This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamin D, Subject name: Pediatrics
[{'content': 'What is true of vitamin D resistant rickets? \nSelect and explain. \nA. X linked recessive, B. No End organ resistance to 1, 25 (OH)2 D3, C. Defect in proximal tubular reabsorption, D. Hyperphosphatemia and high 1, 25 (OH)2 D3', 'role': 'user'}, {'content': "Answer: C \nExplanation: ANSWER: (C) Defect in proximal tubular reabsorptionREF: Nelson's 18th ed page 2720Familial Hypophosphatemia: (Vitamin D-Resistant Rickets, X-Linked Hypophosphatemia)The most commonly encounterednon-nutritional form of rickets is familial hypophosphatemia. The usual mode of inheritance is X-linked dominantPathogenic mechanisms involve defects in the proximal tubular reabsorption of phosphate and in the conversion of 25(OH)D to l,25(OH)2 D, The latter defect is evidenced by 1owt- normal serum l,25(OH)2 D levels despite hypophosphatemia and by the finding that further phosphate depletion of subjects with familial hypophosphatemia does not stimulate 1,25 (OH)2 D synthesis as it does in normal subjectsPatients have a normal or slightly reduced serum calcium level, a moderately^ reduced serum phosphate level, elevated alkaline phosphatase activity, and no evidence of secondary hyperparathyroidism. Urinary phosphate excretion Is large, despite hypophosphatemia, indicating a defect in renal tubular phosphate", 'role': 'assistant'}]