Last Updated on Nov 15, 2019


McArdle disease, also known as Glycogen storage disease type V, occurs due to a defect in the production of muscle phosphorylase.

McArdle disease is a genetic disorder in which the body cannot break down glycogen in the muscles. The disease results from a defect in a gene required for producing an enzyme called muscle phosphorylase (myophosphorylase). This enzyme is required to breakdown glycogen, an important source of energy that is stored in muscle tissue. This results in abnormal accumulation of glycogen in tissues.


McArdle disease (McArdle’s disease) is also known as McArdle syndrome or Glycogen storage disease type V (GSD-V). Its incidence is reported as 1 in 100,000.

McArdle disease is inherited in an autosomal recessive pattern, i.e. a copy of the defective gene from both parents is required for the child to develop the serious ailment. Many people carry one copy of the abnormal gene. Two abnormal copies are needed for McArdle disease to develop. Genetic mutations in the PYGM gene are found in individuals with McArdle disease.

McArdle disease is approximately equally represented in both sexes. Symptoms usually first develop in adulthood (sometimes early or late childhood). Exercise intolerance with muscle cramps is common. A definitive diagnosis usually requires a biochemical assay. No particular race is at a high risk of acquiring the disease.

In general, no permanent cure exists for McArdle disease. The role of a high protein diet in increasing exercise tolerance is controversial. The disease does not appear to affect longevity.


  1. DiMauro S (2007) Muscle glycogenoses: an overview; Acta Myol 26: 35–41
  2. Harrison’s Principles of Internal Medicine 18th Edition
  3. Cecil Medicine 24th Edition.

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