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McArdle syndrome

  • Alternative Names

    Glycogen storage disease type V (GSDV); Myophosphorylase deficiency; Muscle glycogen phosphorylase deficiency; PYGM deficiency


    Symptoms usually start during early childhood. However, it may be difficult to separate these symptoms from those of normal childhood, and diagnosis may not occur until a person is in their 20s or 30s.

    • Burgundy-colored urine (myoglobinuria)
    • Fatigue
    • Exercise intolerance, poor stamina
    • Muscle cramps
    • Muscle pain
    • Muscle stiffness
    • Muscle weakness

    Signs and tests

    The following tests may be performed:

    • Electromyography (EMG)
    • Genetic testing
    • Lactic acid in blood
    • MRI
    • Muscle biopsy
    • Myoglobin in urine
    • Plasma ammonia
    • Serum creatine kinase