Composition, cross-linking and thermal stability of bone and skin collagens in patients with osteogenesis imperfecta.

The composition, cross-linking, and thermal stability of the collagens were determined in bone and skin biopsies from 4 patients with moderate to severe forms of osteogenesis imperfecta (OI). The major modification observed with respect to control subjects was an overhydroxylation of lysine in type I bone collagen (hydroxylysine content doubled in three patients and increased by 50% in the last patient). This overhydroxylation is confirmed by a similar increase in the dihydroxylated cross-link of bone collagen: the dehydrodihydroxylysinonorleucine. The type II collagen from cartilage and the pepsin-soluble collagens from the skin of these patients contained the normal amount of hydroxylysine. A small amount of type III collagen has been found in three patients, while only in one patient a slight increase in the type III/type I collagen ratio was observed in skin. In all patients the thermal stability of the collagen triple helix, measured by differential scanning calorimetry, was normal in both bone and skin. Although in at least three patients the clinical features allowed us to classify our patients into two different groups (Sillence et al., 1979 classification--groups I and III), the biochemical results are similar, suggesting that the overhydroxylation of the lysine in type I bone collagen is a common feature of severe forms of osteogenesis imperfecta.