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Myotonia Congenita

Myotonia Congenita is a condition that results in stiff movement and delayed relaxation of muscles after exercise.

Key Signs

Muscle hypertrophy, Short-strided gait, Protruding tongue, Ptyalism (excessive salivation), Dental abnormalities

Age of Onset

At birth

Present at birth


Autosomal Recessive

For autosomal recessive disorders, cats with two copies of the variant are at risk of developing the condition. Cats with one copy of the variant are considered carriers and are usually not at risk of developing the disorder. However, carriers of some complex variants grouped in this category may be associated with a low risk of developing the disorder. Individuals with one or two copies may pass the disorder-associated variant to their kittens if bred.

Likelihood of the Condition

High likelihood

At risk cats are highly likely to show signs of this disease in their lifetime.

What to Do

Here’s how to care for a cat with Myotonia Congenita

Partner with your veterinarian to make a plan regarding your cat’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about Myotonia Congenita

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.

For Breeders

Planning to breed a cat with this genetic variant?

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.

Technical Details

Gene CLCN1
Variant G>T
Chromosome A2
Coordinate 158,986,498

All coordinates reference FelCat9.0

References & Credit

Credit to our scientific colleagues:

Gandolfi, B., Daniel, R. J., O’brien, D. P., Guo, L. T., Youngs, M. D., Leach, S. B., Jones, B. R., Shelton, G. D., & Lyons, L. A. (2014). A novel mutation in CLCN1 associated with feline myotonia congenita. PLoS ONE, 9(10). View the article