Ultrastructural study on the stapes and skin in a case of type I Osteogenesis Imperfecta.

The results of the ultrastructural study carried out on the stapes and skin from a patient affected by type I Osteogenesis Imperfecta showed the presence of structural alterations of collagenic component. In the stapes the size, the stability and the tridimensional organization of collagen fibrils were affected. In the skin, a reduction of polymeric collagen was observed, chiefly in reticular dermis. The quantitative analysis of the size of collagen fibrils showed that only the collagen fibrils of papillary dermis were significantly thinner than normal. The electron microscope study of the periodic structure of collagen fibrils isolated from the dermis and submitted to negative or positive contrast or to glutaraldehyde fixation, before being negatively stained, showed no significative differences with the controls. These results agree with previous biochemical studies and indicate that both the stability and the processes of growth regulation of collagen fibers and fibrils are affected in this form of the disease, whereas the molecular assembly within the fibrils is normal.