Salivary alpha-synuclein in the diagnosis of Parkinson's disease and Progressive Supranuclear Palsy

Introduction: Alpha-synuclein (alpha-syn) aggregation is the pathological hallmark of Parkinson's Disease (PD). In this study, we measured alpha-syn total (alpha-syn(total)), oligomeric alpha-syn (alpha-syn(olig)) and alpha-syn(olig)/alpha-syn(total) ratio in the saliva of patients affected by PD and in age and sex-matched healthy subjects. We also compared salivary alpha-syn(total) measured in PD with those detected in Progressive Supranuclear Palsy (PSP), in order to assess whether salivary alpha-syn can be used as a biomarker for PD and for the differential diagnosis between PD and PSP. Methods: We studied 100 PD patients, 20 patients affected by PSP and 80 age- and sex-matched healthy subjects. ELISA analysis was performed using two commercial ELISA platforms and a specific ELISA assay for alpha-syn aggregates. Results: We detected lower alpha-syn(total) and higher alpha-syn(olig) in PD than in healthy subjects. Conversely in PSP salivary alpha-syn(total) concentration was comparable to that measured in healthy subjects. Receiver Operating Characteristic analyses revealed specific cut-off values able to differentiate PD patients from healthy subjects and PSP patients with high sensitivity and specificity. However, there was no significant correlation between clinical and molecular data. Conclusion: Salivary alpha-syn detection could be a promising and easily accessible biomarker for PD and for the differential diagnosis between PD and PSP.