Wilm’s Tumour 1 (WT1) Mutations Are Associated with FLT3-ITD Mutation and Poor Prognosis in Normal Karyotype AML.

Our group has previously shown an association between acquired uniparental disomy 11p and homozygous gene mutation of Wilm’s tumour 1 (WT1) in a patient with normal karyotype acute myeloid leukemia (AML). Based on this observation the incidence of WT1 mutation was investigated in a cohort of normal karyotype AMLs. Mutation screening was performed on 70 patients (median age 55 years, range 19–78 years) by a PCR-direct sequencing approach using intronic primers flanking exons 2–10 of WT1. Mutation status was inferred from the resultant traces and confirmed by use of TOPO TA cloning and sequence analysis of the corresponding mutated clones. Mutations were detected in 7/70 (10%) patients; these typically resulted in insertion of 1–16 bp that led to the disruption of the DNA binding domain of the protein. The mutation profile of FLT3-ITD, NPM and CEBPA was also examined in this cohort of patients to compare the additional mutational events present in WT1 mutated and non-mutated cases. A significant positive association was observed between WT1 and FLT3-ITD mutation with 6/7 WT1 mutated cases having a FLT3-ITD compared to 20/63 non mutated cases (p=0.01). There was no association between mutations in WT1 and either of the good prognostic mutational markers, CEBPA and NPM. All 6 patients with both WT1 and FLT3 mutations were refractory to intensive induction chemotherapy with WT1 mutation showing a trend towards a worse overall survival when compared with the non-mutated group (p=0.07). We can conclude therefore that WT1 is mutated in 10% of normal karyotype AML, is positively associated with FLT3-ITD status and identifies a putative subgroup of normal karyotype AML who fail to achieve remission with conventional cytotoxic therapy and have a poor overall survival. Validation of this data in larger series would support the inclusion of WT1 in the current molecular risk stratification of normal karyotype AML based on CEBPA, NPM and FLT3-ITD status.