Different mechanisms of intestinal calcium absorption at different life stages: therapeutic implications and long-term responses to treatment in patients with hereditary vitamin D-resistant rickets.

BACKGROUND: Intestinal calcium absorption is regulated principally by 1,25-dihydroxyvitamin D, but other regulators are also involved. CASE REPORT: The 3 children studied were born with unaffected bones. Two were referred at 21 months of age, with clinical features of severe vitamin D-resistant rickets. They were treated with intravenous calcium for 12-18 months, following an initial lack of response to oral calcium and vitamin D. The third patient, who was exclusively breast-fed, was diagnosed at 4 months of age, due to alopecia. His condition was successfully managed with high doses of oral calcium and vitamin D. All 3 patients were homozygous for a mutation in the DNA-binding domain of vitamin D receptor. At the most recent evaluation of these patients, currently maintained on oral calcium and vitamin D, clinical findings were normal.
CONCLUSION: During gestation, calcium flux across the placenta is normal, preventing bone diseases in affected fetuses. High calcium intake early in life and, perhaps, the maintenance of breastfeeding for several months may constitute an effective approach to ensuring adequate absorption and preventing severe rickets. During childhood, after parenteral calcium treatment to bypass intestinal calcium absorption, it is possible to maintain normal bone through long-term oral calcium supplementation.