Gene expression analysis showed that SP cells from five MM cell lines (RPMI 8226, AMO1, KMS-12-BM, KMS-11, JJN3) express genes involved in the cell cycle and mitosis (e.g., CCNB1, CDC25C, CDC2, BIRC5, CENPE, SKA1, AURKB, KIFs, TOP2A, ASPM), polycomb (e.g., EZH2, EPC1) and ubiquitin-proteasome (e.g., UBE2D3, UBE3C, PSMA5) more strongly than do non-SP cells. Here, SKA1 is linked to Miyoshi myopathy.