Updated diagnostic criteria and nomenclature for neurofibromatosis type 2 and schwannomatosis: An international consensus recommendation.

PURPOSE: Neurofibromatosis type 2 (NF2) and schwannomatosis (SWN) are genetically distinct tumor predisposition syndromes with overlapping phenotypes. We sought to update the diagnostic criteria for NF2 and SWN by incorporating recent advances in genetics, ophthalmology, neuropathology, and neuroimaging. METHODS: We used a multistep process, beginning with a Delphi method involving global disease experts and subsequently involving non-neurofibromatosis clinical experts, patients, and foundations/patient advocacy groups. RESULTS: We reached consensus on the minimal clinical and genetic criteria for diagnosing NF2 and SWN. These criteria incorporate mosaic forms of these conditions. In addition, we recommend updated nomenclature for these disorders to emphasize their phenotypic overlap and to minimize misdiagnosis with neurofibromatosis type 1. CONCLUSION: The updated criteria for NF2 and SWN incorporate clinical features and genetic testing, with a focus on using molecular data to differentiate the 2 conditions. It is likely that continued refinement of these new criteria will be necessary as investigators study the diagnostic properties of the revised criteria and identify new genes associated with SWN. In the revised nomenclature, the term "neurofibromatosis 2" has been retired to improve diagnostic specificity.

A negative feedback signaling network underlies oncogene-induced senescence.

Oncogene-induced senescence functions to limit tumor development. However, a complete understanding of the signals that trigger this type of senescence is currently lacking. We found that mutations affecting NF1, Raf, and Ras induce a global negative feedback response that potently suppresses Ras and/or its effectors. Moreover, these signals promote senescence by inhibiting the Ras/PI3K pathway, which can impact the senescence machinery through HDM2 and FOXO. This negative feedback program is regulated in part by RasGEFs, Sprouty proteins, RasGAPs, and MKPs. Moreover, these signals function in vivo in benign human tumors. Thus, the ultimate response to the aberrant activation of the Ras pathway is a multifaceted negative feedback signaling network that terminates the oncogenic signal and participates in the senescence response.

Superficial neurofibromas in the setting of schwannomatosis: nosologic implications.

First described in the past decade, schwannomatosis is a syndrome distinct from neurofibromatosis 2 (NF2). It is characterized by the development of multiple schwannomas, sparing the vestibular division of cranial nerve VIII, and may also predispose to develop meningiomas. We report two female patients, a 27 and a 44 years old who developed multiple peripheral schwannomas, but without involvement of the vestibular nerves, satisfying clinical criteria for schwannomatosis. Lack of vestibular nerve involvement was confirmed with MRI using an internal auditory canal protocol with 3 mm thick slices in both patients after age 30. Both patients developed a small neurofibroma in axillary subcutaneous tissues and a diffuse cutaneous neurofibroma of the left buttock, respectively. This report highlights that superficial neurofibromas may arise in the setting of schwannomatosis, which may have implications for the diagnostic criteria of this unique syndrome. In particular, the presence of a cutaneous neurofibroma in a patient with multiple schwannomas should not lead to a diagnosis of NF2.

A role for the p53 pathway in the pathology of meningiomas with NF2 loss.

The neurofibromatosis 2 locus (NF2) is inactivated through mutation and loss of heterozygosity (LOH) in 40-65% of all sporadic meningiomas, while the role of the p53 tumor suppression pathway in meningioma initiation and progression is still unclear. This study aims to determine if a p53 codon 72 arginine-to-proline polymorphism, found to be correlated with cancer development and cancer patient survival in other tumors, is associated with sporadic meningioma initiation or progression. We investigated Pro72 incidence in a cohort of 92 sporadic meningiomas and analyzed its association with histological grade (WHO classification) and with NF2 LOH (determined using polymorphic microsatellite markers on 22q). The Pro72 allele was not found to be selected for in the cohort. However, in the subgroup of meningiomas with NF2 LOH and carrying Pro72, 50.0% had high grade tumors (WHO grades II and III) compared to only 14.3% of those without NF2 LOH (OR = 6.0, CI = 1.56-23.11, P = 0.012). The significant association occurred only when considering subgroups of meningiomas with or without NF2 LOH, suggesting that not including NF2 status when analyzing study cohorts may explain the variability seen in the literature where all meningiomas were grouped together. Our data suggests a role for the p53 pathway in the progression of meningiomas in which NF2 is inactivated, and highlights the importance of accounting for NF2 LOH in future studies of meningiomas and the p53 pathway.

