ATXN1 — Ataxin 1

ATXN1 — Ataxin 1

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">ATXN1 — Ataxin 1</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>ATXN1</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Ataxin 1</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>6p22.3</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/6310" target="_blank">6310</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000124788" target="_blank">ENSG00000124788</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/601556" target="_blank">601556</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P54253" target="_blank">P54253</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>[Spinocerebellar Ataxia Type 1](/diseases/spinocerebellar-ataxias)</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Purkinje cells, Cerebellum, Brainstem</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Mutations</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">CAG repeat expansion (>39 repeats pathogenic)</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ataxia" style="color:#ef9a9a">Ataxia</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodegeneration</a></td>
</tr>
<tr>
<td cla

ATXN1 — Ataxin 1

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">ATXN1 — Ataxin 1</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>ATXN1</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Ataxin 1</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>6p22.3</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/6310" target="_blank">6310</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000124788" target="_blank">ENSG00000124788</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/601556" target="_blank">601556</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P54253" target="_blank">P54253</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>[Spinocerebellar Ataxia Type 1](/diseases/spinocerebellar-ataxias)</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Purkinje cells, Cerebellum, Brainstem</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Mutations</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">CAG repeat expansion (>39 repeats pathogenic)</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ataxia" style="color:#ef9a9a">Ataxia</a>, <a href="/wiki/neurodegeneration" style="color:#ef9a9a">Neurodegeneration</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">8 edges</a></td>
</tr>
</table>

ATXN1 — Ataxin 1

Introduction

Atxn1 — Ataxin 1 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Overview

Ataxin 1 (ATXN1) is a nuclear protein encoded by the ATXN1 gene on chromosome 6p22.3. It is best known for causing Spinocerebellar Ataxia Type 1 (SCA1), a progressive autosomal dominant neurodegenerative disorder characterized by cerebellar ataxia, motor dysfunction, and cognitive decline[^1]. The pathogenic mechanism involves a CAG trinucleotide repeat expansion in the coding region, resulting in an expanded polyglutamine (polyQ) tract in the mutant protein. The gene is catalogued as NCBI Gene ID [6310](https://www.ncbi.nlm.nih.gov/gene/6310) and OMIM [601556](https://omim.org/entry/601556).

Function

Normal Biological Role

Ataxin 1 is a transcriptional regulator that localizes primarily to the nucleus[^2]. Its normal functions include:

• Binds to RORα (retinoic acid-related orphan receptor alpha)
• Interacts with histone deacetylases (HDACs)
• Modulates Notch signaling

Protein Structure

Ataxin 1 is an 815-amino acid protein with several key domains[^3]:

• PolyQ tract: Normal range 6-35 glutamines; expanded to 36-130 in SCA1
• AXH domain: Ataxin-1/hesx1 domain (residues 567-689); mediates protein-protein interactions
• Nuclear localization signal (NLS): Arg/Lys-rich sequence for nuclear import
• Phosphorylation sites: Ser776 phosphorylation is critical for toxicity

Brain Expression

• Purkinje cells: Highest expression; primary site of pathology
• Cerebellar cortex: Molecular and granular layers
• Brainstem: Olivary nuclei, pons
• Hippocampus: Lower expression
• Cerebral cortex: Regional expression

Disease Associations

Spinocerebellar Ataxia Type 1 (SCA1)

SCA1 is an autosomal dominant neurodegenerative disorder and one of the most common polyglutamine diseases[^4].

Genetics

• Inheritance: Autosomal dominant
• Mutation: CAG trinucleotide repeat expansion in exon 8
• Normal range: 6-35 repeats
• Full penetrance: >41 repeats
• Intermediate range: 36-39 repeats (reduced penetrance)

Clinical Features

Cerebellar symptoms:

• Progressive gait ataxia (first symptom in ~70%)
• Limb ataxia (dysmetria, dysdiadochokinesia)
• Nystagmus (horizontal, vertical, or rotatory)
• Dysarthria (scanning speech)
• Dysphagia (swallowing difficulties)

• Parkinsonian features (bradykinesia, rigidity)
• Dystonia
• Chorea (less common)

• Oculomotor abnormalities
• Vertigo
• Respiratory dysfunction (late)

• Executive dysfunction
• Memory impairment
• Depression, anxiety
• Psychosis (rare)

• Peripheral neuropathy (less prominent than in other SCAs)
• Reduced reflexes

Disease Progression

• Age of onset: Typically 30-40 years (can be 4-70 years)
• Disease duration: 10-30 years from onset to death
• Rate of progression correlates with repeat length

Other Disease Associations

• Multiple system atrophy (MSA): Some studies show ATXN1 repeat expansions in rare cases
• SCA1-like phenotypes: ATXN1 variants may modify other ataxias

Pathogenesis

The Polyglutamine Toxicity Mechanism

The expanded polyQ tract in ataxin-1 leads to neurodegeneration through multiple interconnected mechanisms[^5]:

