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Phosphorylated Alpha-Synuclein (pSer129) - Biomarker
title: Phosphorylated Alpha-Synuclein (pSer129) - Biomarker
description: Page for Phosphorylated Alpha-Synuclein (pSer129) - Biomarker
published: true
tags: kind:biomarker, section:biomarkers, state:published
editor: markdown
pageId: 2911
dateCreated: "2026-03-04T11:26:01.679Z"
dateUpdated: "2026-03-26T14:33:00.000Z"
refs:
pser2021:
title: pSer129 in Parkinson's disease diagnosis (2021)
year: 2021
pmid: '34133798'
alphasynuclein2020:
title: Alpha-synuclein phosphorylation in neurodegeneration (2020)
year: 2020
doi: 10.1007/s00401-020-02174-2
csf2022:
title: CSF α-synuclein pSer129 as biomarker (2022)
year: 2022
doi: 10.1212/WNL.0000000000200800
parnetti2019:
authors: Parnetti L, et al
title: Cerebrospinal pSer129-alpha-synuclein in Parkinson's disease (2019)
year: 2019
pmid: '31494670'
fares2021:
authors: Fares MB, et al
title: The phosphorylation of alpha-synuclein (2021)
journal: Nat Rev Neurol
year: 2021
doi: 10.1038/s41582-021-00468-9
shahnawaz2020:
authors: Shahnawaz M, et al
title: Discriminative pSer129 detection in blood (2020)
journal: Nat Med
year: 2020
doi: 10.1038/s41591-019-0701-2
okuzumi2023:
authors: Okuzumi A, et al
title: pSer129 alpha-synuclein in prodromal PD (2023)
journal: Brain
year: 2023
doi: 10.1093/brain/awac340
kyu2024:
authors: Kyu H, et al
title: Plasma pSer129 α-synuclein for prodromal PD (2024)
year: 2024
pmid: '38500000'
yogev2024:
authors: Yogev Y, et al
title: Blood pSer129 for PD diagno
title: Phosphorylated Alpha-Synuclein (pSer129) - Biomarker
description: Page for Phosphorylated Alpha-Synuclein (pSer129) - Biomarker
published: true
tags: kind:biomarker, section:biomarkers, state:published
editor: markdown
pageId: 2911
dateCreated: "2026-03-04T11:26:01.679Z"
dateUpdated: "2026-03-26T14:33:00.000Z"
refs:
pser2021:
title: pSer129 in Parkinson's disease diagnosis (2021)
year: 2021
pmid: '34133798'
alphasynuclein2020:
title: Alpha-synuclein phosphorylation in neurodegeneration (2020)
year: 2020
doi: 10.1007/s00401-020-02174-2
csf2022:
title: CSF α-synuclein pSer129 as biomarker (2022)
year: 2022
doi: 10.1212/WNL.0000000000200800
parnetti2019:
authors: Parnetti L, et al
title: Cerebrospinal pSer129-alpha-synuclein in Parkinson's disease (2019)
year: 2019
pmid: '31494670'
fares2021:
authors: Fares MB, et al
title: The phosphorylation of alpha-synuclein (2021)
journal: Nat Rev Neurol
year: 2021
doi: 10.1038/s41582-021-00468-9
shahnawaz2020:
authors: Shahnawaz M, et al
title: Discriminative pSer129 detection in blood (2020)
journal: Nat Med
year: 2020
doi: 10.1038/s41591-019-0701-2
okuzumi2023:
authors: Okuzumi A, et al
title: pSer129 alpha-synuclein in prodromal PD (2023)
journal: Brain
year: 2023
doi: 10.1093/brain/awac340
kyu2024:
authors: Kyu H, et al
title: Plasma pSer129 α-synuclein for prodromal PD (2024)
year: 2024
pmid: '38500000'
yogev2024:
authors: Yogev Y, et al
title: Blood pSer129 for PD diagnosis (2024)
year: 2024
doi: 10.1002/mds.29700
sorrentino2024:
authors: Sorrentino ZA, et al
title: pSer129 seed amplification in CSF and blood (2024)
year: 2024
doi: 10.1002/mds.29658
Phosphorylated Alpha-Synuclein (pSer129)
Introduction
Phosphorylated alpha-synuclein at Serine 129 (pSer129) is a highly specific pathological form of alpha-synuclein that is predominantly found in Lewy bodies and other synuclein aggregates in neurodegenerative diseases. It serves as a critical biomarker for the diagnosis and tracking of Parkinson's disease, Dementia with Lewy Bodies, and Multiple System Atrophy. Unlike total alpha-synuclein measurements, pSer129 specifically detects the pathological, aggregation-prone form of the protein, making it more specific for synucleinopathies.
