[Osteogenesis imperfecta: contribution to pathobiochemistry]

Osteogenesis imperfecta (OI) is a hereditary disease characterized by increased bone fragility and marked skeletal deformities. As a generalized connective tissue disorder, many patients present with other typical symptoms, such as blue sclerae, dentinogenesis imperfecta, impaired hearing, joint laxity, and easy bruising of the skin. According to clinical and genetic characteristics, Sillence classified four different groups. Metabolic alterations of connective tissue components are thought to be responsible for the pathogenesis of OI. Collagen, the main constituent of connective tissue, was analyzed in autoptic tissue and/or skin fibroblasts from patients with OI. In fibroblast culture of patients with OI group I, the range of synthesized collagen type III is elevated to 15-48% (normal up to 15%). Patients in groups II and III show an increased presence of hydroxylysine in alpha-chains of collagen types I and III. The hydroxylation of lysyl residues of the cartilage specific collagen type II is slightly elevated. In both groups, the hydroxypyroline content in all tested collagen types was normal. In our investigation, the collagen of patients with OI group IV appeared normal. Although the clinical features of patients with OI of all groups were not homogeneous, OI group III and some subtypes of group II had similar clinical courses and biochemical findings. In addition, there are patients with OI who present with clinical symptoms, but who cannot be classified into any of the known groups. For a better differentiation, biochemical examination of collagen should be performed complementary to clinical and genetic criteria.