World of Cats & Dogs

Genetic Counseling and Management of Genetic Disease

The hallmark of genetic disease is our ability to predict its occurrence before its onset, allowing us to alter its morbidity or mortality. The vast majority of dogs and cats are not breeding animals, but they still require genetic counseling for inherited disorders. Owners of large-breed puppies are counseled to feed lower calorie foods to provide for a more uniform growth rate and better joint development. Cats genetically predisposed to FLUTD (Feline Lower Urinary Tract Disorders) and obese “pre-diabetic” cats can receive specific dietary recommendations.

We need to be knowledgeable about what genetic tests are available, and in which individuals they should be run. Dogs from breeds with an incidence of von Willebrand’s disease should be tested early in life, so that measures can be taken to prevent excessive hemorrhage during surgery or injury. Dogs at risk of carrying the mdr-1 mutation should be tested early in life, before drug treatment.

In high risk breeds, individual animals should be genetically tested (or verified results documented for parents) before purchase. These include Maine Coon and Ragdoll cats for the autosomal dominant hypertrophic cardiomyopathy gene, Persian and Himalayan cats for autosomal dominant polycystic kidney disease, Boxers for arrythmogenic right ventricular cardiomyopathy, and Doberman Pinschers for dilated cardiomyopathy.

We need to understand the temporal periods when genetic testing will be most accurate, and allow for intervention. Puppy hips should be palpated with a gentle Ortolani procedure at each vaccine visit, and again at spaying or neutering under anesthesia. Juvenile interventional surgery will only benefit those with significant subluxability prior to major growth (for pubic symphysiodesis) or the development of osteoarthritic changes (for triple pelvic osteotomy). Genetic testing for hypothyroidism is based on the presence of thyroglobulin autoantibodies. A dog with normal TgAA levels on two tests at least two years apart between two and six years of age is phenotypically normal. However, TgAA levels should not be measured within 2 to 3 months post-vaccination, as a transient iatrogenic rise can occur during this period.

For most genetic diseases, we know how to either prevent their occurrence, or at least lessen the possibility of producing offspring with genetic disease. This can occur through the genotypic testing of the parents (identification of parents carrying liability genes for genetic disease), phenotypic testing of the parents (identification of parents affected with genetic disease), or pedigree analysis (identification of a carrier and affected risk based on knowledge of the carrier or affected relatives).

The genetic improvement of cats and dogs will only occur through selective breeding. However, improvement will not occur unless we all understand our roles and responsibilities. The responsibility for this improvement lies not just with the breeder; but also with breed organizations, veterinarians, and the general public. Breeders must perform genetic testing on prospective breeding stock before breeding. Breed organizations must identify breed specific health issues through regular breed health surveys, fund research for breed specific disorders, and recommend genetic testing for breeding animals. Veterinarians must counsel prospective owners and breeders on breed specific health issues. They should provide the necessary genetic testing, or direct owners to specialists (ophthalmologists, cardiologists, etc.) that can perform the testing. The general public must become knowledgeable about what genetic tests are needed on parents of prospective kitten and puppy purchases, and how to verify testing status.

Inherent in these responsibilities is the acknowledgement that breeding without genetic testing is irresponsible, and unethical. Genetic testing is health quality control. It is no longer acceptable for a breeder to choose two individuals and breed them together without regard to genetic disease control.