No evidence for hypermethylation of the hSNF5/INI1 promoter in pediatric rhabdoid tumors

Ewing Sarcoma and Atypical Teratoid Rhabdoid Tumor: A FISH and Immunohistochemical Comparison

Ewing sarcoma (ES) and atypical teratoid rhabdoid tumor (ATRT) are high-grade malignancies of childhood, each of which is associated with genetic abnormalities on chromosome 22. ES is typically characterized by rearrangement of the EWSR1 locus and ATRT by deletion of SMARCB1. We report a case with an unusual fluorescence in situ hybridization signal pattern consistent with EWSR1 rearrangement that was shown to have loss of INI1 expression by immunohistochemistry due to deletion in the long arm of one chromosome 22. In light of the unusual findings in this case as well as the proximity of the EWSR1 locus and SMARCB1 locus on chromosome 22 and frequent CD99 staining in both tumors, we examined 16 ES cases and 17 ATRT, renal rhabdoid tumor (RRT), and extrarenal rhabdoid tumor (ERRT) cases for CD99 and INI1 staining and for EWSR1 rearrangement. Staining with INI1 was negative in ATRT, RRT, and ERRT and positive in ES cases; CD99 was positive in ES cases and variable in ATRT cases. All but 2 cases of ES, and no cases of ATRT, showed rearrangement of EWSR1. The present case appears to be best classified as a unique variant of ATRT based on immunohistochemistry, EWSR1 fluorescence in situ hybridization and RT-PCR, and SMARCB1 gene sequencing.

Deep intronic hotspot variant explaining rhabdoid tumor predisposition syndrome in two patients with atypical teratoid and rhabdoid tumor

About one third of patients with rhabdoid tumors (RT) harbor a heterozygous germline variant in SMARCB1. Molecular diagnosis therefore keeps a crucial place in the diagnosis of RT, and genetic counseling should be systematically recommended. However, immunohistochemistry has progressively replaced molecular tools to assess the status of SMARCB1 in tumors; the necessity of analyzing SMARCB1 status in the tumor may thus be less considered by neuropathologists and pediatric neuro-oncologists. In the present manuscript as aforementioned, we report on two patients with bifocal RT in the first month of life and in whom no germline variant was initially found in the SMARCB1 coding sequence. Careful analysis of SMARCB1 status in the tumors revealed that only one of the two inactivating hits was found in the coding sequence. By sequencing the tumor cells RNA, we were able to detect an insertion with an abnormal sequence, due to the same intronic variant of SMARCB1, which led to the exonisation of the first intron. This cryptic variant was absent in the germline DNA of both patients. Of note, we previously reported one patient with the same deep intronic variant in the germline in a soft tissue RT. To our mind, this additional report on two patients clearly demonstrates that this intronic variant is a new hotspot that should now be systematically added to the germline screening of SMARCB1. We therefore recommend searching for and cautiously interpreting germline analysis if SMARCB1 has not been extensively studied in the tumor.

The expanding family of SMARCB1(INI1)-deficient neoplasia: implications of phenotypic, biological, and molecular heterogeneity

