TDP-43 Co-pathology in Corticobasal Syndrome

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TDP-43 Co-pathology in Corticobasal Syndrome

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TDP-43 Co-pathology in Corticobasal Syndrome

Overview

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[@murakami2025].

TDP-43 (TAR DNA-binding protein 43) is a 414-amino acid nuclear protein encoded by the [TARDBP](/genes/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: Current Understanding

Frequency and Distribution

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% |

...

TDP-43 Co-pathology in Corticobasal Syndrome

Overview

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[@murakami2025].

TDP-43 (TAR DNA-binding protein 43) is a 414-amino acid nuclear protein encoded by the [TARDBP](/genes/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: Current Understanding

Frequency and Distribution

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:

Motor cortex (especially layer II)
Basal ganglia (putamen, globus pallidus)
Substantia nigra
Hippocampus (in cases with cognitive impairment)
Spinal cord anterior horns

Clinical Correlations

The presence of TDP-43 pathology influences the clinical presentation of CBS[@murakami2025]:

Cognitive Impairment: Cases with significant TDP-43 pathology show more prominent cognitive decline, often resembling frontotemporal dementia

Language Symptoms: Greater prevalence of aphasia and speech apraxia in CBS with TDP-43

Psychiatric Features: Increased frequency of behavioral changes

Disease Progression: Mixed pathology may be associated with more rapid progression

Mechanisms of TDP-43 Pathology in CBS

Pathological Mechanisms

The mechanisms linking TDP-43 pathology to CBS include:

Mermaid diagram (expand to render)

Genetic Contributions

Several genetic factors influence TDP-43 pathology in CBS:

GRN (Progranulin) Mutations: Associated with increased TDP-43 pathology
C9orf72 Expansions: Can present with CBS phenotype with TDP-43 pathology
TMEM106B Variants: Modify TDP-43 pathology risk

The interaction between tau and TDP-43 pathologies is complex, with evidence suggesting bidirectional relationships.

TDP-43 Inclusion Types in CBS

The pathological manifestations of TDP-43 in CBS are heterogeneous and include multiple inclusion types:

1. Cytoplasmic Inclusions

| 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 |

2. Neuronal Inclusions

Neuronal cytoplasmic inclusions (NCIs): Most common type, found in pyramidal neurons
Neuronal intranuclear inclusions (NIIs): Less common, associated with specific genetic forms
Dystrophic neurites: Abnormal neuritic processes containing TDP-43

3. Glial Inclusions

Astrocytic inclusions: TDP-43 positive astrocytes in affected regions
Oligodendroglial inclusions: Less frequently observed

4. Morphological Variants

The morphology of TDP-43 inclusions in CBS differs from classical ALS/FTD patterns:

More diffuse cytoplasmic staining
Less prominent skein-like inclusions compared to ALS
More frequent co-localization with tau pathology

Relationship Between Tau and TDP-43 Pathology

Bidirectional Interaction Mechanisms

The relationship between tau and TDP-43 in CBS is complex and involves multiple interaction pathways:

Mermaid diagram (expand to render)

Mechanisms of Tau-TDP-43 Co-aggregation

Axonal transport impairment: Hyperphosphorylated tau disrupts microtubule-based transport, leading to TDP-43 mislocalization [@rodriguez2024]

Shared vulnerability factors: Both pathologies target neurons with high metabolic demands

Protein homeostasis disruption: Tau pathology impairs ubiquitin-proteasome and autophagy systems

Stress granule sequestration: Both proteins can be recruited to stress granules

Regional Distribution Patterns

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 Aggregation Mechanisms

Molecular Pathways to Aggregation

1. Nuclear Clearance and Cytoplasmic Mislocalization

TDP-43 normally resides in the nucleus but in disease states accumulates in the cytoplasm. Key mechanisms include:

Nuclear import defects: Reduced importin-α/β function
Nuclear export dysregulation: Enhanced CRM1-mediated export
Stress granule formation: TDP-43 seeded into stress granules

2. Post-translational Modifications

| 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 |

3. Cryo-EM Structures

Recent cryo-EM studies have elucidated TDP-43 filament structures in CBS and related disorders [@arseni2022]:

Type A filaments: Left-handed helical filaments, 10-12 nm diameter
Type B filaments: Right-handed helical filaments, 10-15 nm diameter
Core structure: Residues 274-331 form the filament core
Phosphorylation: Ser409/410 in the disordered outer shell

Aggregation Kinetics

Mermaid diagram (expand to render)

Comparison with ALS/FTD TDP-43 Pathology

Shared Features

| Feature | CBS | ALS | FTD |
|---------|-----|-----|-----|
| Phosphorylated TDP-43 | ✓ | ✓ | ✓ |
| Ubiquitin positive | ✓ | ✓ | ✓ |
| C-terminal fragments | ✓ | ✓ | ✓ |
| Nuclear clearing | ✓ | ✓ | ✓ |

