However, in approximately 90% of cases, OI is caused by defects in COL1A1 or COL1A2 alleles that encode for the Type I collagen alpha 1 and 2 chains, usually in the form of a glycine substitution that inhibits the chains from properly folding into a heterotrimer [4]. Here, COL1A2 is linked to osteogenesis imperfecta.