Don't miss out on up to 30% off our most popular tests!

Shop Now

Congenital Myasthenic Syndrome (Discovered in the Jack Russell Terrier)

Congenital Myasthenic Syndrome (CMS) is a neuromuscular disorder. Affected dogs suffer from exercise intolerance and collapse after 5-30 minutes of exercise.

Key Signs

Temporary collapse, Paralysis induced by exercise

Age of Onset

0 to 2 yrs

Juvenile onset


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 CMS

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 CMS

Initial signs of congenital myasthenic syndrome can be observed in 12 to 16 weeks old puppies. Affected dogs suffer from exercise intolerance and collapse after 5 to 30 minutes of exercise. Before collapsing, affected dogs will start to take shorter and shorter strides and eventually fall down. Affected dogs are able to recover from the transient paralysis after resting for a few minutes, but the signs reappear if the dog continues to run.

The clinical signs can be avoided by limiting exercise to a very short period of time and low intensity. If the dog collapses, allow it to rest and recover and then stop further exercise to prevent further difficulties or collapse.

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 be shown. A carrier dog with one copy of the CMS mutation can be safely bred with a clear dog with no copies of the CMS mutation. About half of the puppies will have one copy (carriers) and half will have no copies of the CMS 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 CMS mutation could develop due to a different genetic or clinical cause.

Technical Details

Variant Insertion
Chromosome 5
Coordinate Start 31,705,136
Coordinate End 31,705,137

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Rinz, C. J., Lennon, V. A., James, F., Thoreson, J. B., Tsai, K. L., Starr-Moss, A. N., … Shelton, G. D. (2015). A CHRNE frameshift mutation causes congenital myasthenic syndrome in young Jack Russell Terriers. Neuromuscular Disorders, 25(12), 921–927. View the article