Canine degenerative myelopathy, DM, is a progressive condition that causes a decline of spinal function over time. It’s most commonly found in dogs eight years and older. It may begin with difficulties in walking, especially in the hind legs. It can rapidly progress to total paralysis of the hindquarters and can also affect the forelimbs. Once thought to affect only German Shepherds, it’s now known that this primarily genetic disease can occur in a number of purebred and mixed breed dogs. The canine gene associated with DM probably has a human counterpart in the gene that’s linked to ALS, also known as Lou Gehrig’s disease.
Because there are other canine diseases that can mimic DM, careful veterinary diagnosis is required. DM can sometimes be managed for a period of time, but it’s not curable and will ultimately be fatal. DM is transmitted by a recessive gene. This means that DM is unlikely to develop unless a dog has inherited two faulty genes, one from each canine parent. A dog with only one faulty gene will probably not develop DM because the normal gene will tend to compensate. Dogs can be genetically tested for DM, but since the results won’t change the ultimate outcome, this information may be of limited value, other than to reassure an owner whose dog has tested negative.
It’s also possible that even a dog with two faulty genes won’t actually develop DM. This is due to other genetic factors called penetrants. This is a way of saying that just because the faulty genes are present doesn’t always mean that they will be expressed, that is, cause a disease. It’s yet another reason why genetic testing for DM may not be a totally accurate predictor of disease. The owner may spend years in dread, and the disease never manifests at all.