Constitutional de novo t(1;22)(p22;q11.2) and ependymoma

De novo Unbalanced 1;22 Translocation with 22q11 Deletion Syndrome

This report describes a newborn girl presenting with some of the common features of DiGeorge syndrome/velocardiofacial syndrome (DGS/VCFS), including hypocalcemia, atrial septal defect, and aortic stenosis. Several genetic tests were carried out to determine the origin of the clinical phenotype. MLPA was initially performed followed by aCGH, cytogenetic analysis, and FISH. Cytogenetic analysis of the proband's parents was also done. MLPA revealed a deletion in 22q11.1q11.2 spanning from the cat eye syndrome region to the most commonly deleted region in DGS/VCFS patients. The size of the deletion as defined by aCGH was 3.2 Mb. The karyotype of the proband was 45,XX,der(1)t(1;22)(p36.3;q11.2)dn,-22, the karyotypes of the parents were normal. FISH analysis showed that the 22q11 deletion occurred in the der(1). No loss or gain of chromosomal material was evident for chromosome 1, as confirmed by MLPA, aCGH, and FISH. Unbalanced translocations resulting in DGS are relatively rare, with limited reports in the literature. To our knowledge, this is the second case involving chromosome 1 and the first one with breakpoints in 1p36 and 22q11.2. This case also emphasizes the importance of combining diagnostic methods to better understand a given genetic abnormality.

The molecular biology of ependymomas

Intracranial ependymomas are the third most common primary brain tumor in the pediatric population. Although an anaplastic variant is recognized, numerous studies examining the prognostic implications of histological features, such as necrosis, endothelial proliferation and mitoses, have yielded contradictory results. In order to improve outcome prediction in affected patients and to refine therapeutic decision-making, there is a strong need for identifying relevant biological correlates of tumor behavior. The molecular biology of tumors is a rapidly expanding field and includes investigations into cytogenetics, oncogenes, growth factors, growth factor receptors, hormonal receptors, proliferation markers, apoptosis, cell cycle genes and cell adhesion molecules, as well as factors potentially related to therapeutic resistance, such as the multidrug resistance gene. The molecular biology of astrocytic tumors in adults has been the subject of many studies; however, relatively few studies have been focused on ependymomas. Herein we review potential oncological markers in ependymomas that have been identified to date and highlight the limitations of our current knowledge as a basis for defining areas for future investigation.

Loss of chromosome 1 in myxopapillary ependymoma suggests a region out of chromosome 22 as critical for tumour biology: a FISH analysis of four cases on touch imprint smears

OBJECTIVE

Ependymomas are glial tumours. They constitute approximately 5-10% of intracranial tumours and are tumours which can recur. Predictive factors of outcome in ependymomas are not well established. Karyotypic studies are relatively scarce and loss of chromosome 22 has been described to correlate with recurrence. We are unaware of any reports involving chromosome 1 aberrations in the malignant progression of ependymomas.

METHODS

Cytogenetic analysis of four myxopapillary ependymomas was performed using double target fluorescent in situ hybridization (FISH), focusing on chromosomes 1 and 22.

RESULTS

One patient's tumour had recurred. FISH was performed on 500 nuclei/tumours. All four cases showed a loss of chromosome 22q while only one showed an additional loss of chromosome 1p, and this was the one that recurred.

CONCLUSIONS

We support the presence of a tumour suppressor gene on 1p associated with relapse in myxopapillary ependymomas and suggest that status of chromosome 1p by FISH may indicate a high-risk group of patients harbouring this tumour. More studies of this type are needed towards this direction as our results refer to a minimal number of individuals analysed.

Analysis of chromosome 7 in adult and pediatric ependymomas using chromogenic in situ hybridization

Few studies have yielded reliable data that distinguish between ependymal neoplasms based on molecular genetic attributes. The present study utilizes chromogenic in situ hybridization (CISH), a relatively recent hybridization technique, to retrospectively examine chromosome 7-copy number in pediatric and adult ependymomas. Of the 27 hybridizations, polysomy of chromosome 7 was detected in 10 out of 15 (66%) adult ependymomas, and in only three out of 12 (25%) pediatric lesions. All myxopapillary ependymomas showed polysomy. The remaining tumors were diploid. The authors conclude that (1) there are distinct genetic subsets of ependymoma, in particular, increases in copy number of chromosome 7 are almost exclusively found in myxopapillary ependymoma, and that (2) CISH is a rapid and sensitive method of stratifying morphological variants of ependymoma and potentially other central nervous system (CNS) tumors. These results encourage further investigations with CISH on a larger scale to determine its merit as an ancillary diagnostic and prognostic tool.