Distinctive Features in CBS

Co-pathology with tau: CBS shows significant tau co-occurrence (~30-40%), whereas ALS is typically tau-negative

Inclusion morphology: CBS has fewer skein-like inclusions than ALS

Regional distribution: More prominent basal ganglia involvement in CBS

Genetic associations: Different spectrum of causal genes

Pathological Staging

| 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 |

Impact on Neuronal Dysfunction

Mechanisms of TDP-43-Mediated Neurotoxicity

1. Loss of Nuclear Function

Impaired RNA splicing (exon skipping, intron retention)
Disrupted RNA transport and localization
Altered gene expression programs

2. Gain of Cytoplasmic Function

Stress granule pathology
Translation dysregulation
Mitochondrial dysfunction
Axonal transport defects

3. Cellular Vulnerability Factors

| Factor | Contribution |
|--------|-------------|
| Neuronal size | Large neurons more vulnerable |
| Metabolic demand | High energy requiring neurons |
| Axonal length | Long projection neurons |
| Calcium dysregulation | Excitotoxicity amplification |

Clinical Manifestations

The presence of TDP-43 pathology in CBS correlates with:

Cognitive impairment: More prominent than in pure tauopathy cases

Language deficits: Aphasia and speech apraxia

Behavioral changes: Disinhibition, apathy

Disease progression: Mixed pathology associated with faster decline

Genetic Factors Modifying TDP-43 in CBS

Major Genetic Contributors

GRN (Progranulin)

[GRN](/genes/grn) mutations cause haploinsufficiency leading to reduced progranulin levels[@baker2006]:

Mechanism: Progranulin deficiency impairs lysosomal function
Result: TDP-43 accumulates due to impaired clearance
Pathology: Type A TDP-43 inclusions

C9orf72 Repeat Expansions

[C9orf72](/genes/c9orf72) hexanucleotide repeat expansions[@dejesushernandez2011]:

Mechanism: RNA foci formation and dipeptide repeat proteins
Result: TDP-43 pathology as downstream effect
Pathology: Type B TDP-43 inclusions

TMEM106B Variants

[TMEM106B](/genes/tmem106b) acts as a modifier[@van2010]:

Risk variant: TMEM106B haplotypes affect lysosomal function
Effect: Modulates TDP-43 pathology severity
Interaction: Effects modified by GRN status

TDP-43 Classification Systems

Biomarker-Based Classification

A 2025 study by Palleis et al. established a biomarker-based classification system for CBS that incorporates TDP-43 pathology[@palleis2025]:

| 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.

Diagnostic Implications

Clinical-Pathological Correlations

Understanding TDP-43 pathology in CBS has practical implications:

Anticipating Clinical Course: Patients with TDP-43-predominant pathology may show faster cognitive decline

Genetic Testing: Presence of TDP-43 pathology may warrant testing for GRN and C9orf72 mutations

Therapeutic Considerations: TDP-43-targeting therapies may benefit specific patient subgroups

Biomarkers for TDP-43 Pathology

Current and emerging biomarkers include:

Neurofilament Light Chain (NfL): Elevated in CSF and blood; higher levels in TDP-43 cases
TDP-43 CSF Levels: Under investigation as direct marker
PET Tracers: Emerging tau PET may help differentiate pathologies

Therapeutic Implications

Targeting TDP-43 Pathology

Therapeutic strategies for TDP-43 in CBS include[@progranulin]:

RNA-Targeting Therapies: Antisense oligonucleotides targeting TDP-43 mRNA

Protein Clearance: Enhancing autophagy and ubiquitin-proteasome system

Reducing Stress Granule Formation: Small molecules targeting stress granule dynamics

Progranulin-Based Therapies

Given the association between GRN mutations and TDP-43 pathology[@progranulina]:

Recombinant Progranulin: Currently in clinical trials for FTD-GRN
Gene Therapy: AAV-mediated PGRN delivery under investigation
Small Molecule Enhancers: Compounds that increase progranulin expression

Relationship to Other CBS Mechanisms

[LRRK2 in CBS and 4R Tauopathies](/mechanisms/lrrk2-cbs-tauopathies) — Shared mechanisms with other 4R tauopathies
[CBS vs PSP: Comparative Mechanism Analysis](/mechanisms/cbs-vs-psp-comparison) — TDP-43 frequency differences
[GRN — Progranulin](/genes/grn) — Genetic factors in TDP-43 pathology
[C9orf72](/genes/c9orf72) — Hexanucleotide repeat expansions with TDP-43 pathology
[TARDBP](/genes/tardbp) — TDP-43 encoding gene
[TDP-43 Proteinopathy](/mechanisms/tdp-43-proteinopathy) — General TDP-43 mechanisms
[Progranulin Therapy](/therapeutics/progranulin-therapy) — Therapeutic approaches

