The pathological characteristic of Parkinson’s disease (PD) and multiple system atrophy (MSA) has been thought to be α-synuclein oligomerization (oligomeric α-syn). The oligomeric α-syn/total α-syn ratio was shown to be higher in the saliva of Parkinson’s disease patients, implying that the seeding activity of salivary oligomeric α-syn may be a potential biomarker for the diagnosis of PD and MSA. For a study, researchers sought to determine the diagnostic significance of salivary-syn seeding activity in individuals with Parkinson’s disease and MSA.

The salivary α-syn real-time quaking-induced conversion (RT-QuIC) test was performed on 75 patients with Parkinson’s disease, 18 individuals with MSA, and 36 nonneurodegenerative healthy control participants.  The salivary α-syn RT-QuIC test identified individuals with Parkinson’s disease with 76.0% sensitivity (95% CI, 66.1–85.9) and 94.4% specificity (95% CI, 86.6–100.0). In MSA patients, the RT-QuIC test sensitivity was 61.1% (95% CI, 36.2–86.1). There were no significant changes in the diameter of salivary α-syn fibrils analyzed by electron microscopy or the thioflavin T fluorescence intensity of salivary α-syn fibrils identified by the RT-QuIC test between PD and MSA patients. Notably, the lag phase of the RT-QuIC test for patients with PD was substantially shorter than that of patients with MSA, suggesting that the lag phase may be therapeutically useful for the differentiation of PD and MSA. Salivary α-syn seeding activity might be a new biomarker for the clinical diagnosis of Parkinson’s disease and multiple sclerosis.