Cause - a genetic defect in the phosphorylase enzyme, which affects the breakdown of glycogen,the stored form of glucose (sugar)

Onset - childhood to adulthood

Symptoms - exercise intolerance; cramps, muscle pain and weakness shortly after beginning exercise; "second wind" after resting

Progression - not progressive

Inheritance - autosomal recessive, or caused by the contribution of a defective gene from each parent

Facts About Metabolic Disease of Muscle