Common Symptoms
Myotubular Myopathy 1 (Boykin Spaniel Type) is an inherited muscle disease affecting dogs. Affected puppies are typically normal at birth, but between 7 to 13 weeks of age they present with muscle weakness, decreased muscle mass, and exercise intolerance. Affected puppies have difficulty standing and holding their heads up. Their whiskers may be bent or crinkled. The disease rapidly progresses from generalized muscle weakness and frequent episodes of collapse to complete inability to stand or even raise their heads within 4 weeks of initial presentation. Dogs that can stand have an arched back and neck and stiff gait. While the disease is not painful, affected dogs are often euthanized early or die due to the rapid and severe progression of the disease.
Testing Tips
Genetic testing of the MTM1 gene will reliably determine whether a dog is a genetic Carrier of myotubular Myopathy 1 (Boykin Spaniel Type). This disease 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 (Boykin Spaniel Type) 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 is not recommended. Female dogs 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.
References
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Olby NJ, Friedenberg S, Meurs K, DeProspero D, Guevar J, Lau J, Yost O, Guo LT, Shelton GD. A mutation in MTM1 causes X-Linked myotubular myopathy in Boykin spaniels. Neuromuscul Disord. 2020 May;30(5):353-359.
[PubMed: 32417001]
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Shelton GD, Rider BE, Child G, Tzannes S, Guo LT, Moghadaszadeh B, Troiano EC, Haase B, Wade CM, Beggs AH. X-linked myotubular myopathy in Rottweiler dogs is caused by a missense mutation in Exon 11 of the MTM1 gene. Skelet Muscle. 2015 Jan 27;5(1):1.
[PubMed: 25664165]
