Definition of McArdle syndrome :

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

Causes, incidence, and risk factors:

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.