CD9 and Miyoshi myopathy: In this study, we checked (1) the CD9 expression and their methylation control mechanism in MM cell lines and primary cases, (2) whether CD9 expression has a special relationship with bortezomib sensitivity in MM and (3) whether a combination of low dose de-methylation reagent 5-Aza-2-deoxycytidine (5-Aza) and bortezomib can overcome bortezomib resistance in MM.