Effect of growth hormone treatment on calcium kinetics in patients with osteogenesis Imperfecta Type III and IV

Using a dual stable isotope technique, the effect of growth hormone (GH) on whole body calcium (Ca) metabolism was studied in children (ages 5–14 years) with type III (n = 9) and IV (n = 8) osteogenesis imperfecta. Each subject was studied twice: at baseline and following a GH (0.1–0.2 U/kg per day) treatment period of 1–1.5 years. Subjects were given 42Ca intravenously and 44Ca orally. The sera and urine 42Ca and 44Ca isotopic enrichments were followed over 7 days using thermal ionization mass spectrometry. The S program was used to fit a three-compartment model to the tracer data. No significant differences were observed between: (1) children with type III and IV disease; or (2) baseline studies of boys and girls within each disease type. However, GH treatment significantly increased: (1) the exchangeable calcium pool (EP) in type III patients (2086 vs. 4422 mg/day, p = 0.02); and (2) the parameter associated with bone calcium accretion in type IV patients (Vo+: 973 vs. 1560 mg/day, p = 0.03) with boys responding with a significantly greater increase than girls (p = 0.008). Although not statistically significant, a trend toward an increase in Vo+ in type III patients and in EP in type IV was observed following treatment. Our observations imply that more Ca was available for bone mineralization following GH treatment in these subjects.