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McArdle syndrome

  • Definition

    McArdle syndrome is the inability to break down glycogen. Glycogen is an important source of energy that is stored in muscle tissue.


    Alternative Names

    Glycogen storage disease type V (GSDV); Myophosphorylase deficiency; Muscle glycogen phosphorylase deficiency; PYGM deficiency


    Causes, incidence, and risk factors

    McArdle syndrome is caused by a defect in a gene that makes an enzyme called glycogen phosphorylase. As a result, the body cannot break down glycogen in the muscles.

    The disease is an autosomal recessive genetic disorder. This means that you must get a copy of the nonworking gene from both parents. A person who gets a nonworking gene from only one parent usually does not develop this syndrome. A family history of McArdle syndrome increases the risk.