IFITM5 and osteogenesis imperfecta: Type V of OI is unique among all types of osteogenesis imperfecta: most patients (approximately 95%) with type V have the same heterozygous mutation in IFITM5, a point mutation in 5′-UTR (c.-14C>T), which generates a new starting codon and adds five residues to the N–terminal end of the protein.