Comparative study of IDH1 mutations in gliomas by immunohistochemistry and DNA sequencing

Background

Mutations involving isocitrate dehydrogenase 1 (IDH 1) occur in a high proportion of diffuse gliomas, with implications on diagnosis and prognosis. About 90% involve exon 4 at codon 132, replacing amino acid arginine with histidine (R132H). Rarer ones include R132C, R132S, R132G, R132L, R132V, and R132P. Most authors have used DNA-based methods to assess IDH1 status. Preliminary studies comparing imunohistochemistry (IHC) with IDH1-R132H mutation-specific antibodies have shown concordance with DNA sequencing and no cross-reactivity with wild-type IDH1 or other mutant proteins. The present study compares results of IHC with DNA sequencing in diffuse gliomas.

Materials and methods

Fifty diffuse gliomas with frozen tissue samples for DNA sequencing and adequate tissue in paraffin blocks for IHC using IDH1-R132H specific antibody were assessed for IDH1 mutations.

Results

Concordance of findings between IHC and DNA sequencing was noted in 88% (44/50) cases. All 6 cases with discrepancy were immunopositive with DIA-H09 antibody. While in 3 of these 6 cases, DNA sequencing failed to reveal any mutations, R132L (arginine replaced by leucine) mutation was found in the rest 3 cases. Interestingly, of the immunopositive cases, 46.6% (14/30) showed immunostaining in only a fraction of tumor cells.

Conclusions

IHC is an easy and quick method of detecting IDH1-R132H mutations, but there may be some discrepancies between IHC and DNA sequencing. Although there were no false-negative cases, cross-reactivity with IDH1-R132L was seen in 3, a finding not reported thus far. Because of more universal availability of IHC over genetic testing, cross-reactivity and staining heterogeneity may have bearing over its use in detecting IDH1-R132H mutation in gliomas.     

Quantitative metabolome analysis profiles activation of glutaminolysis in glioma with IDH1 mutation

Isocitrate dehydrogenase 1 (IDH1), which localizes to the cytosol and peroxisomes, catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG) and in parallel converts NADP⁺ to NADPH. IDH1 mutations are frequently detected in grades 2–4 gliomas and in acute myeloid leukemias (AML). Mutations of IDH1 have been identified at codon 132, with arginine being replaced with histidine in most cases. Mutant IDH1 gains novel enzyme activity converting α-KG to d-2-hydroxyglutarate (2-HG) which acts as a competitive inhibitor of α-KG. As a result, the activity of α-KG-dependent enzyme is reduced. Based on these findings, 2-HG has been proposed to be an oncometabolite. In this study, we established HEK293 and U87 cells that stably expressed IDH1-WT and IDH1-R132H and investigated the effect of glutaminase inhibition on cell proliferation with 6-diazo-5-oxo-l-norleucine (DON). We found that cell proliferation was suppressed in IDH1-R132H cells. The addition of α-KG restored cell proliferation. The metabolic features of 33 gliomas with wild type IDH1 (IDH1-WT) and with IDH1-R132H mutation were examined by global metabolome analysis using capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). We showed that the 2-HG levels were highly elevated in gliomas with IDH1-R132H mutation. Intriguingly, in gliomas with IDH1-R132H, glutamine and glutamate levels were significantly reduced which implies replenishment of α-KG by glutaminolysis. Based on these results, we concluded that glutaminolysis is activated in gliomas with IDH1-R132H mutation and that development of novel therapeutic approaches targeting activated glutaminolysis is warranted.     

Predicting the likelihood of an isocitrate dehydrogenase 1 or 2 mutation in diagnoses of infiltrative glioma

Background

Several variables are associated with the likelihood of isocitrate dehydrogenase 1 or 2 (IDH1/2) mutation in gliomas, though no guidelines yet exist for when testing is warranted, especially when an R132H IDH1 immunostain is negative.