Immunohistochemical analysis supports a role for INI1/SMARCB1 in hereditary forms of schwannomas, but not in solitary, sporadic schwannomas.

The INI1/SMARCB1 protein product (INI1), a component of a transcription complex, was recently implicated in the pathogenesis of schwannomas in two members of a single family with familial schwannomatosis. Tumors were found to have both constitutional and somatic mutations of the SMARCB1 gene and showed a mosaic pattern of loss of INI1 expression by immunohistochemistry, suggesting a tumor composition of mixed null and haploinsufficient cells. To determine if this finding could be extended to all tumors arising in familial schwannomatosis, and how it compares with other multiple schwannoma syndromes [sporadic schwannomatosis and neurofibromatosis 2 (NF2)] as well as to sporadic, solitary schwannomas, we performed an immunohistochemistry analysis on 45 schwannomas from patients with multiple schwannoma syndromes and on 38 solitary, sporadic schwannomas from non-syndromic patients. A mosaic pattern of INI1 expression was seen in 93% of tumors from familial schwannomatosis patients, 55% of tumors from sporadic schwannomatosis, 83% of NF2-associated tumors and only 5% of solitary, sporadic schwannomas. These results confirm a role for INI1/SMARCB1 in multiple schwannoma syndromes and suggest that a different pathway of tumorigenesis occurs in solitary, sporadic tumors.

Patient and physician attitudes regarding clinical trials in neurofibromatosis 1.

Neurofibromatosis 1 (NF1) is a multisystem genetic disorder that primarily affects the skin (freckling and café-au-lait macules), nervous system (neurofibromas, optic gliomas, and learning disabilities), and skeletal system (pseudoarthroses). The interest in pharmacological intervention for patients with NF1 has grown in recent years. However, little is known about the attitudes and priorities of patients, families, and physicians regarding participation in clinical trials. We surveyed 74 adult patients or parents of patients with NF1 and 69 care providers participating in a neurofibromatosis clinic to assess their willingness to participate in clinical trials and their opinions about which conditions they thought were most important to treat. Both patients and care providers are willing to participate in clinical trials for NF1 and both groups rate malignant peripheral nerve sheath tumors as the most urgent for new treatments. There are concordant views among patients and physicians concerning clinical trials for NF1, and patients do not dismiss participation in placebo-controlled trials. Neuroscience nurses are poised to facilitate the research process from conception through implementation as they take the viewpoints of our study populations into consideration.

Temporal control of Rac in Schwann cell-axon interaction is disrupted in NF2-mutant schwannoma cells.

Schwann cell-axon interaction is the hallmark feature of peripheral nerves, yet the intracellular signals underlying this interaction are unknown. Schwann cells extend processes and migrate on developing axons before differentiation, requiring coordinated regulation of the Schwann cell cytoskeleton. Small GTPases of the Rho family, including Rho, Rac, and cell division cycle 42, regulate the actin cytoskeleton. The neurofibromatosis type 2 (NF2) gene is commonly mutated in schwannomas, Schwann cell tumors that contain cells lacking axon interaction. NF2 is involved in suppression of Rac signaling, and cultured schwannoma cells contain elevated, GTP-bound, active Rac. Despite these previous studies, a causal relationship between Rac activation and the abnormal cellular morphology of schwannoma is unknown. We used fluorescence resonance energy transfer to follow Rac activity in normal human Schwann cells and schwannoma cells during interaction with neurons. Normal Schwann cells elongated processes along neurites under low Rac activity. Schwannoma cells showed high Rac activity at distal regions of the cells and failed to align processes with neurites. Application of a Rac-specific inhibitor, the chemical compound NSC23766, to schwannoma cells restored neuronal interaction. The data support the significance of regulated Rac signaling in mediating Schwann cell-axon interaction and suggest that controlling Rac activity as a possible therapy for schwannomas.

