ULTRASTRUCTURAL STUDIES OF BONES FROM PATIENTS WITH OSTEOGENESIS IMPERFECTA

Bone samples from patients suffering from osteogenesis imperfecta (OI) types I, II, III and IV, as well as normal controls, were studied by scanning (SEM) and transmission electron microscopy (TEM). SEM views o f normal bone at low magnification show coherent structure, with regul ar striations due to a lamellar plywood-like arrangement of the minera lized collagen fibrils. Compact lamellar bone was also found in variou s OI specimens, but in limited disconnected regions separated by open spaces. Furthermore, some OI, but not normal, bones have regions of lo ose unconnected fibers and others of apparently abnormally dense miner al deposition. High resolution TEM studies of OI bone fragments have s erved to elucidate the structures of these different textures. There a ppears to be a substantial, though reduced, proportion of normal lamel lar bone even in quite severe OI. However, the regions of loose fibers are largely unmineralized and probably contain abnormal collagen. Oth er regions are overmineralized, with generally small unorganized apati te crystals deposited onto fibril surfaces or in separate clusters. Th ese structural abnormalities, together with the paucity of normal bone , may explain the fragility of OI bones.