The variant allele fraction (VAF) of DNMT3A mutations in patients with T-ALL was consistently ∼50% (Figure 1A), suggestive of heterozygous mutations found in all the tumor cells, presenting DNMT3A mutation as a founding event in T-ALL as in AML23 and myelodysplastic syndromes.19 This evidence concerns the gene DNMT3A and acute lymphoblastic leukemia.