Degenerative Myelopathy

Degenerative Myelopathy, or DM for short, is a gradually progressive neurological disorder of Chessies and many other breeds. It is similar to Amyotrophic Lateral Sclerosis (ALS, or Lou Gehrig's Disease), a condition found in humans. A recently-published paper describes the work done to develop the DNA-based test for Degenerative Myelopathy, and its links to ALS in humans. Click here to see this paper.

The spinal cord is wrapped in a protective membrane called the myelin sheath. Like insulation around an electrical cord, it protects the electrical pathway of the nerves running down the dog's spine. When this membrane becomes weak and starts to deteriorate, it is known as a myelopathy (myelo=myelin sheath, pathy=disease). Once this protective layer deteriorates, the nerves themselves are at risk of degeneration. DM consists of both myelin and spinal cord nerve fiber degeneration.

DM starts slowly, affecting the rear legs first. Early signs may go unnoticed by the owner. Slight dragging of a back foot, wearing of the toenails on the affected foot or feet can be an early sign. The hindquarters become progressively weaker, until the dog can no longer support its own weight. The disease eventually progresses until the front legs become affected, leading to complete paralysis.

DM is difficult to accurately diagnose. Many other conditions start out with similar symptoms. Injuries, bulging or ruptured vertebral disks, hip dysplasia, cruciate ligament ruptures, and many other things can show as a slight dragging of a hind foot, or wobbling when walking. All of these possible other causes must be ruled out before DM is considered as the cause of the dog's symptoms. Correct diagnosis is only possible through MRI to rule out other common causes, or at necropsy (autopsy). Even MRI diagnosis can be incorrect, as it only rules out other, similar diseases, it does not pinpoint DM.

DM is an inherited condition, and is polygenic in inheritance mode. This means that several genes, together with perhaps some environmantal factors, combine to create the disease in dogs. Currently, there is a DNA-based test for DM. It looks at only one of the genes that causes DM. The gene it identifies is a simple recessive. The inheritance mode(s) of the other gene(s) involved with DM are unknown at this time. The test can be ordered online through OFA. A list of Clear dogs, and those Carrier and At Risk dogs whose owners have released the information is available online through the OFA's online database.

Results of the test are reported as Clear, Carrier, or At Risk. Dogs are listed as At Risk, rather than Affected, because having this gene alone may not cause the disease. It is an indicator that the dog may develop DM at some point, but it is not a certainty. Dogs testing At Risk can still be bred; owners should take into consideration the dog's overall value as a breeding animal, and the test status of any mates when doing breedings. Click here to see OFA's breeding recommendations for Carrier and At Risk dogs. Based on test result statistics, the frequency of this allele in Chessies seems high, so eliminating all Carrier and At Risk animals would not be feasible. It would result in removing almost 60% of the breeding population. Obviously, this is not realistic. Instead, breeders should strive to reduce the occurrance of Affected animals, by knowing their dogs' testing status, as well as their bloodline's tendency to actually develop DM symptoms. Carrier and At Risk dogs from lines known to develop DM are a higher risk for producing affected offspring than dogs who test Carrier or At Risk, but are from lines where few or no animals actually develop symptoms. An article by Dr. Jerold Bell of Tufts University has been published through the American Chesapeake Club. The article answers many of the questions breeders have asked since the test came out, and can be accessed here.

Research is ongoing into causes and cures for this disease. The University of Missouri is still looking for dogs for its ongoing DM study. Dogs over ten years old, whether symptomatic or not, are needed. This phase of the study is looking for further factors that contribute to DM. Non-symptomatic dogs over the age of ten who have tested At Risk are especially valuable, as they may have factors which prevent development of DM, even when the gene is present. To submit samples for research, contact U of MO.

Here is a link to an e-mail group devoted to dog owners whose pets have DM.