A palindrome-mediated mechanism distinguishes translocations involving LCR-B of chromosome 22q11.2

Two known recurrent constitutional translocations, t(11;22) and t(17;22), as well as a non-recurrent t(4;22), display derivative chromosomes that have joined to a common site within the low copy repeat B (LCR-B) region of 22q11.2. This breakpoint is located between two AT-rich inverted repeats that form a nearly perfect palindrome. Breakpoints within the 11q23, 17q11 and 4q35 partner chromosomes also fall near the center of palindromic sequences. In the present work the breakpoints of a fourth translocation involving LCR-B, a balanced ependymoma-associated t(1;22), were characterized not only to localize this junction relative to known genes, but also to further understand the mechanism underlying these rearrangements. FISH mapping was used to localize the 22q11.2 breakpoint to LCR-B and the 1p21 breakpoint to single BAC clones. STS mapping narrowed the 1p21.2 breakpoint to a 1990 bp AT-rich region, and junction fragments were amplified by nested PCR. Junction fragment-derived sequence indicates that the 1p21.2 breakpoint splits a 278 nt palindrome capable of forming stem-loop secondary structure. In contrast, the 1p21.2 reference genomic sequence from clones in the database does not exhibit this configuration, suggesting a predisposition for regional genomic instability perhaps etiologic for this rearrangement. Given its similarity to known chromosomal fragile site (FRA) sequences, this polymorphic 1p21.2 sequence may represent one of the FRA1 loci. Comparative analysis of the secondary structure of sequences surrounding translocation breakpoints that involve LCR-B with those not involving this region indicate a unique ability of the former to form stem-loop structures. The relative likelihood of forming these configurations appears to be related to the rate of translocation occurrence. Further analysis suggests that constitutional translocations in general occur between sequences of similar melting temperature and propensity for secondary structure.

Epidemiology and pathology of intraventricular tumors

Tumors that primarily or exclusively involve the ventricular system constitute a rare and heterogeneous group. Certain histologic tumor types predominantly occur in children, whereas others are more common in adults. Tumor location provides additional clues to correct diagnosis. When used in conjunction with clinical and radiologic data, histopathologic features can distinguish among this wide range of possibilities to provide the correct diagnosis for optimal patient management.

Constitutional t(16;22)(p13.3;q11.2 approximately 12) in a primitive neuroectodermal tumor of the pineal region

Constitutional chromosome anomalies are known to determine an increased risk of malignancy in certain disorders. We report the case of a 6-month-old female with a primitive neuroectodermal tumor (PNET) of the pineal region and a constitutional reciprocal translocation t(16;22)(p13.3;q11.2 approximately 12). The clustering of cancer chromosome breakpoints to specific chromosome regions is a well-documented phenomenon, with breakpoints on chromosome 22q11.2 approximately 12 having been identified in several subtypes of small round cell tumors. The finding of a 22q11.2 approximately 12 breakpoint in this patient suggests this constitutional translocation may somehow have predisposed the patient to the development of the tumor.

Analysis of the NF2 gene in oligodendrogliomas and ependymomas

Allelic losses of chromosome 22 are commonly found in ependymomas and oligodendrogliomas, suggesting that at least one tumor suppressor gene on chromosome 22 must be inactivated during the multistep process of tumorigenesis in these glial tumors. The neurofibromatosis 2 gene (NF2) located at 22q12, is a candidate tumor suppressor gene potentially involved in the pathogenesis of gliomas. Because there have been only a few studies of the NF2 gene in glial tumors other than astrocytoma, we screened the entire 17 NF2 exons for mutations in a series of 47 nonastrocytic tumors, including 40 oligodendrogliomas and 7 ependymomas. Only one mutation was detected, a 59-base pair insertion in exon 3 from a spinal anaplastic ependymoma. These results concur with previous findings proposing preferential inactivation of the NF2 gene in a subgroup of ependymomas, and suggest that the NF2 gene is not the target of chromosome 22 aberrations in oligodendrogliomas.

Gain of 1q and loss of 22 are the most common changes detected by comparative genomic hybridisation in paediatric ependymoma

Ependymomas are the third most common brain tumour in the paediatric population. Although cytogenetic and molecular analyses have pinpointed deletions of chromosomes 6q, 17, and 22 in a subset of tumours, definitive patterns of genetic aberrations have not been determined. In the present study, we analysed 40 ependymomas from paediatric patients for genomic loss or gain using comparative genomic hybridisation (CGH). Eighteen of the tumours (45%) had no detectable regions of imbalance. In the remaining cases, the most common copy number aberrations were loss of 22 (25% of tumours) and gain of 1q (20%). Three regions of high copy number amplification were noted at 1q24-31 (three cases), 8q21-23 (two cases), and 9p (one case). Although there was no association with the loss or gain of any chromosome arm or with benign versus anaplastic histologic characteristics, the incidence of gain of 7q and 9p and loss of 17 and 22 was significantly higher in recurrent versus primary tumours. This study has identified a number of chromosomal regions that may contain candidate genes involved in the development of different subgroups of ependymoma.