Methods

A cohort of 89 patients was used to build IDH1/2 mutation prediction models in World Health Organization grades II–IV gliomas, and an external cohort of 100 patients was used for validation. Logistic regression and backward model selection with the Akaike information criterion were used to develop prediction models.

Results

A multivariable model, incorporating patient age, glioblastoma multiforme diagnosis, and prior history of grade II or III glioma, was developed to predict IDH1/2 mutation probability. This model generated an area under the curve (AUC) of 0.934 (95% CI: 0.878, 0.978) in the external validation cohort and 0.941 (95% CI: 0.918, 0.962) in the cohort of The Cancer Genome Atlas. When R132H IDH1 immunostain information was added, AUC increased to 0.986 (95% CI: 0.967, 0.998). This model had an AUC of 0.947 (95% CI: 0.891, 0.995) in predicting whether an R132H IDH1 immunonegative case harbored a less common IDH1 or IDH2 mutation. The models were also 94% accurate in predicting IDH1/2 mutation status in gliomas from The Cancer Genome Atlas. An interactive web-based application for calculating the probability of an IDH1/2 mutation is now available using these models.

Conclusions

We have integrated multiple variables to generate a probability of an IDH1/2 mutation. The associated web-based application can help triage diffuse gliomas that would benefit from mutation testing in both clinical and research settings.     

Molecular genetics of adult grade II gliomas: towards a comprehensive tumor classification system

Adult grade II low-grade gliomas (LGG) are classified according to the WHO as astrocytomas, oligodendrogliomas or mixed gliomas. TP53 mutations and 1p19q codeletion are the main molecular abnormalities recorded, respectively, in astrocytomas and oligodendrogliomas and in mixed gliomas. Although IDH mutations (IDH1 or IDH2) are recorded in up to 85?% of low-grade gliomas, IDH negative gliomas do occur. We have searched for p53 expression, 1p19q codeletion and IDH status (immunohistochemical detection of the common R132H IDH1 mutation and IDH direct sequencing). Internexin alpha (INA) expression previously recorded to be associated with 1p19q codeletion (1p19q+) gliomas was also analysed. Low-grade gliomas were accurately classified into four groups: group 1, IDH+/p53?/1p19q?; group 2, IDH+/p53?/1p19q+; group 3, IDH+/p53+/1p19q?; and group 4, triple negative gliomas. In contrast to the WHO classification, this molecular classification predicts overall survival on uni- and multivariate analysis (P?=?0.001 and P?=?0.007, respectively). Group 4 carries the worst prognosis and group 2 the best. Interestingly, p53?+/INA? expression predicts lack of 1p19q codeletion (specificity 100?%, VPP 100?%). The combined use of these three molecular markers allow for an accurate prediction of survival in LGG. These findings could significantly modify LGG classification and may represent a new tool to guide patient-tailored therapy. Moreover, immunohistochemical detection of p53, INA and mR132H IDH1 expression could represent an interesting prescreening test to be performed before 1p19q codeletion, IDH1 minor mutation and IDH2 mutation detection.     

Detection of 2-hydroxyglutaric acid in vivo by proton magnetic resonance spectroscopy in U87 glioma cells overexpressing isocitrate dehydrogenase–1 mutation

The arginine 132 (R132) mutation of isocitrate dehydrogenase –1 (IDH1^R132) results in production of 2-hydroxyglutarate (2-HG) and is associated with a better prognosis compared with wild-type (WT) in glioma patients. The majority of lower-grade gliomas express IDH1^R132, whereas this mutation is rare in grade IV gliomas. The aim of this study was to noninvasively investigate metabolic and physiologic changes associated with the IDH1 mutation in a mouse glioma model. Using a 7T magnet, we compared MRI and proton magnetic resonance spectroscopy (MRS) in U87 glioma cells overexpressing either the mutated IDH1^R132 or IDH1 wild-type (IDH1^WT) gene in a mouse flank xenograft model. Flank tumors overexpressing IDH1^R132 showed a resonance at 2.25 ppm corresponding to the 2-HG peak described for human IDH1^R132 gliomas. WT tumors lacked this peak in all cases. IDH1 mutant tumors demonstrated significantly reduced glutamate by in vivo MRS. There were no significant differences in T₂, apparent diffusion coefficient (ADC), or perfusion values between the mutant and IDH1^WT tumors. The IDH1^R132 mutation results in 2-HG resonance at 2.25 ppm and a reduction of glutamate levels as determined by MRS. Our results establish a model system where 2-HG can be monitored noninvasively, which should be helpful in validating 2-HG levels as a prognostic and/or predictive biomarker in glioma.     

Prevalence of IDH1/2 Mutations in Different Subtypes of Glioma in the North-East Population of Morocco

Background: Genetic alterations in gliomas have increasing importance for classification purposes. Thus, we are especially interested in studying IDH mutations which may feature potential roles in diagnosis, prognosis and response to treatment. Our aim was to investigate IDH mutations in diffuse glioma patients diagnosed in university hospital centre of Fez in Morocco. Materials and Methods: IDH1 codon 132 and IDH2 codon 172 were direct-sequenced in 117 diffuse glioma samples diagnosed and treated in University Hospital Hassan II between 2010 and 2014. Results: The R132H IDH1 mutation was identified in 43/117 tumor samples and R172K IDH2 mutation was detected in only one anaplastic oligodendroglioma. IDH mutations were observed in 63.2% of astrocytomas, 73.3% of diffuse oligodendrogliomas and 12.90% of glioblastomas. Conclusions: Our results confirmed other studies published earlier for other populations with some small discrepancies.     

Histopathological malignant progression of grade II and III gliomas correlated with IDH1/2 mutation status

The impact of isocitrate dehydrogenase (IDH1/2) mutations on the malignant progression of gliomas was investigated by comparing the histopathological features of 53 grade II and III gliomas after recurrence according to the IDH1/2 status. We identified IDH1/2 mutations in 44.4?% (16 of 36) of astrocytic tumors and 70.6?% (12 of 17) of oligodendroglial tumors. Histopathological malignant progression was observed in 68.8?% (11 in 16) and 55?% (11 in 20) of astrocytic tumors with and without IDH1/2 mutations, respectively. There were 8 secondary glioblastomas (GBM) that had progressed from 5 diffuse astrocytomas (DA) and 3 anaplastic astrocytomas (AA) with IDH1/2 mutations. Seven secondary GBMs were derived from 3 DAs and 4 AAs with wild-type IDH1/2. Malignant progression was observed in 47.1?% (8 of 17) of oligodendroglial tumors. All 12 oligodendroglial tumors with IDH1/2 mutations remained as such without progressing to GBM, whereas 3 of the 5 oligodendroglial tumors without IDH1/2 mutations progressed to GBM at recurrence. In conclusion, grade II and III gliomas developed to more malignant histological types, irrespective of the IDH1/2 mutation status, and the monitoring of the IDH1/2 status could be of value to predict the development of GBM in patients with oligodendroglial tumors.     

IDH1 and IDH2 mutations,immunohistochemistry and associations in a series of brain tumors

A total of 343 brain tumors were studied for IDH1 and IDH2 mutations by direct sequencing and for protein expression by immunohistochemistry with mIDH1^R132H antibody. Of these, 287 were gliomas (17 pilocytic astrocytomas, 13 grade II and 5 grade III astrocytomas, 167 primary (pGBMs) and 19 secondary (sGBMs) glioblastomas, 36 grade II and 26 grade III oligodendrogliomas and 4 grade II–III oligoastrocytomas). In gliomas, IDH1 mutations at codon R132 were identified in 22.3%, of which 93.7% were c.395G>A (p.R132H). Mutations were more frequent in oligodendrogliomas (53.2%) than in astrocytic tumors (22.8%) and in sGBMs (84.2%) upon pGBMs (1.8%). There was a statistically significant correlation between mIDH1^R132H antibody immunostaining and the relevant mutation c.395G>A (p.R132H) (P = 0.0001). No mutations were identified in non-glial tumors which were also negative to immunohistochemistry, with the exception of one PNET. A c.515G>T (p.R172M) mutation of the IDH2 gene was only identified in a grade II oligodendroglioma patient which was wild-type for IDH1. A direct correlation with MGMT promoter hypermethylation status and an inverse correlation with EGFR amplification was found, whereas the relationships with 1p/19q co-deletion and TP53 mutations only showed a trend toward correlation. In all gliomas, a positive correlation was found between IDH1 mutations and a young age (P = 0.0001). In contrast, a correlation with overall survival could only be obtained in low-grade gliomas. Immunohistochemistry appeared to be useful in differential diagnoses, especially toward non-tumor pathologic nervous tissue, and in recognizing infiltrating glioma cells. The mIDH1^R132H antibody positivity was complementary with Cyclin D1 expression.     

Molecular analysis of diffuse intrinsic brainstem gliomas in adults

Diffuse intrinsic brainstem gliomas (DIBG) account for 1–2 % of adult gliomas. Their biological characteristics are scarcely understood and whether DIBG are biologically different from supratentorial gliomas remains to be established. We analyzed 17 DIBG samples for IDH1 R132H, alpha internexin, p53, and Ki67 expression, and, in a subset with sufficient DNA amount, for IDH1 and histone H3 mutational status, genomic profiling and MGMT promoter methylation status. A series of 738 adult supratentorial gliomas was used for comparison. Median age at diagnosis was 41 years (range 18.9–65.3 years). Median overall survival was 48.7 months (57 months for low-grade vs. 16 months for high-grade gliomas, p < 0.01). IDH1 sequencing revealed two mutations (IDH1 ^R132G , IDH1 ^R132C ) out of 7 DIBG whereas the R132H IDH1 enzyme was detected in 1/17 DIBG, suggesting that IDH1 mutations are mostly non R132H in DIBG (2/2), in contrast to supratentorial gliomas (31/313; p = 0.01). Mutations in histone genes H3F3A (encoding H3.3) and HIST1H3B (encoding H3.1) were found in 3/8 (37.5 %) of the DIBG (two H3F3A ^K27M and one HIST1H3B ^K27M ) versus 6/205 (2.9 %) of the supratentorial high-grade gliomas (four H3F3A ^G34R and two H3F3A ^K27M ) (p = 0.002). The CGH array showed a higher frequency of chromosome arm 1q gain, 9q gain and 11q loss in DIBG compared to the supratentorial high-grade gliomas, which had a less frequent chromosome 7 gain, and a less frequent chromosome 10 loss. No EGFR amplification was found. These data suggest that adult DIBG differ from adult supratentorial gliomas. In particular, histone genes (H3F3A ^K27M , HIST1H3B ^K27M ) mutations are frequent in adult DIBG whereas IDH1 ^R132H mutations are rare.     

Absence of R140Q mutation of isocitrate dehydrogenase 2 in gliomas and breast cancers

Somatic mutations of isocitrate dehydrogenase (IDH)-1 and IDH2 proteins have been described in gliomas. The mutations target the R132 amino acid residue and the R172 residue in IDH1 and IDH2, respectively. The same mutations were observed in acute myeloid leukemias with normal karyotype, but a new mutation in IDH2 (R140Q substitution) was detected in malignant myeloid diseases and appears to be the most frequent IDH mutation in these pathologies. To the best of our knowledge, no study thus far has reported the presence of this R140Q mutation in IDH2 in tumors of the nervous system and breast cancers. We evaluated IDH1 and IDH2 exon 4 in 48 low-grade gliomas, 58 primary glioblastomas and 94 breast cancers to evaluate the frequency of mutation and investigated the R140Q substitution in IDH2. The results were compared to our recently obtained results in hematopoietic diseases. The frequency of IDH1 and IDH2 mutations in our panel of gliomas was similar to previously reported mutations. No IDH2 R140 mutation was observed. Compared to hematopoietic diseases, the IDH2 R172 mutation was also more rare and IDH1 mutations more prominent in tumors of the nervous system. No IDH1 or IDH2 mutation was detected in the 94 breast cancer samples. Thus, the IDH2 R140 mutation appears to be restricted to hematopoietic diseases.     

Significance of IDH mutations varies with tumor histology, grade, and genetics in Japanese glioma patients

Mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 are found frequently in malignant gliomas and are likely involved in early gliomagenesis. To understand the prevalence of these mutations and their relationship to other genetic alterations and impact on prognosis for Japanese glioma patients, we analyzed 250 glioma cases. Mutations of IDH1 and IDH2 were found in 73 (29%) and 2 (1%) cases, respectively. All detected mutations were heterozygous, and most mutations were an Arg132His (G395A) substitution. IDH mutations were frequent in oligodendroglial tumors (37/52, 71%) and diffuse astrocytomas (17/29, 59%), and were less frequent in anaplastic astrocytomas (8/29, 28%) and glioblastomas (13/125, 10%). The pilocytic astrocytomas and gangliogliomas did not have either mutation. Notably, 28 of 30 oligodendroglial tumors harboring the 1p/19q co-deletion also had an IDH mutation, and these alterations were significantly correlated (P < 0.001). The association between TP53 and IDH mutation was significant in diffuse astrocytomas (P = 0.0018). MGMT promoter methylation was significantly associated with IDH mutation in grade 2 (P < 0.001) and grade 3 (P = 0.02) gliomas. IDH mutation and 1p/19q co-deletion were independent favorable prognostic factors for patients with grade 3 gliomas. For patients with grade 3 gliomas and without 1p/19q co-deletion, IDH mutation was strongly associated with increased progression-free survival (P < 0.0001) and overall survival (P < 0.0001), but no such marked correlation was observed with grade 2 gliomas or glioblastomas. Therefore, IDH mutation would be most useful when assessing prognosis of patients with grade 3 glioma with intact 1p/19q; anaplastic astrocytomas account for most of these grade 3 gliomas.     

IDH1 mutations are present in the majority of common adult gliomas but rare in primary glioblastomas

We screened exon 4 of the gene isocitrate dehydrogenase 1 (NADP+), soluble (IDH1) for mutations in 596 primary intracranial tumors of all major types. Codon 132 mutation was seen in 54% of astrocytomas and 65% of oligodendroglial tumors but in only 6% of glioblastomas (3% of primary and 50% of secondary glioblastomas). There were no mutations in any other type of tumor studied. While mutations in the tumor protein p53 gene (TP53) and total 1p/19q deletions were mutually exclusive, IDH1 mutations were strongly correlated with these genetic abnormalities. All four types of mutant IDH1 proteins showed decreased enzymatic activity. The data indicate that IDH1 mutation combined with either TP53 mutation or total 1p/19q loss is a frequent and early change in the majority of oligodendroglial tumors, diffuse astrocytomas, anaplastic astrocytomas, and secondary glioblastomas but not in primary glioblastomas.     

