Bone mass, bone markers and prevalence of fractures in adults with osteogenesis imperfecta

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.

To characterize bone mineral density, bone turnover, calcium metabolism and prevalence of fractures in a large cohort of adults with osteogenesis imperfecta.

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.

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.

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.