Feline Health Genetics
Understanding Feline Health Genetics Should Be a Part of Every Breeder’s Toolbox
One of the fundamental reasons for breeding pedigreed cats is to preserve that breed for future generations, and allowing as little variation as possible in the conformation of that breed so that breed’s distinctive characteristics are maintained. In preserving those characteristics, though, breeders must be vigilant when selecting breeding stock and avoid selecting animals that carry inheritable diseases. However, some breeds are so rare that the pool of breed-worthy animals is small, and to preserve a breed, a breeder must select pairs that are more closely related than is desirable. As discussed in the sections on Genetic Diversity, the more closely parents are related to each other, the higher the probability that both parents can pass on an inheritable disease or defect. Fortunately, breeders now have sophisticated tools for avoiding many inheritable diseases, even when in-breeding or line breeding.
Genetic Health Testing
If you have been searching breeder websites for that purrfect new family member, you have undoubtably noticed that many breeders state they have genetically screened their cats, and they are “clear”. But what does that mean to you, and how does that ensure you will be getting a genetically healthy kitten?
What is a Genetic Health Screen?
Genetic testing is very easy to do today. There are multiple laboratories offering at home test kits. CFA partners with two – Wisdom Panel and Neogen. A full panel runs about $100 and only needs to be run once unless new genetic markers are discovered that a breeder wants to test for. Typically, a full panel tests for about 20-30 traits, 40-60 inherited defects, and the cat’s blood type.
The test kits consisted of a clean swab and labeling materials to ensure your cat’s results don’t get mixed up with another one. After isolating the cat from food and other cats, the owner swabs the cat’s cheek next to the gum, collecting a small amount of buccal (cheek) cells on the swab, being careful not to touch the swab with their fingers or any other object. The swab is allowed to dry, packaged up, and mailed off to the laboratory.
I Sent the Sample, Now What?
Once the laboratory receives the sample, they use a technique called polymerase chain reaction (PCR), which looks for a specific segment of DNA that is associated with a particular inheritable disease or trait. Depending on the laboratory, a client can order a single test or a whole panel of tests. Today, most breeders opt for a screening panel, which can contain 40 or more tests for inheritable diseases and 20 or more inheritable traits, as a single test costs between $20 - $100 US and an entire panel usually runs around $100 US. As new genetic markers are found, testing laboratories include them in their panel. The reason laboratories can do entire panels so economically is due to the use of DNA microarray chips. The chips are usually glass slides impregnated with multiple DNA markers encased in plastic. The cat’s DNA is extracted from the buccal cells on the swab, and then inoculated on to the chip. The chip is then analyzed in a highly automated process, so every test is run on every sample, as it is far, far less expensive to manufacture one chip with all the markers of interest for every cat rather than multiple chips with only a few markers.
Depending on the laboratory, it may take a few days to a few weeks to receive a report back on the submitted sample. If you ordered a multi-test panel the first page will usually contain a summary page of key findings, particularly if there were any inheritable disease markers detected. It will be followed by a detailed breakdown of all the markers tested and a layman’s interpretation of the results. If desired, most laboratories provide a more technical report for those who remember their college genetics class or studied the topic on their own.
To Breed or NOT to Breed...
Your cat’s report comes back with an inheritable defect – now what? Some responsible breeders will not accept anything less than an “all clear” report on their breeding cats, and cats with defects detected will be immediately altered and placed in pet homes. However, this is not always necessary or even desirable. Removing an otherwise quality animal from a limited gene pool for one copy of a rare, recessive, single allele trait that has no impact on the carrier or future kittens as long as two copies don’t pair up can have greater consequences than allowing the animal to breed with a partner who has no copies of the defect, particularly if there is a shortage of healthy breeding animals for a particular breed.
Removal is forever…
Here’s why: let’s use pyruvate kinase deficiency (PK def) as an example. This defect is a simple, single allele autosomal recessive defect that causes a cat’s – or person’s – red blood cells to be too fragile, causing them to break faster than the animal’s body can replace them, which over time can cause severe anemia. For the disease to manifest, two copies are required. One copy will not produce disease.
All feline genetic panels test for this disorder, and many university and commercial laboratories offer it as a single test, saving a breeder some money if this is the only result, they care about in a litter of kittens. Since it’s so easy to test for it, a breeder who wants to breed a cat carrying this defect just needs to make 100% sure that the intended mate is also not a carrier or has active disease. Kittens who are potential breeding cats can be tested individually to see if the defect was passed on. If there are kittens of equal merit and one does not carry the defect, it should be the one chosen. What’s right about the line is retained, and the deficiency is “bred out”. If there is not equal merit and a carrier is the best candidate overall, the same process can be repeated – breed the carrier, but make sure they are only bred to clear animals.
You just got your new pedigreed or non-pedigreed kitten – should you genetically health test your kitten?
If you adopted your cat from a shelter, from a box in front of Walmart, or from a sketchy looking breeder who delivered your kitten out of the back of a truck and never produced those papers you were promised, it is a very good idea to genetically health test your pet, even if you never intend to use the cat for breeding. Certain inheritable diseases can be treated quite effectively, and knowing ahead of time that your new fur baby may have problems ahead can allow your vet to treat proactively and head off sudden or severe manifestations. Plus, with many of the commercial panels, you will get a report on it inherited traits [link to traits page] and a report on its breed ancestry. Keep in mind, though, that cat breed analysis is in its infancy, and the number of analyzed animals is much, much smaller when compared to dogs, plus there is less genetic variance between breeds in cats, making it harder to genetically tell them apart. Keep in mind that breed is a man-made designation based on an animal’s observable traits, and different registries don’t always agree what those observable traits look like, creating some variance in the DNA between breeds that makes it even more difficult to 100% identify the breed ancestry. With each sample submitted, however, the database gets larger, and the accuracy improves, so over time, the breed ancestry will become more accurate.
If my breeder tests their cats, do I need to test my kitten? Probably not for health reasons, particularly if your breeder has provided you copies of the parents’ reports and you trust them. If there are no detectable defects in the parents, then if you use the same panel, you are not going to get any different results on the kitten. A parent can’t pass on what they don’t have. However, if your cat is showing signs of an inheritable disease, and you have reason to suspect the breeder has not been forthcoming, then you might want to do the health panel.
Keep in mind, though, that when you get your results back and it shows your Tonkinese is not 100% Tonkinese but is a mix of six different breeds including Tonkinese, that your breeder is likely not trying to pull one over on you, nor is the test inaccurate from an analytical point of view. The Tonkinese is a hybrid breed, meaning it was created out of two or more established breeds, and the database is not large enough yet to uniquely identify a cat as 100% Tonkinese. This is a good reason to test your cats even if you believe them to be genetically healthy, as your contribution to the overall DNA database helps identify future health and trait markers and improves the accuracy of breed identification.