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| Disease found: | McArdle Disease |
| Current as of: | October 8, 2024 |
| Disease Overview: | Deficiency in the myophosphorylase enzyme (gene PYGM) impairs the ability to break down glycogen within muscle tissue specifically. [more info] |
| Signs and Symptoms: | Exercise intolerance, often within first 10 years of life but can present at any age. Strenuous exercise induces muscle cramping, fatigue; risk of rhabdomyolysis and myoglobinuria in severe disease. [more info] "Second wind phenomenon" where exercise tolerance improves after brief rest, or after prolonged moderate exericse. [more info] |
| Diagnosis: | Initial screening with the ischemic forearm test is highly suggestive of disease; Molecular testing for PYGM genetic mutation is preferred to confirm; test available here. Assay of muscle myophosphorylase enzyme activity in a muscle biopsy sample may be considered if genetic testing is inconclusive; this is an older test described here. |
| Treatment: | Patients should be advised to follow a high-complex-carbohydrate diet; extra carbohydrates should be consumed before planned exercise to help avoid rhabdomyolysis. [more info] |
| Clinical Management: | Annual physical exams and diet review/assistance. Promote regular exercise (with a supervised exercise program initially); patients who maintain physical activity have better prognosis. [more info] |
| Referral: | Several large academic medical centers have dedicated Glycogen Storage Disorder programs/clinics. Genetic counseling is recommended. The Scientific Advisory Board of the Association for Glycogen Storage Disease offers a list of hospitals with GSD-focused clinics.Referral to Medical Genetics Department, if available. Initial virtual care is also available through organizations like TeleRare Health. |
| Clinical Trials: | One clinical trial in Denmark is currently recruiting. |