Indirect Molecular Diagnosis of Copper Toxicosis in Bedlington Terriers Is Complicated by Haplotype Diversity

Positional cloning recently identified the mutation causing copper toxicosis (CT) in Bedlington terriers. Isolation of the MURR1 gene will be of great value in developing a reliable diagnostic test for the breeding of a copper toxicosis-free stock. It will replace the current diagnostic test using the CT-linked marker, C04107, which is located in intron 1 of the MURR1 gene with a distance of approximately 8 kb from the exon 2 deletion. Despite the short distance between C04107 and the CT mutation, possible recombinant dogs have been reported with C04107. Although these dogs have a normal phenotype, they carry the C04107 allele 2, which is associated with CT. To study the origin of this possible recombination event we collected a pedigree consisting of two unaffected American Bedlington terriers and their litter of four pups, which were all homozygous for the C04107 2,2 genotype. Mutation analysis showed that two dogs were heterozygous for the CT exon 2 deletion mutation, whereas four dogs were homozygous for the wild-type (WT) allele. Haplotype analysis was performed using two DNA markers in the MURR1 gene and four DNA markers flanking the gene and spanning a region of approximately 600 kb. Surprisingly, we identified a new haplotype (haplotype C) that contains allele 2 of marker C04107 in combination with the WT MURR1 allele. Analysis of the flanking markers suggests there are different genetic backgrounds in the Bedlington terrier population.