Segmental neurofibromatosis type 2: discriminating two hit from four hit in a patient presenting multiple schwannomas confined to one limb

Targeted massively parallel sequencing of candidate regions on chromosome 22q predisposing to multiple schwannomas: An analysis of 51 individuals in a single-center experience

Constitutional LZTR1 or SMARCB1 pathogenic variants (PVs) have been found in ∼86% of familial and ∼40% of sporadic schwannomatosis cases. Hence, we performed massively parallel sequencing of the entire LZTR1, SMARCB1, and NF2 genomic loci in 35 individuals with schwannomas negative for constitutional first-hit PVs in the LZTR1/SMARCB1/NF2 coding sequences; however, with 22q deletion and/or a different NF2 PV in each tumor, including six cases with only one tumor available. Furthermore, we verified whether any other LZTR1/SMARCB1/NF2 (likely) PVs could be found in 16 cases carrying a SMARCB1 constitutional variant in the 3'-untranslated region (3'-UTR) c.*17C>T, c.*70C>T, or c.*82C>T. As no additional variants were found, functional studies were performed to clarify the effect of these 3'-UTR variants on the transcript. The 3'-UTR variants c.*17C>T and c.*82C>T showed pathogenicity by negatively affecting the SMARCB1 transcript level. Two novel deep intronic SMARCB1 variants, c.500+883T>G and c.500+887G>A, resulting in out-of-frame missplicing of intron 4, were identified in two unrelated individuals. Further resequencing of the entire repeat-masked genomics sequences of chromosome 22q in individuals negative for PVs in the SMARCB1/LZTR1/NF2 coding- and noncoding regions revealed five potential schwannomatosis-predisposing candidate genes, that is, MYO18B, NEFH, SGSM1, SGSM3, and SBF1, pending further verification.

Bilateral Vestibular Schwannomas in a Patient with Ring Chromosome 22: Case Report and Review of the Literature

INTRODUCTION

Ring chromosome 22 (r[22]) can lead to the development of intracranial tumors such as meningiomas, neurofibromas, and schwannomas similar to neurofibromatosis 2 (NF2).

CASE PRESENTATION

An 18-year-old female with r(22) and a history of global development delay and cognitive impairment presented with sudden hearing loss. MRI revealed bilateral vestibular schwannomas. Given documented audiologic decline in the patient's hearing, the larger tumor was treated with CyberKnife fractionated stereotactic radiosurgery, and the smaller tumor is being monitored.

CONCLUSION

This case provides further evidence that patients with r(22) can develop clinical features of NF2, including the development of bilateral vestibular schwannomas, and should be monitored for hearing disturbances starting in puberty as a warning sign for these tumors.

The Clinical Spectrum of Mosaic Neurofibromatosis in Children and Adolescents

BACKGROUND

Segmental neurofibromatosis was initially described by Miller and Sparks (1977) as manifestations of neurofibromatosis limited to a dermatomal, localized distribution. Now termed mosaic neurofibromatosis, previous literature described this disease in children and adolescents with individual case reports and small-numbered case series. This study presents a large series of children and adolescents with mosaic neurofibromatosis.

METHODS

A retrospective chart review of a single institution medical record database was performed on all cases of mosaic neurofibromatosis diagnosed between the years 1998 and 2017. Eligible subjects were determined by 2 criteria: (1) segmental or unilateral expression of one of more signs of NF I according to those outlined in the NIH criteria and (2) were under 18 years of age at the time of diagnosis. Select information extracted include location of clinical features, NF manifestations (neurofibromas, plexiform neurofibromas, café-au-lait spots, freckling, Lisch nodules), presence of a diffuse area of cutaneous hyperpigmentation, and other significant medical conditions.

RESULTS

Sixty-eight cases met established criteria. Average age at diagnosis was 8.28 ± 4.47 years. Thirty-seven (54%) were male and 31 (46%) were female. Localization of the dermatologic manifestations is as follows: left side in 28 (41%) cases, right side in 32 (47%) cases, and bilateral in 8 (11%) cases. Café-au-lait lesions appeared in 64 (94%) of cases and 14 (21%) had axillary and inguinal freckling.

