ATXN3
Chr 14ADMultiataxin 3
Also known as: AT3, ATX3, JOS, MJD, MJD1, SCA3
Spinocerebellar ataxia type 3 (Machado–Joseph disease) is caused by an expanded CAG repeat in ATXN3: 44 or fewer is normal, 45–59 intermediate and rarely seen, and about 60–87 pathogenic, with some laboratories using 52. No disease-modifying treatment is approved.
Primary Disease Associations & Inheritance
Clinical highlights
- Definitive · Machado-Joseph disease · AD · Laboratory for Molecular Medicine
- Supportive · Machado-Joseph disease type 1 · AD · Orphanet
- Supportive · Machado-Joseph disease type 2 · AD · Orphanet
- Supportive · Machado-Joseph disease type 3 · AD · Orphanet
SCA3 (Machado–Joseph disease): a CAG repeat in ATXN3
CAG repeat in exon 10 (a polyglutamine tract) — the cause of spinocerebellar ataxia type 3 / Machado–Joseph disease. What matters is the number of repeats.
- Normal · ≤44
- Intermediate · 45–59 — unstable, incomplete penetrance; rarely seen
- Pathogenic · about 60–87 (some laboratories call 52 or more pathogenic)
In a UK series of 6,596 alleles no intermediate allele (41–57) was seen, and expanded alleles ran from 58 to 91 — so the boundaries differ slightly between sources.
Testing: Sequencing does not size this repeat; order the SCA3 repeat test.
Sources: ACMG points to consider 2026 (Table 1); Lian 2024; Nethisinghe 2025.
ClinVar Variant Classifications
0 submitted variants in ClinVar
External Resources
Links to major genomics databases and tools
Clinical Trials
Active and recruiting trials from ClinicalTrials.gov
No active trials found for this gene.
Search ClinicalTrials.gov →External Resources
Links to major genomics databases and tools