1. Protein Misfolding and Aggregation

• Expanded polyQ promotes abnormal protein folding
• Forms insoluble cytoplasmic and nuclear aggregates
• Sequesters essential cellular proteins
• Impairs ubiquitin-proteasome system

2. Transcriptional Dysregulation

• Alters interactions with transcriptional regulators
• Disrupts RORα-mediated gene expression
• Impairs histone acetylation/deacetylation balance
• Affects neurotrophic factor expression (BDNF)

3. Nuclear Transport Dysfunction

• Mutant ataxin-1 accumulates in the nucleus
• Alters nuclear pore function
• Impairs nuclear-cytoplasmic transport

4. Mitochondrial Dysfunction

• Reduces mitochondrial biogenesis
• Increases oxidative stress
• Impairs calcium homeostasis
• Promotes apoptosis

5. Loss of Normal Function

• The mutant protein loses normal regulatory functions
• Dominant-negative effects on wild-type ataxin-1
• Haploinsufficiency contributions

Neuropathology

• Cerebellar degeneration: Loss of Purkinje cells
• Brainstem atrophy: Inferior olivary nuclei, cranial nerve nuclei
• Spinal cord involvement: Spinocerebellar tracts
• Hippocampal pathology: Less severe than cerebellum

Diagnosis

Genetic Testing

• Gold standard: PCR-based CAG repeat sizing
• Confirmatory: Southern blot for large repeats
• Preimplantation testing: Available for family planning

Neuroimaging

• MRI: Cerebellar and brainstem atrophy
• MR spectroscopy: Reduced N-acetylaspartate in cerebellum
• Diffusion tensor imaging: White matter abnormalities

Clinical Evaluation

• Neurological examination: Standardized Ataxia Rating Scales (SARA, ICARS)
• Neuropsychological testing: Cognitive assessment
• Electrophysiology: EMG, nerve conduction studies

Treatment and Management

Current Approaches

No cure exists for SCA1. Management is symptomatic and supportive[^6]:

• Amitriptyline or gabapentin for neuropathic pain
• Clonazepam for myoclonus
• Botulinum toxin for dystonia

Emerging Therapies

Gene Silencing Approaches

| Approach | Status | Mechanism |
|----------|--------|-----------|
| ASOs | Preclinical | Target ATXN1 mRNA for degradation |
| RNAi | Preclinical | siRNA-mediated knock-down |
| CRISPR | Preclinical | allele-specific editing |

Small Molecule Therapies

• HDAC inhibitors: Vorinostat, sodium butyrate (reduce toxic aggregation)
• Autophagy inducers: Rapamycin, trehalose (enhance protein clearance)
• Neurotrophic factors: BDNF mimetics
• Antioxidants: CoQ10, vitamin E

Symptomatic Targets

• Riluzole: Modulates glutamate, some benefit in ataxias
• Varenicline: Cholinergic agonist, showed promise in SCA3
• Aminopyridines: For downbeat nystagmus

Genotype-Phenotype Correlations

| Repeat Length | Age of Onset | Progression | Phenotype |
|--------------|--------------|-------------|------------|
| 36-39 | ~40-50 years | Slow | Mild |
| 40-50 | ~30-40 years | Moderate | Classic SCA1 |
| 51-70 | ~20-30 years | Rapid | Early-onset severe |
| >70 | <20 years | Very rapid | Juvenile onset |

Key Publications

External Links

• NCBI Gene: [https://www.ncbi.nlm.nih.gov/gene/6310](https://www.ncbi.nlm.nih.gov/gene/6310)
• Ensembl: [https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000124788](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000124788)
• OMIM: [https://omim.org/entry/601556](https://omim.org/entry/601556)
• UniProt: [https://www.uniprot.org/uniprot/P54253](https://www.uniprot.org/uniprot/P54253)
• Allen Human Brain Atlas: [ATXN1 expression](https://human.brain-map.org/microarray/search/show?search_term=ATXN1)
• Spinocerebellar Ataxia Type 1 Foundation: [https://ataxin1.org](https://ataxin1.org)
• spinocerebellar-ataxias
• spinocerebellar-ataxias
• polyglutamine-diseases
• [neurons](/cell-types/neurons)
• [Genes Index
• [Proteins Index](/proteins) [--

Background

The study of Atxn1 — Ataxin 1 has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

Brain Atlas Resources

• [Allen Human Brain Brain Atlas - ATXN1 Expression](https://human.brain-map.org/microarray/search/show?search_term=ATXN1)
• [Allen Cell Type Atlas](https://celltypes.brain-map.org/)
• [BrainSpan Transcriptome Atlas](https://brainspan.org/)
• [Allen Mouse Brain Atlas](https://mouse.brain-map.org/)

Pathway Diagram

Disease Mechanism Summary

| GBA Variant | Enzyme Activity | PD Risk | Clinical Features |
|-------------|-----------------|---------|-------------------|
| N370S | 30-40% | 2-3x increased | Typical PD |
| L444P | <10% | 5x increased | Earlier onset |
| Recombinant | Variable | Variable | Severe |

References