Analysis of the MEN1 gene in sporadic pituitary adenomas

The MEN1 gene on chromosome 11q13 is mutated in patients afflicted with multiple endocrine neoplasia syndrome type 1 (MEN1). These patients develop endocrine tumours of the pancreas, the parathyroid, and the anterior pituitary. In order to determine the role of MEN1 in sporadic pituitary adenomas, 61 pituitary adenomas were analysed from patients without evidence of a familial tumour syndrome. Single strand conformation polymorphism (SSCP) analysis was performed for the entire coding sequence of MEN1. Fragments with aberrant migration patterns were sequenced bidirectionally. Only a single somatic mutation was detected in this series. In addition, several previously reported and three novel polymorphisms were observed. Loss of heterozygosity analysis with 12 polymorphic markers, however, identified 13 pituitary adenomas with allelic deletions on chromosome 11. Allelic losses occurred significantly more often in pituitary adenomas with hormone secretion than in non-functioning adenomas. These data suggest that MEN1 mutations are rare events in sporadic pituitary adenomas. However, the discrepancy of only 1/61 adenomas with MEN1 mutation but 13/61 (22 per cent) with allelic loss on chromosome 11 may suggest the presence of a yet unknown tumour suppressor gene, relevant to the pathogenesis of sporadic pituitary adenomas. Copyright © 1999 John Wiley & Sons, Ltd.     

High frequency of mitochondrial DNA mutations in glioblastoma multiforme identified by direct sequence comparison to blood samples

In an earlier study, we showed that heteroplasmy in the mitochondrial genome of gliomas sometimes occurs in a D-loop polycytosine tract. We extended this study by pairwise comparisons between glioma samples and adjacent brain tissue of 55 patients (50 glioblastomas, 1 astrocytoma WHO grade III, 4 astrocytomas WHO grade II). We used a combination of laser microdissection and PCR to detect and quantify variations in the polycytosine tract. New length variants undetectable in the adjacent brain tissue were observed in 5 glioblastomas (9%). In 2 of these cases, samples from a lower tumor stage (WHO grade II) could be analyzed and revealed the early occurrence of these mutations in both cases. Since the mitochondrial D-loop contains additional repeats and highly polymorphic non-coding sequences, we compared 17 glioblastomas with the corresponding blood samples of the same patients by direct sequencing of the complete D-loop. In 6 of these tumors (35%), instability was detected in 1 or 2 of 3 repeat regions; in 1 of these repeats, the instability was linked to a germline T-to-C transition. Furthermore, of 2 tumors (12%) 1 carried 1 and the other 9 additional transitions. In the latter patient, 6.7 kb of the protein coding mtDNA sequence were analyzed. Six silent transitions and 2 missense mutations (transitions) were found. All base substitutions appeared to be homoplasmic upon sequencing, and 89% occurred at known polymorphic sites in humans. Our data suggest that the same mechanisms that generate inherited mtDNA polymorphisms are strongly enhanced in gliomas and produce somatic mutations.     

Molecular genetic analysis of giant cell glioblastomas.

Glioblastomas (GBMs) are a heterogeneous group of tumors. Recently, distinct molecular genetic alterations have been linked to subgroups of patients with GBM. Giant cell (gc)GBMs are a rare variant of GBM characterized by a marked preponderance of multinucleated giant cells. Several reports have associated this entity with a more favorable prognosis than the majority of GBMs. To evaluate whether gcGBM may also represent a genetically defined subgroup of GBM, we analyzed a series of 19 gcGBMs for mutations in the TP53 gene for amplification of the EGFR and CDK4 genes and for homozygous deletions in the CDKN2A (p16/MTS1) gene. Seventeen of nineteen gcGBMs carried TP53 mutations whereas EGFR and CDK4 gene amplification was seen in only one tumor each and homozygous deletion of CDKN2A was not observed at all. The strikingly high incidence of TP53 mutations and the relative absence of other genetic alterations groups gcGBM together with a previously recognized molecular genetic variant of GBM (type 1 GBM). It is tempting to speculate that the better prognosis of gcGBM patients may result from the low incidence of EGFR amplification and CDKN2A deletion, changes known for their growth-promoting potential.     

