Roles, Risk, and Responsibilities - A Blueprint for Genetic Health Improvement
Jerold S. Bell, DVM
Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
The breeding of purebred dogs and pedigreed cats occurs around the world on a continual basis. Breeders select mates for their cats and dogs based on convenience, or their perception of the ideal mate. While there are many breeders who take into account genetic health, the vast majority of matings occur with no consideration of the genetic health of the parents or the offspring.
Dog and cat breeds were created through artificial selection to breed standards. Part of breed development is the monitoring and purging of hereditary disease. For any population, selection of breeding stock is the only process that maintains quality. This applies to conformation, behavior, ability, and also genetic health. Without selection, these qualities will drift away from the desirable to the undesirable. Maintaining breed characteristics and genetic health requires constant selection.
Phenotypic breed characteristics are easier to maintain and select for because they are evident in the individuals. Genetic health is more difficult to maintain because the majority of problematic disorders are either threshold traits that require genetic screening, or are recessive disorders where the carrier state is not evident in the phenotype.
Common genetic disorders in cats and dogs are caused by evolutionarily ancient genes and occur across breed lines. These disorders will vary in frequency between breeds depending on the genetic load of liability genes within the breed. Breed-specific genetic disorders are caused by mutations that occurred later in evolution, often affecting only a few related breeds, or a single breed.
Some genetic disorders have simple inheritance and may have genetic tests that objectively identify affected, carrier, and genetically normal individuals. Other genetic disorders may be complexly inherited disorders. These can require phenotypic screening tests or may require risk assessment for disease liability based on close relatives proven to be carrier or affected.
Each breed has its own assortment of genetic disorders as determined by breed health surveys and genetic screening. Based on this information, breed-specific pre-breeding genetic screening test requirements can be formulated as a template for health-conscious selection decisions. (See Available Resources).
If a puppy or kitten is the result of a designer or mixed-breed mating, each parent should have the required testing for their breed. The most common genetic disorders in dogs and cats are seen in members of breeds as well as in mixed-breed individuals.
Without specific pre-breeding screening recommendations, prospective breeding cats and dogs should be examined for cardiac, ophthalmologic, musculoskeletal and metabolic disease. Their medical history should be reviewed for episodes of common inherited conditions such as allergies, bladder stones, recurrent bladder disease, bloat, seizures, and others.The medical history ofclose relatives should be reviewed to assess the risk of carrying disease liability genes. Pre-breeding health screening and history should become as commonplace as an equine pre-purchase examination.
Selective pressure is the only way to reduce the frequency of genetic disorders in purposely bred dogs and cats. Breeding animals should be selected that are genetically normal, or have less risk of carrying disease liability genes than the average of the breed population. This offers the best prospect of producing healthier offspring.
Genetic screening is health quality control - a prerequisite for disease prevention and genetic improvement. Genetic disease is not random, and in most instances is predictable. The absence of selection based on pre-breeding health screening does not make the appearance of genetic disease random, it increases it.
Selective pressure also involves selecting health-conscious breeders who undertake genetic health screening with their breeding animals. Breeding brings with it responsibilities. Dog and cat breeders create new lives and place them in people's homes. Breeders who do not screen for genetic health need to feel the pressure from veterinarians, fellow breeders, and the public to fulfill their ethical obligation of health screening.
Aside from affecting the animals, genetic disease impacts several groups of people. Each of these groups has a stake in its occurrence, and a role in its prevention.
Parent breed clubs have a leadership role in the genetic health of their breeds. Through the use of regular breed health surveys, parent breed clubs can monitor the type, breed frequency, and trends of genetic disorders in their breed. For life-impacting and regularly occurring hereditary disease, parent breed clubs can offer pre-breeding health screening test recommendations. The club should also support the reporting of test results or affected and carrier individuals in an open health registry. (See Available Resources for all of the above.)
Parent breed clubs also have to monitor whether selection toward extreme phenotypes could be contributing to the frequency of genetic disease. These can include the brachycephalic syndrome, excessive skin and skin folds, extreme or unnatural angulation, and extremes in size. Moderation in selection should be promoted by parent breed clubs to their breeders, as well as in judge's education.
Breeders have a responsibility to produce healthy dogs and cats. This is an obligation: 1) to attempt to avoid painful and life-threatening disease in the living beings that they create, and 2) to the public who take them into their homes as members of their families.
Health guarantees invariably provide for replacement of a sold pet if a hereditary disease is diagnosed within a time period from the date of purchase. However, pets are not like toasters that can be replaced if found to be defective. Once an owner takes in a new dog or cat, they become part of the family and the emotional bond has been set. Replacement guarantees do not replace the ethical responsibility of genetic screening of breeding stock.
Breeders should undertake breed-specific pre-breeding health screening (as recommended by the parent breed club) for any potential breeding individuals. They should also look up screening and carrier risk results in open health registries, and/or request these results from owners of prospective mates. Matings should be planned that minimize the risk of producing individuals with genetic disease. Not all genetic disorders can be predicted and prevented; however, their occurrence can be significantly diminished through health-conscious breeding and selection of mates.
If a breeder is not willing or able to have the prescribed pre-breeding genetic tests performed, then they should find a different hobby or profession. Cats and dogs are living beings. It is not ethical to forgo the obligation of genetic testing.
