Neurofibromatosis Type 1 Gene Research Articles

Genetic analysis of two children with sporadic neurofibromatosis type 1 complicated with nephrotic syndrome

To explore the genetic basis for two children with sporadic neurofibromatosis type 1 (NF1) complicated with nephrotic syndrome (NS). Clinical data of the children were collected. Both children were subjected to high-throughput sequencing, and candidate variants were verified by Sanger sequencing. Both children had café-au-lait macules, subaxillary freckle and Lisch nodules. Child 1 also had congenital tibiofibular pseudarthrosis on the left side. Genetic testing revealed that child 1 has harbored a heterozygous c.844C>T variant in the exon 8 of the NF1 gene, whilst child 2 has harbored a heterozygous c.1246C>T variant in the exon 11 of the NF1 gene. Both children were diagnosed with NF1 and have developed pronounced proteinuria, hypoalbuminemia, hypercholesterolemia and pitting edema at the ages of 3 and 10, respectively. Renal biopsy of child 2 has revealed minimal change nephropathy, and the diagnosis of nephrotic syndrome was established. Child 1 was treated with glucocorticoid, and child 2 was treated with glucocorticoid in combination with mycophenolate mofetil. The NS was relieved with no recurrence during 1 year's follow-up. NF1 combined with NS is rare in the clinical settings. The prognosis of children with NF1 combined with minimal change nephropathy is relatively good. Detection of NF1 gene variant can facilitate early identification and diagnosis of NF1.

Abstract 12

Background: Neurofibromatosis type 1 (NF1) is a common dominant inherited disorder with highly variable expressivity. The highly variable clinical features of NF1 are because of there are many genetic modifiers that lie outside the NF1 gene, which influence NF 1 gene and account for a large fraction of the symptomatic variability seen in NF1. Mutation detection in the NF1 gene is complex due to its large size, the existence of several pseudo genes and the lack of clustering of the mutations. There are no clear mutation hotspots and the spectrum of mutations is very diverse, ranging from micro deletions affecting the entire NF1 gene to minor lesions that include a high proportion of splicing mutations. Objective: Identification of the genetic mutation in mother son duo with neurofibromatosis. Method: Whole exome analysis was performed to identify the genetic defect. The variants were prioritized using standard open-source computational pipelines. Results: Whole exome sequencing and computational analysis identified a novel missense (c.4244A>G) at 17q11.2 cytogenetic location of NF 1 gene. Despite having the same genetic variant, absence ofpheochromocytoma in mother indicates heterogeneous presentation of neurofibromatosis type 1. Conclusion: To the best of our knowledge, this is the first report describing neurofibromatosis due to novel frameshift ANOS1 gene mutations. The report also exemplifies poor correlation of genotype and phenotype in neurofibromatosis cases.

Novel, heterozygous, pathogenic variant (c.4272delA: p.I1426Ffs*2) for the NF1 gene in a large Chinese family with neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is an autosomal dominant with haploinsufficient, and multisystemic disorder including patches of skin Café-au-lait spots, Lisch nodules in the iris, and tumors in the peripheral nervous systems or fibromatous skin. Blood samples were collected and DNA was extracted from a large Chinese pedigree suffering from NF1 disease with three spontaneous abortions or death for proband. Analysis for whole exome sequencing (WES), Sanger sequencing, and co-segregation was carried out. Prenatal gene diagnosis was also carried out in amniotic fluid DNA. The expression of NF1 was conducted by bioinformatics. A large Chinese pedigree with NF1 was recruited and a novel, heterozygous, variant (c.4272delA: p.I1426Ffs*2) for the NF1 gene in the proband was identified. This variant of NF1 produced a truncated protein that losses half of NF1 protein at the C-terminus including the CRAL-TRIO lipid-binding domain, NLS, and a small portion of Ras-GAP domain, thus leading to pathogenicity (ACMG criteria: PVS1 + PM2). NF1 expressions in different human tissues showed low tissue specificity, which may affect multiple organs presenting different phenotypes. Moreover, prenatal gene diagnosis for NF1 showed both alleles as wild types in the fetus of the proband. We thus successfully identified a novel, pathogenic, heterozygous variant (c.4272delA:p.I1426Ffs*2) in the NF1 gene of NF1 disorder, expanding the NF1 mutation spectrum, that will help elucidate the molecular pathogenesis of NF1 disease and to contribute to the NF1 diagnosis, genetic counseling, clinical management in this large Chinese family.

Cerebellum-dependent associative learning is not impaired in a mouse model of neurofibromatosis type 1

Individuals with Neurofibromatosis type 1 (NF1) experience a high degree of motor problems. The cerebellum plays a pivotal role in motor functioning and the NF1 gene is highly expressed in cerebellar Purkinje cells. However, it is not well understood to what extent NF1 affects cerebellar functioning and how this relates to NF1 motor functioning. Therefore, we subjected global Nf1+/− mice to a cerebellum-dependent associative learning task, called Pavlovian eyeblink conditioning. Additionally, we assessed general motor function and muscle strength in Nf1+/− mice. To our surprise, we found that Nf1+/− mice showed a moderately increased learning rate of conditioned eyeblink responses, as well as improved accuracy in the adaptive timing of the eyeblink responses. Locomotion, balance, general motor function, and muscle strength were not affected in Nf1+/− mice. Together, our results support the view that cerebellar function in Nf1+/− mice is unimpaired.

Loss of NF1 in Drosophila Larvae Causes Tactile Hypersensitivity and Impaired Synaptic Transmission at the Neuromuscular Junction.

Autism spectrum disorder (ASD) is a neurodevelopmental condition in which the mechanisms underlying its core symptomatology are largely unknown. Studying animal models of monogenic syndromes associated with ASD, such as neurofibromatosis type 1 (NF1), can offer insights into its etiology. Here, we show that loss of function of the Drosophila NF1 ortholog results in tactile hypersensitivity following brief mechanical stimulation in the larva (mixed sexes), paralleling the sensory abnormalities observed in individuals with ASD. Mutant larvae also exhibit synaptic transmission deficits at the glutamatergic neuromuscular junction (NMJ), with increased spontaneous but reduced evoked release. While the latter is homeostatically compensated for by a postsynaptic increase in input resistance, the former is consistent with neuronal hyperexcitability. Indeed, diminished expression of NF1 specifically within central cholinergic neurons induces both excessive neuronal firing and tactile hypersensitivity, suggesting the two may be linked. Furthermore, both impaired synaptic transmission and behavioral deficits are fully rescued via knock-down of Ras proteins. These findings validate NF1 -/- Drosophila as a tractable model of ASD with the potential to elucidate important pathophysiological mechanisms.SIGNIFICANCE STATEMENT Autism spectrum disorder (ASD) affects 1-2% of the overall population and can considerably impact an individual's quality of life. However, there are currently no treatments available for its core symptoms, largely because of a poor understanding of the underlying mechanisms involved. Examining how loss of function of the ASD-associated NF1 gene affects behavior and physiology in Drosophila may shed light on this. In this study, we identify a novel, ASD-relevant behavioral phenotype in NF1 -/- larvae, namely an enhanced response to mechanical stimulation, which is associated with Ras-dependent synaptic transmission deficits indicative of neuronal hyperexcitability. Such insights support the use of Drosophila neurofibromatosis type 1 (NF1) models in ASD research and may provide outputs for genetic or pharmacological screens in future studies.

Role of nerves in neurofibromatosis type 1-related nervous system tumors.

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder that affects nearly 1 in 3000 infants. Neurofibromin inactivation and NF1 gene mutations are involved in various aspects of neuronal function regulation, including neuronal development induction, electrophysiological activity elevation, growth factor expression, and neurotransmitter release. NF1 patients often exhibit a predisposition to tumor development, especially in the nervous system, resulting in the frequent occurrence of peripheral nerve sheath tumors and gliomas. Recent evidence suggests that nerves play a role in the development of multiple tumor types, prompting researchers to investigate the nerve as a vital component in and regulator of the initiation and progression of NF1-related nervous system tumors. In this review, we summarize existing evidence about the specific effects of NF1 mutation on neurons and emerging research on the role of nerves in neurological tumor development, promising a new set of selective and targeted therapies for NF1-related tumors.

