NOTCH1 and B-cell chronic lymphocytic leukemia: However, TP53 gene mutations and 17p deletion are twice as rare in the CLL#99 subgroup compared to CLL#1 (14% vs. 26% and 11% vs. 26%), while NOTCH1 and SF3B1 gene mutations are almost twice as common (36% vs. 19% and 14% vs. 8%).