VDR and Hypocalcemia: The hallmark of the disease is hypocalcemia despite elevated 1,25-dihydroxy vitamin D [1,25(OH)2D] level, implying resistance to 1,25(OH)2D.1 1,25(OH)2D, the hormonally active form of vitamin D, which binds to the vitamin D receptor (VDR) to modulate its actions through altering expression of target genes, is essential for calcium homeostasis and bone formation.