Myotonia Congenita is a muscular disorder characterized by the inability of muscles to relax after contraction. The disorder is caused by the defective activity of chloride channels in the cell membranes of skeletal muscles. Affected cats have an enlarged tongue, limited range of motion in the jaws, and exhibit drooling. Additional clinical signs include a short-strided, stiff gait and enlarged neck and forelimb musculature. Halitosis (bad breath), various dental abnormalities and poor grooming habits have also been described in affected cats. Physical exam findings may include blepharospasm following testing of the menace response or palpebral reflexes and initially normal proprioceptive positioning that worsens with repetitive testing. Clinical signs of the disease are usually evident in kittens before 1 year of age.

As there is no cure for this disorder, therapy is limited to symptomatic treatments and general supportive care. The average prognosis is considered poor for affected cats and euthanasia may need to be considered for welfare reasons.

There are many responsibilities to consider when breeding cats. Regardless of test results it is important that your cat is in good general health and that you are in a position to care for the kittens if new responsible owners are not found. For first time or novice breeders, advice can be found at most cat registry websites.

This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to be shown. A carrier cat with one copy of the Myotonia Congenita mutation can be safely bred with a clear cat with no copies of the Myotonia Congenita mutation. About half of the kittens will have one copy (carriers) and half will have no copies of the Myotonia Congenita mutation. Kittens in a litter which is expected to contain carriers should be tested prior to breeding. Carrier to carrier matings are not advised as the resulting litter may contain affected kittens. Please note: It is possible that disease signs similar to the ones caused by the Myotonia Congenita mutation could develop due to a different genetic or clinical cause.