FXN Gene (Frataxin)
Overview
<div class="infobox infobox-gene">
<h3>FXN</h3>
<table>
<tr><th>Symbol</th><td>FXN</td></tr>
<tr><th>Full Name</th><td>Frataxin</td></tr>
<tr><th>Chromosomal Location</th><td>9q13</td></tr>
<tr><th>NCBI Gene ID</th><td>[2321](https://www.ncbi.nlm.nih.gov/gene/2321)</td></tr>
<tr><th>OMIM</th><td>[229300](https://www.omim.org/entry/229300)</td></tr>
<tr><th>Ensembl ID</th><td>[ENSG00000165060](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000165060)</td></tr>
<tr><th>UniProt</th><td>[Q16595](https://www.uniprot.org/uniprot/Q16595)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ataxia" style="color:#ef9a9a">Ataxia</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">4 edges</a></td>
</tr>
</table>
</div>
FXN (Frataxin) encodes a small mitochondrial protein that plays a critical role in [iron-sulfur cluster](/proteins/iron-sulfur-cluster) (Fe-S) biogenesis, mitochondrial energy production, and cellular iron homeostasis. Frataxin is essential for the function of [mitochondrial electron transport chain](/mechanisms/mitochondrial-electron-transport-chain) complexes I, II, and III, as well as [aconitase](/proteins/aconitase) in the Krebs cycle[@lill2012].
...FXN Gene (Frataxin)
Overview
<div class="infobox infobox-gene">
<h3>FXN</h3>
<table>
<tr><th>Symbol</th><td>FXN</td></tr>
<tr><th>Full Name</th><td>Frataxin</td></tr>
<tr><th>Chromosomal Location</th><td>9q13</td></tr>
<tr><th>NCBI Gene ID</th><td>[2321](https://www.ncbi.nlm.nih.gov/gene/2321)</td></tr>
<tr><th>OMIM</th><td>[229300](https://www.omim.org/entry/229300)</td></tr>
<tr><th>Ensembl ID</th><td>[ENSG00000165060](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000165060)</td></tr>
<tr><th>UniProt</th><td>[Q16595](https://www.uniprot.org/uniprot/Q16595)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ataxia" style="color:#ef9a9a">Ataxia</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">4 edges</a></td>
</tr>
</table>
</div>
FXN (Frataxin) encodes a small mitochondrial protein that plays a critical role in [iron-sulfur cluster](/proteins/iron-sulfur-cluster) (Fe-S) biogenesis, mitochondrial energy production, and cellular iron homeostasis. Frataxin is essential for the function of [mitochondrial electron transport chain](/mechanisms/mitochondrial-electron-transport-chain) complexes I, II, and III, as well as [aconitase](/proteins/aconitase) in the Krebs cycle[@lill2012].
Deficiency of frataxin, most commonly caused by GAA triplet repeat expansions in the first intron of the FXN gene, causes [Friedreich's ataxia](/diseases/friedreichs-ataxia) (FRDA), an autosomal recessive neurodegenerative disorder. Additionally, frataxin dysfunction has been implicated in other neurodegenerative conditions including [Alzheimer's Disease](/diseases/alzheimers-disease) and [Parkinson's Disease](/diseases/parkinsons-disease), making it an important protein for understanding mitochondrial contributions to neurodegeneration more broadly.
Protein Structure and Function
Domain Architecture
Frataxin is a small, highly conserved mitochondrial protein:
- Precursor: ~210 amino acids
- Mature form: ~130 amino acids after processing
- Molecular weight: ~14 kDa (precursor), ~8 kDa (mature)
The protein has a unique α/β fold:
- N-terminal helix: Mitochondrial targeting sequence (cleaved)
- α-helical domain: Forms the core structure
- β-sheet domain: Contains the iron-binding surface
Iron-Binding and Storage
Frataxin can bind multiple iron atoms:
- Iron-binding sites: Acidic residues on the protein surface
- Ferroxidase activity: Can oxidize Fe²⁺ to Fe³⁺
- Iron storage: Forms a ferric phosphate core (similar to ferritin)
This iron-binding capacity allows frataxin to:
- Deliver iron to Fe-S cluster assembly machinery
- Buffer excess mitochondrial iron
- Prevent iron-catalyzed ROS generation
Role in Iron-Sulfur Cluster Assembly
Frataxin is a central player in the mitochondrial Fe-S cluster (ISC) assembly pathway[@puccio2009]:
Iron delivery: Frataxin transfers iron to the scaffold proteins (ISU2, ISU3)
Electron donor: Provides electrons for Fe-S cluster formation
Cluster transfer: Facilitates transfer of assembled clusters to target proteinsThe ISC machinery produces Fe-S clusters for:
- Mitochondrial enzymes (complexes I-III, aconitase)
- Cytosolic enzymes (DNA polymerases, radicals)
- Extramitochondrial Fe-S proteins
Role in Friedreich's Ataxia
Genetics
Friedreich's ataxia is caused by:
- GAA repeat expansions: In the first intron of FXN (95% of cases)
- Point mutations: In the FXN coding region (5% of cases)
- Autosomal recessive inheritance: Both alleles affected
The GAA repeat:
- Normal: 5-33 repeats
- Intermediate: 34-66 repeats (carrier risk)
- Affected: 66-1,700+ repeats
Repeat length correlates with:
- Disease severity (longer = earlier onset, more severe)
- Frataxin expression levels (longer = lower expression)
Pathogenesis
Frataxin deficiency leads to multiple downstream effects[@koeppen2011]:
Mitochondrial Dysfunction:
- Reduced activity of Fe-S-containing enzymes
- Impaired electron transport chain function
- Decreased ATP production
Iron Dysregulation:
- Mitochondrial iron accumulation
- Increased cellular iron uptake
- Disrupted iron homeostasis
Oxidative Stress:
- ROS generation from mitochondrial iron
- Impaired antioxidant defenses
- Lipid peroxidation and protein oxidation
Cellular Dysfunction:
- Sensory neuron degeneration
- Cardiomyocyte dysfunction
- Diabetes (β-cell failure)
Clinical Features
Friedreich's ataxia presents in childhood with:
Ataxia: Progressive loss of coordination
- Gait instability
- Dysarthria (slurred speech)
- Dysphagia (swallowing difficulty)
Sensory Loss: Loss of proprioception and vibration sense
Cardiomyopathy: Hypertrophic cardiomyopathy (major cause of mortality)
- Heart failure
- Arrhythmias
Diabetes Mellitus: ~30% of patients develop diabetes
Other Features:
- Scoliosis
- Pes cavus
- Hearing loss
- Visual impairment
Role in Other Neurodegenerative Diseases
Alzheimer's Disease
Frataxin has several connections to [Alzheimer's Disease](/diseases/alzheimers-disease):
Mitochondrial Dysfunction: AD brains show reduced frataxin expression
Iron Dysregulation: Both FRDA and AD show mitochondrial iron accumulation
Oxidative Stress: Common pathway in both conditions
Energy Failure: Similar mitochondrial defectsParkinson's Disease
Several links between frataxin and [Parkinson's Disease](/diseases/parkinsons-disease):
Complex I Deficiency: Shared feature with PD
Iron Accumulation: PD substantia nigra shows iron deposition
Oxidative Stress: Central to both conditions
α-Synuclein: Possible interaction with frataxin pathwaysFrataxin deficiency shares features with other mitochondrial disorders:
- MERRF (Myoclonic Epilepsy with Ragged Red Fibers)
- Leigh syndrome
- Ataxia with oculomotor apraxia
Expression Patterns
Tissue Distribution
Frataxin is highly expressed in tissues with high mitochondrial content:
- Heart: Highest expression (cardiac muscle)
- Spinal cord: Motor and sensory neurons
- Dorsal root ganglia: Sensory neurons
- Cerebellum: Purkinje cells and granule cells
- Skeletal muscle: High energy demands
- Liver: Metabolic activity
Cellular Localization
Within cells:
- Mitochondrial matrix: Primary location
- Inner mitochondrial membrane: Associated with complexes
- Mitochondrial cristae: Energy production sites
Developmental Regulation
- High expression during development
- Maintained in adult tissues
- Decreased with age (may contribute to age-related neurodegeneration)
Therapeutic Approaches
Current Treatments
Idebenone (Catena): Antioxidant, approved in Europe
- Reduces oxidative stress
- May slow cardiomyopathy progression
Supportive Care:
- Physical therapy
- Cardiac management
- Diabetes treatment
Emerging Therapies
Gene Therapy:
- AAV-delivered frataxin
- Gene replacement approaches
Protein Replacement:
- Frataxin protein delivery
- Mitochondrial targeting
Small Molecules:
- Frataxin expression enhancers
- Iron chelators
- Antioxidants
Cell Therapy:
- Stem cell approaches
- Cell replacement strategies
Key Research Findings
2018-2024 Research Highlights
Mitochondrial Iron Overload: Frataxin deficiency causes iron accumulation through multiple mechanisms[@bayeva2013].
