Glycogen storage disease type V (Mc Ardle's disease): a report on three cases.

McArdle's disease (myophosphorylase deficiency), an uncommon autosomal recessive metabolic disorder, is characterized clinically by exercise intolerance beginning in childhood, myalgia, cramps, exercise-induced rhabdomyolysis, "second wind" phenomenon, elevated Creatine Kinase (CK) levels at rest, and previous episodes of raised CK levels following exercise. Several mutations in the PYGM gene and geographic variations have been described. We report three biopsy confirmed cases of McArdle's disease.