XBP1 and liver failure: However, the reported IRE1-knockout phenotype is different from that of XBP1 knockouts in mice: whereas the developmental lethality of XBP1-knockout embryos has been attributed to liver failure (Lee et al., 2005), the lethality of IRE1α-knockout mice is attributed to a different organ – specifically, the placenta (Iwawaki et al., 2009).