X-Linked Myotubular Myopathy

X-linked myotubular myopathy is a disease characterized by the presence of muscle weakness and reduced life expectancy, mainly affecting male dogs due to the type of inheritance.

Symptoms

Clinical signs of X-linked myotubular myopathy usually appear early, between 7 and 19 weeks of life. Common symptoms include muscle weakness, loss of muscle mass, problems eating and walking, and low birth weight. Over time, muscle weakness worsens and many affected dogs are euthanized at around six months of age.

Disease Management

There is no curative treatment for X-linked myotubular myopathy. However, management of the disease can focus on supportive care and improving the dog's quality of life. Exercises and physical therapies can be used to improve mobility and prevent muscle stiffness.

Genetic basis

This disease follows an X-linked recessive mode of inheritance. Recessive X-linked inheritance means that female dogs must receive two copies of the mutation or pathogenic variant (one from each parent) to develop the disease, whereas males need only one copy of the mutated gene or variant from the dam to develop the disease. Male dogs usually show symptoms of the disease. Each male puppy born to a mother carrying the mutation has a 50% chance of inheriting the mutation and thus the risk of developing the disease. Bitches that do not carry the mutation are not at increased risk of having affected puppies. Breeding between dogs carrying genetic variants that can cause disease, even if they do not show symptoms, is not recommended.

Technical report

X-linked myotubular myopathy is a genetic disorder that mainly affects males by X-linked type of inheritance. The MTM1 gene encodes the myotubularin protein, an enzyme that appears to play an important role in the development or maintenance of the function and structure of the tubuloreticular network of muscle. Specifically, in skeletal muscle, this enzyme is believed to be involved in the biogenesis or metabolism of lipids. In the Labrador Retriever breed, a nonsense mutation (c.465C>A) has been identified in the MTM1 gene that has been classified as a probable cause of X-linked myotubular myopathy. This mutation involves a nucleotide substitution and it is expected that this change will result in loss of function of the encoded protein, as greatly reduced protein levels are observed in affected dogs.

Most affected breeds

Boykin Spaniel
Labrador Retriever
Rottweiler

Bibliography

Beggs AH, Böhm J, Snead E,et al. 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.