Since the description of atypical teratoid/rhabdoid tumors of the central nervous system and renal/extrarenal malignant rhabdoid tumors in children, the clinicopathologic spectrum of neoplasms having in common a highly variable rhabdoid cell component (0% to 100%) and consistent loss of nuclear SMARCB1 (INI1) expression has been steadily expanding to include cribriform neuroepithelial tumor of the ventricle, renal medullary carcinoma and a subset of collecting duct carcinoma, epithelioid sarcoma, subsets of miscellaneous benign and malignant soft tissue tumors, and rare rhabdoid carcinoma variants of gastroenteropancreatic, sinonasal, and genitourinary tract origin. Although a majority of SMARCB1-deficient neoplasms arise de novo, the origin of SMARCB1-deficient neoplasia in the background of a phenotypically or genetically definable differentiated SMARCB1-intact "parent neoplasm" has been convincingly demonstrated, highlighting the rare occurrence of rhabdoid tumors as "double-hit neoplasia." As a group, SMARCB1-deficient neoplasms occur over a wide age range (0 to 80 y), may be devoid of rhabdoid cells or display uniform rhabdoid morphology, and follow a clinical course that varies from benign to highly aggressive causing death within a few months irrespective of aggressive multimodality therapy. Generally applicable criteria that would permit easy recognition of these uncommon neoplasms do not exist. Diagnosis is based on site-specific and entity-specific sets of clinicopathologic, immunophenotypic, and/or molecular criteria. SMARCB1 immunohistochemistry has emerged as a valuable tool in confirming or screening for SMARCB1-deficient neoplasms. This review summarizes the different phenotypic and topographic subgroups of SMARCB1-deficient neoplasms including sporadic and familial, benign and malignant, and rhabdoid and nonrhabdoid variants, highlighting their phenotypic heterogeneity and molecular complexity.

The silencing of the SWI/SNF subunit and anticancer gene BRM in Rhabdoid tumors

Rhabdoid sarcomas are highly malignant tumors that usually occur in young children. A key to the genesis of this tumor is the mutational loss of the BAF47 gene as well as the widespread epigenetic suppression of other key anticancer genes. The BRM gene is one such epigenetically silenced gene in Rhabdoid tumors. This gene codes for an ATPase catalytic subunit that shifts histones and opens the chromatin. We show that BRM is an epigenetically silenced gene in 10/11 Rhabdoid cell lines and in 70% of Rhabdoid tumors. Moreover, BRM can be induced by BAF47 re-expression and by Flavopiridol. By selective shRNAi knockdown of BRM, we show that BRM re-expression is necessary for growth inhibition by BAF47 re-expression or Flavopiridol application. Similar to lung cancer cell lines, we found that HDAC3, HDAC9, MEF2D and GATA3 controlled BRM silencing and that HDAC9 was overexpressed in Rhabdoid cancer cell lines. In primary BRM-deficient Rhabdoid tumors, HDAC9 was also found to be highly overexpressed. Two insertional BRM promoter polymorphisms contribute to BRM silencing, but only the -1321 polymorphism correlated with BRM silencing in Rhabdoid cell lines. To determine how these polymorphisms were tied to BRM silencing, we conducted ChIP assays and found that both HDAC9 and MEF2D bound to the BRM promoter at or near these polymorphic sites. Using BRM promoter swap experiments, we indirectly showed that both HDAC9 and MEF2D bound to these polymorphic sites. Together, these data show that the mechanism of BRM silencing contributes to the pathogenesis of Rhabdoid tumors and appears to be conserved among tumor types.

Prognostic value of MIB-1, p53, epidermal growth factor receptor, and INI1 in childhood chordomas

BACKGROUND

Chordomas are slow-growing tumors and most commonly involve the sacrum and clivus. Multiple recurrences are frequent. Childhood chordomas are rare and often show exceptionally aggressive behavior, resulting in short survival and a high incidence of metastatic spread.

OBJECTIVE

This study examined the histologic features and immunohistochemical profile of pediatric chordomas and compared them with their adult counterparts.

METHODS

Nine pediatric and 13 adult cases were included in the study. Childhood chordomas were classified into conventional, atypical, and poorly differentiated types. Immunohistochemistry was performed for cytokeratin, epithelial membrane antigen, vimentin, S100, brachyury, p53, INI1, epidermal growth factor receptor (EGFR), and CD117. Cytogenetic analyses were performed in a subset of tumors for SMARCB1/INI1 locus on 22q chromosome by fluorescent in situ hybridization (FISH) and analysis of the SMARCB1/INI1 gene sequence.

