Hypophosphatemic Rickets: Effect of 1α, 25-Dihydroxyvitamin D3 on Growth and Mineral Metabolism

Abstract

Growth retardation nearly invariably accompanies hypophosphatemic rickets. Studies were conducted in an adolescent male with this disorder as follows. Protocol I: age, 6 to 16 years; treatment per day, 5,000 to 80,000 units vitamin D2, 1,760 to 2,200 mg phosphorus, orally as buffered phosphate; growth velocity, 5 to 6 cm/year. Protocol II: age 16 to 17 years; treatment per day, 1α,25-dihydroxyvitaniin D3, 1 µg; 2,200 mg of phosphorus, orally as buffered phosphate; growth velocity, 14 cm/year. The height improved from less than third percentile for the decade during study protocol I to the 25th percentile during protocol II. Mineral balance studies showed a reduction of urinary and stool phosphorus during treatment protocol II, while the patient was receiving metabolic diet. The serum phosphorus improved from 2.2 to 4.3 mg/dl and radiologic healing of rickets was documented. No hypercalcemic episode was encountered. The data support the contention that lα,25-dihydroxyvitamin D3 is the treatment of choice for hypophosphatemic rickets.