Authors found decreased levels of HSPA5 (also known as BiP/GRP78) along with increased levels of ER stress marker eukaryotic translation initiation factor 2 alpha kinase 3 (EIF2AK3/PERK) in skeletal muscle tissue from ME/CFS patients compared with controls, which is consistent with ER stress response failure. Here, HSPA5 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.