title: Comparative study of IDH1 mutations in gliomas by immunohistochemistry and DNA sequencing.
abstract: 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.
  
  
  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.
authors.affiliation: Department of Pathology, All India Institute of Medical Sciences, New Delhi 110029, India.
authors.forename: Shipra
authors.initials: S
authors.lastname: Agarwal
authors.forename: Mehar Chand
authors.initials: MC
authors.lastname: Sharma
authors.forename: Prerana
authors.initials: P
authors.lastname: Jha
authors.forename: Pankaj
authors.initials: P
authors.lastname: Pathak
authors.forename: Vaishali
authors.initials: V
authors.lastname: Suri
authors.forename: Chitra
authors.initials: C
authors.lastname: Sarkar
authors.forename: Kunzang
authors.initials: K
authors.lastname: Chosdol
authors.forename: Ashish
authors.initials: A
authors.lastname: Suri
authors.forename: Shashank Sharad
authors.initials: SS
authors.lastname: Kale
authors.forename: Ashok Kumar
authors.initials: AK
authors.lastname: Mahapatra
authors.forename: Pankaj
authors.initials: P
authors.lastname: Jha
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000235:genetics* / Q000378:metabolism; D001932:Brain Neoplasms / Q000235:genetics* / Q000378:metabolism; D002648:Child; D005260:Female; D005910:Glioma / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007124:Immunoenzyme Techniques; D007521:Isocitrate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D050505:Mutant Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D060787:Neoplasm Grading; D017422:Sequence Analysis, DNA; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor; D050505:Mutant Proteins; D007521:Isocitrate Dehydrogenase; C543588:IDH1 protein, human
keywords: DNA sequencing; IDH1-R132H; IDH1-R132L; diffuse gliomas; immunohistochemistry