Muscular Dystrophy in Dogs

Dystrophin is a protein in the body that is important in maintaining the muscle’s structural integrity while it contracts. A mutation in the gene can disrupt dystrophin production, and its absence in the muscle leads to a degeneration and death of the muscle cells. Those cells are replaced with fatty or bony tissue, which results in the loss of muscle function that can eventually lead to a loss of the ability to walk or breathe. This condition usually affects males, though female cases have been documented and are often misdiagnosed.

Muscular dystrophy refers to a group of over thirty genetic conditions in dogs that cause a breakdown in the muscles involved with movement. This skeletal muscle disease is characterized by stiff muscles and a weakness that limits activity as it worsens. A progressive degeneration is caused by fibrosis, or thickening, of the muscle cells which lead to loss of muscle function. Treatment is limited to symptom relief and cannot stop the progression of the disease, which is often fatal.

Symptoms have an early onset, and are often present at birth or early in life. They include:

• Stiffness in muscles
• Stiff gait
• Weakening of muscles
• Difficulty swallowing
• Progressive generalized weakness
• Plantigrade stance, wherein the toes and metatarsals are flat on the ground
• Muscle atrophy
• Muscle enlargement, which can include tongue, diaphragm, and esophagus
• Difficulty swallowing
• Loss of muscle mass
• Resistance to exercise
• Tremors
• Limb deformity
• Breathing sounds
• Excessive drooling

Types

There are many types of muscular dystrophy that have been seen to affect dogs.

• Golden Retriever Muscular Dystrophy is similar to Duchenne Muscular Dystrophy (DMD) that affects humans and mainly affects Golden Retrievers in the U.S. and Irish Terriers in Europe; along with previously noted symptoms, affected dogs have been reported with heart muscle disease, this type of muscular dystrophy serves as a model for DMD in humans in clinical studies and trials
• Canine X-linked Muscular Dystrophy
• Hereditary Myopathy of Labrador Retrievers affects Labrador Retrievers in North America, Europe and Australia; in this type, muscle loss has been noted in affected dogs as young as 6 months old
• Type that affects Bouviers in Europe, affecting their ability to swallow
• Other variations of this disease may be seen for each affected breed, including Rottweiler, German Shorthaired Pointer, Belgian Sheepdog, Samoyed, Miniature Schnauzer, Brittany Spaniel, Rat Terrier, Groenendaeler Shepherd, and Pembroke Welsh Corgi

Muscular dystrophy in dogs is caused by an inherited mutated dystrophin gene that disrupts the dystrophin protein production, resulting in loss of muscle function. This autosomal recessive gene is located on the X chromosome, which is why most of the reported cases have been male. However, the gene is transmitted through a female carrier who is often free of symptoms, or mildly affected with a limb weakness. Muscle changes are often only seen through muscle biopsy and EMG testing. As such, this condition is often misdiagnosed or undiagnosed in female dogs.

A diagnosis of canine muscular dystrophy is derived from symptoms and abnormalities seen in testing. The leading tests for a positive diagnosis are a microscopic evaluation of muscle tissue fibers from a biopsy, and an immunohistochemical staining test. These two tests can also help to distinguish between the different types of muscular dystrophies. 

The response of muscles to electrical stimulation is sought with an EMG. Elevated serum creatine kinase concentrations are determined through serum tests from a blood sample. Other diagnostic tools include complete blood counts, X-rays, EKGs, and a neurological examination.

There is currently no treatment specifically for this condition, but medication may help with symptoms. Glucocorticosteroids may be administered, but can often have negative consequences.

Surgery may be performed for limb deformity or gait abnormality. Supportive therapies within your dog’s environment can be helpful, such as soft bedding. 

Future treatments may involve the administration of a miniature version of the affected gene, called a microgene, into the body to protect muscles, but is not yet available. This has been seen to allow young dogs to grow normally after treatment.

In general, the recovery from muscular dystrophy is guarded to poor. While some dogs can stabilize after maturity, the progressive nature of the disease leads to weakness, debilitation, and heart muscle disease. Life spans of affected dogs will vary on a case by case basis, and often euthanization is sought.

Prevention is critical in such a debilitating condition. Breeders should take care not to breed affected dogs, though the possibility of an asymptomatic carrier female remaining undiagnosed is always a risk for passing on the gene.