Vitamin D resistant rickets occurs due to all Except: (A) alpha 1 hydroxylase deficiency, (B) Renal tubular acidosis, (C) Fanconi syndrome, (D) Drugs
Answer is A. The disorder is due to missing or inactive PHEX gene. PHEX inactivates phosphatonins that mediate phosphate wasting. Thus, patients with Vitamin D resistant rickets cannot retain phosphate, leading to renal phosphate wasting. ref - Harrisons internal medicine 20e p2920