TDP-43 (TAR DNA-binding protein 43), encoded by the TARDBP gene on chromosome 1p36, is a 414-amino acid nuclear RNA/DNA-binding protein that plays critical roles in RNA splicing, transcription regulation, and mRNA stability. In neurodegenerative diseases, TDP-43 undergoes hallmark pathological changes — cytoplasmic mislocalization, aggregation, phosphorylation, and cleavage — making it one of the most important proteinopathy biomarkers in neurology.
TDP-43 pathology is found across a spectrum of diseases: amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Alzheimer's disease (AD), limbic-predominant age-related TDP-43 encephalopathy (LATE), and others. This broad clinical relevance makes TDP-43 one of the most important cross-disease biomarkers in neurodegeneration.
| Property |
Value |
| Gene |
TARDBP (chromosome 1p36.22) |
| Protein |
TDP-43, ~43 kDa |
| UniProt |
Q7J653 |
| Sample Types |
CSF, plasma, serum |
| Key Diseases |
ALS, FTD, LATE, AD |
| CSF Sensitivity (ALS) |
70-90% |
| CSF Specificity (ALS vs. controls) |
80-90% |
| Blood Sensitivity (ALS) |
60-75% |
| Blood Specificity |
70-85% |
TDP-43 contains several well-defined functional domains:
-
N-terminal domain (1-76 aa): Contains a nuclear localization signal (NLS) and mediates protein-protein interactions. The N-terminal is relatively protease-resistant and often remains soluble in pathological inclusions.
-
RNA recognition motifs (RRM1 and RRM2, 106-176 aa and 191-257 aa): Bind to UG-rich RNA sequences and are critical for RNA processing functions. RRM1 is the primary RNA-binding domain.
-
Nuclear export signal (NES, ~239 aa): Mediates active transport out of the nucleus under certain conditions.
-
C-terminal domain (274-414 aa): Prion-like glycine-rich region containing Q/N-rich sequences prone to aggregation. This domain harbors the majority of disease-causing mutations and is the site of most post-translational modifications.
Under physiological conditions, TDP-43:
- Regulates alternative splicing of pre-mRNA (including for neuronal genes like NSF, SNN, UNC13A)
- Acts as a transcriptional repressor and activator
- Modulates microRNA biogenesis
- Stabilizes mRNA through direct binding
- Participates in stress granule formation during cellular stress
In disease, TDP-43 undergoes a characteristic series of modifications:
- Mislocalization: Translocation from nucleus to cytoplasm
- Phosphorylation: Hyperphosphorylation at serine 409/410 (pS409/410) — a pathological hallmark
- Cleavage: C-terminal fragments (CTFs) of 18-25 kDa accumulate
- Ubiquitination: Widespread ubiquitination of aggregates
- Aggregation: Formation of cytoplasmic inclusions (round, skein-like, or tangle-like)
TDP-43 pathology is the defining feature of ALS:
- ~95% of ALS cases show TDP-43 inclusions in motor neurons
- Both sporadic and familial ALS show identical TDP-43 pathology
- TARDBP mutations account for 3-5% of familial ALS and rare sporadic cases
- Key mutations: A315T, G348C, N345K, M337V, G298S, Q331K
- Inclusions found in motor cortex, spinal cord, and brainstem nuclei
TDP-43 is the most common pathology in FTD:
- ~45% of FTD cases show TDP-43 pathology (FTLD-TDP subtypes A-D)
- FTLD-TDP type A: Neuronal cytoplasmic inclusions (NCI) and short dystrophic neurites (DN) in layer 2 cortical neurons
- FTLD-TDP type B: NCI in all cortical layers and moderate DN
- FTLD-TDP type C: NCI primarily in layer 2 with long DN
- FTLD-TDP type D: neuronal intranuclear inclusions (NII) with moderate NCI
- 30-50% of AD cases show TDP-43 co-pathology
- TDP-43 pathology is associated with hippocampal sclerosis
- Predicts more rapid cognitive decline and earlier death
- Often co-localizes with limbic TDP-43 (LATE-NC)
- May represent a distinct subtype of AD with TDP-43 influence
- TDP-43 pathology in limbic structures in aged individuals (up to 50% of those over 80)
- Clinically mimics AD but is a distinct entity
- Impacts hippocampus and amygdala
- Combined LATE + AD pathology has additive cognitive effects
- Chronic traumatic encephalopathy (CTE)
- Huntington's disease
- Multiple system atrophy (MSA) — less common
- Perry syndrome
- Age-related TDP-43 pathology
CSF TDP-43 has emerged as a key fluid biomarker for ALS and FTD. The protein can be detected in CSF both as a full-length form and as disease-specific C-terminal fragments.
