For all genes investigated, except for MYD88, there was a striking enrichment of mutations in U-CLL compared to M-CLL, particularly for NOTCH1, XPO1, NFKBIE and EGR2. Nevertheless, for all genes investigated, mutations were also detected in a minor proportion of M-CLL patients (1–6% of cases). This evidence concerns the gene MYD88 and B-cell chronic lymphocytic leukemia.