McArdle Disease: Insights Into a Rare Metabolic Myopathy in a Young Boy With Recurrent Exercise-Induced Muscle Weakness.

McArdle disease, or glycogen storage disease type V, is a rare metabolic myopathy caused by a deficiency of myophosphorylase, leading to impaired glycogen breakdown in skeletal muscle. This results in exercise intolerance, muscle cramps, and episodic weakness. Due to its rarity and variable presentation, diagnosis is often delayed or misattributed to other neuromuscular disorders.