Leat-associated seizures the possible role of EAAT2, pyruvate carboxylase and glutamine synthetase

BACKGROUND

Drug-resistant epilepsy is a common condition in patients with brain neoplasms. The pathogenesis of tumor-associated seizures is poorly understood. Among the possible pathogenetic mechanisms, the increase in glutamate concentration has been proposed. Glutamate transporters, glutamine synthetase and pyruvate carboxylase are involved in maintaining the physiological concentration of glutamate in the intersynaptic spaces. In our previous research on angiocentric gliomas, we demonstrated that all tumors lacked the expression of the main glutamate transporter EAAT2, while the expression of glutamine synthetase and pyruvate carboxylase was mostly preserved.

METHODS

In the present study, we evaluated the immunohistochemical expression of EAAT2, glutamine synthetase and pyruvate carboxylase in a heterogeneous series of 25 long-term epilepsy-associated tumors (10 dysembryoplastic neuroepithelial tumors, 7 gangliogliomas, 3 subependymal giant cell astrocytomas, 3 rosette forming glioneuronal tumors, 1 diffuse astrocytoma MYB- or MYBL1-altered and 1 angiocentric glioma). In order to evaluate the incidence of variants in the SLC1A2 gene, encoding EAAT2, in a large number of central nervous system tumors we also queried the PedcBioPortal.

RESULTS

EAAT2 protein expression was lost in 9 tumors (36 %: 3 dysembryoplastic neuroepithelial tumors, 1 ganglioglioma, 3 subependymal giant cell astrocytomas, 1 diffuse astrocytoma MYB- or MYBL1-altered and 1 angiocentric glioma). Glutamine synthetase protein expression was completely lost in 2 tumors (8 %; 1 ganglioglioma and 1 diffuse astrocytoma MYB- or MYBL1-altered). All tumors of our series but rosette forming glioneuronal tumors (in which neurocytic cells were negative) were diffusely positive for pyruvate carboxylase. Consultation of the PedcBioPortal revealed that of 2307 pediatric brain tumors of different histotype and grade, 20 (< 1%) had variants in the SLC1A2 gene. Among the SLC1A2-mutated tumors, there were no angiocentric gliomas or other LEATs CONCLUSIONS: In conclusion, unlike angiocentric gliomas where the EAAT2 loss is typical and constant, the current study shows the loss of EAAT2 expression only in a fraction of the LEATs. In these cases, we may hypothesize some possible epileptogenic role of the EAAT2 loss. The retained expression of pyruvate carboxylase may contribute to determining a pathological glutamate excess unopposed by glutamine synthetase that resulted expressed to a variable extent in the majority of the tumors. Furthermore, we can assume that the EAAT2 loss in brain tumors in general and in LEATs in particular is more conceivably epigenetic.

Myxoid glioneuronal tumor: Histopathologic, neuroradiologic, and molecular features in a single center series

BACKGROUND

Myxoid glioneuronal tumor (MGT) is a benign glioneuronal neoplasm recently introduced in the World Health Organization (WHO) classification of the central nervous system (CNS) tumors. MGTs are typically located in the septum pellucidum, foramen of Monro or periventricular white matter of the lateral ventricle. They were previously diagnosed as dysembryoplastic neuroepithelial tumors (DNT), showing histological features almost indistinguishable from classical cortical DNT. Despite that, MGTs have been associated with a specific dinucleotide substitution at codon 385 in the platelet-derived growth factor receptor alpha (PDGFRA) gene, replacing a lysine residue with either leucine or isoleucine (p. LysK385Leu/Iso). This genetic variation has never been described in any other CNS tumor.

MATERIALS AND METHODS

Thirty-one consecutive tumors, previously diagnosed as DNTs at the Meyer Children's Hospital IRCCS between January 2010 and June 2021 were collected for a comprehensive study of their clinical, imaging, pathological features, and molecular profile.

RESULTS

In six out of the thirty-one tumors we had previously diagnosed as DNTs, we identified the recurrent dinucleotide mutation in the PDGFRA. All six tumors were typically located within the periventricular white matter of the lateral ventricle and in the septum pellucidum. We then renamed these lesions as MGT, according to the latest WHO CNS classification. In all patients we observed an indolent clinical course, without recurrence.

