Degenerative Myelopathy (SOD1A)

Degenerative Myelopathy (DM)

Testing performed in cooperation with our partner laboratory.

Degenerative myelopathy (DM) is a progressive neurodegenerative disease that affects many dog breeds, typically beginning around eight years of age. Currently, over 120 breeds are known to be susceptible to this condition.

DM is caused by a mutation in the superoxide dismutase 1 gene (SOD1). Dogs affected by the disease develop non-painful weakness of the hind limbs, progressing to lack of coordination, gait instability, muscle atrophy, urinary and fecal incontinence, and eventually paralysis.

Symptoms generally appear between 3 and 5 years after the onset of early signs. Although the disease is fatal, it is painless.

In most breeds, DM is associated with the SOD1 mutation c.118G>A.

In Bernese Mountain Dogs, however, another SOD1 mutation (c.52A>T) may be responsible.

DM is inherited in an autosomal recessive manner.

A dog must inherit two mutated copies of the SOD1 gene to be at risk of developing the disease.

Heterozygous dogs (carriers) may show delayed or incomplete symptoms, influenced by environmental factors, modifying genes, or incomplete penetrance.

Because clinical signs appear only in adulthood, genetic testing is essential for determining whether a dog is:

N/N – Clear / Genetically Normal

Does not carry the mutation.

N/P – Carrier / At Risk for Offspring

Has one normal and one mutated copy; does not typically show symptoms but can pass the mutation to offspring.

P/P – Affected / Genetically At Risk

Has two mutated copies of the SOD1 gene; at high risk of developing DM.

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Breeding combinations to avoid (risk of P/P puppies)

Parental Genotypes Offspring Outcome

P/P × P/P 100% of puppies genetically at risk (P/P)

P/P × N/P 50% carriers (N/P), 50% at risk (P/P)

N/P × N/P 25% clear (N/N), 50% carriers (N/P), 25% at risk (P/P)

Breeding combinations that will not produce genetically affected puppies:

Parental Genotypes Offspring Outcome

N/N × N/N 100% clear (N/N)

N/P × N/N 50% clear (N/N), 50% carriers (N/P)

P/P × N/N 100% carriers (N/P)

Note: Many breeding clubs recommend that dogs with the P/P genotype are not used for breeding.

In breeds with a small gene pool, eliminating all P/P dogs may reduce genetic diversity. In such cases, balancing genetic health and diversity is important.

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References

Zeng, R., et al. “Breed Distribution of SOD1 Alleles Previously Associated with Canine Degenerative Myelopathy.” Journal of Veterinary Internal Medicine 28.2 (2014): 515–521.

Crisp, Matthew J., et al. “Canine degenerative myelopathy: biochemical characterization… ” Experimental Neurology 248 (2013).

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