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.

Ocular pathologic findings of neurofibromatosis type 2.

OBJECTIVE: To gain insight into the pathogenesis of neurofibromatosis type 2 (NF2) by investigating the ocular manifestations of this disease. METHODS: Using standard histologic techniques, immunohistochemistry, and electron microscopy, we described the ocular pathologic findings of a 34-year-old woman who died from complications of NF2. RESULTS: We identified 3 types of NF2-associated lesions: juvenile posterior subcapsular cataracts, epiretinal membranes, and an intrascleral schwannoma. CONCLUSIONS: Our analysis indicated that dysplastic lens cells accumulate just anterior to the posterior lens capsule in juvenile posterior subcapsular cataracts and that dysplastic Müller cells may be a major component of NF2-associated epiretinal membranes. Clinical Relevance Our findings suggest that a subset of glial cells with epithelial features (Schwann cells, ependymal cells, and Müller cells) may be particularly sensitive to loss of the NF2 gene. Understanding the molecular basis for this sensitivity may lead to novel strategies for treating NF2.

The neurofibromatosis type 2 gene product, merlin, reverses the F-actin cytoskeletal defects in primary human Schwannoma cells.

Schwannoma tumors, which occur sporadically and in patients with neurofibromatosis, account for 8% of intracranial tumors and can only be treated by surgical removal. Most schwannomas have biallelic mutations in the NF2 tumor suppressor gene. We previously showed that schwannoma-derived Schwann cells exhibit membrane ruffling and aberrant cell spreading when plated onto laminin, indicative of fundamental F-actin cytoskeletal defects. Here we expand these observations to a large group of sporadic and NF2-related tumors and extend them to schwannomatosis-derived tumors. Mutation at NF2 correlated with F-actin abnormalities, but the extent of morphological change did not correlate with the type of NF2 mutation. We used a recently described molecular strategy, TAT-mediated protein transfer, to acutely introduce the NF2 protein, merlin, into primary human schwannoma cells in an attempt to reverse the cytoskeletal phenotype. Abnormal ruffling and cell spreading by cells with identified NF2 mutations were rapidly reversed by introduction of TAT-merlin. The effect is specific to TAT-merlin isoform 1, the growth-suppressive isoform of merlin. TAT-merlin isoform 2, a TAT-merlin mutant (L64P), and merlin lacking TAT were ineffective in reversing the cytoskeletal phenotype. Results show that merlin isoform 1 is sufficient to restore normal actin organization in NF2-deficient human tumor cells, demonstrating a key role for merlin in the NF2 phenotype. These results lay the foundation for epigenetic complementation studies in NF2 mouse models and possibly for experiments to evaluate the utility of merlin transduction into patients as protein therapy.

Unilateral vestibular schwannoma with other neurofibromatosis type 2-related tumors: clinical and molecular study of a unique phenotype.

OBJECT: Although the manifestations of neurofibromatosis Type 2 (NF2) vary, the hallmark is bilateral vestibular schwannomas (VSs). The authors studied the clinical course and genetic basis of unilateral VSs associated with other NF2-related tumors. METHODS: Forty-four adults presenting with unilateral VSs and other NF2-related tumors were identified. A comprehensive review of patient records and cranial imaging was conducted. Molecular analysis of the NF2 locus was performed in available tumors and paired blood specimens. Patient age at symptomatic onset ranged from 11 to 63 years (mean 32 years). Twenty-two patients (50%) presented with eighth cranial nerve dysfunction. Twenty-six presented with multiple lesions. Thirty-eight harbored other intracranial tumors and 27 had spinal tumors, with most lesions situated ipsilateral to the VS. No patient had a relative with NF2, although two of 63 offspring had isolated NF2-related findings. A contralateral VS developed in four patients 3 to 46 years after the symptomatic onset of a unilateral VS, and two of these patients experienced rapid progression to total deafness. Results of a Kaplan-Meier analysis identified actuarial chances of developing contralateral VS: 2.9% (3-17 years after the VS symptomatic onset of unilateral VS), 11% (18-24 years), and 28.8% (25-40 years). Mosaicism for the NF2 gene mutation was proven in eight patients. CONCLUSIONS: The authors describe the clinical features of this unique phenotype--unilateral VS with other NF2-related tumors. Persons with this phenotype should undergo evaluation and monitoring similar to that conducted in patients with NF2, and the possibility of aggressive contralateral VS formation should be considered in their treatment. Molecular genetic analysis is best performed using resected tumor specimens and will enable future studies to determine the genetic risks of individuals with mosaicism.

