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Myotonia Congenita (Discovered in the Labrador Retriever)

Myotonia congenita is a muscle disorder that affects dogs from birth, causing stiff movement and delayed relaxation of muscles after exercise.

Key Signs

Muscle hypertrophy, Bunny hopping gait, Ptyalism (excessive salivation), Difficulty swallowing, Noisy breathing.

Age of Onset

At birth

Present at birth


Autosomal Recessive

For autosomal recessive disorders, dogs with two copies of the variant are at risk of developing the condition. Dogs 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 puppies if bred.

Likelihood of the Condition

High likelihood

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

What to Do

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

Partner with your veterinarian to make a plan regarding your dog’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

The clinical signs of Myotonia congenita can be seen in puppies only a few weeks old. Affected dogs suffer from muscle hypertrophy with stiff movements. There may be difficulties rising after rest or in attempting rapid changes in posture. Affected dog may also display a "bunny-hopping" gait. Additional clinical signs include difficulty swallowing, ptyalism (excessive flow of saliva), and increased respiratory sounds during exercise. The tongue of affected dogs is enlarged and stiffens when touched.

Affected dogs may need assistance after rest or during muscle cramping to allow them to get to their feet and move normally. Some assistance may also be needed for everyday tasks such as stair climbing.

For Breeders

Planning to breed a dog with this genetic variant?

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

This disease is autosomal recessive meaning that two copies of the mutation are needed for disease signs to develop. A carrier dog with one copy of the Myotonia Congenita mutation can be safely bred with a clear dog with no copies of the Myotonia Congenita mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the Myotonia Congenita mutation. Puppies 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 puppies. 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 T>A
Chromosome 16
Coordinate 6,348,929

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Quitt, P. R., Hytönen, M. K., Matiasek, K., Rosati, M., Fischer, A., & Lohi, H. (2018). Myotonia congenita in a Labrador Retriever with truncated CLCN1. Neuromuscular Disorders, 28(7), 597–605. View the article