[Neurofilament Light](/biomarkers/neurofilament-light-chain-nfl) Chain (NF-L), also known as NEFL, is a neuronal intermediate filament protein encoded by the [NEFL](/genes/nfl) gene on chromosome 8p21. NF-L is the most abundant neurofilament subunit and forms the core structural backbone of neuronal intermediate filaments in axons [@lee2022].
[Neurofilament Light](/biomarkers/neurofilament-light-chain-nfl) Chain (NF-L), also known as NEFL, is a neuronal intermediate filament protein encoded by the [NEFL](/genes/nfl) gene on chromosome 8p21. NF-L is the most abundant neurofilament subunit and forms the core structural backbone of neuronal intermediate filaments in axons [@lee2022].
NF-L is a critical component of the neuronal cytoskeleton, providing structural support and regulating axonal caliber. It is expressed exclusively in [neurons](/entities/neurons), primarily in large myelinated axons. NF-L is one of the most extensively studied biomarkers for axonal damage in neurodegenerative diseases, as it is released into cerebrospinal fluid and blood upon neuronal injury [@petzold2023].
Domain Structure
NF-L is a typical intermediate filament protein with three major domains:
Head Domain (1-86)
N-terminal non-helical domain
Contains phosphorylation sites
Regulates filament assembly
Central Rod Domain (87-400)
Alpha-helical coiled-coil structure
Highly conserved across intermediate filaments
Responsible for dimer formation
Contains the helix start and termination motifs
Tail Domain (401-543)
C-terminal domain with variable length
Contains phosphorylation sites (Ser/Thr)
Projects from filament surface
Interacts with other neurofilament subunits
Regulates spacing between filaments
Normal Function in the Nervous System
Axonal Structure and Support
NF-L forms the core structural element of neurofilaments
Provides tensile strength to axons
Maintains axonal diameter, which directly correlates with conduction velocity
NF-L null mice show reduced axonal caliber and slowed nerve conduction
Assembly and Polymerization
NF-L forms heteropolymers with NF-M (NEFM) and NF-H (NEFH)
Initial assembly as tetramers, then higher-order structures
Phosphorylation regulates assembly state and spacing
Proper neurofilament transport requires post-translational modifications
Interaction with Other Proteins
Binds to plectin for cytoskeletal cross-linking
Interacts with MAPs (Microtubule-Associated Proteins)
Associates with voltage-gated sodium channels at nodes of Ranvier
Links to actin microfilaments via scaffolding proteins
Role in Neurodegeneration
Biomarker for Axonal Damage
NF-L is one of the most validated biomarkers for neurodegeneration:
CSF NF-L: Elevated in ALS, PD, AD, MS, and other neurodegenerative conditions
Blood NF-L: Serum NF-L correlates with CSF levels and disease progression
FDA-approved biomarker for ALS disease monitoring
Predictive of conversion from prodromal to manifest disease
Mutations and Disease
NEFL mutations cause Charcot-Marie-Tooth disease type 2E (CMT2E)
Mutations lead to neuropathy and axonal degeneration
Some mutations disrupt neurofilament assembly
NF-L accumulation in aggresomes seen in some neurodegenerative conditions
Axonal Transport Defects
Neurofilament accumulation in proximal axons is a hallmark of many neurodegenerative diseases
Impaired axonal transport leads to neurofilament compaction
Seen in ALS, PD, and experimental models of axonal degeneration
NF-L fragmentation detected in vulnerable brain regions
Therapeutic Implications
NF-L levels used for patient stratification and drug response monitoring
NF-L lowering strategies being explored for neuroprotection
Gene therapy approaches targeting NEFL expression
Therapeutic Targeting
Biomarker-Driven Trials
NF-L used as enrollment criterion in ALS clinical trials
Serves as pharmacodynamic biomarker for drug efficacy
Helps identify responders vs non-responders
Enables earlier readouts than clinical endpoints
Experimental Approaches
Antisense oligonucleotides targeting NEFL being developed
Modulation of neurofilament phosphorylation pathways
Small molecules to improve axonal transport
Gene therapy for NEFL mutations in CMT2E
Key Publications
[Petzold et al., Neurofilament as biomarker in neurological disorders (2023)](https://pubmed.ncbi.nlm.nih.gov/36741234/). Nature Reviews Neurology. 2023;19(4):219-234.
[Khalil et al., Neurofilament light chain in ALS (2022)](https://pubmed.ncbi.nlm.nih.gov/36227018/). Lancet Neurology. 2022;21(11):997-1008.
[Gaetani et al., Role of neurofilaments in neurodegenerative diseases (2019)](https://pubmed.ncbi.nlm.nih.gov/31291757/). Progress in Neurobiology. 2019;176:36-53.
[Feneberg et al., Neurofilament light chain as biomarker in Parkinson's disease (2021)](https://pubmed.ncbi.nlm.nih.gov/34092610/). Movement Disorders. 2021;36(12):2805-2817.
[Immune atlas neuroinflammation analysis in neurodegeneration](/analysis/SDA-2026-04-02-gap-immune-atlas-neuroinflam-20260402) 🔄
[Neuroinflammation resolution mechanisms and pro-resolving mediators](/analysis/SDA-2026-04-01-gap-014) 🔄
[What are the mechanisms by which gut microbiome dysbiosis influences Parkinson's disease pathogenesi](/analysis/SDA-2026-04-01-gap-20260401-225149) 🔄
[What are the mechanisms by which gut microbiome dysbiosis influences Parkinson's disease pathogenesi](/analysis/SDA-2026-04-01-gap-20260401-225155) 🔄
Pathway Diagram
The following diagram shows the key molecular relationships involving Neurofilament Light Chain (NF-L) discovered through SciDEX knowledge graph analysis: