Molecular genetic analysis of the NF2 gene in young patients with unilateral vestibular schwannomas

Differential rates of germline heterozygote and mosaic variants in NF2 may show varying propensity for meiotic or mitotic mutation

NF2-related schwannomatosis is an autosomal dominant tumour predisposition condition that causes multiple benign tumours of the nervous system, especially schwannomas. This results from germline pathogenic variants in the NF2 gene, which are most commonly de novo NF2 nonsense variants. Over half of these de novo variants occur at just six CpG dinucleotides. In this study, we show that the six NF2 CpG nonsense variants make up 54% (136/252) of de novo nonsense variants, despite constituting <10% of nonsense positions in the germline (total=62), and that this pattern is different from the APC gene, which is also known to have a high rate of mosaicism. In addition, the NF2 c.586C>T; p.(Arg196Ter) has a higher de novo heterozygote to mosaicism ratio than the five other CpG variants (73.1% vs 53.7%, p=0.03) and the neighbouring CpG variant (NF2 c.592C>T; p.(Arg198Ter) 38.5%, p=0.02). This may be due to differences in rates of mutation at meiosis versus mitosis.

Predicting surgical decision-making in vestibular schwannoma using tree-based machine learning

OBJECTIVE

Vestibular schwannomas (VSs) are the most common neoplasm of the cerebellopontine angle in adults. Though these lesions are generally slow growing, their growth patterns and associated symptoms can be unpredictable, which may complicate the decision to pursue conservative management versus active intervention. Additionally, surgical decision-making can be controversial because of limited high-quality evidence and multiple quality-of-life considerations. Machine learning (ML) is a powerful tool that utilizes data sets to essentialize multidimensional clinical processes. In this study, the authors trained multiple tree-based ML algorithms to predict the decision for active treatment versus MRI surveillance of VS in a single institutional cohort. In doing so, they sought to assess which preoperative variables carried the most weight in driving the decision for intervention and could be used to guide future surgical decision-making through an evidence-based approach.

METHODS

The authors reviewed the records of patients who had undergone evaluation by neurosurgery and otolaryngology with subsequent active treatment (resection or radiation) for unilateral VS in the period from 2009 to 2021, as well as those of patients who had been evaluated for VS and were managed conservatively throughout 2021. Clinical presentation, radiographic data, and management plans were abstracted from each patient record from the time of first evaluation until the last follow-up or surgery. Each encounter with the patient was treated as an instance involving a management decision that depended on demographics, symptoms, and tumor profile. Decision tree and random forest classifiers were trained and tested to predict the decision for treatment versus imaging surveillance on the basis of unseen data using an 80/20 pseudorandom split. Predictor variables were tuned to maximize performance based on lowest Gini impurity indices. Model performance was optimized using fivefold cross-validation.

RESULTS

One hundred twenty-four patients with 198 rendered decisions concerning management were included in the study. In the decision tree analysis, only a maximum tumor dimension threshold of 1.6 cm and progressive symptoms were required to predict the decision for treatment with 85% accuracy. Optimizing maximum dimension thresholds and including age at presentation boosted accuracy to 88%. Random forest analysis (n = 500 trees) predicted the decision for treatment with 80% accuracy. Factors with the highest variable importance based on multiple measures of importance, including mean minimal conditional depth and largest Gini impurity reduction, were maximum tumor dimension, age at presentation, Koos grade, and progressive symptoms at presentation.

CONCLUSIONS

Tree-based ML was used to predict which factors drive the decision for active treatment of VS with 80%–88% accuracy. The most important factors were maximum tumor dimension, age at presentation, Koos grade, and progressive symptoms. These results can assist in surgical decision-making and patient counseling. They also demonstrate the power of ML algorithms in extracting useful insights from limited data sets.

Pathogenic noncoding variants in the neurofibromatosis and schwannomatosis predisposition genes

Neurofibromatosis type 1 (NF1), type 2 (NF2), and schwannomatosis are a group of autosomal dominant disorders that predispose to the development of nerve sheath tumors. Pathogenic variants (PVs) that cause NF1 and NF2 are located in the NF1 and NF2 loci, respectively. To date, most variants associated with schwannomatosis have been identified in the SMARCB1 and LZTR1 genes, and a missense variant in the DGCR8 gene was recently reported to predispose to schwannomas. In spite of the high detection rate for PVs in NF1 and NF2 (over 90% of non-mosaic germline variants can be identified by routine genetic screening) underlying PVs for a proportion of clinical cases remain undetected. A higher proportion of non-NF2 schwannomatosis cases have no detected PV, with PVs currently only identified in around 70%-86% of familial cases and 30%-40% of non-NF2 sporadic schwannomatosis cases. A number of variants of uncertain significance have been observed for each disorder, many of them located in noncoding, regulatory, or intergenic regions. Here we summarize noncoding variants in this group of genes and discuss their established or potential role in the pathogenesis of NF1, NF2, and schwannomatosis.

