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Acute Myeloid Leukemia With IDH1 or IDH2 Mutation
Frequency and Clinicopathologic Features

Keyur P. Patel MD, PhD, Farhad Ravandi MD, Deqin Ma MD, PhD, Abhaya Paladugu, Bedia A. Barkoh, L. Jeffrey Medeiros MD, Rajyalakshmi Luthra PhD
DOI: http://dx.doi.org/10.1309/AJCPD7NR2RMNQDVF 35-45 First published online: 1 January 2011


Mutations in the isocitrate dehydrogenase 1 (IDH1) and IDH2 genes are reported in acute myeloid leukemia (AML). We studied the frequency and the clinicopathologic features of IDH1 and IDH2 mutations in AML. Mutations in IDH1 (IDH1R132 ) and IDH2 (IDH2R172 ) were assessed by Sanger sequencing in 199 AML cases. Point mutations in IDH1R132 were detected in 12 (6.0%) of 199 cases and in IDH2R172 in 4 (2.0%) of 196 cases. Of the 16 mutated cases, 15 (94%) were cytogenetically normal, for an overall frequency in this group of 11.8%. IDH1R132 and IDH2R172 mutations were mutually exclusive. Concurrent mutations in NPM1, FLT3, CEBPA, and NRAS were detected only in AML with the IDH1R132 mutation. The clinical and laboratory variables of patients with AML with IDH mutations showed no significant differences compared with patients with wild-type IDH. We conclude that IDH1R132 and IDH2R172 mutations occur most often in cytogenetically normal AML cases with an overall frequency of approximately 11.8%.

Key Words:
  • Acute myeloid leukemia
  • Isocitrate dehydrogenase
  • IDH1
  • IDH2
  • Mutation

Identification of somatically acquired gene mutations has provided critical insights into the pathogenesis of acute myeloid leukemia (AML).1 Gene mutations in AML provide useful markers for diagnosis and for monitoring response to therapy and also provide information useful in assessing prognosis and making therapeutic decisions.26 The most recent World Health Organization (WHO) classification of myeloid neoplasms acknowledges the clinical significance of gene mutations in AML and has proposed separate entities for AML with mutations in NPM1 and CEBPA.7 It is interesting that mutations in AML are detected commonly in cytogenetically normal (CN) cases, which account for 40% to 50% of all AMLs.1,8 Currently, no known mutations are identified in about 20% to 30% of CN AML cases, suggesting the possibility that more mutations likely exist.

Recently, the entire genome of a patient with CN AML was sequenced, and a total of 64 somatic mutations, 12 within coding sequences of genes and 52 in conserved or regulatory regions, were identified.9 In particular, a novel mutation was detected in isocitrate dehydrogenase 1 (IDH1), a metabolic gene frequently mutated in gliomas.1012 The mutation occurred consistently at an evolutionary conserved arginine residue at codon 132 (R132) within the substrate binding site of the enzyme and was strongly associated with normal cytogenetic status. A limited number of studies examining the frequency of the IDH1 mutation in AML were performed subsequently.1316 In addition to IDH1R132 , mutations in codon 172 of IDH2 (IDH2R172 ), a mitochondrial isoform of IDH1, have been documented in AML.14,17

Published studies have focused on examining the frequency and correlation with mutational status and clinical outcome. A very limited amount of information is available on the histomorphologic features and immunophenotypic profiles associated with IDH1R132 and IDH2R172 mutations in AML. Only 1 study, involving a Chinese population, reported clinical and biologic features of AML with the IDH1R132 mutation.16 There are no such reports available for the Western population or for AML with the IDH2R172 mutation.

We report the frequency of IDH1R132 and IDH2R172 mutations in 199 AML cases with clinical, histologic, and immunologic characterization of the mutated cases. We also performed a meta-analysis of available studies that have assessed AML cases for IDH1R132 mutations.

Materials and Methods

Study Group

DNA was extracted from diagnostic bone marrow aspirate samples of AML with 20% or more blasts using methods described previously.18 All samples had been sent to the clinical Molecular Diagnostics Laboratory, The University of Texas M.D. Anderson Cancer Center, Houston, at the time of diagnosis. Residual DNA was used under an approved institutional review board protocol. Cases of AML with favorable-risk cytogenetics were excluded from analysis based on data from an earlier study that showed absence of IDH1 mutations in this group.9 Pertinent laboratory information was obtained from the laboratory information system. The patient characteristics are listed in Table 1 and Table 2.

IDH1 and IDH2 Mutation Detection

Exon 4 mutations in codon R132 of IDH1 and codon R172 of IDH2 were detected by using polymerase chain reaction (PCR) amplification followed by Sanger sequencing. Previously described PCR primers were modified with the addition of M13 sequence.19 The PCR primers used were forward, 5′- TGTAAAACGACGGCCAGTC GGTCTTCAGAGAAGCCATT-3′ and reverse, 5′-CA GGAAACAGCTATGACCGCAAAATCACATTATT GCCAAC-3′ for IDH1R132 and forward, 5′-TGTAAAA CGACGGCCAGTAGCCCATCATCTGCAAAAAC-3′ and reverse, 5′-CAGGAAACAGCT ATGACCCTAGGCG AGGAGCTCCAGT-3′ for IDH2R172 . All primers were purchased from Integrated DNA Technologies, Coralville, IA.

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Table 1

For IDH1R132 and IDH2R172 , 2 μL of patient DNA (100 ng/μL) was added to 48 μL of PCR master mix that consisted of 31.7 μL of molecular grade water, 5 mL of 10× PCR buffer II (Applied Biosystems, Carlsbad, CA), 4 μL of 25 mmol/L magnesium chloride, 10 mmol/L deoxynucleoside triphosphate (dNTP) mix, 1 μL each of M13-tagged forward and reverse primers (10 μmol/L), and 0.3 μL of Amplitaq Gold (5 U/μL; Applied Biosystems). PCR conditions for IDH1R132 and IDH2R172 included initial denaturing at 95°C for 10 minutes; 40 cycles of 95°C for 30 seconds, 60°C for 30 seconds, and 72°C for 30 seconds; and final extension at 72°C for 7 minutes.

Post-PCR purification of the products was performed using QIAquick kit (Qiagen, Valencia, CA). PCR products were analyzed on a 2% agarose gel (115 V for 30–40 minutes) using 8 μL of PCR product and 2 μL of 1× gel-loading dye. Sanger sequencing of IDH1R132 and IDH2R172 amplicons was performed using M13-tagged primers in a 20-μL final volume that contained 4 μL of PCR product, 6.8 μL of water, 2 μL of 5× sequencing buffer, 3.2 μL of M13 forward or reverse primer (1 μmol/L), and 4 μL of BigDye v1.1 (Applied Biosystems). Sanger sequencing was performed using M13 forward, 5′-TGTAAAACGACGGCCAGT-3′, and M13 reverse, 5′-CAGGAAACAGCTATGACC-3′, primers.

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Table 2

Sequencing conditions included initial denaturing at 96°C for 1 minute and 25 cycles of 96°C for 10 seconds, 50°C for 5 seconds, and 60°C for 4 seconds. Sequencing products were purified using the DyeEx 96 Spin Kit (Qiagen) and analyzed by capillary gel electrophoresis on the 3130 genetic analyzer (Applied Biosystems).

NPM1 Mutation Detection

Mutations in coding regions of exon 12 of NPM1 were detected using PCR amplification of a 168-base-pair segment followed by capillary gel electrophoresis. PCR primers included forward, 5′-FAM-GATGTCTATGAAGTGTTGTGGT-TCC-3′ and reverse, 5′- GGACAGCCAGATCAACTG-3′. PCR was performed in a 50-μL reaction volume that contained 2 μL of patient DNA (100 ng/μL), 5 μL of 10× ThermoPol Buffer (New England BioLabs, Ipswich, MA) with magnesium sulfate, 5 μL of 10 mmol/L dNTP, 1 μL of NPM1 forward primer (10 μmol/L), 1 μL of NPM1 reverse primer (10 μmol/L), 35.2 μL of water, and 0.75 μL of Vent DNA polymerase (New England Biolabs) (2 U/μL). PCR conditions included initial denaturing at 95°C for 10 minutes, 40 cycles of 95°C for 30 seconds, 55°C for 30 seconds, and 72°C for 30 seconds, and final extension at 72°C for 7 minutes. PCR products were analyzed by capillary electrophoresis on a 3100 or 3130 genetic analyzer (Applied Biosystems).

RAS Mutation Detection

Mutations in codons 12, 13, and 61 of KRAS were detected by using pyrosequencing as described earlier.18 Mutations in codons 12, 13, and 61 of NRAS were detected with the same protocol but using the following primers: codons 12 and 13, forward, 5′-GTTCTTGCTGGTGTGAAATGA-3′; reverse, 5′-BIOTIN-CTCTATGGTGGGATCATATTC-3′; and sequencing, 5′-CAAACTGGTGGTGGTTGGAGCA-3′; and codon 61, forward, 5′-GGACATACTGGATACAGCT-3′; reverse, 5′-BIOTIN-CTGTAGAGGTTAATATCCGCA-3′; and sequencing, 5′-GGACATACTGGATACAGCT-3′.

Detection of KIT, FLT3-ITD, FLT3-D835, CEBPA, and TP53 Mutations

Mutation analysis for KIT, FLT3-ITD, FLT3-D835, CEBPA, and TP53 mutations was performed using Sanger sequencing as described previously.2023 For CEBPA and TP53, an M13 sequence was added to the previously described PCR primers for Sanger sequencing. M13-tagged primers were used for Sanger sequencing.

Morphologic, Immunophenotypic, and Cytogenetic Analysis

Bone marrow aspirate smears were stained with Wright-Giemsa, and aspirate clot and biopsy specimens were stained with H&E. Flow cytometric immunophenotypic analysis was performed using 4-color staining, and conventional G-banded karyotyping was performed as described previously.24


IDH1R132 and IDH2R172 Mutations in AML

A total of 199 AML cases were tested for IDH1R132 mutation, and 196 cases were tested for IDH2R172 mutation (Tables 1 and 2). The IDH1R132 mutation was detected in 12 cases (6.0%), and the IDH2R172 mutation was detected in 4 (2.0%) of 196 cases Figure 1. No mutated cases had both IDH1 and IDH2 mutations, suggesting that these mutations are mutually exclusive.

Cytogenetic Features of IDH-Mutated AML Cases

The AMLs tested included 127 (63.8%) with normal and 72 (36.2%) with abnormal cytogenetics. Subdivided by cytogenetic risk group, 166 cases (83.4%) were intermediate risk and 33 (16.6%) were poor risk. Of 12 AML cases with an IDH1 mutation, 11 (92%) had normal cytogenetics and all 12 (100%) were in the intermediate-risk cytogenetic group. The association between IDH1 mutation and normal cytogenetics approached statistical significance (P = .059; Fisher exact test). All 4 cases with an IDH2 mutation had normal cytogenetics and belonged to the intermediate-risk group. Of the 16 mutated cases (12 IDH1 and 4 IDH2), 15 (94%) were cytogenetically normal, for an overall frequency in this group of 11.8% (15/127).

Molecular Features of IDH-Mutated AML Cases

The 12 AMLs with IDH1R132 mutations were equally distributed between R132H and R132C substitutions Table 3. All IDH2R172 mutations resulted in R172K substitutions (Table 3). IDH1R132 -mutated cases showed a higher frequency of concurrent NPM1 mutation compared with wild-type cases (5/11 [45%] vs 13/54 [24%]), which did not achieve statistical significance (P = .161; Fisher exact test). Additional gene mutations were identified in IDH1-mutated cases, including NPM1, FLT3-ITD, CEBPA, NRAS, KIT, and FLT3-D835 (Table 1). Of 11 IDH1-mutated cases, 8 (73%) met the criteria for the high-risk molecular group. There was no significant association of the IDH1R132 mutation with FLT3-ITD, FLT3-D835, CEBPA, NRAS, KRAS, or KIT mutations or a high-risk molecular profile (Tables 1 and 3).1,25 None of the 4 IDH2R172 -mutated cases showed a concurrent mutation in NPM1, FLT3-ITD, FLT3-D835, CEBPA, NRAS, KRAS, KIT, or IDH1 (Tables 2 and 3). All 4 IDH2R172 -mutated AMLs met the criteria for the high-risk molecular group based on the absence of the NPM1 mutation.

Figure 1

Detection of IDH1 and IDH2 mutations by Sanger sequencing. A, Wild-type IDH1 codon 132: CGT, R132. B, Wild-type IDH2 codon 172: AGG, R172. C, Mutant IDH1 codon 132: TGT, R132C. D, Mutant IDH2 codon 172: AAG, R172K. Note that both IDH1R132 and IDH2R172 mutations are heterozygous missense point mutations.

TP53 Mutations in AML Cases With the IDH1R132 Mutation

In glioma, non-R132H mutations of IDH1 are associated with a higher frequency of TP53 mutations and a distinct gene expression profile compared with the R132H mutations. We therefore tested 11 available IDH1R132 -mutant AML cases for TP53 mutations. We detected a P72R polymorphism, known to predispose to a variety of human cancers, in 4 of 5 R132C cases and 5 of 6 R132H cases. We did not find any significant difference in the frequency of TP53 mutations in R132C and R132H subgroups, as each subgroup had only 1 case with TP53 mutation.

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Table 3

Morphologic and Immunophenotypic Features of AML With IDH Mutations

For AMLs with the IDH1R132 mutation, the mean blast count was 55% (range, 22%–88%). Using the WHO classification, the mutated cases were classified as AML, not otherwise specified (NOS; n = 10) or AML with myelodysplasia-related changes (n = 2). The AML, NOS group was further classified as AML without maturation (French-American-British classification [FAB] M1), AML with maturation (FAB M2), and acute monocytic leukemia (FAB M5). Auer rods were detected in 5 (50%) of 10 cases. Dysplastic features in 1 or more hematopoietic lineages were evident in 10 (83%) of 12 AML cases with the IDH1R132 mutation and 3 (75%) of 4 AMLs with the IDH2 mutation Table 4. Bone marrow cellularity ranged from 25% to 100% (mean, 71%).

For AMLs with IDH2R172 mutations, the mean blast count was 53% (range, 20%–98%). These 4 mutated cases were classified as AML without maturation (n = 3) and AML with maturation (n = 1). IDH2-mutated cases were significantly more often classified as AML without maturation compared with IDH2 wild-type AML cases (3/4 [75%] vs 27/192 [14.1%]; P < .01; Fisher exact test). Auer rods were detected in 3 (75%) of 4 cases. Of 4 AML cases with the IDH2 mutation, 3 (75%) showed dysplastic features in 1 or more hematopoietic lineages (Table 4). Bone marrow cellularity ranged from 60% to 80% (mean, 70%).

Flow cytometric Immunophenotypes of AML with IDH1R132 and IDH2R172 mutations are similar and are listed in Table 5. Overall AMLs with the IDH1R132 or IDH2R172 mutation showed a myeloid immunophenotype: CD117+, HLA-DR+/– (more cases positive than negative), CD34+/–, CD38+, CD13+, CD33+, and myeloperoxidase+/–. CD64 was present in AML M5, consistent with monocytic differentiation.

Clinical Features of IDH-Mutated AML Cases

For the 12 IDH1-mutated AMLs, the mean age was 55 years (range, 37–77 years), and the male/female ratio was 1:3. The mean WBC count was 15,000/μL (15.0 × 109/L). For the 4 IDH2-mutated cases, the mean age was 51 years (range, 22–76 years), and the male/female ratio was 1:3. The mean WBC count was 4,000/μL (4.0 × 109/L). There was no significant difference in age, sex, WBC count, platelet count, hemoglobin level, bone marrow blast count and cellularity, dysplastic features, or morphologic classification between the IDH1- and IDH2-mutated AML cases (Table 1).

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Table 4
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Table 5

These clinical variables in the IDH1- and IDH2-mutated AML cases were also compared with wild-type AMLs. IDH2R172 -mutant AMLs were also significantly associated with a lower WBC count compared with wild-type AMLs (4,300/μL vs 20,000/μL [4.3 vs 20.0 × 109/L]; P < .001; Student t test). There was no significant difference in age, sex, and blast count between IDH1-mutated and unmutated AML cases or between IDH2R172 -mutated and unmutated cases (Table 2).

Meta-analysis of AMLs With IDH1R132 Mutation

We performed a meta-analysis of all available studies that assessed for IDH mutations in AML cases. To date, virtually all studies have focused on IDH1 mutations in AML, with a total of 1,787 AMLs reported, with 146 cases (8.2%) being mutated Table 6. Because the IDH1R132 mutation is predominantly restricted to CN AML, inclusion of AML cases with abnormal karyotypes in earlier studies most likely underrepresents the true frequency of IDH1 mutations in CN AML. We extracted the fraction of CN AMLs with the IDH1R132 mutation from the studies reported. Of 1,152 CN AMLs tested, 129 (11.2%) showed the IDH1R132 mutation compared with 17 (4.7%) of 360 AMLs with an abnormal karyotype. Review of cytogenetic studies showed that all 66 IDH1-mutated AML cases were limited to the intermediate-risk category. IDH1R132 mutations resulted in a higher R132H substitution (73/146 [50.0%]) than R132C substitution (45/143 [31.5%]).

Analysis of available test results for coexisting mutations showed NPM1 to be the most common concurrent mutation, found in 87 (60.4%) of 144, followed by FLT3-ITD (37/146 [25.3%]) and CEBPA (14/155 [9.0%]). None of the 60 AMLs with an IDH1R132 mutation showed a concurrent IDH2 mutation. The number of AML cases assessed for the IDH2 mutation was too few to perform a similar meta-analysis.


IDH1 and IDH2, nicotinamide adenine dinucleotide phosphate+-dependent isocitrate dehydrogenases, catalyze the oxidative carboxylation of isocitrate to α-ketoglutarate. IDH1 has a key role in the production of the cytosolic reduced form of nicotinamide adenine dinucleotide phosphate necessary for the regeneration of reduced glutathione, a main antioxidant in mammalian cells.26 Recurring mutations in IDH1 and IDH2 occur at a very high frequency in many different types of glioma, especially secondary glioblastoma.12,27

IDH mutations in gliomas are always reported at the same arginine residues, R132 in IDH1 and R172 in IDH2, that are responsible for hydrophilic interactions with isocitrate.28 Initial analyses showed that IDH mutations were restricted primarily to gliomas, with rare cases of prostate cancer and B-lymphoblastic leukemia showing IDH mutations.12,29,30

Recently, Mardis and colleagues9 sequenced the entire genome of a cytogenetically normal case of AML and detected a novel IDH1R132 mutation. They subsequently screened 187 AML cases and showed a heterozygous IDH1R132 mutation in 15 cases (8.0%). Sixteen (original case plus 15 additional cases) IDH1R132 -mutated cases had available cytogenetic data, and 13 (81%) were CN AML. In addition, all 16 IDH1-mutated AMLs had intermediate-risk cytogenetics. These findings were in contrast with previous studies that did not detect the IDH1R132 mutation in 145 AML cases.12,30 Differences in the cytogenetic findings in the study groups and sensitivities of the detection assays could underlie these discrepancies. For this reason, we chose to undertake this study reviewing our experience in approximately 200 cases of AML at our institution.

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Table 6

Based on the available data in the literature, we specifically studied AML cases with intermediate- or poor-risk cytogenetic findings.9 Our results show that the frequency of IDH1 mutations is lower in CN AML cases. We detected IDH1R132 mutations in 11 (8.7%) of 127 CN AMLs compared with the initial report of 16%.9 We showed that all AML cases with the IDH1 mutation have intermediate-risk cytogenetics. In addition, we identified IDH2R172 mutations in 4 (2.0%) of 196 AML cases, all of which were CN AML. In no case did we find both IDH1 and IDH2 mutations, strongly suggesting that IDH1R132 and IDH2R172 are mutually exclusive. Only 1 other study has assessed for both IDH1 and IDH2 mutations in a large group of CN AML cases. Marcucci and colleagues14 showed that IDH mutations occur in 33% of cases, with IDH1 in 14% and IDH2 in 19%. The explanation for the higher rate of IDH1 and particularly IDH2 mutations in CN AML cases in this study, compared with our own data, is explained in large part because Marcucci and colleagues14 assessed for IDH2 mutations involving the arginine residue at codon 140 (R140). More than 80% of the IDH2 mutations they detected were R140 mutations. We did not test for IDH2R140 mutations in our study because the significance of mutations at this codon is unknown. These mutations have not been shown to have prognostic significance in AML and are not seen in other human cancers. Other authors have suggested that further studies are needed to determine whether R140 substitutions represent a true pathogenic mutation or a polymorphism.14

