Indications for a tumor suppressor gene at 22q11 involved in the pathogenesis of ependymal tumors and distinct from hSNF5/INI1

Ependymomas account for approximately 9% of all neuroepithelial tumors and represent the most frequent neuroepithelial tumors of the spinal cord. In adults, allelic loss of chromosome arm 22q occurs in up to 60% of the cases studied. Some of these tumors show an altered neurofibromatosis type 2 (NF2) gene; in others, NF2 appears to be unaffected, indicating the involvement of another tumor suppressor gene. Recently, the tumor suppressor gene hSNF5/INI1, located on 22q11.23, has been shown to contribute to the pathogenesis of renal and extrarenal rhabdoid tumors. In addition, this gene may be responsible for a new hereditary syndrome predisposing to a variety of tumors designated "rhabdoid predisposition syndrome." In the present study, we analyzed a series of 53 ependymal tumors of 48 patients [4 myxopapillary ependymomas (WHO grade I), 3 subependymomas (WHO grade I), 18 ependymomas (WHO grade II), 21 anaplastic ependymomas (WHO grade III) and 2 ependymoblastomas (WHO grade IV)] for mutations and homozygous deletions in the coding region of the hSNF5/INI1 gene and for allelic loss of its flanking chromosomal regions in 39 ependymal tumors of 35 patients. Allelic loss was detected in 11 of 35 informative primary ependymal tumors (31%) with a common region of overlap covered by the markers D22S257 and D22S310 on 22q11 including the marker D22S301. However, a detailed molecular analysis of 53 ependymal tumors for mutations and homozygous deletion of the hSNF5/INI1 gene revealed no alterations. We conclude that the hSNF5/INI1 gene is not involved in the pathogenesis of human ependymal tumors with allelic loss on chromosome arm 22q and an intact NF2 locus. In addition, our study localizes a putative ependymoma tumor suppressor gene(s) to a domain of chromosome arm 22q flanked by the microsatellite markers D22S257 and D22S310.     

胶质母细胞瘤9号染色体肿瘤抑制基因的研究

目的寻找胶质母细胞瘤(GBM)9号染色体上可能存在肿瘤抑制基因的杂合性丢失(LOH)区域,为发现和定位肿瘤抑制基因(TSG)提供线索和依据.方法应用聚合酶链反应(PCR)方法,采用荧光标记引物和377型DNA序列自动分析仪,分析2l例GBM9号染色体上20个微卫星多态性标记的LOH.结果21例GBM中,在14例的9号染色体上检测到LOH,33.0%(93/282)可提供信息位点存在LOH.在9p和9q上存在LoH的GBM分别有14例和10例.在位于9p21-23的D9S286位点以及9p21的D9S285～D9S157位点间区域检测到较高LOH率,分别为52.6%、43.8%～46.7%.结论染色体9p上等位基因的丢失可能在GBM分子水平发病机制中起着重要作用.在9p21-23的D9S286位点、9p21的D9S285～D9S157位点间区域可能存在与GBM相关的多个TSG,可能包括位于9p21上的p16和p15基因,在p16、p15所在染色体区域的远端9p21-23可能存在其他未知的TSG.     

Deletion mapping of the short arm of chromosome 1 identifies a common region of deletion distal to D1S496 in human meningiomas

We have studied a series of 63 meningiomas, including 47 benign meningiomas (World Health Organization, WHO, grade I), 13 atypical meningiomas (WHO grade II) and 3 anaplastic meningiomas (WHO grade III), using microsatellite and restriction fragment length polymorphism analysis for loss of heterozygosity (LOH) at 21 polymorphic loci on chromosome 1 (19 loci on 1p and 2 loci on 1q). LOH on 1p was found in 9 of 13 atypical meningiomas (70%) and in 3 of 3 (100%) anaplastic meningiomas, but only in 6 of 47 (13%) benign meningiomas. In 13 tumors allelic loss was observed at all informative loci on 1p. Terminal deletions with retention of heterozygosity at one or more proximal 1p loci were found in 5 tumors. The region commonly deleted in all tumors was located distally to the D1S496 locus, i.e., at cytogenetic bands 1p34 – 1pter, and included the chromosomal segment which is frequently deleted in neuroblastoma, malignant melanoma, and different types of carcinoma. Received: 11 February 1997 / Revised: 9 May 1997 / Accepted: 12 May 1997     

