IGLL5 and B-cell chronic lymphocytic leukemia: Furthermore, TP53 was the gene that was found to undergo mutations most frequently in patients with IGH-t CLL, a finding that was not consistent with that of the largest IGH-t CLL study conducted by Pérez-Carretero et al., which indicated that the most frequently mutated genes were NOTCH1 and IGLL5 (25).