PRA-prcd disease information

Late form of Progressive Retinal Athrophy, called PRA-prcd (progressive rod-code degeneration), is just one of all retinal defects.

Rods degenerate at first. Affected dogs become night-blind. This is very often the first symptom that dog owners recognize. Dogs usually have poor sense of directions and they crash in things. Pupil is widely open even when direct ray of light hit the eye (dogs have shining eyes in pictures). Later, cones start degenerating. Final disease symptoms are cataracts and total blindness.

PRA-prcd defect arises after normal photoreceptors development. Degree of degeneration differs in parts of retina. Lower retina part is affected sooner and more than upper part (this is not obvious by ophthalmology examination). Disease recognition should be made during dog adolescence. Clinical diagnosis by electroretinogram (ERG) or opthalmoscopy of PRA-prcd can be difficult. ERG identifies affected animals sooner than opthalmoscopy.

PRA-prcd is a hereditary disease. Causal mutation G1298A in ninth canine chromosome (CFA9) PRA-prcd was recognized. This mutation is inherited as an autosomal recessive trait. That means the disease affects dogs with P/P genotype only. The dogs with P/N genotype are considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

Parent Heterozygote (P/N)
PN
Parent Heterozygote (P/N) PP/PP/N
NP/NN/N

The disease cannot be cured, but it is possible to eliminate it through genetic testing of litters and proper choice of parents.

DNA test is an advisable alternative to the clinical examination. The test can be performed only once in life of the animal, because the genotype does not change with age. DNA sample should be obtained from blood.

The most often affected breeds include:

  • American Eskimo Dogs
  • Australian Cattle Dogs
  • Australian Shepherds
  • Australian Shepherds, Miniature
  • Australian Stumpy Tail Cattle Dogs
  • Chesapeake Bay Retrievers
  • Chinese Crested Dogs
  • Cockapoos
  • Cocker Spaniels (American)
  • Dwarf Poodles
  • English Cocker Spaniels
  • Entlebucher Mountain Dogs
  • Finnish Lapphunds
  • Goldendoodle
  • Golden Retrievers
  • Karelian Bear Dog
  • Kuvasz
  • Labradoodles
  • Labradoodles, Australian
  • Labrador Retrievers
  • Lapponian Herders
  • Miniature Poodles
  • Norwegian Elkhound
  • Nova Scotia Duck Tolling Retrievers
  • Portuguese Water Dogs
  • Spanish Water Dogs
  • Swedish Lapphunds
  • Toy Poodles
  • Yorkshire Terriers

Percentage distributions of dog- carriers in some breed populations:

  • Labradoodles – more than 24 % carriers in popilation (mutated homozygotes about 2 %)
  • Toy Poodles, Dwarf Poodles, American Cocker Spaniels, English Cocker Spaniels – more carriers than in Labradoodles population
  • Portuguese Water Dogs – more than 40 % carriers in population

Research in Cornell University´s James A. Barker Institute for Animal Health and in The Fred Hutchinson Cancer Research Center v Seattle has found out that canine genetics prcd defect corresponds to autosomal recesive retinitis pigmentosa in humans.

Important! Symptoms, that indicate PRA-prcd, could also accompany another eye defect. There are many PRA forms – PRA-prcd is just one of them! There are another hereditary eye diseases like Congenital stationary night blindness (CSNB) and Collie eye anomaly (CEA).

References

  1. Zangerl B, Goldstein O, Philp AR, Lindauer SJ, Pearce-Kelling SE, Mullins RF, Graphodatsky AS, Ripoll D, Felix JS, Stone EM, Acland GM, Aguirre GD: Identical mutation in a novel retinal gene causes progressive rod-cone degeneration in dogs and retinitis pigmentosa in humans, PMID: 16938425
  2. Lippmann T, Jonkisz A, Dobosz T, Petrasch-Parwez E, Doplen JT, Dekomien G: Haplotype-defined linkage region for gPRA in Schapendoes dogs, Molecular Vision 2007; 13:174-80
  3. Gabriele Dekomien: Kandidatengenanalyse für generalisierte progressive Retina-Atrophie in dreißig Hunderassen, Dissertation zur Erlangung des Grades eines Doktors der Naturwissenschaften der Fakultät für Biologie der Ruhr-Universität Bochum angefertigt in der Medizinischen Fakultät Abteilung für Humangenetik, 2002
  4. Aguirre GD, Laties A: Pigment epithelial dystrophy in the dog, Exp. Eye Res. 23: 247,1976
  5. Beránek J, Vít PJ: Praktická oftalmologie psa, Medicus Veterinarius, 1995/11, 57-58, 69-84