In addition, we found that the UPR-PERK pathway (one of the three UPR-sensing pathways) was activated in TCL cells of CTS patients, as indicated by upregulation of transcriptional factor ATF4 and its downstream target CHOP, an ER stress-induced apoptosis gene53,55 (Fig. 4d). The gene discussed is ATF4; the disease is carpal tunnel syndrome 1.