A child with Exercise fatigue presented to OPD. The features were suggestive
of Mcardle disease. Which of the following enzymes will be deficient in this?
A. My o-Phosphorylase
B. Glucose 6 Phosphatase
C. Lysosomal Glucosidase
D. Phosphofructokinase
Answer. A
Solution. McArdle disease, also known as glycogen storage disease type V, is caused by a
deficiency in the enzyme myophosphorylase. Myophosphorylase is responsible for breaking
down glycogen, a stored form of glucose, into glucose-1-phosphate, which can then be used as
a source of energy. In individuals with McArdle disease, the deficiency of this enzyme leads to
the accumulation of glycogen in muscle cells, causing exercise intolerance and fatigue.