Serum 24,25-Dihydroxyvitamin D Concentrations in Osteogenesis Imperfecta: Relationship to Bone Parameters

Background: Several studies suggest that 24,25-dihydroxyvitamin D [24,25(OH)(2)D] may have an effect on bone mass and metabolism. Objective: We evaluated the relationship between serum 24,25(OH)(2)D levels and bone density and bone metabolism in children with a primary bone disorder-osteogenesis imperfecta (OI). Materials and Methods: The study included 132 patients (age, 1.1 to 17.9 yr; 67 girls) with OI types I, III, or IV who had not received bisphosphonate treatment at the time of analysis. Results: Serum 24,25(OH)(2)D levels were significantly higher in OI type III than in OI type I or IV. Serum 24,25(OH)(2)D concentrations were positively correlated with serum 25-hydroxyvitamin D (25OHD) levels and negatively correlated with serum PTH levels, and were not correlated with serum 1 alpha,25-dihydroxyvitamin D [1,25(OH)(2)D]. The ratio between serum 24,25(OH)(2)D and 25OHD was negatively correlated with age and was independent of serum 25OHD concentrations. Regression analysis revealed that OI severity (P = 0.04), serum 25OHD levels (P < 0.001), and serum PTH concentrations (P = 0.045), but not age, gender, or serum 1,25(OH)(2)D, were independent predictors of serum 24,25(OH)(2)D levels. No correlation was found between serum 24,25(OH)(2)D levels or the ratio between serum 24,25(OH)(2)D and 25OHD and lumbar spine bone mineral density z-scores or bone marker levels (serum osteocalcin and urinary collagen type I N-telopeptide) after adjusting for OI type, age, and gender. Conclusion: Patients with more severe OI type had higher 24,25(OH)(2)D serum levels and higher serum 24,25(OH)(2)D to 25OHD ratios, suggesting an increased 25OHD-24-hydroxylase activity. (J Clin Endocrinol Metab 97: 1243-1249, 2012)