Abnormal mineral composition of osteogenesis imperfects bone as determinedby electron probe X-ray microanalysis on conventional and cryosections

Osteogenesis imperfecta (OI) is a genetic disorder of the connective tissue characterized by frequent bone fractures. The cause of bone fragility is s till unknown even though substantial work on collagen has been done. We mea sured the calcium to phosphorus ratio (Ca/P) of bone mineral from 35 OI bon e samples and 25 age- and site-matched control specimens, using electron pr obe X-ray microanalysis in the transmission electron microscope. Ultrathin cryosections and conventionally prepared resin sections were used. Cryo-ult ramicrotomy avoids any possible artifactual demineralization that may occur in conventional aqueous media. The Ca/P ratio obtained by these two method s was compared and there was no statistical difference between them. The re sults were differentiated according to the clinical types of OI for the fir st time. The Ca/P ratio of OI bone mineral was lower than normal in both re sin and cryosections, and mirrored the severity of the disease. OI type II had the lowest ratio (Ca/P = 1.49) compared with normal age- and site-match ed controls (Ca/P 1.69). This abnormal mineral composition in OI type II co uld be a contributory factor to bone fragility in OI bone.