Two pathogenic variants in the <i>IFITM5</i> gene cause distinct forms of OI: The recurrent c.-14C>T variant causes OI type V (MIM #610967), characterized by hyperplastic callus formation and interosseous membrane ossification, while the rare c.119C>T (p.Ser40Leu) variant causes a phenotypically distinct, severe form of <i>IFITM5</i>-related OI without these hallmark features. The gene discussed is IFITM5; the disease is osteogenesis imperfecta.