We highlight the genetic aberrations recently discovered in isocitrate dehydrogenase, alpha thalassemia/mental retardation syndrome X-linked, death-domain-associated protein, histone H3.3, and telomerase reverse transcriptase and discuss how these mutations lead to unexpected changes in the epigenetic landscape in gliomas.
We review the current state of diagnostic molecular markers for gliomas, focusing on isocitrate dehydrogenase 1 or 2 (IDH1/IDH2) gene mutation, α-thalassemia/mental retardation syndrome X-linked (ATRX) gene mutation, 1p/19q co-deletion and telomerase reverse transcriptase (TERT) promoter mutation in adult tumors, as well as v-raf murine sarcoma viral oncogene homolog B1 (BRAF) and H3 histone family 3A (H3F3A) aberrations in pediatric gliomas.
The results indicate immunohistochemical analysis including IDH1/2, ATRX, p53, and Ki-67 index is valuable for the classification of diffuse gliomas, which is useful for the evaluation of prognosis, especially Grade III gliomas and lower-grade gliomas (i.e., Grade II and III).
Our results showed ATRX-related regulatory functions of the combined profiles from DNA methylation and mRNA expression in astrocytic tumors, and delineated that loss of ATRX impacted biological behaviors of astrocytic tumor cells, providing important resources for future dissection of ATRX role in glioma.
Tumor grade was correlated with the mutational load (the number of non-silent mutations) of the tumor: grade II diffuse gliomas harbour fewer genetic changes than grade III or IV, even within defined molecular subtypes (e.g.ATRX mutated diffuse gliomas).
Loss of α-thalassemia/mental retardation syndrome X-linked (ATRX) or death domain-associated protein 6 (DAXX) expression has been implicated in the pathogenesis of alternative telomere lengthening in pancreatic endocrine neoplasm and glioma.
Those tumors that lacked LOH 1p19q showed a high frequency of IDH1 mutations and loss of alpha thalassemia/mental retardation syndrome X-linked gene (ATRX) immunoreactivity, indicating a possible phenotypic convergence of true oligodendrogliomas and gliomas of the alternative lengthening of telomeres (ALT) pathway. p53 alterations were common irrespective of the 1p19q status.
Remarkably, on the basis of IDH mutation, 1p/19q codeletion, and ATRX expression, our study defined 4 molecularly and prognostically different groups of gliomas, showing the relevance of ATRX expression as a new marker for refining the molecular classification of gliomas and for distinguishing clinically distinct prognostic subgroups of patients.
When categorized according to the classification of Jiao et al., Olig2 LI of I-CF gliomas (cases with IDH and one or more of CIC, FUBP1 or combined 1p/19q loss; mean 71.0 %) was significantly higher than that of I-A gliomas (cases with IDH and ATRX alterations; mean 45.3 %).
Mutations in the critical chromatin modifier ATRX and mutations in CIC and FUBP1, which are potent regulators of cell growth, have been discovered in specific subtypes of gliomas, the most common type of primary malignant brain tumors.