Vitamin D-dependent Hypercalcemia.

Vitamin D metabolism represents a well-integrated, hormonally regulated endocrine unit interlinking calcium and phosphate metabolism. Pathophysiologic processes disturbing vitamin D metabolism comprise classic defects of vitamin D activation and action presenting as different forms of vitamin D-dependent rickets as well as disorders with increased vitamin D activity. The latter may result in hypercalcemia, hypercalciuria, and renal calcifications. Acquired and hereditary disorders causing hypervitaminosis D are discussed, including vitamin D intoxication, granulomatous disease, and idiopathic infantile hypercalcemia that may be caused by either a defective vitamin D degradation or by a primary defect in phosphate conservation.