Common pathogenetic mechanism for three tumor types in bilateral acoustic neurofibromatosis

Current progress in genomics and targeted therapies for neurofibromatosis type 2

Neurofibromatosis type 2 (NF2), a multiple neoplasia syndrome, is a manifestation of an impaired expression of the merlin protein, exerting inhibitory effects on cell proliferation signals due to abnormalities of the NF2 gene located on chromosome 22. About half of patients inherit a germline mutation from a parent, and nearly 60% of de novo NF2 patients are estimated to have somatic mosaicism. The development of technical methods to detect NF2 gene mutation, including targeted deep sequencing from multiple tissues, improved the diagnostic rate of mosaic NF2. With improved understanding of genetics and pathogenesis, the diagnostic criteria for NF2 were updated to assist in identifying and diagnosing NF2 at an earlier stage. The understanding of cell signaling pathways interacting with merlin has led to the development of molecular-targeted therapies. Currently, several translational studies are searching for possible therapeutic agents targeting VEGF or VEGF receptors. Bevacizumab, an anti-VEGF monoclonal antibody, is widely used in many clinical trials aiming for hearing improvement or tumor volume control. Currently, a randomized, double-masked trial to assess bevacizumab is underway. In this randomized control trial, 12 other Japanese institutions joined the principal investigators in the clinical trial originating at Fukushima Medical University. In this review, we will be discussing the latest research developments regarding NF2 pathophysiology, including molecular biology, diagnosis, and novel therapeutics.

Bibliometric analysis of the top 100 most-cited articles in neurofibromatosis

Background:

Neurofibromatosis (NF) is an umbrella term that refers to three distinct disease entities: NF Type 1, Type 2, and schwannomatosis. Here, we reviewed the scientific performance and the most influential publications on NF.

Methods:

A keyword-based search was performed using the Scopus database. The top 100 articles were grouped based on NF types and the studied entities. The differences between the articles, authors, and journals were quantified based on certain parameters. Other parameters were collected for the complete citational analysis.

Results:

The top 100 articles were published between 1961 and 2020. The most trending period of research was in the 1990s and articles studying the clinical aspect and the underlying genetic correlation made up 84% of all articles from the list. The United States of America (USA) had the highest number of contributions (69 articles, 69%). The top institute of contribution to the list was the Howard Hughes Medical Institute, USA (14 articles, 14%). Author-based analysis reveals that the neurologist D. H. Gutmann from St. Louis Children’s Hospital, USA, was the most active and authored 11 articles (11%) on the list.

Conclusion:

The publication trends show that articles studying medical and surgical management were of little interest. The top 100 articles did not include any randomized control trials, and the highest level of evidence was obtained from reviews of pooled knowledge as well as population-based and longitudinal studies.

A murine model of neurofibromatosis type 2 that accurately phenocopies human schwannoma formation

Neurofibromatosis type 2 (NF2) is an autosomal dominant genetic disorder resulting from germline mutations in the NF2 gene. Bilateral vestibular schwannomas, tumors on cranial nerve VIII, are pathognomonic for NF2 disease. Furthermore, schwannomas also commonly develop in other cranial nerves, dorsal root ganglia and peripheral nerves. These tumors are a major cause of morbidity and mortality, and medical therapies to treat them are limited. Animal models that accurately recapitulate the full anatomical spectrum of human NF2-related schwannomas, including the characteristic functional deficits in hearing and balance associated with cranial nerve VIII tumors, would allow systematic evaluation of experimental therapeutics prior to clinical use. Here, we present a genetically engineered NF2 mouse model generated through excision of the Nf2 gene driven by Cre expression under control of a tissue-restricted 3.9kbPeriostin promoter element. By 10 months of age, 100% of Postn-Cre; Nf2(flox/flox) mice develop spinal, peripheral and cranial nerve tumors histologically identical to human schwannomas. In addition, the development of cranial nerve VIII tumors correlates with functional impairments in hearing and balance, as measured by auditory brainstem response and vestibular testing. Overall, the Postn-Cre; Nf2(flox/flox) tumor model provides a novel tool for future mechanistic and therapeutic studies of NF2-associated schwannomas.

Schwannomas and their pathogenesis

Schwannomas may occur spontaneously, or in the context of a familial tumor syndrome such as neurofibromatosis type 2 (NF2), schwannomatosis and Carney's complex. Schwannomas have a variety of morphological appearances, but they behave as World Health Organization (WHO) grade I tumors, and only very rarely undergo malignant transformation. Central to the pathogenesis of these tumors is loss of function of merlin, either by direct genetic change involving the NF2 gene on chromosome 22 or secondarily to merlin inactivation. The genetic pathways and morphological features of schwannomas associated with different genetic syndromes will be discussed. Merlin has multiple functions, including within the nucleus and at the cell membrane, and this review summarizes our current understanding of the mechanisms by which merlin loss is involved in schwannoma pathogenesis, highlighting potential areas for therapeutic intervention.

Molecular mechanisms promoting the pathogenesis of Schwann cell neoplasms

Neurofibromas, schwannomas and malignant peripheral nerve sheath tumors (MPNSTs) all arise from the Schwann cell lineage. Despite their common origin, these tumor types have distinct pathologies and clinical behaviors; a growing body of evidence indicates that they also arise via distinct pathogenic mechanisms. Identification of the genes that are mutated in genetic diseases characterized by the development of either neurofibromas and MPNSTs [neurofibromatosis type 1 (NF1)] or schwannomas [neurofibromatosis type 2 (NF2), schwannomatosis and Carney complex type 1] has greatly advanced our understanding of these mechanisms. The development of genetically engineered mice with ablation of NF1, NF2, SMARCB1/INI1 or PRKAR1A has confirmed the key role these genes play in peripheral nerve sheath tumorigenesis. Establishing the functions of the NF1, NF2, SMARCB1/INI1 and PRKAR1A gene products has led to the identification of key cytoplasmic signaling pathways promoting Schwann cell neoplasia and identified new therapeutic targets. Analyses of human neoplasms and genetically engineered mouse models have established that interactions with other tumor suppressors such as TP53 and CDKN2A promote neurofibroma-MPNST progression and indicate that intratumoral interactions between neoplastic and non-neoplastic cell types play an essential role in peripheral nerve sheath tumorigenesis. Recent advances have also provided new insights into the identity of the neural crest-derived populations that give rise to different types of peripheral nerve sheath tumors. Based on these findings, we now have an initial outline of the molecular mechanisms driving the pathogenesis of neurofibromas, MPNSTs and schwannomas. However, this improved understanding in turn raises a host of intriguing new questions.

Molecular biology of unreresectable meningiomas: implications for new treatments and review of the literature

Even though meningiomas are most often benign tumors, they can be locally invasive and can develop in locations that prevent surgical treatment. The molecular and biologic factors underlying meningioma development are only now beginning to be understood. Genetic factors such as mutations in the neurofibromatosis-2 gene and in chromosomes 1, 9, and 10 play important roles in meningioma development and may be responsible for atypical tumors in some cases. Cellular factors such as telomerase activation and tyrosine kinase receptor mutations may also play an important role. Finally, autocrine and paracrine factors including epidermal growth factor receptor, platelet-derived growth factor-1, and fibroblast growth factor have been implicated in the development of some tumors. Although the relationship between the various factors implicated in tumor development is unknown, understanding these factors will be critical in the treatment of malignant or surgically inaccessible tumors.

Neurofibromatosis type 2

Neurofibromatosis type 2 is an autosomal-dominant multiple neoplasia syndrome that results from mutations in the NF2 tumour suppressor gene located on chromosome 22q. It has a frequency of one in 25,000 livebirths and nearly 100% penetrance by 60 years of age. Half of patients inherit a germline mutation from an affected parent and the remainder acquire a de novo mutation for neurofibromatosis type 2. Patients develop nervous system tumours (schwannomas, meningiomas, ependymomas, astrocytomas, and neurofibromas), peripheral neuropathy, ophthalmological lesions (cataracts, epiretinal membranes, and retinal hamartomas), and cutaneous lesions (skin tumours). Optimum treatment is multidisciplinary because of the complexities associated with management of the multiple, progressive, and protean lesions associated with the disorder. We review the molecular pathogenesis, genetics, clinical findings, and management strategies for neurofibromatosis type 2.

Microbeads and anchorage-dependent eukaryotic cells: the beginning of a new era in biotechnology

Modern methods for the mass cultivation of anchorage-dependent mammalian cells started with the advent of microcarrier technology. Largely for reasons pertaining to their mode of preparation and ease of cultivation, 150-230 microns microbeads have been overwhelmingly adopted and the technology around them developed. To meet high biomass, macroporous microbeads have been developed. Also, the chemistry of the microsupport has been adapted in order to afford better protection of fragile cells to mechanical wear while simultaneously reorienting their differentiation towards the sought aims (production of cytokines, enzymes etc. ...). Future progress depends upon solutions being brought to problems inherent to this new technology (maintenance of steady state conditions of growth etc. ...) as well as to requirements arising from animal cell culture in general (biosensors, bioreactor's design etc. ...). Besides such technical implementations, biology at large is also expected to benefit from the advent of microcarriers in fields as diverse as the preparation of metaphasic chromosomes in bulk, toxicity testing, organ reconstitution following cell transplantation etc.

The phakomatoses

The "phakomatosis" concept was formulated early in the twentieth century by the ophthalmologist van der Hoeve. He included 3 disorders in the group-neurofibromatosis, tuberous sclerosis complex, and von Hippel-Lindau syndrome--on the basis of the occurrence of patchy ophthalmologic manifestations in each disorder. Since the name was coined, much has been learned about the pathogenesis of these 3 disorders. It is clear that 2 of them--neurofibromatosis and tuberous sclerosis--are collective terms for multiple disorders. Each of the conditions is caused by distinct genetic defects, with little commonality in terms of protein function. Yet, in some respects, the disorders share a pathogenetic mechanism, that of the tumor suppressor gene. This review will briefly describe these disorders in light of what has been learned about underlying molecular pathogenesis. In each case, genetic testing is beginning to be available; principles of the use of genetic tests will be described.

The phakomatoses

The phakomatoses are a diverse set of disorders related principally by a similar tendency to produce patchy manifestations that affect the nervous system and various other tissues. All of the disorders involve the occurrence of benign neoplasms or hamartomatous growths, and all involve the action of a distinct gene that functions as a tumor suppressor. At present, none of the phakomatoses is amenable to effective medical treatment, so management is limited to surveillance and treatment of progressive lesions. The radiologist plays a key role in this management, participating in diagnosis and follow-up of affected patients.

Serial Analysis of Gene Expression in Neurofibromatosis Type 2–Associated Vestibular Schwannoma

HYPOTHESIS

The genesis, morphology, and growth characteristics of vestibular schwannomas are determined by genetic alterations which vary gene transcript expression and this transcript expression can be qualitatively and quantitatively evaluated using the SAGE technique. By use of such technique, gene products with tumorigenic potential may be identified, providing insight and targets for future study.

BACKGROUND

Serial analysis of gene expression (SAGE) is a powerful new technique that allows detailed qualitative and quantitative evaluation of cellular gene transcript expression. Tissue in limited quantity (5 x 10 to 2 x 10 cells) may be analyzed by a modified version of SAGE called microSAGE. Application of SAGE or microSAGE to study vestibular schwannoma gene expression has not been previously reported.

METHODS

Fresh, vestibular schwannoma specimen from an individual with the diagnosis of neurofibromatosis type 2 was attained intraoperatively and maintained in a sealed container at -80degreesC until the time of analysis. The tissue was processed according to the microSAGE protocol, using 180 mg of vestibular schwannoma as starting material.

RESULTS

The protocol resulted in the generation and sequencing of a tag library involving 458 tags representing 277 different gene products, including many transcripts known to be expressed in vestibular schwannomas. Several gene products with tumorigenic potential were identified.

CONCLUSIONS

These data demonstrate that microSAGE is a useful technique to study vestibular schwannoma gene expression. Future studies will include building more comprehensive libraries and comparing libraries from various vestibular schwannoma phenotypes to identify useful diagnostic or prognostic markers, and targets for therapeutic intervention.

Meningiomas: Updating Basic Science, Management, and Outcome

BACKGROUND

Meningiomas are biologically complex and clinically and surgically challenging. These features, combined with the rewarding potential for cure, make them of great interest to neurologists, neurosurgeons, and neuroscientists alike.

REVIEW SUMMARY

Initially, we review the clinical context of meningiomas, particularly recent changes in histopathological classification, diagnosis, and neuroimaging. Secondly, the underlying basic science as it has evolved over the last decades is summarized. The status of areas recently of intense interest, such as steroid hormone receptors and oncogenic viruses is described. Additionally, emerging areas of great promise, such as cytogenetics and molecular biology are presented. Lastly, we describe recent advances in management. In particular, skull-base surgery, image-guided surgery, and advances in radiotherapy are emphasized. The possible impact of basic research on management and outcome is also outlined.

CONCLUSIONS

Although usually benign and amenable to cure, meningiomas still present significant diagnostic and treatment challenges. Advances in basic science, surgery, and adjuvant therapy are widening the potential for safe, effective, evidence-based management leading to even better outcomes

Loss of heterozygosity on long arm of chromosome 22 in sporadic colorectal carcinoma

AIM: The loss of heterozygosity (LOH) on tumor suppressor genes is believed to play a key role in carcinogenesis of colorectal cancer. In this study, we analyzed the LOH at 5 loci on the long arm of chromosome 22 in sporadic colorectal cancer to identify additional loci involved in colorectal tumorigenesis.

METHODS: Five polymorphic microsatellite markers were analyzed in 83 cases of colorectal and normal DNA by PCR. PCR products were eletrophoresed on an ABI 377 DNA sequencer; Genescan 3.1 and Genotype 2.1 software were used for LOH scanning and analysis. Comparison between LOH frequency and clinicopathological data were performed by χ² test. P < 0.05 was considered as statistically significant.

RESULTS: The average LOH frequency on chromosome 22q was 28.38%. The region between markers D22S280 and D22S274 (22q12.2-q13.33) exhibited relatively high LOH frequency. The two highest LOH loci with frequencies of 35.09% and 34.04% was identified on D22S280 (22q12.2-12.3) and D22S274 (22q13.32-13.33).8 cases showed LOH at all informative loci, suggesting that one chromosome 22q had been completely lost. On D22S274 locus, LOH frequency of rectal cancer was 50% (9/18), which was higher than that of proximal colon cancer (12%, 2/17) (P = 0.018). The frequency of distal colon cancer was 42% (5/12), also higher than that of proximal colon cancer. But there was no statistical significance. Putting both the tumors in distal colon and rectum together into consideration, the frequency, 47% (14/30), was higher than that of proximal colon cancer (P = 0.015), suggesting the mechanism of carcinogenisis was different in both groups.

CONCLUSIONS: This study provided evidence for the involvement of putative tumor suppressor genes related to the sporadic colorectal carcinoma on chromosome 22q. The tumor-suppressor-gene (s) might locate on the 22q12.2-12.3 and/or 22q13.32-13.33.

Neurocutaneous disorders

"Neurocutaneous disorders" is a catch-all phrase that includes all disorders involving both the nervous systems and the skin. These may range from disorders in which cutaneous findings are essential to diagnosis to those with less significant involvement of the skin. Because of the variety of disorders that involve the skin and the nervous system, this article reviews a few of the more essential diagnoses, and those with recent advancements in diagnosis and management. Many of these diseases are single gene disorders, for which the genes have been discovered in the past few years. The article is divided into sections, highlighting disorders transmitted by different inheritance pattern.

ERM-Merlin and EBP50 protein families in plasma membrane organization and function

The ezrin-radixin-moesin (ERM) family of proteins have emerged as key regulatory molecules in linking F-actin to specific membrane proteins, especially in cell surface structures. Merlin, the product of the NF2 tumor suppressor gene, has sequence similarity to ERM proteins and binds to some of the same membrane proteins, but lacks a C-terminal F-actin binding site. In this review we discuss how ERM proteins and merlin are negatively regulated by an intramolecular association between their N- and C-terminal domains. Activation of at least ERM proteins can be accomplished by C-terminal phosphorylation in the presence of PIP2. We also discuss membrane proteins to which ERM and merlin bind, including those making an indirect linkage through the PDZ-containing adaptor molecules EBP50 and E3KARP. Finally, the function of these proteins in cortical structure, endocytic traffic, signal transduction, and growth control is discussed.

The tumour suppressor protein NF2/merlin: the puzzle continues

Neurofibromatosis type 2 (NF2) is a dominantly inherited disease characterized by the formation of bilateral acoustic schwannomas and other benign tumours associated with the central nervous system. The NF2 protein, also known as merlin or schwannomin, is a recently cloned tumour suppressor and is mutated or inactivated in most schwannomas and meningiomas. Homology analysis indicates that merlin is most closely related to members of the protein 4.1 superfamily especially ezrin, radixin and moesin, the ERM proteins. ERM proteins link membrane proteins to the cytoskeleton. It has been speculated that disruption of a similar membrane-linking role for merlin is involved in the development of tumours. This review focuses on what is now known of the organization and role of merlin's functional domains and how its activity might be regulated. Recent evidence of post-translational regulatory mechanisms which offer hope for new drug intervention strategies to help alleviate this debilitating disease are asses sed.

Calpain-dependent proteolysis of NF2 protein: involvement in schwannomas and meningiomas

The neurofibromatosis type 2 (NF2) protein, known as merlin or schwannomin, is a tumor suppressor, and the NF2 gene has been found to be mutated in the majority of schwannomas and meningiomas, including both sporadically occurring and familial NF2 cases. Although the development of these tumors depends on the loss of merlin, the presence of tumors lacking detectable NF2 mutations suggests different mechanisms for inactivating merlin. Recent studies have demonstrated cleavage of merlin by calpain, a calcium-dependent neutral cysteine protease, and marked activation of the calpain system resulting in the degradation of merlin in these tumors. Increased turnover of merlin by calpain in some schwannomas and meningiomas exemplifies tumorigenesis linked to the calpain-mediated proteolytic pathway.

Enhanced proliferation and potassium conductance of Schwann cells isolated from NF2 schwannomas can be reduced by quinidine

Neurofibromatosis type 2 (NF2) is an autosomal dominant disease that is characterized mainly by schwannomas, as well as menigiomas and gliomas. The NF2 gene product merlin/schwannomin acts as a tumor suppressor. Schwann cells derived from NF2 schwannomas showed an enhanced proliferation rate, and electrophysological studies revealed larger K(+) outward currents as compared with controls. Schwann cells isolated from schwannomas of NF2 patients or multiorgan donors were treated with different concentrations of the K(+) current blockers quinidine, tetraethylammonium chloride, and 4-aminopyridine and K(+) outward currents and proliferation rates of these cells were compared. K(+) outward currents of both cell types can be blocked by quinidine. Importantly, treatment with quinidine reduces proliferation of NF2 Schwann cells in a concentration dependent manner but did not reduce proliferation of normal Schwann cells. Therefore, the use of quinidine or quinidine-like components would possibly provide a novel adjuvant therapeutic option for NF2 patients to slow down or freeze growth of schwannomas.

The mouse ortholog of the human SMARCB1 gene encodes two splice forms

The human SMARCB1 gene (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily b, member 1, previously named the INI1/hSNF5 gene) is a tumor suppressor gene located on chromosome 22q11.2 and is inactivated in malignant rhabdoid tumors. By using an EST-based approach, we cloned two splice forms of the Smarcb1 gene in mouse and a longer splice form of the human ortholog. Proteins corresponding to the longer (385 aa) and the shorter (376 aa) forms are 100% conserved between human and mouse. Meningiomas and schwannomas are tumors frequently deleting various regions on chromosome 22, including the SMARCB1 locus. We therefore directly sequenced seven SMARCB1 exons (90% of the open reading frame) in search for mutations in 41 meningiomas and 23 schwannomas. No inactivating mutations were observed, which suggests that the SMARCB1 gene is not involved in the pathogenesis of these tumors.

Merlin: the neurofibromatosis 2 tumor suppressor

In recent years, it has become clear that the ERMs occupy a crucial position as protein linkers that both respond to and participate in reorganization of membrane-cytoskeletal interactions. With the identification of new binding partners, the ERMs are also implicated in linked regulation of the activities of particular membrane proteins. Thus, they reside at a junction in a complex web of interactions that must respond to stimuli from both outside and inside the cell. As expected from its structural motifs, merlin behaves in a manner similar to the ERM proteins, but with some notable differences. Chief among these is the absence of intramolecular interaction to mask intermolecular interaction domains in isoform 2. The full range of merlin's intermolecular interactions remains to be delineated, but it can be expected from the comparison to ERMs that merlin also sits within a web of interactions that may involve multiple partners and signaling pathways, some of which it shares with the ERMs. Defining merlin's tumor suppressor function will likely require identifying those differences that are peculiarly important in the target cell types of NF2. However, the fact that inactivation of merlin in the mouse by targeted mutagenesis produces a variety of malignant tumors with a high rate of metastasis [33] suggests that merlin's suppression of tumor formation may involve different partners and pathways in different cell types and genetic backgrounds. Consequently, the disruptions due to merlin inactivation in the progression of malignant mesothelioma may represent a tumor suppressor role operating by a different pathway than that in schwannoma or meningioma.

Neurofibromatosis Type 2: Genetic and Clinical Features

For decades, neurofibromatosis type 2 (NF2) was misclassified with the more common neurofibromatosis type 1 (NF1), until 1987 when it was found via genetic linkage analysis that the gene for NF1 was localized to chromosome 17 and the gene for NF2 was localized to chromosome 22.

Large, population-based studies have shown that vestibular schwannomas (VS), the hallmark of NF2, do not occur at increased frequency inpatients with NF1. Typical clinical features of NF2 are bilateral VS or a family history of NF2, plus either unilateral VS or any two of the following: meningioma, glioma, neurofibroma, schwannoma or posterior subcapsular lenticular opacities. Presymptomatic genetic tests are now possible in the majority of families, and it is hoped that somatic gene therapy will be developed for the treatment of this disease.

Neurofibromatosis: a common neurocutaneous disorder

Neurofibromatosis (NF) type 1 (NF-1) is one of the most common of the neurocutaneous conditions, whereas NF type 2 (NF-2) accounts for an extremely small percentage of the total cases of NF. Indeed, most physicians will probably encounter at least one or two patients with NF-1 during the course of their practice. The manifestations can be varied and subtle; thus, the condition can sometimes be difficult to recognize. Nonetheless, the diagnosis of NF-1 is often clinically possible by the time the person is 10 years old. In this article, the diagnostic criteria for the most common types of NF are discussed, the common and some of the serious manifestations of both NF-1 and NF-2 are described, and suggestions for follow-up care are offered. Of importance, physicians must recognize that, although NF-1 and NF-2 share a common name, they are due to mutations in two different genes. Cure is not yet possible; thus, treatment is primarily symptomatic. A multi-disciplinary treatment team is often helpful, particularly for patients with complicated problems.

Loss of heterozygosity on chromosome 22q and 17p correlates with aggressiveness of meningiomas

According to reported cytogenetic studies, there is a significant association between chromosomal aberrations and aggressiveness in meningiomas. With the method of restriction fragment length polymorphism analysis (RFLP), we examined tumor specific LOH on chromosome 17p and 22q in 30 cases of intracranial meningiomas. There were eight cases of meningiomas with aggressive characteristics, such as invasive meningioma, malignant meningioma, hemangiopericytic meningioma, and multiple meningiomas with central neurofibromatosis. Twenty-five of 30 cases (83%) were constitutionally heterozygous for at least one of the chromosome 22q DNA markers and sixteen of 25 informative cases (64%) displayed loss of heterozygosity (LOH). All of the 8 informative cases (100%) of meningiomas with aggressive characteristics, showed LOH on chromosome 22q whereas non-aggressive cases revealed LOH in eight of 17 informative cases (47%). At the loci on chromosome 17p, only two cases of malignant meningionas showed LOH. Our results suggest that the inactivations of putative tumor suppressor genes on chromosome 22q and 17p may correlate with aggressiveness and malignant transformation of meningiomas.

Isolation and characterization of Schwann cells from neurofibromatosis type 2 patients

Neurofibromatosis type 2 (NF2) is an autosomal dominant disease of the nervous system characterized by multiple schwannomas. The NF2 gene product, termed schwannomin or merlin, was hypothesized to function as a cytoskeleton-membrane linking protein due to homology to members of the protein 4.1 superfamily and to function as a tumor suppressor. We isolated and characterized pure Schwann cell cultures from schwannomas derived from neurofibromatosis 2 patients with identified germline mutations and loss of heterozygosity. We describe striking differences between NF2 and control Schwann cells in morphology, cell-cell contacts, and growth. NF2 Schwann cells form multiple long processes with filopodial and lamellopodial extensions. NF2 Schwann cells lack contact inhibition, grow in multiple layers, and show a higher proliferation rate than control cells. For the first time Schwann cells derived from patients with the NF2 genotype were cultured and characterized in vitro. These cultures are highly valuable for investigating the effects of NF2 mutations and the development of therapies.

Neurofibromatosis type 2: growth stimulation of mixed acoustic schwannoma by concurrent adjacent meningioma: possible role of growth factors. Case report

The authors report the case of a young man suffering from neurofibromatosis type 2 (NF2) who harbored bilateral acoustic schwannomas and a parasellar meningioma. Neuroimaging studies performed during a 4-year follow-up period showed that the bilateral schwannomas had grown very little and at similar rates. However, after the meningioma had infiltrated the tentorium and approached the ipsilateral schwannoma at the incisura, both Schwann cell tumors started to grow rapidly, particularly the one adjacent to the meningioma, of which the percentage of annual growth rate increased by approximately a factor of 10(2). At the same time, magnetic resonance imaging showed that this tumor also changed its features. During surgery, the acoustic schwannoma was firmly adherent to both meningioma and tentorium. Histological examination revealed meningotheliomatous cells in the schwannoma adjacent to the meningioma. Antiphosphotyrosine immunoblotting of PC12 cells was compatible with the presence of an epidermal growth factor (EGF)-like molecule in the cerebrospinal fluid (CSF) of the patient. This factor was not detected in the CSF of five other NF2 patients, two of whom bore associated bilateral acoustic schwannomas and meningioma in remote locations. It is hypothesized that the meningotheliomatous cells infiltrating the schwannoma triggered an autocrine/paracrine growth-stimulatory mechanism that involved an EGF-like factor.

The neurosurgical aspects of neurofibromatosis 2: diagnosis and management

NF-2 is an extremely rare form of neurofibromatosis (NF) characterized by central system (CNS) neural crest-derived tumors and frequently cafe au lait spots (CLS). The purpose of this study was to report the clinical and imaging findings of seven patients with this disorder and to stress that value of surgical treatment in its management. Seven patients between 8 and 32 years of age who had NF-2 were included in the study. Clinical charts, surgical and pathological findings, and imaging studies were reviewed retrospectively. Patients were followed up for to 142 months. Clinical evaluation and neuroimaging studies detected the clinical criteria of NF-2 in all patients. Two deaths occurred after surgical intervention in our series. None of the patients suffered from recurrent tumor following surgery. Our results show that NF-2 is an uncommon entity which has a good prognosis after surgical intervention, in spite of the presence of multiple cranial and/or spinal lesions.

Neurofibromatosis type 2: growth stimulation of mixed acoustic schwannoma by concurrent adjacent meningioma: possible role of growth factors

The authors report the case of a young man suffering from neurofibromatosis type 2 (NF2) who harbored bilateral acoustic schwannomas and a parasellar meningioma. Neuroimaging studies performed during a 4-year follow-up period showed that the bilateral schwannomas had grown very little and at similar rates. However, after the meningioma had infiltrated the tentorium and approached the ipsilateral schwannoma at the incisura, both Schwann cell tumors started to grow rapidly, particularly the one adjacent to the meningioma, of which the percentage of annual growth rate increased by approximately a factor of 102. At the same time, magnetic resonance imaging showed that this tumor also changed its features. During surgery, the acoustic schwannoma was firmly adherent to both meningioma and tentorium. Histological examination revealed meningotheliomatous cells in the schwannoma adjacent to the meningioma. Antiphosphotyrosine immunoblotting of PC12 cells was compatible with the presence of an epidermal growth factor (EGF)-like molecule in the cerebrospinal fluid (CSF) of the patient. This factor was not detected in the CSF of five other NF2 patients, two of whom bore associated bilateral acoustic schwannomas and meningioma in remote locations. It is hypothesized that the meningotheliomatous cells infiltrating the schwannoma triggered an autocrine/paracrine growth-stimulatory mechanism that involved an EGF-like factor.

Phenotypic diversity of neurofibromatosis 2: association with plexiform schwannoma

AIMS

Plexiform schwannoma (PS) is a rare variant of benign schwannoma characterized by a multinodular and plexiform growth pattern. In contrast to plexiform neurofibroma. PS is not associated with neurofibromatosis 1 (NF-1; von Recklinghausen's disease) and has no propensity for malignant transformation. The purpose of this study was to clarify the relationship between PS and the entities of neurofibromatosis 2 (NF-2; bilateral acoustic neurofibromatosis) and schwannomatosis.

METHODS AND RESULTS

Six cases of PS associated with NF-2 or meningioma were retrospectively studied clinicopathologically and immunohistochemically. Four cases of PS were found among the patients with NF-2, and all of these had multiple PSs; three cases also had multiple schwannomas of the spinal nerve roots and two of these had meningioma. Two other patients had meningioma, but not NF-2. Four patients were male and two were female. The ages ranged from 18 to 52 years (mean 29.6 years). Histologically, PS showed the histological features that have been previously described, i.e. schwannoma composed of a predominant Antoni A-type component with a plexiform growth pattern. Immunohistochemically, the tumour cells were positive for S100 protein. Each nodule was surrounded by perineural cells which were positive for epithelial membrane antigen.

CONCLUSIONS

It is important to recognize that PS could be associated with NF-2 or meningioma. The combination of PS and meningioma may be a 'formes frustes' of NF-2, and is clinically overlapped with schwannomatosis.

Clinical manifestations of mutations in the neurofibromatosis type 2 gene in vestibular schwannomas (acoustic neuromas)

Vestibular schwannomas (acoustic neuromas) continue to cause significant facial nerve and hearing morbidity, despite marked improvement in diagnosis and treatment. Mutation of a tumor-suppressor gene on human chromosome 22 has been found to be associated with vestibular schwannoma formation. The central hypothesis of this study is that specific mutations in the neurofibromatosis type 2 (NF2) gene may produce specific clinical characteristics or phenotypic expressions. The purposes of this investigation are: 1. to determine what proportion of vestibular schwannomas from patients with spontaneous unilateral and familial bilateral schwannomas have mutations present within the NF2 gene; 2. to determine whether specific types of mutations are associated with a specific clinical manifestation of this disease; and 3. to further define the relationship between newly discovered mutations within the NF2 tumor-suppressor gene and possible clinical applications of this knowledge to advance diagnosis and treatment of patients with NF2 and spontaneous vestibular schwannomas. DNA from 61 schwannomas (29 unilateral vestibular schwannomas and 32 from patients with bilateral vestibular schwannomas [NF2]) were examined, and 33 unique mutations were identified. Significant differences were found in the frequency, distribution, and type of mutation between the NF2 schwannomas and the spontaneous vestibular schwannomas. Three clinical subtypes of NF2 were identified. In tumors from 28 patients, no mutations were identified. Of the 33 mutations identified in the NF2 gene, 30 were likely to result in loss of tumor-suppressor function from protein truncation; however, three milder mutations termed missense mutations were associated with milder clinical manifestations of the disease and had a slower estimated growth rate. Variable clinical presentation in patients whose tumors had severe or truncating types of mutations suggest that factors in addition to the mutation class are likely to be responsible for a portion of the clinical expression of disease. New diagnostic options are now available for NF2 that will improve the likelihood of hearing and facial nerve preservation and ultimately have significant impact on the management of vestibular schwannomas.

Human cancer syndromes: clues to the origin and nature of cancer

More than 20 different hereditary cancer syndromes have now been defined and attributed to specific germline mutations in various inherited cancer genes. Collectively, the syndromes affect about 1 percent of cancer patients. An individual who carries a mutant allele of an inherited cancer gene has a variable risk of cancer that is influenced by the particular mutation, other cellular genes, and dietary, lifestyle, and environmental factors. Though hereditary cancer syndromes are rare, their study has provided powerful insights into more common forms of cancer. Somatic mutations in sporadic cancers frequently alter the inherited cancer genes, and the functions of cell signaling pathways have been illuminated by study of the affected genes. Further investigation of inherited mutations that affect susceptibility to cancer will aid efforts to effectively prevent, detect, and treat the disease.

A comparative study of embedded nerve tissue in six NF2-associated schwannomas and 17 nonassociated NF2 schwannomas

BACKGROUND

Neurofibromatosis-2 (NF2) is an autosomal dominant disorder in which patients typically show bilateral acoustic tumors, and they are usually diagnosed histopathologically as schwannomas. The nerve of origin of a schwannoma is often demonstrated on the periphery along the capsule but not penetrating the substance of the tumor. However, there is a possibility that NF2 schwannomas and solitary schwannomas differ from participation in nerve components.

METHODS

In this study, the authors noted the relationship between the tumor and the original nerves. To detect whether there were embedded nerves in the tumor, immunohistologic staining using neurofilament and myelin basic protein antibodies was performed on 6 NF2 schwannomas and 17 non-NF2 schwannomas.

RESULTS

Four of five NF2 schwannomas had embedded nerves and one of four, which was considered to be the early stage of the tumor occurrence, remarkably embedded original nerves. On the other hand, embedded nerves were not seen in non-NF2 schwannomas.

CONCLUSIONS

The authors concluded that the NF2 schwannomas tend have original nerves embedded in the tumor substance, which may be based on the difference of the motility of tumor cells, and the authors believe that it is difficult to remove NF2 schwannomas while preserving the original nerve.

The Nf2 tumor suppressor gene product is essential for extraembryonic development immediately prior to gastrulation

The neurofibromatosis type II (NF2) tumor suppressor encodes a putative cytoskeletal associated protein, the loss of which leads to the development of Schwann cell tumors associated with NF2 in humans. The NF2 protein merlin belongs to the band 4.1 family of proteins that link membrane proteins to the cytoskeleton and are thought to be involved in dynamic cytoskeletal reorganization. Beyond its membership in this family, however, the function of merlin remains poorly understood. In order to analyze the function of merlin during embryogenesis and to develop a system to study merlin function in detail, we have disrupted the mouse Nf2 gene by homologous recombination in embryonic stem cells. Most embryos homozygous for a mutation at the Nf2 locus fail between embryonic days 6.5 and 7.0, exhibiting a collapsed extraembryonic region and the absence of organized extraembryonic ectoderm. The embryo proper continues to develop, but fails to initiate gastrulation. These observations are supported by the expression patterns of markers of the extraembryonic lineage and the lack of expression of mesodermal markers in the mutant embryos. Mosaic studies demonstrate that merlin function is not required cell autonomously in mesoderm, and support the proposition that merlin function is essential for the development of extraembryonic structures during early mouse development.

Loss of heterozygosity on chromosome 22 in human gliomas does not inactivate the neurofibromatosis type 2 gene

The molecular genetic alterations that underlie development of gliomas, the most common neoplasm of the human central nervous system, include activation of cellular proto-oncogenes as well as inactivation of tumor suppressor genes. Although research has identified some affected loci, others clearly remain to be identified. We have investigated loss of heterozygosity on chromosome 22 in a panel of sporadic gliomas, and have assessed the possibility that inactivation of the neurofibromatosis type 2 (NF2) tumor suppressor gene on 22q plays a role in development of sporadic gliomas in humans. Loss of heterozygosity for loci on chromosome 22 loci was observed in 15 of 47 informative blood-tumor pairs, although no common area of loss of heterozygosity shared by all of these tumors could be identified. The most frequently affected segment, distal to the NF2 locus and bounded proximally by D22S15 and distally by a gene for myoglobin, was shared by as many as 11 tumors. Loss of heterozygosity at the NF2 locus was observed in 10 tumors. No rearrangements of the NF2 gene could be detected by Southern analysis of restriction endonuclease-digested genomic DNA, and no abnormally migrating bands were detected on single strand conformation analysis of individual exons of the NF2 gene. Thus, although frequent loss of heterozygosity on chromosome 22 suggests that inactivation of a tumor suppressor gene on this chromosome plays a role in development of gliomas, there is no evidence that inactivation of the NF2 gene is implicated in this process, confirming the results of other studies of the NF2 gene in human gliomas. The identity of the putative tumor suppressor gene on 22q involved in development of gliomas remains unknown.

Meningioma in the pediatric population

Pediatric meningiomas are rare. They are usually seen in association with neurofibromatosis type 2 (NF-2) or following radiation therapy. The tumors are more frequently intraventricular, cystic, and infratentorial than are those in adult patients. Pathologically they are more histologically aggressive than in adults and tend to recur more frequently. Complete resection is the surgical goal. The treatment of subtotally resected meningiomas, particularly in NF-2, remains controversial.

Neurofibromatosis type 2: a new mechanism of tumor suppression

Neurofibromatosis type 2 (NF2) is an autosomal dominant disease which predisposes primarily to CNS tumors such as schwannomas (vestibular and spinal), meningiomas, ependymomas and juvenile posterior lenticular opacities. Allelic losses on chromosome 22q first suggested the existence of a tumor suppressor on this autosome in accordance with Knudson's 'two hit' model. The gene was identified by positional cloning and found to encode a novel protein schwannomin (also known as merlin), with high sequence similarity to the band 4.1 family of proteins. This similarity suggested a new mechanism of tumor suppression since it was the first time a structural protein had been associated with a human tumor. Mutation analysis confirmed that inactivation of the NF2 gene occurred in NF2 tumors and a majority of sporadic schwannomas and meningiomas. Expression and functional studies have provided additional information on the possible involvement of this novel tumor suppressor in cell differentiation, embryogenesis and growth suppression.

Ophthalmological issues in the neurofibromatoses

The neurofibromatoses are a set of at least two distinct disorders characterized by the development of nerve sheath tumors and diverse other features. Both are genetically determined as autosomal dominant traits, and both genes have been identified, with resultant major insights into pathogenesis. The neurofibromatoses have prominent effects on the visual system, which are important both for diagnosis and clinical management. This review focuses on clinical aspects of the neurofibromatoses, highlighting ophthalmological issues and recent advances in molecular genetics.

Maternal and perinatal risk factors for childhood brain tumors (Sweden)

Childhood brain tumors (CBT) include a diversity of rare neoplasms of largely unknown etiology. To assess possible maternal and perinatal risk factors for CBT according to subtype, we carried out a nested (within Swedish birth-cohorts, 1973-89) case-control study, utilizing data from the nationwide Birth Registry. We ascertained incident brain tumor cases through linkage of the nationwide Birth and Cancer Registries and randomly selected five living controls from the former, matching each case on gender and birthdate. There were 570 CBT cases, including 205 low grade astrocytomas, 58 high grade astrocytomas, 93 medulloblastomas, 54 ependymomas, and 160 'others.' Risks for all brain tumors combined were elevated in relation to: (i) three maternal exposures-oral contraceptives prior to conception (odds ratios [OR] = 1.6, 95 percent confidence interval [CI] = 1.0-2.8), use of narcotics (OR = 1.3, CI = 1.0-1.6), or penthrane (OR = 1.5, CI = 1.1-2.0) during delivery); (ii) characteristics of neonatal distress (a combined variable including low one-minute Apgar score, asphyxia [OR = 1.5, CI = 1.1-2.0]) or treatments for neonatal distress (use of supplemental oxygen, ventilated on mask, use of incubator, scalp vein infusion, feeding with a jejunal tube [OR = 1.6, CI = 0.9-2.6]); and (iii) neonatal infections (OR = 2.4, CI = 1.5-4.0). Higher subtype-specific risks, observed for a few risk factors, did not differ significantly from the risk estimates for all subtypes combined for the corresponding risk factors. Childhood brain tumors were not associated significantly with other maternal reproductive, lifestyle, or disease factors; perinatal pain, anesthetic medications, birth-related complications; or with birthweight, birth defects, or early neonatal diseases. These findings suggest several new leads, but only weak evidence of brain tumor subtype-specific differences.

Frequent type 2 neurofibromatosis gene transcript mutations in sporadic intramedullary spinal cord ependymomas

OBJECTIVE

To further investigate the role of Type 2 neurofibromatosis (NF2) gene transcript mutations in the sporadically occurring counterparts of NF2-associated tumors.

METHODS

Reverse transcription-polymerase chain reaction followed by agarose gel electrophoresis, single strand conformation polymorphism analysis, and automated deoxyribonucleic acid sequence analysis were used to screen for mutations in the NF2 gene transcript in seven unrelated patients with sporadic intramedullary spinal cord ependymomas.

RESULTS

Five of seven intramedullary spinal cord ependymomas harbored detectable mutations. All of these mutations occurred in the region of the transcript that is homologous to known cytoskeletal proteins and resulted in significant truncation of the predicted protein product.

CONCLUSION

Mutations of the NF2 transcript occur in the majority of sporadic intramedullary spinal cord ependymomas. These mutations are frequent in a region of the transcript that is homologous to a family of cytoskeletal proteins, and they probably render the protein product inactive. These results add to the body of knowledge concerning the role of the NF2 gene transcript in tumorigenesis.

Neurofibromatosis 2: loss of merlin's protective spell

Schwannomas and meningiomas occur as multiple tumors in sufferers of neurofibromatosis 2 (NF2) and as solitary tumors in the general population due to the inactivation of a gene at chromosome 22q12. In 1993, a location cloning approach revealed this tumor suppressor, dubbed merlin, as a novel member of a family of proteins that link elements of the cytoskeleton and the cell membrane. Subsequent investigations have confirmed merlin's role in tumor formation, but have yet to reveal its mechanism of action.