Fluorescence in situ hybridization determination of 22q12-q13 deletion in two intracerebral ependymomas

The sole cytogenetic abnormalities encountered in two childhood anaplastic intracerebral ependymomas were an isodicentric chromosome 22 in one case and an unbalanced chromosome 22 translocation associated with a partial deletion in the other. Fluorescence in situ hybridization analysis showed that the common 22q arm loss did not involve the rhabdoid region but included the EWS and NF2 loci. These results, in conjunction with data in the literature, suggest that the most frequently recurrent genomic loss in ependymomas does not involve the proximal 22q11.2 chromosome region but is localized distally to the hSNF5/INI1 locus. A tumor-suppressor gene, independent of the NF2 gene, which seems to be exclusively involved in intramedullary spinal cord ependymomas, might be implicated in the genesis of these intracranial tumors.

A novel translocation t(3;22)(q21;q11) involving 3q21 in myelodysplastic syndrome-derived overt leukemia with thrombocytosis

We report here a novel translocation t(3;22)(q21;q11) in myelodysplastic syndrome (MDS)-derived overt leukemia with thrombocytosis. A 44-year-old female was initially diagnosed as MDS with a low platelet count and normal karyotype. After 4 months, blood leukemic cells and platelets rapidly increased concomitantly and a diagnosis of acute myeloblastic leukemia (AML M1) was made. Chromosome analysis showed 46, XX, t(3;22)(q21;q11) in 14 of 20 metaphases. Fluorescence in situ hybridization analysis confirmed both the der(3)t(3;22) and the der(22)t(3;22). Our results suggest that unidentified gene(s) at 3q21 breakpoint may be implicated in the pathogenesis of abnormal thrombopoiesis as observed in the 3q21q26 syndrome.

Evidence for an ependymoma tumour suppressor gene in chromosome region 22pter-22q11.2

Ependymomas are glial tumours of the brain and spinal cord. The most frequent genetic change in sporadic ependymoma is monosomy 22, suggesting the presence of an ependymoma tumour suppressor gene on that chromosome. Clustering of ependymomas has been reported to occur in some families. From an earlier study in a family in which four cousins developed an ependymoma, we concluded that an ependymoma-susceptibility gene, which is not the NF2 gene in 22q12, might be located on chromosome 22. To localize that gene, we performed a segregation analysis with chromosome 22 markers in this family. This analysis revealed that the susceptibility gene may be located proximal to marker D22S941 in 22pter-22q11.2. Comparative genomic hybridization showed that monosomy 22 was the sole detectable genetic aberration in the tumour of one of the patients. Loss of heterozygosity studies in that tumour revealed that, in accordance to Knudson's two-hit theory of tumorigenesis, the lost chromosome 22 originated from the parent presumed to have contributed the wild-type allele of the susceptibility gene. Thus, our segregation and tumour studies collectively indicate that an ependymoma tumour suppressor gene may be present in region 22pter-22q11.2.

Cytogenetic study of 33 ependymomas

Ependymomas are glial tumors. They constitute approximately 5-10% of intracranial tumors. Ependymomas are tumors which can recur. Predictive factors of outcome in ependymomas are not well-established. Karyotypic studies on ependymomas are relatively scarce, and no specific chromosomal change has been described in these neoplasms. We performed a cytogenetic study of 33 ependymomas, of which eight were recurrent tumors, to determine the type and incidence of cytogenetic changes.

Karyotype studies in 18 ependymomas with literature review of 107 cases

Cytogenetic studies from 17 pediatric ependymomas and 1 ependymoblastoma are presented. Eight tumors had abnormal karyotypes. Another 107 published cases of cytogenetic analyses from pediatric and adult ependymomas or ependymoblastomas were reviewed. Of the total 125 tumors, 83 (66%) had abnormal karyotypes, of which 24 had a sole autosomal abnormality. Approximately one third had monosomy 22 (-22) or breakpoint 22q11-13, with a higher incidence in adult (56%) versus pediatric (28%) tumors. Structural abnormalities of chromosomes 1, 6, and 17, and numerical abnormalities of 7, 9, 12, and 20, in particular, are also discussed. Although no primary cytogenetic abnormality is evident, these findings may provide direction for additional investigations regarding the classification of these tumors.

