<prompt> A 72-year-old man is recently found to have hypocalcemia and Osteomalacia is suspected based on the decrease in the cortical bone thickness and osteopenia seen on x-rays. Which of the following is the most likely mechanism of the resistance to the effects of vitamin D?excess parathyroid hormone secretioninsufficient parathyroid hormone secretiondefective receptors for 25OH vitamin Ddefective receptors for 1,25OH2 vitamin D  <response>: Deficient or defective 1,25OH2 vitamin D receptors will result in vitamin D resistance. Parathyroid hormone levels increase secondary to decreased vitamin D effect. The 1OH vitamin D is an intermediate metabolite. 