CONCLUSION

MGT represent a rare but distinct group of neoplasm with a typical molecular profiling, a characteristic localization, and a relative indolent clinical course.

Pediatric High Grade Glioma Classification Criteria and Molecular Features of a Case Series

Pediatric high-grade gliomas (pHGGs) encompass a heterogeneous group of tumors. Three main molecular types (H3.3 mutant, IDH mutant, and H3.3/IDH wild-type) and a number of subtypes have been identified. We provide an overview of pHGGs and present a mono-institutional series. We studied eleven non-related pHGG samples through a combined approach of routine diagnostic tools and a gene panel. TP53 and H3F3A were the most mutated genes (six patients each, 54%). The third most mutated gene was EGFR (three patients, 27%), followed by PDGFRA and PTEN (two patients each, 18%). Variants in the EZHIP, MSH2, IDH1, IDH2, TERT, HRAS, NF1, BRAF, ATRX, and PIK3CA genes were relatively infrequent (one patient each, 9%). In one case, gene panel analysis documented the presence of a pathogenic IDH2 variant (c.419G>A, p.Arg140Gln) never described in gliomas. More than one-third of patients carry a variant in a gene associated with tumor-predisposing syndromes. The absence of constitutional DNA did not allow us to identify their constitutional origin.

Dysembryoplastic neuroepithelial tumors: A single-institutional series with special reference to glutamine synthetase expression

Dysembryoplastic neuroepithelial tumors (DNT) is a benign (World Health Organisation, WHO, grade I) glioneuronal tumor and it represent one of the most frequent neoplasm in patient affected by seizures. The epileptic neuronal activity can be determined by abnormal synchronization, excessive glutamate excitation and\or inadequate GABA inhibition. Increasing evidence suggests that the astrocytes might be involved in this process even if neurons play a relevant role. In particular astrocytes promote the clearance of glutamate, a potent excitatory neurotransmitter of the central nervous system. Indeed, elevated concentrations of extracellular glutamate may determine iper-excitability and seizures as well as other neurological disorders. So, astrocytes, converting glutamate into glutamine via the enzyme glutamine synthetase (GS), could play a protective anti-seizures role. In the present study, we analyzed the immunohistochemical expression of GS in 20 DNTs specimens documenting a constant immunoistochemical expression of GS in astrocytes of the lesional tissue and of the cerebral cortex.

Primary Intracerebral Alveolar Soft Part Sarcoma: Report of a Case and Review of the Literature

Alveolar soft part sarcomas (ASPSs) are rare malignant tumors representing ∼1% of all soft tissue sarcomas. Most ASPS occurring in the central nervous system are metastases. In contrast, primary intracranial ASPSs are extremely rare and only 8 cases have been previously reported in English literature. Here, we report a case of primary alveolar soft part sarcoma in a 16-year-old female patient with no evidence of primary extracranial tumors. Histologically this case fulfilled the criteria of ASPS, and a molecular confirmation has been archived. To date, only 9 primary intracranial ASPS cases, including ours, have been reported in the literature. This report highlights the clinical and pathological characteristics, differential diagnosis, and molecular analysis of primary ASPS of the central nervous system.

Inflammatory Myofibroblastic Tumor of the Tongue. Report of a Pediatric Case and Review of the Literature

BACKGROUND

Inflammatory myofibroblastic tumor (IMT) is an uncommon mesenchymal lesion composed of myofibroblastic and fibroblastic spindle cells, accompanied by inflammatory infiltration. IMT may occur in the tongue. Five cases have been previously reported at this site.

CASE REPORT

An inflammatory myofibroblastic tumor arose in the tongue of a 10 month old infant, confirmed by anaplastic lymphoma kinase (ALK) immunohistochemical staining and the clinical response to the tyrosine kinase inhibitor.

CONCLUSIONS

IMT can occur in the tongue. This report highlights the differential diagnosis of IMT. ALK staining is both a helpful diagnostic marker and a predictive marker for targeted therapy in this tumor type.