A pyrosequencing-based assay for the rapid detection of IDH1 mutations in clinical samples

Mutations of both the IDH1 and IDH2 (isocitratedehydrogenase enzyme 1 and 2) genes have recently been described in cases of human glioma. Since IDH1 mutations have been associated with better clinical outcome, they are suitable predictive markers for adult glioma patients. We have developed a pyrosequencing assay that allows both the sensitive and rapid detection of mutant IDH1 alleles in DNA extracted from formalin-fixed, paraffin-embedded tissues. PCR products that span exon 4 of IDH1 were used as a template for pyrosequencing. For validation, PCR products were additionally cloned and sequenced conventionally by Sanger sequencing. Sensitivity was measured by titration of wild-type and mutant sequences. PCR kinetic experiments were performed to investigate the influences of PCR cycle number on the accuracy of the assay. We found that a minimum of 5% of mutant IDH1 alleles can easily be detected with the pyrosequencing approach. So far, there are few data regarding IDH1 mutation status in high-grade gliomas of childhood. Therefore, we applied this assay to 47 pediatric high-grade glioma samples (age range 6 weeks to 23 years). Mutations were found in 5/14 astrocytoma III and in 6/33 glioblastomas. In conclusion, we have developed a pyrosequencing-based assay for the detection of mutations at the hotspot regions of IDH1 and provide proof for its applicability as a molecular diagnostic assay for clinical samples.