Additional evidence of UPR activity in patients with RA comes from a study by Clavarino G. et al. In this study, increased expression of GADD34, which is involved in the PERK-eIF2a-ATF4 signal transduction pathway, was observed and, in this case, the tested material was PBMCs [17]. The gene discussed is PPP1R15A; the disease is rheumatoid arthritis.