Myotubular Myopathy is an inherited muscle disease affecting Labrador Retrievers. Affected puppies are typically normal at birth, but between 7 and 19 weeks of age they present with muscle weakness especially in the hind limbs, decreased muscle mass, a hoarse bark and difficulty eating. Puppies are smaller than littermates, walk with a short, choppy gait and often fall over. The disease rapidly progresses from generalized muscle weakness and frequent episodes of collapse to a complete inability to stand or even raise their heads within 4 weeks of initial presentation. Dogs that are able to stand have an arched back and neck. While the disease is not painful, affected dogs are often euthanized between 3 and 6 months of age due to the rapid and severe progression of the disease.
Breed-Specific Information for the Labrador Retriever
The Mutation of the MTM1 gene associated with myotubular Myopathy 1 has been identified in Labrador Retrievers, although its overall frequency in this breed is unknown.
Genetic testing of the MTM1 gene in Labrador Retrievers will reliably determine whether a dog is a genetic Carrier of myotubular Myopathy 1. Myotubular Myopathy 1 is inherited in an X-linked manner in dogs meaning that female dogs must receive two copies of the mutated gene (one from each parent) to develop the disease while male dogs only require one copy of the mutated gene from the mother in order to develop the disease. Therefore, male dogs more commonly present with symptoms of the disease. Each male pup that is born to a female dog known to be a carrier myotubular myopathy 1 has a 50% chance of inheriting the disease. 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. Female 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.
Beggs AH, Böhm J, Snead E, Kozlowski M, Maurer M, Minor K, Childers MK, Taylor SM, Hitte C, Mickelson JR, Guo LT, Mizisin AP, Buj-Bello A, Tiret L, Laporte J, Shelton GD. MTM1 mutation associated with X-linked myotubular myopathy in Labrador Retrievers. Proc Natl Acad Sci U S A. 2010 Aug 17; 107(33):14697-702.
Cosford KL, Taylor SM, Thompson L, Shelton GD. A possible new inherited myopathy in a young Labrador retriever. Can Vet J. 2008 Apr; 49(4):393-7.