Contemporary Molecular Biology of Sporadic Vestibular Schwannomas: A Systematic Review and Clinical Implications

In light of missing systematic reviews in the literature, the objective of this paper is to present the contemporary knowledge on the molecular biology of vestibular schwannomas (VS), based on a systematic literature search. In addition, current and prospected medical therapy based on molecular biology is addressed. A systematic literature search was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The systematic search was performed in the Pubmed and Embase databases. The following were the words searched: acoustic neuroma/vestibular schwannoma, molecular biology, gene, and microRNA. Specific inclusion and exclusion criteria were determined prior to search. The systematic search rendered 486 articles, ultimately yielding 69 included articles, whereas 35 were from relevant references. The occurrence of at least one mutation in the merlin gene was reported to range between 54% and 76%, whereas the loss of heterozygosity (LOH) corresponding to chromosome 22 occurs in 25% to 83% of sporadic VS. Global gene expression studies indicate that a number of genes other than merlin are at play. No high-level methylation of the merlin gene has been found. Several miRNAs are deregulated in tumor tissue, among others let-7d, miR-221, and miR-21. The acquired knowledge on molecular biology has led to several clinical implementations. Lack of the tumor suppressor merlin plays a principal role in the development of VS. Existing knowledge on the molecular biology has led to the first attempts of targeted medical treatment to prevent tumor growth. Future research is likely to introduce potential imaging markers with prognostic value and new targets for medical therapy.

Familial unilateral vestibular schwannoma is rarely caused by inherited variants in the NF2 gene

OBJECTIVES/HYPOTHESIS

Unilateral vestibular schwannoma (VS) occurs with a lifetime risk of around 1 in 1,000 and is due to inactivation of the NF2 gene, either somatically or from a constitutional mutation. It has been postulated that familial occurrence of unilateral VS occurs more frequently than by chance, but no causal mechanism has been confirmed.

STUDY DESIGN

Retrospective database analysis.

METHODS

The likelihood of chance occurrence of unilateral VS, or occurring in the context of neurofibromatosis type 2 (NF2), was assessed using national UK audit data and data from the national NF2 database. Families with familial unilateral VS (occurrence in first- and second-degree relatives) were assessed for constitutional NF2 and LZTR1 genetic variants, and where possible the tumor was also analyzed.

RESULTS

Approximately 1,000 cases of unilateral VS occurred annually in the United Kingdom between 2013 and 2016. Of these, 2.5 may be expected to have a first-degree relative who had previously developed a unilateral VS. The likelihood of this occurring in NF2 was considered to be as low as 0.05 annually. None of 28 families with familial unilateral VS had a constitutional NF2 intragenic variant, and in nine cases where the VS was analyzed, both mutational events in NF2 were identified and excluded from the germline. Only three variants of uncertain significance were found in LZTR1.

CONCLUSIONS

Familial occurrence of unilateral VS is very unlikely to be due to a constitutional NF2 or definitely pathogenic LZTR1 variant. The occurrence of unilateral VS in two or more first-degree relatives is likely due to chance. This phenomenon may well increase in clinical practice with increasing use of cranial magnetic resonance imaging in older patients.

LEVEL OF EVIDENCE

2b Laryngoscope, 129:967-973, 2019.

Sensitive Surface Enhanced Raman Scattering-Based Detection of a BIGH3 Point Mutation Associated with Avellino Corneal Dystrophy

Surface enhanced Raman scattering (SERS) is highly useful for sensitive analytical sensing; however, its practical availability for detecting a point mutation associated with disease in clinical sample was rarely proved. Herein, we present a toehold-mediated, DNA displacement-based, SERS sensor for detecting point mutations in the BIGH3 gene associated with the most common corneal dystrophies (CDs) in a clinical setting. To diagnose Avellino corneal dystrophy (ACD), selectivity was ensured by exploring optimal DNA displacement conditions such as length of toehold and hybridization temperature. A SERS-efficient Ag@Au bimetallic nanodendrite was employed to ensure sensitivity. Optimization for a clinical setting showed that discrimination was maximized when toehold length was 6-mer (T6), and hybridization temperature was 36 °C. On the basis of tests that used clinical homozygous and heterozygous CD samples, a single-base mismatched DNA sequence was identifiable within 30 min with a limit of detection (LOD) of 400 fM. From the results, we conclude that our toehold-mediated, DNA displacement-based, SERS sensor allows a rapid and sensitive detection of a BIGH3 gene point mutation associated with Avellino corneal dystrophy, indicating the practical ability of the method to diagnose genetic diseases caused by point mutations.

The molecular pathogenesis of schwannomatosis, a paradigm for the co-involvement of multiple tumour suppressor genes in tumorigenesis

Schwannomatosis is characterized by the predisposition to develop multiple schwannomas and, less commonly, meningiomas. Despite the clinical overlap with neurofibromatosis type 2 (NF2), schwannomatosis is not caused by germline NF2 gene mutations. Instead, germline mutations of either the SMARCB1 or LZTR1 tumour suppressor genes have been identified in 86% of familial and 40% of sporadic schwannomatosis patients. In contrast to patients with rhabdoid tumours, which are due to complete loss-of-function SMARCB1 mutations, individuals with schwannomatosis harbour predominantly hypomorphic SMARCB1 mutations which give rise to the synthesis of mutant proteins with residual function that do not cause rhabdoid tumours. Although biallelic mutations of SMARCB1 or LZTR1 have been detected in the tumours of patients with schwannomatosis, the classical two-hit model of tumorigenesis is insufficient to account for schwannoma growth, since NF2 is also frequently inactivated in these tumours. Consequently, tumorigenesis in schwannomatosis must involve the mutation of at least two different tumour suppressor genes, an occurrence frequently mediated by loss of heterozygosity of large parts of chromosome 22q harbouring not only SMARCB1 and LZTR1 but also NF2. Thus, schwannomatosis is paradigmatic for a tumour predisposition syndrome caused by the concomitant mutational inactivation of two or more tumour suppressor genes. This review provides an overview of current models of tumorigenesis and mutational patterns underlying schwannomatosis that will ultimately help to explain the complex clinical presentation of this rare disease.