CONCLUSIONS

This study expands our understanding of the disease characteristics seen in children and adolescents with mosaic neurofibromatosis and confirms the need to focus on pigmentary changes in children with mosaic neurofibromatosis.

Early Genetic Diagnosis of Neurofibromatosis Type 2 From Skin Plaque Plexiform Schwannomas in Childhood

Importance

Neurofibromatosis type 2 (NF2) is a devastating genetic condition characterized by the development of multiple tumors of the nervous system. An early diagnosis of individuals with NF2 would facilitate treatment and reduction of disease impact because most severe effects of the disease do not usually develop before adolescence. Little attention has traditionally been paid to dermatological signs in NF2. However, skin plaques are commonly seen in patients with NF2, normally appearing either at birth or early childhood, providing an opportunity for early NF2 detection and testing.

Objective

To determine the clinical utility of skin plaque identification and characterization in children for reaching an early diagnosis of patients with NF2 and to evaluate their molecular pathogenesis and their use in the genetic diagnostics of NF2.

Design, Setting, and Participants

Diagnostic test study by the histological and genetic characterization of skin plaques from patients with NF2. Patients were 7 individuals with NF2 or clinical suspicion of NF2 treated at the Spanish Reference Center on Phakomatoses.

Main Outcomes and Measures

Histological evaluation of all skin plaques was performed. Fresh skin plaques were cultured to obtain Schwann cells and the NF2 gene was genetically analyzed. For all 7 patients, NF2 clinical history was reviewed.

Results

In all 7 patients (4 male and 3 female), all skin plaques analyzed were histologically characterized as plexiform schwannomas. Genetic analysis of primary Schwann cell cultures derived from them allowed the identification of a constitutional and a somatic NF2 mutation. Genetic testing allowed the early diagnosis of NF2 in a child only exhibiting the presence of skin plaques. Most of the patients with NF2 analyzed had an early presentation of skin plaques and a severe NF2 phenotype.

Conclusions and Relevance

This work emphasizes the clinical utility of a careful dermatological inspection and the correct identification of skin plaques in children for an early diagnosis of NF2. We show for the first time that Schwann cells derived from skin plaque plexiform schwannomas bear the double inactivation of the NF2 gene and thus constitute an excellent source of tissue for genetic testing, especially in the context of mosaicism.

Long-term therapy with bevacizumab in a young patient affected by NF-2: a case report and review of the literature

Neurofibromatosis type 2 (NF-2) is an autosomal dominant inherited disease caused by heterozygous mutations in the NF-2 tumor suppressor gene. It is characterized by the development of multiple benign tumors in the central nervous system. A majority of these tumors can be treated with surgery or radiotherapy in the case of the symptomatic disease. Cytotoxic chemotherapy has no established role in the treatment of NF-2. Vascular endothelial growth factor (VEGF) is a critical mediator of tumor angiogenesis and vessel permeability. VEGF and its receptor VEGFR-1 have been detected in schwannomas, and increased levels of these factors correlate with increased rates of tumor growth. The use of bevacizumab has made many progresses in recent years in NF-2 patients. We report a case of a young patient treated with more than 100 administration of bevacizumab, with clinical and instrumental benefits.

Genetic Evaluation of Common Neurocutaneous Syndromes

The neurocutaneous syndromes are a group of multisystem disorders that affect the skin and central nervous system. Neurofibromatosis 1, neurofibromatosis 2, tuberous sclerosis complex, and Sturge-Weber syndrome are the four major neurocutaneous disorders that mainly present in childhood. In this review, we discuss the clinical findings and genetic diagnosis, related genes/pathways and genotype-phenotype correlations of these four neurocutaneous syndromes.

Mosaicism in Cutaneous Disorders

Genetic mosaicism arises when a zygote harbors two or more distinct genotypes, typically due to de novo, somatic mutation during embryogenesis. The clinical manifestations largely depend on the differentiation status of the mutated cell; earlier mutations target pluripotent cells and generate more widespread disease affecting multiple organ systems. If gonadal tissue is spared-as in somatic genomic mosaicism-the mutation and its effects are limited to the proband, whereas mosaicism also affecting the gametes, such as germline or gonosomal mosaicism, is transmissible. Mosaicism is easily appreciated in cutaneous disorders, as phenotypically distinct mutant cells often give rise to lesions in patterns determined by the affected cell type. Genetic investigation of cutaneous mosaic disorders has identified pathways central to disease pathogenesis, revealing novel therapeutic targets. In this review, we discuss examples of cutaneous mosaicism, approaches to gene discovery in these disorders, and insights into molecular pathobiology that have potential for clinical translation.

Childhood neurofibromatosis type 2 (NF2) and related disorders: from bench to bedside and biologically targeted therapies

Neurofibromatosis type 2 [NF2; MIM # 101000] is an autosomal dominant disorder characterised by the occurrence of vestibular schwannomas (VSs), schwannomas of other cranial, spinal and cutaneous nerves, cranial and spinal meningiomas and/or other central nervous system (CNS) tumours (e.g., ependymomas, astrocytomas). Additional features include early onset cataracts, optic nerve sheath meningiomas, retinal hamartomas, dermal schwannomas (i.e., NF2-plaques), and (few) café-au-lait spots. Clinically, NF2 children fall into two main groups: (1) congenital NF2 - with bilateral VSs detected as early as the first days to months of life, which can be stable/asymptomatic for one-two decades and suddenly progress; and (2) severe pre-pubertal (Wishart type) NF2- with multiple (and rapidly progressive) CNS tumours other-than-VS, which usually present first, years before VSs [vs. the classical adult (Gardner type) NF2, with bilateral VSs presenting in young adulthood, sometimes as the only disease feature]. Some individuals can develop unilateral VS associated with ipsilateral meningiomas or multiple schwannomas localised to one part of the peripheral nervous system [i.e., mosaic NF2] or multiple non-VS, non-intradermal cranial, spinal and peripheral schwannomas (histologically proven) [schwannomatosis]. NF2 is caused by mutations in the NF2 gene at chromosome 22q12.1, which encodes for a protein called merlin or schwannomin, most similar to the exrin-readixin-moesin (ERM) proteins; mosaicNF2 is due to mosaic phenomena for the NF2 gene, whilst schwannomatosis is caused by coupled germ-line and mosaic mutations either in the SMARCB1 gene [SWNTS1; MIM # 162091] or the LZTR1 gene [SWNTS2; MIM # 615670] both falling within the 22q region and the NF2 gene. Data driven from in vitro and animal studies on the merlin pathway [e.g., post-translational and upstream/downstream regulation] allowed biologically targeted treatment strategies [e.g., Lapatinib, Erlotinib, Bevacizumab] aimed to multiple tumour shrinkage and/or regression and tumour arrest of progression with functional improvement.

A mosaic pattern of INI1/SMARCB1 protein expression distinguishes Schwannomatosis and NF2-associated peripheral schwannomas from solitary peripheral schwannomas and NF2-associated vestibular schwannomas

BACKGROUND

The INI1/SMARCB1 gene protein product has been implicated in the direct pathogenesis of schwannomas from patients with one form of schwannomatosis [SWNTS1; MIM # 162091] showing a mosaic pattern of loss of protein expression by immunohistochemistry [93% in familial vs. 55% in sporadic cases].

AIM OF STUDY

To verify whether such INI1/SMARCB1 mosaic pattern could be extended to all schwannomas arising in the sporadic and familial schwannomatoses [i.e. to SMARCB1-related (SWNTS1) or LZTR1-related (SWNTS2) schwannomatosis or to SMARCB1/LZTR1-negative schwannomatosis] and whether it could be involved in classical NF2 or solitary peripheral schwannomas METHODS: We blindly analysed schwannoma samples obtained from a total of 22 patients including (a) 2 patients (2 males; aged 38 and 55 years) affected by non-familial SMARCB1-associated schwannomatosis (SWTNS1); (b) 1 patient (1 female; aged 33 years) affected by familial schwannomatosis (SWTNS1/ SMARCB1 germ line mutations); (c) 5 patients (3 males, 2 females; aged 33 to 35 years) affected by non-familial (sporadic) LZTR1-associated schwannomatosis (SWNTS2); (d) 3 patients (3 males; aged 35 to 47 years) affected by familial schwannomatosis (SWTNS2/ LZTR1 germ line mutations); (e) 2 patients (1 male, 1 female; aged 63 and 49 years, respectively) affected by non-familial schwannomatosis (SWTNS, negative for SMARCB1, LZTR1 and NF2 gene mutations); (f) 4 patients (3 males, 1 females; aged 15 to 24 years) affected by classical NF2 (NF2: harbouring NF2 germ line mutations; and (g) 5 patients (3 males, 2 females; aged 33 to 68 years) who had solitary schwannomas. [follow-up = 15-30 years; negative for constitutional/somatic mutation analysis for the SMARCB1, LZTR1 and NF2 genes] were (blindly) analyzed. The INI1/SMARCB1 immunostaining pattern was regarded as (1) diffuse positive nuclear staining [= retained expression] or (2) mosaic pattern [mixed positive/negative nuclei = loss of expression in a subset of tumour cells].

RESULTS

All solitary peripheral schwannomas and NF2-associated vestibular schwannomas showed diffuse nuclear INI1/SMARCB1 staining in 97-100% of neoplastic cells; schwannomas obtained from all cases of non-familial and familial schwannomatosis and NF2-associated non-vestibular schwannomas showed a mosaic pattern ranging from 10 to 70% of INI1/SMARCB1-positive expression. We did not record a complete lack of nuclear staining.

CONCLUSIONS

The present data suggests that (a) mosaic loss of immunohistochemical INI1/SMARCB1 expression, despite the interlesional variability, is a reliable marker of schwannomatosis regardless of the involved gene and it might help in the differential diagnosis of schwannomatosis vs. solitary schwannomas and (b) INI1/SMARCB1 expression is not useful in the differential with mosaic NF2, since NF2-associated peripheral schwannomas show the same immunohistochemical pattern.

Diagnostic and Prognostic Relevance of the Cutaneous Manifestations of Neurofibromatosis Type 2

Neurofibromatosis type 2 is an autosomal dominant hereditary disease with complete penetrance. It gives rise to multiple central and peripheral nervous system tumors, ocular alterations, and various types of skin lesion. In general, neither dermatologists nor other specialists have in-depth knowledge of the clinical manifestations of neurofibromatosis type 2. In some cases, this can lead to delayed diagnosis, which can increase morbidity and mortality. We describe the less well known clinical manifestations of NF2, focusing particularly on skin lesions specific to this disease. Identification of these lesions, when present, can facilitate diagnosis.

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.

Mosaic Neurocutaneous Disorders and Their Causes

Neurocutaneous disorders are a heterogeneous group of conditions (mainly) affecting the skin [with pigmentary/vascular abnormalities and/or cutaneous tumours] and the central and peripheral nervous system [with congenital abnormalities and/or tumours]. In a number of such disorders, the skin abnormalities can assume a mosaic patterning (usually arranged in archetypical patterns). Alternating segments of affected and unaffected skin or segmentally arranged patterns of abnormal skin often mirror similar phenomena occurring in extra-cutaneous organs/tissues [eg, eye, bone, heart/vessels, lung, kidney and gut]. In some neurocutaneous syndromes the abnormal mosaic patterning involve mainly the skin and the nervous system configuring a (true) mosaic neurocutaneous disorder; or an ordinary trait of a neurocutaneous disorder is sometimes superimposed by a pronounced linear or otherwise segmental involvement; or, lastly, a neurocutaneous disorder can occur solely in a mosaic pattern. Recently, the molecular genetic and cellular bases of an increasing number of neurocutaneous disorders have been unravelled, shedding light on the interplays between common intra- and extra-neuronal signalling pathways encompassing receptor-protein and protein-to-protein cascades (eg, RAS, MAPK, mTOR, PI3K/AKT and GNAQ pathways), which are often responsible of the mosaic distribution of cutaneous and extra-cutaneous features. In this article we will focus on the well known, and less defined mosaic neurocutaneous phenotypes and their related molecular/genetic bases, including the mosaic neurofibromatoses and their related forms (ie, spinal neurofibromatosis and schwannomatosis); Legius syndrome; segmental arrangements in tuberous sclerosis; Sturge-Weber and Klippel-Trenaunay syndromes; microcephaly/megalencephaly-capillary malformation; blue rubber bleb nevus syndrome; Wyburn-Mason syndrome; mixed vascular nevus syndrome; PHACE syndrome; Incontinentia pigmenti; pigmentary mosaicism of the Ito type; neurocutaneous melanosis; cutis tricolor; speckled lentiginous syndrome; epidermal nevus syndromes; Becker's nevus syndrome; phacomatosis pigmentovascularis and pigmentokeratotica; Proteus syndrome; and encephalocraniocutaneous lipomatosis.

Diagnosis, Management, and New Therapeutic Options in Childhood Neurofibromatosis Type 2 and Related Forms

Neurofibromatosis type 2 (NF2; MIM # 101000) is an autosomal dominant disorder characterized by the development of vestibular schwannomas (VSs); schwannomas of other cranial, spinal, and cutaneous nerves; cranial and spinal meningiomas or other central nervous system tumors (eg, ependymomas and astrocytomas) or both. Additional features include eye (eg, early onset cataracts, optic nerve sheath meningiomas, retinal or pigment epithelial hamartomas or both, and epithelial retinal membranes) and skin abnormalities (eg, flat dermal [NF2 plaques] or spherical subcutaneous nodular schwannomas or both, and few, atypical café-au-lait spots). Clinically, children with NF2 fall into 2 main groups: (1) congenital NF2 with bilateral VSs detected as early as the first days to months of life, which can be stable or asymptomatic for 1-2 decades and suddenly progress; and (2) severe prepubertal (Wishart type) NF2 with multiple (and rapidly progressive) central nervous system tumors other-than-VS, which usually presents first, years before VSs, both associated with more marked skin and eye involvement (vs the classical mild adult [Gardner type] NF2, with bilateral VSs presenting in young adulthood, sometimes as the only disease feature). Individuals manifesting unilateral VS associated with ipsilateral meningiomas or multiple schwannomas localized to a part of the peripheral nervous system have mosaic or segmental NF2; individuals developing multiple nonVS, nonintradermal cranial, spinal, and peripheral schwannomas (histologically proven) have schwannomatosis (SWNTS). NF2 is caused by mutations in the NF2 gene at chromosome 22q12.1, which encodes for a protein called merlin or schwannomin, most similar to the exrin-readixin-moesin proteins; mosaic or segmental NF2 is because of mosaic phenomena for the NF2 gene, whereas SWNTS is caused by germline and possibly mosaic mutations either in the SMARCB1 gene (SWNTS1; MIM # 162091) or the LZTR1 gene (SWNTS2; MIM # 615670), both falling within the 22q region. Data driven from in vitro and animal studies on the merlin pathway allowed biologically targeted treatment strategies (employing Lapatinib, Erlotinib, Everolimus, Picropodophyllin, OSU.03012, Imatinib, Sorafenib, and Bevacizumab) aimed at multiple tumor shrinkage or regression or both and tumor arrest of progression with functional improvement.