Osteogenesis imperfecta (OI) is a remarkably heterogeneous monogenic disease characterized by bone fragility and low bone mass, more than 90% of which are caused by dominant mutations in encoding genes of type I procollagen chains proα1 (COL1A1, MIM 120150) or proα2 (COL1A2, MIM 120160) [1], [2]. The gene discussed is COL1A1; the disease is osteogenesis imperfecta.