Managing NF2-associated vestibular schwannomas in children and young adults: review of an institutional series regarding effects of surgery and bevacizumab on growth rates, tumor volume, and hearing quality

We reviewed our experience in managing of NF2-associated vestibular schwannoma (VS) in children and young adults regarding the effect of surgery and postoperative bevacizumab treatment. A total of 579 volumetric and hearing data sets were analyzed. The effect of surgery on tumor volume and growth rate was investigated in 46 tumors and on hearing function in 39 tumors. Long-term hearing follow-up behavior was compared with 20 non-operated ears in additional 15 patients. Sixteen operated VS were treated with bevacizumab. Mutation analysis of the NF2 gene was performed in 25 patients. Surgery significantly slowed down VS growth rate. Factors associated with a higher growth rate were increasing patient age, tumor volume, and constitutional truncating mutations. Immediately after surgery, functional hearing was maintained in 82% of ears. Deterioration of hearing was associated with initial hearing quality, larger tumor volumes, and larger resection amounts. Average hearing scores were initially better in the group of non-operated VS. Over time, hearing scores in both groups worsened with a similar dynamic. During bevacizumab treatment of residual tumors, four different patterns of growth were observed. Decompression of the internal auditory canal with various degrees of tumor resection decreases the postoperative tumor growth rates. Carefully tailored BAEP-guided surgery does not cause additional hearing deterioration. Secondary bevacizumab treatment showed heterogenous effects both regarding tumor size and hearing preservation. It seems that postoperative tumor residuals, that grow slower, behave differently to bevacizumab than reported for not-operated faster growing VS.

Surgical management of peripheral nerve sheath tumours in children, with special consideration of neurofibromatoses

INTRODUCTION

Peripheral nerve sheath tumours in children are a rare and heterogeneous group, consisting mostly of benign tumours as well as malignant neoplasms. Especially in the paediatric population, diagnostics and indication for therapy pose relevant challenges for neurosurgeons and paediatric neurologists alike. Most paediatric cases that need surgical intervention are associated to neurofibromatosis type 1 (NF1).

METHODS

We retrospectively reviewed all paediatric cases treated at the Department of Neurosurgery in Tübingen between 2006 and 2017 for peripheral nerve sheath tumours. We analysed clinical signs, symptoms, histology, association to an underlying phacomatosis and sensory/motor function.

RESULTS

Of the 82 identified patients, the majority had NF1 (76.8%). Nine children bore a sporadic tumour without underlying phacomatosis (11%), 8 had NF2 (9.8%) and 2 schwannomatosis (2.4%), A total of 168 surgical interventions were performed, and 206 tumours were removed. Indication for surgery was in most instances significant tumour growth (45.2%) followed by pain (33.9%). New deficits led to surgery in 12.5% of interventions; malignancy was suspected in 8.3%. Histopathology revealed mostly neurofibromas (82.5%), divided into cutaneous neurofibromas (10.7%), infiltrating plexiform neurofibromas (25.7%) and peripheral nerve-born neurofibromas (46.1%). 12.1% of tumours were schwannomas, 2.9% MPNST, 1.5% ganglioneuroma (n = 3) and 1 hybrid-neurofibroma and perineurinoma each. Leading symptoms, such as pain and motor and sensory deficits, improved after 125/166 interventions (74.4%), remained unchanged following 39 interventions (23.2%) and worsened in 4 occasions (2.4%).

CONCLUSION

Surgery is safe and effective for (neurofibromatosis associated) peripheral nerve sheath tumours in the paediatric population; however, management needs a multidisciplinary setting. We propose early surgical resection in paediatric patients with peripheral nerve sheath tumours with significant growth, or pain, or motor deficit, or suspected malignancy.