Because IDH1R132 is mainly limited to CN AML, the frequency of the IDH1R132 mutation in AMLs is likely to vary from one study to the next, depending on the percentage of AML cases with abnormal karyotypes. For example, the IDH1R132 mutation was detected in 7% of CN AMLs but in only 4% of all AML cases in a study by Ho and colleagues.15 It is therefore important to account for the cytogenetic composition of the study group when interpreting the frequency of IDH1R132 in AML. We performed meta-analysis of our study and other available studies to obtain a more global view of IDH1 mutations in AML. A total of 146 AMLs with the IDH1R132 mutation have been reported. Most cases with the IDH1 mutation have been CN AMLs and restricted to the intermediate-risk cytogenetic group. The overall frequency of the IDH1R132 mutation in CN AML is 11.0% (141/1,279). The male/female ratio is 1:1.1.

Despite the recent interest in IDH mutations in AML, a limited amount of information is available on morphologic and immunophenotypic features. Morphologic classification using the FAB system is available for 82 cases. The most common morphologic types were M1 in 34 cases (41%) and M2 in 25 cases (30%). Very few cases have been classified using the 2008 WHO system. The classification of cases in our study closely matches what has been reported. The IDH1-mutated cases were classified as AML, NOS (n = 10) or AML with myelodysplasia-related changes (n = 2). It is interesting that the IDH2-mutated cases were all AML, NOS. In this category, 7 cases were AML without maturation (FAB M1), 5 cases were AML with maturation (FAB M2), and 3 cases were acute monocytic leukemia (FAB M5). The immunophenotype of most cases in our study was typical myeloid, with expression of CD13, CD33, and CD117 in most cases and expression of CD34 in 9 of 15 assessed. These findings are generally consistent with a recent report in a Chinese population by Chou and colleagues.16 However, Chou et al16 reported that monocytic differentiation (FAB M4) and expression of CD13, CD14, and HLA-DR are unusual in AML with the IDH mutation. Our experience differs because 3 cases showed monocytic differentiation (FAB M5), and most cases expressed CD13 and HLA-DR.

Our study is the first to report bone marrow aspirate and biopsy findings of AML with IDH mutations in some detail. It is interesting to note that more than 80% of AML cases with the IDH1 or IDH2 mutation showed varying degrees of dysplastic findings in erythroid, myeloid, and megakaryocytic lineages. IDH1 mutations are shown to be early events in the development of astrocytomas and oligodendrogliomas. It seems plausible that IDH1 mutations are also an early event in myeloid neoplasia. A recent article reported IDH1 mutations in early myelodysplastic syndrome (MDS) and in secondary AML arising from MDS or MDS/myeloproliferative neoplasms (MPNs).31 In our study, 1 patient with AML with an IDH1R132 mutation had a history of MDS (case 12, Tables 3, 4, and 5). In 2 available studies on IDH1 mutations in MPN, one showed an IDH1 mutation with a coexisting JAK2 mutation, and the other failed to detect an IDH1 mutation in an MPN that transformed to leukemia.32,33 The involvement of IDH1 in myeloid neoplasms could be explained by a high requirement of glutamate, an essential amino acid that is converted to α-ketoglutarate and acts as a substrate for the mutant IDH1, as described subsequently, in myeloid cells.17,26,34 Indeed, acivicin, a glutamine antagonist, treatment decreased the growth and viability of a variety of leukemia cell lines.35

