Degenerative Myelopathy is a progressive disease affecting the spinal cord in older dogs.

The idea of health testing dogs for use in a breeding program is not a new idea. However, utilizing some of the new genetic testing has caused a large “gray area” to emerge in recent years. Presently, there are more than 80 different DNA tests available for mutations that are inherited conditions in the domestic dog. These tests have been brought to light after sequencing the dog genome was completed, and the results made publicly available, in 2004 by the National Guman Genome Research Institute. Completed after years of dedicated research, the project carried hefty price tag of $30 million dollars.

The French Bulldog Club of America (FBDCA), as well many other dog breed clubs hold raffles and other fund raising events to contribute funds to researchers in hopes of finding the genetic markers for many inherited diseases. The development of DNA tests allow identification of the genetic marker, enabling breeders to make informed decisions regarding future breedings to hopefully eliminate or minimize inherited diseases.

Some of these disorders have a very late onset of clinical disease. Without DNA tests it would be impossible to determine if a dog was a carrier or in fact going to be affected by the disease until the dog showed clinical signs. When clinical signs are obvious, the dog may be 8-12 years old. When the problem is eventually realized, the damage has been done and these dogs may be firmly embedded in the current pedigrees.

One such disease that has been garnering attention in our breed is a condition called Degenerative Myelopathy (DM). Degenerative Myelopathy is a progressive disease affecting the spinal cord in older dogs.

Symptoms usually start with a weakness in the hind limbs. This can include knuckling of the rear feet when walking, wobbling and an unsteady gait, which later can progress to the dragging of the back legs. The disease will escalate up the spinal cord until the dog is unable to stand without assistance, and un-assisted ambulation will be impossible.

The course of DM can vary from 6 months to 36 month before the dog becomes paraplegic. DM will eventually cause urinary and fecal incontinence and progress into the front limbs as well.

Although this is not a painful disease to the dog, it is devastating to their quality of life and leaves a loving owner with a diagnosis of despair.

At the cellular level DM causes a degeneration of the myelin or white matter of the spinal cord (material that insulates the nerve fibers so they can conduct impulses) and loss of axons (nerve fibers). The exposure of the nerve fibers deceases or eliminates their ability to communicate and coordinated movement commands between the brain and limbs. This is similar to an electrical cord without the protective casing around the cord to focus the electricity from the plug to an appliance. The focus of the problem usually starts in the mid-lumbar area of the back and continues to progress.

Confirming a case of Degenerative Myelopathy is challenging. DM is a diagnosis of exclusion. It can mimic many other conditions including orthopedic maladies, intervertebral disc disease etc. The main difference is DM is not a painful condition. Evaluation by a neurologist is recommended, including spinal fluid analysis, EMG (electromyelogram), MRI (Magnetic Resonance Imaging), etc. Unfortunately, the only way to absolutely confirm a diagnosis of DM is with a necropsy, or post mortem exam – (autopsy). Examination of the spinal cord fibers microscopically will confirm the tell tale signs of the disease which are unmistakable to the pathologist.

Presently there is no effective treatment for DM or for slowing the course of the disease. The discovery of the gene that identifies dogs at risk for developing DM, and careful breeding practices based on this knowledge, could hold the key to eliminating the disease in the future.

DNA testing in General

Most of the DNA tests presently available are for autosomal recessive mutations with single gene traits (simple Mendelian genetics). Many times it is the practice of breeders to eliminate the undesirable gene entirely, i.e. carriers. This can be a detrimental mistake and decrease the gene pool substantially, thus minimalizing genetic diversity.

Decreasing diversity by eliminating one undesirable characteristic may actually amplify others and this practice must be done with caution. It is recommended that if a mutation is frequently seen within a breed, breeders and veterinarians should be counseled to include carriers in a breeding population for at least one or two generations. What does this mean? It means elimination could result in unwanted consequences to breed type or to health.

This undesirable mutation did not arrive in the gene pool overnight and should not be eliminated this way either. Genetic testing is merely a tool to prevent further disease and undesirable characteristics’, testing is not a hard and fast, yes or no answer. The compilation of an accurate database is essential to understand the scope of the condition within the breed. Therefore, it is advantageous to choose the laboratory for running these samples with care. Most of the research labs that have developed such tests are the best place to send samples for testing. These researchers maintain databases that can be used to accurately reflect the significance of the disease in each breed affected. By using a private laboratory the results remain anonymous and the perception of the extent of the disease is altered. Although, OFA results are anonymous unless normal, all results in the case of DM are compiled in the database at the University of Missouri. This knowledge allows for an accurate picture of prevalence of disease within the breed. Presently, the Welsh Pembroke Corgi and Boxer have been found to have very few animals that are not carriers or affected. It will take these breeds quite some time to emerge from this quagmire.

Degenerative myelopathy is a recessive mutation that is not completely penetrant but highly associated with disease. The mutation tested for is a nucleotide SOD1, and the presence of this mutation increases the risk of developing DM at some time during the dog’s lifetime. Researchers suspect the presence of additional mutations or other environmental factors that may trigger the activation of the disease process. This “activation” may be the reason that dogs with two copies of the gene remain disease free despite having two copies of the gene, one from both parents. Degenerative myelopathy may have a similar model to Multiple Sclerosis (MS) in humans. People with MS need to have the “perfect storm” of circumstances to become clinical. This includes a genetic defect, a contributing environmental condition and an inflammatory or autoimmune factor.

In fact, the OFA releases a letter with each result that states: Guidelines for Breeding.

Owners with dogs testing as Carriers (A/N), or At-Risk (A/A) are strongly encouraged to share these results with their attending veterinarians and seek genetic counseling when making breeding decisions.

The “A” (mutated) allele appears to be very common in some breeds. In these breeds, an overly aggressive breeding program to eliminate dogs testing A/A or A/N might be devastating to the breed as a whole, because it would eliminate a large fraction of the high quality dogs that would otherwise distribute desirable qualities to the breed. Nonetheless, DM should be taken seriously. It is a fatal disease with devastating consequences for the dog, and can be a trying experience for the owners that care for them. A realistic approach when considering which dogs to select for breeding would be to treat the test results as one would treat any other undesirable trait or fault. Dogs testing At-Risk (A/A) should be considered to have a more serious fault than those testing as carriers (A/N). By incorporating this information into their selection criteria breeders can proceed as conscientious breeders have always done: making their breeding selections based on all the dog’s strengths and all the dog’s faults. Using this approach, and factoring the DM test results into the breeding decisions, should reduce the prevalence of DM in the subsequent generations while continuing to maintain and improve upon positive, sought after traits.

We recommend that breeders take into consideration the DM test results as they plan their breeding programs: however, they should not over-emphasize the test results. Instead, the test result should be one factor among many in a balanced breeding program.

There are many genetic tests that plague our beloved breed. According to the Canine Health Information Center, tests recommended for those that breed French Bulldogs include, hips, eyes, heart, and patellas. Another recent DNA test for Juvenile Cataracts was also added by the FBDCA as a requirement for the Registry of Merit award in an attempt to keep our breed healthier.

However, in the case of degenerative myelopathy, breeders must recognize this test as a tool and not a silver bullet. There are other factors that must be considered when breeders make that commitment to produce a litter of puppies. Hopefully people that are concerned with this latest health test will also appreciate and take advantage of health testing for the previously described conditions outlined by CHIC, and not just focus on the “test de jour.” All of these diagnostics must be incorporated into sound judgment about each individual dog. Other factors such as temperament, breed type, and soundness are equally important elements in producing not only a lovely show dog but also a fantastic pet.