An 8-Year-Old Boy Is Evaluated for Exercise Intolerance

question 105

Multiple Choice

An 8-year-old boy is evaluated for exercise intolerance.  The patient experiences fatigue, muscle pain, and cramps during exercise as well as severe muscle stiffness following strenuous activity.  Physical examination is unremarkable.  A forearm ischemic exercise test is performed by applying a blood pressure cuff on the patient's exercising forearm and sampling blood lactate several minutes after the exercise.  The patient's blood samples show no rise in lactate levels.  Biochemical analysis of a muscle biopsy reveals absent lactate dehydrogenase activity.  In this patient, strenuous exercise leads to inhibition of glycolysis in skeletal muscle due to intracellular depletion of which of the following substances?

• A)AMP
• B)Carnitine
• C)Citrate
• D)FADH₂
• E)NAD⁺
• F)Pyruvate

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