The stigma of the presence of genetic disease has been a major factor in hampering genetic health improvement. No one wants to produce individuals with genetic disease. However, genetic health improvement cannot occur without the knowledge of the health status of individuals and their relatives - especially with complexly (polygenic) inherited disease or those without carrier tests. Breeders should release carrier or affected test results to open health registries.
With the common knowledge of testable or reportable disorders in the breed, the stigma shifts from those who openly report test results and carrier status of their dogs and cats to those who hide those results. When an affected individual is unintentionally produced, and it is later discovered that other breeders knew of the carrier risk of the parents, the fault lies with those that hide diagnoses and do not openly report negative test results.
Breeders should discuss breed genetic health issues with prospective owners and provide documentation of health testing of their breeding stock. Even if they have no puppies or kittens at the time, they should discuss health-conscious breeding to educate the public. Breed maintenance takes dedication of breeders for the betterment of the breed. Breed health is a community effort.
Veterinarians should be knowledgeable about the specific disorders occurring in breeds. They should know the screening tests that are available for diagnosing affected animals as well as for identifying carrier individuals (See Available Resources). This assists them not only in genetic counseling, but in the differential diagnosis of disease in their patients.
Veterinarians should counsel their breeder clients on pre-breeding health screening tests for prospective breeding animals. If these tests cannot be performed in the veterinary clinic, then they should inform the breeder of specialists (ophthalmologists, cardiologists, etc.) or of health screening clinics where the testing can be performed (See Available Resources). Veterinarians must emphasize the ethical responsibility of pre-breeding genetic testing, or a decision to not breed their animal.
It is only through the open reporting of affected dogs and cats that knowledge of disease risk can be identified through the test results or health status of close relatives. It is important that veterinarians encourage open reporting of health results by counseling breeders to initial the boxes for open disclosure of test results on the OFA submission forms. For many breeds of dogs, tracking hip dysplasia for example, over one-third of the applicants check the box on the OFA form for open reporting.
Genetic counseling does not just encompass working with breeders, but working with owners of pet animals as well. The hallmark of genetic disease is the ability to predict morbidity and mortality. If genetic expression can be altered by medications, diet, husbandry, or surgery, the veterinarian plays a role in improving the genetic health of their patients. Screening tests and evaluation for such heritable disorders should be conducted early in life. These include tests for bleeding disorders (especially prior to elective surgery), metabolic defects that alter drug metabolism, and other alterable disorders.
The expression of some genetic disorders cannot be altered. If a genetic test is available, it should be utilized pre-purchase so that owners are not burdened with predictable genetic disease. However, for owned animals it is a personal decision whether the owner wants to know if their pet has a high likelihood of developing a non-treatable genetic condition later in life.
There are genetic disorders that currently cannot be predicted prior to their onset, but, once diagnosed, can be managed to maintain good health. It is important to recognize that some of the most frequently seen disorders in veterinary practice are due to genetic influence. Their management requires long-term control and not just intermittent treatment during clinical episodes. These include allergies, feline bladder disease, chronic colitis, inherited skeletal disorders, and others.
The public has a responsibility to make informed decisions where they purchase or acquire dogs and cats. If purchasing from a breeder or broker, they need to ask about the results of breed-specific parental health testing. This is the only way that they can improve the chance of having a genetically healthy pet.
If test results on breeding animals for common disorders are not available in open health registries or official test certification is not available from the breeder, then it should be assumed that those individuals failed their health screening tests. Health-conscious breeders are happy to provide health test certifications.
If a breeder is only willing to offer excuses or guarantees without health screening certification, the prospective owner should walk away. If ethical guidelines do not cause a breeder to perform health screening, then the loss of sales from owners looking for healthy pets will be the only pressure that can change the system.
If genetic screening is not done, it doesn't hurt the breeder - it hurts the dogs and cats and their owners. The current ignorance and illiteracy of breeders, veterinarians, and the public on the necessity for health-conscious breeding must undergo a paradigm shift for the state of the genetic health of dogs and cats to improve.
The WSAVA Canine and Feline Hereditary Disease (DNA) Testing Laboratory website hosted by PennGen lists breed-related mutations (with references) and laboratories that test for them: http://research.vet.upenn.edu/WSAVA-LabSearch.
The OFA is a not-for-profit animal health foundation dedicated to the improvement of the genetic health of companion animals. Their website (www.offa.org) contains a wealth of information on genetic diseases and their control, as well as genetic disease registries. An excellent monograph on the use of health registry databases on genetic disease control is available (www.offa.org/pdf/monograph_2012_web.pdf). Most of the OFA information pertains to dogs. The OFA site has live-time breed health surveys (www.offa.org/surveys/index.html), genetic disease statistics by breed or disorder (www.offa.org/stats.html), breed-specific pre-breeding health test listings (www.offa.org/breedtests.html), listings of health screening clinics in the US (www.offa.org/clinics.html), and searchable health registries that show an individual's health screening test results as well as those of its close relatives (www.offa.org/search.html).
The International Cat Care website lists heritable and testable disorders for cat breeds (http://icatcare.org/advice/cat-breeds).
An excellent resource for canine health screening clinics in the US and Canada is on the CavalierHealth.org website (www.cavalierhealth.org/health_clinics.htm).