An 18-year old patient complains of excessive fatigue after prolonged exercise, and notes that several of his family members have similar symptoms. Lab tests show myoglobinuria (the presence of myoglobin in the urine), which is a sign of muscle damage. The patient is given an ischemic work test, in which a blood pressure cuff is applied to the upper arm and inflated, severely restricting blood flow to the arm. The patient then squeezes a dense rubber fall for 60 seconds. The blood pressure cuff is removed and a blood sample collected. The blood sample shows elevated pyruvate and lower than normal lactate levels. Can you propose an explanation for these symptoms? The patient has a mutation in the gene encoding lactate dehydrogenase. He can?t process pyruvate to lactate. Therefore, he won?t be able to make ATP under anaerobic conditions because he will run out of NAD+, which is needed for future rounds of glycolysis. See OMIM: HYPERLINK "http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=150000" http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=150000 What other biochemical tests could you order to confirm your explanation? You could check his NAD levels: NADH should be high and NAD+ should be low.
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