Calcium Absorption, Kinetics, Bone Density, and Bone Structure in Patients with Hereditary Vitamin D-Resistant Rickets

Background: Hereditary 1,25-dihydroxyvitamin D-resistant rickets (HVDRR) is caused by mutations in the vitamin D receptor gene. Children with HVDRR suffer from severe hypocalcemia and rickets that are treatable with extremely high-dose calcium supplements. Surprisingly, spontaneous recovery of calcium metabolism occurs after the end of puberty without the need for further calcium supplementation. Objectives: To evaluate the role of vitamin D receptor in intestinal calcium absorption and bone, we investigated intestinal fractional calcium absorption (FCA), bone calcium accretion (Vo+), bone mineral density (BMD), and bone structure parameters in HVDRR patients from infancy into adulthood. Patients and Methods: Seventeen HVDRR patients aged 1.5–37 yr were investigated. FCA and Vo+ were determined by stable-calcium isotopes. BMD was determined by dual-energy x-ray absorptiometry and bone structure by high-resolution magnetic resonance imaging. Results: FCA in patients aged 1.5–17 yr was 34.9 ± 11.2% compared...