Progressive retinal atrophy

"CPRA" redirects here. For other uses, see California Public Records Act.

Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats. Similar to retinitis pigmentosa in humans,[1] it is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trait, with the exception of the Siberian Husky (inherited as an X chromosome linked trait) and the Bullmastiff (inherited as an autosomal dominant trait).[2] There is no treatment.

Diagnosis

Progressive vision loss in any dog in the absence of canine glaucoma or cataracts can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia. Other symptoms include dilated pupils and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus, increased reflection from the tapetum due to thinning of the retina, and later in the disease a darkened, atrophied optic disc. Secondary cataract formation in the posterior portion of the lens can occur late in the disease. In these cases diagnosis of PRA may require electroretinography (ERG). For many breeds there are specific genetic tests of blood or buccal mucosa for PRA.[2]

Absent a genetic test, animals of breeds susceptible to PRA can be cleared of the disease only by the passage of time—that is, by living past the age at which PRA symptoms are typically apparent in their breed. Breeds in which the PRA gene is recessive may still be carriers of the gene and pass it on to their offspring, however, even if they lack symptoms, and it is also possible for onset of the disease to be later than expected, making this an imperfect test at best.

Types of PRA

Generalized PRA is the most common type and causes atrophy of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).

Generalized PRA can be divided into either dysplastic disease, where the cells develop abnormally, and degenerative, where the cells develop normally but then undergo a damaging change. PRA can be further divided into affecting either rod or cone cells. Rod cells detect shape and motion, and function in dim light. Cone cells detect color and definition, and function in bright light.

Generalized PRA

Commonly affected breeds:[3]

Rod-cone dysplasia

This type of PRA has an early onset of severe vision loss. It is caused by a defect in the gene for cGMP-phosphodiesterase, which leads to retinal levels of cyclic guanosine monophosphate ten times normal.[4]

Rod-cone dysplasia type 1

Rod-cone dysplasia type 2

Rod-cone dysplasia type 3

Rod dysplasia

Early retinal degeneration

Photoreceptor dysplasia

This is caused by an abnormal development of both rod and cone cells. Dogs are initially night blind and then progress to day blindness.

Cone degeneration

Cone-rod dystrophy

Progressive rod-cone degeneration (PRCD)

This is a disease with normal rod and cone cell development but late onset degeneration of the rod cells that progresses to the cone cells. It is inherited as an autosomal recessive trait and has been linked to the ninth canine chromosome.[1]

X-linked PRA

This condition is linked to the X chromosome.

Dominant PRA

Feline PRA

Central progressive retinal atrophy (CPRA)

CPRA is also known as retinal pigment epithelial dystrophy (RPED). The cause of this condition is the loss of the retinal pigment epithelium's ability to effectively process the photoreceptor outer segment (POS) and subsequent accumulation of POS material in the RPE and loss of function. The loss of function of the RPE leads to photoreceptor degeneration.[4] Vitamin E deficiency may play a role in the development of CPRA.[7] It is characterized by accumulation of pigment spots in the retina surrounded by retinal atrophy and a mottled appearance of the pigmented nontapetal fundus. The pigmented spots eventually coalesce and fade as the atrophy of the retina increases. It is an inherited condition (in the Labrador Retriever it is inherited as an autosomal dominant trait with variable penetrance).[2] CPRA occurs in older dogs. Peripheral vision is retained for a long time. Vision is better in low light and better for moving or distant objects. Not all affected dogs go blind. Secondary cataracts are common.

Commonly affected breeds

It can also be found in the poodle varieties

Hereditary retinal dysplasia

There is another retinal disease in Briards known as hereditary retinal dysplasia. These dogs are night blind from birth, and day vision varies. Puppies affected often have nystagmus. It is also known as lipid retinopathy.[3]

See also

References

  1. 1 2 3 4 5 6 7 8 Petersen-Jones, Simon M. (2003). "Progressive Retinal Atrophy: An Overview". Proceedings of the 28th World Congress of the World Small Animal Veterinary Association. Retrieved 2007-03-10.
  2. 1 2 3 "Inherited Retinopathies". The Merck Veterinary Manual. 2006. Retrieved 2007-03-10.
  3. 1 2 3 4 5 6 7 8 9 10 11 Gelatt, Kirk N. (ed.) (1999). Veterinary Ophthalmology (3rd ed.). Lippincott, Williams & Wilkins. ISBN 0-683-30076-8.
  4. 1 2 Bedford, Peter (2006). "Hereditary Retinal Diseases" (PDF). Proceedings of the 31st World Congress of the World Small Animal Veterinary Association. Retrieved 2007-03-10.
  5. Giuliano E, van der Woerdt A (1999). "Feline retinal degeneration: clinical experience and new findings (1994-1997)". J Am Anim Hosp Assoc 35 (6): 511–4. doi:10.5326/15473317-35-6-511. PMID 10580912.
  6. Rah H, Maggs D, Lyons L (2006). "Lack of genetic association among coat colors, progressive retinal atrophy and polycystic kidney disease in Persian cats". J Feline Med Surg 8 (5): 357–60. doi:10.1016/j.jfms.2006.04.002. PMID 16777456.
  7. Davidson M, Geoly F, Gilger B, McLellan G, Whitley W (1998). "Retinal degeneration associated with vitamin E deficiency in hunting dogs". J Am Vet Med Assoc 213 (5): 645–51. PMID 9731258.

External links

This article is issued from Wikipedia - version of the Friday, April 03, 2015. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.