Molecular genetic analysis of ependymal tumors. NF2 mutations and chromosome 22q loss occur preferentially in intramedullary spinal ependymomas

Ependymal tumors are heterogeneous with regard to morphology, localization, age at first clinical manifestation, and prognosis. Several molecular alterations have been reported in these tumors, including allelic losses on chromosomes 10, 17, and 22 and mutations in the NF2 gene. However, in contrast to astrocytic gliomas, no consistent molecular alterations have been associated with distinct types of ependymal tumors. To evaluate whether morphological subsets of ependymomas are characterized by specific genetic lesions, we analyzed a series of 62 ependymal tumors, including myxopapillary ependymomas, subependymomas, ependymomas, and anaplastic ependymomas, for allelic losses on chromosome arms 10q and 22q and mutations in the PTEN and NF2 genes. Allelic losses on 10q and 22q were detected in 5 of 56 and 12 of 54 tumors, respectively. Six ependymomas carried somatic NF2 mutations, whereas no mutations were detected in the PTEN gene. All six of the NF2 mutations occurred in ependymomas of WHO grade II and were exclusively observed in tumors with a spinal localization (P = 0.0063). These findings suggest that a considerable fraction of spinal ependymomas are associated with molecular events involving chromosome 22 and that mutations in the NF2 gene may be of primary importance for their genesis. Furthermore, our data suggest that the more favorable clinical course of spinal ependymomas may relate to a distinct pattern of genetic alterations different from that of intracerebral ependymomas.

Intracranial ependymomas: a review

Ependymomas are rare neuroectodermal tumors arising from ependymal cells of the ventricular system, choroid plexus, filum terminale, and central canal of the spinal cord (1,2). This review focuses on intracranial ependymomas with special emphasis on pathology, etiology, cytogenetic characteristics, and adjuvant radiation therapy. Recent advances in neurosurgical technique, radiation therapy, and molecular biology have affected management of these tumors and have the potential to increase long-term cure rates. The role of highly advanced radiation therapy techniques such as stereotactic radiosurgery will need to be better defined.

Constitutional balanced translocations in alveolar rhabdomyosarcoma

Chromosomal analysis of tumor tissue from two children with alveolar rhabdomyosarcoma revealed t(1;5)(q32;q31) and t(1;22)(q21;q11.2) in all metaphases examined, respectively. Peripheral blood lymphocytes carried the same cytogenetic abnormality as that of the tumor cells in both patients. Parental lymphocytes were karyotypically normal in the patient with t(1;22), indicating a de novo constitutional translocation, but t(1;5) was paternally inherited in the other patient. The presence of constitutional translocations in these two children might have contributed to the development of alveolar rhabdomyosarcoma.

Genetics of pediatric central nervous system tumors

PURPOSE

Pediatric central nervous system (CNS) tumors comprise a wide variety of histologic subtypes ranging from the benign juvenile pilocytic astrocytoma to the highly aggressive atypical teratoid/rhabdoid tumor. Although some brain tumors are seen in association with inherited genetic disorders which predispose to malignancies, most are sporadic. Current knowledge regarding the cytogenetic and molecular genetic events which have been implicated in the development or progression of common brain tumors in children in the subject of this review.

METHODS

Combined cytogenetic and molecular genetic approaches, including fluorescence in situ hybridization, have been used to identify genomic alterations in different histologic types of pediatric brain tumors.

RESULTS

The most frequent abnormality in primitive neuroectodermal tumor/medulloblastoma is an i(17q), present in approximately 50% of cases. This finding implicates the presence of a tumor suppressor gene on 17p, which is important in tumor development. A number of genes on 17p have been eliminated as candidates for this locus, including TP53. A tumor suppressor gene in chromosome band 22q11.2 has been hypothesized to play a role in atypical teratoid/rhabdoid tumors, and positional cloning strategies are in progress to identify a rhabdoid tumor gene. Chromosome 22 deletions are also seen in meningiomas and a small percentage of ependymomas, but it is not yet known whether the same gene is responsible for more than one malignancy. With regard to childhood astrocytomas, tumor-associated genetic changes have not yet been identified for the common juvenile pilocytic or low grade diffuse astrocytoma. In contrast, malignant anaplastic astrocytomas and glioblastoma multiforme have abnormalities similar to those seen in adults, including loss of alleles on 17p13 and TP53 mutations, trisomy 7, EGFR rearrangements, and loss of chromosomes 10 and 22.

CONCLUSIONS

The presence of tumor-associated genetic abnormalities has clinical utility in a differential diagnostic setting, and has lead to the identification of genes which contribute to tumorigenesis.