Neurofibromatosis type 2 French cohort analysis using a comprehensive NF2 molecular diagnostic strategy

Surgical Management of Peripheral Nerve Pathology in Patients With Neurofibromatosis Type 2

BACKGROUND

Neurofibromatosis type 2 (NF2) is rare genetic disorder mainly characterized by the development of central nervous system lesions, but peripheral nerve pathology may also cause high morbidity including pain, motor, and sensory loss.

OBJECTIVE

To describe the tumor burden of patients with peripheral nerve pathology in NF2 including peripheral neuropathies and schwannomas and the results of surgery in the latter group.

METHODS

We conducted a retrospective chart review of all patients with NF2 followed up at our NF2 Reference Center to include all patients suffering from peripheral nerve pathology. Tumor detection relied on focal MRIs based on symptoms.

RESULTS

Thirty-four patients harboring 105 peripheral nerve schwannomas and 1 perineurioma were included. Schwannomas were mainly located in major nerves (n = 74, 71%) compared with subcutaneous (n = 23, 22%) and intramuscular (n = 8, 7%) cases. Most schwannomas (81/90-90%) were classical discrete tumors while multinodular cases represented only 9 cases (10%). During follow-up, 63 (60%) tumors were operated in 24 patients, including 39 schwannomas of major nerves. A complete resection was achieved in most of the cases (52/63, 83%) with a complete relief of preoperative pain in most patients (57/60, 95%). Persistent motor deficits (5/39, 13%) were mostly encountered in patients operated from multinodular schwannomas (4/5, 80%). Six patients had an associated peripheral neuropathy with 5 cases of pseudo-Charcot-Marie-Tooth-associated amyotrophy.

CONCLUSION

Surgery remains a safe and effective method of treating peripheral nerve schwannoma-associated pain in NF2, with the exception of rare multinodular tumors. Special attention should be drawn to patients harboring severely debilitating neuropathies and perineuriomas.

Reviewing the occurrence of large genomic rearrangements in patients with inherited cancer predisposing syndromes: importance of a comprehensive molecular diagnosis

INTRODUCTION

Hereditary cancer predisposition syndromes are caused by germline pathogenic or likely pathogenic variants in cancer predisposition genes (CPG). The majority of pathogenic variants in CPGs are point mutations, but large gene rearrangements (LGRs) are present in several CPGs. LGRs can be much more difficult to characterize and perhaps they may have been neglected in molecular diagnoses.

AREAS COVERED

We aimed to evaluate the frequencies of germline LGRs in studies conducted in different populations worldwide through a qualitative systematic review based on an online literature research in PubMed. Two reviewers independently extracted data from published studies between 2009 and 2020. In total, 126 studies from 37 countries and 5 continents were included in the analysis. The number of studies in different continents ranged from 3 to 48 and for several countries there was an absolute lack of information. Asia and Europe represented most of the studies, and LGR frequencies varied from 3.04 to 15.06% in different continents. MLPA was one of the methods of choice in most studies (93%).

EXPERT OPINION

The LGR frequencies found in this review reinforce the need for comprehensive molecular testing regardless of the population of origin and should be considered by genetic counseling providers.

Genomics, Epigenetics, and Hearing Loss in Neurofibromatosis Type 2

OBJECTIVES

In this review, we discuss current knowledge about the genetics and epigenetics of vestibular schwannoma (VS) in relation to hearing loss. A multistep and sequential genetic algorithm suitable for the identification of Neurofibromatosis Type 2 (NF2) constitutional and somatic mutations is discussed.

DATA SOURCES, STUDY SELECTION

A review was performed of the English literature from 1990 to 2019 using PubMed regarding genetics and epigenetics of vestibular schwannoma and NF2.

CONCLUSION

NF2 is a genetic disorder characterized by NF2 mutations that affect the function of a tumor suppressor called merlin. In particular, individuals with NF2 develop bilateral VS that can lead to hearing loss and even deafness. Recent advances in genetic and epigenetic studies have improved our understanding of the genotype-phenotype relationships that affect hearing in NF2 patients. Specific constitutional NF2 mutations including particular truncating, deletion, and missense mutations have been associated with poorer hearing outcomes and more severe clinical manifestations. Epigenetic events, such as DNA methylation and histone modifications, also contribute to the development and progression of hearing loss in NF2 patients. Furthermore, the accumulation of multiple NF2 and non-NF2 genetic and epigenetic abnormalities at the level of the tumor may contribute to worse hearing outcomes. Understanding genetic and epigenetic signatures in individual NF2 patients and particularly in each VS will allow us to develop novel gene therapies and precision medicine algorithms to preserve hearing in NF2 individuals.

