Characteristics of the isocitrate dehydrogenase gene and telomerase reverse transcriptase promoter mutations in gliomas in Chinese patients.

Abstract Objectives To explore the characteristics of IDH and TERT promoter mutations in gliomas in Chinese patients. Methods A total of 124 Chinese patients with gliomas were enrolled to study the frequencies of mutations in isocitrate dehydrogenase (IDH) and telomerase reverse transcriptase promoter (TERTp). Among the 124 patients, 59 patients were enrolled to study the classification of gliomas based on mutations in IDH and TERTp. Results Isocitrate dehydrogenase mutations are positively correlated with a good prognosis but mutations in TERTp cannot predict prognoses independently. The combined analysis of the mutations of IDH and TERTp can predict the prognosis more accurately. Patients with IDH and TERTp glioma mutations have the best prognosis, followed by only IDH mutation patients and only TERTp mutation patients, which have the worst prognosis. IDH and TERTp mutations occur frequently in males, younger patients or lower‐grade patients. In contrast, only TERTp mutations occur frequently in females, older patients or higher‐grade patients. Conclusions Patients with IDH and TERTp glioma mutations have the best prognosis, and only IDH mutation patients and only TERTp mutation patients have the worst prognosis. Moreover, the molecular classification of gliomas by mutations of IDH and TERTp is not suitable for pediatric patients.


| Patients and samples
Tumor tissue samples for genetic testing were taken from 124 patients who underwent surgeries at the Shanxi Provincial People's Hospital from April 2017 to November 2017. The ethics committee of the Shanxi Provincial People's Hospital approved the study.
Written informed consent was obtained from all participants in the study.

| DNA extraction
We performed DNA extraction from serial thick sections cut from the tumor tissue samples and control sections. Pathologists evaluated the invasive tumor content to ensure more than 50% of the cells were tumor cells. The DNA was isolated from the FFPE using the HiPure FFPE DNA Kit (D3126, Magen). Sanger sequencing (Shanghai Tongshu Biotechnology Co., Ltd) was used to determine the frequency of mutations in IDH1, IDH2, and TERTp (Sanger, Nicklen, & Coulson, 1997

| Demographic data of the patients
Among the 124 patients, only 67 patients had detailed clinical data.
According to 2016 CNS WHO, the patients were classified as grade I   Figure 1). For gliomas with mutations in both IDH and TERTp, the distribution between pathological grades (p = .001) was statistically significant, but there were no significant differences between the groups of different gender (p = .262) or age (p = .128). There was only 6.8% (4/59) of gliomas with only IDH mutations, and there were no significant differences between the groups of different gender

| D ISCUSS I ON
Gliomas with IDH mutations have been reported to have a good prognosis (3) and our results also revealed a positive correlation between IDH mutation and a better OS in the Chinese population. IDH mutations occur in 80% of clinically diagnosed grade II and III gliomas but are rare in grade IV (Andronesi et al., 2012;Turcan et al., 2012). In our study, among the gliomas with IDH mutations, the lower-grade (grade II or III) gliomas accounted for 85.7% (18/21) and the highergrade (grade IV) gliomas accounted for 14.3% (3/21). About 95% of all IDH mutations are in IDH1, and among those, over 90% are type R132H and less common mutants such as R132C, R132G, R132S, and R132L have also been identified (Balss et al., 2008;Hartmann et al., 2009;Ichimura et al., 2009;Pusch et al., 2014). In our study, mutations in R132H and R132S were 97.7% and 2.3%, respectively.
In our study, only 9.5% (2/21) of patients with IDH mutated gliomas were older than 55 years. The incidence of IDH mutations in males was twice that in females, but the results did not show statistical significance.
Several studies have proposed that mutations in TERTp in glioblastomas are independently associated with a poor prognosis (Malkki, 2014;Simon et al., 2015). However, in studies involving different gliomas, Pekmezci et al. (2017) revealed that the wild-type TERTp group was associated with a good prognosis only in wild-type IDH1/IDH2 and the TERTp and IDH co-altered group also had a better prognosis than found in the IDH mutation group. In our study, when we only considered the relationship between OS and TERTp mutation status, the wild-type TERTp group showed worse prognosis than the TERTp mutation group, indicating that TERTp could not predict the prognosis independently (Figure 2b). TERTp F I G U R E 1 Prevalence of the glioma molecular groups in different grades. Bars Grades II-IV, Grades II-III, and Grades IV represent overall view, lower grade, and higher grade, respectively. * The distribution of different molecular groups between lower grade and higher grade was statistically significant F I G U R E 2 Kaplan-Meier estimates of overall survival of the gliomas with (a) IDH mutations; (b) TERTp mutations; (c) molecular classification based on IDH and TERTp mutation mutations occur in 70%-83% of glioblastomas, 74%-78% of oligodendrogliomas, 25%-50% of oligoastrocytomas, and 10%-25% of astrocytomas (Pekmezci et al., 2017). Our results showed that TERTp mutations occurred in 76.9% of glioblastomas, 75% of oligodendrogliomas, and 63.2% of astrocytomas. Moreover, in our study, neither IDH mutations nor TERTp mutations occurred in pediatric gliomas. Previous studies also reported a low incidence of IDH mutations or TERTp mutations in pediatric gliomas: 16.3% and 0.5%, respectively (Koelsche et al., 2013;Pollack et al., 2011). This result indicates that IDH or TERTp mutations are not characteristic in pediatric patients with gliomas.
The IDH and TERTp mutation status is often taken into consideration in molecular classification studies of gliomas (Kim et al., 2018;Pekmezci et al., 2017). Patients with IDH and TERTp glioma mutations have the best prognosis whereas only IDH mutation patients and only TERTp mutation patients have the worst prognosis (Robinson & Kleinschmidt-DeMasters, 2017

ACK N OWLED G M ENTS
We are particularly grateful to all the people who have given us help on our article.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no conflict of interest.

AUTH O R S ' CO NTR I B UTI O N S
CXQ, HMG, and XCS acquired data. CXQ, HMG, and DWH drafted the manuscript. DWH, HB, LQZ, and XCS contributed substantially to its revision. All authors take responsibility for the paper as a whole. All authors read and approved the final manuscript.

E TH I C S A PPROVA L A N D CO N S E NT TO PA RTI CI PATE
I confirm that I have read the Editorial Policy pages. This study was conducted with approval from the Ethics Committee of Shanxi Provincial People's Hospital. This study was conducted in accordance with the declaration of Helsinki.

DATA AVA I L A B I L I T Y S TAT E M E N T
We declared that materials described in the manuscript, including all relevant raw data, will be freely available to any scientist wishing to use them for noncommercial purposes, without breaching participant confidentiality.