About McArdle Disease
McArdle Disease is caused by bi-allelic mutations in the PYGM gene, resulting in complete absence of myophosphorylase — the muscle isoform of glycogen phosphorylase — which blocks glycogen breakdown in skeletal muscle during exercise. This leads to exercise intolerance, myalgia, and rhabdomyolysis, but the pathognomonic 'second wind' phenomenon — a spontaneous improvement in exercise capacity after 8–10 minutes — distinguishes it from other exercise-induced myopathies. Severe rhabdomyolysis can cause acute kidney injury.
Common Clinical Features
Clinical Trial Eligibility Tips
What to know before applying to McArdle Disease trials.
Forearm ischaemic (or non-ischaemic) exercise test showing absent venous lactate rise with normal ammonia rise is diagnostic and frequently documented as part of eligibility screening
Genetic confirmation of bi-allelic PYGM mutations is required; the common p.R50X variant is found in approximately 60% of European alleles and can be rapidly screened
Cardiopulmonary exercise testing (CPET) and peak VO2 are increasingly used as primary endpoints; a structured exercise test with a physiologist prior to trial application is highly recommended
Patient Resources
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