XBP1s mRNA encodes a potent transcription factor that enhances the expression of specific UPR target genes, such as the chaperone ERdJ4 mRNA, which was in fact significantly increased in IUGR rats (2.35 ± 1.43 vs 1 ± 0.7; p<0.05). The gene discussed is DNAJB9; the disease is fetal growth restriction.