Minimal Effect of Bevacizumab Treatment on Residual Vestibular Schwannomas after Partial Resection in Young Neurofibromatosis Type 2 Patients

Hearing-preserving partial resection of neurofibromatosis type 2 (NF2) associated vestibular schwannomas (VS) is a preferred treatment strategy, particularly for children and adolescents. However, the residual tumors do grow and lead at some point to continued hearing deterioration. An adjuvant bevacizumab treatment may provide an option for slowing down this process. In this retrospective study, we reviewed tumor volume and hearing data of 16 operated VS in nine patients younger than 30 years over a period of 63 to 142 months. All these patients had one or more bevacizumab treatment periods and most of them had a non-treatment period after surgery. Four different patterns of growth were observed for the residual tumors: (1) growth in the non-treatment periods, which slowed down in the treatment periods; (2) growth slowed down in one but not in another on-period; (3) unaffected growth; (4) no or minimal growth regardless of the treatment. Neither radiological regression of tumor volume nor hearing improvement were observed in the treatment periods. Accelerated hearing deterioration was observed in several non-treatment periods, but also in some treatment periods. No straightforward correlation can be drawn between tumor growth and hearing scores. Tumor growth and worsening of hearing between two measurement points were slightly less in the treatment periods; however, the differences were not significant, because variations were large. In conclusion, our comprehensive follow-up on 16 VS in nine NF2 patients did show heterogenous effects of bevacizumab on small residual vestibular schwannomas after surgery both regarding tumor size and hearing preservation. Thus, smaller and slower growing tumor residuals seem to behave differently to bevacizumab than reported for not-operated faster growing VS.

Distinctive low epidermal nerve fiber density in schwannomatosis patients provides a major parameter for diagnosis and differential diagnosis

Schwannomatosis and neurofibromatosis type 2 (NF2) are two distinct neuro‐genetic tumor predisposition disorders, which, however, share some clinical and genetic features. While germline mutations in the NF2 gene are only found in NF2, a majority of schwannomatosis patients have germline mutations in the SMARCB1 or LZTR1 genes. The overlapping clinical phenotypes pose a serious challenge in differential diagnosis and in risk stratification of these two entities which is further complicated by frequent mosaicism in both disorders. Chronic neuropathic pain which is a typical consequence of small fiber neuropathy, is characteristic for schwannomatosis. By contrast, NF2 patients do not have chronic pain but may have moderate to severe sensory deficits and paresis which are not characteristic for schwannomatosis. In the present study, we determined intraepidermal nerve fiber density (IEND) in skin biopsies of 34 clinically ascertained schwannomatosis and 25 NF2 patients. In the NF2 group, 11/25 (44%) presented with IEND below the age‐ and gender‐matched bottom 5% normative reference IEND. In contrast, nearly all (33/34 = 97%) schwannomatosis patients showed IEND below or on the bottom 5% normative reference. The reduction of IEND in schwannomatosis patients was age‐independent. Paired t‐test revealed no difference between the NF2‐IEND and the corresponding bottom 5% normative reference (P = 0.98). By contrast, IEND in the schwannomatosis patients were highly significantly lower than the corresponding 5% normative reference IEND (P < 0.0001). In addition, the difference between the IEND of our patients and the 5% lowest normative reference IEND was highly significantly larger in schwannomatosis patients than in NF2 patients (P < 0.0001). IEND of our patients did not correlate with neither the presence nor types of germline mutations in neither the NF2 nor the LZTR1 gene. In conclusion, schwannomatosis patients have marked low IEND which provides a major parameter for diagnosis and differential diagnosis.

Management of NF2-associated vestibular schwannomas in children and young adults: influence of surgery and clinical factors on tumor volume and growth rate

OBJECTIVE

The authors' aim was to evaluate the tumor volume and growth rate of neurofibromatosis type 2 (NF2)-associated vestibular schwannomas (VSs) and the clinical factors or type of mutations before and after surgery in children and adults younger than 25 years at the time of diagnosis.

