For studies of phenotypic variability in OI based on different substitutions at the same collagen glycine residue, a new conditional OI mouse model (Col1a1 Gly349Ser, p.Gly527Ser, henceforth “Brtl Ser”) was generated based on our previously established Brtl Cys (Gly349Cys) mouse [10]. The gene discussed is COL1A1; the disease is osteogenesis imperfecta.