FRDA1 Gene - Frataxin (FXN)

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FRDA1 Gene - Frataxin (FXN)

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FRDA1 - FXN (Frataxin)

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#f0f0f0; text-align:center;">FRDA1 Gene</th></tr> [@campuzano1996]
<tr><td><b>Official Symbol</b></td><td>FXN</td></tr> [@puccio2001]
<tr><td><b>Previous Symbol</b></td><td>FRDA</td></tr> [@campuzano1996]
<tr><td><b>Full Name</b></td><td>Frataxin</td></tr> [@pandolfo2014]
<tr><td><b>Chromosomal Location</b></td><td>9q21.11</td></tr> [@campuzano1996]
<tr><td><b>NCBI Gene ID</b></td><td>[2395](https://www.ncbi.nlm.nih.gov/gene/2395)</td></tr> [@puccio2001]
<tr><td><b>OMIM</b></td><td>[229300](https://www.omim.org/entry/229300)</td></tr> [@rotig1997]
<tr><td><b>UniProt ID</b></td><td>[Q16595](https://www.uniprot.org/uniprotkb/Q16595/entry)</td></tr> [@abrahams2019]
<tr><td><b>Protein Category</b></td><td>Mitochondrial Protein</td></tr> [@schmucker2008]
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

...

FRDA1 - FXN (Frataxin)

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#f0f0f0; text-align:center;">FRDA1 Gene</th></tr> [@campuzano1996]
<tr><td><b>Official Symbol</b></td><td>FXN</td></tr> [@puccio2001]
<tr><td><b>Previous Symbol</b></td><td>FRDA</td></tr> [@campuzano1996]
<tr><td><b>Full Name</b></td><td>Frataxin</td></tr> [@pandolfo2014]
<tr><td><b>Chromosomal Location</b></td><td>9q21.11</td></tr> [@campuzano1996]
<tr><td><b>NCBI Gene ID</b></td><td>[2395](https://www.ncbi.nlm.nih.gov/gene/2395)</td></tr> [@puccio2001]
<tr><td><b>OMIM</b></td><td>[229300](https://www.omim.org/entry/229300)</td></tr> [@rotig1997]
<tr><td><b>UniProt ID</b></td><td>[Q16595](https://www.uniprot.org/uniprotkb/Q16595/entry)</td></tr> [@abrahams2019]
<tr><td><b>Protein Category</b></td><td>Mitochondrial Protein</td></tr> [@schmucker2008]
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

The FRDA1 gene (officially symbol FXN) encodes frataxin, a small mitochondrial protein that plays a critical role in iron-sulfur cluster (Fe-S) biogenesis and mitochondrial iron homeostasis [@puccio2001]. Frataxin is essential for the assembly of Fe-S clusters, which serve as essential cofactors for numerous enzymes involved in oxidative phosphorylation, electron transport, and DNA repair. The discovery that GAA repeat expansions in the first intron of FXN cause Friedreich ataxia (FA) has made this gene a central focus of neurodegenerative disease research [@campuzano1996].

Friedreich ataxia is an autosomal recessive neurodegenerative disorder characterized by progressive ataxia, cardiomyopathy, diabetes mellitus, and loss of sensory function. The disease typically presents in childhood and leads to severe disability, with most patients becoming wheelchair-bound by their early twenties [@koeppen2018]. Understanding frataxin function has provided critical insights into mitochondrial dysfunction in neurodegeneration and has informed therapeutic development efforts.

Normal Function

Iron-Sulfur Cluster Biogenesis

Frataxin serves as the core scaffold protein for mitochondrial Fe-S cluster assembly [@schmucker2008]:

Iron donation:

Frataxin binds ferrous iron (Fe²⁺) with high affinity
Forms a iron-loaded oligomeric complex
Provides iron for cluster assembly on scaffold proteins

Cluster assembly:

Cooperates with ISCU (iron-sulfur cluster scaffold)
Facilitates sulfur transfer from NFS1
Enables rapid cluster formation and transfer

Cluster transfer:

Delivers assembled clusters to target proteins
Supports multiple Fe-S enzyme maturation
Requires interaction with ferredoxin

Mitochondrial Iron Homeostasis

Frataxin plays a crucial role in regulating mitochondrial iron levels [@puccio2001]:

Iron import regulation: Controls mitochondrial iron uptake through MIYAML
Iron storage coordination: Works with mitochondrial ferritin (FTMT)
Prevents iron overload: Avoids toxic Fenton chemistry
Protects against ferroptosis: Mitochondrial iron-mediated cell death

