In addition to the widely studied MM-related antigens CD38 (9–11) and signaling lymphocyte activation molecule F7 (SLAMF7) (12–14), against which three mAbs have already received FDA approval for clinical use (10, 14), and the B-cell maturation antigen (BCMA) (15, 16), there is growing evidence for the key role of Syndecan1 (CD138 or SDC1), a transmembrane heparan sulfate proteoglycan (HPSG), in MM tumorigenesis (17–19). This evidence concerns the gene SDC1 and Miyoshi myopathy.