Different IDH Mutation and 1p/19q Codeletion Rates between Astrocytoma, Oligodendrocytoma and Mixed Gliomas

Abstract

Background: The mutations of isocitrate dehydrogenase (IDH-mt) and loss of chromosome 1p and 19q (1p/19q codeleltion) have been used in diagnosis of gliomas, especially in identification of oligodendrocytoma. We have performed and analyzed genetic detections with 3 types of gliomas diagnosed by morphological methods. Methods: The DNA extracted from tumor tissues of 136 patients with astrocytoma, oligodendrogliomas and mixed gliomas were subjected to fluorescence PCR capillary electrophoresis for detection of 1p and 19q codeletion and DNA sequencing for IDH mutations. The results were analyzed by SPSS 22.0 software with chi-square test for significant difference (p<0.05). Results: Among 136 patients, 77 cases (56.6%) were histopathologically diagnosed as astrocytoma (AA, WHO ), 11 (8.0%) as pure oligodendroglial tumors including both low-grade oligodendrogliomas (OA, WHO ) and anaplastic oligodendrogliomas (AOA, WHO ), and 48 (35.4%) as mixed glioma with the features of OA and AA in the same tumor tissue. The genetic detections have shown that 39 cases (28.7%) were with IDH mutations (37 IDH1-mt p.R132H and 2 IDH2-mt), and 47 (34.6%) with 1p/19q co-deletion. The significant differences of the IDH mt (p=0.008) and 1p/19q codeletion (p=0.011) were between 3 pathological types of astrocytoma, oligodendrogliomas and mixed glioms (p=0.008). In three glioma types, the rate of 1p/19q co-deletion was highest in the group of oligodendrogliomas (p=0.040). In 11 patients who were histopathologically diagnosed as oligodendroglioma, only 5 cases meet the WHO criterion that requires the presence of both 1p/19q codeletion and IDH1-mt or IDH2-mt. Conclusion: The rate of IDH mutations and 1p/19q codeletion is significantly different in three groups of gliomas, and highest in oligodendrogliomas. Some cases of oligodendrogliomas with only IDH mutation but without 1p/19q codeletion. Therefore, the genetic detections should be complemented for diagnosis of gliomas.