IRF4 and Miyoshi myopathy: Pathological dysregulation of c-Myc and IRF4 are a common feature of MM cells compared with normal plasma cells.6, 7, 8, 9 The proposed c-Myc-IRF4-positive autoregulatory loop is only transiently active during the expansion phase after normal B-cell activation.10, 11, 12, 13, 14 Subsequently, c-Myc becomes downregulated to allow for differentiation to the plasma cell stage.