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For further information, see CMDT Part 24-36: Myopathic Disorders

Key Features

  • Glycogen storage disease due to mutations in the gene encoding acid alfa-1,4-glucosidase

  • Age at presentation ranges from infancy to the late fifties and depends on the degree of residual enzyme activity

Clinical Findings

  • Juvenile and adult-onset forms present with slowly progressive proximal muscle weakness that includes respiratory failure

  • Cardiomyopathy less common in the adult form

  • Mildly elevated serum creatine kinase

  • Muscle biopsy shows glycogen containing lysosomal vacuoles


  • Suggested by detecting reduced acid-1,4-alfa-glucosidase activity on a dried blood spot

  • Confirmed by genetic testing


  • Recombinant alfa-glucosidase (20 mg/kg intravenously every 2 weeks) or avalglucosidase alfa (20–40 mg/kg intravenously every 2 weeks) stabilizes disease progression and results in improvement in respiratory function

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