Disease-Associated α-Synuclein Aggregates as Biomarkers of Parkinson Disease Clinical Stage

BACKGROUND AND OBJECTIVES: Robust biomarkers that can mirror Parkinson disease (PD) are of great significance. In this study, we present a novel approach to investigate disease-associated α-synuclein (αSyn) aggregates as biomarkers of PD clinical stage. METHODS: We combined both seed amplification assay (SAA) and ELISA to provide a quantitative test readout that reflects the clinical severity of patients with PD. To attain this goal, we initially explored the potential of our test using 2 sets of human brain homogenates (pilot and validation sets) and then verified it with 2 independent human CSF cohorts; discovery (62 patients with PD and 34 controls) and validation (49 patients with PD and 48 controls) cohorts. RESULTS: We showed that oligomers-specific ELISA robustly quantified SAA end product from patients with PD or dementia with Lewy bodies with high sensitivity and specificity scores (100%). Analysis also demonstrated that seeding activity could be detected earlier with oligomeric ELISA as the test readout rather than SAA alone. Of more importance, multiplexing the assays provided robust information about the patients' clinical disease stage. In the discovery cohort, levels of CSF-seeded αSyn oligomers correlated with the severity of the clinical symptoms of PD as measured by the Unified Parkinson Disease Rating Scale (UPDRS) motor (r = 0.58, p < 0.001) and Hoehn and Yahr (H&Y) scores (r = 0.43, p < 0.01). Similar correlations were observed in the validation cohort between the concentrations of CSF-seeded αSyn oligomers and both UPDRS motor (r = 0.50, p < 0.01) and H&Y scores (r = 0.49, p < 0.01). At 20 hours, receiver operating characteristic curves analysis yielded a sensitivity of 91.9% (95% CI 82.4%–96.5%) and a specificity of 85.3% (95% CI 69.8%–93.5%), with an area under the curve of 0.969 for CSF-seeded αSyn oligomers differentiating those with PD from controls in the discovery CSF cohort, whereas, a sensitivity of 80.7% (95% CI 69.1%–88.5%), a specificity of 76.5% (95% CI 60.0%–87.5%), and area under the curve of 0.860 were generated with thioflavin T maximum intensity of fluorescence at the same time point. DISCUSSION: We showed that combining SAA and ELISA assays is a more promising diagnostic tool than SAA alone, providing information about the disease stage by correlating with clinical measures of disease severity. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that CSF-seeded αSyn oligomers can accurately discriminate patients with PD and normal controls and CSF-seeded αSyn oligomers levels correlate with PD severity.