MODEL RELEASED. Brittle bone disease. Image 1 of 2. Patient with severe osteogenesis imperfecta (OI). OI is a brittle bone disorder, caused by a dominant genetic mutation 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 prone to multiple broken and fractured bones. In severe cases of OI, as here, the patient has a barrel-chest, spinal curvature, severe bone deformities, loose joints, and poor muscle development in the limbs. There is no treatment for OI. See M230/346 for a view of the same patient in profile.