Linkage Mapping of Canine Rod Cone Dysplasia Type 2 (rcd2) toCFA7, the Canine Orthologue of Human 1q32

Abstract

To map the canine rcd2 retinal degeneration locus. Rod-cone dysplasia type 2 (rcd2), an early-onset autosomal recessive form of progressive retinal atrophy (PRA), is phenotypically similar to early-onset forms of retinitis pigmentosa collectively termed Leber congenital amaurosis and segregates naturally in the collie breed of dog. Multiple genes have previously been evaluated as candidates for rcd2, but all have been excluded. A set of informative experimental pedigrees segregating the rcd2 phenotype was produced. A genome-wide scan of these pedigrees using a set of 241 markers was undertaken. To refine the localized homology between canine and human maps, an RH map of the identified rcd2 region was built using a 3000 cR panel. A positional candidate gene strategy was then undertaken to begin to evaluate potentially causative genes. A locus responsible for the rcd2 phenotype was mapped to CFA7 in a region corresponding to human chromosome 1, region q32.1-q32.2. Maximum linkage was observed between rcd2 and marker FH3972 (theta = 0.02; lod = 25.53), and the critical region was flanked by markers FH2226 and FH3972. As CRB1 is the closest gene on human chromosome 1q known to cause retinal degeneration, canine gene-specific markers for CRB1 were developed, and this gene was excluded as a positional candidate for rcd2. The rcd2 locus represents a novel retinal degeneration gene. It is anticipated that when identified, this gene will offer new insights into retinal developmental and degenerative processes, and new opportunities for exploring experimental therapies.