RNA sequencing (RNA-seq) of MGUS and MM cells from MIcγ1-derived and BIcγ1-derived mice defined a common transcriptional signature with respect to normal BM PCs, including the upregulation of PC genes (that is, Prdm1, Irf4, Xbp1, Sdc1 encoding Cd138, Tnfrsf17 encoding Bcma, Tnfrsf13b encoding Taci and Slamf7) and the downregulation of B cell genes (that is, Pax5 and Cd19; Fig. 2a and Supplementary Table 2). The gene discussed is XBP1; the disease is Miyoshi myopathy.