Progressive Retinal Atrophy, X-Linked 1

Other Names: X-Linked Progressive Retinal Atrophy 1, PRA, XLPRA1
Affected Genes: RPGR
Inheritance: X-Linked Recessive
Mutation: Deletion
Breed(s): Samoyed, Siberian Husky

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Common Symptoms

Progressive retinal Atrophy, X-linked 1 (XLPRA1) is an inherited eye disease affecting dogs. XLPRA1 occurs as a result of degeneration of both Rod and cone type Photoreceptor Cells of the Retina, which are important for vision in dim and bright light, respectively. Evidence of retinal disease in affected dogs can first be seen on an Electroretinogram by a year of age, but visual deficits may not be evident until dogs are at least 2 years of age. The rod type cells are affected first and affected dogs will initially have vision deficits in dim light (night blindness) and loss of peripheral vision. As the disease progresses, cone photoreceptor cells also degenerate resulting in complete blindness. Other signs of progressive retinal atrophy involve changes in reflectivity and appearance of a structure behind the retina called the Tapetum that can be observed on a veterinary eye exam. Due to its X-Linked Inheritance, male dogs are more frequently affected with this disease than female dogs. Other inherited disorders of the eye can appear similar to XLPRA. Genetic testing may help clarify if a dog is affected with XLPRA or another inherited condition of the eye.


Testing Tips

Genetic testing of the RPGR gene will reliably determine whether a dog is a genetic Carrier of progressive retinal Atrophy, X-linked 1 (XLPRA1). XLPRA1 is inherited in an X-linked manner in dogs meaning that female dogs must receive two copies of the mutated gene (one from each parent) to develop the disease while male dogs only require one copy of the mutated gene from the mother in order to develop the disease. Therefore, male dogs more commonly present with symptoms of the disease. Each male pup that is born to a female dog known to be a carrier of RPGR has a 50% chance of inheriting the disease. Reliable genetic testing is important for determining breeding practices. In order to eliminate this Mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Female dogs that are not carriers of the mutation have no increased risk of having affected pups. However, because there are multiple types of PRA caused by mutations in other genes, a normal result in RPGR does not exclude PRA in a pedigree.


There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


References

  • Acland GM, Blanton SH, Hershfield B, Aguirre GD. XLPRA: a canine retinal degeneration inherited as an X-linked trait. Am J Med Genet. 1994 Aug 1;52(1):27-33. [PubMed: 7977457]
  • Appelbaum T, Becker D, Santana E, Aguirre GD. Molecular studies of phenotype variation in canine RPGR-XLPRA1. Mol Vis. 2016 Apr 9;22:319-31. [PubMed: 27122963]
  • Guyon R, Pearce-Kelling SE, Zeiss CJ, Acland GM, Aguirre GD. Analysis of six candidate genes as potential modifiers of disease expression in canine XLPRA1, a model for human X-linked retinitis pigmentosa 3. Mol Vis. 2007 Jul 11;13:1094-105. [PubMed: 17653054]
  • Zangerl B, Johnson JL, Acland GM, Aguirre GD. Independent origin and restricted distribution of RPGR deletions causing XLPRA. J Hered. 2007;98(5):526-30. Epub 2007 Jul 23. [PubMed: 17646274]
  • Zeiss CJ, Acland GM, Aguirre GD. Retinal pathology of canine X-linked progressive retinal atrophy, the locus homologue of RP3. Invest Ophthalmol Vis Sci. 1999 Dec;40(13):3292-304. [PubMed: 10586956]