RESULTS

All tumors showed expression of cytokeratin, epithelial membrane antigen, S100, vimentin, brachyury, and EGFR. Atypical morphology, p53 expression, higher MIB-1 labelling index (LI), and INI1 loss were more frequently seen in pediatric chordomas as compared with adults. None of the tumors showed CD117 expression. No point mutation in the SMARCB1/INI1 gene was noted in the tumors examined; however, 4 pediatric and 1 adult chordoma showed loss of this locus on FISH analysis.

CONCLUSIONS

A subset of pediatric chordomas with atypical histomorphologic features needs to be identified, as they behave in an aggressive manner and require adjuvant therapy. Pediatric chordomas more frequently show p53 expression, INI1 loss, and higher MIB-1 LI as compared with adults, whereas EGFR expression is common to both.

SMARCB1 protein and mRNA loss is not caused by promoter and histone hypermethylation in epithelioid sarcoma

About 10% of epithelioid sarcomas have biallelic mutation of the SMARCB1 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily b, member 1) gene resulting in a lack of this nuclear protein. It has been suggested that SMARCB1 may be silenced by epigenetic changes in the remaining 90% of tumors. Thus, we hypothesized that the promoter of SMARCB1 is hypermethylated. We also examined SMARCB1 mRNA level to determine if a post-translational change was possible. Thirty-six cases of epithelioid sarcomas were studied. Immunohistochemistry and mutation analysis of the SMARCB1 gene were performed to select appropriate cases. Methylation status was assessed by methylation-specific PCR. Laser capture microdissection of tumor cells followed by real-time PCR was applied to examine the expression of SMARCB1 mRNA. Of 36 epithelioid sarcomas, 31 (86%) displayed a lack of SMARCB1 nuclear protein. In all, 4 (13%) of 31 SMARCB1-negative cases harbored biallelic deletion while 9 (33%) cases showed single-allelic deletion. One (4%) frameshift deletion of exon 3 and one point mutation of exon 7 were also found. In 16 (59%) cases, both alleles were intact. Altogether, 25/31 (81%) SMARCB1-negative cases had at least one intact allele. None of these cases demonstrated promoter hypermethylation. Low levels of SMARCB1 mRNA were found in all cases with tumor tissue extracted RNA (because of the minimal normal cell contamination) but no mRNA could be detected in laser dissected cases (containing only tumor cells). Enhancer of zeste homolog 2 (EZH2) overexpression was not characteristic of epithelioid sarcoma. Thus, loss of SMARCB1 expression in epithelioid sarcoma is caused neither by DNA hypermethylation nor by post-translational modifications. Most likely it is the microRNA destruction of SMARCB1 mRNA but further investigations are needed to elucidate this issue.

Proximal-type Epithelioid Sarcoma of the Head and Neck (HN): A Study with Immunohistochemical and Molecular Analysis of SMARCB1

Proximal-type epithelioid sarcoma is an aggressive variant of epithelioid sarcoma most often occurring in soft tissues of the proximal limbs, characterized by polygonal cells, marked nuclear atypia, and varied rhabdoid features. Malignant rhabdoid tumor is an aggressive, well characterized entity typically with rhabdoid morphology and involving the kidney of pediatric patients. Rarely, tumors with morphologic and biologic features identical to those in kidney occur in extra-renal sites and are regarded as an extrarenal presentation of the same entity in kidney, named malignant extra-renal rhabdoid tumor. Morphologic and immunophenotypical similarities between proximal-type epithelioid sarcoma and malignant rhabdoid tumor pose a diagnostic challenge and may suggest a relationship between the two. Both tumors are characterized by loss of SMARCB1 (INI1/BAF47/SNF5) expression; however, the molecular events involved differ. Here we describe the immunohistochemical and molecular analysis of three head and neck tumors with morphologic features shared by proximal-type epithelioid sarcoma and malignant rhabdoid tumor. All tumors showed loss of SMARCB1expression. Direct sequencing of the promoter and nine coding exons of SMARCB1, multiplex ligation-dependent probe amplification, and whole genome single nucleotide polymorphism array were performed on the two adult cases and showed only a heterozygous deletion of chromosome 22 in a minority of cells in one of the cases. Though rare, proximal-type epithelioid sarcoma could occur in the head and neck and should be differentiated from other epithelioid tumors by the loss of SMARCB1 expression. The lack of detectable genetic alteration in the SMARCB1 locus in head and neck proximal-type epithelioid sarcoma warrants further investigation into the molecular mechanism underlying loss of SMARCB1 expression.

