How is degenerative myelopathy diagnosed?
A firm diagnosis of DM can only be made in a dog suspected to have the disease by examining the spinal cord microscopically after death. However, there is a DNA test that can be used to check your dog for a genetic mutation in the SOD1 gene. This is the most common, but not the only, gene associated with the development of canine DM. Dogs with two bad copies of the SOD1 gene are at risk for developing DM and can pass one bad copy of this gene along to each of their offspring. Dogs that carry only one bad copy of the SOD1 gene are less likey to develop signs of DM but will pass on a single copy of this gene to about half of their offspring. To read more about the science behind the genetics of DM, as well as how genetic test results can be used for breeding decisions, click here.
The SOD1 mutation commonly associated with DM has been detected in dogs from at least 124 different breeds. But not every dog with two bad copies of the SOD1 gene goes on to develop DM. In this way, the genetic mutation is considered a risk factor, or it is said to have incomplete penetrance. Because of this, genetic testing alone cannot be used to make a diagnosis of DM. You and your veterinarian should look at the results of genetic testing in combination with additional tests to make sure that other common causes of spinal disease can be taken off the list of concerns for your dog.