胶质母细胞瘤11 号-染色体杂合性丢失的研究

目的 :寻找胶质母细胞瘤 (GBM) 11号染色体上可能存在肿瘤抑制基因的杂合性丢失 (LOH)区域。方法 :应用聚合酶链反应方法 ,采用荧光标记的引物和ABIPRISMTM3 77型DNA序列自动分析仪 ,分析GBM 11号染色体上 18个微卫星多态性标记的LOH。结果 :在 47 6%GBM 11号染色体上观察到LOH ,11p和 11q的LOH率分别为 42 9%和 2 3 8%。 11q上所有位点的LOH率都较低 (<3 0 % ) ,在 11p上的下列区域检测到较高的LOH率 :11p 15 5上的D11S40 46(3 3 3 % )位点、11p12 p13上的D11S90 5 (4 1 2 % ) D11S93 5(3 7 5 % )区域。结论 :在 11p 15 5上的D11S40 46位点、11p12 p13上的D11S90 5 D11S93 5区域可能存在多个与GBM相关的肿瘤抑制基因     

胶质母细胞瘤6号，8号染色体杂合性丢失的初步研究

目的：寻找胶质母细胞瘤（GBM）6号,8号染色体上可能存在肿瘤抑制基因的杂合性丢失（LOH）区域,为发现和定位肿瘤抑制基因（TSG）提供线索和依据。方法：应用PCR方法和DNA序列自动分析仪,分析了21例GBM6号,8号染色体上20个,14个微卫星多态性标记的LOH。结果：6号染色体的LOH率为47．6％,在28．1％能提高信息位点上检测到了LOH,其中,6p和6q的LOH率分别是28．6％,38．1％,在6qtel上距短臂端粒201．1cM的微卫星位点D6S281检测到了较高的LOH率（50％）;6q16.3上D6S287的LOH率也高达50％,另外,6p21.1-p21.3上D6S276的LOH率也较高（35．3％）,本组病例的8号染色体LOH率较低（23．8％）,在16．3％能提高信息位点检测到LOH,其中8p12-p22上D8S550和D8S549的LOH率较高,分别是27．8％,30．0％。结论：6号染色体分子遗传学变化可能在GBM的发病中起着重要作用,8号染色体异常改变所起的作用可能不如6号染色体重要,但在8p12-p22上D8S550－D8549位点间区域也有可能存在与GBM相关的TSG。     

脑膜瘤第1、10、14和22对染色体的LOH和MI与相关因素分析

目的 研究脑膜瘤第1,10,14和22对染色体的LOH和MI及其相关因素,方法 对39例脑膜瘤用PCR方法检测D1S188,D10S187,D14S43和D22S1 4个位点的LOH和MI,探讨其与病理学表现,FCM及肿瘤复发等关系。结果 间变型脑膜瘤4个位点的LOH比率显著高于良性型;间变型D14S43 LOH也显著高于非典型型,4个位点LOH（＋）组DI均分别显著高于LOH（－）组,D1S188,D14S43和D22S1LOH（＋）组的超二倍体率均显著高于LOH（－）组,6例复发性脑膜瘤组,LOH（＋）者5例,显著高于初发性组,各组的MI未见显著性差异。结论脑膜瘤的D1S188,D10S187,D14S43和D22S1 LOH与肿瘤的发生和恶性生物学行为密切有关。     

Deletions on the long arm of chromosome 17 in pilocytic astrocytoma

Summary Pilocytic astrocytomas are the most common astrocytic tumors of childhood and differ clinically and histopathologically from those astrocytomas that affect adults. Studies of adult astrocytic tumors have revealed allelic losses on chromosomes 10, 17p, 19q and alterations in the epidermal growth factor receptor (EGFR) gene. We have previously examined pilocytic astrocytomas for allelic losses on chromosomes 10 and 19q and for amplification of the EGFR gene, but did not detect genomic alterations at these loci. In the present study we assayed 20 pilocytic astrocytomas for loss of allelic heterozygosity of chromosome 17p, including one locus in the p53 tumor suppressor gene. In addition, because pilocytic astrocytomas frequently affect patients with neurofibromatosis type 1 (NF1) and the NF1 gene has been mapped to 17q11.2, we also examined multiple loci on the long arm of chromosome 17. Allelic loss was observed on chromosome 17 in four cases (three sporadic, one NF1); all lost portions of the long arm in chromosome 17, and one tumor lost the short arm as well. One tumor showed an interstitial delection on the long arm that included the region of the NF1 gene. These data suggest the presence of a tumor suppressor gene on 17q that is associated with pilocytic astrocytomas. A potentiel candidate for this gene is the NF1 tumor suppressor gene.Supported by grant CD 455 from the American Cancer Society (BRS) and by a grant from the Preuss Foundation (to BRS). AvD is a postdoctoral fellow supported by the Deutsche Forschungsge-meinschaft; DNL is a recipient of NIH Public Health Service NRSA CA 09144     

Molecular pathogenesis of pituitary tumors

Pituitary tumors are the result of a monoclonal outgrowth where the intrinsic genetic defects involve oncogenes, tumor suppressor genes (TSG), and most likely genes responsible for differentiation. In addition, hypothalamic and intrapituitary derived growth factors are imposed upon these aberrant cells, contributing to their growth characteristics. While histological examination will not identify those tumors likely to progress toward an invasive phenotype or those destined toward recurrence recent advances in the molecular pathology of these tumors holds significant promise for prediction of recurrence and the design of novel treatment strategies. Moreover, emerging data clearly indicate that different molecular mechanisms are involved in the pathogenesis of the various pituitary tumor subtypes. Until recently the gsp oncogene was the only oncogene significantly associated with pituitary tumors; however, emerging data have describe a role for PTTG and cyclin D1 in pituitary tumorigenesis. For known and putative TSG loci, allelic losses on the long arms of chromosomes 10, 11, and 13 are significantly associated with the transition from the noninvasive to the invasive and metastatic phenotype, while losses on chromosome 9p occur early in pituitary tumorigenesis. Studies of known TSG at these loci, including the menin gene and RB1, would suggest a limited role, if any, in pituitary tumors. However, loss of pRB is evident in a proportion of somatotropinomas but is not associated with allelic loss of an RB1 intragenic marker. The gene encoding p16/CDKN2A is neither deleted nor mutated in pituitary tumors; however, its associated CpG island is frequently methylated and is associated with a loss of p16 protein expression. Allelic losses on chromosome 9p, frequent methylation, and loss of p16 protein appear as early changes in nonfunctional tumors, whereas they are infrequent events in somatotropinomas. The functional consequence of enforced expression of p16/CDKN2A in the mouse corticotroph cell line AtT20 has shown that it is responsible for a profound reduction in cell proliferation and the mechanism is a G(1) arrest, mimicking the in vivo role of this cell cycle regulator in most tissues. The combined data from several groups show that the allelic losses reported at known TSG loci are not accompanied by mutation in the retained allele. However, since abnormal methylation patterns may precede and predispose toward genetic instability this could account for the allelic losses on these chromosomes. Equally, since DNA methylation may lead to reduced expression of a gene it might also account for the reduced expression of as yet unidentified TSGs implicated in pituitary tumorigenesis. Collectively these studies hold significant promise as markers predictive of tumor behavior and point to novel treatment strategies, which may include the reactivation of TSGs that are intact but silenced through epigenetic mechanisms.     

Loss of heterozygosity at 6q is frequent and concurrent with 3p loss in sporadic and familial capillary hemangioblastomas

Capillary hemangioblastoma is a benign tumor, occurring sporadically or as a manifestation of von Hippel-Lindau (VHL) disease. Inactivation of the VHL gene at 3p25-26 has been demonstrated in all VHL-associated hemangioblastomas. However, the VHL gene has been found to be inactivated in only 20% to 50% of sporadic tumors. So far, no other gene has been reported to be involved in the development of hemangioblastomas. DNA losses at 6q are frequent alterations in hemangioblastomas, as shown by comparative genomic hybridization. We therefore analyzed 15 hemangioblastomas for loss of heterozygosity (LOH) on chromosome 3p and 6q to reveal the frequency of allelic losses and to determine minimal deleted areas. We detected LOH at 6q for one or more markers in 11 (73%) out of 15 cases (in 9 of 11 sporadic and in 2 of 4 VHL-associated tumors). The analyses revealed a minimal 3-megabase (Mb) deleted region at 6q23-24, where 9 of 11 (82%) informative cases showed LOH. LOH at 3p was seen in 14 out of 15 tumors. LOH occurred concurrently at 6q and 3p in 67% of cases. Our data strongly suggests that a tumor suppressor gene located at 6q23-24 is involved in tumorigenesis of hemangioblastomas, in addition to the VHL gene.     

Molecular analysis of alterations of the p18INK4c gene in human meningiomas

Meningiomas are common primary brain tumours frequently presenting with deleted and/or mutated NF2 gene located on 22q.1p has been reported as the second most commonly deleted chromosomal region in these neoplasms. A new member of the INK4 family of CDK inhibitors, the p18INK4c gene, has recently been mapped to this chromosomal arm. By virtue of its structural and functional similarities with the p16 gene, p18 has been implicated as a tumour suppressor gene in a variety of cancers. In this paper 40 human meningiomas were analysed for loss of heterozygosity (LOH) at the p18 locus, mutations and inactivating methylation of the p18 gene. LOH at D1S193, D1S463 and D1S211 microsatellite marker loci mapped to 1p32 was detected in 13 of 35 (37%), four of 20 (20%), and six of 24 (25%) tumour samples, respectively. One sample presented with homozygous deletion at D1S193. Mutational analysis using single stranded conformational polymorphism (SSCP) and direct sequencing did not detect any missense mutation but revealed a novel silent mutation, G to T, at coding nucleotide 435. Analysis of HgaI, BsaHI, ScrFI and Eco0109I restriction sites of p18 exon 1 revealed absence of inactivating methylation. Immunohistochemistry with p18 monoclonal antibody detected presence of cytoplasmic p18 staining in 21 of 22 examined samples. One sample did not stain and was shown to carry homozygous deletion at D1S193. Despite the high frequency of LOH at 1p32 microsatellite markers, the lack of genetic and epigenetic aberrations in the p18 gene together with the presence of p18 protein in all but one meningioma samples argues against the role of p18 as a tumour suppressor gene important for meningioma development.     

Genetic alterations commonly found in diffusely infiltrating cerebral gliomas are rare or absent in pleomorphic xanthoastrocytomas

Pleomorphic xanthoastrocytoma (PXA) is a rare, usually well-circumscribed and superficially located neoplasm that preferentially arises in the cerebral cortex of children and young adults. The molecular aberrations that are associated with these tumors have not been studied systematically so far. We here report on a molecular genetic analysis of 62 PXAs (46 PXAs of World Health Organization [WHO] grade II and 16 PXAs with anaplastic features) for alterations of 5 candidate genes known to be frequently aberrant in diffusely infiltrating astrocytic gliomas, i.e. TP53, CDKN2A (p16(INK4a)), CDK4, MDM2, and EGFR. Only 3 PXAs (5%) carried a TP53 mutation. None of the 62 PXAs had lost both copies of the CDKN2A gene. The CDK4, MDM2, or EGFR genes were not amplified in any of the tumors. Fourteen PXAs were additionally analyzed for loss of heterozygosity (LOH) at microsatellite markers located on the chromosomes/chromosomal arms 1, gp, 9p, 10, 17, 19q, and 22q. Two PXAs (14%) had LOH at all informative markers on 9p, while 1 PXA demonstrated an interstitial area of allelic imbalance between D22S533 and D22S417 at 22q11.2-q13.3. Further analysis of 10 PXAs for inactivation of the CDKN2A. p14(ARF), and CDKN2B (p15(INK4b)) genes on 9p21 did not reveal any homozygous deletion, mutation, promoter hypermethylation, or complete loss of mRNA expression. Taken together, our results indicate that the chromosomal and genetic aberrations in PXAs are different from those typically associated with the diffusely infiltrating astrocytic and oligodendroglial gliomas. These genetic differences likely contribute to the more favorable behavior of PXAs and may be helpful for the molecular differential diagnosis of cerebral gliomas.     

Common regions of deletion on chromosome 22q12.3-q13.1 and 22q13.2 in human astrocytomas appear related to malignancy grade.

Approximately 30% of human astrocytomas have been reported to display allelic loss of the long arm of chromosome 22, suggesting the presence of a chromosome 22q astrocytoma suppressor gene. To define the most likely location for this putative tumor suppressor, we performed deletion mapping on 141 tumors using 16 chromosome 22q microsatellite markers. Allelic loss of 22q was observed in 2/12 (17%) of astrocytomas, 9/29 (31%) of anaplastic astrocytomas, and 38/100 (38%) of glioblastomas, consistent with a role for chromosome 22q loss in astrocytoma progression as well as formation. Twenty-two tumors exhibited allelic loss at every informative locus, consistent with loss of the entire arm of 22q. Twenty-seven tumors showed partial deletions, with one common region of deletion at 22q12.3-q13.1 between markers D22S280 and D22S282, and a second candidate region at 22q13.2 near the marker D22S1170. For the proximal candidate region, the incidence of allelic loss was similar between grades; for the distal locus, the incidence increased with grade, raising the possibility that the distal locus is involved in a later stage of astrocytoma tumorigenesis.     

胶质母细胞瘤染色体10q杂合性缺失的初步研究

目的寻找胶质母细胞瘤10号染色体长臂(10q)上可能存在肿瘤抑制基因的杂合性缺失(LOH)区域,为发现和定位肿瘤抑制基因提供线索和依据。方法应用聚合酶链反应(PCR)方法分析10例胶质母细胞瘤(GBM)染色体10q上9个微卫星多态性标记的LOH。结果在90％(9/10例)肿瘤组织染色体10q上检出LOH。以在10q23上的D10s2492-D10s541位点间和10q25-26上的D10s1723-D10s216位点间区域的LOH频率最高。结论染色体10q23上的D10s2492-D10s541位点间和10q25-26上的D10s1723-D10s216位点间区域可能存在与GBM有关的多个肿瘤抑制基因。     

Loss of heterozygosity on chromosome 22 in human ependymomas

Ependymomas are glial tumors of the brain and spinal cord. The most frequent genetic change in sporadic ependymomas is monosomy 22, suggesting the presence of an ependymoma tumor suppressor gene on chromosome 22. Thirty-three pairs of matched normal and tumor specimens from ependymoma patients were genotyped using 12 polymorphic microsatellite markers spanning the long arm of chromosome 22. Allelic deletion was found in 12 of 33 tumors (36.4%). Eight tumors showed partial deletions and 4 tumors exhibited loss of the entire arm of 22q. We identified two common regions of deletion: one at 22q11.21-12.2 flanked by markers D22S420 and D22S300, and a second candidate region at 22q13.1-13.3 between D22S274 and D22S1149. The size of each region was 21.1 and 2.4 cM, respectively. Thus, our results suggest that one or more tumor suppressor genes associated with ependymoma may be present on chromosome 22. Comparison of these results with clinicopathological data indicate that allelic losses on 22q tend to occur more frequently in intracranial anaplastic ependymomas in children and intraspinal ependymomas in adults.     

The retinoblastoma gene is involved in malignant progression of astrocytomas

Loss of chromosome 13q occurs in up to 50% of human astrocytomas, suggesting the presence of an astrocytoma tumor suppressor gene on that chromosome. To determine whether the retinoblastoma susceptibility gene (Rb) on 13q 14 contributes to the formation of astrocytomas, we examined 85 tumors for loss of heterozygosity (LOH) at the intragenic Rb 1.20 locus. LOH was detercted in 16 of 54 informative high-grade astrocytomas (30%), but was not detected in 12 low-grade gliomas. Deletion mapping with flanking markers on 13q revealed that the Rb 1.20 region was preferentially targeted by the deletions. Tumors with LOH at Rb 1.20 were examined for mutations in the remaining Rb allele using single-strand conformational polymorphism (SSCP) analysis and direct DNA sequencing. Mutations were detected in exon 8 (1 tumor), exon 24 (2 tumors), and intron 24 (1 tumor). Rb protein expression, as assessed by immunohistochemistry, was altered in 3 of 9 cases with LOH and in 1 tumor without LOH. Our results demonstrate that Rb inactivation contributes to the formation of high-grade astrocytomas, and therefore implicate a second, known tumor suppressor gene in astrocytoma tumorigenesis.     

Loss of heterozygosity on chromosome 19 in secondary glioblastomas

Glioblastomas develop rapidly de novo (primary glioblastomas) or slowly through progression from low-grade or anaplastic astrocytoma (secondary glioblastomas). Recent studies have shown that these glioblastoma subtypes develop through different genetic pathways. Primary glioblastomas are characterized by EGFR amplification/overexpression, PTEN mutation, homozygous p16 deletion, and loss of heterozygosity (LOH) on entire chromosome 10, whereas secondary glioblastomas frequently contain p53 mutations and show LOH on chromosome 10q. In this study, we analyzed LOH on chromosomes 19q, 1p, and 13q, using polymorphic microsatellite markers in 17 primary glioblastomas and in 13 secondary glioblastomas that progressed from low-grade astrocytomas. LOH on chromosome 19q was frequently found in secondary glioblastomas (7 of 13, 54%) but rarely detected in primary glioblastomas (1 of 17, 6%, p = 0.0094). The common deletion was 19q13.3 (between D19S219 and D19S902). These results suggest that tumor suppressor gene(s) located on chromosome 19q are frequently involved in the progression from low-grade astrocytoma to secondary glioblastoma, but do not play a major role in the evolution of primary glioblastomas. LOH on chromosome 1p was detected in 12% of primary and 15% of secondary glioblastomas. LOH on 13q was detected in 12% of primary and in 38% of secondary glioblastomas and typically included the RB locus. Except for 1 case, LOH 13q and 19q were mutually exclusive.     