METHODS

A total of 579 volumetric measurements were performed in 46 operated tumors in 28 NF2 patients, using thin-slice (< 3 mm) T1-weighted contrast-enhanced MRI. The follow-up period ranged from 21 to 167 months (mean 75 months). Growth rate was calculated using a multilinear regression model. Mutation analysis of the NF2 gene was performed in 25 patients.

RESULTS

Surgery significantly (p = 0.013) slowed the VS growth rate from 0.69 ± 1.30 cm3/yr to 0.23 ± 0.42 cm3/yr. Factors significantly associated with a higher growth rate of VSs were increasing patient age (p < 0.0005), tumor volume (p = 0.006), tumor size (p = 0.001), and constitutional truncating mutations in the NF2 gene (p = 0.018). VS growth rates tended to be higher in patients with spinal ependymomas and in right-sided tumors and lower in the presence of peripheral schwannomas; however, no statistical significance was achieved.

CONCLUSIONS

Decompression of the internal auditory canal with various degrees of tumor resection decreases the postoperative tumor growth rate in children and young adults with NF2-associated VS. Patients with potential risk factors for accelerated growth (e.g., large volume, truncating mutations) and with increasing age should be monitored more closely before and after surgery.

Peripheral nervous system alterations in infant and adult neurofibromatosis type 2

OBJECTIVE

To examine the involvement of dorsal root ganglia and peripheral nerves in children with neurofibromatosis type 2 compared to healthy controls and symptomatic adults by in vivo high-resolution magnetic resonance neurography.

METHODS

In this prospective multicenter study, the lumbosacral dorsal root ganglia and sciatic, tibial, and peroneal nerves were examined in 9 polyneuropathy-negative children diagnosed with neurofibromatosis type 2 by a standardized magnetic resonance neurography protocol at 3T. Volumes of dorsal root ganglia L3 to S2 and peripheral nerve lesions were assessed and compared to those of 29 healthy children. Moreover, dorsal root ganglia volumes and peripheral nerve lesions were compared to those of 14 adults with neurofibromatosis type 2.

RESULTS

Compared to healthy controls, dorsal root ganglia hypertrophy was a consistent finding in children with neurofibromatosis type 2 (L3 +255%, L4 +289%, L5 +250%, S1 +257%, and S2 +218%, p < 0.001) with an excellent diagnostic accuracy. Moreover, peripheral nerve lesions occurred with a high frequency in those children compared to healthy controls (18.89 ± 11.11 vs 0.90 ± 1.08, p < 0.001). Children and adults with neurofibromatosis type 2 showed nonsignificant differences in relative dorsal root ganglia hypertrophy rates (p = 0.85) and peripheral nerve lesions (p = 0.28).

CONCLUSIONS

Alterations of peripheral nerve segments occur early in the course of neurofibromatosis type 2 and are evident even in children not clinically affected by peripheral polyneuropathy. While those early alterations show similar characteristics compared to adults with neurofibromatosis type 2, the findings of this study suggest that secondary processes might be responsible for the development and severity of associated polyneuropathy.

Manifestations and Treatment of Adult-onset Symptomatic Optic Pathway Glioma in Neurofibromatosis Type 1

This report describes the diagnosis and treatment of a 27-year-old patient with neurofibromatosis 1 (NF1) and late progression of a pre-existing optic pathway glioma (OPG) that caused significant reduction in vision. OPG is one of the diagnostic criteria for establishing the diagnosis of NF1. Most common findings of NF1 are café-au-lait spots, axillary and inguinal freckling of the skin, iris hamartoma (Lisch nodules), and tumors of the central nervous system and peripheral nerves. We successfully applied a modified International Society of Paediatric Oncology chemotherapy regimen for low-grade glioma in children with carboplatin dose adjustment according to the area under the plasma drug concentration-time curve calculation. During and after the chemotherapy, a clear improvement of the visual capacity was achieved. Age-adapted chemotherapy for symptomatic adult-onset OPG in patients with NF1 should be considered in individual cases.