High frequency of inactivating mutations in the neurofibromatosis type 2 gene (NF2) in primary malignant mesotheliomas

Malignant mesotheliomas (MMs) are aggressive tumors that develop most frequently in the pleura of patients exposed to asbestos. In contrast to many other cancers, relatively few molecular alterations have been described in MMs. The most frequent numerical cytogenetic abnormality in MMs is loss of chromosome 22. The neurofibromatosis type 2 gene (NF2) is a tumor suppressor gene assigned to chromosome 22q which plays an important role in the development of familial and spontaneous tumors of neuroectodermal origin. Although MMs have a different histogenic derivation, the frequent abnormalities of chromosome 22 warranted an investigation of the NF2 gene in these tumors. Both cDNAs from 15 MM cell lines and genomic DNAs from 7 matched primary tumors were analyzed for mutations within the NF2 coding region. NF2 mutations predicting either interstitial in-frame deletions or truncation of the NF2-encoded protein (merlin) were detected in eight cell lines (53%), six of which were confirmed in primary tumor DNAs. In two samples that showed NF2 gene transcript alterations, no genomic DNA mutations were detected, suggesting that aberrant splicing may constitute an additional mechanism for merlin inactivation. These findings implicate NF2 in the oncogenesis of primary MMs and provide evidence that this gene can be involved in the development of tumors other than nervous system neoplasms characteristic of the NF2 disorder. In addition, unlike NF2-related tumors, MM derives from the mesoderm; malignancies of this origin have not previously been associated with frequent alterations of the NF2 gene.

Neurofibromatosis type 2 and von Hippel-Lindau disease: from gene cloning to function

Most of the genes for hereditary tumor syndromes cloned thus far have subsequently been shown to be mutated not only in the germlines and tumors from patients with the relatively rare inherited disease, but also in the much more common sporadic tumor counterparts in the general population. Thus, the isolation and functional characterization of genes associated with hereditary tumor syndromes have emerged as a major strategy to gain insights into some of the most fundamental mechanisms of tumorigenesis. The search for the genes causing two hereditary tumor syndromes of the nervous system, neurofibromatosis type 2 (NF2) and von Hippel-Lindau disease (VHL), has recently culminated in the cloning of both disease genes. This represents another successful application of the so-called positional cloning approach, i.e., the isolation of a hereditary disease gene with unknown function, based on the determination of its chromosomal location in the human genome. The gene for NF2, a syndrome typically associated with vestibular schwannomas and meningiomas, is homologous with a family of genes whose members appear to play an important role in bridging the cell membrane with the intracellular cytoskeleton, including moesin, ezrin, radixin, and protein 4.1. Recent mutation analyses have revealed that the NF2 tumor suppressor gene is frequently mutated not only in vestibular schwannomas and meningiomas from NF2 patients, but also in their sporadic counterparts, which represent approximately one-third of all human brain tumors. Furthermore, malignant human tumors seemingly unrelated to the NF2 syndrome, such as neural crest-derived malignant melanomas, as well as malignant mesotheliomas (a pleural mesoderm-derived tumor), have also been found to be frequently mutated or deleted in the NF2 locus, suggesting a broader role for the NF2 gene in the initiation and progression of human neoplasms. VHL is a rare tumor syndrome characterized by certain types of nervous system tumors (cerebellar and spinal hemangioblastomas as well as retinal angiomas), in conjunction with bilateral renal cell carcinomas and pheochromocytomas. Similar to NF2, recent genetic mutation studies have revealed that the VHL tumor suppressor gene is not only mutated in the hereditary tumors from VHL patients, but also in their sporadic counterparts. Importantly, the VHL gene represents the most frequently mutated cancer-related gene thus far identified in sporadic renal cell carcinoma. In contrast to most other hereditary cancer syndromes, however, VHL mutations are surprisingly specific for tumors typically associated with the VHL syndrome, and have not been detected in any other tumor type unrelated to VHL. The cloning and initial genetic characterization of the NF2 and VHL genes have now provided a rational basis for subsequent functional studies on the elucidation of the normal and tumor-associated cellular signaling pathways of these tumor suppressor genes.

Combined molecular genetic studies of chromosome 22q and the neurofibromatosis type 2 gene in central nervous system tumors

Monosomy of chromosome 22 or deletions of 22q have been described in meningiomas and astrocytic tumors, the incidence of which is increased in Type 2 neurofibromatosis. Recently, the gene for neurofibromatosis Type 2 (NF2) has been identified at Chromosome 22q12, and a tumor suppression role has been suggested. Because there have been only a few studies of the NF2 gene on central nervous system tumors other than vestibular schwannomas, we investigated the potential role of NF2 as a tumor suppressor gene in a group of sporadic meningiomas and astrocytomas. Forty-four tumors (26 meningiomas and 18 astrocytic tumors of different grades) were screened for NF2 mutations for the entire 17 exons by the polymerase chain reaction-single-strand conformation polymorphism method. In addition, 37 tumors and their respective constitutional deoxyribonucleic acid were analyzed for loss of heterozygosity of 22q alleles by four polymorphic microsatellite markers. Seven inactivating mutations were found in Exons 4, 5, 6, and 10 in 7 of 26 (27%) meningiomas, but none were found in astrocytic tumors. Altogether, 69% of meningiomas and 20% of astrocytic tumors revealed a loss of heterozygosity of 22q markers. All tumors with NF2 mutations showed concurrent loss of alleles on 22q, thus fulfilling Knudson's criteria for tumor suppressor genes in meningiomas. We conclude that inactivation of the NF2 gene is involved in the pathogenesis of a proportion of meningiomas but not in astrocytic tumors. Because many meningiomas and some astrocytic tumors had allelic loss of 22q but intact NF2, there is a possibility that other tumor suppressor genes exist on 22q and may be involved in the pathogenesis of central nervous system tumors.

Evidence for clonal spread in the development of multiple meningiomas

Meningiomas are common intracranial tumors that arise from the arachnoid cells of the meninges. Occasionally patients develop multiple meningiomas. Because the underlying mechanism of multiple meningioma formation is unknown, the authors examined the pattern of X chromosome inactivation in multiple meningiomas. Fifteen intracranial meningiomas were resected in four patients with multiple meningiomas to determine whether the tumors in patients with multiple meningiomas originate from a common progenitor cell or arise independently. Specimens were examined using polymerase chain reaction assays to detect the pattern of X chromosome inactivation. In each patient, all tumors showed inactivation of the same X chromosome, suggesting that tumors arose from the same clone of cells (p < 0.0005). The authors conclude that multiple meningiomas arise from the uncontrolled spread of a single progenitor cell.