Overexpression of isocitrate dehydrogenase mutant proteins renders glioma cells more sensitive to radiation

Mutations in isocitrate dehydrogenase 1 (IDH1) or 2 (IDH2) are found in a subset of gliomas. Among the many phenotypic differences between mutant and wild-type IDH1/2 gliomas, the most salient is that IDH1/2 mutant glioma patients demonstrate markedly improved survival compared with IDH1/2 wild-type glioma patients. To address the mechanism underlying the superior clinical outcome of IDH1/2 mutant glioma patients, we investigated whether overexpression of the IDH1^R132H protein could affect response to therapy in the context of an isogenic glioma cell background. Stable clonal U87MG and U373MG cell lines overexpressing IDH1^WT and IDH1^R132H were generated, as well as U87MG cell lines overexpressing IDH2^WT and IDH2^R172K. In vitro experiments were conducted to characterize baseline growth and migration and response to radiation and temozolomide. In addition, reactive oxygen species (ROS) levels were measured under various conditions. U87MG-IDH1^R132H cells, U373MG-IDH1^R132H cells, and U87MG-IDH2^R172K cells demonstrated increased sensitivity to radiation but not to temozolomide. Radiosensitization of U87MG-IDH1^R132H cells was accompanied by increased apoptosis and accentuated ROS generation, and this effect was abrogated by the presence of the ROS scavenger N-acetyl-cysteine. Interestingly, U87MG-IDH1^R132H cells also displayed decreased growth at higher cell density and in soft agar, as well as decreased migration. Overexpression of IDH1^R132H and IDH2^R172K mutant protein in glioblastoma cells resulted in increased radiation sensitivity and altered ROS metabolism and suppression of growth and migration in vitro. These findings provide insight into possible mechanisms contributing to the improved outcomes observed in patients with IDH1/2 mutant gliomas.     

Analysis of IDH1 and IDH2 mutations in Japanese glioma patients

A recent study reported on mutations in the active site of the isocitrate dehydrogenase 1 ( IDH1 ) gene in several types of gliomas. All mutations detected resulted in an amino acid exchange at position 132. We analyzed the genomic region spanning wild-type R132 of IDH1 by direct sequencing in 125 glial tumors. A total of 39 IDH1 mutations were observed. Mutations of the IDH2 gene, homologous to IDH1 , were often detected in gliomas without IDH1 mutations. In the present study, R172 mutation of the IDH2 gene was detected in one anaplastic astrocytoma. IDH1 or IDH2 mutations were frequently in oligodendrogliomas (67%), anaplastic astrocytomas (62%), anaplastic oligoastrocytomas (75%), anaplastic oligodendrogliomas (50%), secondary glioblastomas (67%), gangliogliomas (38%), and anaplastic gangliogliomas (60%). Primary glioblastomas were characterized by a low frequency of mutations (5%) at amino acid position 132 of IDH1 . Mutations of the IDH1 or IDH2 genes were significantly associated with improved outcome in patients with anaplastic astrocytomas. Our data suggest that IDH1 or IDH2 mutation plays a role in early tumor progression of several types of glioma and might arise from a common glial precursor. The infrequency of IDH1 mutation in primary glioblastomas revealed that these subtypes are genetically distinct entities from other glial tumors. ( Cancer Sci  2009; 100: 1996–1998)     

Mechanism for enhanced 5-aminolevulinic acid fluorescence in isocitrate dehydrogenase 1 mutant malignant gliomas

Fluorescence-guided surgery using 5-aminolevulinic acid (5-ALA) has become the main treatment modality in malignant gliomas. However unlike glioblastomas, there are inconsistent result about fluorescence status in WHO grade III gliomas. Here, we show that mutational status of IDH1 is linked to 5-ALA fluorescence. Using genetically engineered malignant glioma cells harboring wild type (U87MG-IDH1^WT) or mutant (U87MG-IDH1^R132H) IDH1, we demonstrated a lag in 5-ALA metabolism and accumulation of protoporphyrin IX (PpIX) in U87MG-IDH1^R132H cells. Next, we used liquid chromatography–mass spectrometry (LC-MS) to screen for tricarboxylic acid (TCA) cycle-related metabolite changes caused by 5-ALA exposure. We observed low baseline levels of NADPH, an essential cofactor for the rate-limiting step of heme degradation, in U87MG-IDH1^R132H cells. High levels of NADPH are required to metabolize excessive 5-ALA, giving a plausible reason for the temporarily enhanced 5-ALA fluorescence in mutant IDH1 cells. This hypothesis was supported by the results of metabolic screening in human malignant glioma samples. In conclusion, we have discovered a relationship between enhanced 5-ALA fluorescence and IDH1 mutations in WHO grade III gliomas. Low levels of NADPH in tumors with mutated IDH1 is responsible for the enhanced fluorescence.     

