Continued Characterization of a Feline Rod–Cone Dysplasia

Abstract

Abstract: : Purpose: Naturally occurring, inherited retinal degeneration has been recognized in humans, dogs, rodents, and cats. Retinitis pigmentosa (RP) is a heterogeneous group of heritable retinopathies causing blindness in humans. Progressive retinal atrophy (PRA) is the counterpart term in veterinary medicine. A complete and early–onset retinal degeneration with suggested autosomal recessive inheritance has been noted in the Persian breed of cats, but only the terminal stages of the disease (15 weeks of age) have been described. Characterization of an early–onset PRA with autosomal recessive inheritance was initiated to develop a novel feline model for RP. Our objective was to genetically map the PRA–causing gene on feline chromosomes. Methods: The backcross pedigree includes 56 individuals for linkage mapping and disease characterization. Ophthalmic and neuro–ophthalmic examinations were performed on each animal on multiple occasions to determine disease status and aid identification of similar diseases in other species. Genomic DNA was extracted either from blood samples or splenic tissue. Thirteen candidate genes for PRA were selected based on similar disease phenotypes of humans, dogs, rats, and mice (AIPL1, CRB1, CRX, GUCY2D, MERTK, PDE6A, PDE6B, RDS, RGPRIP1, RHO, RP1, RPE65 and TULP1). Fifty feline microsatellite markers were selected from the second generation feline RH map and linkage mapping was performed on the expanded pedigree. Two–point linkage analysis was performed using the program LINKAGE. The feline BAC library (RPCI–86) was screened with radioactive probes of successful PCR products or overgo primers to identify genes of interest and to isolate gene–associated microsatellites from these genomic clones. Results: To date, 19 of 50 markers tested have been excluded at &#952 = 0.1 and 7 markers at &#952 = 0.2. FCA304, a microsatellite predicted to be in the same region as gene RHO showed an increased exclusion from PRA disease phenotype at &#952 = 0.26 with LOD score –2.0. Microsatellite markers spanning the inferred regions as GUCY2D/AILP1 and PDE6A based on chromosome conservation, were excluded from this early onset feline PRA. Twenty–nine clones corresponding to the candidate genes were isolated from the feline BAC library. These clones cover 10 of the 13 candidate genes (AIPL1, CRX, GUCY2D, MERTK, PDE6A, PDE6B, RDS, RGPRIP1, RHO and RPE65). Conclusions: Our preliminary linkage data suggested that genes RHO, GUCY2D/AIPL1 and PDE6A can be excluded for this feline rod–cone dysplasia.

Keywords: retinal degenerations: hereditary • linkage analysis • retina