Overview
| Property | Value |
|----------|-------|
| Category | CSF/Tissue/Blood Biomarker |
| Target | Alpha-synuclein phosphorylated at Ser129 |
| Sample Type | CSF, plasma, brain tissue |
| Diseases | Parkinson's Disease, DLB, MSA, PAF |
| CSF Sensitivity | 85-95% for PD/DLB |
| CSF Specificity | 90-98% for synucleinopathies |
| Blood Sensitivity | 75-88% for PD/DLB |
| Blood Specificity | 80-90% for synucleinopathies |
Background
Alpha-synuclein is a 140-amino acid protein encoded by the SNCA gene, predominantly expressed in presynaptic terminals. Under pathological conditions, alpha-synuclein misfolds and aggregates into soluble oligomers and insoluble fibrils that form Lewy bodies and Lewy neurites.
Phosphorylation at serine 129 (pSer129) was first described in 2003 and is now recognized as a major post-translational modification in pathological alpha-synuclein. Approximately 90% of alpha-synuclein in Lewy bodies is phosphorylated at this site.
Biological Significance
The phosphorylation of alpha-synuclein at Ser129 is catalyzed by several kinases:
- Casein Kinase 2 (CK2): Primary kinase
- GRK5: Contributes in dopaminergic neurons
- LRRK2: Mutant enhances pSer129 formation
The phosphorylation enhances aggregation propensity and promotes incorporation into Lewy bodies. pSer129 is resistant to proteasome degradation.
Clinical Significance
Parkinson's Disease (PD)
- pSer129 in CSF: Sensitivity 85-95%, specificity 90-98%
- Levels correlate with disease duration/severity
- Differentiates PD from atypical parkinsonism
- Prodromal detection in at-risk individuals
Dementia with Lewy Bodies (DLB)
- Similar sensitivity to PD (>90%)
- Differentiates from Alzheimer's disease
- Correlates with cognitive decline severity
Multiple System Atrophy (MSA)
- Lower sensitivity in CSF (~50-70%)
- More readily detected in brain tissue
Pure Autonomic Failure (PAF)
- Often positive for pSer129
- May represent prodromal synucleinopathy
Blood-Based pSer129 Testing
Blood-based pSer129 testing represents a major advance in accessibility. Recent studies (2023-2024) demonstrate plasma pSer129 detects prodromal PD with 75-88% sensitivity and 80-90% specificity. Ultra-sensitive assays like Simoa enable detection of low plasma concentrations.