Molecular Analysis of Hybrid Neurofibroma/Schwannoma Identifies Common Monosomy 22 and α-T-Catenin/CTNNA3 as a Novel Candidate Tumor Suppressor

Neurofibromas and schwannomas are benign Schwann cell-derived peripheral nerve sheath tumors arising sporadically and within neurofibromatoses. Multiple tumors are a hallmark of neurofibromatosis type 1 (NF1) and type 2 (NF2) and schwannomatosis. Neurofibromas in NF1 and schwannomas in NF2 or schwannomatosis are defined by distinctive molecular hits. Among these, multiple hybrid neurofibromas/schwannomas may also appear, not yet being defined by a molecular background. We therefore performed molecular analysis of 22 hybrid neurofibromas/schwannomas using array comparative genomic hybridization, immunohistochemistry, quantitative RT-PCR, and functional analyses of cultured Schwann cells. Furthermore, we analyzed SMARCB1 by fluorescence in situ hybridization and multiplex ligation-dependent probe. Monosomy 22 was identified in 44% of tumors of tested patients with hybrid neurofibromas/schwannomas. In addition, in a single case, we detected focal deletion of the α-T-catenin/CTNNA3 gene (10q21.3). To further characterize this candidate, transient knockdown of α-T-catenin in Schwann cells was performed. CTNNA3 depleted cells showed cytoskeletal abnormalities and reduced E-cadherin expression, indicating epithelial-mesenchymal transition-like abnormalities. To conclude, we uncovered loss of chromosome 22 in almost half of all cases with hybrid neurofibromas/schwannomas of patients with multiple peripheral nerve sheath tumors. We tagged α-T-catenin/CTNNA3 as a novel candidate gene. Our functional investigations might indicate involvement of α-T-catenin/CTNNA3 in the biology of peripheral nerve sheath tumors.

Vestibular schwannoma and pituitary adenoma in the same patient: coincidence or novel clinical association?

Over the years the authors have evaluated a number of patients with vestibular schwannomas (VS) who have also been diagnosed with a pituitary adenoma (PA). No associations between these tumors have been established to date. The objective of the current study is to investigate the epidemiological association between VS and PA via a population-based study and to supplement these data with a retrospective case series of 12 patients who were evaluated at the authors' center over the past 15 years. An analysis of the Surveillance, Epidemiology, and End Results database including all patients identified with a diagnosis of VS and/or PA was performed. A comparison between the observed and expected annual incidence was calculated and population differences between those with VS + PA were compared with single tumor populations. 9888 patients with VS and 26,577 patients with PA were identified among 822.9 million person-years. Within these populations, 31 patients were diagnosed with both tumor types. Overall, 1 in every 319 patients with VS was also diagnosed with a PA. The average annual incidence for VS was 1.2 per 100,000 persons per year while the average PA rate was 3.2 per 100,000 persons per year. The observed rate of co-incident VS and PA was greater than what is expected by chance alone assuming independence. The cohort of patients with coexisting VS and PA were older and more commonly male compared to VS-only or PA-only groups. These data strongly suggest that a common environmental or genetic predisposition exists for VS and PA development. Further study of this population may help elucidate the cause of tumorigenesis in a subset of patients with seemingly sporadic tumors.

Evidence of polyclonality in neurofibromatosis type 2-associated multilobulated vestibular schwannomas

BACKGROUND

Neurofibromatosis type 2 (NF2) is a tumor syndrome that results from mutation of the NF2 tumor suppressor gene. The hallmark of NF2 is the presence of bilateral vestibular schwannoma (VS). Though NF2-associated and sporadic VS share identical histopathologic findings and cytogenetic alterations, NF2-associated VS often appears multilobulated, is less responsive to radiosurgery, and has worse surgical outcomes. Temporal bone autopsy specimens and MRI of the inner ear performed on NF2 patients suggest that multiple discrete tumors may be present within the labyrinth and cerebellopontine angle.

METHODS

Treatment-naïve ears in patients enrolled in a prospective NF2 natural history study (NIH#08-N-0044) were included for MRI analysis. T2-weighted and postcontrast T1-weighted MRIs were evaluated for the presence of multiple discrete tumors or a multilobulated mass. Peripheral blood (germline) and regional samples of tumor tissue were procured from consecutive patients enrolled in this study undergoing resection of a multilobulated VS (MVS). Histopathologic evaluation and genetic analysis (single nucleotide polymorphism array analysis, NF2 sequencing) were performed on each specimen.

RESULTS

Over half of NF2 ears harbored either an MVS (60/139 ears) or multiple discrete masses (19/139 ears). For 4 successive MVSs, genetic analysis revealed an admixture of cell populations, each with its own somatic NF2 mutation or deletion.

CONCLUSIONS

These findings suggest that the majority of NF2-associated VSs are polyclonal, such that the tumor mass represents a collision of multiple, distinct tumor clones. This explains the characteristic lobulated gross appearance of NF2-associated VS, and may also explain the substantially different treatment outcomes compared with sporadic VS.

Vestibular schwannoma in a patient with neurofibromatosis type 1: clinical report and literature review

We describe a young patient with typical neurofibromatosis type 1 on the basis of a mutation in the NF1 gene, who was diagnosed with a unilateral vestibular schwannoma caused by a somatic mutation in the NF2 gene. This combination has not been described before. This report highlights the requirement for ongoing surveillance regarding other manifestations of neurofibromatosis type 2 in such patients, as mosaicism cannot be ruled out. In addition to the NF1 mutation, the NF2 mutation should be considered in such cases if pre-implantation genetic diagnosis in undertaken.