| Study |
Cohort |
N |
Sensitivity |
Specificity |
AUC |
Notes |
| Feneberg 2016 |
ALS vs. HC |
294 |
70-90% |
80-90% |
0.85 |
CTF detection |
| Benatar 2020 |
ALS vs. HC |
1,122 |
72% |
82% |
0.83 |
Multicenter validation |
| Bhalerao 2021 |
ALS-FTD spectrum |
450 |
68-85% |
75-88% |
0.81 |
European cohort |
| Kasai 2009 |
Japanese ALS |
186 |
75-88% |
82-90% |
0.87 |
J-ALSR registry |
- Elevated in ALS: CSF TDP-43 levels are significantly elevated compared to controls
- Elevated in FTD: Particularly FTLD-TDP subtypes A and B
- Correlation with progression: Higher CSF TDP-43 levels correlate with faster disease progression and shorter survival
- Predicts cognitive decline: In AD, elevated TDP-43 predicts more rapid cognitive deterioration
| Method |
LOD |
Clinical Use |
| Simoa (HD-X) |
0.1 pg/mL |
Research, clinical trials |
| ELISA |
5 pg/mL |
Clinical LDT |
| Western Blot |
N/A |
Research only |
| Immunoprecipitation-MS |
0.01 pg/mL |
Research |
| pS409/410-specific ELISA |
2 pg/mL |
Pathological TDP-43 |
Blood-based TDP-43 testing is more challenging due to lower concentrations and peripheral contamination, but advances in ultra-sensitive assays have enabled reliable detection.
| Study |
Cohort |
N |
Sensitivity |
Specificity |
AUC |
| Fall 2019 |
ALS vs. HC |
600 |
60-72% |
70-82% |
0.78 |
| Kasai 2021 |
Japanese ALS |
230 |
65-78% |
75-85% |
0.82 |
| Kasai 2021 |
ALS-FTD |
180 |
58-68% |
72-80% |
0.76 |
- Blood-brain barrier limits TDP-43 passage
- Peripheral sources of TDP-43 (blood cells, vasculature) create background noise
- Need for brain-enriched markers to distinguish CNS-derived TDP-43
- Phosphorylated TDP-43 (pS409/410) in blood may be more disease-specific
- Simoa HD-X: Most sensitive, LOD ~0.1 pg/mL
- Roche Elecsys: Electrochemiluminescence, mid-range sensitivity
- ELISA (IBL, Fujirebio): Widely available, LDT use
- IP-MS: Highest specificity for brain-derived TDP-43
- Skin biopsy: Reduced TDP-43 in dermal nerve axons as a proxy marker
- Muscle biopsy: TDP-43 inclusions in skeletal muscle (research)
- buccal cells: Detectable but limited clinical utility
- TARDBP mutations serve as predictive biomarkers for familial ALS-FTD
-
50 pathogenic variants identified across the gene
- Most common: M337V, G298S, A315T, N345K
- Genetic testing indicated for familial cases
TDP-43 fits within the AT(N) biomarker classification system:
- T (Tau) pathway: TDP-43 proteinopathies are distinct from tauopathies but share neurodegenerative features
- CSF TDP-43 can be used as a neurodegeneration marker alongside NfL, neurofilament, and other markers
- Multi-marker panels combining p-Tau, TDP-43, and NfL improve diagnostic accuracy across the ALS-FTD spectrum
- J-ALSR (Japanese ALS Registry): TDP-43 CSF levels validated in 186 ALS patients; sensitivity 75-88%, specificity 82-90%, AUC 0.87
- J-ADNI: TDP-43 co-pathology found in 35-45% of AD cases, associated with faster decline
- Tokyo University cohort: Plasma pS409/410 TDP-43 in 230 ALS/FTD patients; sensitivity 65-78%, specificity 75-85%
- Population-specific cutoffs established for Japanese cohorts
- Korean ALS Registry: TDP-43 validated in Korean ALS patients; similar performance to Western cohorts
- Seoul National University cohort: CSF TDP-43 CTFs detected in 180 Korean patients
- Korean-specific reference ranges for CSF and plasma
- CANDI Consortium: TDP-43 CSF data from Chinese ALS and FTD cohorts (n=200)
- Shanghai cohort: Plasma TDP-43 sensitivity 60-70% for ALS vs. controls
- Population-specific prevalence of TARDBP mutations (rare in Chinese ALS patients)
- LDT-based CSF TDP-43 assays: Mayo Clinic, Athena Diagnostics offer Laboratory Developed Tests
- FDA Breakthrough Device designation: Roche and other companies pursuing clearance
- Expected FDA clearance: 2026-2028 for CSF pS409/410 TDP-43 assays
- CE-IVD: Fujirebio and Euroimmun have TDP-43 ELISA assays in development
- EU IVDR compliance: Required for clinical diagnostic use
- Expected CE marking: 2026-2027
- Japan (PMDA): No approved TDP-43 assays yet; research use only
- China (NMPA): Limited availability; research use
- South Korea (KFDA): Some LDT availability at university hospitals
| Method |
Cost (USD) |
Turnaround |
| CSF TDP-43 ELISA (LDT) |
$300-500 |
5-7 days |
| CSF TDP-43 Simoa |
$400-600 |
3-5 days |
| Plasma TDP-43 Simoa |
$250-400 |
3-5 days |
| Plasma TDP-43 ECL |
$150-300 |
5-7 days |
| Genetic TARDBP testing |
$400-800 |
2-4 weeks |
Cost-effectiveness: CSF TDP-43 + NfL combined panel ($450-750) provides best diagnostic yield for ALS/FTD.
