TDP-43 and FUS RNA proteinopathies represent a class of neurodegenerative diseases characterized by the cytoplasmic aggregation of RNA-binding proteins, dysregulated RNA processing, and stress granule dynamics. This comparison examines how these two related protein families manifest across Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Huntington's disease (HD).
TDP-43 (encoded by TARDBP) and FUS (encoded by FUS) are both DNA/RNA-binding proteins with prion-like domains that drive liquid-liquid phase separation (LLPS). Their pathological aggregation defines the majority of ALS cases and a substantial portion of FTD cases. Recent research has revealed that TDP-43 pathology extends beyond ALS-FTD to affect AD, PD, and HD, making cross-disease comparison essential for understanding shared therapeutic targets[@neumann2006][@ling2013].
TDP-43 and FUS RNA proteinopathies represent a class of neurodegenerative diseases characterized by the cytoplasmic aggregation of RNA-binding proteins, dysregulated RNA processing, and stress granule dynamics. This comparison examines how these two related protein families manifest across Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Huntington's disease (HD).
TDP-43 (encoded by TARDBP) and FUS (encoded by FUS) are both DNA/RNA-binding proteins with prion-like domains that drive liquid-liquid phase separation (LLPS). Their pathological aggregation defines the majority of ALS cases and a substantial portion of FTD cases. Recent research has revealed that TDP-43 pathology extends beyond ALS-FTD to affect AD, PD, and HD, making cross-disease comparison essential for understanding shared therapeutic targets[@neumann2006][@ling2013].
| Feature | Alzheimer's Disease | Parkinson's Disease | ALS | Frontotemporal Dementia | Huntington's Disease |
|---------|-------------------|-------------------|-----|----------------------|-------------------|
| TDP-43 inclusions | Common (50-60% AD) | Moderate (30-40% PD) | >95% ALS cases | ~50% FTD cases | Rare (co-pathology) |
| Inclusion type | Cytoplasmic NFTs | Lewy body co-pathology | NCIs, skein-like | Diverse (Types A-D) | Sparse, cytoplasmic |
| Phospho-TDP-43 (S409/410) | Yes, in limbic regions | Yes, variable | Strong positivity | Strong positivity | Rare |
| C-terminal fragments | 25kDa, 35kDa | Variable | Prominent | Prominent | Not prominent |
| Nuclear loss | Early event | Moderate | Severe | Severe | Mild |
| TARDBP mutations | Not associated | Not associated | ~5% familial ALS | Rare | None reported |
| C9orf72 influence | Not prominent | Not prominent | Primary cause | Primary cause | None |
| Stress granule involvement | Moderate | Variable | Severe | Severe | Moderate |
| Propagation pattern | Braak-like staging | Brainstem to cortex | Multi-focal | Multi-focal | Striatal to cortical |
| Feature | Alzheimer's Disease | Parkinson's Disease | ALS | Frontotemporal Dementia | Huntington's Disease |
|---------|-------------------|-------------------|-----|----------------------|-------------------|
| FUS inclusions | Rare | Rare | ~5% familial ALS | ~10% FTD (FTLD-FUS) | Rare |
| Inclusion type | Sparse, nuclear | Very rare | Cytoplasmic in motor neurons | FTLD-FUS subtypes | Sparse |
| FUS mutations | Not associated | Not associated | ~5% familial ALS | Rare | None reported |
| Phase separation dysregulation | Not prominent | Not prominent | Severe | Severe | Moderate |
| Cytoplasmic mislocalization | Minimal | Minimal | Marked (NLS mutations) | Moderate | Mild |
| P525L mutation | Not present | Not present | Severe, juvenile | Rare | None |
| R521C mutation | Not present | Not present | Most common adult | Rare | None |
| Stress granule incorporation | Minimal | Minimal | Severe | Severe | Moderate |
| Nucleocytoplasmic transport defect | Mild | Mild | Severe | Severe | Moderate |
| Feature | Alzheimer's Disease | Parkinson's Disease | ALS | Frontotemporal Dementia | Huntington's Disease |
|---------|-------------------|-------------------|-----|----------------------|-------------------|
| TDP-43 splicing targets | Moderate disruption | Moderate disruption | Severe disruption | Severe disruption | Mild |
| FUS splicing targets | Minimal | Minimal | Severe | Severe | Minimal |
| KCNQ2 mis-splicing | Not reported | Not reported | Documented[@joseph2025] | Documented | Not reported |
| Cryptic polyadenylation | Not reported | Not reported | Documented[@bryce-smith2025] | Documented | Not reported |
| UPF1 dysfunction | Not reported | Not reported | Documented[@alessandrini2026] | Documented | Not reported |
| NMD pathway impairment | Mild | Mild | Severe | Severe | Moderate |
| Alternative splicing changes | 100s of transcripts | 100s of transcripts | 100s of transcripts | 100s of transcripts | 50-100 transcripts |
| Neuronal transcript specificity | High | High | Very high | Very high | Moderate |
| Feature | Alzheimer's Disease | Parkinson's Disease | ALS | Frontotemporal Dementia | Huntington's Disease |
|---------|-------------------|-------------------|-----|----------------------|-------------------|
| SG formation | Moderate increase | Variable | Severe increase | Severe increase | Moderate |