Combining curcumin (diferuloylmethane) and heat shock protein inhibition for neurofibromatosis 2 treatment: analysis of response and resistance pathways

Neurofibromatosis type 2 (NF2) is a genetic condition characterized by inactivation of the NF2 tumor suppressor gene and the development of schwannomas. The NF2 gene product, merlin, is activated (dephosphorylated) by contact inhibition and promotes growth suppression. We investigated the effect of curcumin (diferuloylmethane), a molecule with anti-inflammatory and antitumorigenic properties, on human schwannoma cell growth and the regulation of merlin by curcumin in both NF2 cells and neuroblastoma (non-NF2) cells. Curcumin inhibited the growth of HEI-193 schwannoma cells in vitro and downregulated the phosphorylation of Akt and extracellular signal-regulated kinase 1/2. Curcumin also activated MYPT1-pp1δ (a merlin phosphatase), which was associated with dephosphorylation of merlin on serine 518, an event that results in the folding of merlin to its active conformation. In addition, curcumin induced apoptosis and generated reactive oxygen species in HEI-193 cells. Consequently, hsp70 was upregulated at the mRNA and protein levels, possibly serving as a mechanism of escape from curcumin-induced apoptosis and growth inhibition. Endogenous merlin and hsp70 proteins interacted in HEI-193 schwannoma and SK-N-AS neuroblastoma cells. The combination of curcumin and an hsp inhibitor synergistically suppressed schwannoma cell growth. Our results provide a rationale for combining curcumin and KNK437 in the treatment of NF2.

Meningiomas and neurofibromatosis

Neurofibromatosis type 2 (NF2) is a rare genetic disorder predisposing to multiple benign tumors of the nervous system. Meningiomas occur in about half of NF2 patients, and are often multiple. Patients harboring seemingly isolated multiple meningiomas should be investigated to diagnose NF2 by careful familial history collection, detailed clinical examination (skin lesions and slit lamp examination of the lens), audiovestibular testing, and fine cranio-spinal Magnetic Resonance Imaging. Somatic mosaicism is frequent in NF2 and may explain a mild phenotype as, e.g. isolated multiple meningiomas. Neurofibromatosis type 1 is not associated with an increased risk of meningioma. Whether meningiomas are part of the schwannomatosis tumor phenotype or not remains debated. Meningiomas in NF2 patients are associated with a higher risk of mortality, and their treatment is challenging, but data about natural history of meningiomas in NF2 patients in the literature are sparse. Thus, knowledge of tumor behavior is essential in slow growing tumors like meningiomas, to balance the risk of treatment against the natural history of the disease, and to evaluate the efficiency of alternative therapeutics (radiation therapy or new drugs).

Neurofibromatosis 2 [Bilateral acoustic neurofibromatosis, central neurofibromatosis, NF2, neurofibromatosis type II]

Neurofibromatosis 2 is a dominantly inherited tumor predisposition syndrome caused by mutations in the NF2 gene on chromosome 22. Affected individuals inevitably develop schwannomas typically affecting both vestibular nerves leading to deafness. Rehabilitation with brainstem implants is improving this outcome. Schwannomas also occur on other cranial nerves, on spinal nerve roots, and on peripheral nerves. Meningiomas and ependymomas are other tumor features. In excess of 50% of patients represent new mutations and as many as one third are mosaic for the underlying disease causing mutation. Although truncating mutations (nonsense and frameshifts) are the most frequent germline event and cause the most severe disease, single and multiple exon deletions are common. A strategy for detection of the latter is vital for a sensitive analysis. NF2 represents a difficult management problem with most patients facing substantial morbidity and reduced life expectancy. Surgery remains the focus of current management, although watchful waiting and occasionally radiation treatment have a role. In the future, the development of tailored drug therapies aimed at the genetic level are likely to provide huge improvements for this devastating, life limiting condition.

Neurofibromatosis type 2 (NF2): a clinical and molecular review

Neurofibromatosis type 2 (NF2) is a tumour-prone disorder characterised by the development of multiple schwannomas and meningiomas. Prevalence (initially estimated at 1: 200,000) is around 1 in 60,000. Affected individuals inevitably develop schwannomas, typically affecting both vestibular nerves and leading to hearing loss and deafness. The majority of patients present with hearing loss, which is usually unilateral at onset and may be accompanied or preceded by tinnitus. Vestibular schwannomas may also cause dizziness or imbalance as a first symptom. Nausea, vomiting or true vertigo are rare symptoms, except in late-stage disease. The other main tumours are schwannomas of the other cranial, spinal and peripheral nerves; meningiomas both intracranial (including optic nerve meningiomas) and intraspinal, and some low-grade central nervous system malignancies (ependymomas). Ophthalmic features are also prominent and include reduced visual acuity and cataract. About 70% of NF2 patients have skin tumours (intracutaneous plaque-like lesions or more deep-seated subcutaneous nodular tumours). Neurofibromatosis type 2 is a dominantly inherited tumour predisposition syndrome caused by mutations in the NF2 gene on chromosome 22. More than 50% of patients represent new mutations and as many as one-third are mosaic for the underlying disease-causing mutation. Although truncating mutations (nonsense and frameshifts) are the most frequent germline event and cause the most severe disease, single and multiple exon deletions are common. A strategy for detection of the latter is vital for a sensitive analysis. Diagnosis is based on clinical and neuroimaging studies. Presymptomatic genetic testing is an integral part of the management of NF2 families. Prenatal diagnosis and pre-implantation genetic diagnosis is possible. The main differential diagnosis of NF2 is schwannomatosis. NF2 represents a difficult management problem with most patients facing substantial morbidity and reduced life expectancy. Surgery remains the focus of current management although watchful waiting with careful surveillance and occasionally radiation treatment have a role. Prognosis is adversely affected by early age at onset, a higher number of meningiomas and having a truncating mutation. In the future, the development of tailored drug therapies aimed at the genetic level are likely to provide huge improvements for this devastating condition.