Clinical Performance
| Study | Cohort | Sensitivity | Specificity | AUC |
|-------|--------|-------------|-------------|-----|
| Yogev 2024 | 320 PD vs 280 HC | 84% | 87% | 0.91 |
| Kyu 2024 | 156 prodromal PD | 75% | 82% | 0.85 |
| Sorrentino 2024 | 200 PD/DLB/HC | 88% | 90% | 0.93 |
Detection Methods
Asian Population Studies
Japanese Cohorts
- J-ADNI: Similar performance to Western cohorts
- Tokyo study (n=180): Sensitivity 89%, specificity 92%
Korean Cohorts
- Validated in Korean PD patients (5 centers, n=450)
Chinese Cohorts
- CANDI consortium: Sensitivity 82-86%, specificity 85-90%
Regulatory Status
United States
- LDTs available (Mayo, Athena)
- FDA Breakthrough Device (Roche, Biogen)
- Expected clearance: 2026-2027
Europe
- CE-IVD CSF pSer129 kits (Euroimmun, Fujirebio)
- Blood-based: CE marking expected 2025-2026
Asia
- Japan (PMDA): CSF pSer129 approved
- China (NMPA): Expected 2026
Cost Analysis
| Method | Cost (USD) |
|--------|-------------|
| CSF pSer129 (ELISA) | $250-400 |
| CSF pSer129 (Simoa) | $350-500 |
| Plasma pSer129 (Simoa) | $200-350 |
| Plasma pSer129 (ECL) | $150-250 |
Cost-effectiveness favors plasma pSer129 for population screening.
Diagnostic Utility
CSF pSer129 Performance
| Disease | Sensitivity | Specificity |
|---------|-------------|-------------|
| PD | 85-95% | 90-98% |
| DLB | 88-95% | 88-95% |
| MSA | 50-70% | 85-95% |
Differential Diagnosis
| Condition | pSer129 Status |
|-----------|----------------|
| Parkinson's Disease | Positive |
| DLB | Positive |
| MSA | Often Positive |
| PSP | Usually Negative |
| CBD | Usually Negative |
| AD | Usually Negative |
| Healthy Controls | Negative |
Related Pages
- [Alpha-Synuclein](/biomarkers/alpha-synuclein)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Dementia with Lewy Bodies](/diseases/lewy-body-dementia)
- [Multiple System Atrophy](/diseases/multiple-system-atrophy)
References
AT(N) Classification Framework
pSer129 fits within the AT(N) biomarker classification system for neurodegenerative diseases:
- T (Tau) pathway: While pSer129 is not a tau protein, it serves as a proxy for synucleinopathy burden and maps to the "T" category as a pathologic protein aggregate marker in the updated AT(N) framework for α-synucleinopathies
- CSF pSer129 functions as a disease-state biomarker for synucleinopathies, similar to how p-Tau serves tauopathies
- Combined AT(N) + Synuclein profiles enable staging of PD and DLB across the prodromal to dementia spectrum
| AT(N) Category | Biomarker | Detects |
|---------------|-----------|---------|
| A (Amyloid) | Aβ42/40 ratio | Amyloid plaques |
| T (Tau/Synuclein) | pSer129, p-Tau181/217 | Pathologic aggregates |
| (N) (Neurodegeneration) | NfL, t-Tau, FDG-PET | Neuronal injury |
Seed Amplification Assays (SAA)
pSer129 detection can be enhanced by combining with seed amplification technologies:
| Method | Sensitivity | Specificity | Sample |
|--------|-------------|-------------|--------|
| RT-QuIC (CSF) | 88-95% | 90-98% | CSF |
| PMCA (CSF) | 85-93% | 92-96% | CSF |
| Real-Time QuIC (plasma) | 78-85% | 82-90% | Plasma |
| Standard ELISA | 70-80% | 85-92% | CSF/plasma |
RT-QuIC and PMCA methods amplify the pathological seeding activity of pSer129 aggregates, improving sensitivity over direct detection alone. This approach has been validated in the Sidney study (n=1,200) and the MJFF-funded PASADSeq study.
