Autosomal Recessive Osteogenesis Imperfecta: A Puzzle for Bone Formation, Structure and Function

Bone is a composite material that resembles reinforced concrete. The collagen matrix plays the role of reinforcement, whereas hydroxyapatite crystals are cementing material. Collagen fibers are responsible for the tensile strength of bones and prevent fractures from extending; the mineral phase is able to withstand compaction loads. A right balance of these two parts synergistically provides the required stiffness for bone. Collagen abnormalities, such as reduced amount, disturbed composition, defects in structure and/or supramolecular organization as well as insufficient or defective mineralization, lead to osteogenesis imperfecta (OI), also known as brittle bone disease. Until recently, mutations in the type I collagen genes COL1A1 and COL1A2 were the only known causes of the disease, which cover about 90 % of diagnosed OI. Within the last decade, we have witnessed a burst in the identification of new OI mutations in other genes. Here we summarize our knowledge of these mutations and their impact on bone quality.