Genetic testing for inherited diseases and subsequent selective breeding by cat breeders can, over several years, make large differences to the prevalence of these diseases in the population. (Langford Veterinary Services 2016)
Let’s prove this with ‘A Tale of Two Breeds’
Around the mid 1990s two forms of gangliosidosis had been diagnosed in Korats in Europe and the USA. Kittens left their breeder for their new homes fit and well, only to lose the ability to climb, jump, run and finally went blind, not making it to their first birthday. It became critical to understand the problem and find a solution.
By the end of the decade thanks to Dr Henry Baker of the Scott-Ritchey Research Centre at Auburn University (USA) the first genetic testing of cats was underway. Fortunately, as the genetic defects responsible had already been diagnosed in people, and tests were developed, researchers knew where to look and what action to take for the Korat. The one big difference was the genetic defect was found in about 3% of the human ethnic group known to be at risk, whereas over 30% of Korats tested worldwide were found to be carriers, though none were in the UK, and all breeding lines were tested. With the gradual removal of carriers where they were present, and the screening of imports into the UK, a potential disaster for a small breed had been not just prevented, but stopped dead in its tracks.
At the beginning of this century Persian-related Polycystic Kidney Disease (PKD) was estimated to be affecting almost 49% of the breed (UK statistic based on ultrasonography). In Korats carriers of the abnormality were unaffected, but just one copy of the PKD causing defect meant a Persian would develop problems at some stage in its life, some of them while still very young. Ultrasound screening was extensively used by responsible breeders, but it could well be that cats had been bred from before any abnormality was detected. A DNA test (as for the same form of human PKD) was much needed. The breakthrough was announced in 2004, and since testing became possible a year later a dramatic decline in the disease has been tracked to date. It is far more difficult to lose a dominant gene from a population than a recessive. It has to be done slowly to ensure genetic diversity is maintained. The graph shows just how successful GCCF’s Persian breeders have been.
Maine Coon and Ragdoll breeders working to remove genes responsible for HCM in their breeds have charted similar success to the Persians. Somalis no longer experience the occasional cat with PKDef, and many other breeds have included preventative strategies in their GCCF registration policies to ensure a disease known to have affected their breed in the past does not carry forward into the future. Thanks to DNA testing Burmese breeders no longer have to exclude imports, a policy which prevented disease, but with high risk of a critical loss of genetic diversity. Now they can now be sure they do not unwittingly add a gene causing a fatal craniofacial defect to the UK Burmese gene pool.
The DNA of Cinnamon, a four-year old Abyssinian, with a well-documented pedigree, was used to give the first complete sequence of the feline genome (research published in 2007). The work was funded in the USA, because the cat can serve as a model for human disease, but our breeds have benefitted from this. Professor Leslie Lyons, based first at UC Davis California and more recently at the University of Missouri, has been the leading expert overseeing the development of not only tests for disease, but also for parentage, ancestry tracing, blood grouping and many coat colours, patterns, and hair types. Among the most recent are a test for congenital myasthenic syndrome (CMS) that causes muscle weakness in Devon Rex and Sphynx, and one for russet in Burmese cats of Australian and New Zealand lines.
New DNA test for Silver
What will the Silver test determine?
The Silver/Inhibitor test will determine if your cat has one or two copies of the DNA variant causing the silver coat coloration. The DNA variant acts dominantly, thus, only one copy is needed to express silver.
Why would I use this test?
Because the DNA mutation causing silver color acts dominantly, a cat could have one or two copies of the mutation, which can’t be determined by the fur color. Some people think cats with 2 copies have less rufousing (redness) in the coat. For cats with two copies, every offspring will be silver and have at least one copy of the variant. Thus, a breeder can predict colorations more reliably and conduct more predictable matings.
Cats that are White, pointed, high white (van) or have other dilution colorations, such as dilution, orange, sunshine, extreme sunshine, can be difficult to determine if they are silver as well. This test will help decipher tricky colorations.
What does the Silver gene (Inhibitor locus) do?
Inhibitor removes all the yellow/red pigment from the hair, known as pheomelanin. The gene does not control the width of the band of the yellow pigment. The resulting color is silver. Silver cats can be smokes (when non-agouti, aa) or have very wide bands (chinchilla) or intermediate band lengths (shaded).
The full lists of genetic tests can be found at:
* discounts available to GCCF club members
Genetic Testing Available
These are the two GCCF recommended laboratories.
UC Davis and Bristol Veterinary College both have key research roles in feline medicine and genetics. The profits they make from testing go to ensuring this can continue.
There are other laboratories that offer DNA testing services to breeders. Some may be cheaper than VGL and Langford, but please be aware that they may also offer tests that may not have been validated for a specific breed (such as HCM in British Shorthaired cats). Treat with caution and check with the GCCF Genetics Committee if you want further information.
Practical information on how to collect DNA from your cat and pack and send it to the laboratories is available on their websites. It’s not a difficult diy job, but some registration policies require that it’s done by/or under the supervision of a vet. Check the policy for your breed.
NB: If a DNA test is being made to satisfy the requirements of a registration policy then your cat will need to be microchipped in advance of the test being made.
Mail email@example.com if you have any queries.