UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory

Progressive Rod-Cone Degeneration (PRA-prcd)

Progressive rod-cone degeneration (PRCD) is an inherited form of late-onset progressive retinal atrophy (PRA) that has been identified in many dog breeds. PRCD affects the photoreceptor cells in the eye involved in both night and day vision. The cells of the retina involved in low light vision, known as rods, are affected first resulting in night blindness. Subsequently, the bright light photoreceptors known as cones, which are also important for color vision, are also affected resulting in daytime visual deficit. The age of onset and rate of progression vary among breeds but retinal changes can be identified by screening performed by a veterinary ophthalmologist from adolescence to early adulthood. Most PRCD-affected dogs have noticeable visual impairment by 4 years of age typically progressing to complete blindness.

PRCD is caused by a single nucleotide change (G>A) at position 5 in the Progressive rod-cone degeneration (PRCD) gene that changes the second amino acid from cysteine to tyrosine (C2Y). This amino acid change occurs in a highly conserved region of the protein. The mode of inheritance for this disease is autosomal recessive, which means that males and females are equally affected and that two copies of the mutation are needed to cause PRCD. Exceptionally, a few dogs between 10-13 years of age have been identified that were clinically normal but had two copies of the PRCD mutation. The breeds involved in these cases were American Eskimo, American Cocker Spaniel, English Cocker Spaniel and Toy Poodle. It has been postulated that genetic modifier(s) that have not yet been identified may play a role in the progression of the disease.
Testing for PRCD assists veterinarians with diagnosis of PRA and helps breeders identify carriers among breeding stock to select appropriate mates that will reduce the risk of producing affected offspring. To avoid the possibility of producing affected puppies, matings between known carriers are not recommended. 

Progressive retinal atrophy (PRA) is a medical classification that represents several inherited forms of retinal degeneration that are caused by mutations in different genes. PRCD is one form of PRA. Thus, a normal test result for PRCD (N/N or N/PRCD) does not exclude the possibility that a dog may carry or be affected by another PRA mutation.

Testing is recommended for: Many breeds including, but not limited to: American Eskimo Dog, American Hairless Terrier, Australian Cattle Dog, Australian Cobberdog, Australian Shepherd, Black Russian Terrier, Barbet, Chesapeake Bay Retriever, Chinese Crested, Chihuahua, Cockapoo, American Cocker Spaniel, Coton de Tulear, English Cocker Spaniel, English Shepherd, Entlebucher Mountain Dog, Field Spaniel, Finnish Lapphund, German Spitz, Giant Schnauzer, Golden Retriever, Golden Doodle, Jack Russell Terrier, Japanese Chin, Lab/Golden Cross, Labradoodle, Australian Labradoodle, Labradoodle/Goldendoodle Cross, Labrador Retriever, Miniature American Shepherd, Norwegian Elkhound, Nova Scotia Duck Tolling Retriever, Pomeranian, Poodle (Standard, Medium, Miniature and Toy), Portuguese Water Dog, Puli, Silky Terrier, Schipperke, Spanish Water Dog, Standard Poodle, Swedish Jamthund, Swedish Lapphund, Tibetan Terrier, Xoloitzcuintle, Yorkshire Terrier.

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Results reported as:

N/N

No copies of the PRCD mutation detected. Dog is clear of this mutation.

N/PRCD

1 copy of the PRCD mutation detected. Dog is a carrier. If bred to another carrier, 25% of offspring are predicted to be affected.

PRCD/PRCD

2 copies of the PRCD mutation detected. Dog is likely to be affected and develop progressive retinal atrophy.

References:

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. 2006. Identical mutation in a novel retinal gene causes progressive rod-cone degeneration in dogs and retinitis pigmentosa in humans. Genomics 88 (5):551-63. [PubMed: 16938425].


Dostal J, A Hrdlicova, Horak P. 2011. Progressive rod-cone degeneration (PRCD) in selected dog breeds and variability in its phenotypic expression. Veterinarni Medicina 56 (5):243–247.

 
Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL