Neurofibromatosis Type 2-Related Eye Disease Correlated With Genetic Severity Type

The molecular biology of NF2/Merlin on tumorigenesis and development

The neurofibromatosis type 2 (NF2) gene, known for encoding the tumor suppressor protein Merlin, is central to the study of tumorigenesis and associated cellular processes. This review comprehensively examines the multifaceted role of NF2/Merlin, detailing its structural characteristics, functional diversity, and involvement in various signaling pathways such as Wnt/β-catenin, Hippo, TGF-β, RTKs, mTOR, Notch, and Hedgehog. These pathways are crucial for cellular growth, proliferation, and differentiation. NF2 mutations are specifically linked to the development of schwannomas, meningiomas, and ependymomas, although the precise mechanisms of tumor formation in these specific cell types remain unclear. Additionally, the review explores Merlin's role in embryogenesis, highlighting the severe developmental defects and embryonic lethality caused by NF2 deficiency. The potential therapeutic strategies targeting these genetic aberrations are also discussed, emphasizing inhibitors of mTOR, HDAC, and VEGF as promising avenues for treatment. This synthesis of current knowledge underscores the necessity for ongoing research to elucidate the detailed mechanisms of NF2/Merlin and develop effective therapeutic strategies, ultimately aiming to improve the prognosis and quality of life for individuals with NF2 mutations.

NF2-Related Schwannomatosis (NF2): Molecular Insights and Therapeutic Avenues

NF2-related schwannomatosis (NF2) is a genetic syndrome characterized by the growth of benign tumors in the nervous system, particularly bilateral vestibular schwannomas, meningiomas, and ependymomas. This review consolidates the current knowledge on NF2 syndrome, emphasizing the molecular pathology associated with the mutations in the gene of the same name, the NF2 gene, and the subsequent dysfunction of its product, the Merlin protein. Merlin, a tumor suppressor, integrates multiple signaling pathways that regulate cell contact, proliferation, and motility, thereby influencing tumor growth. The loss of Merlin disrupts these pathways, leading to tumorigenesis. We discuss the roles of another two proteins potentially associated with NF2 deficiency as well as Merlin: Yes-associated protein 1 (YAP), which may promote tumor growth, and Raf kinase inhibitory protein (RKIP), which appears to suppress tumor development. Additionally, this review discusses the efficacy of various treatments, such as molecular therapies that target specific pathways or inhibit neomorphic protein-protein interaction caused by NF2 deficiency. This overview not only expands on the fundamental understanding of NF2 pathophysiology but also explores the potential of novel therapeutic targets that affect the clinical approach to NF2 syndrome.

Retinal Ischemia as a Presenting Ocular Sign of Neurofibromatosis Type 2

Purpose. Specific retinal abnormalities of neurofibromatosis type 2 (NF2) commonly include retinal astrocytoma and combined hamartoma of the retina and retinal pigment epithelium. Vasculopathy is an uncommon manifestation of NF2. We reported an NF2 patient presenting with retinal ischemia. Observations. An 18-year-old healthy Chinese female with acute decreased vision. The fundus examination and optical coherence tomography revealed optic disc hamartoma in the right eye and paracentral acute middle maculopathy (PAMM) and cotton wool spot indicating retinal ischemia in the left eye. Brain MRI showed bilateral acoustic neuroma, parasellar meningioma, and cervical extramedullary tumor. The genetic test confirmed the diagnosis of NF2. Conclusions and Importance. Our case suggests that retinal ischemia could be the presenting sign of NF2. NF2 could be associated with retinal vasculopathy in addition to retina tumors.

