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X-linked cone dystrophy caused by mutation of the red and green cone opsins

Jessica C Gardner1, Tom R Webb, Naheed Kanuga

  • 1UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK.

American Journal of Human Genetics
|June 29, 2010
PubMed

Insights

Genetic mapping identified a novel X-linked cone dystrophy (XLCOD5) linked to cone opsin gene mutations. A specific mutation causes protein misfolding, leading to progressive vision loss, distinct from other inherited retinal diseases.

Area of Science:

  • Ophthalmology and Genetics
  • Molecular Biology of Vision
  • Inherited Retinal Diseases

Background:

  • X-linked cone and cone-rod dystrophies (XLCOD/XLCORD) are progressive photoreceptor disorders.
  • Mutations in RPGR exon ORF15 are a common cause, but other genetic factors exist.
  • Previous studies excluded RPGR exon ORF15 in some XLCOD families.

Purpose of the Study:

  • To genetically map the locus for a previously unexplained form of XLCOD.
  • To identify the specific gene and mutation responsible for this XLCOD.
  • To investigate the molecular mechanism and clinical spectrum of the identified mutation.

Main Methods:

  • Genetic linkage analysis was performed to map the disease locus to Xq26.1-qter.
  • The cone opsin gene array on Xq28 was analyzed for mutations.
  • Functional studies assessed protein misfolding and endoplasmic reticulum retention; pharmacological chaperone rescue was tested.

Main Results:

  • Genetic mapping identified the XLCOD locus encompassing the cone opsin gene array.
  • A missense mutation (c.529T>C [p.W177R]) in the LW/MW opsin gene, resulting from gene conversion, segregated with the disease.
  • This mutation causes protein misfolding and ER retention, not rescued by 9-cis-retinal, leading to XLCOD5.

Conclusions:

  • Mutations in the LW/MW cone opsin gene array are a cause of X-linked cone dystrophy (XLCOD5).
  • The W177R mutation leads to protein misfolding and progressive photoreceptor dysfunction.
  • This expands the spectrum of cone opsin gene mutations causing inherited retinal diseases, from color blindness to severe dystrophy.

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