Impaired osteoblasts differentiation is a common features of OI types XII, XIV, XV, XVI, XVII, XVIII, caused by recessive mutations in SP7, TMEM38B, WNT1, CREB3L1, SPARC and MBTPS2. WNT1 also causes less severe dominantly inherited bone fragility. The gene discussed is SP7; the disease is osteogenesis imperfecta.