While corticobasal syndrome (CBS) is classically characterized as a 4-repeat (4R) tauopathy, a significant subset of cases exhibit TDP-43 pathology. This overlap between tauopathies and TDP-43 proteinopathies has important implications for understanding disease heterogeneity, clinical presentation, and therapeutic approaches. Research from 2025, including studies by Murakami et al., has clarified the frequency and significance of TDP-43 pathology in CBS[1].
TDP-43 pathology in CBS is more common than traditionally recognized:
| Pathological Category | Percentage of CBS Cases |
|---|---|
| Pure 4R tauopathy (no TDP-43) | ~50-60% |
| Mixed tau + TDP-43 pathology | ~25-35% |
| TDP-43 predominant | ~10-15% |
The distribution of TDP-43 pathology in CBS includes:
The presence of TDP-43 pathology influences the clinical presentation of CBS[1:1]:
TDP-43 pathology in CBS manifests in multiple inclusion types, similar to those observed in other TDP-43 proteinopathies but with some distinct features.
The most common TDP-43 inclusion type in CBS are neuronal cytoplasmic inclusions[1:2]:
Less common but pathologically significant:
TDP-43 pathology in CBS can also involve glial cells:
| Inclusion Type | Frequency in CBS | Similarity to ALS/FTD |
|---|---|---|
| NCI (Type A) | ~40% | Similar to FTLD-TDP Type A |
| NCI (Type B) | ~30% | Similar to FTLD-TDP Type B |
| NCI (Type C) | ~15% | Similar to FTLD-TDP Type C |
| NII | ~20% | Associated with GRN mutations |
The interaction between tau and TDP-43 pathologies in CBS represents a complex interplay that significantly impacts disease phenotype and progression.
Studies show distinct patterns of tau and TDP-43 co-localization[1:3][2]:
Multiple mechanisms link tau and TDP-43 pathologies:
| Pathology Type | Cognitive Symptoms | Motor Symptoms | Progression |
|---|---|---|---|
| Pure Tau | Mild | Severe | Slower |
| Mixed Tau+TDP-43 | Moderate-Severe | Moderate | Faster |
| Pure TDP-43 | Severe | Moderate | Variable |
TDP-43 aggregation in CBS follows a multi-step process similar to other TDP-43 proteinopathies:
| Factor | Mechanism | Therapeutic Target |
|---|---|---|
| Progranulin deficiency | Loss of neurotrophic support | Recombinant PGRN |
| C9orf72 expansions | DPR toxicity, RNA foci | Antisense oligonucleotides |
| Tau pathology | Cellular stress, shared kinases | Tau-directed therapies |
| Aging | Declining proteostasis | Autophagy enhancers |
CBS with TDP-43 pathology shares significant overlap with ALS and frontotemporal dementia, but exhibits distinct features.
Both ALS/FTD and CBS show:
| Feature | ALS/FTD | CBS |
|---|---|---|
| Primary proteinopathy | TDP-43 | 4R Tau (usually) |
| Inclusion morphology | Variable | More compact |
| Glial involvement | Extensive | Moderate |
| Motor neuron pathology | Common | Less frequent |
| Spinal cord involvement | Universal | Variable |
| Property | ALS/FTD | CBS-TDP43 |
|---|---|---|
| Full-length TDP-43 | Present | Present |
| C-terminal fragments | ~45-50 kDa | ~45-50 kDa |
| Phosphorylation pattern | Similar | Similar |
| Solubility | Insoluble | Variable insolubility |
The comparison with ALS/FTD has practical implications for CBS[2:1][3]:
TDP-43 pathology contributes to neuronal dysfunction in CBS through multiple mechanisms.
Nuclear TDP-43 loss causes:
| Pathway | Impact | Consequence |
|---|---|---|
| Mitochondrial function | Reduced expression | Energy deficit |
| Synaptic proteins | Splicing changes | Synaptic dysfunction |
| Axonal transport | mRNA misregulation | Axonal degeneration |
| Cell survival | Pro-apoptotic changes | Increased cell death |
Cytoplasmic TDP-43 aggregates:
TDP-43 pathology significantly impacts synaptic function:
TDP-43 in glial cells contributes to neuronal dysfunction:
The mechanisms linking TDP-43 pathology to CBS include:
Several genetic factors influence TDP-43 pathology in CBS:
The interaction between tau and TDP-43 pathologies is complex, with evidence suggesting bidirectional relationships.
A 2025 study by Palleis et al. established a biomarker-based classification system for CBS that incorporates TDP-43 pathology[2:2]:
| Biomarker Profile | Underlying Pathology | Prevalence |
|---|---|---|
| Tau-positive, TDP-43 negative | Primary 4R tauopathy | ~55% |
| Tau-positive, TDP-43 positive | Mixed tau + TDP-43 | ~30% |
| TDP-43 positive, tau negative | Primary TDP-43opathy | ~15% |
This classification has diagnostic and prognostic implications.
Understanding TDP-43 pathology in CBS has practical implications:
Current and emerging biomarkers include:
Therapeutic strategies for TDP-43 in CBS include[3:1]:
Given the association between GRN mutations and TDP-43 pathology[4]:
Recent cryo-electron microscopy studies have provided unprecedented insights into TDP-43 filament structure in CBS and related disorders[5]. These structural studies reveal:
The structural insights from cryo-EM are informing the development of structure-targeted therapeutic agents.
Animal models have been developed to study TDP-43 pathology in CBS context:
| Model | Key Observation | Relevance to CBS |
|---|---|---|
| TDP-43 A315T | Motor cortex pathology | Motor symptoms |
| GRN-/- | Age-dependent TDP-43 | Genetic forms |
| Tau/P-301L | Accelerated aggregation | Mixed pathology |
These models have identified potential therapeutic targets and are being used for drug screening.
Beyond established biomarkers, several emerging approaches show promise:
The integration of biomarker data with clinical assessment enables more accurate diagnosis and monitoring.
TDP-43 pathology is present in a substantial minority of CBS cases, influencing clinical presentation, disease progression, and therapeutic approaches. The 2025 research by Murakami et al. and others has clarified that:
Understanding the TDP-43 component of CBS is essential for precision medicine approaches to this heterogeneous disorder.
Murakami et al. Frontotemporal Lobar Degeneration with TDP-43 presenting as PSP syndrome (2025). 2025. ↩︎ ↩︎ ↩︎ ↩︎
Palleis et al. A Biomarker-Based Classification of Corticobasal Syndrome (2025). 2025. ↩︎ ↩︎ ↩︎
Tian et al. Progranulin deficiency promotes TDP-43 proteinopathy through lysosomal disruption (2024). 2024. ↩︎ ↩︎
Gao et al. Progranulin as a biomarker for frontotemporal dementia (2024). 2024. ↩︎
Shi et al. Cryo-EM structure of TDP-43 filaments from frontotemporal lobar degeneration (2024). 2024. ↩︎