ATXN2
Chr 12ADMultiataxin 2
Also known as: ATX2, SCA2, TNRC13
Spinocerebellar ataxia type 2 is caused by an expanded CAG repeat in ATXN2: 31 or fewer is normal, 33–34 reduced penetrance, and 37 or more pathogenic. Shorter intermediate lengths — about 30–33 in European studies — do not cause ataxia but raise the risk of ALS. CAA interruptions stabilise the repeat and are linked to a parkinsonism presentation.
Primary Disease Associations & Inheritance
Clinical highlights
SCA2 and ALS risk: a CAG repeat in ATXN2
CAG repeat in exon 1 (a polyglutamine tract) — the cause of spinocerebellar ataxia type 2 (SCA2), and a risk factor for ALS. What matters is the number of repeats.
- Normal · ≤31 for SCA2 — but see the ALS note
- Borderline · 33–34 reduced penetrance (late-onset ataxia possible); 32 and 35–36 are not assigned by the sources
- Pathogenic · ≥37 — SCA2
Intermediate lengths below the SCA2 range — about 30–33 repeats in European studies (27–33 in the first report) — raise the risk of ALS rather than cause ataxia; the lower cut-off differs between populations.
CAA interruptions stabilise the repeat; interrupted expansions lean towards a parkinsonism presentation.
Testing: Sequencing does not size this repeat; order the SCA2 repeat test. In ALS the same test reports the intermediate range.
Sources: ACMG points to consider 2026 (Table 1); Saucier, Neurol Genet 2026; Elden, Nature 2010; Wang meta-analysis 2014.
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
External Resources
Links to major genomics databases and tools