McArdle disease (glycogen storage disease type V)

What happens in this disease?

The muscles hold a store of sugar called glycogen. When exercise starts, this store is quickly turned into energy. In this disease, the muscle enzyme that does this job is missing. The muscle cannot find enough energy, especially at the start of exercise.

Which symptoms can occur?

Symptoms usually begin in childhood or the teenage years. They can range from mild to severe.

• Early tiredness, pain and cramps at the start of exercise
• Relief after a short rest, called the "second wind" (common)
• Muscle breakdown after hard exercise (in about half)
• Dark, red-brown urine after muscle breakdown
• Kidney problems caused by muscle breakdown (sometimes)
• Lasting muscle weakness in later years (sometimes)

How is it diagnosed?

CK, a muscle enzyme, is measured in the blood. The "second wind" finding helps with the diagnosis. Today, the diagnosis is usually made with a genetic test on a blood sample. In the past, a muscle biopsy and an arm exercise test were used.

Treatment and care

There is no approved treatment specific to the disease. Regular light-to-moderate aerobic exercise under a doctor's supervision is helpful. Sudden and very hard exercise is avoided. A diet rich in complex carbohydrates may be recommended. For some people, taking sugar before exercise may be recommended. Research is ongoing. The doctor who follows the disease decides which treatment is suitable.

For the family: inheritance and genetic counselling

The disease is passed on through recessive inheritance. The mother and father are usually healthy carriers. For a couple who are both carriers, the chance of having an affected child is 1 in 4 in each pregnancy. In marriages between relatives, the chance of carrying the same gene is higher. Genetic counselling is recommended for the family.