INVESTIGATION OF THE ROLE OF OPSIN GENE POLYMORPHISM IN GENERALIZED PROGRESSIVE RETINAL ATROPHIES IN DOGS

The generalized progressive retinal atrophies (gPRAs) form a group of retinal degenerations of pedigree dogs and cats, which have a variety of genetic origins (mostly unknown). We have examined the opsin gene f or polymorphisms in several breeds of pedigree dog suffering from dist inct forms of gPRA, by methods including single-strand conformation po lymorphism analysis, microsatellite analysis and direct sequencing. Th e breeds examined included the Tibetan terrier, the miniature schnauze r, the Irish setter, the miniature poodle, the Labrador retriever and the English cocker spaniel, as well as individuals from breeds in whic h PRA has not been described and of mixed breed. Individuals from each of the named breeds suffering from PRA were compared with clinically normal dogs. Two polymorphisms were found. One, segregating within the Tibetan terrier population, but not seen in other breeds, was a synon ymous transition at nucleotide position 780 in exon 3. Inheritance of this polymorphism suggests that opsin is unlikely to contain mutations causative of gPRA in this breed. The other polymorphism occurred betw een all miniature schnauzers examined and dogs of other breeds. It con sisted of a single base insertion in intron 2. No polymorphisms in the opsin sequence were detected in any other breed. DNA sequencing allow ed rigorous exclusion of mutations in opsin as a cause of gPRA in mini ature poodles, English cocker spaniels or Labrador retrievers.