Myotonia Congenita (Australian Cattle Dog Type)

Other Names: Congenital myotonia, Inherited myotonia, Myotonia, Myotonia hereditaria
Affected Genes: CLCN1
Inheritance: Autosomal Recessive
Mutation: Insertion
Breed(s): Australian Cattle Dog, Australian Stumpy Tail Cattle Dog, Border Collie

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Common Symptoms

Myotonia congenita (Australian cattle dog type) 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.


Testing Tips

Genetic testing of the CLCN1 gene 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. Dogs that are not carriers of the mutation have no increased risk of having affected pups.


References

  • 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]