Common Symptoms
Myotonia congenita is an inherited muscle disorder affecting dogs. The muscle cells of an affected dog are over-excitable, which causes muscles to remain contracted rather than relaxing after voluntary activity. Signs of the disorder usually present when puppies begin to walk. Their gait may appear stiff and uncoordinated and they may fall frequently. Affected dogs frequently have a “bunny hop” type gait. Episodes do not appear to be painful and the muscle stiffness may improve with increased exercise. Episodes can worsen with hot weather and excitement. Other features include enlargement of the muscles, especially of the neck and limbs, abnormal posture, and an upper jaw that is much longer than the lower jaw. Dogs with this disorder typically have a normal lifespan.
Breed-Specific Information for the Australian Stumpy Tail Cattle Dog
Australian stumpy tail cattle dog is included as a breed susceptible to myotonia congenita (Australian cattle dog type) because of its close relatedness to the Australian cattle dog breed, which is known to develop this disease due to Mutation of the CLCN1 gene. The frequency of the causal mutation in the general Australian stumpy tail cattle dog population is unknown.
Testing Tips
Genetic testing of the CLCN1 gene in Australian stumpy tail cattle dogs will reliably determine whether a dog is a genetic Carrier of myotonia congenita (Australian cattle dog type). Myotonia congenita (Australian cattle dog type) is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the CLCN1 gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Australian stumpy tail cattle dogs that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
References
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Finnigan DF, Hanna WJ, Poma R, Bendall AJ. A novel mutation of the CLCN1 gene associated with myotonia hereditaria in an Australian cattle dog. J Vet Intern Med. 2007 May-Jun; 21(3):458-63.
[PubMed: 17552451]
