Overexpression of MAF in MM that is not attributable to a translocation can be driven by TNFRSF13B (also known as TACI) and/or XBP1, as high expression of TNFRSF13B is associated with high expression of MAF and lymphoid-specific XBP1 transgenic mice show deregulated c-MAF and MAFB expression [270,271]. The gene discussed is XBP1; the disease is Miyoshi myopathy.