Breast cancer risk in neurofibromatosis type 1 is a function of the type of NF1 gene mutation: a new genotype-phenotype correlation

Background

Neurofibromatosis type 1 (NF1) predisposes to breast cancer (BC), but no genotype-phenotype correlations have been described.

Methods

Constitutional NF1 mutations in 78 patients with NF1 with BC (NF1-BC) were compared with the NF1 Leiden Open Variation Database (n=3432).

Results

No cases were observed with whole or partial gene deletions (HR 0.10; 95% CI 0.006 to 1.63; p=0.014, Fisher’s exact test). There were no gross relationships with mutation position. Forty-five (64.3%; HR 6.4–83) of the 70 different mutations were more frequent than expected (p<0.05), while 52 (74.3%; HR 5.3–83) were significant when adjusted for multiple comparisons (adjusted p≤0.125; Benjamini-Hochberg). Higher proportions of both nonsense and missense mutations were also observed (adjusted p=0.254; Benjamini-Hochberg). Ten of the 11 missense cases with known age of BC occurred at <50 years (p=0.041). Eighteen cases had BRCA1/2 testing, revealing one BRCA2 mutation.

Discussion

These data strongly support the hypothesis that certain constitutional mutation types, and indeed certain specific variants in NF1 confer different risks of BC. The lack of large deletions and excess of nonsenses and missenses is consistent with gain of function mutations conferring risk of BC, and also that neurofibromin may function as a dimer. The observation that somatic NF1 amplification can occur independently of ERBB2 amplification in sporadic BC supports this concept. A prospective clinical-molecular study of NF1-BC needs to be established to confirm and build on these findings, but regardless of NF1 mutation status patients with NF1-BC warrant testing of other BC-predisposing genes.

Ultra-deep amplicon sequencing indicates absence of low-grade mosaicism with normal cells in patients with type-1 NF1 deletions

Different types of large NF1 deletion are distinguishable by breakpoint location and potentially also by the frequency of mosaicism with normal cells lacking the deletion. However, low-grade mosaicism with fewer than 10% normal cells has not yet been excluded for all NF1 deletion types since it is impossible to assess by the standard techniques used to identify such deletions, including MLPA and array analysis. Here, we used ultra-deep amplicon sequencing to investigate the presence of normal cells in the blood of 20 patients with type-1 NF1 deletions lacking mosaicism according to MLPA. The ultra-deep sequencing entailed the screening of 96 amplicons for heterozygous SNVs located within the NF1 deletion region. DNA samples from three previously identified patients with type-2 NF1 deletions and low-grade mosaicism with normal cells as determined by FISH or microsatellite marker analysis were used to validate our methodology. In these type-2 NF1 deletion samples, proportions of 5.3%, 6.6% and 15.0% normal cells, respectively, were detected by ultra-deep amplicon sequencing. However, using this highly sensitive method, none of the 20 patients with type-1 NF1 deletions included in our analysis exhibited low-grade mosaicism with normal cells in blood, thereby supporting the view that the vast majority of type-1 deletions are germline deletions.

Cerebrovascular Insult as Presenting Symptom of Neurofibromatosis Type 2 in Children, Adolescents, and Young Adults

