Congenital Myasthenic Syndrome Labrador Retriever Type (CMS)
Congenital myasthenic syndrome Labrador retriever type belongs in a group of conditions, known as Congenital myasthenic syndromes (CMS). CMS is an inherited neuromuscular transmission disorder. It results in structural or functional defects of the neuromuscular junction, the place where nerve and muscle cells meet. It has been identified in humans and dogs. First CMS in dogs was documented in Jack Russel terriers in the 1970’s. Since then, the CMS was reported in few other breeds, such as Labrador Retriver, Smooth Fox Terriers, Jack Russell Terriers, Smooth Haired Dachshunds and Old Danish Pointers. Congenital myasthenic syndrome Old Danish Pointing Dog Type differs from CMS of other breeds in pathological mechanism.
Characteristics and symptoms
Characteristics of congenital myasthenic syndrome Labrador retriever type are fatigable weakness of skeletal muscle. The weakness is a result of a defect in the synthesis of the neurotransmitter acetylcholine. Affected dogs are able to run normally for 5 to 30 minutes. Shortly after, dog’s strides become shorter and shorter, eventually resulting in a collapse. The dog recovers after some minutes of rest, and is able to walk or run for a certain period of time, before the symptoms’s reappearance. The first symptoms usually occur between 12 to 16 weeks of age, but it can vary between breeds. Congenital myasthenic syndrome symptoms appear similar to myasthenia gravis. But while myasthenia gravis is an autoimmune, CMS is an inherited disease caused by gene mutation.
In CMS affected Labrador retirevers a COLQ missense mutation has been identified, identical mutation as the one found in two human CMS patients. CMS is inherited in an autosomal recessive pattern. In case of showing the signs of CMS, the healthy parents of a cub with an autosomal recessive form of CMS are obligate heterozygotes, and therefore carry one mutant allele. Heterozygotes have no symptoms. At conception, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
Until now, no cure for CMS has been discovered, and only way to prevent it, is to breed dogs which are not carriers of the mutation. Defected genes for autosomal recessive disease can be passed for many generations without affected individuals occurring until two carriers are bred to one another. The only way to find out if there is a chance of getting an affected puppy is to do genetic testing.
Rinz CJ, Levine J, Minor KM, Humphries HD, Lara R, et al. (2014) A COLQ Missense Mutation in Labrador Retrievers Having Congenital Myasthenic Syndrome. PLoS ONE 9(8): e106425. doi:10.1371/journal.pone.0106425