Still little is known about the manifestations of osteogenesis imperfecta (OI) in adults. We therefore initiated this study of bone mass, bone turnover and prevalence of fractures in a large cohort of adult patients. We found a surprising low prevalence (10%) of osteoporosis. These patients, however, expressed the most severe disease.
Purpose: To characterize bone mineral density, bone turnover, calcium metabolism and prevalence of fractures in a large cohort of adults with osteogenesis imperfecta.
Methods: One hundred fifty-four patients with adult OI participated and 90 (age range 25-83) provided dual X-ray absorptiometry (DXA) measurements. According to Sillence classification criteria, 68 persons were classified as OI type I, 9 as type III, 11 type IV and 2 were unclassified. Fracture numbers were based on self-reporting. Biochemical markers of bone turnover were measured and bone mineral density (BMD) of the spine, femoral neck and total body were determined by DXA.
Results: Only 10% of adults with OI exhibited osteoporotic T scores (T ≤ -2.5) but compared to patients with normal T scores this subgroup had a threefold higher fracture risk (22 vs. 69). s-PTH, s-Ca and 25[OH] vitamin D were all normal. Bone markers did not display major deviations from normal, but patients with OI type III displayed higher resorption marker levels than type I and IV. Multivariate regression analysis showed that only gender and total body BMD were significant determinants of fracture susceptibility, and the differences for total body BMC, BMD and Z scores were significant between the OI subtypes.
Conclusions: In adult OI, DXA measurements only identified few patients as osteoporotic. These patients, however, exhibited a much higher fracture propensity. Due to deformities, low body height and pre-existing fractures, DXA assessment is complicated in this disease, and further studies are needed to work out how to minimize the impact of these confounders.