Coat Colors: Myelopathy Risk?

There are several instances of coat colour and coat colour patterns that are linked with neurological and ophthalmic manifestations of disease. For example, deafness related to coat colour has been observed in numerous species, including cats, dogs, horses, llamas, and alpacas. These animals typically have substantial white patterning or merle- or dappled-coloured coats. Additionally, coat colour dilution lethal, or lavender foal syndrome, is a coat colour-related neurological condition seen in Arabian foals, which can result in intermittent paddling movements of the limbs, ocular strabismus, and spontaneous nystagmus.

In terms of degenerative myelopathy, it is an inherited neurological disorder caused by a mutation of the SOD1 gene, found in many breeds of dog. The disease affects the white matter tissue of the spinal cord and causes gradual muscle atrophy and loss of coordination, typically beginning in the hind limbs. While the mutation has been identified in flat-coated retrievers, the overall frequency of the disease in this breed is unreported. Genetic testing can determine whether a dog is a carrier of degenerative myelopathy, but the results may not be a totally accurate predictor of the disease.

Is degenerative myelopathy linked to deafness in dogs?

Degenerative myelopathy (DM) is a fatal neurodegenerative disease that affects the spinal cord in dogs, causing progressive muscle weakness and loss of coordination. It is not currently known to be linked to deafness. However, DM acts similarly to Lou Gehrig's disease, or ALS (amyotrophic lateral sclerosis), in humans.

DM typically affects dogs around eight years of age or older, causing gradual muscle wasting and incoordination in the hind limbs. It then progresses to an inability to walk after six to twelve months, and the muscle weakness may extend to the forelimbs in the late stages of the disease.

The exact cause of DM is unknown, but a genetic mutation, SOD-1, has been identified as a major risk factor. DM is considered a disease of middle-aged to older dogs, including German Shepherds, German Shepherd crosses, Siberian Huskies, and Collies. Several other breeds have also been identified as being at risk, and DM has been identified in more than 24 different breeds to date.

The clinical signs of DM often start in one hind limb and then progress to include both. Early clinical signs include the hind paws "knuckling" or turning under, the dog's hindquarters swaying when standing still, the dog falling over easily when pushed from the side, and the hind feet scraping the ground when walking. As the disease progresses, these symptoms worsen and eventually lead to paralysis of the hind end. In the later stages of the disease, clinical signs progress to paralysis of the hind limbs, urinary and fecal incontinence, and difficulty swallowing. Eventually, all limbs become weak.

There is currently no cure or effective treatment for DM, and dogs affected by the disease often become non-ambulatory within 11 months of the initial signs. Physical rehabilitation and therapeutic laser or photobiomodulation therapy may help to delay the clinical progression of the disease and maintain muscle health. Dogs with DM will need to be kept on a clean, padded bed and will need assistance with bladder management as they will lose the ability to urinate on their own.

What is degenerative myelopathy?

Degenerative myelopathy (DM), also known as chronic degenerative radiculomyelopathy (CDRM) or German shepherd degenerative myelopathy, is a fatal neurodegenerative disease that affects the spinal cord in dogs, causing progressive muscle weakness and loss of coordination. The disease results in a slow degeneration of the white matter of the spinal cord and is similar to Lou Gehrig's Disease or amyotrophic lateral sclerosis (ALS) in humans.

The exact cause of DM is unknown, but it is believed to be linked to a mutation in the gene superoxide dismutase 1 (SOD1). This mutation has been identified as a major risk factor for DM, and dogs with two copies of the mutant allele are at risk for developing the disease. The disease typically affects middle-aged to older dogs, with an average onset age of around eight to nine years.

The clinical signs of DM often start in one hind limb and then progress to both, with early symptoms including scuffed toenails, stumbling, and weakness in the hind legs. As the disease progresses, dogs may experience paralysis of the hind limbs, urinary and fecal incontinence, and difficulty swallowing. There is currently no cure or effective treatment for DM, and affected dogs often become non-ambulatory within 11 months of the initial signs. Physical rehabilitation and maintaining a healthy weight may help slow the progression of the disease and maintain muscle mass.

DM has been identified in over 24 different dog breeds, including German Shepherds, Siberian Huskies, Collies, and Golden Retrievers. While a genetic mutation is highly suspected, the exact cause of DM is still unknown, and other genetic and environmental factors are believed to contribute to its development.

What breeds of dog are most susceptible to degenerative myelopathy?