Background and Purpose: Neurofibromatosis Type 2 (NF2) is an autosomal-dominant tumor-prone disorder characterized by the manifestations of central nervous system lesions. However, the first clinical signs of disease are often non-tumorous. Cerebrovascular insults are known in NF2, however, not yet described as first symptom in young NF2 patients. Methods: Magnetic resonance image scans of 298 NF2 patients treated in our neurofibromatosis center in Tübingen from 2003 to 2017 were retrospectively evaluated focusing on presence of aneurysms and ischemic stroke. Clinical data were used to clarify whether or not ischemic stroke or aneurysm rupture were the first presentation of disease. Blood of the patients were subjected to genetic screening for constitutional NF2 mutations. Results: We identified 5 cases under age of 25 years with aneurysms or ischemic stroke. Among them three had ischemic strokes of the brain stem and one aneurysmal subarachnoid hemorrhage as the first symptom of the disease. Incidental finding of 2 intracranial aneurysm occurred in one patient. All aneurysms were clipped. Patients with ischemia suffered from dysarthria, gait disturbances, dizziness, and hemiparesis. Residual signs of hemiparesis and dysarthria persisted in one patient. All others fully recovered from the cerebrovascular insult. Bilateral vestibular schwannomas and intracranial meningiomas were found in all five patients. Conclusions: A cerebrovascular insult in the vertebrobasilar territory may occur as first symptom of disease in young NF2 patients. The brain stem seems to be especially prone to ischemic stroke. Multicenter studies on large NF2 cohorts are needed to determine the prevalence and pattern of cerebrovascular insults and disease in NF2 patients.

Serial MRIs provide novel insight into natural history of optic pathway gliomas in patients with neurofibromatosis 1

BACKGROUND

Optic pathway gliomas (OPGs) are present in 20% of children with neurofibromatosis 1 (NF1) but are less frequently observed in adults. Our goal was to determine the natural history of OPGs in children and adults with NF1.

RESULTS

We analyzed the features of OPGs and other intracranial lesions on 1775 head MRI scans of 562 unselected adults and children with NF1 collected between 2003 and 2015. 52 (9.3%) of 562 patients in this study had an OPG diagnosed on their MRI. The median age at first scan with an OPG present was 12.7 years. Of the 52 OPG patients, the intraorbital optic nerves were affected in 29 patients (56%), the prechiasmatic optic nerves were affected in 32 patients (62%), the optic chiasm was affected in 17 patients (33%) and the optic radiations were affected in 19 patients (37%). 29 patients had two or more areas affected. One patient had a newly-appearing OPG, and 1 patient showed progression. The rate of progression over 5 years was 2.4% (95% CI: 0.4% to 16%). Four patients showed partial regression of their OPGs, but we observed no case of complete regression during this study. The rate of regression over 5 years was 8.9% (95% confidence intervals: 2.8% to 26%). We found the presence of UBOs and the presence of OPGs in individual patients to be highly associated (p = 0.0061).

CONCLUSION

OPGs are more common in older adults with NF1 than previously thought. The occurrences of unidentified bright objects (UBOs) and asymptomatic OPGs are associated with each other. This suggests the possibility that OPGs that remain asymptomatic may differ pathogenically from those that become symptomatic.

Dorsal root ganglia volume differentiates schwannomatosis and neurofibromatosis 2

Schwannomatosis and neurofibromatosis type 2 are hereditary tumor syndromes, and peripheral neuropathy has been reported in both. We prospectively applied in vivo morphometric measurement of dorsal root ganglia volume in 16 schwannomatosis patients, 14 neurofibromatosis type 2 patients, and 26 healthy controls by magnetic resonance neurography. Compared to healthy controls, dorsal root ganglia hypertrophy was a consistent finding in neurofibromatosis type 2 (L3, + 267%; L4, + 235%; L5, + 241%; S1, + 300%; S2, + 242%; Bonferroni-adjusted p < 0.001) but not in schwannomatosis. Dorsal root ganglia may be a vulnerable site in origination of areflexia and sensory loss and a useful diagnostic marker in neurofibromatosis type 2. Ann Neurol 2018;83:854-857.

Motor dysfunction in NF1: Mediated by attention deficit or inherent to the disorder?

AIM

Attention deficit and compromised motor skills are both prevalent in Neurofibromatosis type 1 (NF1), but the relationship is unclear. We investigated motor function in children with NF1 and in children with Attention Deficit/Hyperactivity Disorder (ADHD), and explored if, in patients with NF1, attention deficit influences motor performance.

