Inherited myopathy Great Dane Type (CNM)
Inherited myopathy Great Dane type (CNM) is a hereditary, non-inflammatory myopathy affecting young great Danes. It is a degenerative muscle disorder with an early age of onset. The first form of myopathy in dogs was registered in 1970’s and the affected dog was a Labrador retriever breed. Form of myopathy detected in Laboratory retrievers differs from myopathy in Great Danes and is caused by a different mutation. Inherited myopathy in Great Danes was originally reported in 1994. as a central core myopathy, the same as central core myopathy condition in human beings. Inherited myopathy in Great Danes can be histologically confirmed with the characteristic centrally located cytoarchitectural abnormalities, but the histochemical characteristics of the distinct cytoarchitectural structures typical for this conditions differ between human beings and great Danes. For inherited myopathy of Great Danes human counterpart cannot be identified, unlike in some other dog breeds. A myopathy with similar features has been described in male springer spaniel, sheep and cattle.
The first symptoms of the inherited myopathy Great Dane type usually occur before one year of age and it is identified in both sexes. The disorder is characterized by a progressive exercise intolerance, muscle wasting and an exercise-induced tremor. After exercise, affected dogs collapse into sternal recumbent. The time duration of the exercise before the dog’s collapse varies and depends on severity of the disorder. In severely affected dogs, it is needed only few steps to induce the collapse and in mildly affected dogs, up to 60 minutes of exercise are possible. Condition frequently found in affected dogs are elevated serum creatinine kinase concentrations and spontaneous electrical activity in skeletal muscles. Researches revealed generalized muscle atrophy when affected dogs were compared with unaffected siblings. Tremor in affected dogs is present also when standing and becomes more prominent with movement and excitement.
Inherited myopathy in Great Danes is caused by a mutation in the BIN1 gene. The disorder is inherited in an autosomal recessive manner. In case of showing the CNM symptoms, the healthy parents of the affected cub are obligate heterozygotes, and therefore carry one mutant allele. Heterozygotes have no symptoms. At conception, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. There is no cure for this disorder, and only way to prevent it, is to breed dogs which are not carriers of the mutation. Defected genes for autosomal recessive disease can be passed for many generations without affected individuals occurring until two carriers are bred to one another. The only way to find out if there is a chance of getting an affected puppy is to do genetic testing.