Pathogenesis of Vitamin D-Resistant Rickets and the Response to a High Calcium Intake

Four patients with vitamin D-resistant rickets underwent simultaneous calcium47 kinetic and calcium, phosphorus and nitrogen balance studies before and after the institution of a high calcium intake. The renal tubular transport of phosphorus was evaluated by the response to a 9-hr calcium infusion. Bone formation and resorption were 2–5 times normal in all patients. Oral calcium supplements produced a 20–30% reduction in bone resorption, but little initial change in bone formation. Long-term supplements in all patients produced a gradual and parallel fall of the skeletal turnover and serum alkaline phosphatase. The intestinal absorption of calcium was subnormal in the presence of probable secondary hyperparathyroidism. No defect in the renal tubular transport of phosphorus could be demonstrated with calcium infusion.