Comparative pathology of nerve sheath tumors in mouse models and humans.

Despite the progress made in our understanding of the biology of neurofibromatosis (NF), the long-term clinical outcome for affected patients has not changed significantly in the past decades, and both NF1 and NF2 are still associated with a significant morbidity and a decreased life span. A number of NF1 and NF2 murine models have been generated to aid in the study of NF tumor biology and in the development of targeted therapies for NF patients. A single, universal pathological classification of the lesions generated in these murine models is essential for the validation of the models, for their analysis and comparison with other models, and for their future effective use in preclinical treatment trials. For the formulation of a pathological classification of these lesions, the WHO classification of human tumors was used as a reference. However, it was not adopted for the classification of the GEM lesions because of some important differences between the human and murine lesions. A novel classification scheme for peripheral nerve sheath tumors in murine models was therefore devised.

Inactivation patterns of NF2 and DAL-1/4.1B (EPB41L3) in sporadic meningioma.

The molecular basis of tumorigenesis and tumor progression in meningiomas is not fully understood. The neurofibromatosis 2 (NF2) locus is inactivated in 50-60% of sporadic meningiomas, but the genetic basis of sporadic meningiomas not inactivated at the NF2 locus remains unclear. Specifically, there is conflicting data regarding the role of the tumor suppressor gene DAL-1/4.1B. Using microsatellite markers, we studied 63 sporadic meningiomas to determine loss of heterozygosity (LOH) at the NF2 and DAL-1/4.1B loci. Array comparative genomic hybridization analysis of 52 of these tumors was performed to determine copy number changes on chromosomes 18 and 22. Forty-one of 62 informative tumors showed LOH at the NF2 locus (66%) while only 12 of 62 informative tumors (19%) showed LOH of DAL-1/4.1B. Eleven of 12 (92%) tumors with DAL-1/4.1B LOH also had NF2 LOH. Monosomy or large deletions of chromosomes 18 and 22 were the main mechanism for LOH in these tumors. These studies implicate the DAL-1/4.1B locus in sporadic meningiomas less commonly than reported previously, and suggest that it is a progression rather than an initiation locus. Furthermore, we found the majority of meningiomas developed monosomy rather than isodisomy at the NF2 and DAL-1/4.1B loci as the mechanism for LOH.

Somatic instability of the NF2 gene in schwannomatosis.

CONTEXT: Schwannomatosis is a newly described form of neurofibromatosis of unclear pathogenesis. PATIENT AND METHODS: We studied the NF2 locus on chromosome 22 in 7 tumor specimens resected from a 36-year-old man with schwannomatosis of the right ulnar nerve. RESULTS: Unrelated truncating NF2 gene mutations were detected in 4 tumor specimens. None of the NF2 mutations were present in the blood specimen. Loss of heterozygosity at the NF2 locus was seen in all tumors, and in every case the same allele was lost. Loss of distal chromosome 22 markers was variable. Fluorescence in situ hybridization results were consistent with monosomy 22 in 4 tumors and mitotic recombination or nondisjunction in 1. CONCLUSIONS: Molecular analysis of tumor specimens distinguishes schwannomatosis from other forms of neurofibromatosis. Further work is needed to understand the natural history and molecular biology of this condition.

