Copper toxicosis is an autosomal recessive disorder affecting Bedlington 
terriers, characterized by elevated liver copper levels and early death of 
affected dogs. Genetic linkage mapping studies initially identified linkage 
between the disease and the microsatellite marker C04107. Subsequently, the 
deletion of exon 2 of the copper metabolism domain containing 1 (COMMD1) gene 
(formerly MURR1) was shown to be the major cause of copper toxicosis, although 
the deletion breakpoints were not defined. In this investigation, polymerase 
chain reaction (PCR)-based techniques and sequencing were used to isolate the 
deletion breakpoints, utilizing the newly available dog genome sequence. The 
breakpoints were positioned at 65.3091 and 65.3489 Mb of dog chromosome 10, in 
intron 1 and intron 2 of COMMD1 respectively, a deletion of 39.7 kb. The two 
breakpoints share sequence homology suggesting that homologous recombination may 
have been responsible for the deletion. Using this information, a genomic 
diagnostic test for the COMMD1 deletion was developed and compared with 
microsatellite C04107 genotypes of 40 Bedlington terriers. Results from the 40 
samples showed allele 2 of C04107 to be in linkage disequilibrium with the 
COMMD1 deletion.