Identification of affected dogs.
Copper toxicosis was first recognised in the USA in the mid 1970’s. Subsequent research established that it was a genetic disorder and the evidence suggested that it was caused by an autosomal recessive mutation inherited on classical Mendelian lines.
An unfortunate characteristic of the inherited form of copper toxicosis is that irreversible adverse changes occur in the liver tissue a considerable time before any overt signs of the disease occur in the dog. Moreover, in many cases these signs do not develop or their significance is not recognised.
1. Liver Biopsy.
Initially, the only way in which affected animals, i.e. those with copper toxicosis, could be identified was by examination of liver tissue samples. This involved:
a. Determination of the amount of copper, measured in micrograms per gram.
b. Histo-chemistry to check the level of visible stainable copper
c. Histo-pathology to check for changes in the liver cells that are characteristic of copper toxicosis
Unfortunately, this technique will only differentiate between a “normal”, i.e. unaffected dog, and one that is “affected”. It does not identify “carriers”, i.e. those dogs carrying only a single copy of the mutation.
This is a serious shortcoming because of the significance of dogs that would/could be classed as “carriers”and which would never develop copper toxicosis but, never-the-less, had the potential to pass on a copy of the mutant gene to their offspring.
Moreover, liver biopsy involves invasive surgery necessitating the use of an anaesthetic.
However, until such time as a genetic (DNA) test could be developed, the use of liver biopsy as a diagnostic test continued.
2. Genetic (DNA) Tests.
Obviously, a genetic test would be more effective in that it would allow differentiation between the normal, carrier or affected status.
The DNA required for the test can be extracted from a cheek cell swab, eliminating the need for invasive surgery. Obtaining a cheek swab is a straight-forward procedure and is usually carried out by the owner of the dog. A major advantage of genetic tests is that samples for testing can be submitted from puppies - the results are generally available within 5-6 weeks, i.e. long before any puppy which is shown to be affected will begin to accumulate significant amounts of copper in the liver.
Note: Although a blood sample may occasionally be used for DNA extraction, the sample can only to be taken by a veterinary surgeon.
Scroll down to the bottom of the Home page and click on “DNA testing” in the “What We Do” list. Click on “Canine DNA Testing” in the “Related Links” panel and then scroll down the page to make the appropriate links for “Bedlington terrier” - “Copper Toxicosis”.
At the bottom of the home page click on “Learn More Canine ” under ”DNA Disease and Genetic Testing” and then click on “CT” in the “Genetic tests “ list.
Although the COMMD1 test, seemingly, had the potential to identify the CT status of a dog, it became evident that some results were incorrect. Consequently, despite the fact that it cannot identify the “carrier” status, examination of tissues obtained by means of a liver biopsy still remains the method for positively diagnosing the disease, i.e. of identifying affected dogs. Moreover, it remains the only way whereby any new DNA test can be validated.