Degenerative Myelopathy Early-Onset Risk Modifier (Pembroke Welsh Corgi Type)

Common Symptoms

The degenerative myelopathy risk modifier (Pembroke Welsh corgi type) is a genetic Mutation that affects the onset of degenerative myelopathy (DM) in the Pembroke Welsh corgi in a dog already at risk for the disease. In Pembroke Welsh corgis that also have two copies of the common DM mutation in SOD1, a mutation in the SP110 gene may increase the chance of developing DM by decreasing the age of disease onset. In the absence of two copies of the common SOD1 DM mutation, this SP110 variant does not have any effect on a dog’s health. While this SP110 mutation has been identified in breeds other than the Pembroke Welsh corgi, it is unknown if this mutation increases the risk of DM in these breeds when also present with two copies of the SOD1 common DM mutation. Dogs identified with one or two copies of the SP110 variant and no mutation in SOD1 are not at an increased risk of DM. Therefore, efforts to prevent puppies from being born with degenerative myelopathy should focus on preventing puppies from being born with two copies of the SOD1 gene mutation rather than selection against the SP110 mutation.

Degenerative myelopathy is an inherited neurologic disorder of dogs. The SOD1 gene mutation associated with degenerative myelopathy is found in many breeds of dog, including the Pembroke Welsh corgi. While it is not clear for some of the other breeds, Pembroke Welsh corgis are known to develop degenerative myelopathy associated with a mutation of the SOD1 gene. The variable presentation between breeds suggests that there are environmental or other genetic factors responsible for modifying disease expression. A mutation of the SP110 gene is associated with an increased risk of developing clinical signs of degenerative myelopathy and an earlier age of onset in Pembroke Welsh corgis which have also inherited two copies of the SOD1 gene mutation associated with degenerative myelopathy. 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 degenerative myelopathy can be difficult to distinguish from the gait of dogs with hip dysplasia, arthritis of other joints of the hind limbs, or intervertebral disc disease. Late in the progression of disease, dogs may lose fecal and urinary continence and the forelimbs may be affected. Affected dogs may fully lose the ability to walk 6 months to 2 years after the onset of symptoms. Affected small breed dogs, such as the Pembroke Welsh corgi, often progress more slowly than affected large breed dogs and owners may postpone euthanasia until the dog is paraplegic.

Testing Tips

Genetic testing of the SP110 gene in Pembroke Welsh corgis will reliably determine whether a dog is a genetic Carrier of degenerative myelopathy modifier (Pembroke Welsh corgi type). Degenerative myelopathy modifier (Pembroke Welsh corgi type) increases the risk of degenerative myelopathy in an Autosomal Dominant manner meaning that dogs that have two copies of the SOD1 gene Mutation only need to inherit one copy of the SP110 gene mutation to be at an increased risk of developing degenerative myelopathy. In general, dogs that are not at-risk for degenerative myelopathy will not have features of the disease even when they have one or two copies of the degenerative myelopathy modifier (Pembroke Welsh corgi type) mutation; therefore, testing for the degenerative myelopathy modifier (Pembroke Welsh Corgi Type) is only needed for dogs that are also at-risk for degenerative myelopathy. 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 more of the modifying environmental or genetic factors are determined, genetic testing remains the only reliable way to detect neurological disease associated with the SOD1 gene mutation prior to death. Pembroke Welsh corgis that are not carriers of the mutation have no increased risk of developing degenerative myelopathy.

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

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• Coates JR, March PA, Oglesbee M, Ruaux CG, Olby NJ, Berghaus RD, O'Brien DP, Keating JH, Johnson GS, Williams DA. Clinical characterization of a familial degenerative myelopathy in Pembroke Welsh Corgi dogs. J Vet Intern Med. 2007 Nov-Dec; 21(6):1323-31. [PubMed: 18196743]
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• Shelton GD, Johnson GC, O’Brien DP, Katz ML, Pesayco JP, Chang BJ, Mizisin AP, Coates JR. Degenerative myelopathy associated with a missense mutation in the superoxide dismutase 1 (SOD1) gene progresses to peripheral neuropathy in Pembroke Welsh Corgis and Boxers. J Neurol Sci. 2012 Jul 15;318(1-2):55-64. [PubMed: 22542607]
• Zeng R, Coates JR, Johnson GC, Hansen L, Awano T, Kolicheski A, Ivansson E, Perloski M, Lindblad-Toh K, O'Brien DP, Guo J, Katz ML, Johnson GS. Breed Distribution of SOD1 Alleles Previously Associated with Canine Degenerative Myelopathy. J Vet Intern Med. 2014 Feb 13. doi: 10.1111/jvim.12317. [PubMed: 24524809]