Neurofibromatosis 2 in the pediatric population.

Neurofibromatosis 2 is a severe autosomal dominant disorder characterized by the occurrence of bilateral vestibular schwannomas and other benign tumors of the nervous system. Excellent natural history studies exist for adults with neurofibromatosis 2, but limited outcome data are available for children with neurofibromatosis 2. In this study, we present clinical data on 12 patients with neurofibromatosis 2 and age at diagnosis before 18 years. Full record review included surgical reports, pathology reports, and imaging studies; all patients were personally examined by a single author. One third of the patients presented with hearing impairment and another third presented with other cranial nerve dysfunction. Tumor load was extensive, including cranial meningiomas in 75%, cranial schwannomas other than vestibular schwannomas in 83%, and spinal cord tumors in 75%. Family history was present in two thirds of the patients. Surgical removal of vestibular schwannomas was performed in 58%; none had full preservation of hearing postsurgery. Functionally, 75% of children had hearing loss, 83% had visual impairment, 25% had abnormal ambulation, and 25% were performing below grade level. In conclusion, increased clinical awareness, better imaging techniques, and molecular diagnostics have made pediatric diagnosis of neurofibromatosis 2 feasible, but outcomes appear to be worse than in adult patients. Further work is needed to determine optimal management of pediatric neurofibromatosis 2.

Spinal ependymomas in neurofibromatosis Type 2: a retrospective analysis of 55 patients.

OBJECT: The aim of this paper was to define the clinical characteristics of spinal ependymomas associated with neurofibromatosis Type 2 (NF2). METHODS: The authors retrospectively reviewed the clinical records of patients with NF2 who had imaging findings consistent with ependymomas and were seen at Massachusetts General Hospital between 1994 and 2007. Clinical characteristics of these patients were obtained from hospital records, imaging studies, surgical reports, and pathology reports. Mutational analysis of the NF2 gene was performed in 37 of 44 unrelated patients. RESULTS: Fifty-five patients met inclusion criteria for the study. The median age at diagnosis of NF2 was 21 years; the median time after diagnosis until identification of ependymomas was 5 years. Multiple ependymomas were present in 58% of patients. The most common site of involvement was the cervical cord or cervicomedullary junction (86% of imaging studies), followed by the thoracic and lumbar cords (62% and 8%, respectively). The majority of patients had no symptoms related to their tumors (42 patients [76%]). After a median follow-up of 50 months, surgery was performed in 11 patients (20%) for symptomatic progression (indications for surgery). Mutational analysis of the NF2 gene detected alterations in 28 (76%) of 37 unrelated patients, with nonsense and frameshift mutations accounting for 64% of detected mutations. The high rate of truncating mutations may help explain the high tumor burden in these patients. CONCLUSIONS: Neurofibromatosis Type 2-related ependymomas exhibit an indolent growth pattern with tumor progression limited to a minority of patients. The authors believe that surveillance is reasonable for asymptomatic ependymomas, including those with cystic areas that expand the cord. For symptomatic tumors, resection may be warranted depending on age, overall clinical status, and ease of resectability.

Three-dimensional volumetrics for tracking vestibular schwannoma growth in neurofibromatosis type II.

OBJECTIVE: Vestibular schwannomas (VS) are common, benign, VIIIth cranial nerve tumors. Treatment in patients with the genetic disorder neurofibromatosis type II (NF2) is complicated by their development of bilateral VS and risk of complete deafness. Intervention decisions consider several clinical factors including tumor size and growth rate evaluated using magnetic resonance imaging. The current study evaluated the relative sensitivity of volumetric versus linear diameter measurement for assessing VS growth rate and progression. METHODS: Retrospective analysis was performed on 43 magnetic resonance imaging scans acquired longitudinally (range, 2-7 yr) from 10 patients with NF2. Fifteen VS were measured (five patients had unilateral lesions meeting inclusion criteria) using both maximum linear diameter and semiautomated volumetric analysis. Progression was defined according to Response Evaluation Criteria in Solid Tumors and its volumetric (cubed linear) equivalent. Measurement techniques were compared by assessing sensitivity to lesion growth. RESULTS: Volumetric measures were significantly more sensitive to VS growth, both for total change and change per year percentages; cubed linear growth measures (proportional to volume growth) underestimated volume growth by 50%. Seven lesions showed progression on volumetric analysis, but two of these did not show progression based on linear measures. Thus, for 29% of lesions showing progression based on volume, linear measures did not detect progression. CONCLUSION: Linear measurements underestimate VS growth rate compared with volumetric measures in NF2 patients. These results provide clear, quantitative proof that diameter measures are not as sensitive to change as volumetric measurements and that volumetric measurements should be strongly considered when making VS treatment decisions.

