MODEL RELEASED. Brittle bone disease. Eighteen year-old girl with osteogenesis imperfecta (OI), studying at home. OI is a brittle bone disorder, caused by an inherited abnormality of the gene for collagen, a vital protein found in bones. Sufferers either have too little, or have poor quality collagen. Consequently the skeleton is fragile and is prone to multiple broken and fractured bones. There is no treatment for OI. Instead, prevention and control of symptoms is accomplished by minimising the risk of fractures. Wheelchairs or mobility aids (right) are often required by people with severe types of OI.