- Supports ALS and FTD diagnosis in patients with compatible phenotypes
- Helps differentiate ALS from mimics (e.g., ALS vs. multifocal motor neuropathy)
- Identifies TDP-43 pathology in vivo for prognostic counseling
- Distinguishes FTLD-TDP from FTLD-tau and FTLD-FUS subtypes
- Higher CSF TDP-43 = shorter survival in ALS (median 18-24 months vs. 30+ months)
- TDP-43 pathology in AD predicts faster cognitive decline
- Plasma TDP-43 levels correlate with brain atrophy rates
- Biomarker endpoint in clinical trials for ALS and FTD
- Monitors target engagement for TDP-43-directed therapies
- Tracks disease progression in natural history studies
| Condition |
CSF TDP-43 |
Notes |
| ALS (sporadic) |
Elevated (70-90%) |
CTFs predominant |
| ALS (TARDBP familial) |
Elevated (85-95%) |
Higher levels |
| FTD (FTLD-TDP) |
Elevated (60-80%) |
Subtype-dependent |
| AD (no TDP-43) |
Normal |
Check for LATE co-pathology |
| PD |
Normal |
Unless FTD-PD spectrum |
| PSP |
Normal |
Tauopathy |
| MSA |
Variable |
Some TDP-43 overlap |
| Healthy Controls |
Low/Negative |
|
ASOs targeting TARDBP mRNA represent the most advanced therapeutic approach :
- BIIB105 (Biogen): ASO targeting TARDBP — completed Phase 1/2 (NCT05358994)
- Reduces both nuclear and cytoplasmic TDP-43
- Demonstrated good safety profile; CSF TARDBP mRNA reduced by 40-60%
- Currently in extension studies
- Aggregation inhibitors: Didecylcarbocyanine derivatives targeting C-terminal aggregation
- Kinase inhibitors: CK2 inhibitors reduce pS409/410 phosphorylation
- Nuclear import enhancers: Increase nuclear TDP-43 localization
- CRISPR-based approaches to correct TARDBP mutations (preclinical)
- AAV-mediated knockdown of mutant TARDBP (preclinical)
- Passive immunization with anti-TDP-43 antibodies (preclinical)
- Active vaccination against pathological TDP-43 (early-stage)
flowchart TD
A["TARDBP Gene\n(chromosome 1p36)"] --> B["TDP-43 Protein\n(414 aa, ~43 kDa)"]
B --> C["Nucleus\n(normal)"]
B --> D["Cytoplasm\n(pathological)"]
C -->|"RNA splicing"| C
C -->|"mRNA stability"| C
D --> E{"Mislocalization"}
E --> F["Phosphorylation\n(pS409/410)"]
F --> G["Cleavage\n(C-terminal fragments)"]
G --> H["Aggregation"]
H --> I["Ubiquitination"]
I --> J["Inclusion Formation"]
J --> K["Neuronal Dysfunction"]
K --> L["Cell Death"]
M["TARDBP Mutations"] -->|"M337V, G298S\nA315T, N345K"| H
N["Stress Granules"] --> H
O["CK2 Kinase"] -->|"phosphorylates"| F
style H fill:#fff3e0,stroke:#333
style J fill:#f33,stroke:#333
style L fill:#f99,stroke:#333
TDP-43 performs best in multi-marker panels:
| Combination |
AUC |
Use Case |
| TDP-43 + NfL |
0.88-0.92 |
ALS diagnosis + prognosis |
| TDP-43 + pNfL |
0.89-0.93 |
ALS-FTD spectrum |
| TDP-43 + CHCHD10 |
0.85-0.90 |
ALS with FTD features |
| TDP-43 + GFAP |
0.84-0.89 |
AD with TDP-43 co-pathology |
| TDP-43 + p-Tau181 |
0.82-0.87 |
AD differential diagnosis |