Preventive measures are an increasing part of our case load as small animal practitioners. As such, involvement in screening procedures and testing for inherited diseases is an evolving area of our professional duties.

But how to manage and handle breeding advices regarding cases not yet possible to screen or test?

Screening Programs

In many disciplines screening for an early detection to predict clinical outcome and prevention from breeding of affected animals have been in place for more than half a century (e.g., screening for radiographic signs of hip and elbow dysplasia is now routine in many countries) and has proven its value in populations where a larger proportion of breeding stock is screened and unaffected. Likewise, palpatory screening for patellar luxation is well validated for its purpose.

Screening for hereditary eye conditions has also been in place for more than half a century; screening for signs of mitral valve disease and cardiomyopathy are available for some breeds in some countries as well as screening for syringomyelia.

More recently, examination for brachycephalic airway obstructive syndrome has been offered in many countries.

DNA Testing

Since the canine genome was revealed in 2005, testing for “genetic diseases” has become increasingly popular within many disciplines.

Longtime mutations for many disorders with a simple recessive inheritance have been identified. Especially hereditary eye conditions as several variants of PRA have been revealed over the last decades and also lens luxation. Out of common neurological diseases, the mutations for several more or less breed-specific epilepsies have been found as well as more rare conditions with a mitochondrial transmission like SAN in golden retrievers.

The Controversy on Risk Gene Tests

Besides these altogether fairly rare conditions with a simple inheritance there are very few genetic tests (risk gene tests) for more complex diseases that have fully proven their value as indicators of the risk to be clinically affected.

Top Causes of Deaths

By availability of epidemiological data from insurance databases (Bonnet et al. 1997, 2005), breed club surveys (Adams et al. 2010) or general practices (Lewis et al. 2018) we now know the top causes of deaths (mortality) as well as reasons for veterinary care (morbidity). Table 1 lists a number of common more or less specified causes of deaths as well as veterinary care. Some of them are causes of euthanasia rather than “deadly diseases.” Many of those indicated are not just one disease. At a closer look at these diagnoses it can be seen that they are commonly not just one but rather several variants of a cruder diagnose. Lymphoma, cardiomyopathy, and epilepsy are not just one disease but rather lymphomas, cardiomyopathies and epilepsies. Likewise, diabetes, elbow dysplasia and PRA are of various forms. To refine these diagnoses is of utmost importance for clinical management of the cases as well as handling the selection of breeding stock.

Most complex diseases and not yet fully revealed complex diseases (that is, those with many genes involved and often more or less known environmental factors) still make up the great majority of cases handled by general practitioners and specialists in almost every sub discipline.

Most common causes of death as well as other severe diseases are not possible to either screen for at an early age or to predict by molecular genetic screening.

Table 1. Common causes of canine death by discipline with
an indication on available screening programs and DNA tests

The Need for Specific Diagnoses

Based on research the colleges and other specialist organisations are best suited to propose diagnostic criteria based on research for each of these diseases.

General practitioners and registration bodies like OFA and several kennel clubs are key elements for the use of more specific information in its use for breeding advice.

Death Registries

As a complement to epidemiological data currently available it is proposed that death registries—either for all diagnoses as specific as possible or for specified diagnoses with diagnostic criteria—is established by national Kennel Clubs or breed clubs as a valuable complement to current registrations of phenotypic screening and results from DNA testing.

Researchers and specialist organisations have been and are still involved in the establishments of phenotypic as well as genotypic screening programs.

They are now urged also to reveal—within their disciplines—the more refined aetiology and diagnostic criteria to be used for proper registration of the most common causes of deaths.

It is then of utmost importance also that such refined diagnostic criteria are used in general practices and when possible also registered together with the ancestral background of a potential breeding animal.

By collaborative efforts by researchers, specialist organisations, general practitioners and registration bodies a novel tool to handle also diseases not yet possible to screen for.

With information in death registries on age and causes of death, a powerful complement to current screening programs would enhance selection of breeding stock for a long and sustainable life.

References

1.  Bonnett BN, Egenvall A, Olson P, Hedhammar Å. Mortality in insured Swedish dogs: rates and causes of death in various breeds. Vet Rec. 1997;141(2):40–44.

2.  Bonnett BN, Egenvall A, Hedhammar Å, Olson P. Mortality in over 350,000 insured Swedish dogs from 1995–2000: I. Breed-, gender-, age- and cause-specific rates. Acta Vet Scand. 2005;46(3):105–120.

3.  Adams VJ, Evans KM, Sampson J, Wood JL. Methods and mortality results of a health survey of purebred dogs in the UK. J Small Anim Pract. 2010;51(10):512–524.

4.  Lewis TW, Wiles BM, Llewellyn-Zaidi AM, Evans KM, O’Neill DG. Longevity and mortality in Kennel Club registered dog breeds in the UK in 2014. Canine Genet Epidemiol. 2018;5:10.