Atypical teratoid rhabdoid tumors (ATRTs): the British Columbia's Children's Hospital's experience, 1986-2006

As "atypical teratoid rhabdoid tumors" (ATRTs) may mimic "small round blue cell tumors" (SRBCT), we reexamined our ATRT experience focusing upon INI-1 immunohistochemistry (IHC). All high-grade pediatric brain tumors occurring from 1986-2006 at our institution underwent INI-1 IHC. Clinicopathologic data from each INI-1 immunonegative case were reviewed. Additional genetic, epigenetic and IHC analyses (including interrogation of INI-1 and CLDN6) were performed on a subset of the INI-1 immunonegative cases. Twelve INI-1 IHC negative tumors were identified retrospectively, of which only two previously carried the diagnosis of ATRT. Overall, the clinicopathologic and genetic data supported the assertion that all 12 cases represented ATRT. Unexpectedly, three long-term survivors (4.2, 7.0 and 8.5 years) were identified. As hypothesized, "teratoid" and "rhabdoid" histologic features were relatively infrequent despite gross total resections in some cases. Methylation specific polymer chain reaction (PCR) (MSP) revealed a uniform methylation pattern across all cases and gene promoters tested (ie, MGMT, HIC1, MLH3 and RASSF1); notably, all cases demonstrated unmethylated MGMT promoters. Our data demonstate that a primitive non-rhabdoid histophenotype is common among ATRTs and highlights the diagnostic importance of INI-1 IHC. Epigenetically, the MGMT promoter is usually unmethylated in ATRT, suggesting that potential temozolomide-based chemotherapy may be of limited efficacy.

Absence of mutations on the SNF5 gene in hematological neoplasms with chromosome 22 abnormalities

BACKGROUND

The relation with SNF5 mutation and chromosome 22 abnormalities is not clear in hematological neoplasms.

METHODS

To elucidate the relevance of the SNF5 gene on 22q11.2, karyotypes were reviewed in 283 hematological neoplasms. Loss of heterozygosity (LOH) on 22q was analyzed in 21 plasma cell myelomas without chromosome 22 abnormalities. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) on the SNF5 gene was analyzed in 8 hematological neoplasms with 22q- or -22, and 8 chronic myelogenous leukemias (CMLs) in blast crisis. Fluorescence in situ hybridization (FISH) was performed in 1 myelodysplastic syndrome (MDS) case with -22,del(22)(q11.2 q13).

RESULTS

22q- or -22 was observed in 36 patients. LOH on 22q was detected in 1 of the 21 myelomas. Mobility shifts were found by PCR-SSCP analysis in 2 CMLs, whereas sequence analysis showed polymorphisms. FISH analysis revealed the SNF5 gene was not deleted in the MDS case.

CONCLUSION

These results suggest that alterations of the SNF5 gene are rare in hematological neoplasms with chromosome 22 abnormalities. Haploinsufficiency may contribute to the development of these neoplasms.

Histology and molecular pathology of pediatric brain tumors

In recent years, brain tumors have become the single most frequent cause of cancer-related mortality in children, although their frequency is approximately 50% less than leukemia. According to the classification of the World Health Organization, histopathological diagnosis is of paramount importance for clinicians to choose the most appropriate treatment option and tailor treatment intensity to disease risk. However, histopathological assessment is often difficult, and adding molecular information to classic neuropathological analyses may help ensure diagnostic accuracy, improve risk stratification of patients within a given tumor entity, and help in identifying novel therapeutic targets for an individualized treatment approach. Therefore, this review focuses both on established histopathology as well as on molecular features in the most important brain tumors in children.

