Glycogen Storage Disease Type V is a genetic disorder where the body lacks an enzyme called myophosphorylase. This enzyme is crucial for turning stored sugar (glycogen) into glucose, which provides energy to our muscles, especially during exercise.
People with GSDV face challenges during physical activity, experiencing muscle pain, cramping, and fatigue. Although their muscle strength might be normal, intense or prolonged workouts can damage muscles. In about half of those with GSDV, muscle breakdown releases a protein called myoglobin, turning urine dark red or brown. This protein can harm kidneys and may lead to kidney failure in severe cases. Symptoms can start at any age, but they often appear in childhood or adolescence. The severity varies, ranging from mild or no symptoms to severe muscle weakness. Symptoms usually worsen over time, although some individuals do not experience progression. Exercise under supervision, especially moderate-intensity training, can enhance tolerance. However, high-intensity workouts should be avoided, as they might harm muscles and kidneys. Consuming simple sugars before exercise (like sports drinks) and having a carbohydrate-rich diet can improve exercise tolerance for individuals with GSDV. Careful management, exercise guidance, and dietary adjustments are essential in ensuring a healthier lifestyle for those living with this condition.
GSDV is caused by pathogenic (disease-causing) variants in the PYGM gene and exhibits autosomal recessive inheritance. This means that both parents must be carriers to have a 25% chance to have a child with the condition. The risk of being a carrier is based on a person’s ancestry or ethnic background. For example, individuals of Sephardic Jewish descent have a 1 in 84 chance to be a carrier.
Other names for this condition are McArdle disease, muscle glycogen phosphorylase deficiency, muscle phosphorylase deficiency, myophosphorylase deficiency, and PYGM deficiency.