Genetic Counselling in Veterinary Medicine

Once a DNA test is obtained on a cat, this is where the story and the communications should begin. The client and the veterinarian need to recognize that the current DNA tests for cats do not predict severity of disease. In the case of polycystic kidney disease (PKD), many cats can have mild presentations of cysts throughout their lives, never succumbing to renal failure, and dying of other causes. However, some cats develop end-stage renal disease within a few years and have an early death. A second example is hypertrophic cardiomyopathy (HCM) in Maine Coon cats.⁶⁰ The genetic mutation is known, it clearly confers risk - but the extent of the risk is nebulous.⁶¹ Thus, genetic tests should be used as a tool for the veterinarian and the owner, supporting the overall picture of a given cat's healthcare. In the case of PKD, ultrasound and/or creatinine levels should be used to monitor disease progression in PKD positive cats. Ultrasound monitoring remains the standard for HCM testing, although early detection biomarkers are being explored. DNA never replaces, but should always enhance, interactions between the client and the veterinarian.

Veterinarians are expected to obtain, understand, and interpret DNA results and provide this "genetic counselling." However, since a majority of the cat population and cliental does not represent fancy breed cats, breeders are not generally the largest portion of clients in a standard veterinary practice and genetic testing in random bred cats is minimal. But what pertains to cats, certainly pertains to dogs, and the use of genetics for "marker-assisted selection" on the farm is also becoming a standard practice. Genetic testing for marbling of meat, milk fat, and milk production and even "speed" for horse racing are genetic tests currently on the market to be considered by the farmer. Farmers have considered genetics regarding their crop seed selection for decades, now it also pertains to their livestock and companion animal farm workers - the cat and dog.

For the past 10–15 years, many veterinarians have received formal training in genetics within their veterinary curriculum in the USA. Minimally, different modes of inheritance are reviewed and younger veterinarians should be able to provide minimal genetic counselling as a result. The mode of inheritance, (autosomal versus sex-linked, recessive, dominant) incomplete penetrance, variable expression, age of onset, and risk are terms the modern veterinarian should know and understand. Directed versus non-directed counselling is also a concept that should be considered. Most veterinarians want to provide "directed" counselling - your cat has PKD - then you should alter it and never breed the cat again. Directed counselling is extremely taboo in human medicine, and if the "big picture" is considered in veterinary medicine, directed counselling should also be very non-standard in animal genetic counselling as well. The "big picture" not only pertains to the cat itself, but the breed population and the livelihood of the breeder. As determined by sequencing of thousands of humans, each individual, human or cat, has several severe mutations in their genome that should render them unfit! We yet do not understand how all the ~ 21,000 genes of the body interact, thus, explaining terms like "incomplete penetrance" and "variable expression." Cats have a PKD or HCM mutation - definitely - but we cannot predict their overall health because of the interaction of thousands of other genes in the body, which are designed to be redundant and maintain our fitness. Thus, in genetic counselling, one should consider all the good things as well as the bad things that a cat has to determine future breeding and population management. Certainly the present health condition of the cat should be the utmost concern; however, this cat's nature, reproductive success, resistance to other health problems, as well as their aesthetic qualities need to be considered. By understanding the mode of inheritance, diseases can be slowly removed from populations, importantly to not cause other bottlenecks and other inbreeding concerns.

References

60. Meurs KM, Sanchez X, David RM, et al. A cardiac myosin binding protein C mutation in the Maine Coon cat with familial hypertrophic cardiomyopathy. Hum Mol Genet. 2005;14(23):3587–3593.

61. Longeri M, Ferrari P, Knafelz P, et al. Myosin-binding protein C DNA variants in domestic cats (A31P, A74T, R820W) and their association with hypertrophic cardiomyopathy. J Vet Intern Med. 2013;27(2):275–285.