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Same Disease but Different Mutations: DM and SOD1B in Berners

By May 1, 2024No Comments

For many of the pet DNA tests we offer, there is typically one known mutation that leads to the canine disease or coat type. This usually makes healthcare and dog breeding decisions relatively straightforward once pet DNA test results are received. However, there are rare situations where an additional more recent mutation can arise within a single or select number of breeds that can lead to the same disease or coat type. In this case, it is important to understand the test results for more than one mutation and the unique result combinations that can ultimately lead to disease.

We first need to discuss where genetic mutations come from and how they are passed to future generations. Mutations happen naturally and can randomly arise in any individual animal. Many mutations are recessive which means you won’t notice anything until the animal is bred to another animal that carries the same mutation and the disease or coat type is visible in the offspring. An example of a disease that can be caused by more than one mutation is Degenerative Myelopathy (DM) in the Bernese Mountain Dog breed. Symptoms of this disease appear later in the dog’s life and consist of progressive loss of movement that eventually leads to complete paralysis and necessitates the dog be euthanized typically one year after symptoms appear.

One mutation that can lead to DM in Bernese Mountain Dogs is a mutation that can be found in many other breeds. This mutation arose early in dog history and was propagated across many breeds as dogs became more diversified through breeding. This mutation occurs in exon 2 of the gene and is typically referred to as the “DM” mutation in many breeds and the “SOD1A” mutation in the Berner community. More recently, a second mutation in the same gene was discovered that to date has only been detected in Bernese Mountain Dogs. This mutation is located in exon 1 of the gene and is referred to as the “SOD1B” mutation and very likely arose fairly recently in a single Berner and was propagated through breeding this individual. So, unfortunately, Bernese Mountain Dogs are subject to double jeopardy when it comes to DM.

The SOD1A and SOD1B mutations are not currently known to occur together on the same gene copy which makes test result interpretation and breeding healthcare decisions relatively straightforward for most combinations. The complexity arises when an individual tests as a carrier for both tests which means the dog has inherited one copy of both the SOD1A and SOD1B mutations. This situation is referred to as a compound heterozygote which means the dog lacks a good copy of the gene and will likely suffer from the disease. One gene copy contains the SOD1A mutation and one copy contains the SOD1B mutation which means the dog can be considered equivalent to a dog that tests affected for either SOD1A or SOD1B.

As more research is conducted, situations similar to DM in Bernese Mountain Dogs will likely arise where the same disease or coat type may result from more than one mutation. Some other more recent examples include coat tests like E Locus and Length which now have several breed-specific mutations that have been discovered. To be a part of the research, please consider submitting test results and health summaries to resources like Berner-Garde that track specific animals and are critical to continued understanding of genetic diseases like DM in the Bernese Mountain Dog breed.

And of course, please don’t hesitate to contact us if we can help you better understand your test results because with better understanding comes better decisions and improved overall pet health.