SDC1 and Miyoshi myopathy: Hh activity is concentrated in CD138−/CD19+ MM CSCs but not in CD138+/CD19- MM PCs, demonstrating that stromal-derived Hh ligands promote MM CSC proliferation without differentiation (161).In CD138+ plasma cells and MM CSCs, overexpression of the retinoic acid receptor alpha 2 (RAR2), results in abnormal Wnt and Hh pathway activation and increased cell self-renewal, proliferation, migration, and drug resistance (160, 162).