Pompe disease — also known as Glycogen Storage Disease Type II (GSD II) — is a rare but serious metabolic disorder that affects both humans and dogs. It is named after the Dutch pathologist Joannes Cassianus Pompe, who first described the condition in 1932 after observing its effects on infants. This disorder is caused by a deficiency of the enzyme acid alpha-glucosidase (GAA), which is crucial for breaking down glycogen into glucose within lysosomes. When GAA is deficient or absent, glycogen accumulates in various tissues, particularly in muscle cells, leading to progressive muscle weakness and other systemic complications.

Here’s what you should know about the symptoms, causes, and treatments of the condition.

Symptoms of Pompe disease in dogs

The symptoms of Pompe disease in dogs can vary widely depending on the age of onset, the severity of enzyme deficiency, and the rate at which glycogen builds up in various tissues. In general, GSD II can present in two forms: juvenile-onset and adult-onset.

• Juvenile-onset form: Puppies may show symptoms as early as a few weeks to months of age. Common signs include generalized muscle weakness, difficulty swallowing, and poor growth. This form progresses quickly and can lead to severe respiratory distress and cardiac issues.
• Adult-onset form: Dogs may not show symptoms until later in life, usually between two and five years of age. Affected dogs may exhibit signs of exercise intolerance, muscle weakness, stiffness, and a gradual decline in mobility. Unlike the juvenile form, the progression is typically slower but can still be debilitating over time.

Juvenile-onset cases generally have a poorer prognosis due to rapid disease progression and the early onset of life-threatening symptoms. Without treatment, affected dogs may live only up to two years. In contrast, adult-onset cases may have a relatively better prognosis but still face significant challenges related to muscle weakness and mobility issues. Therefore, early diagnosis and a comprehensive management plan are vital for improving the quality of life and extending the lifespan of dogs with Pompe disease.

Causes of Pompe disease in dogs

The underlying mechanism of Pompe’s disease in dogs mirrors that in humans. Lysosomes, which act as the cellular recycling centers, rely on GAA to break down glycogen. In dogs suffering from GSD II, a mutation in the gene coding for GAA impairs this process. The resulting glycogen buildup occurs predominantly in muscle cells, including skeletal and cardiac muscles, which are highly reliant on efficient energy production. Over time, the excess glycogen disrupts normal cellular functions, leading to the degeneration and death of affected cells.

Pompe disease is inherited in an autosomal recessive manner. This means that a dog must inherit two copies of the defective gene — one from each parent — to develop the disease. Dogs who inherit only one defective gene are considered carriers and do not typically show symptoms. However, they can pass the gene to their offspring.

While Pompe’s disease can potentially affect any breed, certain breeds appear to be at higher risk due to genetic predispositions. These include:

• Finnish Lapphund
• Swedish Lapphund
• Lapponian Herder

If you suspect your dog may be affected, the first step is to consult your vet. You’ll want to discuss any unusual signs you’ve noticed, such as vomiting, fatigue, or difficulty breathing. Your vet will initially conduct a physical exam and review your dog’s medical history to rule out more common conditions that could present with similar symptoms.

To confirm the diagnosis, your vet may recommend blood tests to measure the levels of certain enzymes, specifically GAA, which is deficient in dogs with Pompe disease. Genetic testing can also provide further confirmation by identifying mutations in the GAA gene. In some cases, muscle biopsies might be performed to assess the extent of glycogen accumulation in the muscle tissues.

Treatments for Pompe disease in dogs

Currently, there is no cure for Pompe disease, and treatment is primarily supportive and symptomatic. The goal is to improve the quality of life and prolong the survival of affected dogs. Some treatment options for Pompe disease include:

• Enzyme replacement therapy (ERT): ERT is a promising treatment that involves administering a synthetic form of the GAA enzyme. Though ERT has shown some success in humans, its application in veterinary medicine is still under research and development.
• Physical therapy: Regular physical therapy can help maintain muscle function and delay the progression of muscle weakness. Tailored exercise programs should be supervised by a vet or a veterinary physiotherapist.
• Medications: Anti-inflammatory drugs, bronchodilators, and cardiac medications may be prescribed to manage secondary complications associated with Pompe’s disease.
• Respiratory support: In advanced cases, dogs may require respiratory support, such as oxygen therapy or mechanical ventilation, particularly if respiratory muscles are significantly weakened.
• Dietary management: Proper diet and nutritional support can help manage symptoms and improve overall health. A diet low in complex carbohydrates may be recommended to reduce the buildup of glycogen.

Given that Pompe disease is an autosomal recessive disorder, responsible breeding practices are essential to prevent its propagation. Genetic counseling can help breeders understand the risk of passing the disease to offspring. DNA testing should be used to identify carriers and make informed breeding decisions, ultimately reducing the prevalence of this debilitating condition in future generations.