HyperCKemia as the only sign of McArdle's disease in a child

An asymptomatic 13-year-old boy, who never complained of exercise intoleran ce or myalgia, was found to have markedly elevated serum creatine kinase (C K) levels during a routine check-up. General physical and neurologic examin ations were normal. Surprisingly, histochemical and biochemical analysis of muscle showed myophosphorylase deficiency and genetic analysis showed that the patient was homozygous for the most common mutation encountered in McA rdle's disease (R49X). This case illustrates the fuzzy correlation between molecular defect and clinical phenotype in patients with McArdle's disease, and suggests that a thorough study of the muscle biopsy is important in pa tients with idiopathic hyperCKemia for correct diagnosis and careful follow -up.