Congenital myasthenic syndrome (CMS) is an inherited Neuromuscular Disease affecting Labrador retrievers. Affected dogs typically present around 2-3 weeks of age with severe exercise-induced weakness of all four limbs leading to collapse. Affected dogs will have decreased reflexes in all limbs and a short-strided gait that becomes more pronounced with exercise. Dogs may be humanely euthanized at a young age due to disease severity. Treatments used for a similar, acquired form of the disease known as myasthenia gravis, are ineffective for CMS.
Breed-Specific Information for the Labrador Retriever
The Mutation of the COLQ gene associated with congenital myasthenic syndrome (Labrador retriever type) has been identified in the Labrador retriever, although its overall frequency in this breed is unknown.
Genetic testing of the COLQ gene in Labrador retrievers will reliably determine whether a dog is a genetic Carrier of CMS. CMS is inherited in an Autosomal Recessive manner in dogs meaning that they must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup that is born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the COLQ gene mutation. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Labrador retrievers that are not carriers of the mutation have no increased risk of having affected pups.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
Rinz CJ, Levine J, Minor KM, Humphries HD, Lara R, Starr-Moss AN, Guo LT, Williams DC, Shelton GD, Clark LA. A COLQ missense mutation in Labrador retrievers having congenital myasthenic syndrome. PLoS One. 2014 Aug 28;9(8):e106425.
Shelton GD. Myasthenia gravis and congenital myasthenic syndromes in dogs and cats: A history and mini-review. Neuromuscul Disord. 2016 Jun;26(6):331-4.