A morphometric analysis of osteoid collagen fibril diameter in osteogenesis imperfecta

Osteogenesis imperfecta is a genetic disorder of connective tissue characterised by frequent bone fracture following minimal trauma. Mutations of type I procollagen genes have been widely reported as the cause of OI and such mutations have been shown to introduce kinks into the collagen molecule. A study was performed to examine type I collagen fibrils at the ultrastructural level in the transmission electron microscope (TEM). Type I collagen fibrils from the bone osteoid of OI patients and age- and site-matched normal control bone were photographed in the electron microscope. A histomorphometric analysis of the diameters of collagen fibrils photographed in the TEM indicated that type I collagen in OI bone was larger in diameter compared with normal bone. This increase in diameter of type I collagen fibrils may represent an alteration in the quaternary structure of the collagen fibril as a consequence of kinked, poorly packed collagen molecules. Such alteration in the collagen fibrils may affect the formation and stability of bone mineral associated with it.