Degenerative myelopathy (DM) is a degenerative disease of the axons and myelin of the thoracic and lumbar spinal cord of older dogs of large breeds (in particular, German shepherds). The G118A mutation within the SOD1 gene encoding superoxide dismutase 1 is one of the possible causes of the disease. This mutation is autosomal recessive and is a point mutation associated with the conversion of glutamic acid into lysine. The presence of lysine leads to a change in the conformation of the protein and an impaired functioning of the protein. Abnormal conformation (folding) of SOD1 prevents the transport of molecules along the axon of the motor neuron, which leads to the death of nerve cells. The disease causes ataxia and inertia of the limbs. Characteristic symptoms of the disease are: weakness of the hind limbs, difficulty in walking, reluctant jumping, tripping, twitching of the muscles of the hind limbs, loss of muscles in the hind limbs, as well as urinary and faecal incontinence. The disease progresses very rapidly: from diagnosis to death, only a few months to several months pass.