However, complete absence of the proα2(I) chain encoded by COL1A2 may cause variable clinical manifestations, including an osteogenesis imperfecta-EDS overlap syndrome associated with the production of a stable mutant proα2(I) chain that is degraded but may trigger an unfolded protein response (UPR) [7]. The gene discussed is COL1A2; the disease is osteogenesis imperfecta.