We are often contacted by our customers who want to know exactly what their genetic test result means when it comes to disease outcomes. We believe it’s important for our customers to understand the implications of their results so that they can make good healthcare and breeding decisions. Although the testing process is straightforward, the interpretation of the result is not always easy and can be different from test to test. The disease outcome is well-defined for some mutations we test for because every animal known to carry the mutation is known to suffer from the disease. However, there are other genetic tests we offer that are referred to as risk-based genetic tests that can be more complex when it comes to predicting disease outcomes.
There are a few different scenarios that can lead to a test being classified as risk-based. Often times when researchers are looking for the mutation responsible for a particular disease, they will find mutations surrounding or related to the causative mutation early in the research process. These linked mutations will typically be strongly associated with the disease and although not always the full story, these associated mutations can still act as a good guide for decision-making until more research can provide a better understanding of the disease. A good example of this type of true risk-based test is Dermatomyositis (DMS) in Collies and Shetland Sheepdogs. This test provides a risk-based result of low, medium, high, or unknown that can reliably predict the likelihood of a dog developing DMS and can assist with breeding program decisions.
There are other risk-based genetic tests that can present with a spectrum of severity. This means that not every dog that has the mutation will present symptoms. Within animals that do present symptoms, not all will show the same level of disease severity. This can be due to a number of factors including genetic background and environment. A good example of this type of risk-based test is Chondrodystrophy (CDDY) which leads to shortened limbs and also has an inherent risk for Intervertebral Disc Disease (IVDD). Some dogs with the CDDY mutation require minimal treatment and exhibit minor symptoms while other dogs may have a more severe disease presentation. Other genetic diseases that present with a spectrum of severity can be due to environmental factors and are predominantly controlled through diet. Two good examples of these types of risk-based mutations are Copper Toxicosis in Labrador Retrievers (CT-LAB-A and CT-LAB-B) and Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) in Cavalier King Charles Spaniels. Both genetic disorders can be easily managed through a carefully controlled diet that limits either copper for Copper Toxicosis or certain types of fats for MCADD.
One final scenario that can lead to a risk-based test is something known as incomplete penetrance. This means that not every dog that carries the mutation will present clinically with the disease. A good example of incomplete penetrance is the mutation for Degenerative Myelopathy (DM) that can be found in a large number of breeds. Some breeds like German Shepherds, Bernese Mountain Dogs, and Boxers are examples of breeds that are very likely to suffer from the disease when two copies of the mutation are present. However, other breeds may also carry two copies of the mutation and no animals within the breed are known to show clinical symptoms of the disease. This would be a case where more research is needed to fully understand the cause of the disease.
Interpreting the outcome of risk-based tests can be complicated so at GenSol we try to provide as much information as possible to help you understand the implications for your genetic test results. We start by providing a brief description of each test result on all result certificates. We have more in-depth test and result descriptions for each test on our website and we have staff ready to answer questions or provide more information so that you have the knowledge you need to make better healthcare and breeding decisions. As always, don’t hesitate to contact us if you have any questions, and together, we can support better pet health.
