How Canine X-Linked Muscular Dystrophy Affects Dogs
It is difficult to speculate about how a dog that has a severe muscle disorder is affected by the disease. Many puppies born with canine X-linked muscular dystrophy (CXMD) are weak and die shortly after birth. If an affected dog lives, certainly its inability to eat and swallow normally must cause it some degree of frustration or distress. Moreover, aspiration pneumonia is unpleasant under any circumstances, with its associated coughing, sore throat, difficulty breathing and general malaise. The ability of a dog with CXMD to get around (ambulate) normally will be markedly limited throughout its life, which will prevent it from enjoying what most people think of as important companion canine experiences such as running, fetching balls, chasing squirrels, going on long walks and the like. However, in the absence of secondary respiratory difficulties, affected dogs will have lived with their condition since the time they were born and will know no other way of life. One might say that they won’t know what they are missing, as long as they are comfortable, pain-free and loved.
Symptoms of Canine X-Linked Muscular Dystrophy
The common denominator among the different types of muscular dystrophies is progressive muscle weakness. Of the various forms of the disease in dogs, canine X-linked muscular dystrophy is the most severe. It mainly affects newborns and young puppies. Dogs with CXMD have stunted growth. Some breeders observe affected puppies having difficulty nursing starting from birth. By as early as 6 weeks of age, but more commonly by 10 to 12 weeks, owners of affected animals notice one or more of the following signs:
- Difficulty swallowing (dysphagia)
- Difficult grasping food (abnormal food prehension)
- Excessive drooling (ptyalism)
- Exercise intolerance
- Muscle stiffness
- Muscle tremors
- Abnormal “bunny-hopping” gait (characteristic trait of CXMD)
- Stiff, stilted movement
- Outward-turned elbows (front limb abduction)
- Inward-turned hocks (hind limb adduction)
- Sagging of the back (sway-backed appearance; ventroflexion of the spine)
- Muscle atrophy (muscle wasting; especially along the trunk and around the temples of the face)
- Enlargement of the tongue (hypertrophy)
Problems eating and swallowing tend to be the first things that owners report in puppies with canine X-linked muscular dystrophy. By about 6 to 9 months of age, the signs of CXMD usually have stabilized. By this time, the puppy’s esophagus (the muscular tubular organ that carries food and fluids from the mouth to the stomach), diaphragm (the muscular partition between the chest and abdominal cavities) and heart (also a muscular organ) can become affected by the progressive disease. Many puppies develop a condition called megaesophagus, in which the esophagus becomes abnormally stretched (dilated) and lacks the tone necessary for normal food passage. This can cause food to accumulate in loose pockets along the lining of the esophagus. When the diaphragm is also affected, the dog may develop secondary aspiration pneumonia as a result of: Coughing, Regurgitation, Difficulty breathing (dyspnea; respiratory distress).
When the heart muscle becomes weakened, the dog may develop signs of heart failure, including coughing, dyspnea and abnormal abdominal distension from the build-up of fluid. Heart failure is a very serious potential consequence of CXMD.
While the symptoms of this disease tend to stabilize by one year of age, unfortunately they usually begin to worse at some later time. This is a progressively degenerative disease that rarely stays static for long.
Dogs at Increased Risk
Canine X-linked muscular dystrophy is most commonly reported in male dogs – particularly male Golden Retrievers. However, it has also been seen in male Labrador Retrievers, Samoyeds, Rat Terriers, Miniature Schnauzers, Alaskan Malamutes, Rottweilers, Japanese Spitz, Irish Terriers, Samoyeds, Belgian Shepherds, Belgian Tervurens, German Shorthair Pointers, Groenendaeler Shepherds, Pembroke Welsh Corgis and Brittany Spaniels. It has even been reported in domestic shorthair cats. While males are the primary targets of CXMD, females can also be born with this disease if a female carrier of the genetic mutation is bred to a male that actually has the disease.