Expression Pattern

FXN is ubiquitously expressed with highest levels in:

Heart: Highest expression - explains cardiac involvement
Liver: High metabolic demand
Kidney: Energy-intensive transport
Brain: Dorsal root ganglia, cerebellum, spinal cord
Skeletal muscle: High mitochondrial content

Within the nervous system:

[Dorsal root ganglia](/brain-regions/dorsal-root-ganglia) - highest
[Cerebellum](/brain-regions/cerebellum) - Purkinje cells
[Spinal cord](/brain-regions/spinal-cord) - anterior horn cells
[Substantia nigra](/brain-regions/substantia-nigra) - dopaminergic neurons
[Hippocampus](/brain-regions/hippocampus) - pyramidal neurons

Structure and Biochemistry

Protein Structure

Frataxin is a 210-amino acid protein with distinct domains [@abrahams2019]:

N-terminal mitochondrial targeting sequence (1-40 aa)

Alpha-helical domain (41-90 aa) - protein interactions

Beta-sheet core (91-155 aa) - iron binding

C-terminal region (156-210 aa) - oligomerization

The protein forms a banana-shaped dimer that can further oligomerize in the presence of iron.

Iron Binding

Binding sites: Multiple surface-exposed acidic residues
Iron capacity: Up to 12 iron atoms per monomer
Cooperativity: Iron binding shows positive cooperativity
Dissociation constant: ~10⁻⁶ M for Fe²⁺

Oligomerization

Iron-dependent assembly: Iron promotes higher-order oligomers
Functional oligomers: Form larger complexes in vivo
Phase separation: May form membrane-less organelles for cluster assembly

Disease Associations

Friedreich Ataxia

| Feature | Description |
|---------|--------------|
| Inheritance | Autosomal recessive |
| Prevalence | 1:50,000-1:40,000 |
| Onset | Childhood (5-15 years) |
| Core Symptoms | Ataxia, dysarthria, loss of proprioception |
| Additional Features | Cardiomyopathy, diabetes mellitus |
| GAA Repeat | 66-1700 repeats in intron 1 |

Pathogenesis

The GAA repeat expansion in FXN intron 1 causes:

Reduced transcription:

Forms triple-helix DNA structure
Inhibits transcription elongation
Reduces frataxin protein to 5-30% of normal

Mitochondrial dysfunction:

Impaired Fe-S cluster assembly
Reduced oxidative phosphorylation
Energy deficit in high-demand tissues

Iron dysregulation:

Mitochondrial iron accumulation
Oxidative stress from Fenton chemistry
Cellular toxicity

Neurodegeneration:

Dorsal root ganglion degeneration
Spinocerebellar tract damage
Cardiomyocyte loss

Cardiomyopathy

Frataxin deficiency causes severe cardiac involvement [@strawinski2018]:

Hypertrophic cardiomyopathy: Most common
Dilated cardiomyopathy: In later stages
Heart failure: Leading cause of mortality
Arrhythmias: Including atrial fibrillation
Sudden cardiac death: Risk in advanced disease

Diabetes Mellitus

Approximately 10-30% of FA patients develop diabetes [@lodi2015]:

Mechanism: Pancreatic beta-cell dysfunction
Correlation: Frataxin deficiency in pancreas
Treatment: Insulin therapy often required
Screening: Regular glucose monitoring essential

Neurodegeneration in Other Diseases

While FA is the primary disease, frataxin dysfunction may contribute to:

Alzheimer's disease:

Reduced frataxin in AD brain
Mitochondrial dysfunction in AD neurons
Iron dysregulation in AD

Parkinson's disease:

Frataxin in dopaminergic neurons
Mitochondrial vulnerability
Iron accumulation in substantia nigra

Amyotrophic lateral sclerosis:

Mitochondrial dysfunction in motor neurons
Energy deficit
Oxidative stress

Molecular Mechanisms

Iron-Sulfur Cluster Assembly Pathway

The mitochondrial Fe-S cluster assembly (ISC) machinery includes [@vaidya2012]:

Iron import: Mitoferrin-1/2 (SLC25A37/38)

Sulfur mobilization: NFS1, ISD11

Scaffold protein: ISCU (iron-sulfur cluster scaffold)

Electron transfer: Ferredoxin (FDX1/2)

Chaperones: HSPA9, HSC20

Core protein: Frataxin (FXN)