Synaptic Dysfunction: Frataxin is critical for synaptic maintenance in cerebellar neurons[@rancancoj2019].
Ubiquitin System: Frataxin deficiency disrupts the ubiquitin-proteasome system[@bruyne2018].
Therapeutic Advances: Multiple clinical trials are ongoing for new FRDA treatments.Mermaid diagram (expand to render)
Cross-Links to Related Pages
- [Friedreich's Ataxia](/diseases/friedreichs-ataxia)
- [Iron-sulfur cluster biogenesis](/mechanisms/iron-sulfur-cluster-biogenesis)
- [Mitochondrial dysfunction](/mechanisms/mitochondrial-dysfunction)
- [Mitochondrial disorders](/diseases/mitochondrial-disorders)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Iron-sulfur cluster](/proteins/iron-sulfur-cluster)
- [Mitochondria](/entities/mitochondria)
- [Aconitase](/proteins/aconitase)
- [Oxidative stress](/mechanisms/oxidative-stress)
References
[Campuzano et al., Frataxin is reduced in Friedreich's ataxia (1996)](https://doi.org/10.1093/hmg/5.12.1771)
[Pandolfo, Friedreich's ataxia: clinical features, pathogenesis and therapy (2008)](https://doi.org/10.1016/S1474-4422(08)70091-1)
[Martelli & Puccio, Frataxin: from pathology to therapeutic approaches (2014)](https://doi.org/10.1002/emmm.201303897)
[Puccio, Iron-sulfur cluster assembly and human disease (2009)](https://doi.org/10.1016/j.gde.2009.04.001)
[Rotig et al., Frataxin and mitochondrial iron homeostasis (2000)](https://doi.org/10.1172/JCI9356)
[Lodi et al., Cardiac involvement in Friedreich's ataxia (2001)](https://doi.org/10.1136/heart.86.6.687)
[Koeppen, Friedreich's ataxia: pathology, pathogenesis, and molecular genetics (2011)](https://doi.org/10.1016/j.jns.2010.09.020)
[Lill & Mühlenhoff, Mechanisms of iron-sulfur cluster assembly in mitochondria (2012)](https://doi.org/10.1146/annurev-biochem-052709-130043)
[Gakh et al., Frataxin: a mitochondrial iron chaperone (2010)](https://doi.org/10.1016/j.cmet.2010.10.014)
[Bayeva et al., Frataxin deficiency and cellular iron overload (2013)](https://doi.org/10.1016/j.cmet.2013.10.007)
[Rancancoj et al., Frataxin deficiency promotes synaptic senescence (2019)](https://doi.org/10.1523/JNEUROSCI.2048-18.2019)
[Schmucker et al., Frataxin and the Fe-S cluster assembly machinery (2011)](https://doi.org/10.1093/hmg/ddr285)
[Cook & Giunti, Therapeutic approaches to Friedreich's ataxia (2014)](https://doi.org/10.1093/bmb/ldt050)
[Straw et al., Mitochondrial dysfunction in Friedreich's ataxia (2015)](https://doi.org/10.1016/j.freeradbiomed.2015.02.009)
[Gehring et al., Frataxin mutations and mitochondrial dysfunction (2019)](https://doi.org/10.1016/j.mito.2019.04.005)
[De Bruyne et al., Frataxin deficiency and the ubiquitin-proteasome system (2018)](https://doi.org/10.1016/j.nbd.2018.04.012)External Links
- [NCBI Gene: 2321](https://www.ncbi.nlm.nih.gov/gene/2321)
- [OMIM: 229300](https://www.omim.org/entry/229300)
- [Ensembl: ENSG00000165060](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000165060)
- [UniProt: Q16595](https://www.uniprot.org/uniprot/Q16595)
- [GeneCards: FXN](https://www.genecards.org/cgi-bin/carddisp.pl?gene=FXN)
- [Friedreich's Ataxia Research Alliance (FARA)](https://www.curefa.org/)