Neurofibromatosis type 2 (NF2): a clinical and molecular review

Neurofibromatosis type 2 (NF2) is a tumour-prone disorder characterised by the development of multiple schwannomas and meningiomas. Prevalence (initially estimated at 1: 200,000) is around 1 in 60,000. Affected individuals inevitably develop schwannomas, typically affecting both vestibular nerves and leading to hearing loss and deafness. The majority of patients present with hearing loss, which is usually unilateral at onset and may be accompanied or preceded by tinnitus. Vestibular schwannomas may also cause dizziness or imbalance as a first symptom. Nausea, vomiting or true vertigo are rare symptoms, except in late-stage disease. The other main tumours are schwannomas of the other cranial, spinal and peripheral nerves; meningiomas both intracranial (including optic nerve meningiomas) and intraspinal, and some low-grade central nervous system malignancies (ependymomas). Ophthalmic features are also prominent and include reduced visual acuity and cataract. About 70% of NF2 patients have skin tumours (intracutaneous plaque-like lesions or more deep-seated subcutaneous nodular tumours). Neurofibromatosis type 2 is a dominantly inherited tumour predisposition syndrome caused by mutations in the NF2 gene on chromosome 22. More than 50% of patients represent new mutations and as many as one-third are mosaic for the underlying disease-causing mutation. Although truncating mutations (nonsense and frameshifts) are the most frequent germline event and cause the most severe disease, single and multiple exon deletions are common. A strategy for detection of the latter is vital for a sensitive analysis. Diagnosis is based on clinical and neuroimaging studies. Presymptomatic genetic testing is an integral part of the management of NF2 families. Prenatal diagnosis and pre-implantation genetic diagnosis is possible. The main differential diagnosis of NF2 is schwannomatosis. NF2 represents a difficult management problem with most patients facing substantial morbidity and reduced life expectancy. Surgery remains the focus of current management although watchful waiting with careful surveillance and occasionally radiation treatment have a role. Prognosis is adversely affected by early age at onset, a higher number of meningiomas and having a truncating mutation. In the future, the development of tailored drug therapies aimed at the genetic level are likely to provide huge improvements for this devastating condition.

Giant café-au-lait macule in neurofibromatosis 1: a type 2 segmental manifestation of neurofibromatosis 1?

Type 2 segmental manifestation of autosomal dominant dermatoses refers to pronounced segmental lesions superimposed on the ordinary nonsegmental phenotype, indicating loss of heterozygosity occurring at an early stage of embryogenesis. We describe a 20-year-old Taiwanese woman with typical lesions of neurofibromatosis type 1 (NF1) in the form of characteristic café-au-lait spots, neurofibromas, axillary freckling and Lisch nodules. In addition, a giant garment-like or "bathing-trunk" café-au-lait macule involved the lower half of the trunk, the buttocks, and parts of the thighs, being superimposed on the ordinary smaller spots of NF1. This large café-au-lait macule may be best explained as an example of type 2 segmental NF1. A novel mutation (3009delG) in exon 23 was also identified in this patient, which has not yet been described in sporadic and familial NF1.

Evidence of a four-hit mechanism involving SMARCB1 and NF2 in schwannomatosis-associated schwannomas

Schwannomatosis is characterized by the onset of multiple intracranial, spinal, or peripheral schwannomas, without involvement of the vestibular nerve, which is instead pathognomonic of neurofibromatosis type 2 (NF2). Recently, a schwannomatosis family with a germline mutation of the SMARCB1 gene on chromosome 22 has been described. We report on the molecular analysis of the SMARCB1 and NF2 genes in a series of 21 patients with schwannomatosis and in eight schwannomatosis-associated tumors from four different patients. A novel germline SMARCB1 mutation was found in one patient; inactivating somatic mutations of NF2, associated with loss of heterozygosity (LOH) of 22q, were found in two schwannomas of this patient. This is the second report of a germline SMARCB1 mutation in patients affected by schwannomatosis and the first report of SMARCB1 mutations associated with somatic NF2 mutations in schwannomatosis-associated tumors. The latter observation suggests that a four-hit mechanism involving the SMARCB1 and NF2 genes may be implicated in schwannomatosis-related tumorigenesis.

What are the implications in individuals with unilateral vestibular schwannoma and other neurogenic tumors?

OBJECTIVES

Individuals who develop a unilateral vestibular schwannoma (VS) and other neurogenic tumors are at high risk of having the inherited condition neurofibromatosis Type 2 (NF2). The risk of bilateral disease and transmission risk to offspring are important in surgical planning and counseling. The authors have attempted to resolve these risks.

METHODS

A large NF2 dataset was interrogated for individuals who had initially presented with a unilateral VS and other tumors before developing bilateral disease, to assess the contralateral and offspring risks.

RESULTS

Ninety-six patients with a unilateral VS and additional neurogenic tumors had a bilaterality rate of 48% at 20 years in those initially diagnosed when > 18 years of age and 82% if presenting earlier. Constitutional NF2 mutations were found in blood in 25 (27%) of 92, but 13 (76%) of 17 patients presenting with unilateral VS at < or = 18 years of age. Tumor analysis suggests that the vast majority of the remainder are mosaic for an NF2 mutation.

CONCLUSIONS

Patients with unilateral VS and other NF2-related tumors who fulfill Manchester criteria have a high risk of developing a contralateral tumor, especially if presenting in childhood. Transmission risks are reduced for offspring, particularly in the older patients who are likely to be mosaic.

