Defective collagen fibril formation and mineralization in osteogenesis imperfecta with congenital joint contractures (Bruck syndrome)

Abstract

We describe a male patient with osteogenesis imperfecta (OI) who was born with contractures of the knee, elbow and ankle joints. During the first 4 years he suffered from recurrent fractures. He has white sclerae, mild dentinogenesis imperfecta, multiple wormian bones, severe scoliosis and short stature. Morphological analysis of cortical bone revealed typical characteristics of OI including varying width of the osteoid, swollen mitochondria and a dilated endoplasmic reticulum of the osteoblasts. Collagen fibrils of the osteoid had a varying diameter, a feature not found in typical OI patients. Analysis of compact bone showed that the size of apatite crystals and the extractability of collagen with pepsin were markedly elevated compared to controls and other OI type III and IV patients. Lysyl hydroxylation of collagen from the organic bone matrix and the electrophoretic mobility of collagen alpha 1(I)- and alpha 2(I)-chains were normal. Our results provide evidence that this patient belongs to a subtype of OI. The biochemical studies indicate that the underlying defect involves defective fibril-formation of collagen type I leading to an altered mineralization of bone.