The present study examined the mRNA expression of nine genes with a possible influence on bortezomib sensitivity and refractoriness in MM, viz., ABCB1, CXCR4, MAF, MARCKS, POMP, PSMB5, RPL5, TXN, and XBP1. Of these, RPL5 was down-regulated in MM patients as compared with the normal individuals. This evidence concerns the gene MAF and Miyoshi myopathy.