By phenotypic dissection of myeloma B cell lymphopoiesis, we identified a significant increase in expression of CD34 and CD38 on early B cell progenies (hsc, pre-pro-B, and pro-B) and of CD19 on pre-B cells (both pre-BI and pre-BII) in both premalignant and active MM stages, whereas decreased CD10 (known as common acute lymphoblastic leukemia antigen, CALLA) expression was observed only on pre-BII cells of premalignant MM stages, indicating immunophenotypic aberrations already at the first step of B cell precursor differentiation. The gene discussed is MME; the disease is Miyoshi myopathy.