| LLPS dysregulation | Aβ-mediated | LRRK2-mediated | TDP-43/FUS-mediated | TDP-43/FUS-mediated | mHTT-mediated |
| G3BP1 sequestration | Mild | Variable | Severe | Severe | Mild |
| TIA-1 alterations | Mild | Moderate | Severe | Severe | Not prominent |
| Persistent stress granules | Rare | Rare | Common | Common | Variable |
| Solidification transition | Occurs | Occurs | Frequent | Frequent | Occurs |
| Clearance via autophagy | Impaired (mTOR) | Impaired (LRRK2) | Impaired | Impaired | Impaired (mHTT) |
| Demixing within SGs | Not well characterized | Not well characterized | Documented[@yan2025] | Documented | Not well characterized |
| Feature | Alzheimer's Disease | Parkinson's Disease | ALS | Frontotemporal Dementia | Huntington's Disease |
|---------|-------------------|-------------------|-----|----------------------|-------------------|
| Nuclear import defects | Moderate | Moderate (LRRK2) | Severe | Severe | Moderate |
| Nuclear export enhancement | Mild | Mild | Severe | Severe | Mild |
| Importin-α/β dysfunction | Not prominent | LRRK2-mediated | TDP-43/FUS mutations | TDP-43 mutations | Not prominent |
| NPC integrity | Impaired | Impaired | Severely impaired | Severely impaired | Moderately impaired |
| Ran-GTP gradient disruption | Mild | Mild | Severe | Severe | Moderate |
| NLS mutations | None | None | FUS P525L, R521C | Rare | None |
| Ribosomal protein sequestration | Mild | Mild | Severe | Severe | Moderate |
TDP-43 is a 414-amino acid RNA-binding protein with distinct structural domains that govern its normal function and pathogenicity[@dormann2011]:
Normal Functions:
FUS is a 526-amino acid RNA-binding protein with structural features shared with TDP-43 and the FET protein family[@murakami2015][@kwok2020]:
Normal Functions:
Both TDP-43 and FUS regulate overlapping sets of RNA targets, and their dysfunction causes convergent splicing defects[@joseph2025][@bryce-smith2025][@alessandrini2026]:
Key Shared Targets:
TDP-43 pathology is highly prevalent in AD, affecting 50-60% of cases[@jeong2023]:
Clinical Significance:
TDP-43 co-pathology occurs in 30-40% of PD cases, particularly in advanced disease:
Clinical Significance:
ALS represents the paradigmatic disease for RNA proteinopathies[@ling2013][@kwok2020]:
TDP-43-ALS (>95% of ALS cases):
FTD represents the cognitive counterpart to ALS within the disease spectrum[@dormann2011]:
TDP-43-FTD (FTLD-TDP, ~50% of FTD):
RNA proteinopathy is less prominent in HD but shows overlapping mechanisms:
TDP-43 in HD:
Stress granules serve as critical intermediates in RNA proteinopathy pathogenesis[@wolozin2019][@gasset2024]:
Normal SG Function:
| Disease | Primary SG Modifier | Mechanism |
|---------|--------------------|-----------|
| AD | Aβ oligomers | eIF2α phosphorylation, oxidative stress |
| PD | LRRK2 mutations | Rab GTPase cycle, trafficking defects |
| ALS | TDP-43/FUS mutations | Prion-like domain alterations, NLS mutations |
| FTD | TDP-43/FUS mutations | Same as ALS, converging pathways |
| HD | mHTT | Interference with SG dynamics, autophagy defects |
Phase Separation Modulators:
Impaired nucleocytoplasmic transport is a shared feature across RNA proteinopathies[@buttner2020][@chen2019]:
Nuclear Import Impairment:
| Disease | Primary Defect | Molecular Link |
|---------|---------------|----------------|
| AD | Moderate import impairment | Aging, Aβ toxicity |
| PD | LRRK2-mediated Rab dysfunction | RAB29, RAB10, RAB8A |
| ALS | NLS mutations (FUS), phosphorylation (TDP-43) | Direct protein dysfunction |
| FTD | Same as ALS | Same as ALS |
| HD | NPC integrity impairment | mHTT-mediated |
| Target | Approach | Disease | Development Stage |
|--------|----------|---------|-------------------|
| TDP-43 expression | ASO silencing | ALS, FTD | Phase 1-2 |
| FUS expression | ASO targeting | FUS-ALS | Preclinical |
| C9orf72 repeat | ASO, small molecules | ALS, FTD | Phase 1-2 |
| Aggregation | Small molecule inhibitors | ALS, FTD, AD | Preclinical |
| Phase separation | LLPS modulators | ALS, FTD | Preclinical |
| Stress granules | SG dynamics modulators | ALS, FTD, AD, PD | Preclinical |
| Autophagy | TFEB activators, mTOR inhibitors | ALS, FTD, AD, PD | Preclinical |
| Nuclear import | Importin modulators | ALS, FTD | Research |
| KCNQ2 splicing | ASO correction | ALS, FTD | Preclinical |
| YAP signaling | YAP activators | ALS, FTD | Research[@zhang2025] |
| SUMOylation | SUMO2/3 enhancers | ALS, FTD | Research |
| NMD pathway | UPF1 modulators | ALS, FTD | Research |
Active/Recruiting ALS-FTD Trials:
| Biomarker | Source | Disease | Clinical Use |
|-----------|--------|---------|--------------|
| Phospho-TDP-43 (S409/410) | CSF, plasma | ALS, FTD, AD, PD | Disease-specific marker |
| Total TDP-43 | CSF, plasma | ALS, FTD | Disease activity marker |
| Neurofilament light (NfL) | CSF, plasma | ALS, FTD, AD, PD | Progression, prognosis |
| Neurofilament heavy (NfH) | CSF, plasma | ALS | Prognosis |
| CSF TDP-43 | CSF | ALS, FTD | Diagnostic |
| FUS in CSF | CSF | FUS-ALS, FUS-FTD | Diagnostic (emerging) |
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