METHODS

Motor performance was measured using the Movement Assessment Battery for Children (M-ABC) in 71 children (26 with NF1 plus ADHD, 14 with NF1 without ADHD, and 31 with ADHD without NF1) aged 6-12 years.

RESULTS

There was a significant effect of group on motor performance. Both NF1 groups scored below children with ADHD without NF1. Attention performance mediated motor performance in children with ADHD without NF1, but not in children with NF1.

CONCLUSIONS

Motor function is not mediated by attention performance in children with NF1. While in ADHD, attention deficit influences motor performance, motor problems in NF1 seem to be independent from attention deficit. This argues for different pathomechanisms in these two groups of developmental disorders.

Consideration of the haplotype diversity at nonallelic homologous recombination hotspots improves the precision of rearrangement breakpoint identification

Precise characterization of nonallelic homologous recombination (NAHR) breakpoints is key to identifying those features that influence NAHR frequency. Until now, analysis of NAHR-mediated rearrangements has generally been performed by comparison of the breakpoint-spanning sequences with the human genome reference sequence. We show here that the haplotype diversity of NAHR hotspots may interfere with breakpoint-mapping. We studied the transmitting parents of individuals with germline type-1 NF1 deletions mediated by NAHR within the paralogous recombination site 1 (PRS1) or paralogous recombination site 2 (PRS2) hotspots. Several parental wild-type PRS1 and PRS2 haplotypes were identified that exhibited considerable sequence differences with respect to the reference sequence, which also affected the number of predicted PRDM9-binding sites. Sequence comparisons between the parental wild-type PRS1 or PRS2 haplotypes and the deletion breakpoint-spanning sequences from the patients (method #2) turned out to be an accurate means to assign NF1 deletion breakpoints and proved superior to crude reference sequence comparisons that neglect to consider haplotype diversity (method #1). The mean length of the deletion breakpoint regions assigned by method #2 was 269-bp in contrast to 502-bp by method #1. Our findings imply that paralog-specific haplotype diversity of NAHR hotspots (such as PRS2) and population-specific haplotype diversity must be taken into account in order to accurately ascertain NAHR-mediated rearrangement breakpoints.

Human dorsal root ganglion in vivo morphometry and perfusion in Fabry painful neuropathy

Objective:

To evaluate functional and morphometric magnetic resonance neurography of the dorsal root ganglion and peripheral nerve segments in patients with Fabry painful neuropathy.

Methods:

In this prospective study, the lumbosacral dorsal root ganglia and proximal peripheral nerve segments of the lower extremity were examined in 11 male patients with Fabry disease by a standardized 3T magnetic resonance neurography protocol. Volumes of L3 to S2 dorsal root ganglia, perfusion parameters of L5-S1 dorsal root ganglia and the spinal nerve L5, and the cross-sectional area of the proximal sciatic nerve were compared to healthy controls.

Results:

Dorsal root ganglia of patients with Fabry disease were symmetrically enlarged by 78% (L3), 94% (L4), 122% (L5), 115% (S1), and 119% (S2) (p < 0.001). In addition, permeability of the blood-tissue interface was decreased by 53% (p < 0.001). This finding was most pronounced in the peripheral zone of the dorsal root ganglion containing the cell bodies of the primary sensory neurons (p < 0.001). Spinal nerve permeability showed no difference between patients with Fabry disease and controls (p = 0.7). The sciatic nerve of patients with Fabry disease at the thigh level showed an increase in cross-sectional area by 48% (p < 0.001).

Conclusions:

Patients with Fabry disease have severely enlarged dorsal root ganglia with dysfunctional perfusion. This may be due to glycolipid accumulation in the dorsal root ganglia mediating direct neurotoxic effects and decreased neuronal blood supply. These alterations were less pronounced in peripheral nerve segments. Thus, the dorsal root ganglion might play a key pathophysiologic role in the development of neuropathy and pain in Fabry disease.

