You are a doctor specializing in disorders of metabolic enzymes. An 18-year-old man has been referred to you. He is experiencing muscular pain and tightness during physical exertion, especially in the cold. This is making it difficult for him to perform activities of daily life and to stay employed. He also suffers from muscular cramps in his legs when he is at rest. He has previously been diagnosed with hemolytic anemia. Urine tests are negative and he has not noticed any changes in urine color. You perform an ischemic exercise test, having him contract the muscles of the forearm while restricting blood flow with a blood pressure cuff. You take blood samples following the exercise every 30 seconds for 5 minutes. The results of this test show normal hemoglobin and blood glucose levels, but decreased levels of blood lactate when compared to a healthy adult performing the same test. A muscle biopsy shows normal levels of muscle glycogen and glucose. However, it shows levels of glucose-6 phosphate that are much lower than normal. Diagnose him with a deficiency of a metabolic enzyme.
