Hypercalciuria and renal function and in children affected by osteogenesis imperfecta

Background: Osteogenesis Imperfecta (OI) is an heterogeneous group of inherited disorders of connective tissue characterized by bone fragility, reduced bone mass, laxity of ligaments, blue sclera and different levels of low stature. Hypercalciuria is a condition characterized by an increased urinary calcium without hypercalcemia. It is characterized by an urinary calcium excretion >4mg/kg/die or urinary Ca/Cr ratio >0,21. The relation between hypercalciuria and OI had been already analyzed in several studies. Objective: The aim of this study is to observe the incidence of hypercalciuria among patients affected by OI and the possible correlation with the severity of the underneath condition. We also want to verify the presence of any kidney damage related with the increased urinary calcium or with the ongoing treatment with bisphosphonates. Methods: We have recruited 36 patients, followed at our clinic, treated with bisphosphonates. We collected, in a period of 3 months (T0-T1), auxological, clinical and laboratory parameters. All patients performed an abdominal ultrasound. Results: Through urinary Ca/Cr ratio we have identified 11 hypercalciuric patients in T0, 15 in T1. We didn’t found any alterations in kidney function both in biochemical and in imaging data. But estimating the urinary calcium in mg/kg/die in T1, we’ve also observed that hypercalciuric patients were only 6. Conclusion: We haven’t found correlation between hypercalciuria and severity of OI. Urinary Ca/Cr ratio is not specific enough to detect hypercalciuria in our patients, maybe because of low creatinine levels as a consequence of OI. It is important, in these children, to integrate Calcium and Vitamin D. Hypercalciuria and the treatment with bisphosphonates do not cause any significant kidney alteration. The next studies with DXA are going to make a better evaluation of the influence of hypercalciuria on bones of patients affected by OI.