COL1A1 and osteogenesis imperfecta: COL1A1 and COL1A2 mutations account for about 85–90% of cases of OI; despite this, many other genes involved in collagen biosynthesis, bone mineralization, and osteoblast differentiation have been identified as causative of both OI and hereditary early-onset osteoporosis, thus expanding the molecular mechanisms of bone fragility [7,8,9].