COL1A1 and osteogenesis imperfecta: While pathogenic variants in multiple genes can cause various subtypes of OI, more than 90% of OI is caused by pathogenic variants in COL1A1 or COL2A1 and in genes encoding proteins that posttranslationally modify type I collagen (CRTAP, PPIB, and LEPRE1; refs. 3, 24).