Myotonia congenita is an inherited condition characterized by delayed relaxation of skeletal muscle after voluntary contraction without associated symptoms of weakness or muscular dystrophy (Rhodes 1999). The delay in skeletal muscle relaxation is not accompanied by pain. This inherited pathogenic condition affects skeletal muscle because of poor voltage-dependent chloride channel CIC-1 conductance. This electrochemical disorder originates from a missense mutation in the canine CLCN1 gene.
Dogs affected with this disease have significant excessive growth of the muscles (muscle hypertrophy), non-painful muscle spasms, collapse associated with exercise and activity, so-called "bunnyhop" type movement which can be improved by training, noisy breathing (stridor), troubled breathing (dyspnea), problem with the voice (dysphonia)... Difficulty in swallowing, excessive salivation and an abnormal bark are often present. All affected miniature Schnauzers exhibit an abnormal set of teeth and have a deformed lower jaw, and sometimes abnormal barking. Young dogs start to show symptoms as early as of a few weeks of age.
Inheritance: Autosomal recessive - read more.
Mutation: CLCN1 gene (Rhodes et. al. 1999)
Genetic test: Disease or carrier can be identified by genetic testing at any age. The PCR method used for testing is extremely accurate and allows complete differentiation between affected animals, carriers and healthy dogs.
Disease control: read more.
Affected breeds: Miniature Schnauzer
Sample: EDTA whole blood (1.0 ml) or buccal swabs. Detailed information about sampling are found here.