McArdle Disease (Type V)
McArdle Disease, also called glycogen storage disease type V (GSD-V), is an inherited disorder caused by an inability to break down glycogen in muscle cells, interfering with the function of muscle cells.
McArdle Disease is caused by a deficiency of glycogen phosphorylase, which breaks glycogen down into glucose. This function is particularly important in muscles during the first few minutes of exercise, and people with McArdle Disease typically experience fatigue, muscle pain, and cramps during this period (exercise intolerance). However, prolonged exercise allows compensation by increased blood flow (coronary response) and improves symptoms, leading to the classic "second wind phenomenon".
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