Modeling NF2 with human arachnoidal and meningioma cell culture systems: NF2 silencing reflects the benign character of tumor growth.

Meningiomas, common tumors arising from arachnoidal cells of the meninges, may occur sporadically, or in association with the inherited disorder, neurofibromatosis 2 (NF2). Most sporadic meningiomas result from NF2 inactivation, resulting in loss of tumor suppressor merlin, implicated in regulating membrane-cytoskeletal organization. To investigate merlin function in an authentic target cell type for NF2 tumor formation, we established primary cultures from genetically-matched meningioma and normal arachnoidal tissues. Our studies revealed novel and distinct cell biological and biochemical properties unique to merlin-deficient meningioma cells compared to merlin-expressing arachnoidal and meningioma cells, and other NF2-deficient cell types. Merlin-deficient meningioma cells displayed cytoskeletal and cell contact defects, altered cell morphology and growth properties, most notably cell senescence, implicating the activation of senescence pathways in limiting benign meningioma growth. Merlin suppression by RNAi in arachnoidal cells replicated merlin-deficient meningioma features, thus establishing these cell systems as disease-relevant models for studying NF2 tumorigenesis.

Dopa-responsive hypersomnia and mixed movement disorder due to sepiapterin reductase deficiency.

Sepiapterin reductase deficiency (SRD) is a rare, treatable disorder of monoamine metabolism with cognitive delay and l-dopa responsive movement disorder. We describe a patient with SRD and distinctive phenotypic feature of marked hypersomnolence. Our patient showed improvement with therapies directed at both serotonergic and dopaminergic deficiencies. This case illustrates symptoms that characterize the SRD phenotype and demonstrates the importance of systematic treatment trials addressing the various biochemical abnormalities present.

Multiple meningiomas: Investigating the molecular basis of sporadic and familial forms.

Meningiomas are common tumors of the coverings of the central nervous system (CNS), comprising 20% of intracranial neoplasms. The only genes known to be associated with sporadic meningiomas are NF2 on chromosome 22 and the related cytoskeleton element DAL-1 on chromosome 18. Between 1 and 8% of patients with meningiomas develop multiple meningiomas, a trait transmitted occasionally in an autosomal dominant fashion. We investigated the DAL-1 and NF2 loci in 7 unrelated multiple meningioma patients without clinical evidence of NF2 by mutational and pathological analysis. Five novel intragenic microsatellite polymorphisms were developed for specific detection of loss of heterozygosity (LOH) at the DAL-1 locus. Three of 7 patients had affected relatives and all affected individuals were female. No tumors from familial patients were of a fibroblastic subtype. Truncating NF2 mutations were detected in 3 tumor specimens, but were not present in the corresponding blood samples. Two tumors showed LOH at the NF2 locus. All tumors showing mutations at the NF2 locus originated from patients without affected relatives and were of the fibroblastic subtype. Five non-truncating alterations in the DAL-1 gene were found, however, LOH of chromosome 18 markers was not seen in any tumor. In contrast to the NF2 results, all DAL-1 alterations were found in paired blood specimens. Our findings provide further evidence that the molecular basis of sporadic and familial multiple meningiomas is fundamentally different and extend this dichotomy to pathologic subtypes. DAL-1 does not function as a true tumor suppressor in these patients.