Degenerative myelopathy (DM) is a disease that affects the spinal cord in dogs, causing progressive muscle weakness and loss of coordination. It is an inherited neurological disorder caused by a mutation of the SOD1 gene. The disease is most common in older medium to large breed dogs, with German Shepherds and Boxers being the most commonly affected breeds. However, it is seen in several other breeds as well, including:

• Siberian Huskies
• Miniature and Standard Poodles
• Pembroke and Cardigan Welsh Corgis
• Chesapeake Bay Retrievers
• Rhodesian Ridgebacks
• Bernese Mountain Dogs
• Kerry Blue Terriers
• Golden Retrievers
• Wire-haired Fox Terriers
• American Eskimo Dogs
• Soft-coated Wheaten Terriers
• Pugs
• Flat-coated Retrievers
• Collies
• Nova Scotia Duck Tolling Retrievers

DM typically affects dogs around eight years of age or older, with a mean age of nine years old. The disease causes gradual muscle wasting and incoordination in the hind limbs, eventually progressing to an inability to walk after six to twelve months. This muscle weakness may extend to the forelimbs in the late stages of the disease.

While there is no cure for DM, routine physical therapy and other management tactics may help delay the clinical progression of the disease and improve the dog's quality of life.

Can degenerative myelopathy be treated?

Canine degenerative myelopathy (DM) is a progressive and irreversible spinal cord disorder that affects dogs, causing a general paresis of the back legs. While DM is not curable, certain treatments can help slow down the progression of the disease and keep the dog as comfortable as possible.

DM is caused by a mutation in the SOD1 gene, which has also been linked to Lou Gehrig's disease (amyotrophic lateral sclerosis or ALS) in humans. The disease usually manifests as a loss of control and weakness in the back legs, followed by a lack of coordination in the muscles. It progresses slowly and painlessly until the dog's quality of life is significantly compromised.

While there is no cure for DM, several approaches can be taken to manage the disease and improve the dog's comfort and quality of life. These include:

• Exercise: Regular exercise beyond just playing in the yard is important for dogs with DM. Walking and swimming are particularly beneficial, as they help build muscle strength and increase muscle tone without putting excessive stress on the joints.
• Vitamins and supplements: Specific vitamins and supplements, such as B-complex vitamins, nutritional yeast, vitamin E, vitamin C, and selenium, can help correct immune dysfunction and reduce inflammation associated with DM.
• Supportive medications: A combination of aminocaproic acid and N-acetylcysteine, along with dietary supplements and exercise, can help treat the immune dysfunction associated with DM.
• Acupuncture: Acupuncture can provide analgesia and relief from acute and chronic pain without the side effects of analgesic drugs. It may also help slow down the progression of DM, especially in dogs with concurrent arthritis.
• Assistive devices: The use of assistive devices such as belly slings, harnesses, or wheelchairs can help support the dog's hind legs during exercise or when navigating stairs. These devices can help maintain the dog's mobility and quality of life.
• Bladder expression: As DM can lead to paralysis of the bladder, learning how to express a dog's bladder can help prevent distension and pain, making the dog more comfortable.
• Heartworm medication: Revolution, a topical heartworm preventative, is recommended for dogs with DM as it does not alter the immune response like other monthly products.
• Gene therapy: While still in the research phase, gene therapy offers a potential treatment option for DM by introducing new genetic material into the dog's DNA to correct the faulty gene.

It is important to note that DM progresses at different rates in each dog, and stress can play a role in its advancement. Therefore, it is crucial to minimize stressful situations and carefully consider the benefits and risks of any major surgical procedures, as they can result in a marked increase in clinical signs.

What genes are associated with coat colour?

The colour of a dog's coat is determined by its genes, which control the pigments produced (eumelanin and phaeomelanin) and where these pigments are produced. Eumelanin and phaeomelanin are the two basic pigments that determine the colour of canines. Eumelanin is, by default, a black pigment, but variation in colour occurs because genes modify eumelanin to create other colours such as liver (brown), blue (grey), or isabella (pale brown). Phaeomelanin is the second pigment that determines canine coat colour and is responsible for reds, golds, creams, and yellows.

There are eight genes in the dog genome associated with coat colour:

• A (agouti) locus: This site is responsible for different coat patterns in dogs. The agouti protein controls the release of melanin into the hair and is involved in switching between the two pigments (eumelanin and phaeomelanin).
• E (extension) locus: This locus creates the black facial mask of many dogs, as well as yellow or red coats. The four alleles of this gene in order of dominance are: melanistic mask (Em), grizzle (Eg), black (E) and red (e).
• K (dominant black) locus: This gene controls dominant black, brindle, and fawn colours. This relatively new locus includes colourations previously linked to other genes like Agouti.
• B (brown) locus: This locus is linked to brown, chocolate, and liver colours. There are two brown alleles, B (dominant brown) and b (recessive brown).
• D (dilute) locus: This genetic site is responsible for diluted pigment which lightens coats from black or brown to grey, blue, or very pale brown. A mutation in the melanophilin (MLPH) gene is the cause of colour dilution.
• M (merle) locus: The mutation that causes merle in all its forms. This site creates coats of irregularly shaped patches of diluted pigment and solid colour.
• H (harlequin) locus: This site is associated with white dogs that have black patches and often interacts with the Merle locus to create different combinations of spots and colours.
• S (spotting) locus: This locus is associated with interesting coat colour patterns such as piebald, particolour, and extreme white, which produce coats with less symmetrical white spots.

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