Ataxin

any of a group of proteins (of no known function) that contain glutamine repeats that expand in various forms of spinocerebellar ataxia (SCA). The gene for ataxin-1 (at 6p23) encodes a polypeptide of 792 — 830 amino acids depending on the length (6 — 44 residues) of the repeat. Ataxin-1 is predominant in neuronal nuclei but also occurs in the cytoplasm in other tissues. The repeat length expands to 39 — 82 residues in SCA 1. Ataxin-2 (≈140 kDa) is encoded by a gene at 12q24. It has a tissue distribution similar to that of ataxin-1. Its wild-type repeat of 15 — 32 residues expands to 36 — 63 in SCA 2. Ataxin-3 (locus at 14q24.3 — q31) has a wild-type repeat of 17 — 41 residues, which expands to 62 — 84 residues in SCA 3 (or Machado — Joseph disease). Ataxin-7 (locus at 3p12 — p13) is expressed ubiquitously but especially in the cerebellum, and is present in nuclei. The wild-type repeat of 4 — 35 residues expands to 37 — 306 in SCA 7. Ataxins-4, -5, -6, -8, -9, and -10 have different chromosomal loci and their repeat lengths also expand in the respective types of SCA.

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