[Synchronous schwannoma and ependymoma of the cauda equina]

The article presents a case of surgical treatment of primary multiple benign tumors of the cauda equine of different histological origin: spinal nerve root schwannoma and ependymoma of the filum terminale.

Targeted next-generation sequencing for differential diagnosis of neurofibromatosis type 2, schwannomatosis, and meningiomatosis

Background

Clinical overlap between neurofibromatosis type 2 (NF2), schwannomatosis, and meningiomatosis can make clinical diagnosis difficult. Hence, molecular investigation of germline and tumor tissues may improve the diagnosis.

Methods

We present the targeted next-generation sequencing (NGS) of NF2, SMARCB1, LZTR1, SMARCE1, and SUFU tumor suppressor genes, using an amplicon-based approach. We analyzed blood DNA from a cohort of 196 patients, including patients with NF2 (N = 79), schwannomatosis (N = 40), meningiomatosis (N = 12), and no clearly established diagnosis (N = 65). Matched tumor DNA was analyzed when available. Forty-seven NF2-/SMARCB1-negative schwannomatosis patients and 27 NF2-negative meningiomatosis patients were also evaluated.

Results

A NF2 variant was found in 41/79 (52%) NF2 patients. SMARCB1 or LZTR1 variants were identified in 5/40 (12.5%) and 13/40 (∼32%) patients in the schwannomatosis cohort. Potentially pathogenic variants were found in 12/65 (18.5%) patients with no clearly established diagnosis. A LZTR1 variant was identified in 16/47 (34%) NF2/SMARCB1-negative schwannomatosis patients. A SMARCE1 variant was found in 3/39 (∼8%) meningiomatosis patients. No SUFU variant was found in the cohort. NGS was an effective and sensitive method to detect mutant alleles in blood or tumor DNA of mosaic NF2 patients. Interestingly, we identified a 4-hit mechanism resulting in the complete NF2 loss-of-function combined with SMARCB1 and LZTR1 haploinsufficiency in two-thirds of tumors from NF2 patients.

Conclusions

Simultaneous investigation of NF2, SMARCB1, LZTR1, and SMARCE1 is a key element in the differential diagnosis of NF2, schwannomatosis, and meningiomatosis. The targeted NGS strategy is suitable for the identification of NF2 mosaicism in blood and for the investigation of tumors from these patients.

Coexistence of schwannomatosis and glioblastoma in two families

Schwannomatosis is a rare affection predisposing to multiple peripheral neurologic tumors development. Approximatively, one third of patients with schwannomatosis are carriers of a germline mutation in LZTR1 (Leucin Zipper Transcription Regulator 1). Tumorigenesis in schwannomatosis responds to a somatic 5-hit/3-step mechanism resulting in a loss of function (LOF) of LZTR1 and the contiguous genes of locus 22q11.2q12.2. Effectively, LZTR1 is mapped on 22q11.2 and centromeric to SMARCB1 also implicated in the determinism of schwannomatosis and NF2, responsible for neurofibromatosis type 2. On a somatic point of view, LZTR1 mutations are known to drive with a significant frequency glioblastoma (GB) development. We report here two families in which segregate both multiple schwannomas and GB. In the first family, the proband received a diagnosis with of schwannomatosis after a surgery for a lumbar schwannoma at age 43, molecularly confirmed by identification of a germline heterozygous mutation in LZTR1. Her father, having unremarkable medical history deceased from an apparently isolated GB at age 59. In the second family, LZTR1-related schwannomatosis was diagnosed in the index case at age 70 after multiple schwannomas surgeries. Her elder sister had no neurological medical history before occurrence of a lethal GB at age 78. Molecular analysis of GB sample from both affected relatives showed the presence of the familial mutation. These observations hypothesize a potential link between schwannomatosis and the GB development.