Centronuclear Myopathy (CNM) testing in the Great Dane and Labrador retriever

Centronuclear myopathy or CNM for short is a hereditary health condition that has been identified as present in the gene pools of the Great Dane and Labrador retriever dog breeds. The condition was previously known as hereditary myopathy before its mode of action became better understood.

Centronuclear myopathy leads to poor muscle function in affected dogs, which occurs due to a gene mutation of the PTPLA gene, which affects the nuclei of muscle fibres.

Dogs with the condition appear to be healthy and normal at birth, but abnormalities usually become apparent shortly afterwards-usually between the ages of two and five months. The earliest symptoms begin with a general failure to thrive and gain adequate weight to support growth, and a progressive loss of muscle tone of the oesophagus.

Centronuclear myopathy progresses quickly, and by the time the dog is around five or six months old, they will exhibit all of the signature symptoms of the condition, which include poor muscle tone and lack of muscle control, a strange walking gait, and a high level of exercise intolerance that is worse in cold weather rather than hot weather, unlike generalised exercise intolerance.

Centronuclear myopathy cannot be cured or reversed, and affected dogs will always suffer from the symptoms outlined above to some extent.

Generally, affected dogs will live for a normal lifespan, but the condition can of course have a significant effect on the dog’s quality of life, depending on how pronounced the symptoms are.

The condition is hereditary and not contagious, and so the only way that a dog can develop the condition is by means of inheritance, and so finding out the status of the potential parent dogs of any litter will allow you to find out the status of the litter.

The Kennel Club oversees a testing and monitoring scheme for the condition in the Great Dane and Labrador retriever dog breeds, and in this article we will look at how to get your dog tested and how the heredity of the condition works. Read on to learn more.

More about Centronuclear myelopathy

Exactly how acute the symptoms of Centronuclear myelopathy are in any given dog and so, how badly it affects them can vary from case to case. The signatures of the condition include a stiff, arched-back gait with a low carriage of the head, which when combined with exertion, causes the affected dog to face-plant or nose dive head first into the ground, due to the extreme level of exercise intolerance that accompanies it.

The only way to formally diagnose the condition is by means of genetic testing, as the condition is caused by a fault in the PTPLA gene. While the condition cannot be cured or reversed, it does tend to stabilise by the time the dog in question has reached a year old, which makes management easier on an ongoing basis.

What sort of dogs can be affected by the condition?

In the UK, Centronuclear myelopathy has been identified as present within the Labrador retriever and Great Dane dog breeds, which means that both pedigree and non-pedigree dogs of these breeds may potentially inherit the condition from untested parents.

Cross breed dogs that have one ancestor from the two breeds may also inherit the mutated gene that is necessary to cause the condition, however, one is not enough; unless said dog is back-crossed to one of the two potentially affected breeds, they will not inherit the two copies of the gene necessary to pass on the condition to their own offspring.

Crossing a Labrador retriever and a Great Dane presents the same theoretical risks of inheriting the condition as crossing a pure bred pair from either breed.

How does the heredity of the condition work?

Centronuclear myelopathy is inherited by means of the autosomal recessive mode of heredity, which means that the status of both of the parent dogs combined dictates the status of their puppies. One copy of the faulty gene alone is not enough to lead to the affected form of the condition, although it can cause the dog to possess carrier status.

In order to understand the status of the pups that result from any given mating, the following information outlines the mode of the heredity:

• Two clear dogs will have clear puppies.
• Two affected dogs will have affected puppies.
• Two carriers will have a mix of 50% carrier, 25% affected and 25% clear.
• A clear dog and a carrier will have 50% clear and 50% carriers.
• A clear dog and an affected dog will produce a litter of carriers.
• A carrier and an affected dog will produce 50% carriers and 50% affected.

How to get your dog tested

In order to find out your dog’s status and so, make an informed decision about any breeding match, you just need to ask your vet to take a DNA sample from your dog, which you then send off to one of the laboratories approved by The Kennel Club to test for the markers of the condition.

The results of your dog’s status will then be returned to you.