COL1A2 and osteogenesis imperfecta type 3: Patients carrying COL1A1 mutation showed the mildest skeletal phenotypes, whereas those carrying COL1A2 or biallelic mutation had more severe phenotypes, including shorter height Z-score (− 0.8 vs. − 2.2, P < 0.001; − 0.8 vs. − 1.6, P = 0.004), more long bone deformity (41.9% vs. 60.4%, P = 0.001; 41.9% vs. 59.2%, P = 0.027) and ribcage deformity (7.0% vs. 17.1%, P = 0.004; 7.0% vs. 26.5%, P < 0.001), poorer mobility (31.3% vs. 45.9%, P = 0.008; 31.3% vs. 57.1%, P = 0.001) and higher OI type III frequency (13.2% vs. 24.3%, P = 0.010; 13.2% vs. 26.5%, P = 0.020) (Table 2, Fig. 3a).