SDC1 and Miyoshi myopathy: Furthermore, MM cells are highly decorated with the cell surface marker heparan sulfate proteoglycan (HSPG) syndecan-1 (CD138) which facilitates communication with the cells of the niche by providing docking sites for bioactive molecules, such as secreted cytokines, chemokines and growth factors, promoting both signal transduction and adhesion [13, 14].