IFITM5 and osteogenesis imperfecta: ,4 Genetic analyses have identified more than 20 OI causative genes involved in type I collagen synthesis (COL1A1 and COL1A2), posttranslational modification and processing (CRTAP, P3H1, and PPIB), bone mineralization (IFITM5), and osteoblast differentiation (SP7, CREB3L1, and WNT1).4–7