DEFECTIVE COLLAGEN FIBRIL FORMATION AND MINERALIZATION IN OSTEOGENESIS IMPERFECTA WITH CONGENITAL JOINT CONTRACTURES (BRUCK SYNDROME)

We describe a male patient with osteogenesis imperfecta (OI) who was b orn with contractures of the knee, elbow and ankle joints. During the first 4 years he suffered from recurrent fractures. He has white scler ae, mild dentinogenesis imperfecta, multiple wormian bones, severe sco liosis and short stature. Morphological analysis of cortical bone reve aled typical characteristics of OI including varying width of the oste oid, swollen mitochondria and a dilated endoplasmic reticulum of the o steoblasts. Collagen fibrils of the osteoid had a varying diameter, a feature not found in typical OI patients. Analysis of compact bone sho wed that the size of apatite crystals and the extractability of collag en with pepsin were markedly elevated compared to controls and other O I type III and IV patients. Lysyl hydroxylation of collagen from the o rganic bone matrix and the electrophoretic mobility of collagen alpha1 (I)- and alpha2(I)-chains were normal. Our results provide evidence th at this patient belongs to a subtype of OI. The biochemical studies in dicate that the underlying defect involves defective fibril-formation of collagen type I leading to an altered mineralization of bone.