You may have heard that Persian cats tend to have kidney issues, but did you know that the same genetic mutation could also cause kidney disease and even renal failure in many other breeds? These include Burmillas, Himalayans, American Shorthairs, British Shorthairs, Scottish Folds, and in fact, any cat, whether purebred or your average domestic shorthair, that may have had a Persian cat for a great-granddaddy... So, should you be testing Kitty for PKD? We have some answers for you here.
This is the second part of an interview held with Professor Leslie A. Lyons, an expert on feline genetics and associate professor at the University of Missouri School of Veterinary Medicine and Surgery. In the first part of the interview, Prof. Lyons told us how she became involved in studying cat genetics, and we talked about chromosomes, DNA, epigenetic switches and the domestication of the cat. In this, the second part, Prof. Lyons shares her thoughts about available genetic testing kits and specifically, testing for PKD (Polycystic Kidney Disease).
The Persian's Diseased Genetic Legacy
Prof. Lyons was involved in developing genetic testing kits for Polycystic Kidney Disease (PKD), a relatively common condition known to affect Persian cats. Before genetic testing became available, veterinarians used ultrasounds to determine that Persian cats in Europe, Australia and the US all had similar rates of PKD. It became clear that there's a genetic mutation which had spread early on, probably when Persian cats were just beginning to move around the world. Prof. Lyons and her team identified the mutation and developed an affordable testing kit.
I asked her whether she thought owners of Persian cats should have their kitties tested. According to Prof. Lyons, it's not just owners of purebred Persians that should be concerned. While originally considered "a Persian thing", in fact quite a few breeds have a higher risk factor for PKD.
How come so many breeds are affected? It's all about the way new breeds are developed. Prof. Lyons explained that there are two methods used to get a specific look in a breed. Take, for example, a feature such as a shorter face. Let's say a breeder develops a new breed from an accidental mutation, such as folded ears or curly hair, and he or she wants to achieve a short-face (or flat-face) effect. One way to get the new breed to be short-faced would be to select for that feature and choose the cats with the shortest faces over many generations. It could take a long time, sometimes decades, before you achieve the look you want. The second way would be to take a shortcut by crossing with an existing breed that has the desired feature, in this case, Persian cats. You will get short-faced cats faster this way, but, Prof. Lyons warns, you could end up introducing other genetic traits typical of Persian cats, such as PKD.
That's why all of the breeds that were created using Persian cats are at risk for PKD. "Anybody who has a Persian-derived cat should be looking for polycystic disease," Prof. Lyons suggested during the interview. "That can be a pet cat [with Persian parentage], it could be a Burmilla, which is a Persian and a Burmese, Scottish Folds, Himalayans, American Shorthairs and unfortunately, a lot of British Shorthairs as well now."
A similar thing happened with Aussie cats, according to Prof. Lyons. "Aussie cats were crosses with Abyssinians. Pyruvate Kinase Deficiency, retinal degeneration and anything else that’s in an Abyssinian, you need to worry about what’s in that cross as well. It can happen at any time, and you have to pay attention to what you breed with," she cautioned breeders.
Should I have Kitty tested for PKD?
"With polycystic kidney disease, the gene is dominant, so you only have to have one copy of the mutation and you will have disease," Prof. Lyons explains. "With two copies, the disease is so severe that kittens are never born. It’s like the Manx trait - if there are two copies you never see these cats born".
Dealing with a dominant gene for such a potentially severe disease means anyone who wants to breed Persian, Himalayan, or otherwise Persian-derived cats should have the cat tested for the PKD gene. If the cat is a carrier, then they should not be bred. This holds true whether the cat is registered or not. Ethical registered breeders know this and carefully screen their breeding stock. Another good reason to avoid backyard breeding of cats.
If you don't intend to breed your cat, you may still consider the PKD test if your cat displays kidney-related symptoms. Prof. Lyons suggested this test could give you initial answers, being that it's cheaper than other diagnostic tools available for PKD, such as an ultrasound or an echocardiogram. However, she added that this would only be the first step.
"Many Persian cats have very mild disease and never die of renal failure," said the Professor. "Some cats have very severe disease and they die quickly from renal failure. So, once you get a test result back from genetics, you then want to go to the veterinarian and say, 'Does my cat have mild disease? Does my cat have severe disease?' If it has mild disease you might not have to come back for a couple of years."
What about other medical conditions in other breeds?
So, we have PKD testing covered, but what's next? Are there other medical conditions that you should be testing for?
Prof. Lyons told me about several other genetic issues but mentioned that these were of concern only to breeders. Ethical breeders know what genetic traits the breed carries and are aware of the risks associated with their breed and their lines. Prof. Lyons mentioned the Birman and Devon Rex cats as breeds with associated blood type issues that can be tested for.
For Abyssinian cats, there is increased risk for retinal degeneration that may result in blindness. Cats can be tested for a genetic mutation called CEP290 to see if they carry the gene or not.
Ragdolls and Maine Coons both have two known heart disease mutations, however, Prof. Lyons emphasized that these are only risk factors for heart disease. Genetic testing can reveal increased risk for heart disease but cannot predict whether an individual cat will get sick.
"We’re going to start finding that a majority of the mutations that we find confer some type of risk", she mentioned. "Hypertrophic cardiomyopathy is one of the best examples for that. You have to balance that “what is my risk” for getting HCM versus how good this cat is as a queen or as a tom, how pretty it looks. Then you select against HCM in the next generation. Your breeding is going to be the same, but now you’re going to be armed with more information to make decisions. Some people might fret over having that information. It makes your decisions harder, especially if you’re an ethical breeder. You have harder decisions to make."
Continue to the third and final part of this interview, Prof. Lyons reveals why scientists genetically engineered a cat that glows in the dark, and how that can help with developing gene therapy for felines and humans.