Hereditary ataxias are genetically heterogeneous, with repeat expansions being a major cause. Over 50 disease-associated repeat loci have been identified, including coding CAG·CTG repeats (polyQ) in dominant ataxias (SCA1, 2, 3, 6, 7, 17) and non-coding expansions (e.g., FGF14, NOTCH2NLC, RAPGEF2, THAP11). Despite advances, critical gaps persist: mechanisms of repeat instability and somatic expansion; coding and non-coding pathogenesis; lack of reliable biomarkers; and no disease-modifying therapies. Emerging therapeutic avenues include antisense oligonucleotides, gene editing, and small molecules. This Special Issue focuses on repeat expansions in ataxia and neurodegenerative disease, inviting studies on novel repeat discovery, molecular mechanisms, biomarkers, and preclinical/clinical interventions. Gene & Protein in Disease (GPD) provides an ideal venue bridging genetics, pathogenesis, protein biochemistry, and therapeutics.

We invite high-quality original research and review articles on topics including, but not limited to:
· Novel genes in ataxias, especially those containing repeat expansions;
· Genetic modifiers in hereditary ataxia, especially on repeat expansions;
· Clinical trials and natural history studies in hereditary ataxias and related neurodegenerative syndromes;
· Mechanisms of repeat instability in relation to cerebellar development and cerebellar syndrome;
· Advances in coding and non‑coding repeat pathogenesis;
· Repeat expansions in overlapping neurodegenerative syndromes;
· Fluid and neuroimaging biomarkers for hereditary ataxias;
· Gene therapy and genome editing for repeat expansions and hereditary ataxias;
· Small molecule approaches for cerebellar ataxias.