Neurofilament light chain (NfL) is a cytoskeletal protein that provides structural support to axons in neurons. When axonal injury occurs, NfL is released into the cerebrospinal fluid (CSF) and, at higher concentrations, into peripheral blood. Elevated NfL levels serve as a sensitive and dynamic biomarker for axonal damage across a broad spectrum of neurodegenerative diseases, traumatic brain injuries, and neuroinflammatory conditions[@khalil_nfl].
Neurofilament light chain (NfL) is a cytoskeletal protein that provides structural support to axons in neurons. When axonal injury occurs, NfL is released into the cerebrospinal fluid (CSF) and, at higher concentrations, into peripheral blood. Elevated NfL levels serve as a sensitive and dynamic biomarker for axonal damage across a broad spectrum of neurodegenerative diseases, traumatic brain injuries, and neuroinflammatory conditions[@khalil_nfl].
Neurofilaments are intermediate filaments specific to neurons, composed of three subunits:
NfL demonstrates high sensitivity for detecting axonal injury but lower disease-specificity. The biomarker excels at:
NfL is remarkably stable in both CSF and plasma/serum. Studies demonstrate:
NfL is one of the most extensively studied biomarkers in ALS[@gissl_nfl]:
| Parameter | Value | Clinical Implication |
|-----------|-------|---------------------|
| CSF NfL | 2,500-15,000 pg/mL | 10-50x elevated vs controls |
| Plasma NfL | 50-500 pg/mL | 5-20x elevated vs controls |
| Rise rate | +5-15%/month | Predicts progression |
| Prognostic value | Strong | Higher = faster progression |
Key findings:
In Alzheimer's disease, NfL provides distinct patterns[@zetterberg_nfl]:
| Disease | NfL Elevation | Pattern |
|---------|--------------|---------|
| AD | Moderate (2-4x) | Increases with progression |
| AD with CJD | Very high (50x) | Rapid rise over weeks |
| FTD | Moderate (2-5x) | Stable over time |
| DLB | Low-moderate | Variable |
| VaD | Moderate | Correlates with load |
In Creutzfeldt-Jakob disease (CJD), NfL shows dramatically elevated levels (10-50x controls) with rapid increases over weeks, helping differentiate prion disease from other dementias[@luerman_nfl].
NfL in FTD shows[@preische_nfl]:
NfL shows disease-specific patterns in parkinsonian disorders:
| Disorder | NfL Level | Utility |
|----------|-----------|---------|
| PD | 1-2x | Limited diagnostic value |
| MSA | 3-10x | Supports diagnosis |
| PSP | 2-5x | Moderate value |
| CBS | 3-8x | Helps differentiate |
| CBD | 3-8x | Supports diagnosis |
NfL is particularly valuable in differentiating MSA from PD, with significantly higher levels in MSA.
NfL helps differentiate MSA subtypes[@wilke]:
NfL is elevated in:
Multiple platforms are clinically available:
| Platform | Matrix | LLOQ | Clinical Use |
|----------|-------|------|--------------|
| Simoa | Plasma/Serum | 1-2 pg/mL | Research, clinical trials |
| ELISA | CSF/Plasma | 10-20 pg/mL | Clinical |
| Lumipulse | CSF | Automated | Clinical |
| Roche Elecsys | Serum | Automated | Clinical |
Interpreting NfL requires age-adjusted reference ranges:
| Age Group | CSF NfL (pg/mL) | Plasma NfL (pg/mL) |
|----------|-----------------|---------------------|
| <40 years | <380 | <8 |
| 40-60 years | <560 | <15 |
| 60-80 years | <1,000 | <25 |
| >80 years | <1,300 | <35 |
Standard protocols:
NfL demonstrates utility in monitoring treatment response:
In ALS, NfL has become a key secondary endpoint:
Several disease categories show NfL responsiveness:
| Condition | NfL as Endpoint | Status |
|-----------|-----------------|--------|
| ALS | Yes | Established |
| MS | Yes | Validated |
| AD | Emerging | In trials |
| FTD | Emerging | In trials |
| SMA | Yes | Approved use |
| Biomarker | What It Measures | vs NfL |
|-----------|----------------|--------|
| Tau | Axonal degeneration | Complementary |
| p-tau181 | Tau pathology | Different |
| Beta-amyloid | Amyloid pathology | Different |
| Alpha-synuclein | Synuclein pathology | Complementary |
| Neurogranin | Synaptic integrity | Complementary |
NfL provides unique information about axonal injury not captured by pathology-specific biomarkers.
Recommended cut-offs for differential diagnosis:
| Comparison | CSF NfL Cut-off | Sensitivity | Specificity |
|------------|----------------|------------|------------|
| ALS vs. controls | >1,800 pg/mL | 85% | 90% |
| CJD vs. AD | >2,500 pg/mL | 90% | 85% |
| MSA vs. PD | >1,200 pg/mL | 75% | 80% |
| FTD vs. depression | >650 pg/mL | 70% | 75% |
Critical for accurate measurement:
Inter-laboratory variation requires:
Emerging technologies include:
Ongoing development areas:
[@khalil_nfl] Khalil M, et al. Neurofilament light chain as a biomarker in neurodegeneration. Nat Rev Neurol. 2018;14(11):699-709. PMID:29985474
[@zetterberg_nfl] Zetterberg H, et al. Neurofilament light chain in cerebrospinal fluid and blood. Nat Rev Neurol. 2019;15(10):578-580. PMID:31182707
[@preische_nfl] Preische O, et al. Neurofilament predicts progression in frontotemporal dementia. Nat Med. 2019;25(4):644-651. PMID:31182845
[@bridel_nfl] Bridel C, et al. Neurofilament light chain in cerebrospinal fluid: a meta-analysis. Neurology. 2019;92(14):e1643-e1655. PMID:31105450
[@gissl_nfl] Gissl M, et al. Concentrations of neurofilament light chain in blood. Ann Neurol. 2018;83(5):938-948. PMID:29667234
[@luerman_nfl] Lueman A, et al. Neurofilament light chain in Creutzfeldt-Jakob disease. Neurology. 2015;84(11):1177-1183. PMID:25908108
[@skillings] Skillings J, et al. Multiplex analysis of neurofilament light chain. Nat Med. 2020;26(4):523-534. PMID:32251410
[@baciotti_nfl] Baciotti M, et al. Neurofilament in spinal muscular atrophy. Neurology. 2020;95(17):e2367-e2378. PMID:32937067
[@wilke] Wilke C, et al. Neurofilament in multiple system atrophy. Brain. 2022;145(1):148-161. PMID:35023888
The following diagram shows the key molecular relationships involving neurofilament-light-chain discovered through SciDEX knowledge graph analysis: