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Whole-exome sequencing identifies mutations of BCOR in acute myeloid leukemia with normal karyotype

ABSTRACT: Among acute myeloid leukemias (AML) with normal karyotype (CN-AML), NPM1 and CEBPA mutations define WHO provisional entities accounting for ~60% of cases, but the remaining ~40% remains poorly characterized. By whole exome-sequencing (WES) of one CN-AML patient lacking mutations in NPM1, CEBPA, FLT3, MLL-PTD and IDH1, we newly identified a clonal somatic mutation in BCOR (BCL6 co-repressor), a gene located in chromosome X. Further analyses showed that BCOR mutations occurred in 11/262 (4.2%) CN-AML cases and represented a substantial fraction (14/82, 17.1%) of CN-AML patients showing the same genetic background as the index patient subjected to WES. BCOR somatic mutations were: i) disruptive events similar to germline BCOR mutations causing the oculo-cranio-facial-dental (OCFD) genetic syndrome; ii) associated with markedly decreased BCOR mRNA levels, absence of full-length BCOR and absent or low expression of a truncated BCOR protein; iii) almost mutually exclusive with NPM1 mutations and frequently associated with DNMT3A and RUNX1 mutations, pointing to a cooperation between these events. Finally, BCOR mutations correlated with poor outcome among a cohort of 160 CN-AML patients (28% versus 66% overall survival at 2 yrs, P=0.024). Our results implicate for the first time BCOR in the pathogenesis of CN-AML without NPM1 mutations.

ORGANISM(S): Homo sapiens

PROVIDER: GSE30442 | GEO | 2011/12/16

SECONDARY ACCESSION(S): PRJNA143515

REPOSITORIES: GEO

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Project description:The clinical impact of aberrant CEBPA promoter methylation (PM) in AML is controversial discussed. The aim of this study was to clarify the significance of aberrant CEBPA PM with regard to clinical features in a cohort of 572 de novo AML with wildtype CEBPA and normal karyotype. The distal promoter was methylated in 54/572 cases (9.41%) whereas proximal PM was never detected. Methylation of the core promoter was detected in only 8 of 326 cases (2.45%) and thus seems to be a rare event in AML. There was no correlation between CEBPA distal PM, age, sex, white blood cell (WBC) count or Hb levels at diagnosis. We also were not able to detect a significant correlation between the presence of CEBPA distal PM and molecular mutations such as FLT3-ITD, NPM1, AML1, MLL-PTD and IDH1. Solely the frequency of IDH2R140 mutations was significantly reduced in CEBPA distal PM positive compared to CEBPA distal PM negative cases (p=0.01). Furthermore, analysis of CEBPA mRNA expression level revealed no difference between CEBPA distal PM positive and CEBPA distal PM negative cases, suggesting that CEBPA distal PM has no influence on CEBPA expression. CEBPA distal PM did not show impact on overall survival (OS), event free survival (EFS) or incidence of relapse. Also when other mutations were taken into regard no prognostic impact of CEBPA distal PM could be shown. In contrast, a distinct expression profile of CEBPA distal PM positive cases compared to CEBPA mutated and CEBPA distal PM negative cases was observed. In addition, a significantly higher frequency of CEBPA distal PM was detected in RUNX1-RUNX1T1 positive AML compared to the CEBPA witdtype cases. We conclude that the presence of aberrant CEBPA PM has no clinical relevance and is therefore a negligible prognostic marker in de novo AML with normal karyotype. To detect underlying common differences in their gene expression profiles, we investigated 9 CEBPA methylated (unmutated), 8 CEBPA single-mutated, 10 CEBPA double-mutated, and 10 non-methylated/non-mutated cases (Affymetrix HG-U133 Plus 2.0 microarrays; Santa Clara, CA). The microarray sample preparation assay was performed as previously reported. Gene expression raw data were processed according to the manufacturer’s recommendations.

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Whole-exome sequencing identifies mutations of BCOR in acute myeloid leukemia with normal karyotype

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