UPR PERK and BiP were reduced in osteoblasts with Gly352Ser from type III and IV OI patients and in osteoblasts with Gly589Ser from a type III OI patient, while both proteins were increased in Gly589Ser osteoblasts from the type IV patient. The gene discussed is EIF2AK3; the disease is osteogenesis imperfecta type 3.