COL1A1 and osteogenesis imperfecta: Osteogenesis imperfecta (OI) is a phenotypically and genetically heterogeneous group of bone disorders characterized by bone fragility and skeletal deformity, owing to the abnormality of type I collagen formed by two α1(I) chains (encoded by COL1A1 gene) and one α2(I) chain (encoded by COL1A2 gene).