Purpose:
Retinitis pigmentosa (RP) is a group of human hereditary retinal degenerations comprising multiple specific disorders, distinguished by mode of inheritance, age of onset, clinical phenotype, and genetic cause. A large subtype of RP comprises the adult onset autosomal recessive rod-cone degenerations, and this subclass itself is known to be caused by several different identified genes and mapped loci. The canine hereditary retinal degenerations, known collectively as progressive retinal atrophy (PRA), provide large animal models for RP, but only one such model for adult onset autosomal recessive rod-cone degeneration currently exists, the PRCD dog. The purposes are: (i) To characterize the mode of inheritance and clinical phenotype of PRA in Italian Greyhound dogs (IGPRA); (ii) determine if the previously identified canine PRCD gene mutation was causative for IGPRA; and (iii) undertake genome-wide association study (GWAS) and linkage analysis to identify the responsible locus.
Methods:
Clinical diagnosis was established by indirect ophthalmoscopy, and in selected cases by electroretinography. Pedigree analysis and experimental breedings were undertaken to establish the mode of inheritance. DNA was extracted from blood samples from cases and controls. Representative cases were genotyped at the previously identified PRCD locus, and a GWAS was undertaken using the Affymetrix Version 2, Canine SNP chip.
Results:
Ophthalmoscopic evidence of retinal thinning typically first became apparent in affected dogs between 5 and 8 years of age. Clinically and electroretinographically the disorder was characterized as a rod-cone degeneration, with early loss of rod function progressing in older dogs to complete blindness. Inheritance was established as autosomal recessive. Candidate gene analysis excluded PRCD as the causative locus. Analysis of GWAS and linkage studies are currently in progress.
Conclusions:
IGPRA provides a novel and valuable large animal model of adult onset autosomal recessive rod-cone degeneration, not caused by the previously identified PRCD gene.
Keywords: retinal degenerations: hereditary • genetics • candidate gene analysis