Copper toxicosis in Bedlington Terriers is caused by an imbalance in the levels of copper, and essential trace factor involved in many enzymatic processes. In affected dogs there is insufficient excretion of copper via bile. The copper therefore accumulates in the liver and becomes toxic. This leads to chronic hepatitis and progressive cirrhosis (scarring) of the liver and eventually premature death.
This DNA test targets a variant in the COMMD1 gene that has been associated with Copper Toxicosis in Bedlington Terriers. However, another form of Copper Toxicosis that is caused by something other than the COMMD1 variant, has also been reported.
The 39.7kb deletion in the gene called COMMD1 that causes Copper Toxicosis in Bedlington Terrier is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Copper Toxicosis during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Copper Toxicosis as a result of the COMMD1 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Copper Toxicosis should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the COMMD1 mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with Copper Toxicosis, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.