients, 80 HC subjects, and 20 patients with progressive supranuclear palsy (PSP). This evidence concerns the gene SNCA and Parkinson disease.