X-Linked Muscular Dystrophy in Dogs

CXMD affects males almost exclusively because it is linked to the X-chromosome that is only found in male dogs. Females that have similar chromosomal deficiencies do not show many symptoms, if any. Therefore, they are thought to be carriers. It is a hereditary disease that is seen mostly in the Golden Retriever, but is also being reported in other breeds such as the Samoyed, Terrier, Corgi, Pointer, Rottweiler, Spitz, Belgian Shepherd, and Schnauzer.

X-linked Muscular Dystrophy (CXMD) is a hereditary degenerative muscle disease that is caused by a lack of dystrophin, which is a protein that builds and sustains muscles. This is a progressive disease that affects male puppies and will eventually be fatal in almost all dogs that have it. Dogs with CXMD start out with signs of being undernourished due to the difficulty they have in nursing around six to eight weeks of age, which is sometimes not noticed because this is the time that they are introduced to regular food.

The puppy with CXMD will have trouble picking up and eating food, which is also sometimes difficult to notice because puppies are just learning to eat so their inability to eat may be mistaken for clumsiness. Once the muscles start to become affected, the puppy will start to show signs of not keeping up with the other puppies, falling, and dragging their hind legs.

The first symptom of CXMD you may notice is the inability of a newborn to suckle. This alone may not be cause for concern if the puppy eventually gets the hang of it, but accompanied by other signs, it will become obvious that your puppy has a problem. Some of these signs are:

• Drooling more than usual
• Nausea and vomiting
• Stiff muscles
• Walking like a bunny (hopping)
• Weakness and inability to walk and play
• Wasting away of some muscles (face and trunk) while others get larger (tongue)
• Back legs turned in
• Front legs turned outward
• Sagging back
• Trouble swallowing
• Difficulty in picking up food
• Aspiration pneumonia (coughing, wheezing, difficulty breathing)
• Heart muscle weakening (fluid buildup in abdomen, labored breathing, coughing)
• Death

The cause of CXMD is a hereditary defect that creates a dystrophin deficiency. The most commonly affected dogs include:

• Young dogs under one year old
• Male dogs are also more susceptible than females
• Golden Retriever
• Basset Griffon
• Groenendaeler Shepherd
• Japanese Spitz
• Alaskan Malamute
• Irish Terrier
• Pembroke Welsh Corgi
• Samoyed
• Rottweiler
• Belgian Shepherd
• Rat Terrier
• Brittany Spaniel
• Labrador Retriever
• German Short-Haired Pointer
• Miniature Schnauzer

Getting the right diagnosis for your dog is important if he has CXMD because it helps track the disease and lets breeders know to have their dogs tested before breeding. It is also important because the diagnoses and prognoses are different for the various types of muscular dystrophy. There are also other disorders that can produce similar symptoms such as an infection from neospora caninum or toxoplasma gondii. Your veterinarian will need a complete medical history and immunization records before doing the physical examination.

Blood tests will likely show that your dog’s serum creatinine kinase (CK) levels and liver enzymes are markedly increased and there may be a slight increase in white blood cells. A muscle biopsy will need to be performed and will usually disclose that the muscle fibers are mineralized and translucent. X-rays, CT scans, and an ultrasound are helpful in checking the progression of the disease.

Even though there is no cure for CXMD, there are treatments that can help slow the progression and some dogs spontaneously recover on their own, although this is rare. Some of the treatments include medications, hematopoietic stem cell transplantation, gene therapy, and adeno-associated viral (AAV) vector-mediated gene replacement strategies.

Medications

One of the most common complications of CXMD is aspiration pneumonia, so antibiotics and prednisone are usually given for this problem. Also, glucocorticosteroids have been administered to help with pain and relieve the inflammation.

Hematopoietic Stem Cell Transplantation

In this procedure, stem cells are retrieved from the lining of blood vessels of healthy dogs and then injected into the sick dogs. Once there, these stem cells help form the dystrophin protein needed.

Gene Therapy

Adeno-Associated Viral (AAV) Vector-Mediated Gene Replacement therapy is a relatively new treatment for dogs with CXMD that has shown promise in rebuilding dystrophin and muscle. Exon skipping is another form of gene therapy that is used. This is done by tricking the body into skipping the bad parts of the deformed gene.

The prognosis is not good for canines with this disease. However, if your dog is still in good health by one year of age, the chances of a normal life span is much better because this disease is stabilized after that.