Hypercalciuric Rickets: Metabolic Studies and Pathophysiological Considerations

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Abstract
Extensive metabolic studies were performed in a 14 yr old boy suffering from childhood idiopathic hypercalciuria associated with dwarfism, renal tubular abnormalities and bone lesions. The salient features were the following: hyperphosphaturia with hypophosphatemia, hypercalciuria with normocalcemia, elevated serum 1,25-dihydroxycholecalciferol [1,25(OH)2D3] levels, marked intestinal hyperabsorption of Ca and P, with low serum parathyroid hormone (PTH) and urinary cAMP. Bone biopsy confirmed the clinical and radiological diagnosis of rickets. It appears that the following pathophysiological sequence is operating: primary renal phosphate leak with hypophosphatemia, increased 1,25(OH)2D3 synthesis, enhanced intestinal Ca absorption which in turn inhibits release of PTH and cAMP. Hypercalciuria is seen to be secondary to both avid intestinal Ca absorption and depressed PTH activity, and rickets the result of phosphate depletion. Treatment with oral P only resulted in an acceleration of growth rate, cure of rickets and return of urinary Ca excretion to normal values.