Felis ISSN 2398-2950

Retina: inherited degenerations

Synonym(s): Photoreceptor dysplasia, photoreceptor degeneration, Rod-Cone Dysplasia (Rdy), autosomal dominant progressive retinal atrophy, Rod-Cone Degeneration of Abyssinian cats (RdAC), autosomal recessive progressive retinal atrophy

Contributor(s): Natasha Mitchell, David Gould

Introduction

  • Cause: genetic disease - Rod-Cone Dysplasia (Rdy) and Rod-Cone Degeneration in Abyssinian cats (RdAC) are two proven inherited forms of retinal degeneration in cats in which the causal genetic defect is known. There are other inherited forms of photoreceptor dysplasia or degeneration in different breeds, in which the causal defect is not yet known.
  • Signs: bilateral retinal degeneration leading to blindness.
  • Diagnosis: ophthalmoscopy. Rdy and RdAC can be confirmed with DNA tests.
  • Treatment: no treatment is available
  • Prognosis: retinal degeneration is irreversible, and the speed of progression to blindness varies among the different conditions.
These conditions are uncommon in cats. They have received a disproportionate level of study because they provide useful animal models for investigating similar blinding conditions in people.

 

Pathogenesis

Etiology

Inheritance

  • Rdy in the Abyssinian and Somali: autosomal dominant.
  • RdAC in the Abyssinian, Somali, Siamese and Ocicat: autosomal recessive.
  • Photoreceptor dysplasia in the Persian: autosomal recessive.
  • Photoreceptor degeneration in the Bengal: autosomal recessive.

Molecular genetic defect

  • Rdy in the Abyssinian and Somali: single base pair deletion in the CRX gene.
  • Photoreceptor degeneration in the Abyssinian, Somali, Siamese and Ocicat: mutation in the CEP290 gene.
  • Photoreceptor dysplasia in the Persian: not yet determined.
  • Photoreceptor degeneration in the Bengal: not yet determined, but not CEP290 or CRX variants.

Pathophysiology

  • Rdy is inherited in an autosomal dominant fashion and is caused by a single base pair deletion in the CRX gene. It leads to photoreceptor degeneration prior to maturation, hence the term dysplasia. The disease is very early in onset and the cones appear to be affected before the rods. Therefore, although it has historically been called Rod-Cone Dysplasia, it is more accurately a cone-rod dysplasia.
  • Later onset photoreceptor degeneration is inherited in an autosomal recessive fashion and is caused by a mutation in the CEP290 gene in affected Abyssinian, Siamese, Somali and Ocicat breeds. Rod photoreceptor outer segments become disorganized and eventually degenerate, followed by disruption of the cones until retinal degeneration is complete by 3-5 years.

Timecourse

  • Rdy in the Abyssinian and Somali: onset from 4-8 weeks; total retinal degeneration by 3-4 months.
  • RdAC in the Abyssinian, Somali, Siamese and Ocicat: onset from 18 months of age; total retinal degeneration by 3-5 years.
  • Photoreceptor dysplasia in the Persian: onset from 2-3 weeks; total retinal degeneration by 4 months.
  • Photoreceptor degeneration in the Bengal: onset from 9 weeks of age; total retinal degeneration by 1 year.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

Photoreceptor dysplasia (Rdy)

  • Occelli L M, Tran N M, Narfström K et al (2016) CrxRdy Cat: A Large Animal Model for CRX-Associated Leber Congenital Amaurosis. Invest Ophthalmol Vis Sci 57 (8), 3780-92 PubMed.
  • Menotti-Raymond M, Deckman K H, David V et al (2010) Mutation discovered in a feline model of human congenital retinal blinding disease. Invest Ophthalmol Vis Scie 51 (6), 2852- 2859 PubMed.
  • Rah H, Maggs D J, Blankenship T N et al (2005) Early-onset, autosomal recessive, progressive retinal atrophy in Persian cats. Invest Ophthalmol Vis Scie 46 (5), 1742-1747 PubMed.

Photoreceptor degeneration (RdAC)

  • Ofri R, Reilly C M, Maggs D J et al (2015) Characterization of an Early-Onset, Autosomal Recessive, Progressive Retinal Degeneration in Bengal Cats. Invest Ophthalmol Vis Sci 56 (9), 5299-5308 PubMed.
  • Narfström K, David V, Jarret O et al (2009) Retinal degeneration in the Abyssinian and Somali cat (rdAc): correlation between genotype and phenotype and rdAc allele frequency in two continents. Vet Ophthalmol 12 (5), 285-291 PubMed.
  • Menotti-Raymond M, David V A, Schäffer A A et al (2007) Mutation in CEP290 discovered for cat model of human retinal degeneration. Journal of Heredity 98 (3), 211-220 PubMed.

Other sources of information

  • Feline Ophthalmology - The Manual. (2015) Natasha Mitchell & James Oliver. Grupo Asis. ISBN 978-84-16315-11-6


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