Identification and Enrollment of Individuals Prior to Parkinson's Disease Diagnosis: Biomarker‐Driven Adaptive Eligibility and Enrollment into the Parkinson's Progression Markers Initiative

To better understand the earliest stages of alpha‐synucleinopathy, the Parkinson's Progression Markers Initiative (PPMI) has enrolled participants prior to the diagnosis of Parkinson's disease (PD) or dementia with Lewy Bodies (DLB). In this review, we describe lessons learned from prior enrollment and current strategies for PPMI eligibility. Severe hyposmia remains the strongest clinical predictor of aggregated synuclein as measured by a positive cerebrospinal fluid alpha‐synuclein seed amplification assay (CSF aSyn SAA). CSF aSyn SAA is positive before dopamine transporter binding decreases, as measured by dopamine imaging. PPMI's adaptive eligibility criteria have enabled efficient identification of people in the early stage of neuronal synuclein disease defined by biomarkers alone and can inform future therapeutic studies. ANN NEUROL 2026