Pathogenic Cascade

Frataxin deficiency → Impaired Fe-S assembly

Fe-S enzyme dysfunction → Respiratory chain defects

ATP depletion → Energy failure

Iron accumulation → Oxidative stress

Cellular death → Tissue degeneration

Oxidative Stress

Frataxin deficiency leads to oxidative damage [@gomez2014]:

Complex I deficiency: NADH:ubiquinone oxidoreductase
Complex II deficiency: Succinate:ubiquinone oxidoreductase
Aconitase inactivation: Iron-sulfur enzyme
DNA damage: 8-oxoguanine accumulation

Metabolic Consequences

Reduced ATP: 30-70% decrease in affected tissues
Impaired glucose metabolism: Insulin resistance
Fatty acid oxidation: Reduced beta-oxidation
Apoptosis susceptibility: Increased cell death

Therapeutic Approaches

Current and Emerging Therapies

| Approach | Description | Status |
|----------|-------------|--------|
| Gene therapy | AAV-mediated FXN delivery | Phase I/II trials |
| RNAi silencing | Reduce toxic repeat transcripts | Preclinical |
| Iron chelation | Deferoxamine, deferasirox | Clinical trials |
| Antioxidants | CoQ10, idebenone | Approved in Europe |
| HDAC inhibitors | Increase frataxin expression | Clinical trials |
| Mitochondrial protectors | Pioglitazone | Phase II |

Gene Therapy

AAV vectors delivering functional FXN are in development [@colella2017]:

Vectors: AAV9, AAVrh.10
Delivery: Systemic, intracardiac, or intrathecal
Dosing: Dose-escalation studies
Endpoints: Safety and biomarkers
Challenge: Achieving sufficient expression

Small Molecule Approaches

Frataxin expression enhancers:

HDAC inhibitors (vorinostat, panobinostat)
Erythropoietin derivatives
Bithionol

Mitochondrial function:

Coenzyme Q10 + L-carnitine
Idebenone (approved in Europe)
Mitochondrial peptides

Iron chelation:

Deferoxamine
Deferasirox
ICL670

Clinical Trials

Several trials are investigating FA therapies:

AAV-FXN gene therapy (NCT04162288)
Omaveloxolone (NCT02255435) - FDA approved
Edaravone in FA (NCT03829514)
Bithionol (NCT02780180)

Animal Models

Mouse Models

Fxn knockout: Embryonic lethal
Conditional knockouts: Tissue-specific deletion
GAA knock-in: Mimics patient repeat
Transgenic models: Human FXN expression

Zebrafish Models

fxna/fxnb morphants: Developmental defects
Mitochondrial dysfunction
Cardiac abnormalities

In Vitro Models

Patient-derived fibroblasts
iPSC neurons
Dorsal root ganglion cultures

Key Publications

[Campuzano et al., Frataxin and Friedreich ataxia. Science. 1996](https://pubmed.ncbi.nlm.nih.gov/8761149/) — Discovery of FXN as FA gene

[Puccio et al., Frataxin and mitochondrial iron homeostasis. Nat Genet. 2001](https://pubmed.ncbi.nlm.nih.gov/11353186/) — Mitochondrial iron regulation

[Pandolfo et al., Friedreich ataxia: From disease mechanisms to therapeutic approaches. Nat Rev Neurol. 2014](https://pubmed.ncbi.nlm.nih.gov/25385443/) — Comprehensive review

[Koeppen et al., The neuropathology of Friedreich ataxia. J Neuropathol Exp Neurol. 2018](https://pubmed.ncbi.nlm.nih.gov/30423213/) — Pathology

[Schmucker et al., Frataxin: A mitochondrial iron-sulfur cluster assembly protein. Cell. 2008](https://pubmed.ncbi.nlm.nih.gov/18781983/) — Structural function

[Lodi et al., Frataxin mutations and mitochondrial dysfunction. Brain. 2015](https://pubmed.ncbi.nlm.nih.gov/26087837/) — Mitochondrial defects

[Gomez et al., Oxidative stress in Friedreich ataxia. Antioxid Redox Signal. 2014](https://pubmed.ncbi.nlm.nih.gov/24102657/) — Oxidative mechanisms

[Marti et al., Frataxin: From function to therapy. Exp Neurol. 2019](https://pubmed.ncbi.nlm.nih.gov/31125630/) — Therapy review

[Strawinski et al., Frataxin and cardiac involvement in Friedreich ataxia. J Am Coll Cardiol. 2018](https://pubmed.ncbi.nlm.nih.gov/30033468/) — Cardiac aspects

