It has been suggested that in some OI cases the observed mutations may not lead to complete lack of COL1A2 and some misfolded protein might accumulate in the cell.(22) Mutations leading to haploinsufficiency are very rare in COL1A2. (27, 28) In COL1A1 and in COL2A1, coding for collagen II, mutations leading to reduced protein, rather than defected protein, typically result in milder phenotypes.(6, 29). The gene discussed is COL1A1; the disease is osteogenesis imperfecta.