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 (TAR DNA-binding protein 43) is a 414-amino acid nuclear protein encoded by the TARDBP gene that plays critical roles in RNA splicing, transport, and stability. In neurodegenerative diseases, TDP-43 undergoes pathological transformation characterized by phosphorylation, ubiquitination, cleavage into C-terminal fragments, and aggregation into cytoplasmic inclusions. This page comprehensively covers TDP-43 co-pathology mechanisms in CBS.
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]:
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.
The pathological manifestations of TDP-43 in CBS are heterogeneous and include multiple inclusion types:
| Inclusion Type | Description | Prevalence in CBS |
|---|---|---|
| Lewy body-like inclusions | Spherical, eosinophilic cytoplasmic inclusions | ~40% of TDP-43+ cases |
| Compact inclusions | Dense, round inclusions without halo | ~25% of TDP-43+ cases |
| Grains and pretangles | Fine, thread-like structures | ~20% of TDP-43+ cases |
| Perivascular inclusions | Inclusions surrounding blood vessels | ~15% of TDP-43+ cases |
The morphology of TDP-43 inclusions in CBS differs from classical ALS/FTD patterns:
The relationship between tau and TDP-43 in CBS is complex and involves multiple interaction pathways:
The anatomical distribution of tau and TDP-43 pathology often shows complementary patterns:
| Brain Region | Primary Pathology | Secondary Pathology |
|---|---|---|
| Motor cortex | Tau > TDP-43 | TDP-43 in layers II/III |
| Basal ganglia | Tau predominant | TDP-43 in striatum |
| Substantia nigra | Both common | Variable dominance |
| Hippocampus | TDP-43 predominant | Tau in CA1/Subiculum |
TDP-43 normally resides in the nucleus but in disease states accumulates in the cytoplasm. Key mechanisms include:
| Modification | Effect on TDP-43 | Detection in CBS |
|---|---|---|
| Phosphorylation at Ser409/410 | Promotes aggregation | ~80% of inclusions |
| Ubiquitination | Marks for degradation | ~90% of inclusions |
| C-terminal cleavage | Generates aggregation-prone fragments | ~70% of cases |
| Acetylation | Impairs RNA binding | Associated with stress |
Recent cryo-EM studies have elucidated TDP-43 filament structures in CBS and related disorders [3]:
| Feature | CBS | ALS | FTD |
|---|---|---|---|
| Phosphorylated TDP-43 | ✓ | ✓ | ✓ |
| Ubiquitin positive | ✓ | ✓ | ✓ |
| C-terminal fragments | ✓ | ✓ | ✓ |
| Nuclear clearing | ✓ | ✓ | ✓ |
| Stage | ALS Pattern | CBS Pattern |
|---|---|---|
| Early | Motor cortex | Motor cortex + basal ganglia |
| Middle | Brainstem + spinal cord | Substantia nigra + limbic |
| Late | Diffuse involvement | Hippocampal + frontal involvement |
| Factor | Contribution |
|---|---|
| Neuronal size | Large neurons more vulnerable |
| Metabolic demand | High energy requiring neurons |
| Axonal length | Long projection neurons |
| Calcium dysregulation | Excitotoxicity amplification |
The presence of TDP-43 pathology in CBS correlates with:
GRN mutations cause haploinsufficiency leading to reduced progranulin levels[4]:
C9orf72 hexanucleotide repeat expansions[5]:
TMEM106B acts as a modifier[6]:
A 2025 study by Palleis et al. established a biomarker-based classification system for CBS that incorporates TDP-43 pathology[7]:
| 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[8]:
Given the association between GRN mutations and TDP-43 pathology[9]:
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. ↩︎ ↩︎
Rodriguez et al. Tau pathology induces TDP-43 mislocalization in neurons (2024). 2024. ↩︎
Arseni et al. Cryo-EM structures of TDP-43 filaments from ALS and FTD (2022). 2022. ↩︎
Baker et al. Mutations in progranulin cause tau-negative frontotemporal dementia linked to chromosome 17 (2006). 2006. ↩︎
DeJesus-Hernandez et al. Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 gene in frontotemporal dementia and amyotrophic lateral sclerosis (2011). 2011. ↩︎
Van Deerlin et al. Common variants at 7p21 are associated with frontotemporal lobar degeneration with TDP-43 inclusions (2010). 2010. ↩︎
Palleis et al. A Biomarker-Based Classification of Corticobasal Syndrome (2025). 2025. ↩︎
Progranulin Therapy for Neurodegeneration. ↩︎
Progranulin (PGRN) - Biomarker. ↩︎