X-Linked Myotubular Myopathy

X-linked Myotubular Myopathy (XLMTM) is a condition of the muscles that results in trouble eating, breathing, and moving around.

Key Signs

Progressive muscle weakness, Muscle atrophy, Absence of patellar reflexes, Inability to rise and walk, Difficulty chewing and swallowing

Age of Onset

0 to 2 yrs

Juvenile onset


X-linked Recessive

For X-linked recessive disorders, the genetic variant is found on the X chromosome. Female dogs must have two copies of the variant to be at risk of developing the condition, whereas male dogs only need one copy to be at risk. Males and females with any copies of the variant may pass the disorder-associated variant to their puppies if bred.

Likelihood of the Condition

High likelihood

At risk dogs are highly likely to show signs of this disease in their lifetime.

What to Do

Here’s how to care for a dog with XLMTM

Partner with your veterinarian to make a plan regarding your dog’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about XLMTM

The clinical signs of X-linked myotubular myopathy can be seen in puppies as young as 10 to 19 weeks of age with early signs of muscle atrophy being apparent earlier in some cases. Pelvic limb weakness is typically observed as one of the first signs. Affected dogs also lack patellar reflexes. X-linked myotubular myopathy is characterized by rapidly progressing muscle weakness and muscle atrophy. Affected dog won’t be able to rise and move unassisted within a few weeks of the onset of clinical signs and may also have difficulties chewing and swallowing. There is no cure for the condition.

Affected puppies are usually euthanized on welfare grounds because of the severity of the condition.

For Breeders

Planning to breed a dog with this genetic variant?

There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.

This disorder is X-linked recessive, meaning the genetic variant is found on the X chromosome. Given males only have one X chromosome, a single affected copy will increase the risk of being diagnosed with the disorder. Females typically require two copies to be at an elevated risk for full clinical signs but are not generally seen due to the poor prognosis for affected males. Use of dogs with one or two copies of the variant is not recommended for breeding as there is a risk that the resulting litter will contain affected puppies. Please note: It is possible that clinical signs similar to the ones caused by this variant could develop due to a different genetic or clinical cause.

Technical Details

Gene MTM1
Variant C>A
Chromosome X
Coordinate 118,885,117

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Beggs, A. H., Böhm, J., Snead, E., Kozlowski, M., Maurer, M., Minor, K., … Shelton, G. D. (2010). MTM1 mutation associated with X-linked myotubular myopathy in Labrador Retrievers. Proceedings of the National Academy of Sciences of the United States of America, 107(33), 14697–14702. View the article

Snead, E. C. R., Taylor, S. M., van der Kooij, M., Cosford, K., Beggs, A. H., & Shelton, G. D. (2015). Clinical Phenotype of X-Linked Myotubular Myopathy in Labrador Retriever Puppies. Journal of Veterinary Internal Medicine, 29(1), 254–260. View the article