Non-optic glioma in adults and children with neurofibromatosis 1

BACKGROUND

Non-optic gliomas occur in 5% of children with NF1, but little is known about these tumours in adults. We aimed to investigate progression, spontaneous regression and the natural history of non-optic gliomas in adults and compare these findings to the results found in children.

RESULTS

One thousand seven hundred twenty-two brain MRI scans of 562 unselected individuals with NF1 were collected at the NF outpatient department of the University Hospital Hamburg-Eppendorf between 2003 and 2015. The number of scans per patient ranged from one to 12; patients were followed for a median of 3.7 years. We identified 24 patients (4.3%) with non-optic gliomas. Median age at first scan with glioma was 21.2 years, much higher than in previous publications. Only seven of the 24 non-optic glioma patients were symptomatic. Five of 24 patients had multiple non-optic gliomas. Four individuals developed a new tumour, and 4 cases showed progression. The risk of new tumour development was 0.19% (95% confidence interval 0.06% to 0.52%) per patient year of follow-up for patients over 10 years. The rate of progressing non-optic gliomas per patient year of follow-up in the first 5 years after tumour diagnosis was 4.7% (95% confidence interval 1.5% to 12%).

CONCLUSIONS

Non-optic gliomas are twice as common in an unselected cohort of NF1 patients as previously reported. This is likely due to increased frequency of diagnosis of asymptomatic tumours when routine MRIs are performed and a higher prevalence in older individuals.

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.

The importance of nerve microenvironment for schwannoma development

Schwannomas are predominantly benign nerve sheath neoplasms caused by Nf2 gene inactivation. Presently, treatment options are mainly limited to surgical tumor resection due to the lack of effective pharmacological drugs. Although the mechanistic understanding of Nf2 gene function has advanced, it has so far been primarily restricted to Schwann cell-intrinsic events. Extracellular cues determining Schwann cell behavior with regard to schwannoma development remain unknown. Here we show pro-tumourigenic microenvironmental effects on Schwann cells where an altered axonal microenvironment in cooperation with injury signals contribute to a persistent regenerative Schwann cell response promoting schwannoma development. Specifically in genetically engineered mice following crush injuries on sciatic nerves, we found macroscopic nerve swellings in mice with homozygous nf2 gene deletion in Schwann cells and in animals with heterozygous nf2 knockout in both Schwann cells and axons. However, patient-mimicking schwannomas could only be provoked in animals with combined heterozygous nf2 knockout in Schwann cells and axons. We identified a severe re-myelination defect and sustained macrophage presence in the tumor tissue as major abnormalities. Strikingly, treatment of tumor-developing mice after nerve crush injury with medium-dose aspirin significantly decreased schwannoma progression in this disease model. Our results suggest a multifactorial concept for schwannoma formation—emphasizing axonal factors and mechanical nerve irritation as predilection site for schwannoma development. Furthermore, we provide evidence supporting the potential efficacy of anti-inflammatory drugs in the treatment of schwannomas.

Methylation-based classification of benign and malignant peripheral nerve sheath tumors

