Myotonia Congenita (Schnauzer Type)

Other Names: Congenital myotonia, Inherited myotonia, Myotonia, Myotonia hereditaria
Affected Genes: CLCN1
Inheritance: Autosomal Recessive
Mutation: chr16:6366383 (canFam3): C>T
Breed(s): Miniature Schnauzer, Schnoodle, Standard Schnauzer

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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 cold and excitement. Other features include enlargement of the muscles, abnormal posture, an upper jaw that is much longer than the lower jaw, and dental abnormalities. Dogs may also exhibit excessive panting and salivation, have an abnormal bark and loud raspy breathing, and have difficulty swallowing. 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 (schnauzer type). Myotonia congenita (schnauzer 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.

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

  • Bhalerao DP, Rajpurohit Y, Vite CH, Giger U. Detection of a genetic mutation for myotonia congenita among Miniature Schnauzers and identification of a common carrier ancestor. Am J Vet Res. 2002 Oct; 63(10):1443-7. [PubMed: 12371774]
  • Vite CH, Cozzi F, Rich M, Klide AK, Volk SW, Lombardo R. Myotonic myopathy in a miniature Schnauzer: case report and data suggesting abnormal chloride conductance across the muscle membrane. J Vet Intern Med. 1998 Sep-Oct;12(5):394-7. [PubMed: 9773418]
  • Vite CH, Melniczek J, Patterson D, Giger U. Congenital myotonic myopathy in the miniature schnauzer: an autosomal recessive trait. J Hered. 1999 Sep-Oct;90(5):578-80. [PubMed: 10544501]