Question

An adolescent male patient presents to you with exercise intolerance. He gives a history of developing cramps on exertion. Which of the following enzyme deficiencies could be the cause? 

• A. Myophosphorylase
• B. Hexokinase
• C. Glucose-6-phosphatase
• D. Hepatic glycogen phosphorylase

Answer 1

The Correct Option is A

The adolescent male patient's symptoms of exercise intolerance and cramps on exertion suggest an issue with muscle metabolism. Among the given enzyme options, a deficiency in Myophosphorylase is the most likely cause of these symptoms.

Myophosphorylase is an enzyme that plays a crucial role in muscle glycogen breakdown. It catalyzes the first step in glycogenolysis, which is the conversion of glycogen to glucose-1-phosphate in muscle tissues. This process is critical during physical exertion, as it provides the necessary energy for muscle contractions.

The condition associated with myophosphorylase deficiency is known as McArdle's Disease (Glycogen Storage Disease Type V). It is characterized by exercise intolerance, muscle cramps, and sometimes myoglobinuria in response to strenuous activities.

In contrast, other enzymes such as Hexokinase, Glucose-6-phosphatase, and Hepatic glycogen phosphorylase have different roles:

• Hexokinase: Involved in the initial stages of glycolysis, converting glucose to glucose-6-phosphate.
• Glucose-6-phosphatase: Plays a role in gluconeogenesis and glycogenolysis in the liver, not directly affecting muscle energy metabolism under exertion.
• Hepatic glycogen phosphorylase: Functions similar to myophosphorylase but specifically in the liver, not the muscles.

Thus, the enzyme deficiency responsible for the exercise intolerance symptoms is Myophosphorylase.