From previous studies, ER stress and subsequent UPR are recognized as the main mechanisms of BTZ-induced apoptosis.15, 16, 17 In addition, several studies18, 19 have reported associations of expression levels of genes in the IRE1-XBP1 pathway with BTZ sensitivity, based on the analysis of patients with MM receiving BTZ-containing therapy, and have suggested that low expression of XBP1 in primary MM cells is associated with a poor response to BTZ-containing therapy or poor prognosis. The gene discussed is ERN1; the disease is Miyoshi myopathy.