Diagnostic Value of Salivary Real-Time Quaking-Induced Conversion in Parkinson's Disease and Multiple System Atrophy

Background Aggregation of alpha-synuclein (oligomeric alpha-syn) has been considered as the pathological hallmark of Parkinson's disease (PD) and multiple system atrophy (MSA). Studies showed oligomeric alpha-syn/total alpha-syn ratio was increased in the saliva of patients with PD, suggesting that seeding activity of salivary oligomeric alpha-syn may be a novel biomarker for the diagnosis of PD and MSA. Objective This study aimed to evaluate the diagnostic value of salivary alpha-syn seeding activity in patients with PD and MSA. Methods A total of 75 patients with PD, 18 patients with MSA, and 36 nonneurodegenerative healthy control subjects underwent salivary alpha-syn real-time quaking-induced conversion (RT-QuIC) assay. Results Salivary alpha-syn RT-QuIC assay distinguished patients with PD with 76.0% sensitivity (95% confidence interval [CI], 66.1-85.9) and 94.4% specificity (95% CI, 86.6-100.0). RT-QuIC assay sensitivity reached 61.1% (95% CI, 36.2-86.1) in patients with MSA. No significant differences were observed in the diameter of salivary alpha-syn fibrils examined by electron microscopy and in thioflavin T fluorescence intensity of salivary alpha-syn fibrils detected by RT-QuIC assay between patients with PD and MSA. Notably, the lag phase of RT-QuIC assay from patients with PD was significantly shorter than that of patients with MSA, which might be clinically applicable to the discrimination between PD and MSA. Conclusions Salivary alpha-syn seeding activity may serve as a novel biomarker for the clinical diagnosis of PD and MSA.(c) 2022 International Parkinson and Movement Disorder Society (c) 2022 International Parkinson and Movement Disorder Society