ARE MUTATIONS IN THE IDH2 GENE SUITABLE MOLECULAR MARKERS FOR MRD MONITORING IN AML PATIENTS?

Background:

Heterozygous missense mutations in isocitrate dehydrogenase 2 gene (IDH2) have been recently reported in pacients with acute myeloid leukemia (AML), notably in cytogenetically normal AML (incidence 12,1 %). These mutations affect mainly arginine codons p.R140 and/or p.R172, both localized in exon 4. The most frequently is c.G419A (p.R140Q). Potential of detected IDH2 gene mutations for monitoring of minimal residual disease (MRD) in AML patiens is unclear and is now under investigation.

Aims:

i) to verify the use of most frequently detected mutation c.G419A (p.R140Q) for MRD monitoring in AML patients, and ii) to compare these results with those obtained from routine monitoring of NPM1 mutations in AML patients, who harbor IDH2 and NPM1 mutations simultaneously.

Methods:

Method of DNA-based RQ-PCR with a specific set of primers and Locked Nucleid Acid (LNA) probe were used for quantification of IDH2 c.G419A (p.R140Q) mutation in a total of  73 samples (45 bone marrow and 28 peripheral blood samples) of 9 AML patients. These samples were obtained during AML treatment at the different time points. All patients signed an informed consent before the samples were collected. Six of nine (6/9) analyzed patients harbored parallel mutation in NPM1 gene. Quantification of NPM1 mutation was performed according to previously published work.  The results were reported as the normalized copy numbers (NCN) defined as the number of mutated IDH2 or NPM1 gene copies for every 10⁶ cell equivalents (CE).

Results:

In our cohort, 7/9 AML patients revealed concordant results for the NCN of the IDH2 c.G419A mutation and disease status. Moreover, in 5/6 analysed patients, the kinetics of IDH2 mutations was nearly identical to the kinetics of NPM1 mutations.  However, in the remaining two patients, IDH2 mutation status did not correspond to clinical course of AML. Both patients revealed persistent IDH2 c.G419A  positivity (10⁵ – 10⁶ NCN) althougt they were in hematological remission. Moreover, one of them was also in molecular remission according to NPM1. In these discrepant cases (2/9) further analyses were performed and  germinal origin of IDH2 mutation were excluded.

Summary / Conclusion:

Our data indicate that, in the majority of AML patients, status of IDH2 mutation correlate with the clinical course of disease. Thus mutation c.G419A in IDH2 gene seems to be suitable marker for MRD monitoring in AML patients. However, we have shown that discrepant cases exist. Therefore further studies will be necessary to identify cases where the IDH2 mutation burden does not correlate with clinical course of AML.

Supported by the project (Ministry of Health, Czech Republic) for conceptual development of research organization 65269705 (University Hospital Brno, Brno, Czech Republic) and research grant (Ministry of Education, Youth and Sports, Czech Republic) MSMT0021622430.

Keywords: Acute myeloid leukemia, Minimal residual disease (MRD)

Abstrakta v časopise Haematologica 2013, Suppl1

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