COL1A1 and osteogenesis imperfecta: Current evidences demonstrate that COL1A1 and COL1A2 are the main factors in the cause of OI, as approximately 85% to 90% of cases are disturbed by them, and all of the four subtypes are involved in COL1A1 and COL1A2 genes (http://www.le.ac.uk/ge/collagen/).