We identified significant upregulation of memory B cell marker CD27 expression on both unswitched (associated with modulation of CD19 and CD22 in SMM and both active MM stages and overexpression of IgD and IgM in MGUS) and switched memory B cells (along with mIg, such as IgM, IgG, and IgA in the MM cohort), supporting immunophenotypic changes in memory B cells of MM. Here, CD19 is linked to Miyoshi myopathy.