Degenerative Myelopathy is a debilitating disease that causes gradual paralysis in many dog breeds. It is caused by a degeneration of the spinal cord that onsets typically between 8 and 14 years of age. It presents first with the loss of coordination of the hind legs. It will typically worsen over six months to a year, resulting in paralysis of the hind legs. If signs progress for a longer period of time, loss of urinary and fecal continence may occur and eventually weakness will develop in the front limbs. An important feature of DM is that it is not a painful disease.
DM Research Publication in the Proceedings of the National Academy of Sciences: “Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis”
Explanation of DNA Test Results
This dog is homozygous N/N for the mutation that is the most common cause of DM, with two normal copies of the gene. Among the hundreds of dogs studied so far at the University of Missouri, only two dogs with test results of N/N (Normal) have been confirmed to have DM. The N/N (Normal) dog can only transmit the normal counterpart of the common mutation to its offspring, and it is unlikely that this dog or its offspring will ever develop DM.
This dog is heterozygous A/N, with one mutated copy of the gene and one normal copy of the gene, and is classified as a carrier. Carriers are far less likely to develop DM, but we have confirmed DM in a few carrier dogs. They may be used carefully in breeding programs to keep their good qualities while reducing risk of DM in future generations.
This dog is homozygous A/A, with two mutated copies of the gene, and is at risk for developing Degenerative Myelopathy (DM). Although almost all dogs in the research study with confirmed DM have had A/A DNA test results, recent evidence suggest that there are other causes of DM in some breeds. In addition, not all dogs testing as A/A have shown clinical signs of DM. DM is typically a late onset disease, and dogs testing as A/A that are clinically normal may still begin to show signs of the disease as they age. Some dogs testing A/A did not begin to show clinical signs of DM until they were 15 years of age. Research is ongoing to estimate what percentage of dogs testing as A/A will develop DM within their lifespan. At this point, the mutation can only be interpreted as being at risk of developing DM within the animal’s life. For dogs showing clinical signs with a presumptive diagnosis of DM, affected (A/A) test results can be used as an additional tool to aid in the diagnosis of DM. Dogs testing At-Risk (A/A) can only pass the mutated gene on to their offspring.
An Equivocal test result indicates that the test results were inconclusive. This is typically the result of poor sample collection. When the test yields an equivocal result, a second punch will be taken from the FTA card and the test rerun. If the second test is still equivocal, the owner will be contacted and asked to submit a new sample.
Although any dog can be tested for DM, it is possible that the genetic background that predominates in some breeds prevents the development of symptoms even in dogs testing affected (at risk). At this time we are reluctant to recommend testing for members of breeds where the University of Missouri has not yet proven susceptibility to DM through microscopic examination of spinal cords from deceased dogs that exhibited symptoms of the disease. The required evidence of association between the genetic mutation and actual spinal cord evaluations has only been proven in the breeds listed: