C124 - Canine Myotonia Congenita

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. Recent molecular genetic studies have identified the CLCN1 gene encoding the skeletal muscle voltage-dependent chloride channel, ClC-1, as responsible for this condition in human, mouse, goat and dog forms of the disease. Congenital myotonia has been observed in certain dog breeds, and recently was described in Miniature Schnauzers. Myotonia in this dog breed exhibits many of the same features as human myotonia congenital including moderate to severe action myotonia, muscle hypertrophy, decreased myotonia severity with continued activity (`warm-up'), abnormal upper respiratory sounds especially when beginning to move, and low sarcolemmal chloride conductance.

Canine Myotonia Congenita shows an autosomal recessive mode of inheritance; therefore two copies of the defective gene, one inherited from each parent, have to be present for a dog to be affected by the disease. Carriers (dogs with one copy of the mutant gene and one copy of the normal gene) have about one half normal enzyme activity in red blood cells and muscle tissue, and are clinically unaffected, but can pass the defective gene onto their offspring.

This DNA test provides reliable identification of dogs that carry mutant gene(s). The DNA test allows a breeder to control the mutant gene frequency in Miniature Schnauzers thus preventing the production of puppies affected with Canine Myotonia Congenita. This DNA test accurately and specifically identifies normal, carriers (heterozygous) and affected dogs.