COL1A2 and osteogenesis imperfecta type 4: As shown in Figure 4, OI type III (β = 1.542, p = 0.018), OI type IV (β = 1.155, p = 0.014), and COL1A2 mutation (β = 1.091, p = 0.020) were positively correlated with a longer duration of BP treatment before patients entered drug holiday.