OCs are bone resorbing cells whose activity and viability are upregulated in MM bone disease because of the presence, in the BM microenvironment, of several factors implicated in their differentiation and activation (RANKL, IL-3, IL-6, MIP-1α, MIP-1β, BAFF, DcR3, TNF-α, and Activin A). This evidence concerns the gene TNFSF11 and Miyoshi myopathy.