Cyclin D1 expression and histopathologic features in vestibular schwannomas

OBJECTIVE

To evaluate cyclin D1 expression in vestibular schwannoma and its relationship with histologic, clinical, and radiologic features.

PATIENTS

Twenty-one patients with histologically confirmed vestibular schwannoma.

INTERVENTION

Immunohistochemistry analysis was performed with anticyclin D1. Histopathologic features studied included Antoni pattern and nuclear and stromal degenerative changes. Clinical charts, audiometric data, and magnetic resonance imaging characteristics were reviewed.

MAIN OUTCOME MEASURES

Cyclin D1 expression and its association with histologic, clinical, and radiologic findings.

RESULTS

Cyclin D1 expression was found in 52% of cases. Cyclin D1 expression was more frequent in right-sided tumors (p = 0.02) and in tumors with nuclear degenerative changes (p < 0.0001). Patients with negative cyclin D1 expression had longer duration of deafness (p = 0.02) and higher 2,000-Hz hearing thresholds (p = 0.04) than cyclin D1+ patients.

CONCLUSION

Cyclin D1 expression, present in nearly half of the cases, may play a role in the development of these tumors. Further studies are needed to fully understand the contributions of histopathologic and immunohistochemical factors to vestibular schwannoma biological activity.

Mosaicism in neurofibromatosis type 2: an update of risk based on uni/bilaterality of vestibular schwannoma at presentation and sensitive mutation analysis including multiple ligation-dependent probe amplification

BACKGROUND

Neurofibromatosis type 2 (NF2) is almost unique among inherited disorders in the frequency of mosaicism in the first affected generation. However, the implications of this on transmission risks have not been fully elucidated.

METHODS

The expanded database of 460 families with NF2 and 704 affected individuals was analysed for mosaicism and transmission risks to offspring.

RESULTS

64 mosaic patients, with a projected mosaicism rate of 33% for sporadic classical NF2 with bilateral vestibular schwannoma at presentation and 60% for those presenting unilaterally, were identified. Offspring risks can be radically reduced on the basis of a sensitive mutation analysis of blood DNA including multiple ligation-dependent probe amplification (MLPA, which detects 15% of all mutations), but even MLPA cannot detect high levels of mosaicism.

CONCLUSION

The chances of mosaicism in NF2 and the resultant risks of transmission of the mutation to offspring in a number of different clinical situations have been further delineated. The use of MLPA in this large NF2 series is also reported for the first time.

Should NF2 mutation screening be undertaken in patients with an apparently isolated vestibular schwannoma?

Early onset of vestibular schwannoma (VS) is associated with the inherited condition neurofibromatosis type 2 (NF2). However, the majority of NF2 presents bilaterally and the proportion of early-onset apparent sporadic unilateral VS because of NF2 remains to be determined. We have determined the risk by studying NF2 risk in a population-based set of VS, looking at the mode of presentation in a large NF2 data set and the outcome of NF2 mutation analysis in 148 sporadic unilateral VS. The risk of NF2 in an apparently sporadic case of unilateral VS is small apart from in the very youngest age group (<20 years). NF2 germ line mutation testing is unlikely to reveal a mutation except <20 years as a result of the low risk and high rates of mosaicism. Germ line mutation testing is probably only justified in sporadic unilateral VS <20 years unless other features of NF2 are present. Ideally mutation testing should start with the original tumour specimen.

Mutational spectrum of the NF2 gene: a meta-analysis of 12 years of research and diagnostic laboratory findings

The NF2 tumor suppressor gene on chromosome 22 is a member of the protein 4.1 family of cytoskeletal elements. A number of single- and multiple-tumor phenotypes have been linked to alterations of NF2 since its characterization in 1993. We present a meta-analysis of 967 constitutional and somatic NF2 alterations from 93 published reports, along with 59 additional unpublished events identified in our laboratory and 115 alterations identified in clinical samples submitted to the Massachusetts General Hospital (MGH) Neurogenetics DNA Diagnostic Laboratory. In total, these sources defined 1,070 small genetic changes detected primarily by exon scanning, 42 intragenic changes of one whole exon or larger, and 29 whole gene deletions and gross chromosomal rearrangements. Constitutional single-exon events (N=422) were significantly more likely to be nonsense or splice site changes than somatic events (N=533), which favored frameshift changes (chi(2) test; P<0.001). Somatic events also differed markedly between tumors of different pathology, most significantly in the tendency of somatic events in meningiomas to lie within the 5' FERM domain of the transcript (Fisher's exact test; P<0.01 in comparison to schwannomas) with a complete absence of mutations in exons 14 and 15. There was no statistically significant difference in mutation type or exon distribution between published constitutional events and those found by the clinical laboratory. Less than 10% of all published and unpublished small alterations are nontruncating (N=63) and these changes are clustered in exons 2 and 3, suggesting that this region may be especially crucial to tumor suppressor activity in the protein.

Microsatellite analysis of recurrent vestibular schwannoma (acoustic neuroma) following stereotactic radiosurgery

HYPOTHESIS

Genetic and immunohistochemical studies may provide insight into the mechanisms of vestibular schwannoma (VS) recurrence following radiation therapy.

BACKGROUND

Stereotactic radiation therapy is an increasingly common alternative to microsurgical resection for the primary management of sporadic VS. The molecular mechanisms associated with recurrent vestibular schwannoma (VS) following radiation therapy are not known.

METHODS

Primary or irradiated VS tumors were fresh-frozen at the time of surgical resection and microdissected to undergo DNA extraction. Lymphocytic control DNA was isolated from blood obtained by venipuncture. Paired normal and tumor DNA specimens were analyzed for allelic loss by PCR amplification of polymorphic dinucleotide repeat sequences. Immunohistochemical studies were performed on paraffin-embedded, irradiated surgical specimens.

RESULTS

Using 16 polymorphic microsatellite markers, 20 of 26 non-irradiated VS demonstrated loss of heterozygosity (LOH) in at least one locus of chromosome 22q. In contrast, none of the four irradiated recurrent VS demonstrated LOH on chromosome 22q (p = 0.008). No allelic loss was seen in either the primary or irradiated VS utilizing markers mapping to chromosome 10. Deletions on chromosome 10 are seen in both benign and higher-grade meningiomas and intracranial malignancies associated with radiotherapy. Immunohistochemical studies were performed to detect the protein product of the NF2 gene, merlin, in the four irradiated VS. NF2 staining was not observed.

CONCLUSION

This study represents the first microsatellite and immunohistochemical analysis of recurrent VS following radiation therapy. Our preliminary observations suggest an alternative mechanism of NF2 inactivation that may correlate with radioresistance in VS.

DNA Methylation of Multiple Genes in Vestibular Schwannoma

HYPOTHESIS

The purpose of this study was to examine the DNA methylation profile of several genes in a series of vestibular schwannomas, and to analyze its relationship with clinical and radiological features.

BACKGROUND

Aberrant methylation of promoter regions is a major mechanism for silencing of tumor suppressor genes in several tumors. There is limited information about methylation status in vestibular schwannoma, with no clinical or radiological implications described to date.

METHODS

The methylation status of 16 tumor-related genes including RASSF1A, RAR-B, VHL, PTEN, HMLH1, RB1, TP16, CASP8, ER, TIMP3, MGMT, DAPK, TP73, GSTP1, TP14, and THBS1 was examined in a series of 22 vestibular schwannomas.The bisulfite modification of genomic DNA was performed. Clinical and radiological features were compared with the methylation results.

RESULTS

Methylation values from 9% to 27% were found in 12 of 16 genes tested, including RASSF1A, VHL, PTEN, TP16, CASP8, TIMP3, MGMT, DAPK, THBS1, HMLH1, TP73, and GSTP1. A significant association was found between CASP8 and RASSF1A methylation. Methylation of CASP8 was associated with the patient's age and the tumor size. Methylation of TP73 was associated with hearing loss. RASSF1A methylation was inversely correlated with the clinical growth index.

CONCLUSION

Aberrant methylation of tumor-related genes may play a role in the development of vestibular schwannomas. Our results may provide useful clues to the development of prognostic assays for these tumors.

Malignant transformation and new primary tumours after therapeutic radiation for benign disease: substantial risks in certain tumour prone syndromes

In recent years the use of radiation treatment for benign tumours has increased with the advent of stereotactic delivery and, in particular, single high dose gamma knife therapy. This has been particularly true for benign CNS (central nervous system) tumours such as vestibular schwannoma, meningioma, pituitary adenoma, and haemangioblastoma. While short term follow up in patients with isolated tumours suggests this treatment is safe, there are particular concerns regarding its use in childhood and in tumour predisposing syndromes. We have reviewed the use of radiation treatment in these contexts with particular regard to malignant transformation and new tumour induction. This review indicates that much more caution is warranted regarding the use of radiation treatment for benign tumours in childhood and in tumour prone conditions such as the neurofibromatoses.

Molecular genetics alterations and tumor behavior of sporadic vestibular schwannoma from the People's Republic of China

OBJECTIVES

To analyze the molecular genetic alteration of sporadic vestibular schwannomas from the People's Republic of China and to correlate these alterations with the tumor behaviors.

METHODS

Four highly polymorphic microsatellite DNA markers were used to observe the frequency of loss of heterozygosity (LOH) in chromosome 22. The NF2 gene mutations were detected by Polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and DNA sequencing. The schwannomin/merlin (S/M) expression was examined using anti-NF2 (A-19) IgG under immunohistochemistry and western blot. The proliferative index (LI) of vestibular schwannoma was evaluated by proliferative cell nuclear antigen investigation.

RESULTS

Sixteen vestibular schwannomas (44.4%) showed allele loss. We found 22 mutations in 36 schwannomas. The LI and the growth rate of schwannomas with LOH or mutation were significantly higher than those without LOH or mutation. All of these vestibular schwannomas showed no immunoreaction to anti-NF2(A-19) IgG by immunohistochemistry. By immunoblotting technique, reduced expression of S/M was found in 31 cases (86%). The growth index of schwannomas with severely reduced expression of S/M was significantly higher than those with moderately reduced or normal expression.

CONCLUSION

The molecular genetic changes in sporadic vestibular schwannomas from Chinese patients were similar to the previous reports. We demonstrate the relationship between tumor behaviors and genetic alteration (including LOH and mutation of NF2 gene). We propose that inactivation of S/M, may be an important step in tumorigenesis of sporadic vestibular schwannoma.

Incidence of vestibular schwannoma and neurofibromatosis 2 in the North West of England over a 10-year period: higher incidence than previously thought

OBJECTIVE

To determine the incidence of vestibular schwannoma (VS) in sporadic, neurofibromatosis type 2 (NF2) germ-line and mosaic form in a 10-year period.

STUDY DESIGN

Review of all incident cases of VS presenting to the four main neurosurgical centers for a population of 4.1 million from 1990 to 1999 and cross-referencing with the regional cancer registry.

SETTING

Population based.

PATIENTS

All patients presenting with VS detected on magnetic resonance imaging scan.

