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 Bernese mountain dog, can be difficult to manage and owners often elect euthanasia when their dog can no longer support weight in the hind limbs.
Testing Tips
Genetic testing of the SOD1 gene 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. Dogs 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]