Summary

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:

Approximately 40-50% of CBS cases have some degree of TDP-43 pathology

Mixed pathology is common and influences clinical phenotype

Genetic factors (GRN, C9orf72, TMEM106B) modify risk

Biomarker-based classification can predict underlying pathology

Therapeutic implications include TDP-43-targeted approaches for appropriate patients

Understanding the TDP-43 component of CBS is essential for precision medicine approaches to this heterogeneous disorder.

External Links

[PubMed](https://pubmed.ncbi.nlm.nih.gov/)
[KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

References

[Murakami et al., Frontotemporal Lobar degeneration with TDP-43 presenting as PSP syndrome (2025) (2025)](https://pubmed.ncbi.nlm.nih.gov/40635087/)

[Palleis et al., A Biomarker-Based Classification of Corticobasal Syndrome (2025) (2025)](https://pubmed.ncbi.nlm.nih.gov/41048081/)

Unknown, Progranulin Therapy for Neurodegeneration (n.d.)

Unknown, Progranulin (PGRN) - Biomarker (n.d.)

[Rodriguez et al., Tau pathology induces TDP-43 mislocalization in neurons (2024) (2024)](https://doi.org/10.1002/alz.14389)

[Arseni et al., Cryo-EM structures of TDP-43 filaments from ALS and FTD (2022) (2022)](https://doi.org/10.1038/s41586-022-04431-7)

[Baker et al., Mutations in progranulin cause tau-negative frontotemporal dementia linked to chromosome 17 (2006) (2006)](https://pubmed.ncbi.nlm.nih.gov/16437542/)

[DeJesus-Hernandez et al., Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 gene in frontotemporal dementia and amyotrophic lateral sclerosis (2011) (2011)](https://pubmed.ncbi.nlm.nih.gov/21944778/)

[Van Deerlin et al., Common variants at 7p21 are associated with frontotemporal lobar degeneration with TDP-43 inclusions (2010) (2010)](https://pubmed.ncbi.nlm.nih.gov/20220177/)

[Neumann et al., Ubiquitinated TDP-43 in frontotemporal dementia and amyotrophic lateral sclerosis (2006) (2006)](https://pubmed.ncbi.nlm.nih.gov/16437557/)

[Hasegawa et al., Phosphorylated TDP-43 in frontotemporal dementia and ALS (2008) (2008)](https://pubmed.ncbi.nlm.nih.gov/18614990/)

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TDP-43 Co-pathology in Corticobasal Syndrome

TDP-43 Co-pathology in Corticobasal Syndrome

Overview

TDP-43 Pathology in CBS: Current Understanding

Frequency and Distribution

TDP-43 Co-pathology in Corticobasal Syndrome

Overview

TDP-43 Pathology in CBS: Current Understanding

Frequency and Distribution

Clinical Correlations

Mechanisms of TDP-43 Pathology in CBS

Pathological Mechanisms

Genetic Contributions

TDP-43 Inclusion Types in CBS

1. Cytoplasmic Inclusions

2. Neuronal Inclusions

3. Glial Inclusions

4. Morphological Variants

Relationship Between Tau and TDP-43 Pathology

Bidirectional Interaction Mechanisms

Mechanisms of Tau-TDP-43 Co-aggregation

Regional Distribution Patterns

TDP-43 Aggregation Mechanisms

Molecular Pathways to Aggregation

1. Nuclear Clearance and Cytoplasmic Mislocalization

2. Post-translational Modifications

3. Cryo-EM Structures

Aggregation Kinetics

Comparison with ALS/FTD TDP-43 Pathology

Shared Features

Distinctive Features in CBS

Pathological Staging

Impact on Neuronal Dysfunction

Mechanisms of TDP-43-Mediated Neurotoxicity

1. Loss of Nuclear Function

2. Gain of Cytoplasmic Function

3. Cellular Vulnerability Factors

Clinical Manifestations

Genetic Factors Modifying TDP-43 in CBS

Major Genetic Contributors

GRN (Progranulin)

C9orf72 Repeat Expansions

TMEM106B Variants

TDP-43 Classification Systems

Biomarker-Based Classification

Diagnostic Implications

Clinical-Pathological Correlations

Biomarkers for TDP-43 Pathology

Therapeutic Implications

Targeting TDP-43 Pathology

Progranulin-Based Therapies

Relationship to Other CBS Mechanisms

Summary

See Also

External Links

References

💬 Discussion