The vast majority of peripheral nerve sheath tumors derive from the Schwann cell lineage and comprise diverse histological entities ranging from benign schwannomas and neurofibromas to high-grade malignant peripheral nerve sheath tumors (MPNST), each with several variants. There is increasing evidence for methylation profiling being able to delineate biologically relevant tumor groups even within the same cellular lineage. Therefore, we used DNA methylation arrays for methylome- and chromosomal profile-based characterization of 171 peripheral nerve sheath tumors. We analyzed 28 conventional high-grade MPNST, three malignant Triton tumors, six low-grade MPNST, four epithelioid MPNST, 33 neurofibromas (15 dermal, 8 intraneural, 10 plexiform), six atypical neurofibromas, 43 schwannomas (including 5 NF2 and 5 schwannomatosis associated cases), 11 cellular schwannomas, 10 melanotic schwannomas, 7 neurofibroma/schwannoma hybrid tumors, 10 nerve sheath myxomas and 10 ganglioneuromas. Schwannomas formed different epigenomic subgroups including a vestibular schwannoma subgroup. Cellular schwannomas were not distinct from conventional schwannomas. Nerve sheath myxomas and neurofibroma/schwannoma hybrid tumors were most similar to schwannomas. Dermal, intraneural and plexiform neurofibromas as well as ganglioneuromas all showed distinct methylation profiles. Atypical neurofibromas and low-grade MPNST were indistinguishable with a common methylation profile and frequent losses of CDKN2A. Epigenomic analysis finds two groups of conventional high-grade MPNST sharing a frequent loss of neurofibromin. The larger of the two groups shows an additional loss of trimethylation of histone H3 at lysine 27 (H3K27me3). The smaller one retains H3K27me3 and is found in spinal locations. Sporadic MPNST with retained neurofibromin expression did not form an epigenetic group and most cases could be reclassified as cellular schwannomas or soft tissue sarcomas. Widespread immunohistochemical loss of H3K27me3 was exclusively seen in MPNST of the main methylation cluster, which defines it as an additional useful marker for the differentiation of cellular schwannoma and MPNST.

Unilateral gynaecomastia in a 16-month-old boy with neurofibromatosis type 1 - case report and brief review of the literature

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease that shows high penetrance with a wide variability in the phenotype. Prepubertal enlargement of the breast in male subjects affected by this condition is well known, but rarely reported. The present case report describes diagnosis and therapy of unilateral gynaecomastia in a toddler showing integumental stigmata of NF1. Furthermore, the report provides a brief review of the literature concerning this finding in NF1. According to this review, the present case appears to be one of the youngest NF1-affected males affected by gynaecomastia that has been reported.

Ipsilateral Sphenoid Wing Dysplasia, Orbital Plexiform Neurofibroma and Fronto-Parietal Dermal Cylindroma in a Patient with Segmental Neurofibromatosis

Neurofibromatosis type 1 (NF1) is an autosomal-dominant inherited disease affecting various parts of the body. Penetrance is almost complete but the phenotype varies considerably. Recently, mosaicism in NF1 has come into the focus of scientific interest. This report refers to a patient with orbitotemporal-confined neurofibromatosis who developed a rare skin tumor in the region.

Fine mapping of meiotic NAHR-associated crossovers causing large NF1 deletions

Large deletions encompassing the NF1 gene and its flanking regions belong to the group of genomic disorders caused by copy number changes that are mediated by the local genomic architecture. Although nonallelic homologous recombination (NAHR) is known to be a major mutational mechanism underlying such genomic copy number changes, the sequence determinants of NAHR location and frequency are still poorly understood since few high-resolution mapping studies of NAHR hotspots have been performed to date. Here, we have characterized two NAHR hotspots, PRS1 and PRS2, separated by 20 kb and located within the low-copy repeats NF1-REPa and NF1-REPc, which flank the human NF1 gene region. High-resolution mapping of the crossover sites identified in 78 type 1 NF1 deletions mediated by NAHR indicated that PRS2 is a much stronger NAHR hotspot than PRS1 since 80% of these deletions exhibited crossovers within PRS2, whereas 20% had crossovers within PRS1. The identification of the most common strand exchange regions of these 78 deletions served to demarcate the cores of the PRS1 and PRS2 hotspots encompassing 1026 and 1976 bp, respectively. Several sequence features were identified that may influence hotspot intensity and direct the positional preference of NAHR to the hotspot cores. These features include regions of perfect sequence identity encompassing 700 bp at the hotspot core, the presence of PRDM9 binding sites perfectly matching the consensus motif for the most common PRDM9 variant, specific pre-existing patterns of histone modification and open chromatin conformations that are likely to facilitate PRDM9 binding.