Genomic analysis using high-density single nucleotide polymorphism-based oligonucleotide arrays and multiplex ligation-dependent probe amplification provides a comprehensive analysis of INI1/SMARCB1 in malignant rhabdoid tumors

PURPOSE

A high-resolution genomic profiling and comprehensive targeted analysis of INI1/SMARCB1 of a large series of pediatric rhabdoid tumors was done. The aim was to identify regions of copy number change and loss of heterozygosity (LOH) that might pinpoint additional loci involved in the development or progression of rhabdoid tumors and define the spectrum of genomic alterations of INI1 in this malignancy.

EXPERIMENTAL DESIGN

A multiplatform approach using Illumina single nucleotide polymorphism-based oligonucleotide arrays, multiplex ligation-dependent probe amplification, fluorescence in situ hybridization, and coding sequence analysis was used to characterize genome-wide copy number changes, LOH, and genomic alterations of INI1/SMARCB1 in a series of pediatric rhabdoid tumors.

RESULTS

The biallelic alterations of INI1 that led to inactivation were elucidated in 50 of 51 tumors. INI1 inactivation was shown by a variety of mechanisms, including deletions, mutations, and LOH. The results from the array studies highlighted the complexity of rearrangements of chromosome 22 compared with the low frequency of alterations involving the other chromosomes.

CONCLUSIONS

The results from the genome-wide single nucleotide polymorphism array analysis suggest that INI1 is the primary tumor suppressor gene involved in the development of rhabdoid tumors with no second locus identified. In addition, we did not identify hotspots for the breakpoints in sporadic tumors with deletions of chromosome 22q11.2. By employing a multimodality approach, the wide spectrum of alterations of INI1 can be identified in the majority of patients, which increases the clinical utility of molecular diagnostic testing.

Atypical teratoid-rhabdoid tumor spreading along the trigeminal nerve

We here describe the case of a boy with an atypical teratoid-rhabdoid tumor (ATRT) of the 4th ventricle at 1 year of age and a local tumor recurrence at 19 months of age. Due to brainstem infiltration, only incomplete tumor resection was possible each time. High-dose chemotherapy, stem cell transplantation and irradiation resulted in complete tumor remission on a control MRI. At 8 years of age, another tumor appeared extending from the cerebellopontine angle along the right trigeminal nerve through Meckel's cave into the cavernous sinus. The trigeminal tumor was not in continuity with the primary ATRT but was located within the field of prior irradiation, neuroradiologically mimicking a schwannoma or a meningioma. The origin of the trigeminal tumor as a late metastasis of the former ATRT or as a less likely irradiation-induced secondary ATRT and the operative approach are discussed.

Molecular genetics of atypical teratoid/rhabdoid tumors

Rhabdoid tumors are extremely aggressive malignancies that generally occur in infants and young children. The most common locations are the kidney and central nervous system (atypical teratoid/rhabdoid tumor [RT]), although RTs can also arise in most soft-tissue sites. Rhabdoid tumors in all anatomical locations have a similar molecular origin. Mutation or deletion of both copies of the hSNF5/INI1 gene that maps to chromosome band 22q11.2 is observed in approximately 70% of primary tumors. An additional 20 to 25% of tumors have reduced expression at the RNA or protein level, indicative of a loss-of-function event. The INI1 protein is a component of the SWI/SNF chromatin-remodeling complex. The complex is recruited to promoters of a large variety of genes involved in cell signaling, growth, and differentiation. This review summarizes what is currently known regarding the molecular genetics of RTs.

