McArdle syndrome is the inability to break down glycogen. Glycogen is an important source of energy that is stored in all tissues, but especially in the muscles and liver.
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
The disease is an
Symptoms usually start during early childhood. However, it may be difficult to separate these symptoms from those of normal childhood, and diagnosis may not occur until a person’s 20s or 30s.
Burgundy-colored urine (myoglobinuria)
Exercise intolerance, poor stamina
- Muscle stiffness
- Muscle weakness
Signs and tests
The following tests may be performed:
Lactic acid in blood MRI Muscle biopsy Myoglobin in urine
- Plasma ammonia
Serum creatine kinase
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.
For additional information and resources, visit the Association for Glycogen Storage Disease at
People with McArdle syndrome can live a normal life by managing their physical activity.
Exercise may produce muscle pain, or even a breakdown of skeletal muscle (
Calling your health care provider
Contact your health care provider if you have repeated episodes of sore or cramped muscles after exercise, especially if you also have burgundy or pink urine.
Consider genetic counseling if you have a family history of McArdle disease.