Molecular analysis of chromosome 1, 10 and 19 abnormalities in human oligodendroglial tumors: relationship between frequency of LOH grade, age and gender

BACKGROUND: Loss of heterozygosity (LOH) on 1p and 19q is observed in most oligodendroglial tumors. LOH on 10q appears to be less common in these tumors as compared to other gliomas. PATIENTS AND METHODS: We reviewed 14 patients with oligodendroglial tumors (10 low-grade and 4 anaplastic oligodendroglioma) to evaluate the frequency of LOH on 1p, 10q and 19q and correlate it with tumor grade and patients' age and gender; 5 loci on 1p and 5 on 19q as well as 4 on 10q were analyzed for LOH using PCR techniques. RESULTS: LOH on 1p together with 19q was detected in 6 tumors, 1 tumor showed deletion of 19q accompanied with deletion on 10q. Deletion on 1p was associated with deletion of 19q (p < 0.005) and mutual associations among deletions at loci on 19q (p < 0.05) were found. Patients with LOH on 1p were younger on average than patients with retained heterozygosity (p = 0.05). Grade II oligodendrogliomas predominated among younger patients (p < 0.01) while grade III oligodendrogliomas predominated among women (p < 0.005). No association between LOH on 1p nor 19q and tumor grade or patients' gender was found. CONCLUSION: Our study provides several clinically interesting findings and further supports the hypothesis of chromosome 1p and 19q involvement in the oligodendroglial cancerogenesis.     

Analysis of NF1 somatic mutations in cutaneous neurofibromas from patients with high tumor burden

Neurofibromatosis type 1, (NF1) is a complex, autosomal dominant disorder characterized by benign and malignant tumors which result from NF1 gene mutations. The molecular mechanisms that underlie NF1 tumorigenesis are still poorly understood although inactivation of other modifying loci in conjunction with NF1 mutations is postulated to be involved. These modifying loci may include deficiencies in mismatch repair genes and elements involved in cell cycle regulation (TP53, RB1, and CDKN2A). We have analyzed the somatic mutations in 89 cutaneous neurofibromas derived from three unrelated NF1 patients with high tumor burden, by loss of heterozygosity (LOH) analysis of the NF1, TP53, RB1, and CDKN2A genes, by assessing microsatellite instability (MSI), by direct sequencing of the NF1, TP53, and several mismatch repair (MMR) genes and by multiplex ligation-dependent probe amplification of the NF1 and TP53 genes. The aim was both to assess the possible clonality of these tumors and also to assess the involvement of other potential genetic loci in the development of these neurofibromas. Somatic NF1 mutations were identified in 57 (64%) of neurofibroma samples. Each mutation was distinct demonstrating the independent origin of each tumor. While somatic LOH of the TP53 gene was identified in four tumors, no specific deletions or sequence variations were identified. LOH of markers flanking the RB1 gene was also found in one tumor but no CDKN2A mutations were detected. Although evidence of MSI was seen in 21 tumors, no MMR gene alterations were identified. The identification of LOH involving TP53 and RB1 loci is a novel finding in benign cutaneous neurofibromas possibly demonstrating an alternative underlying molecular mechanism associated with the development of these benign tumors from this cohort of patients.     

Mutational analysis of INI1 in sporadic human brain tumors

The INI1/SMARCB1/hSNF5 gene on chromosome 22 is frequently mutated in rhabdoid tumors. An association of INI1 mutations with allelic losses on chromosome 22 supports a classical tumor suppressor mechanism. Several brain tumor entities including astrocytomas, glioblastomas and ependymomas are characterized by allelic losses on chromosome 22. In the present study we examined a series of 200 brain tumors by Single-strand conformation polymorphism analysis and direct sequencing for point mutations in INI1. In addition, all tumors were analyzed for homozygous deletions spanning both exons 3 and 8 of INI1. No mutations or homozygous deletions were detected in astrocytomas, glioblastomas, oligodendroglial tumors, neurinomas or medulloblastomas. However, a point mutation could be identified in the single case of plexus carcinoma. Our data suggest that INI1 mutations are involved in the pathogenesis of plexus carcinoma; however, INI1 alterations are not a frequent event in the majority of brain tumor entities.