Effect of High-Dose Vitamin D on Bone Density in Osteogenesis Imperfecta

* Overall Objective: To test the hypothesis that oral vitamin D supplementation at higher than currently prescribed doses has a beneficial effect on the skeleton of young patients with osteogenesis imperfecta (OI). * Specific Aims: 1. To determine whether 12 months of high-dose vitamin D supplementation, compared to standard-dose vitamin D supplementation, increases areal bone mineral density z-scores at the lumbar spine. 2. To examine the effectiveness of high-dose vitamin D supplementation to increase trabecular and cortical bone mineral density at the radius. 3. To examine whether high-dose vitamin D supplementation has an effect on physiological determinants of bone mass (parathyroid hormone, activity of bone metabolism, muscle function). * Background: In a preliminary cross-sectional study of 282 OI patients we observed an inverse relationship between serum 25-hydroxyvitamin D and parathyroid hormone levels and a positive relationship between circulating levels of 25-hydroxyvitamin D and lumbar spine areal bone mineral density z-scores. This suggested that high-dose vitamin D supplementation would have a beneficial effect on bone density. Most OI patients currently receive oral vitamin D supplementation of 400 International Units per day, but doses of 2000 International Units per day are safe and have been shown to be beneficial in studies on healthy adolescents. * Study Design: This is a parallel-group double-blind randomized controlled trial of 12 months duration on 60 children and adolescents aged 6 to 19 years with a clinical diagnosis of OI. One group of 30 participants will be randomized to receive vitamin D3 at a dose of 2000 international units per day ('high-dose group'). The other group of 30 participants will be randomized to receive vitamin D3 at a dose of 400 international units per day ('standard-dose group'). Randomization will be stratified according to pubertal status and bisphosphonate treatment status. * Clinical Relevance: The proposed study