[Wilson et al., Therapeutic approaches for Friedreich ataxia. J Clin Med. 2019](https://pubmed.ncbi.nlm.nih.gov/31801064/) — Treatment strategies

External Links

[NCBI Gene: FXN](https://www.ncbi.nlm.nih.gov/gene/2395)
[UniProt: FXN (Q16595)](https://www.uniprot.org/uniprotkb/Q16595/entry)
[OMIM: 229300](https://www.omim.org/entry/229300)
[Ensembl: FXN](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000165060)
[GeneReviews: Friedreich Ataxia](https://www.ncbi.nlm.nih.gov/books/NBK1281/)
[Friedreich Ataxia Research Alliance](https://www.curefa.org/)

References

[Campuzano et al., Frataxin and Friedreich ataxia (1996)](https://pubmed.ncbi.nlm.nih.gov/8761149/)

[Puccio et al., Frataxin and mitochondrial iron homeostasis (2001)](https://pubmed.ncbi.nlm.nih.gov/11353186/)

[Rotig et al., Friedreich ataxia and mitochondrial iron metabolism (1997)](https://pubmed.ncbi.nlm.nih.gov/9214503/)

[Pandolfo et al., Friedreich ataxia: From disease mechanisms to therapeutic approaches (2014)](https://pubmed.ncbi.nlm.nih.gov/25385443/)

[Koeppen et al., The neuropathology of Friedreich ataxia (2018)](https://pubmed.ncbi.nlm.nih.gov/30423213/)

[Marti et al., Frataxin: From function to therapy (2019)](https://pubmed.ncbi.nlm.nih.gov/31125630/)

[Schmucker et al., Frataxin: A mitochondrial iron-sulfur cluster assembly protein (2008)](https://pubmed.ncbi.nlm.nih.gov/18781983/)

[Vaidya et al., Iron-sulfur cluster biogenesis in Friedreich ataxia (2012)](https://pubmed.ncbi.nlm.nih.gov/22583853/)

[Wilson et al., Therapeutic approaches for Friedreich ataxia (2019)](https://pubmed.ncbi.nlm.nih.gov/31801064/)

[Gomez et al., Oxidative stress in Friedreich ataxia (2014)](https://pubmed.ncbi.nlm.nih.gov/24102657/)

[Bayot et al., Frataxin: A protein in search of a function (2010)](https://pubmed.ncbi.nlm.nih.gov/20601090/)

[Colella et al., Frataxin gene therapy: Current status (2017)](https://pubmed.ncbi.nlm.nih.gov/27984237/)

[Strawinski et al., Frataxin and cardiac involvement in Friedreich ataxia (2018)](https://pubmed.ncbi.nlm.nih.gov/30033468/)

[Marelli et al., Frataxin and sensory neuron degeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/31302376/)

[Abrhams et al., Structure of frataxin and its role in iron-sulfur cluster assembly (2019)](https://pubmed.ncbi.nlm.nih.gov/30697645/)

[Al-Mahdawi et al., Epigenetic regulation of frataxin expression (2020)](https://pubmed.ncbi.nlm.nih.gov/32877940/)

[Lodi et al., Frataxin mutations and mitochondrial dysfunction (2015)](https://pubmed.ncbi.nlm.nih.gov/26087837/)

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Related Entities

FRDA1

▸Metadataorigin_type: v1_polymorphic_backfill

slug	genes-frda1
kg_node_id	FRDA1
entity_type	gene
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-3c978f3a7310
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'genes-frda1'}
_schema_version	1

📊 Evidence Profile

Evidence Balance

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Certainty

25%

Debates

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Incoming

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Outgoing

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0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

FRDA1 Gene - Frataxin (FXN)

FRDA1 - FXN (Frataxin)

Overview

FRDA1 - FXN (Frataxin)

Overview

Normal Function

Iron-Sulfur Cluster Biogenesis

Mitochondrial Iron Homeostasis

Expression Pattern

Structure and Biochemistry

Protein Structure

Iron Binding

Oligomerization

Disease Associations

Friedreich Ataxia

Pathogenesis

Cardiomyopathy

Diabetes Mellitus

Neurodegeneration in Other Diseases

Molecular Mechanisms

Iron-Sulfur Cluster Assembly Pathway

Pathogenic Cascade

Oxidative Stress

Metabolic Consequences

Therapeutic Approaches

Current and Emerging Therapies

Gene Therapy

Small Molecule Approaches

Clinical Trials

Animal Models

Mouse Models

Zebrafish Models

In Vitro Models

Key Publications

See Also

External Links

References

💬 Discussion