The genetic landscape and possible therapeutics of neurofibromatosis type 2

Neurofibromatosis type 2 (NF2) is a genetic condition marked by the development of multiple benign tumors in the nervous system. The most common tumors associated with NF2 are bilateral vestibular schwannoma, meningioma, and ependymoma. The clinical manifestations of NF2 depend on the site of involvement. Vestibular schwannoma can present with hearing loss, dizziness, and tinnitus, while spinal tumor leads to debilitating pain, muscle weakness, or paresthesias. Clinical diagnosis of NF2 is based on the Manchester criteria, which have been updated in the last decade. NF2 is caused by loss-of-function mutations in the NF2 gene on chromosome 22, leading the merlin protein to malfunction. Over half of NF2 patients have de novo mutations, and half of this group are mosaic. NF2 can be managed by surgery, stereotactic radiosurgery, monoclonal antibody bevacizumab, and close observation. However, the nature of multiple tumors and the necessity of multiple surgeries over the lifetime, inoperable tumors like meningiomatosis with infiltration of the sinus or in the area of the lower cranial nerves, the complications caused by the operation, the malignancies induced by radiotherapy, and inefficiency of cytotoxic chemotherapy due to the benign nature of NF-related tumors have led a march toward exploring targeted therapies. Recent advances in genetics and molecular biology have allowed identifying and targeting of underlying pathways in the pathogenesis of NF2. In this review, we explain the clinicopathological characteristics of NF2, its genetic and molecular background, and the current knowledge and challenges of implementing genetics to develop efficient therapies.

Updated protocol for genetic testing, screening and clinical management of individuals at risk of NF2-related schwannomatosis

Genetic testing and management of individuals at risk for NF2-related schwannomatosis is complicated by the high rate of mosaicism resulting in a milder, later onset, more asymmetrical disease and the phenotypic overlap with the related schwannomatosis conditions. This updated protocol has been devised for the English NF2-related schwannomatosis service. It provides those affected with mosaic NF2-related schwannomatosis estimated risks of having an affected child; and management guidelines both for individuals at risk of NF2-related schwannomatosis, or with potential disease, due to having features that fall short of consensus diagnostic criteria. Risks of mosaicism and inferred transmission risks were derived from genetic testing of over 1000 individuals through the Manchester NF2 genetic testing service. This updated protocol, reflects the lower transmission risks now inferred in mosaic NF2-related schwannomatosis, informed by the greater sensitivity of Next Generation Sequencing in detecting low levels of mosaicism in blood, along with improved ability to analyse tumour DNA. Screening for features of NF2-related schwannomatosis is proposed until the risk of having the condition falls below a pragmatic threshold of 1%. Using these revised transmission figures, this threshold can now be reached at a younger age in many of those at risk, with earlier reassurance and discharge.

Splicing-Disrupting Mutations in Inherited Predisposition to Solid Pediatric Cancer

The prevalence of hereditary cancer in children was estimated to be very low until recent studies suggested that at least 10% of pediatric cancer patients carry a germline mutation in a cancer predisposition gene. A significant proportion of pathogenic variants associated with an increased risk of hereditary cancer are variants affecting splicing. RNA splicing is an essential process involved in different cellular processes such as proliferation, survival, and differentiation, and alterations in this pathway have been implicated in many human cancers. Hereditary cancer genes are highly susceptible to splicing mutations, and among them there are several genes that may contribute to pediatric solid tumors when mutated in the germline. In this review, we have focused on the analysis of germline splicing-disrupting mutations found in pediatric solid tumors, as the discovery of pathogenic splice variants in pediatric cancer is a growing field for the development of personalized therapies. Therapies developed to correct aberrant splicing in cancer are also discussed as well as the options to improve the diagnostic yield based on the increase in the knowledge in splicing.

Revisiting the UK Genetic Severity Score for NF2: a proposal for the addition of a functional genetic component

BACKGROUND

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder characterised by the development of multiple schwannomas, especially on vestibular nerves, and meningiomas. The UK NF2 Genetic Severity Score (GSS) is useful to predict the progression of the disease from germline NF2 pathogenic variants, which allows the clinical follow-up and the genetic counselling offered to affected families to be optimised.

METHODS

52 Spanish patients were classified using the GSS, and patients' clinical severity was measured and compared between GSS groups. The GSS was reviewed with the addition of phenotype quantification, genetic variant classification and functional assays of Merlin and its downstream pathways. Principal component analysis and regression models were used to evaluate the differences between severity and the effect of NF2 germline variants.

RESULTS

The GSS was validated in the Spanish NF2 cohort. However, for 25% of mosaic patients and patients harbouring variants associated with mild and moderate phenotypes, it did not perform as well for predicting clinical outcomes as it did for pathogenic variants associated with severe phenotypes. We studied the possibility of modifying the mutation classification in the GSS by adding the impact of pathogenic variants on the function of Merlin in 27 cases. This revision helped to reduce variability within NF2 mutation classes and moderately enhanced the correlation between patient phenotype and the different prognosis parameters analysed (R²=0.38 vs R²=0.32, p>0001).

CONCLUSIONS

We validated the UK NF2 GSS in a Spanish NF2 cohort, despite the significant phenotypic variability identified within it. The revision of the GSS, named Functional Genetic Severity Score, could add value for the classification of mosaic patients and patients showing mild and moderate phenotypes once it has been validated in other cohorts.

Current Understanding of Neurofibromatosis Type 1, 2, and Schwannomatosis

Neurofibromatosis (NF) is a neurocutaneous syndrome characterized by the development of tumors of the central or peripheral nervous system including the brain, spinal cord, organs, skin, and bones. There are three types of NF: NF1 accounting for 96% of all cases, NF2 in 3%, and schwannomatosis (SWN) in <1%. The NF1 gene is located on chromosome 17q11.2, which encodes for a tumor suppressor protein, neurofibromin, that functions as a negative regulator of Ras/MAPK and PI3K/mTOR signaling pathways. The NF2 gene is identified on chromosome 22q12, which encodes for merlin, a tumor suppressor protein related to ezrin-radixin-moesin that modulates the activity of PI3K/AKT, Raf/MEK/ERK, and mTOR signaling pathways. In contrast, molecular insights on the different forms of SWN remain unclear. Inactivating mutations in the tumor suppressor genes SMARCB1 and LZTR1 are considered responsible for a majority of cases. Recently, treatment strategies to target specific genetic or molecular events involved in their tumorigenesis are developed. This study discusses molecular pathways and related targeted therapies for NF1, NF2, and SWN and reviews recent clinical trials which involve NF patients.

Nf2 fine-tunes proliferation and tissue alignment during closure of the optic fissure in the embryonic mouse eye

Uveal coloboma represents one of the most common congenital ocular malformations accounting for up to 10% of childhood blindness (~1 in 5000 live birth). Coloboma originates from defective fusion of the optic fissure (OF), a transient gap that forms during eye morphogenesis by asymmetric, ventral invagination. Genetic heterogeneity combined with the activity of developmentally regulated genes suggests multiple mechanisms regulating OF closure. The tumor suppressor and FERM domain protein Neurofibromin 2 (NF2) controls diverse processes in cancer, development and regeneration, via Hippo pathway and cytoskeleton regulation. In humans, NF2 mutations can cause ocular abnormalities, including coloboma, however, its actual role in OF closure is unknown. Using conditional inactivation in the embryonic mouse eye, our data indicate that loss of Nf2 function results in a novel underlying cause for coloboma. In particular, mutant eyes show substantially increased retinal pigmented epithelium (RPE) proliferation in the fissure region with concomitant acquisition of RPE cell fate. Cells lining the OF margin can maintain RPE fate ectopically and fail to transition from neuroepithelial to cuboidal shape. In the dorsal RPE of the optic cup, Nf2 inactivation leads to a robust increase in cell number, with local disorganization of the cytoskeleton components F-actin and pMLC2. We propose that RPE hyperproliferation is the primary cause for the observed defects causing insufficient alignment of the OF margins in Nf2 mutants and failure to fuse properly, resulting in persistent coloboma. Our findings indicate that limiting proliferation particularly in the RPE layer is a critical mechanism during OF closure.

Retinal manifestations of the neurocutaneous disorders

PURPOSE OF REVIEW

The neurocutaneous disorders are a genetically and phenotypically diverse group of congenital syndromes characterized by cutaneous, ocular, and central nervous system manifestations. This review provides an overview of the clinical features and retinal findings in selected neurocutaneous disorders.

RECENT FINDINGS

Advances in genetics and diagnostic retinal and neuroimaging allow for the recognition of retinal features of common neurocutaneous syndromes and for improved characterization of rarer entities based on previously underdiagnosed or unrecognized retinal findings.

SUMMARY

Better characterization of the neurocutaneous disorders allows for earlier recognition and the potential for expeditious vision-saving and life-saving treatment.

The Role of Neuro-Ophthalmologists in the Care of Patients With Neurofibromatosis Type 2

Neurofibromatosis type 2 (NF2) is a rare genetic disorder, affecting the central nervous system and leading to various degrees of disability. Its hallmark is bilateral vestibular schwannomas that invariably lead to progressive hearing loss. Specific ophthalmic abnormalities in patients with NF2 may help to establish an early diagnosis. These include juvenile cataract, epiretinal membrane, combined hamartoma of the retina and the retinal pigment epithelium, optic disc glioma, and optic nerve sheath meningioma. In addition, intracranial tumors may produce a variety of neuro-ophthalmic abnormalities that have the potential to impair visual function, such as postpapilledema optic atrophy, compression of the visual pathways, keratopathy, ocular motor cranial nerve palsies, and amblyopia. Care of NF2 patients is best provided by interdisciplinary medical teams including a neuro-ophthalmologist.

Neurofibromatosis type 2 and related disorders

PURPOSE OF REVIEW

Neurofibromatosis type 2 (NF2) is a schwannoma predisposition syndrome, alongside schwannomatosis related to germline LZTR1 and SMARCB1 pathogenic variants. This review highlights their overlapping phenotypes, new insight into NF2 phenotype and treatment outcomes.

RECENT FINDINGS

Mosaic NF2 is more prevalent than previously thought. Use of next-generation sequencing and tumour testing is needed to differentiate mosaic NF2 and schwannomatosis. Developing NF2 phenotypic insights include vasculopathy with brainstem infarction and vessel stenosis; focal cortical dysplasia in severe phenotypes; swallowing/speech difficulties and continued debate into malignancy in NF2. Proposed are: use of visual evoked potentials to monitor optic nerve sheath meningioma; potential routine magnetic resonance angiogram in adolescence and a genetic score to cohort patients with similar pathogenic_variants, for natural history/treatment outcome studies. Cohort studies found survival analysis to hearing loss and unilateral visual loss in severe mutation groups was 32 and 38 years; active management gave better outcomes than surveillance in spinal ependymoma; gamma knife, bevacizumab and hearing preservation surgery maintained or improved short-term hearing in selected patients, and gamma knife had a good long-term tumour control in mild patients with small tumours.

SUMMARY

Further long-term outcome studies are needed comparing similar severity patients to allow informed decision making.

