McArdle's disease is a metabolic muscle disorder that was first described by Dr Brian McArdle in 1951. The disorder is also sometimes referred to as Glycogen Storage Disease Type V (GSD V). People with the condition are unable to produce an enzyme called muscle phosphorylase, which is important in producing the fuel required by muscles for exercise. This means they suffer severe muscle pain and fatigue in the first few minutes of exercise. Continuing to exercise despite the pain usually causes a severe muscle spasm or tightness (contracture).

Many people with McArdle's disease experienced painful symptoms from when they were children, however they were rarely diagnosed before adulthood. Some people notice a slow deterioration in their symptoms over many years, particularly with muscle wasting across their back and shoulders. Most people though learn to increase their exercise tolerance and remain able to walk. McArdle's disease does not affect life expectancy.

McArdles's disease is inherited in an autosomal recessive pattern.

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