Decreased Ig secretion may also be due, at least in part, to disruptions of the UPR pathway, as illustrated by decreased expression of genes such as CANX. Mutations in genes involved in the UPR, particularly XBP1, have been documented in MM [19], with Xbp1s-deficient tumor cells acquiring resistance to proteasome inhibitors [67]. This evidence concerns the gene XBP1 and Miyoshi myopathy.