This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'A 30 year old male was found to have excessive urinary glucose levels. However, his blood glucose levels were normal. Further investigations revealed high levels of only L-xylulose in urine. A genetic defect in which of the following pathway is most likely? \nSelect and explain. \nA. TCA cycle, B. Uronic acid pathway, C. Glycolysis, D. HMP shunt', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Essential Pentosuria\xa0defect in Uronic Acid Pathway:\n\nPentosuria is a condition where the sugar xylitol, a pentose, presents in the urine in unusually high concentrations.\nIt was characterized as an inborn error of carbohydrate metabolism in 1908. It is associated with a deficiency of L-xylulose reductase, necessary for xylitol metabolism.\nL-Xylulose is a reducing sugar, so it may give false diagnosis of diabetes, as it is found in high concentrations in urine.\nHowever, glucose metabolism is normal in people with pentosuria\xa0and they are not diabetic.\nPatients of pentosuria have a low concentration of the sugar d-xyloketose. Using\xa0phenyl pentosazone crystals, phloroglucin reaction, and absorption spectrum, pentose can be traced back as the reducing substance in urine, with those that have pentosuria.\n\n\xa0\nKey Concept:\xa0\nL-Xylulose is a reducing sugar, so it may give false diagnosis of diabetes, as it is found in high concentrations in urine.', 'role': 'assistant'}]