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McArdle syndrome

Contents of this page:

Alternative Names   

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

Definition    Return to top

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

Causes    Return to top

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 get a copy of the defective gene from both parents. A person who gets a defective gene from only one parent usually does not develop this syndrome. A family history of McArdle syndrome increases the risk.

The disease usually starts when a person is in their 20s or 30s, but there is a very rare form that begins in infants.

Symptoms    Return to top

Exams and Tests    Return to top

The following tests may be performed:

Treatment    Return to top

There is no specific treatment, but you can manage the symptoms by improving exercise tolerance and controlling physical activity. Avoid excessive or intense exercise.

Dietary management should include having a supply of glucose (candy, for example) on hand if you need to replace energy.

Avoid general anesthesia.

Support Groups    Return to top

For additional information and resources, visit the Association for Glycogen Storage Disease at

Outlook (Prognosis)    Return to top

People with McArdle syndrome can live a normal life by managing their physical activity.

Possible Complications    Return to top

Exercise may produce muscle pain, or even breakdown of skeletal muscle, a condition called rhabdomyolysis. This is associated with burgundy-colored urine and a risk for kidney failure, if severe.

When to Contact a Medical Professional    Return to top

Contact your health care provider if you have repeated episodes of sore or cramped muscle after exercise, especially if accompanied by burgundy or pink urine.

Consider genetic counseling if you have a family history of McArdle disease.

Update Date: 10/15/2008

Updated by: Diana Chambers, MS, EdD, Certified Genetics Counselor (ABMG), Charter Member of the ABGC, University of Tennessee, Memphis, TN. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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