Epigenetic repression of RASSF1A but not CASP8 in supratentorial PNET (sPNET) and atypical teratoid/rhabdoid tumors (AT/RT) of childhood

Supratentorial primitive neuroectodermal tumors (sPNET) and atypical teratoid/rhabdoid tumors (AT/RT) of the CNS represent a biological and clinical enigma, despite advances in both molecular techniques and clinical management for these two rare embryonal brain tumors of childhood. Epigenetic changes hold great potential as possible disease mechanisms and may be manipulated therapeutically. We thus studied aberrant methylation of the genes RASSF1A and CASP8 and its consequence on expression in cell lines and primary tumors using a combination of semiquantitative methylation specific PCR (MSP), bisulfite sequencing and RT-PCR. In all, 17 samples of autopsy-derived normal appearing brain served as controls. Opposed to control tissues 19/24 sPNET and 4/6 AT/RT demonstrated aberrant methylation for the RASSF1A promoter region. Treatment of cell lines using 5-Aza-2'-deoxycytidine (5AZA) alone or in combination with trichostatin A (TSA) succeeded in re-establishing expression of RASSF1A in cell lines derived from a renal rhabdoid, an AT/RT and a medulloblastoma. A 5' CpG-rich region of CASP8 was methylated in normal tissues and in tumors. However, CASP8 showed inconsistent expression patterns in normal and tumor tissues. Our results indicate that aberrant methylation of the RASSF1A promoter region may be of importance in the origin and progression of sPNET and AT/RT while the analysed 5'-CpG rich region of the CASP8 gene does not seem to play an important role in these tumors. Further studies of epigenetic changes in these rare tumors are warranted as their biology remains obscure and treatment efforts have been rather unsuccessfull.

INI1 expression is retained in composite rhabdoid tumors, including rhabdoid meningiomas

Rhabdoid cells are encountered in specific entities, such as malignant rhabdoid tumor and atypical teratoid/rhabdoid tumor, as well as in composite rhabdoid tumors derived secondarily from other tumor types. Although rhabdoid tumors are uniformly aggressive, distinction of the entity from the phenotype remains important for its therapeutic implications. The majority of malignant rhabdoid tumors and atypical teratoid/rhabdoid tumors affect infants and young children, harbor chromosome 22q deletions, and inactivate the INI1/hSNF5/BAF47 tumor suppressor gene on 22q11.2. In contrast, most composite rhabdoid tumors are diagnosed in adults, with FISH detectable 22q losses the exception rather than the rule. However, this assay remains limited since 22q dosages are maintained in 20-30% of malignant rhabdoid tumors and atypical teratoid/rhabdoid tumors. Furthermore, chromosome 22 losses are common in some parent tumor types, particularly meningiomas. The recently developed INI1 antibody shows loss of nuclear expression in malignant rhabdoid tumors and atypical teratoid/rhabdoid tumors, though its status in composite rhabdoid tumors is largely unknown. Therefore, we utilized immunohistochemistry and FISH to study INI1 expression and 22q dosages, respectively, in 40 composite rhabdoid tumors, including 16 meningiomas, 15 carcinomas, three melanomas, two sarcomas, two glioblastomas, and 1 neuroblastoma. Approximately 70% of rhabdoid meningiomas had a 22q deletion, but this was rare in other tumor types. Except for one retroperitoneal leiomyosarcoma, nuclear INI1 expression was retained in all composite rhabdoid tumors, including meningiomas with 22q deletion. Therefore, we conclude that INI1 immunohistochemistry is a relatively simple, sensitive, and specific technique for distinguishing malignant rhabdoid tumor and atypical teratoid/rhabdoid tumor from composite rhabdoid tumor.

Cyclin D1 is overexpressed in atypical teratoid/rhabdoid tumor with hSNF5/INI1 gene inactivation

OBJECT

Although atypical teratoid/rhabdoid tumor (AT/RT) is known to generate through inactivation of the hSNF5/INI1 gene on chromosome 22q, the downstream molecular mechanism remains unclear. We histologically and molecularly reviewed our pediatric brain tumors for unrecognized AT/RTs and evaluated the role of cyclin D1, a potential molecular target of hSNF5/INI1.

