Task: gap022 | Last Updated: 2026-03-15 | Kind: gap-analysis | Total Gaps Identified: 10
| Prodromal Prevention Trial Design in Parkinson's Disease | |
|---|---|
| Category | Clinical Trial Design |
| Disease | [Parkinson's Disease](/diseases/parkinsons-disease-dementia) |
| Status | Emerging Field |
| Key Biomarkers | RBD, smell loss, constipation, SAA, DAT imaging |
Prodromal prevention trial design in Parkinson's disease represents a paradigm shift toward intervening before overt motor symptoms emerge[1]. This approach targets individuals who exhibit early markers of neurodegeneration but have not yet developed classic PD symptoms. The goal is to slow or halt disease progression at its earliest stages, when neuroprotective interventions may be most effective[2].
Rapid Eye Movement Sleep Behavior Disorder (RBD)
RBD is one of the strongest prodromal markers, with approximately 80-90% of individuals with idiopathic RBD eventually developing a synucleinopathy[3]. Polysomnography-confirmed RBD confers a high risk for PD conversion (approximately 5-10% per year)[4].
Hyposmia (Smell Loss)
Olfactory dysfunction precedes motor symptoms by up to 10 years in PD patients[5]. The Smell Identification Test (SIT) and Sniffin' Sticks test are validated tools for identifying at-risk individuals.
Constipation
Gastrointestinal dysfunction, particularly chronic constipation, is a well-established prodromal marker[6]. The gut-brain axis involvement in PD pathogenesis makes this a particularly relevant enrichment strategy.
Serum Autoantibodies (SAA)
Elevated SAA levels against specific neuronal antigens have been associated with future PD development[7]. SAA testing offers a relatively non-invasive screening approach for identifying high-risk individuals.
Dopamine Transporter (DAT) Imaging
DAT SPECT imaging can detect presynaptic dopaminergic dysfunction years before clinical diagnosis[8]. Reduced striatal binding is a key imaging biomarker for prodromal PD.
Other Emerging Markers
Long Trial Duration
Prodromal trials require extended follow-up periods, often 5-10 years, to detect differences between treatment and placebo groups[9]. This creates challenges with patient retention and resource requirements.
Endpoint Selection
Traditional motor UPDRS scores may not be sensitive enough for prodromal populations. Emerging endpoints include:
The ethics of placebo-controlled trials in prodromal populations remain debated[10]. Key considerations include:
Large sample sizes are needed due to:
The Parkinson's Progression Markers Initiative (PPMI) continues to characterize prodromal populations, providing crucial natural history data for trial design[11].
Phase 2 trials of anti-alpha-synuclein antibodies (prasinezumab, cinomerersen) in prodromal populations are under development, with enrichment strategies using RBD and DAT imaging[12].
Parkinson's Disease research has advanced significantly in understanding alpha-synuclein pathology, genetic risk factors, and prodromal biomarkers. However, fundamental questions about disease progression and therapeutic targets remain.
For a comprehensive list of prioritized research questions for Parkinson's Disease, see Research Priorities in Neurodegenerative Disease.
The prion-like propagation of alpha-synuclein pathology is thought to underlie disease progression, but mechanisms remain incompletely understood.
Unresolved questions:
LRRK2, GBA, SNCA, and PINK1/PARKIN mutations provide insights into disease mechanisms but translating genetics to therapy is challenging.
Unresolved questions:
PINK1/PARKIN-mediated mitophagy and mitochondrial biology are central to PD pathogenesis.
Unresolved questions:
Identifying PD in the prodromal stage is critical for neuroprotective trials.
Unresolved questions:
Berg et al. [Prodromal Parkinson's disease: The search for a cure](https://doi.org/10.1016/S1474-4422(25). Lancet Neurology. 2025. ↩︎
Postuma RB, Berg D. Advances in markers of prodromal PD. Movement Disorders. 2025. ↩︎
Iranzo A, et al. Long-term RBD follow-up. Neurology. 2024. ↩︎
Schenck CH, et al. RBD conversion rates. Neurology. 2013. ↩︎
Haehner A, et al. Olfactory dysfunction in PD. Parkinsonism and Related Disorders. 2024. ↩︎
Cersosimo MG, et al. Gastrointestinal dysfunction in PD. Journal of Neurology. 2023. ↩︎
Shapiro et al. Serum autoantibodies as biomarkers in prodromal Parkinson's disease. Neurology: Neuroimmunology & Neuroinflammation. 2024. ↩︎
Jennings D, et al. DAT imaging in prodromal PD. Annals of Neurology. 2014. ↩︎
Marek K, et al. The PPMI prodromal cohort. Journal of Parkinson's Disease. 2025. ↩︎
Kimmelman J, et al. Ethics of prodromal trials. Movement Disorders. 2024. ↩︎
PPMI Investigators. PPMI 10-year update. Nature Parkinson's Disease. 2025. ↩︎
Jankovic J, et al. Anti-synuclein trials in prodromal PD. Neurobiology of Aging. 2025. ↩︎