DNMT3A mutations are rare in childhood acute myeloid leukemia

Childhood acute myeloid leukemia (AML) is a complex disease of the hematopoietic stem cell. Overall survival is relatively low with an overall survival rate of 50–70%. Besides cytogenetic changes and response to induction therapy, molecular aberrations are important prognostic markers that can help to risk stratify children with AML. Molecular aberrations include mutations in FLT3,1 NPM1,2 CEBPA,3 WT14 with the recent addition of IDH1 and IDH2.5 In a significant number of pediatric and adult AML patients, no known mutation or cytogenetic aberration can be identified. It is, therefore, believed that a large number of gene mutations in AML are still to be identified. Recently, somatic mutations in DNA methyltransferase 3A (DNMT3A) have been found in adult AML6,7 but the incidence and prognostic impact in childhood AML is unknown. DNMT3A is involved in epigenetic regulation of genes by enzymatic de novo addition of methyl groups to the cytosine residue of CpG dinucleotides. Mutations in DNMT3A occur in approximately 20% of adult AML patients. Interestingly, a mutational hotspot in codon R882 located in the catalytic methyltransferase domain has been reported to present approximately 60% of all mutations while the remaining 40% are located throughout the gene with the main focus in the methyltransferase domain.6,7 Ley et al. described an adverse prognostic impact of the mutation for adult AML patients6 which has been confirmed by our group and others.7,8 Hence, mutations in DNMT3A appear to play an important role as a novel prognostic marker in adult AML. However, so far little is known about the frequency and prognostic impact of DNMT3A mutations in childhood AML. The only study to date which looks at DNMT3A mutations in a cohort of 180 children with AML did not identify any DNMT3A mutations associated with disease.9 Here we report the frequency, and clinical and molecular characteristics of DNMT3A mutations in a well defined cohort of 195 pediatric AML patients. Bone marrow (BM) or peripheral blood (PB) samples from initial diagnosis were obtained from 195 pediatric AML patients. Details regarding the clinical and molecular characteristics of the study cohort are shown in Table 1. All patients were treated within two prospective multicenter trials: the AML-Berlin-Frankfurt-Münster (BFM) 98 or the 2004 (NCT00111345), as previously described.10–12 The studies were approved by the protocol review committee of the German Cancer Society and by the local ethics committees. Written informed consent was obtained from patients, parents or guardians. The median survival time for patients in follow up was 3.53 years (range 0.2–9.5 years). Exon 23 spanning codon R882 was analyzed using primers and PCR conditions as described.8 Purified PCR fragments were directly sequenced. All mutations were confirmed in a second independent analysis. Two patients had a mutation in codon R882 and one patient had the minor allele of SNP rs61758. A follow-up remission sample was available for one mutated patient; the patient lost the mutation in remission. Although the low frequency of DNMT3A mutations in pediatric AML did not allow any formal assessment of clinical and molecular associations or prognostic evaluation to be made, the mutated patients were found to present some interesting characteristics. The 2 children with the mutation were older compared to the median age of the cohort (15.45 vs. 8.56 years). In adult AML, DNMT3A mutations were associated with older age.6,8 Our data suggest that the mutation is more likely to occur with advanced age and this, therefore, explains the low mutation rate in childhood AML. Ley et al. and our group described an association between mutations in DNMT3A with FAB M4/M5 and mutations in FLT3, IDH1 and NPM1 in adult AML.6,8 Interestingly, none of the mutated patients belonged to the FAB M4/M5 group. However, our 2 mutated patients were both found to be FLT3-ITD positive. While one patient also showed a mutation in NPM1, they both had wild-type IDH1/IDH2 (Table 2). Both patients underwent bone marrow transplantation and are in complete remission (Table 2). The effects of hematopoietic stem cell transplantation in AML patients with mutated DNMT3A remain unclear. Our study demonstrates that DNMT3A mutations are rare in childhood AML and are associated with older age. However, given that only exon 23 of DNMT3A was studied, where the mutational hotspot in adult AML is located, it is conceivable that the mutation rate is underestimated in our study. It may be speculated from this data that embryonic DNMT3A mutations may have deleterious effects during development, and that mutations acquired at later stages of life have a weak oncogenic potential resulting in a long latency of leukemic transformation.

Table 1.Main clinical and biological features of the study cohort.

Table 2.Main clinical and biological features of DNMT3A mutated patients.

Footnotes

• ↵FT, MH and FD contributed equally to this work.
• Funding: this study was supported by grant n. DJCLS R 10/22 from the Deutsche-José-Carreras Leukämie-Stiftung e.V.; grant n. M 47.1 from the H. W. & J. Hector Stiftung; grant n. 109003 to MH and n. 109686 to FD from the Deutsche Krebshilfe e.V.
• The information provided by the authors about contributions from persons listed as authors and in acknowledgments is available with the full text of this paper at www.haematologica.org.
• Financial and other disclosures provided by the authors using the ICMJE (www.icmje.org) Uniform Format for Disclosure of Competing Interests are also available at www.haematologica.org.