SNCA and Parkinson disease: In summary, we found that oligomeric forms of α-synuclein could be a potential biomarker for diagnosis and monitoring disease progression of PD patients and salivary total α-synuclein could be useful to screen different phenotype or genotype of PD patients, which the level is inversely associated with age, and closely correlated with genotypic distribution of rs894278/rs11931074 in PD.