Inheritance of PRA in the English Springer Spaniel
C. A. Wheeler, DVM. MS. DACVO, Animal Eye Care of Michigan, Laingsburg, MI
Purpose: Progressive retinal degeneration (PRA) has been cited as occurring in over 100 breeds of dog. With one exception, PRA in all breeds studied so far has been described as an autosomal recessive disorder. [Editor's note: see ESSFTA: Recessive Gene Inheritance Patterns for information on the inheritance of recessive disease.] In the English Springer spaniel, PRA has been described as a late onset form. According to some, it is similar to PRA described in the Miniature Poodle, the English and American Cocker spaniel and the Labrador Retriever. Recent clinical study suggests PRA in the Springer may be an aberrant form of PRA. Most of the PRA cases reported in the Springer population are to be found in those animals used for show. Animals used for field purpose have been identified with PRA, but to a lesser degree. The purpose of this study was to determine the inheritance of PRA in the population of show English Springer Spaniels.
Methods: Pedigrees were collected from forty two English Springer Spaniels identified as blind with advanced retinal degeneration of a progressive nature over a 20 year period. All animals in this collection were examined by a Veterinary Ophthalmologist. A copy of the CERF examination form was obtained. Blood samples were obtained from a small, significant portion of the affected dogs for genetic evaluation. Animals that produced affected offspring were presumed carriers.
Results: Pedigree analysis revealed over 10 generations of related dogs representing over 125 dogs. A high degree of inbreeding in successive generations was identified tracing back to 5 individuals, who were themselves related as sire, grandsire and siblings. These dogs in turn were the result of intensive inbreeding in the preceding 7 generations. A representative sample of the pedigrees is presented on the following page.
Conclusions: Breeding practices of the late 19th century and early 20th century allowed for both Cocker Spaniels and Springer Spaniels to be in the same litter, the only distinction being made for size. It would be logical to assume that the PRA seen in the American and English Cocker spaniels would be the same in the English Springer spaniel. Cross-breeding studies to a breed (such as the American or English Cocker spaniel) where the condition has been defined as progressive rod-cone degeneration (prcd) have not been done. Blood samples from a representative family in this pedigree will be evaluated by DNA markers/designate genes to determine if the disorder present is prcd or a variant of this gene. The animals in this study were representative of the breeding population of show English Springer spaniels across the United States and Canada. Based on the pedigrees evaluated, progressive retinal degeneration in the English Springer spaniel appears to be an autosomal recessive trait.
This research supported in part by the English Springer Spaniel Field Trial Association, Inc.