Osteogenesis imperfecta (OI), also known as brittle bone disease, is a genetically and phenotypically heterogeneous collection of rare genetic disorders. It is characterized by increased bone fragility, which results in frequent fractures, especially during childhood. Most cases are caused by mutations in either COL1A1 or COL1A2, the genes encoding the alpha-chains of type I collagen, the main organic part of bone. However, in recent years, new mutations in more than twenty collagen-related genes have been found to cause OI. Despite the different causes, hypermineralization is a common feature of the great majority of OI cases. Current treatments, such as bisphosphonates, often fail in preventing bone fractures.