Tag archives: variable expressivity

The Veterinarian’s Corner: Variable Disease Presentation and How Genetic Testing Can Help

The Veterinarian’s Corner: Variable Disease Presentation and How Genetic Testing Can Help

Every veterinarian leaves veterinary school with a mental laundry list of animal diseases and their textbook presentations. While this knowledge serves the young graduate well in most circumstances, with clinical experience and mentorship comes the ability for veterinarians to expand their mental notes about the various ways some diseases can present in the real world. For some inherited canine diseases, genetic testing has allowed the practitioner to correlate a broader set of clinical signs for dogs affected by identical underlying genetic mutations. This variability in disease phenotype, known as variable expressivity, is a result of the combined effect of all genetic and environmental factors influencing each individual and can add significant challenge to some diagnoses. However, supplementing a disease workup with genetic test results can prove invaluable in diagnosing inherited diseases that have the frustrating attribute of rarely presenting the same way twice.

Collie Eye Anomaly

Now known to occur in well over a dozen breeds, the recessively inherited collie eye anomaly or CEA (also known as choroidal hypoplasia) is a relatively common eye disease of dogs and a good example of a disorder which can have diagnostic challenges due to its phenotypic variability. CEA is caused by a deletion ...

The Variability of Certain Canine Diseases

The Variability of Certain Canine Diseases

In my last blog, I defined words that described when symptoms may present themselves in a dog affected with a genetic condition.  Today’s topic of discussion is how those symptoms show up (or not show up).  These terms are easily confused with each other.  I’ve even heard some geneticists can get these definitions mixed up.  Let me introduce two terms: Incomplete penetrance and variable expressivity.

Incomplete penetrance is a term that describes symptoms, which may or may not be present in a dog with an at-risk or affected genotype.  The dog has the mutated gene in the right number of copies to cause the disease, but the dog may not show physical symptoms of the disease.  As you can imagine, this can cause some confusion when examining the pedigrees of your dogs and this is when genetic testing becomes an important tool.  If genetic testing is positive, we know the dog has the mutation that causes the disease. Regardless if there are symptoms, this dog can pass this mutation on to its offspring.  Knowing this information may impact breeding practices, as discussed in previous blogs.  The concept of incomplete penetrance is an ...