Breeds Affected: Miniature Schnauzer
Samples Accepted: Blood, Buccal Swabs
Disease Information: Myotonia Congenita is a disorder in which it takes an unusually long period of time for skeletal muscles to relax after contracting. Affected animals show stiffness when moving, particularly when starting to move, and severe overgrowth (hypertrophy) of the muscles. Predominant signs include a stiff gait, skeletal muscle hypertrophy, difficulty swallowing, and increased salivation. Pups are usually identified at 2-3 months of age.
Inheritance Information: Myotonia Congenita is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/mc The dog is a carrier, and can pass the allele on to approximately 50% of any offspring. If bred to another N/mc carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
mc/mc The dog is affected. If bred to a normal animal, 100% of the offspring will be carriers. If bred to an N/mc carrier, 50% of the offspring will be carriers and 50% will be affected.
– Carriers may be bred to normal animals (N/mc x N/N) without any risk of producing affected offspring. The offspring should be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/mc x N/mc) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (mc/mc) should not be used for breeding.
Test Information: This mutation test identifies a single base pair change in the CLCN1 gene.
Rhodes, T.H., Vite, C.H., Giger, U., Patterson, D.F., Fahlke, C., George, A.L.: A missense mutation in canine ClC-1 causes recessive myotonia congenita in the dog FEBS Letters 456:54-58, 1999. Pubmed reference: 10452529.
Further information is available at the Online Mendelian Inheritance in Animals website.