Non-allelism of three genes (rcd1, rcd2 and erd) for early-onset hereditary retinal degeneration.

Cross-breeding experiments were utilized to study the genetics of three autosomal recessive, early onset retinal degenerations in dogs. Irish setters affected with rod-cone dysplasia type 1 (rcd1) were bred to Norwegian elkhounds affected with early retinal degeneration (erd). All offspring (15 pups-two litters) surviving to diagnostic age were phenotypically normal, as assessed by electroretinography, retinal morphology and assay of retinal cyclic nucleotide content. One phenotypically normal female Irish setter-Norwegian elkhound crossbred dog (the progeny of the above breeding and thus heterozygous at both the rcd1 and the erd locus) was bred to a collie dog affected with rod-cone dysplasia type 2 (rcd2). All 11 pups from this breeding also proved phenotypically normal by the above methods. These results establish that the genes rcd1, rcd2 and erd are non-allelic. Biochemical data are also presented that establish that erd, unlike rcd1 and rcd2, is not associated with abnormal metabolism of retinal cyclic guanosine monophosphate (cyclic GMP).