Calcium and Phosphorus Metabolism in the Fanconi Syndrome

Calcium and phosphorus balance studies were performed in a child with hypophosphatemic rickets secondary to the Fanconi syndrome. Evidence was obtained of a normal capacity for intestinal absorption of calcium and phosphorus. The data indicated that an increased renal clearance of phosphate with resultant hypophosphatemia was the major determinant in the failure of normal bone formation. This tubular abnormality was corrected by administration of large amounts of vitamin D, but was not influenced by acute hypercalcemia, pointing to a primary tubular defect in reabsorption of phosphorus. Renal excretion of calcium was unrelated to intestinal calcium absorption and was increased despite the presence of alkalosis. The close correlation found between rates of urinary excretion of calcium and sodium suggested a mechanism for the variation in calcium excretion reported in this syndrome.