Spinocerebellar ataxia type 7 (SCA7) shows a cone-rod dystrophy phenotype

Exp Eye Res. 2002 Jun;74(6):737-45. doi: 10.1006/exer.2002.1169.


Autosomal dominant spinocerebellar ataxia 7 is associated with retinal degeneration. SCA7, the causative gene, encodes ataxin-7, a ubiquitous 892 amino acid protein of variable sub-cellular localization, and the disease is due to expansion of an unstable CAG repeat in the coding region of the gene. Recent increases in understanding of the mechanisms ofSCA7 -related retinopathy from in vitro and murine model studies prompted us to perform a detailed study of the retinal phenotype of affected members of a family with SCA7 mutation (45-47 CAG repeats). There was a spectrum of severity from mild to severe dysfunction. Early functional abnormalities were at both photoreceptor and post-receptoral levels. When cone and rod photoreceptor dysfunction was present, it was approximately equal. Regional retinal dysfunction was evident: there was more dysfunction centrally than peripherally with least effect in the midperiphery. In vivo cross-sectional retinal images with optical coherence tomography showed an early disease stage of altered foveal lamination (abnormal area of low reflectivity splitting the outer retina-choroidal complex) accompanied in the parafovea by reduced retinal thickness. Later disease stages showed foveal and parafoveal retinal thinning. The phenotype in this family with SCA7 is that of a cone-rod dystrophy. These observations increase interest in a recent hypothesis that ataxin-7 may interfere with the function of CRX (cone-rod homeobox), a transcription factor regulating photoreceptor genes and a cause of a cone-rod dystrophy phenotype in man.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Aged
  • Ataxin-7
  • Electroretinography
  • Female
  • Humans
  • Male
  • Middle Aged
  • Mutation*
  • Nerve Tissue Proteins / genetics*
  • Pedigree
  • Phenotype
  • Retinal Cone Photoreceptor Cells / physiopathology
  • Retinal Degeneration / etiology*
  • Retinal Degeneration / genetics
  • Retinal Degeneration / physiopathology
  • Retinal Rod Photoreceptor Cells / physiopathology
  • Spinocerebellar Ataxias / complications*
  • Spinocerebellar Ataxias / genetics
  • Spinocerebellar Ataxias / physiopathology
  • Visual Field Tests
  • Visual Fields


  • ATXN7 protein, human
  • Ataxin-7
  • Nerve Tissue Proteins