Mutant IDH1 is required for IDH1 mutated tumor cell growth

Frequent somatic hotspot mutations in isocitrate dehydrogenase 1 (IDH1) have been identified in gliomas, acute myeloid leukemias, chondrosarcomas, and other cancers, providing a likely avenue for targeted cancer therapy. However, whether mutant IDH1 protein is required for maintaining IDH1 mutated tumor cell growth remains unknown. Here, using a genetically engineered inducible system, we report that selective suppression of endogenous mutant IDH1 expression in HT1080, a fibrosarcoma cell line with a native IDH1R132C heterozygous mutation, significantly inhibits cell proliferation and decreases clonogenic potential. Our findings offer insights into changes that may contribute to the inhibition of cell proliferation and offer a strong preclinical rationale for utilizing mutant IDH1 as a valid therapeutic target.     

Molecular Investigation of Isocitrate Dehydrogenase Gene (IDH) Mutations in Gliomas: First Report of IDH2 Mutations in Indian Patients

Recent genome wide sequencing has identified mutations in IDH1/IDH2 predominantly in grade II-III gliomasand secondary glioblastomas which are associated with favorable clinical outcome. These mutations have becomemolecular markers of significant diagnostic and prognostic relevance in the assessment of human gliomas. In thecurrent study we evaluated IDH1 (R132) and IDH2 (R172) in 32 gliomas of various grades and tumor subtypes.Sequencing analysis revealed R132H mutations in 18.7% tumors, while none of the cases showed IDH2 (R172)mutations. The frequency of IDH1 mutations was higher in females (21.4%) than males (11.1%), and it wassignificantly higher in younger patients. Histological analyses demonstrated presence of necrosis and microvascular proliferation in 69% and 75% respectively. Interestingly, IDH1 mutations were predominantly presentin non-necrotic tumors as well as in cases showing microvascular proliferation. Of the six IDH1 positive cases,three were glioblastomas (IV), and one each were anaplastic oligoastrocytoma (III), anaplastic oligodendrogliomaIII (n=1) and diffuse astrocytoma. In conclusion, IDH1 mutations are quite frequent in Indian glioma patientswhile IDH2 mutations are not observed. Since IDH mutations are associated with good prognosis, their use inroutine clinical practice will enable better risk stratification and management of glioma patients.     

Comparison of immunohistochemistry, DNA sequencing and allele-specific PCR for the detection of IDH1 mutations in gliomas

Previous studies have identified mutations of the isocitrate dehydrogenase 1 (IDH1) gene in more than 70% of World Health Organization (WHO) grade II and III gliomas. The most frequent mutation leads to a specific amino acid change from arginine to histidine at codon 132 (c.395G>A, p.R132H). IDH1 mutated tumors have a better prognosis than IDH1 non-mutated tumors. The aim of our study was to evaluate and compare the methods of mIDH1 R132H immunohistochemistry, allele-specific PCR and DNA sequencing for determination of IDH1 status. We performed a retrospective study of 91 patients with WHO grade II (n=43) and III (n=48) oligodendrogliomas. A fragment of exon 4 spanning the sequence encoding the catalytic domain of IDH1, including codon 132, was amplified and sequenced using standard conditions. Allele-specific amplification was performed using two forward primers with variations in their 3' nucleotides such that each was specific for the wild-type or the mutated variant, and one reverse primer. Immunohistochemistry was performed with mouse monoclonal mIDH1 R132H. DNA was extracted from FFPE sections following macrodissection. IDH1 mutations were found in 55/90 patients (61.1%) by direct sequencing. R132H mutations were found in 47/55 patients (85.4%). The results of the allele-specific PCR positively correlated with those from DNA sequencing. Other mutations (p.R132C, p.R132S and pR132G) were found by DNA sequencing in 3, 3 and 2 tumors, respectively (8/55 patients, 14.6%). mIDH1 R132H immunostaining was found in the 47 patients presenting the R132H mutation (sensitivity 47/47, 100% for this mutation). None of the tumors presenting a wild-type IDH1 gene were stained (specificity 35/35, 100%). Our results demonstrate that immunohistochemistry using the mIDH1 R132H antibody and allele-specific amplification are highly sensitive techniques to detect the most frequent mutation of the IDH1 gene.     

