CGMP phosphodiesterase-alpha mutation causes progressive retinal atrophy in the Cardigan Welsh corgi dog

PURPOSE. TO screen the alpha-subunit of cyclic guanosine monophosphate (cGM P) phosphodiesterase (PDE6A) as a potential candidate gene for progressive retinal atrophy (PRA) in the Cardigan Welsh corgi dog. METHODS. Single-strand conformation polymorphism (SSCP) analysis was used t o screen short introns of the canine PDE6A gene for informative polymorphis ms in members of an extended pedigree of PRA-affected Cardigan Welsh corgis . After initial demonstration of linkage of a polymorphism in the PDE6A gen e with the disease locus, the complete coding region of the PDE6A gene of a PRA-affected Cardigan Welsh corgi was cloned in overlapping fragments and sequenced. SSCP-based and direct DNA sequencing tests were developed to det ect the presence of a PDE6A gene mutation that segregated with disease stat us in the extended pedigree of PRA-affected Cardigan Welsh corgis. Genomic DNA sequencing was developed as a diagnostic test to establish the genotype of Cardigan Welsh corgis in the pet population. RESULTS. A polymorphism within intron 18 of the canine PDE6A gene was invar iably present in the homozygous state in PRA-affected Cardigan Welsh corgis . The entire PDE6A gene was cloned from one PRA-affected dog and the gene s tructure and intron sizes established and compared with those of an unaffec ted animal. Intron sizes were identical in affected and normal dogs. Sequen cing of exons and splice junctions in the affected animal revealed a 1-bp d eletion in codon 616. Analysis of PRA-affected and obligate carrier Cardiga n Welsh corgis showed that this mutation cosegregated with disease status. CONCLUSIONS. A single base deletion at codon 616 in the PDE6A gene cosegreg ated with PRA status with zero discordance in Cardigan Welsh corgis with PR A. A lod score of 4.816 with a recombination fraction (theta) of zero stron gly suggests that this mutation is responsible for PRA in the breed. The mu tation is predicted to lead to a frame shift resulting in a string of 28 al tered codons followed by a premature stop codon. The authors suggest that t his type of PRA be given the name rod-cone dysplasia 3 (rcd3).