LETTERS TO THE EDITOR Wilms’ tumour 1 mutations are associated with FLT3-ITD and failure of standard induction chemotherapy in patients with normal karyotype AML Leukemia (2007) 21, 550–551. doi:10.1038/sj.leu.2404514; published online 4 January 2007 Wilms’ tumour 1 gene (WT1) is highly expressed in various types of leukaemia which has advanced its position both as a target for immunotherapy and as a means of monitoring minimal residual disease (MRD). The precise role of WT1 in haematopoi- esis and its contribution to leukemogenesis are open to speculation. 1 One hypothesis is that wild-type WT1 may act both as an enhancer of cellular quiescence in haematopoietic stem cells and later as an inducer of cellular differentiation in committed precursors. 2 Hence, abrogation of WT1 function could promote stem cell proliferation and induce a block in differentiation, the hallmarks of the two-step hypothesis for the development of acute myeloid leukemia (AML). Mutations in WT1 occur in 10–15% of AMLs, and a link between mutation and failure to respond to standard induction chemotherapy has been proposed. 3 In support of this study, Nyvold et al. 4 noted the emergence of a WT1 - mutated subclone following therapy suggesting that mutation of WT1 could lead to progression of leukemia by conferring drug resistance. Our group recently reported an association between acquired uniparental disomy of 11p and homozygous mutation of WT1 in a patient with normal karyotype AML. 5 As this patient was also refractory to first-line chemotherapy, we investigated the relationship between WT1 mutation and treatment outcome in patients with normal cytogenetics. Local Research Ethics Committee approval was obtained before initiation of the study. WT1 mutation analysis was performed on DNA from a group of 70 patients with normal karyotype AML (female 38/male 32; median age at diagnosis 55.2 years, range 19–78, FAB type M1-31; M2-14, M4-14; M5- 9, M6-2; 46 patients o60 years) using a polymerase chain reaction-direct sequencing approach. Intronic primers (available on request) flanking exons 2–10 were used to amplify individual exons, and resultant products were directly sequenced by the use of an ABI 377 DNA sequencer (PE Applied Biosystems, Foster City, CA, USA). Mutations were inferred from the resultant trace and confirmed by the use of TOPO TA cloning (Invitrogen Ltd, Paisley, UK) and sequence analysis of the corresponding mutated clones. Statistical analysis was per- All Patients Mutated patients Non Mutated Patients WT1 + FLT3- ITD FLT 3-ITD only WT1 only Number of patients Entering CR1 with first line 70 6 20 1 43 Treated with curative intent 63 5 17 1 40 treatment 39 0 10 1 28 Primary Refractory (% of treated) 16 5 (100%) 4 (23%) 0 7 (18%) Deaths during treatment 8 0 3 0 5 Median Survival (All - years) 0.94 0.47 0.52 0.52 1.07 a b Figure 1 (a) Schematic representation of the WT1 gene and protein structure. All eight mutations arose within the DNA-binding domain encoded by exons 7 and 9. Mutations are assigned according to Accession No. NM_024426. (b) Tabulation of the treatment response of patients with respect to WT1 and FLT3-ITD mutation status. Leukemia (2007) 21, 550–590 & 2007 Nature Publishing Group All rights reserved 0887-6924/07 $30.00 www.nature.com/leu