COL1A1 and osteogenesis imperfecta: In 90% of cases, OI results from mutations in COL1A1 or COL1A2, the genes encoding the α1 and α2 chains of collagen type I. In other cases, mutations typically affect genes involved in the post-translational modification of collagen type I. The clinical spectrum of OI varies widely, ranging from mild phenotypes to severe forms that may result in perinatal or neonatal lethality [12,13,14,15].