HSPA5 and pachyonychia congenita: To determine the effect of TUDCA on ER stress, the expression of ER stress markers was assessed after TUDCA treatment, and the levels of GRP78, CHOP, and IREα were shown to be significantly reduced (p < 0.05; Figures 6A–6E) These findings suggested that AOPP-induced PC defects are associated with an increase in ER stress.