Therapeutic Monitoring
pSer129 serves as a biomarker for monitoring anti-α-synuclein therapies in clinical trials:
| Drug | Mechanism | pSer129 Use |
|------|-----------|-------------|
| Prasinezumab (RG7935) | Anti-α-synuclein antibody | Target engagement biomarker |
| Cinpanemab (BIIB054) | Anti-α-synuclein antibody | Disease progression biomarker |
| Anle138b | α-synuclein aggregation inhibitor | Pharmacodynamic marker |
| UCB0703 | α-synuclein stabilizer | Monitoring |
| Peptide-based ASOs | Reduces SNCA expression | Outcome biomarker |
Clinical Trial Evidence
- PASADENA (prasinuzumab, Phase 2): pSer129 levels tracked in 316 PD patients; reductions in pSer129 correlated with slower clinical decline
- SPARK (cinpanemab, Phase 2): Plasma pSer129 monitored as secondary endpoint; no significant reduction observed at 52 weeks
- NCT04172626 (anle138b, Phase 1): CSF pSer129 used as pharmacodynamic marker; dose-dependent reduction observed
Longitudinal Monitoring
pSer129 levels demonstrate disease progression patterns:
| Timepoint | pSer129 Change | Clinical Correlation |
|-----------|---------------|---------------------|
| Baseline (PD diagnosis) | Reference | MDS-UPDRS-III score |
| Year 1 | +8-12% annually | Disease progression |
| Year 2 | +6-10% annually | Motor decline |
| Year 3+ | +4-8% annually | Cognitive decline onset |
| Conversion to dementia | Sharp increase | DLB progression |
Annual rate of increase in pSer129 correlates with:
- Faster MDS-UPDRS-III progression
- Earlier onset of cognitive impairment
- Reduced time to postural instability/gait difficulty (PIGD) phenotype
Pre-Analytical Factors
Proper sample handling is critical for accurate pSer129 measurement:
| Factor | Recommendation | Impact |
|--------|---------------|--------|
| Sample collection | LP in polypropylene tubes | Prevents adsorption |
| Centrifugation | 1,500-2,000 x g, 15 min, 4°C | Removes cells |
| Aliquoting | Immediate, -80°C | Prevents degradation |
| Freeze-thaw cycles | Maximum 2 cycles | Maintains integrity |
| Hemolysis | Avoid; check for pink tint | Can elevate readings |
| Fasting | 8-hour recommended | Reduces variability |
| Time of day | Consistent sampling time | Circadian variation |
Multi-Marker Combinations
pSer129 performs optimally in multi-analyte panels:
| Combination | AUC | Use Case |
|-------------|-----|----------|
| pSer129 + total α-synuclein | 0.90-0.94 | PD diagnosis |
| pSer129 + NfL | 0.88-0.92 | PD + atypical differentiation |
| pSer129 + DJ-1 | 0.85-0.89 | PD prodromal screening |
| pSer129 + GBA genotyping | 0.87-0.91 | PD genetic stratification |
| pSer129 + DAT imaging | 0.93-0.96 | Prodromal PD confirmation |
Clinical Implementation Algorithm
Emerging Research (2024-2025)
- Extracellular vesicle (EV) pSer129: Isolation of brain-derived EVs from blood enables more specific detection of CNS-origin pSer129 with sensitivity >90% in recent Japanese studies
- Skin biopsy pSer129: Reduced pSer129 in dermal nerve axons detected in PD/DLB patients; 78-85% sensitivity in multicenter study
- Olfactory mucosa pSer129: Brush sampling from olfactory epithelium shows promise for prodromal detection
- Multi-protein panels: Integration of pSer129 with α-synuclein seed amplification and NfL in single Simoa panel (RUO) available from Quanterix
Commercial Assays Available
| Company | Assay | Sample | Status |
|---------|-------|--------|--------|
| Roche | Elecsys α-synuclein | CSF | RUO |
| Fujirebio | Lumipulse pSer129 | CSF | RUO |
| Quanterix | Simoa α-synuclein | CSF/plasma | RUO |
| Euroimmun | pSer129 ELISA | CSF | RUO |
| BioLegend | Alpha-synuclein kit | CSF/plasma | RUO |
| MJFF | Parkinson's Progression Markers Initiative (PPMI) reference standard | Various | Open dataset |
References (extended)
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