The C-X-C chemokine ligand 12 (CXCL12; also known as stromal-derived factor-1 [SDF-1]), abundantly produced by BMSCs [29,30,31,32], is the ligand for the C-X-C chemokine receptor 4 (CXCR4), which is expressed universally on MM PCs from MM patients [33,34,35]. Here, CXCL12 is linked to Miyoshi myopathy.