Degenerative Myelopathy (Bernese Mountain Dog Variant)

Common Symptoms

Degenerative myelopathy SOD1B (Bernese mountain dog type) is caused by a Mutation of the SOD1 gene currently only identified in the Bernese mountain dog.  Bernese mountain dogs are known to develop a more slowly progressive form of degenerative myelopathy (DM) associated with this mutation. In general, there is variable presentation between dogs with this disease suggesting that there are environmental or other genetic factors responsible for modifying disease expression. The average age of onset for dogs with DM is approximately nine years of age. The disease affects the White Matter tissue of the spinal cord and is considered the canine equivalent to amyotrophic lateral sclerosis (Lou Gehrig’s disease) found in humans. Affected dogs usually present in adulthood with gradual muscle Atrophy and loss of coordination typically beginning in the hind limbs due to degeneration of the nerves. The condition is not typically painful for the dog, but will progress until the dog is no longer able to walk. The gait of dogs affected with DM can be difficult to distinguish from those with hip dysplasia, arthritis of other joints of the hind limbs, or intervertebral disc disease. Late in the progression of DM, dogs may lose fecal and urinary continence and the forelimbs may be affected. Affected dogs may fully lose the ability to walk within 2 years after the onset of symptoms. Medium to large breed dogs that are affected with DM, such as the Bernedoodle, can be difficult to manage and owners often elect euthanasia when their dog can no longer support weight in the hind limbs.

Breed-Specific Information for the Bernedoodle

Bernedoodle is included as a breed susceptible to Degenerative myelopathy (Bernese Mountain Dog Type) because of its close relatedness to the Bernese mountain dog breed, which is known to develop this disease due to Mutation of the SOD1 gene. The frequency of the causal mutation in the general Bernedoodle population is unknown. The Bernedoodle is also at risk for a more common, but different mutation in the SOD1 gene that has been associated with DM in over 100 breeds of dog. Therefore, Bernedoodles that are carriers or clear of the SOD1B (Bernese mountain dog type) mutation may still be at-risk for the more common DM SOD1 mutation.

Because dogs inherit one copy of the SOD1 gene from their mother and one copy of the SOD1 gene from their father, they may be at risk of carrying either the SOD1 common DM mutation, the SOD1B mutation or both. When a dog is a Carrier of both types of SOD1 mutations, the laboratory cannot distinguish the presence of both mutations on one copy of the gene, or one mutation on each copy of the gene without further studies which could include studying that dog’s parents or litter mates. Dogs that carry one copy of each type of SOD1 mutation on different copies of the gene are referred to as compound heterozygotes, which means that both genes are impacted by different mutations and the dog may be at-risk/affected for DM. Bernese mountain dogs inheriting two copies of the more common SOD1 gene mutation may also develop degenerative myelopathy, even if they have not inherited the SOD1B mutation.

Testing Tips

Genetic testing of the SOD1 gene in Bernedoodles will reliably determine whether a dog is a genetic Carrier of the degenerative myelopathy SOD1B (Bernese mountain dog type) Mutation. Degenerative myelopathy SOD1B (Bernese mountain dog type) is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the SOD1 gene mutation. Reliable genetic testing is important for determining breeding practices. Because symptoms may not appear until adulthood and some at-risk/affected dogs do not develop the disease, genetic testing should be performed before breeding. Until the exact modifying environmental or genetic factor is determined, genetic testing remains the only reliable way to detect neurological disease associated with this mutation prior to death. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Bernedoodles that are not carriers of the mutation have no increased risk of having affected pups due to this mutation.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.

References

• Awano T, Johnson GS, Wade CM, Katz ML, Johnson GC, Taylor JF, Perloski M, Biagi T, Baranowska I, Long S, March PA, Olby NJ, Shelton GD, Khan S, O'Brien DP, Lindblad-Toh K, Coates JR. Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A. 2009 Feb 24; 106(8):2794-9. [PubMed: 19188595]
• Coates JR, Wininger FA. Canine degenerative myelopathy. Vet Clin North Am Small Anim Pract. 2010 Sep; 40(5):929-50. [PubMed: 20732599]
• Pfahler S, Bachmann N, Fechler C, Lempp C, Baumgärtner W, Distl O. Degenerative myelopathy in a SOD1 compound heterozygous Bernese mountain dog. Anim Genet. 2014 Apr;45(2):309-10. [PubMed: 24450472]