Analysis of NADP+-dependent isocitrate dehydrogenase-1/2 gene mutations in pediatric brain tumors: report of a secondary anaplastic astrocytoma carrying the IDH1 mutation

Somatic mutations of the isocitrate dehydrogenase-1 gene (IDH1), most commonly resulting in replacement of arginine at position 132 by histidine (p.R132H), have been reported for WHO grade II and III diffuse gliomas and secondary glioblastomas. We investigated IDH1/2 mutations in a retrospective series of 165 pediatric brain tumors, including atypical teratoid/rhabdoid tumors (AT/RT) and choroid plexus tumors, which had not previously been investigated. Mutation analysis was performed by use of pyrosequencing and, additionally, data were validated for a cohort of 70 gliomas from among the series by use of the arrayed primer extension technique. We identified one tumor which harbored mutation of IDH1 at codon 132 and no alteration was identified in the matched-germline DNA. No IDH2 mutations were detected. Most noteworthy, the IDH1 mutant tumor was an anaplastic astrocytoma involving the cortex in the left frontal lobe which appeared seven years after radiation treatment for an extensive sellar/suprasellar craniopharyngioma. This anaplastic astrocytoma was regarded as secondary to radiation treatment because it seemed to originate within the irradiation field that received a dose varying from a maximum of 30.6 Gy of 4 MV X-rays down to very few Gy of lower-energy scattered radiation. In this work our observations agree with those in previous reports showing the rarity of IDH1/2 mutations in childhood tumors. The interesting identification of an IDH1 mutation in a radiation-induced secondary malignant glioma raises the likelihood that these types of tumor may develop IDH1/2 mutations. Thus, caution is needed when dealing with these tumors, and further genetic analysis is warranted.     

Combination genetic signature stratifies lower-grade gliomas better than histological grade

We studied if combination genetic signature potentially stratifies lower-grade gliomas better than histology by investigating 214 lower-grade gliomas for IDH1/2 and TERTp mutations, 1p/19q codeletion and EGFR amplification as to their impact on prognostication. Prognostic association of grading was independent of other prognostic variables including age, histological type, IDH1/2, 1p/19q and TERTp status. No single marker, including IDH1/2, superseded grading in prognostication, indicating grading was still a very important tool. Prognosis was most favorable in 31.7% of patients with IDH1/2 mutation and either 1p/19q codeletion or TERTp mutation (IDHmut-OT), intermediate in 45.8% of patients with IDH1/2 mutation only (IDHmut) and 16.9% of patients without any of the alterations (IDHwt), and poorest in 5.6% of patients with wild-type IDH1/2 and either TERTp mutation or EGFR amplification (IDHwt-ET). Our results suggested not all IDH1/2 wild-type lower-grade gliomas are aggressive and additional biomarkers are required to identify glioblastoma-equivalent tumors. Multivariate analysis revealed independent prognostic values of grading and genetic signature. Grade II IDHwt-ET gliomas exhibited shorter survival than IDH1/2 mutated grade III gliomas, suggesting combination genetic signature potentially superseded grading in prognostication. In summary, biomarker-based stratification is useful in the diagnosis and prognostication of lower-grade gliomas, and should be used together with grading.