At the molecular level, OI type V patients lack detectable mutations in the COL1A1 and COL1A2 genes that are found in more than 90% of cases of OI types I through IV or in recessive OI genes.6 In 2012, it was reported that a mutation in the 5′ untranslated region (5′UTR) of the IFITM5 gene (IFITM5 c.–14C > T) can cause OI type V.7,8 Interferon-inducible transmembrane protein 5 (IFITM5), otherwise known as bone restricted ifitm-like protein (BRIL), is a two-transmembrane domain membrane protein that presents its termini extracellularly. Here, IFITM5 is linked to osteogenesis imperfecta.