METHODS

We analyzed 16 tumors under three years of age: seven medulloblastomas, three anaplastic ependymomas (E IIIs), two each of supratentorial primitive neuroectodermal tumors (sPNETs) and choroid plexus carcinomas (CPCs), and one each of neuroblastoma and pineoblastoma. Immunohistochemistry for glial fibrillary acidic protein, vimentin, epithelial membrane antigen, smooth muscle actin and cyclin D1 was performed. Polymerase chain reaction (PCR)-single-strand conformation polymorphism analysis with direct sequencing, differential PCR and microsatellite analysis were conducted for hSNF5/INI1mutation, homozygous deletion and loss of heterozygosity (LOH) on 22q, respectively. Because of the presence of rhabdoid cells and the polyimmunophenotypic features, the diagnosis was revised to AT/RT in five (31%) tumors, namely, two E IIIs and one each of medulloblastoma, CPC and pineoblastoma. Three of them harbored such hSNF5/INI1 aberrations as germline single base deletion (492/6 delC) and missense mutation (C157T) together with LOH 22q or homozygous deletion. Cyclin D1 was overexpressed in those three tumors but not in the two that lacked hSNF5/INI1 inactivation.

CONCLUSION

AT/RT can be misdiagnosed as a variety of tumors, including ependymoma that potentially harbors LOH 22q. Our data indicate that cyclin D1 is a target of hSNF5/INI1in primary tumors.

Molecular heterogeneity of meningioma with INI1 mutation

BACKGROUND

INI1 (hSNF5) mutations are linked to rhabdoid tumours, but mutations in meningiomas with hot spot mutations in position 377 have also been reported.

AIMS

To analyse the INI1 gene in meningioma.

METHODS

Exons 1, 4, 5, and 9 of the INI1 gene were analysed by the polymerase chain reaction and direct sequencing in 80 meningiomas. For all cases, western blotting of the INI1 protein was performed.

RESULTS

Only one of the 80 samples showed a cytosine insertion in codon 376. This mutation changed the open reading frame in almost the whole exon 9 and resulted in a longer hSNF5 protein. Complex analysis of the above described tumour sample by western blotting, DNA sequencing, and loss of heterozygosity (LOH) analysis showed that this particular meningioma consisted of heterogeneic cellular components. One of these components had a mutated INI1 gene, whereas in the other component INI1 was intact.

CONCLUSIONS

INI1 mutation is a rare event in the molecular pathology of meningiomas. It is possible for the INI1 gene to be mutated in only a proportion of meningioma cells.

Molecular analysis of the rhabdoid predisposition syndrome in a child: a novel germline hSNF5/INI1 mutation and absence of c-myc amplification

The authors report a case of the rhabdoid predisposition syndrome (RPS) secondary to a germline hSNF5/INI1 mutation, whose brain tumor was originally unclassified but finally diagnosed as an atypical teratoid/rhabdoid tumor (AT/RT) by molecular analysis. A 7-month-old infant presented with hydrocephalus secondary to a huge pineal tumor and subsequently developed a renal rhabdoid tumor. The histology of the brain tumor was initially undetermined; however, an AT/RT was strongly suspected because of her clinical course. Mutational screening of the hSNF5/INI1 gene by heteroduplex and direct sequence analysis detected a missense mutation at codon 53 (CGA --> TGA, arginine --> stop) in both tumors, as well as in normal tissue of the kidney. Polymerase chain reaction (PCR)-based microsatellite analysis showed in both tumors allelic loss on chromosome arm 22q to which the hSNF5/INI1 gene maps. c-myc amplification was examined by differential PCR but not detected. Histologic review of the brain tumor by immunohistochemistry confirmed focal expression of epithelial membrane antigen and smooth muscle actin. These findings suggest that the brain tumor was really an AT/RT as a component of RPS secondary to a germline hSNF5/INI1 mutation. The present mutation has never been reported in the literature.