McArdle syndrome (glycogen storage disease type V)

Definition:

McArdle syndrome is a metabolic disease characterized by abnormal storage of glycogen in muscle tissue.

Muscle pain, cramps, and stiffness with poor tolerance for exercise are the primary problems -- these usually do not occur until the affected person has reached adulthood. Avoiding strenuous exercise decreases the severity of these problems and of the disease.

Alternative Names:

Glycogen storage disease type V; Muscle phosphorylase deficiency

Causes, incidence, and risk factors:

McArdle disease is a genetic disease which results from deficiency of a specific enzyme called phosphorylase in muscles. It is recessive, which means that it only occurs when defective genes are inherited from both parents.

Without phosphorylase, glycogen (an important source of sugar and energy) can not be broken down and it builds up to high level in muscle. As a result, there is decreased ability to exercise which can produce muscle symptoms such as weakness, cramps, and pain.

Symptoms:

Muscle pain, cramps
Muscle weakness
Intolerance for exercise
Exercise can produce a "burgundy-colored" urine (myoglobinuria)

Signs and tests:

Brief, intense exercise does not lead to increase in blood lactic acid.
Presence of myoglobin in "burgundy-colored" urine.
Increased serum creatine kinase (rhabdomyolysis) especially after exercise
Muscle biopsy shows stored glycogen and decreased phosphorylase activity.
Specialized centers may be able to show abnormal muscle metabolism using an MRI machine in a test called spectroscopy.

Treatment:

The most important treatment is avoiding strenuous exercise. In particular, brief, intense exercise such as carrying a heavy load and prolonged exercise such as climbing long hills must be avoided.

Rarely, severe exercise-induced muscle-ache associated with burgundy urine (rhabdomyolysis) may need hospital-based treatments such as intravenous fluids.

Support Groups:

Association for Glycogen Storage Disease (202) 966-5557

Expectations (prognosis):

While most patients are not diagnosed with this disease until they reach their 20's or 30's, many report that they had poor tolerance for exercise in childhood. Aside from avoiding strenuous exercise, McArdle patients can live a normal life.

Complications:

Strong exercise may produce muscle pain or even breakdown of skeletal muscle (rhabdomyolysis). This is associated with a "burgundy-colored" urine, and an increased risk for kidney failure (if severe).

Calling your health care provider:

Call if you have repeated episodes of sore or cramped muscle after exercise, especially if accompanied by burgundy or pink urine. Call if you have a family history of McArdle disease.

Prevention:

There is no known prevention for this relatively benign disease.

Review Date: 9/9/2001
Reviewed By: David G. Brooks, M.D., Ph.D., Division of Medical Genetics, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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