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.
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 ...