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Schnyder corneal dystrophy: for professionals

Clinical phenotype

Incidence
  • Unknown
Corneal Features
  • Variable patterns of corneal opacification depending on age
  • 2nd decade of life or younger: Full-thickness central stromal haze
  • 4th decade of life and onwards: Deposition of a peripheral arcus and progressive haziness of the mid-peripheral cornea
  • May be accompanied by a central plaque of sub-epithelial cholesterol crystalline deposits (absent in 50% of cases)[1]
  • Reduced corneal sensation
Systemic association
  • Two-third of patients have hypercholesterolaemia[2]
Symptoms
  • Progressive reduction of visual acuity by the 3rd or 4th decade of life
  • Glare
There is a yellowish ring-like deposits at the outer edge of the cornea, bordering with the white of the eye. This is a cholesterol deposit. The central cornea is relatively clear.
A mild case of Schnyder corneal dystrophy with an early onset of a lipid arcus and central diffuse stromal haze. Sub-epithelial cholesterol crystals are not present in this case.

Credit: Mr Stephen Tuft, consultant ophthalmologist, Moorfields Eye Hospital, London

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Genetics

Gene (OMIM no.) and associated function
  • UBIAD1 (#611632)
  • Encodes a membrane-embedded enzyme called UbiA prenyltransferase domain-containing protein-1
  • Involved in biosynthesis of coenzyme Q10 and Vitamin K2[3]
  • Cholesterol homeostasis[3]
  • Dysfunction leads to accumulation of unesterified cholesterol and phospholipids[4]
Inheritance pattern

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Key investigations

  • Anterior segment OCT– dense and hyper-reflective organised material in the anterior stroma not involving the epithelium or Bowman layer[5]
  • Serum lipid profile
  • Serum lipids profile and plasma electrophoresis should be performed in an elderly patient with no family history as monoclonal gammopathy of unknown significance (MGUS/paraproteinemia) can present similarly with crystalline corneal deposits[6]

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Diagnosis

Schnyder corneal dystrophy can be diagnosed clinically. Genetic testing can be undertaken to confirm the diagnosis, facilitate genetic counselling, provide accurate advice on prognosis and future family planning, and aid in clinical trial participation.

This can be achieved through a variety of next generation sequencing (NGS) methods:

  • Targeted gene panels (anterior segment dysgenesis)
  • Whole exome sequencing
  • Whole genome sequencing

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Management

  • Glasses or contact lenses to correct refractive errors
  • Superficial stromal opacities can be removed by excimer laser phototherapeutic keratectomy (PTK)
  • Corneal thickness must be measured prior to PTK as it may thin the cornea
  • The number of PTK attempts are limited due to progressive corneal thinning with repeated procedures
  • Deeper lesions will need to be addressed with lamellar corneal transplantation

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Further information and support

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References

  1.  Weiss JS. Visual morbidity in thirty-four families with Schnyder crystalline corneal dystrophy (an American Ophthalmological Society thesis). Trans Am Ophthalmol Soc. 2007;105:616-48
  2.  Lisch W, Weiss JS. Clinical and genetic update of corneal dystrophies. Exp Eye Res. Sep 2019;186:107715. doi:10.1016/j.exer.2019.107715
  3.  Jo Y, Hamilton JS, Hwang S, et al. Schnyder corneal dystrophy-associated UBIAD1 inhibits ER-associated degradation of HMG CoA reductase in mice. Elife. Feb 20 2019;8doi:10.7554/eLife.44396
  4.  Weiss JS, Kruth HS, Kuivaniemi H, et al. Mutations in the UBIAD1 gene on chromosome short arm 1, region 36, cause Schnyder crystalline corneal dystrophy. Invest Ophthalmol Vis Sci. Nov 2007;48(11):5007-12. doi:10.1167/iovs.07-0845
  5.  Siebelmann S, Scholz P, Sonnenschein S, et al. Anterior segment optical coherence tomography for the diagnosis of corneal dystrophies according to the IC3D classification. Surv Ophthalmol. May-Jun 2018;63(3):365-380. doi:10.1016/j.survophthal.2017.08.001
  6.  Lisch W, Wasielica-Poslednik J, Kivelä T, et al. The hematologic definition of monoclonal gammopathy of undetermined significance in relation to paraproteinemic keratopathy (An American Ophthalmological Society Thesis). Transactions of the American Ophthalmological Society. 2016;114
  7.  Acar BT, Bozkurt KT, Duman E, Acar S. Bilateral cloudy cornea: is the usual suspect congenital hereditary endothelial dystrophy or stromal dystrophy? BMJ Case Rep. Apr 22 2016;2016doi:10.1136/bcr-2015-214094
  8.  Rødahl E, Knappskog PM, Bredrup C, Boman H. Congenital Stromal Corneal Dystrophy. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews(®). University of Washington, Seattle Copyright © 1993-2020, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.; 1993

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Updated on November 30, 2020
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