PPP1R15A and Hutchinson-Gilford progeria syndrome: A wide range of ER stress‐related genes, such as HSP90B1, HSPA5, CALR, and DNAJC3, and the bona fide UPR genes DDIT3, ATF4, EIF2AK3, ERN1, PPP1R15A, and the spliced form of XBP1 were upregulated in HGPS patient cells (Fig 2D).