Genetic basis of Degenerative myelopathy - it is most commonly caused by a mutation in the SOD1 gene (superoxide dismutase 1). The disease is inherited in an autosomal recessive manner with incomplete penetrance, meaning dogs must inherit two copies of the mutated gene (one from each parent) to be at higher risk, but not all will necessarily develop clinical disease. A DNA test is available to identify clear, carrier, and at-risk breeding animals.
Pathophysiology - Degenerative myelopathy is a neurodegenerative disease leading to immune-mediated destruction of nerve fibers in the spinal cord. The mutation impairs normal nerve function and results in progressive loss of myelinated fibers, primarily in the white matter of the spinal cord. Clinical onset is usually in middle-aged to older dogs (around 7–10 years), beginning with hind limb proprioceptive deficits, knuckling of the feet, and ataxia. Eventually, paralysis ascends to forelimbs and respiratory muscles as neurodegeneration progresses. Once nerve loss occurs, it is irreversible.
Complications - Affected dogs experience gradual muscle wasting, incoordination, progression to paralysis, and ultimately respiratory failure. Most dogs are euthanized for humane reasons before advanced complications such as loss of bladder/bowel control or breathing difficulties occur, as there is no cure and supportive therapies have limited effectiveness in later stages.
Why This Matters to Breeders and Vets - Early identification is critical due to irreversible progression. Breeders should use DNA screening to avoid breeding carriers together and thus reduce disease prevalence. Veterinarians must recognize symptoms early, educate owners, and recommend testing in predisposed breeds. Early supportive treatment may slow progression but becomes ineffective once advanced deficits manifest. Because post-mortem examination is required for a definitive diagnosis and many cases go undiagnosed, the true incidence is likely underestimated in surveys.
Summary - Degenerative myelopathy is a devastating inherited neurodegenerative disease affecting the spinal cord of middle-aged and older dogs, with highest risk in German Shepherds but present in many breeds. It is linked to autosomal recessive SOD1 mutations, causes progressive paralysis from hind limbs forward, and has no cure. DNA testing guides responsible breeding, while early recognition is critical for maximally effective management.