Upregulation of BiP and ER stress/UPR–related factors is also observed in several other types of muscle diseases (reviewed in ref. 29), including limb-girdle muscular dystrophy caused by mutations in FKRP (30, 31) and caveolin 3 (32), sporadic inclusion body myositis caused by mutations in GNE (33), and tibial muscular dystrophy caused by mutations encoding Titin (34). Here, TTN is linked to inclusion body myositis.