COL1A1 and osteogenesis imperfecta: In our study cohort of Taiwanese OI patients, COL1A1 mutations occurred 3.1 times (28:9) more frequently than COL1A2 mutations, and the replacement of glycine residues by other residues within the Gly-X-Y triplet domain of the triple helix in both COL1A1 and COL1A2 was common.