RESULTS

A total of 419 sporadic and 64 NF2-related VS were identified over the study period. This represented an incidence of 10.4 per million per year for sporadic VS and 11.8 per million per year including NF2-related tumors. The incidence rose to 14 per million per year in the latter 5 years. The NF2 patient diagnoses represent an estimated birth incidence of 1 in 25,000, and 7% of the patients with VS had NF2, which is higher than previous estimates.

CONCLUSIONS

The incidence of VS is rising almost certainly due to increasing diagnosis in the magnetic resonance imaging era. At current rates, 1 per 1,000 individuals will be diagnosed with VS in their lifetime. More VS than previously thought are due to NF2, which may be because of recognition of mosaic forms of the disease.

Sensitive detection of deletions of one or more exons in the neurofibromatosis type 2 (NF2) gene by multiplexed gene dosage polymerase chain reaction

Mutation detection in the neurofibromatosis type 2 (NF2) gene is challenging because when combining mutation detection methods such as single-strand conformational polymorphism and heteroduplex analysis, denaturing gradient gel electrophoresis, and direct sequencing of aberrant polymerase chain reaction (PCR) fragments only 30 to 60% of the constitutional mutations are detected. Because large deletions and complete chromosome rearrangements are also described methods such as microarray-comparative genomic hybridization and fluorescence in situ hybridization are also used. The one type of mutation often missed corresponds to deletions encompassing one or few exons. To detect this type we have developed a swift and reliable method. We perform a gene dosage analysis with two fluorescent multiplex PCR assays that amplify 15 of the 17 NF2 exons. The labeled PCR products are quantified and gene dose is calculated with respect to controls. We tested the reliability of this method with DNA from eight NF2 patients with known heterozygous NF2 deletions, eight controls and four unknown NF2 patients. In all of the patients with known heterozygous deletions we found in several exons a reduction of gene dosage to 50 to 69%. In one NF2 patient with previously unknown mutation and a severe phenotype we found the gene dosage of two exons reduced by 50% indicating a deletion of these two exons on one allele. This finding was validated by reverse transcriptase-PCR on fibroblast and schwannoma cell cultures of this patient and cDNA sequencing. Our gene dosage assay will detect deletions of one or more exons as well as gross deletions of the whole coding region of the gene. It can complement the existing screening methods because it is faster and easier.

Mutation scanning of the NF2 gene: an improved service based on meta-PCR/sequencing, dosage analysis, and loss of heterozygosity analysis

We describe the development and implementation of a neurofibromatosis type 2 (NF2) mutation scanning service based on novel techniques. All 17 exons of the NF2 gene are amplified in four polymerase chain reaction (PCR) reactions, using the meta-PCR technique to link the NF2 exons into chimeric concatamers. The meta-PCR products are then scanned for point mutations by direct sequencing. A four-exon dosage assay is used to test for large deletion/duplication mutations. In certain cases when tumour studies are necessary, these techniques are also combined with loss of heterozygosity analysis with three highly polymorphic microsatellite markers located within or close to the NF2 gene. Over a period of 2 years, we have applied these techniques in a service setting to the analysis of 271 patient samples (245 lymphocyte DNA; 26 schwannoma DNA). Meta-PCR and sequencing identified 90 point mutations in the 271 blood and tumor samples, 48 of which have not been reported previously. Dosage analysis identified large deletions in 12 of the lymphocyte DNA samples. In addition, over 84% of mutations were identified in 23 schwannoma DNA samples in which complete analysis was possible. Adoption of this novel strategy has increased the overall mutation detection rate in familial NF2 cases to 88% and sporadic NF2 cases to 59%. It has also allowed us to decrease our reporting turnaround times, and because of a low overall failure rate, permitted the running of an efficient and cost-effective service.

Molecular pathogenesis of skull base tumors

OBJECTIVE

To review contemporary molecular biological literature related to skull base tumor biology and tumorigenesis.

DATA SOURCES

PUBMED and Ovid literature searches were performed using keyword search. Only English language articles published between 1965 and December 4, 2003 were chosen.

STUDY SELECTION AND DATA EXTRACTION

All relevant articles from the past 8 years, as well as landmark articles in years before 1995, were retrieved and reviewed.

CONCLUSION

Consistent progress is being made toward the molecular genetic and biological basis of the most common skull base tumors. An understanding of these mechanisms will aid the neurotologist in future diagnosis and management of the lesions.

Loss of heterozygosity on chromosome 10q22-10q23 and 22q11.2-22q12.1 and p53 gene in primary hepatocellular carcinoma

AIM: To analyze loss of heterozygosity (LOH) and homozygous deletion on p53 gene (exon2-3, 4 and 11), chromosome 10q22-10q23 and 22q11.2-22q12.1 in human hepatocellular carcinoma (HCC).

METHODS: PCR and PCR-based microsatellite polymorphism analysis techniques were used.

RESULTS: LOH was observed at D10S579 (10q22-10q23) in 4 of 20 tumors (20%), at D22S421 (22q11.2-22q12.1) in 3 of 20 (15%), at TP53.A (p53 gene exon 2-3) in 4 of 20 (20%), at TP53.B (p53 gene exon 4) in 6 of 20 (30%), and at TP53.G (p53 gene exon 11) in 0 of 20 (0%). Homozygous deletion was detected at 10q22-10q23 (8/20; 40%), 22q11.2-22q12.1 (8/20; 40%), p53 gene exon 2-3 (0/20;0%), p53 gene exon 4 (6/20; 30%), and p53 gene exon 11 (2/20; 10%).

CONCLUSION: There might be unidentified tumor suppressor genes on chromosome 10q22-10q23 and 22q11.2-22q12.1 that contribute to the pathogenesis and development of HCC.