We detected equal distribution of R132H and R132C mutations in 12 AMLs with the IDH1R132 mutation. In the meta-analysis, R132H (73/146 [50.0%]) and R132C (45/146 [30.8%]) were the most frequent mutations detected. These findings suggest a different pattern of distribution of IDH1R132 mutations in AMLs than in gliomas, in which the R132H mutation constitutes about 90% of IDH1R132 mutations.12 In addition, we did not detect differences in TP53 mutation profiles of R132H and R132C AML cases, unlike those shown in gliomas.36 These findings suggest possible differences in the role of IDH1 mutations between glioma and AML. In fact, IDH1 mutations are associated with a good prognosis in glioma, whereas the limited amount of literature in AML suggests shorter disease-free survival in young patients with the IDH1-mutant/NPM1-mutant/FLT3-ITD–wild-type group.14,37

IDH1R132 mutations are frequently accompanied by NPM1, FLT3, CEBPA, RAS, and KIT mutations. We found NPM1 (5/11 [45%]) and FLT3-ITD (3/12 [25%]) mutations to be the 2 most frequent. Comparable frequencies of NPM1 (87/144 [60.4%]) and FLT3-ITD (29/146 [19.9%]) were detected in the meta-analysis. Unlike a recent study, we did not find statistically significant correlations of IDH1R132 and IDH2R172 mutations with NPM1-mutated and an FLT3-ITD–negative low-risk molecular profile.14 The frequent presence of coexisting mutations suggests that IDH1 mutations may act cooperatively in leukemogenesis. In contrast, no additional mutations were detected with IDH2R172 mutations in 4 cases. This finding is consistent with 13 cases in the only other available study.14

The details of a possible pathogenic role of IDH mutations are just beginning to emerge. Traditionally, up-regulation of a cancer-associated transcription factor, hypoxia-induced factor, has been considered to be a major pathogenic mechanism.26,38 More recently, accumulation of 2-hydroxyglutarate in the cells and the serum of patients with glioma and with AML with the IDH1 mutation has been shown.17,28,39,40 This could be used as a potential diagnostic test in the management of patients with IDH mutations.

All reported studies have used Sanger sequencing–based assays, which have a sensitivity of about 20%.9,1317 Because IDH1 and IDH2 are heterozygous mutations, a minimum blast count of 40% and/or enrichment of myeloblasts will be needed for the Sanger sequencing–based detection of IDH mutations. In practice, however, we have detected IDH mutations in samples with a minimum blast count of 22%. Because there is an indication that the mutation is retained at relapse, highly sensitive laboratory assays will be needed for monitoring therapy response and early relapses.16,39 The involvement of specific codons allows the use of sensitive approaches such as high-resolution melt curve analysis and pyrosequencing-based assays, which are currently under development in our laboratory.

IDH1R132 and IDH2R172 mutations represent a novel class of point mutations in CN AML. Both mutations occur predominantly in CN AML, leading to overproduction of an oncometabolite, 2-hydroxyglutarate. These mutations are heterozygous in nature and mutually exclusive. Despite many similarities, it is possible that molecularly and clinically, they represent distinct subgroups. IDH1R132 is frequently accompanied by other mutations, whereas IDH2R172 is commonly the only mutation detected. Most AML cases with an IDH mutation, IDH1 or IDH2, are morphologically classified as AML with or without myeloid maturation (FAB M1 or M2), have morphologic evidence of dysplasia, and have a nondistinctive myeloid immunophenotype.


Upon completion of this activity you will be able to:

  • describe the physiologic role of IDH1 and IDH2.

  • describe the nature of IDH1 and IDH2 mutations.

  • discuss the characteristics of acute myeloid leukemia with IDH1 and IDH2 mutations.

The ASCP is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The ASCP designates this educational activity for a maximum of 1 AMA PRA Category 1 Credit ™ per article. This activity qualifies as an American Board of Pathology Maintenance of Certification Part II Self-Assessment Module.

The authors of this article and the planning committee members and staff have no relevant financial relationships with commercial interests to disclose.

Questions appear on p 163. Exam is located at www.ascp.org/ajcpcme.


We acknowledge the excellent technical services of Neelima Reddy and Xue Ao in performing the IDH1 and IDH2 assays.


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