CBLIF and complement factor I deficiency: Mutations in the cubilin (CUBN, OMIM # 602997) [3] and amnionless (AMN, OMIM # 605799) genes [4] account for most cases of IGS, whereas mutations in the gastric intrinsic factor gene (GIF, OMIM # 609342), which cause intrinsic factor deficiency (IFD), phenocopy genuine IGS [5].