Pathogenesis of rickets in chronic hepatobiliary disease in children.

To investigate whether hepatobiliary rickets is caused by defective intestinal absorption of vitamin D or by impaired hepatic hydroxylation of the vitamin, we studied three children who developed severe rickets, hypocalcemia, and hypophosphatemia, two despite having received 400 to 800 IU vitamin D per day by mouth, and one despite prolonged treatment with 10,000 IU daily. On oral vitamin D therapy, plasma vitamin D and 25-hydroxyvitamin D levels were low. When two children were treated with weekly intravenous doses of 3,000 IU vitamin D to approximate the recommended prophylactic allowance, their plasma calcium and phosphate values improved promptly, the radiographic lesions healed, and the plasma concentrations of vitamin D and 25-hydroxyvitamin D became normal. Our studies indicate that the primary cause of hepatobiliary rickets is intestinal malabsorption of vitamin D, not impairment of the hepatic metabolism of the vitamin.