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Congenital Myasthenic Syndrome (CMS) – Labrador Retriever Type
| Acronym: | CMS |
| Gene: | COLQ |
| Mutation: | c.1010T>C |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Congenital myasthenic syndrome Labrador retriever type belongs to 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. The first CMS in dogs was documented in Jack Russel terriers in the 1970s. Since then, the CMS was reported in a few other breeds, such as Labrador Retriever, Smooth Fox Terriers, Jack Russell Terriers, Smooth Haired Dachshunds, and Old Danish Pointers. Characteristics of congenital myasthenic syndrome Labrador retriever type are a 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, the dog’s strides become 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 reappear. The first symptoms usually occur between 12 to 16 weeks of age, but they can vary between breeds. Congenital myasthenic syndrome symptoms appear similar to myasthenia gravis. But while myasthenia gravis is autoimmune, CMS is an inherited disease caused by a gene mutation.
In CMS-affected Labrador retrievers, a COLQ missense mutation has been identified, an identical mutation to 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 the only way to prevent it is to breed dogs that 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.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
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