Dog breeders often ask, why are the risks for some health conditions difficult to detect with genetic testing?
The short answer is: genetics can be simple or complex—scientific terms that mainly refer to patterns of inheritance or transmission of a disease-causing mutation. Some health issues currently have a DNA test available to see if your dog has a causative variant (a genetic mutation known to be the cause of the disease or disorder). But other health conditions are more challenging because they can be caused by the interaction of multiple genes and environmental factors.
Below, our veterinary experts and geneticists highlight key differences between simple and complex genetics, so you can better understand your test results and how to apply them. Our team is also available for one-on-one consults to discuss health concerns and options available for your breeding program.
Mendelian or simple genetics
You’re probably familiar with Mendelian genetics—where health conditions are inherited in a recessive or dominant manner. From most Progressive Retinal Atrophy (PRA) to certain types of bladder stones (like HUU), almost all the DNA tests currently offered are based on a recessive mode of inheritance (MOI), where two copies of the variant are necessary to be considered at-risk for the disease from the variant (or have the known phenotype). Other genetic variants have a dominant MOI, where dogs with one or two copies of the variant can express the phenotype.
In each case, because the variants can be treated as single attributes, developing a genetic test for a specific health condition is often straightforward—which is a good thing, because breed carrier frequencies of simple disorders can be very high: from 10–30%. Breeders may apply the results of their dog’s DNA test to their breeding programs, to decrease the incidence of an unwanted variant.
But Mendelian genetics doesn’t always tell the whole story. Unlike simple genetic disorders, some conditions—like epilepsy, hip dysplasia, some heart conditions, and cancers—are considered complex, because they’re the result of the interplay of multiple genes +/- environmental factors. This makes it challenging to identify the underlying genes, especially when there are no clear inter-generational patterns to confirm transmission of the disorder, or genetic interactions with environmental exposures.
More research is needed to know how to avoid propagating complex disorders in breeding programs.
So until then, many breed clubs and registry organizations recommend combining a DNA test with non-genetic tests, like cardiac examinations, hip or elbow X-rays, or endocrine testing.
As always, transparency is key. If your dog is diagnosed with a medical condition that may have a complex genetic basis, communicate with your breed club registry, Embark, the Orthopedic Foundation for Animals (OFA), or the Canine Health Information Center (CHIC) to help track the condition. Filling out our health surveys will help provide us with more information. And you can always add documents to your dog’s Embark profile, here. Watch for future Embark blogs that will take a deeper look at complex genetic diseases.
Decoding the future
Embark is uniquely positioned to tackle the complex disorders that have previously confounded researchers. Every Embarked dog can be opted into research. Every completed health survey will be analyzed by our team of scientists. Every new development will be shared across our ecosystem. Together, we can accelerate genetic discovery for better management of complex disease in dogs.