An update on the CNS manifestations of neurofibromatosis type 2

Neurofibromatosis type II (NF2) is a tumor predisposition syndrome characterized by the development of distinctive nervous system lesions. NF2 results from loss-of-function alterations in the NF2 gene on chromosome 22, with resultant dysfunction of its protein product merlin. NF2 is most commonly associated with the development of bilateral vestibular schwannomas; however, patients also have a predisposition to development of other tumors including meningiomas, ependymomas, and peripheral, spinal, and cranial nerve schwannomas. Patients may also develop other characteristic manifestations such as ocular lesions, neuropathies, meningioangiomatosis, and glial hamartia. NF2 has a highly variable clinical course, with some patients exhibiting a severe phenotype and development of multiple tumors at an early age, while others may be nearly asymptomatic throughout their lifetime. Despite the high morbidity associated with NF2 in severe cases, management of NF2-associated lesions primarily consists of surgical resection and treatment of symptoms, and there are currently no FDA-approved systemic therapies that address the underlying biology of the syndrome. Refinements to the diagnostic criteria of NF2 have been proposed over time due to increasing understanding of clinical and molecular data. Large-population studies have demonstrated that some features such as the development of gliomas and neurofibromas, currently included as diagnostic criteria, may require further clarification and modification. Meanwhile, burgeoning insights into the molecular biology of NF2 have shed light on the etiology and highly variable severity of the disease and suggested numerous putative molecular targets for therapeutic intervention. Here, we review the clinicopathologic features of NF2, current understanding of the molecular biology of NF2, particularly with regard to central nervous system lesions, ongoing therapeutic studies, and avenues for further research.

Neuro-ophthalmic manifestations of the phakomatoses

PURPOSE OF REVIEW

The phakomatoses are a group of inherited disorders with variable clinical manifestations that are characterized by brain, cutaneous, ocular and other distinct lesions in multiple organs. Correctly recognizing the neuro-ophthalmic signs and symptoms can lead to early diagnosis and treatment. The group is composed of neurofibromatosis (type 1 and 2), tuberous sclerosis complex, von Hippel-Lindau, ataxia-telangiectasia and Sturge-Weber syndromes. However, more than 60 syndromes have been described in the medical literature. This review provides an update on the diagnosis and management of phakomatoses with a focus on their clinical neuro-ophthalmic manifestations.

RECENT FINDINGS

Phakomatoses are a group of inherited syndromes with variable clinical manifestations that are characterized by brain, cutaneous, ocular and other distinct lesions in multiple organs. Recent advances in diagnostic and treatment options that have contributed to prompt recognition and management of these disorders are discussed with an emphasis on the beneficial effects on vision.

SUMMARY

Phakomatoses, also known as neuro-oculo-cutaneous syndromes, are inherited disorders with characteristic lesions in multiple organs. Because of their frequent ocular involvement thorough ophthalmologic and neuro-ophthalmic evaluation is critical in this patient population in order to prevent vision loss and life-threatening complications that are often associated with these disorders.

Identifying the deficiencies of current diagnostic criteria for neurofibromatosis 2 using databases of 2777 individuals with molecular testing

PURPOSE

We have evaluated deficiencies in existing diagnostic criteria for neurofibromatosis 2 (NF2).

METHODS

Two large databases of individuals fulfilling NF2 criteria (n = 1361) and those tested for NF2 variants with criteria short of diagnosis (n = 1416) were interrogated. We assessed the proportions meeting each diagnostic criterion with constitutional or mosaic NF2 variants and the positive predictive value (PPV) with regard to definite diagnosis.

RESULTS

There was no evidence for usefulness of old criteria "glioma" or "neurofibroma." "Ependymoma" had 100% PPV and high levels of confirmed NF2 diagnosis (67.7%). Those with bilateral vestibular schwannoma (VS) alone aged ≥60 years had the lowest confirmation rate (6.6%) and reduced PPV (80%). Siblings as a first-degree relative, without an affected parent, had 0% PPV. All three individuals with unilateral VS and an affected sibling were proven not to have NF2. The biggest overlap was with LZTR1-associated schwannomatosis. In this category, seven individuals with unilateral VS plus ≥2 nondermal schwannomas reduced PPV to 67%.

CONCLUSIONS

The present study confirms important deficiencies in NF2 diagnostic criteria. The term "glioma" should be dropped and replaced by "ependymoma." Similarly "neurofibroma" should be removed. Dropping "sibling" from first-degree relatives should be considered and testing of LZTR1 should be recommended for unilateral VS.