Characteristic chromosomal imbalances in primary central nervous system lymphomas of the diffuse large B-cell type

We performed a genome wide screening for genomic alterations on a series of 19 sporadic primary central nervous system lymphomas (PCNSL) of the diffuse large B-cell type by comparative genomic hybridization (CGH). The tumors were additionally analyzed for amplification and rearrangement of the BCL2 gene at 18q21 as well as for mutation of the recently cloned BCL10 gene at 1p22. Eighteen tumors showed genomic imbalances on CGH analysis. On average, 2.1 losses and 4.7 gains were detected per tumor. The chromosome arm most frequently affected by losses of genomic material was 6q (47%) with a commonly deleted region mapping to 6q21-q22. The most frequent gains involved chromosome arms 12q (63%), 18q and 22q (37% each), as well as 1q, 9q, 11q, 12p, 16p and 17q (26% each). High-level amplifications were mapped to 9p23-p24 (1 tumor) and to 18q21-q23 (2 tumors). However, PCR-based analysis, Southern blot analysis and high-resolution matrix-CGH of the BCL2 gene revealed neither evidence for amplification nor for genetic rearrangement. Mutational analysis of BCL10 in 16 PCNSL identified four distinct sequence polymorphisms but no mutation. Taken together, our data do not support a role of BCL2 rearrangement/amplification and BCL10 mutation in PCNSL but indicate a number of novel chromosomal regions that likely carry yet unknown tumor suppressor genes or proto-oncogenes involved in the pathogenesis of these tumors.     

Analysis of the PTEN gene in human meningiomas

N. Peters, R. Wellenreuther, B. Rollbrocker, Y. Hayashi, B. Meyer-Puttlitz, E-M. Duerr, D. Lenartz, D.J. Marsh, J. Schramm, O.D. Wiestler, R. Parsons, C. Eng & A. von Deimling (1998) Neuropathology and Applied Neurobiology 24, 3–8
Analysis of the PTEN gene in human meningiomas
Previous observations demonstrated that the neurofibromatosis type 2 gene (NF2) plays an important role in the pathogenesis of the transitional, fibroblastic and malignant variants of human meningiomas. No specific genes have been associated with the pathogenesis of meningothelial meningiomas and with the progression to anaplastic meningiomas. However, allelic losses on chromosomal arms 1p, 10q and 14q have been implicated in the process of malignant progression. Recently, PTEN (phosphatase and tensin homolog deleted on chromosome ten) also termed MMAC1 (mutated in multiple advanced cancers 1) or TEP1 (TGF—regulated and epithelial cell-enriched phosphatase), emerged as a candidate gene on chromosome 10q23.3. Initial studies revealed mutations of PTEN in limited series of glioblastomas, breast, kidney and prostate carcinomas mainly as cell lines. In order to evaluate the involvement of PTEN in the development of meningiomas, we have analysed the entire coding sequence of the gene in a series of 55 meningiomas (WHO grade I), 10 atypical meningiomas (WHO grade II) and 10 anaplastic meningiomas (WHO grade III). No PTEN mutations were seen in the WHO grade I meningiomas. However, one of the anaplastic meningiomas carried a somatic mutation. In addition, all tumours were examined for the presence of homozygous deletions of PTEN but these were not detected in any of the meningiomas. Our data suggest that mutations in PTEN are not involved in the formation of low grade meningiomas, but may contribute to malignant progression in a fraction of anaplastic meningiomas.     

Comprehensive allelotype and genetic anaysis of 466 human nervous system tumors

Brain tumors pose a particular challenge to molecular oncology. Many different tumor entities develop in the nervous system and some of them appear to follow distinct pathogenic routes. Molecular genetic alterations have increasingly been reported in nervous system neoplasms. However, a considerable number of affected genes remain to be identified. We present here a comprehensive allelotype analysis of 466 nervous system tumors based on loss of heterozygosity (LOH) studies with 129 microsatellite markers that span the genome. Specific alterations of the EGFR, CDK4, CDKN2A, TP53, DMBT1, NF2, and PTEN genes were analyzed in addition. Our data point to several novel genetic loci associated with brain tumor development, demonstrate relationships between molecular changes and histopathological features, and further expand the concept of molecular tumor variants in neuro-oncology. This catalogue may provide a valuable framework for future studies to delineate molecular pathways in many types of human central nervous system tumors.