MGUS is a CD19−, CD45− and CD56+ plasma cell disorder associated with an asymptomatic monoclonal paraproteinaemia and has a 1% average annual progression rate to multiple myeloma (MM).1–3 MGUS, like smoldering multiple myeloma (SMM) and MM, is a neoplastic disease that retains many of the phenotypic properties of healthy CD138+, CD19+, CD45+, CD56− plasma cells. The gene discussed is PTPRC; the disease is plasma cell neoplasm.