Research Of NPM1 Gene Mutations In Adult Patients With Acute Myeloid Leukemia

[Background and Objectives]NPM1, also called B23, numatrin or NO38, is a ubiquitously expressed nucleolar phosphoprotein. NPM1 plays an important role in tumor-stress pathway through binding to P53,P19ARF and P14ARFprotein. The outstanding study performed by Falini and colleagues in 2005, NPM1 exon 12 mutations were identified as the most frequent gene mutation in adult acute myeloid leukemia (AML). (1) To clarify the prevalence and the clinical profile of NPM1 mutations in adult AMLs, we analyzed a cohort of 156 newly diagnosed adult AMLs for this mutation. (2) To evaluate the impact and correlation of FLT3 internal tandem duplication (ITD) mutations and NPM1 gene mutations in 86 cases of 156 adult AMLs.[Methods]156 adult patients (range, 15-73 years) were newly diagnosed AMLs according to French-American-British (FAB) Cooperative Group criteria at Jiangsu Institute of Hematology from January 2005 to April 2006. (1) Genomic DNAs were prepared from bone marrow samples of these patients. NPM1 exon 12 mutations were detected using capillary electrophoresis (CE) of DNA-PCR products. We randomly chose some cases for cloning with pMD18-T Vector and sequencing to analyze mutational location and type. (2) Follow up the clinical and lab datas of these cases, then summarize the characteristics. (3) Estimate the clinical prognosis based on the response to therapies of inpatients. (4) FLT3-ITD mutations were determined by agarose electrophoresis of genomic DNA-PCR products.[Results]NPM1 mutations were present in 28.2% (44/156) of the overall population, including 1/1(100%) of M0, 11/27(40.7%) of M1, 11/46(23.9%) of M2, 0/29(0%) of M3, 2/9(22.2%) of M4, 18/39(46.2%) of M5 and 1/5(20.0%) of M6. NPM1 gene mutations were more prevalent in patients with a normal karyotype (37 of 90; 41.1%), when compared with patients with karyotypic abnormalities (7 of 66; 10.6%; P<0.001). Sequence analysis of 32 NPM1 mutated cases revealed known mutations (type A, B, D, NM, and PM) as well as a novel sequence variation (here named as type S). All mutational types were heterozygous and showed a 4 bp insertion between position nucleotide 960 and 961 (Genebank accession number: NM-002500). NPM1 mutations were significantly associated with old age (P<0.05), high peripheral white cell count (P<0.05) and FAB-M1/M5, but negatively associated with expression of CD34 (P<0.05) and CD117 (P<0.05).Compared to NPM1-nonmutaed AMLs, complete remission (CR) rate was higher(66.7% vs 54.8%) in NPM1-mutated AMLs. Longer survival time showed a trend towards better prognosis. In NPM1+/FLT3-ITD-, NPM1-/FLT3-ITD-, NPM1+/FLT3-ITD+, NPM1-/FLT3-ITD+AML groups, the percentage was 25.6%,56.9%,8.1%,9.3% and CR rate was 66.7%,60.0%,50.0%,42.9%, respectively. But there was no significant difference (P<0.05).[Conclusions]NPM1 mutations also represent a common genetic abnormality in adult AMLs at our department, especially in the presence of a normal karyotype. The occurrence of NPM1 mutations indicates an age-dependent characteristic. NPM1 mutated cases show a special clinical subtype of AML. NPM1 gene mutations are associated with FLT3-ITD in AMLs. NPM1 mutations and not FLT3-ITD mutations are probably related to favourable prognosis. Further studies are urgently needed to confirm the role of NPM1 mutations in leukemogenesis. The altered nucleo-cytoplasmic transport of NPM1 mutated protein is probably a potential therapeutic target for AML with NPM1 mutations.