client presents a 4‐year‐old Abyssinian cat that they feel is having issues with vision. An eye examination shows hyperreflective retinas and attenuation of retinal vessels. You recommend an examination by a veterinary ophthalmologist but also send out a genetic test for the rdAc form of PRA. The genetic test result shows that the cat is affected with this simple autosomal recessive disease.
A client brings you the results of a direct‐to‐consumer multiplex test on their French bulldog which reports that it is homozygous for the sod1 mutation and is “at risk” of developing degenerative myelopathy. You report to the owner that their dog has little to no risk of developing degenerative myelopathy as it has never been documented in the breed and the breed likely lacks other mutations required to cause this complexly inherited genetic disease.
Genetic testing includes physical and phenotypic examinations as well as DNA testing.
Genetic testing is important in pet and breeding animals.
There are many different types of genetic tests that all have different interpretations for the tested patient.
Genetic testing should be done for a purpose, and not just because a genetic test exists.
Genetic test results that are valid in one breed may not be valid in other breeds. That is, a genetic mutation that is associated with a specific disease in one breed may not be associated with the same disease in other breeds.
3.6.6 Cautions
Some genetic tests being offered commercially have not been validated to cause or predispose to clinical disease. Peer‐reviewed publication of a mutation does not mean it is validated to cause disease in one or more breeds.
Some genetic tests may be valid in some breeds but not in others, where the results may have no bearing on health or traits.
Some genetic testing laboratories use unvalidated analytical techniques in running genetic tests that can produce false results.
Recommended Reading
1 Ackerman, L. (2011). The Genetic Connection: A Guide to Health Problems in Purebred Dogs, 2e. Lakewood, CO: AAHA Press.
2 Bell, J.S., Cavanaugh, K.E., Tilley, L.P., and Smith, F.W.K. (2012). Veterinary Medical Guide to Dog and Cat Breeds. Jackson, WY: Teton NewMedia.
3 Gough, A., Thomas, A., and O'Neill, D. (2018). Breed Predispositions to Disease in Dogs and Cats, 3e. Oxford, UK: Wiley Blackwell.
4 Mellersh, C. (2016). DNA testing man's best friend: roles and responsibilities. Veterinary Journal 207: 10–12.
3.7 Genetic Health Registries and Research Organizations
Anita M. Oberbauer, PhD
Department of Animal Science, University of California, Davis, Davis, CA, USA
3.7.1 Summary
Owners want the healthiest companions they can have, and veterinary healthcare teams play a key role in achieving this goal. Predicting health characteristics is critically important for responsible pet ownership and that requires accurate health data. Veterinarians should recommend relevant health testing for all pets and then encourage owners to submit the results of those tests to existing health registries. Genetic health registries compile health data, making that information available to breeders who can then breed with intentionality, owners who can better predict the health of their individual pet, and researchers who can use that information to study disease inheritance and prevalence, and identify emerging health conditions. The value of such health information in breeding and health research cannot be overstated. It is through this type of collated information that genetic diseases are described and tools to reduce incidence discovered.
3.7.2 Terms Defined
Carrier: The animal has a normal and a mutant copy of a gene, i.e., is heterozygous.
Health Registry: Database containing the health screening information and identifying characteristics such as breed, sex, age, and pedigree of individuals.
Health Screening: The use of tests to identify individuals that do not exhibit overt clinical signs yet have risk factors or early stages of disease.
Homozygous: Both copies of a gene are the same, i.e., the DNA sequence is the same.
Linked Test: A test that targets the region of DNA that is generally associated with the disease.
Mutation Test: A test that targets the actual DNA change that causes the disease; sometimes referred to as a direct genetic test.
Phenotypic Test: A test that detects visible or measurable differences related to a disease.
3.7.3 The Need
Many veterinary organizations consider health testing an essential component of veterinary medicine. Their policies on inherited disorders often include the goals of maximizing the health and welfare of companion animals and the education of breeders, owners, and the public on the responsibilities involved to minimize inherited disorders in the pet population. In order to achieve that goal, an understanding of the inheritance and genetics underlying disease is necessary (see 3.1 Genetic Basics and 3.2 Modes of Inheritance). Such understanding requires a foundation of knowledge on disease prevalence, mode of inheritance, and, ideally, determination of the DNA mutations that cause the disease (see 3.3 The Genetics of Disease). Aggregation of descriptive health data is necessary to characterize diseases of companion animals and thereby enable the research that will lead to that fundamental knowledge of what diseases are relevant to a given breed and, importantly, the development of tests needed to reduce the incidence of those diseases.
To that end, veterinarians should encourage the use of health screening in all their clients. For the clients, screening plays a role in managing the health of an individual pet and developing a holistic, long‐range health plan based upon knowledge of susceptibility to certain diseases. Adverse reactions can be avoided or preemptive care can be initiated if known disease risk is identified through screening. Additionally, screening is an important tool for the health of all companion animals in reducing the incidence of disease and discovery of trends
