For the millions at genetic or environmental risk of Parkinson's disease, the therapeutic window may be far earlier than anyone is currently treating — a realization that is fundamentally reorienting how prevention trials should be designed, who they should enroll, and what success even means.
A comprehensive review in the Journal of Parkinson's Disease dissects why every major clinical trial aimed at slowing PD progression has failed to demonstrate clear efficacy, and what must change. The core argument is structural: conventional motor and non-motor rating scales lack the sensitivity to detect neurodegeneration in its earliest, most modifiable phases. Compounding this, PD's significant phenotypic heterogeneity means that pooling biologically distinct patient subtypes into single trials dilutes any true treatment signal. The review highlights that emerging biomarker platforms — spanning cerebrospinal fluid alpha-synuclein seed amplification assays, neuroimaging, and peripheral tissue markers — now offer the means to enroll presymptomatic individuals with confirmed synuclein pathology, stratified by biological subtype rather than clinical presentation alone.
This represents a meaningful inflection point in the field, though not yet a solved problem. The history of neurodegenerative disease trials is littered with compounds that showed preclinical promise and clinical futility, largely because interventions arrived decades after irreversible neuronal loss had begun. The shift toward biologically-defined synucleinopathy frameworks — analogous to what happened in Alzheimer's research with amyloid-tau-neurodegeneration staging — could finally enable trials that test interventions before the clinical Parkinson's phenotype fully manifests. Practically, this means identifying cohorts such as REM sleep behavior disorder patients or LRRK2/GBA variant carriers who represent enriched, tractable prevention populations. The review is best read as a research roadmap rather than a report of new data — it synthesizes consensus thinking rather than presenting novel findings. The path it describes is scientifically sound but operationally demanding, requiring regulatory creativity, long follow-up periods, and ethics frameworks comfortable with treating presymptomatic individuals.