Five-Year Disease Progression in Synuclein Seeding Positive Sporadic Parkinson's Disease.

OBJECTIVE: To provide a comprehensive description of disease progression in synuclein seeding assay (SAA) positive sporadic Parkinson Disease participants, using Neuronal Synuclein Disease integrated biological and functional impairment staging framework. METHODS: We analyzed 5-year longitudinal data from 345 participants recruited in the Parkinson's Progression Markers Initiative with the diagnosis of early (less than 2 years of clinical diagnosis at baseline and untreated) sporadic Parkinson's Disease, who were synuclein seeding assay positive. We assessed 5-year progression in a spectrum of clinical and biomarker measures. We used Cox proportional hazards models to assess the association between baseline stage and time to survival, postural instability, cognitive impairment, and other meaningful milestones. Biomarker analysis included dopamine transporter binding measures, CSF-SAA, amyloid-beta, phosphorylated tau and total tau, as well as serum urate, and neurofilament light chain. RESULTS: At baseline there was clear separation of participants by Neuronal Synuclein Disease Stages (23% Stage 2b, 67% Stage 3, 10% Stage 4). Participants in stage 4 at baseline had a significantly higher rate of reaching disability, postural instability, cognitive decline, and the autonomic dysfunction milestones. There was a stage-dependent increase in dopamine deficit at baseline. There was no difference in fluid biomarkers between the stages at baseline and longitudinally. INTERPRETATION: This study highlights the heterogeneity in the early Parkinson's Disease population defined by clinical diagnostic criteria and underscores the importance of shifting from clinical to biologically and functional impairment defined inclusion criteria for clinical trials. Biological drivers of stage heterogeneity must be further explored.