The diagnosis of CLL was confirmed by demonstration of expression of mature B-cell markers (CD19, CD22, CD20 dim), the co-expression of CD5 and CD23 and the absence of immaturemarkers, such as CD34, Terminal deoxynucleotidyltransferase (TdT) and CD10. The gene discussed is DNTT; the disease is B-cell chronic lymphocytic leukemia.