Canine Myotonia Congenita (MC)
Canine myotonia congenita is an inherited condition characterized by delayed relaxation of skeletal muscle after voluntary contraction without associated symptoms of weakness or muscular dystrophy. Another symptom of canine myotonia congenita is skeletal muscular hypertrophy. Myotonia congenita results from genetic defects in the skeletal muscle chloride ion channel (ClC-1) and the ensuing reduced chloride ion conductance across the sarcolemma.
Canine myotonia congenita has been characterized best in Miniature Schnauzers. In this breed it is inherited as an autosomal recessive trait. Myotonic Miniature Schnauzers have hypertrophic skeletal muscles, difficulty in rising after a period of rest, a stiff and stilted gait when walking, and a bunnyhop type movement when running. In addition, there are increased respiratory sounds, difficulty when swallowing, ptyalism, dental abnormalities, and superior prognathism, a unique feature of myotonia congenita in this breed.
Bhalerao, D.P., Rajpurohit, Y., Vite, C.H., and Giger, U. (2002). Detection of a genetic mutation for myotonia congenita among Miniature Schnauzers and identification of a common carrier ancestor. American Journal of Veterinary Research 63, 1443–1447.
Rhodes, T.H., Vite, C.H., Giger, U., Patterson, D.F., Fahlke, C., and George Jr., A.L. (1999). A missense mutation in canine ClC-1 causes recessive myotonia congenita in the dog1. FEBS Letters 456, 54–58.