Type 5 glycogenosis is a metabolic disorder that is caused by a deficiency of muscle glycogen phosphorylase typically due to a mutation in the gene PYGM, resulting in the extra glycogen storage in cells. It is a form of glycogenosis that refers to metabolic disorders caused by an improper metabolism of glycogen. Type 5 glycogenosis is a condition characterized by the following common symptoms: exercise-induced cramps, rhabdomyolysis, renal failure by myoglobinuria, and second wind phenomenon. This metabolic disorder is caused by a deficiency in myophosphorylase. Myphosphorylase is an enzyme that breaks down glycogen into glucose-1-phosphate for use within the muscle cell. The deficiency of this enzyme is associated with a mutation in the gene PYGM, which in humans is located on chromosome 11q13. It is inherited in an autosomal recessive pattern. This condition is also referred to as McArdle disease since it is first described in 1951 by Dr. Brian McArdle, a British physician in Guy’s Hospital, London. Synonyms: McArdle disease, McArdle-Schmid-Pearson disease, muscle phosphorylase deficiency, myophosphorylase deficiency, glycogen storage disease type V (GSD-V).
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