Neurofibroma Development in Neurofibromatosis Type 1: Insights from Cellular Origin and Schwann Cell Lineage Development

Simple SummaryNeurofibromas have been thought to originate from cells within the Schwann cell lineage, while no consensus has been reached so far about the specific time of initiation and the exact cellular origin. Moreover, the role of Schwann cell lineage transition in different developmental stages of neurofibromas, together with other determinant factors, remains controversial, despite intensive studies. In this review, we summarized the accumulating evidence about the full range of neurofibroma development based on cellular and molecular pathogenesis.Background: Neurofibromatosis type 1 (NF1), a genetic tumor predisposition syndrome that affects about 1 in 3000 newborns, is caused by mutations in the NF1 gene and subsequent inactivation of its encoded neurofibromin. Neurofibromin is a tumor suppressor protein involved in the downregulation of Ras signaling. Despite a diverse clinical spectrum, one of several hallmarks of NF1 is a peripheral nerve sheath tumor (PNST), which comprises mixed nervous and fibrous components. The distinct spatiotemporal characteristics of plexiform and cutaneous neurofibromas have prompted hypotheses about the origin and developmental features of these tumors, involving various cellular transition processes. Methods: We retrieved published literature from PubMed, EMBASE, and Web of Science up to 21 June 2022 and searched references cited in the selected studies to identify other relevant papers. Original articles reporting the pathogenesis of PNSTs during development were included in this review. We highlighted the Schwann cell (SC) lineage shift to better present the evolution of its corresponding cellular origin hypothesis and its important effects on the progression and malignant transformation of neurofibromas. Conclusions: In this review, we summarized the vast array of evidence obtained on the full range of neurofibroma development based on cellular and molecular pathogenesis. By integrating findings relating to tumor formation, growth, and malignancy, we hope to reveal the role of SC lineage shift as well as the combined impact of additional determinants in the natural history of PNSTs.

A Case of Neurofibromatosis Type 1 with Severe Mood and Behavioral Symptoms

INTRODUCTION: Neurofibromatosis type 1 (NF1) is a genetic disorder caused by a mutation in the NF1 gene. In addition to physical manifestations, complications such as cognitive and behavioral deficits have been described. CLINICAL FINDINGS: We describe a case of a 14-year-old male with a past psychiatric history of obsessive-compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), and multiple suicide attempts, who presented with suicidal ideation and command hallucinations. The patient became aggressive, physically assaulting hospital staff, and required sedative medication and physical restraints for several days. He required inpatient hospital admission due to rhabdomyolysis. Throughout his admission, the patient was intermittently verbally and physically abusive to people around him. They described his outbursts as impulsive and thought to be out of motivation to get what he wants. He preferred to keep to himself and did not have relationships with people at his home. CONCLUSION: This case report provides insight into the behavioral characterization of children diagnosed with NF1. While the mechanism of how NF1 relates to behavioral issues is unknown, the association between NF1 and behavioral issues should be carefully considered in NF1 patients presenting with aggression.

Identification of Germinal Neurofibromin Hotspots.

Neurofibromin is engaged in many cellular processes and when the proper protein functioning is impaired, it causes neurofibromatosis type 1 (NF1), one of the most common inherited neurological disorders. Recent advances in sequencing and screening of the NF1 gene have increased the number of detected variants. However, the correlation of these variants with the clinic remains poorly understood. In this study, we analyzed 4610 germinal NF1 variants annotated in ClinVar and determined on exon level the mutational spectrum and potential pathogenic regions. Then, a binomial and sliding windows test using 783 benign and 938 pathogenic NF1 variants were analyzed against functional and structural regions of neurofibromin. The distribution of synonymous, missense, and frameshift variants are statistically significant in certain regions of neurofibromin suggesting that the type of variant and its associated phenotype may depend on protein disorder. Indeed, there is a negative correlation between the pathogenic fraction prediction and the disorder data, suggesting that the higher an intrinsically disordered region is, the lower the pathogenic fraction is and vice versa. Most pathogenic variants are associated to NF1 and our analysis suggests that GRD, CSRD, TBD, and Armadillo1 domains are hotspots in neurofibromin. Knowledge about NF1 genotype–phenotype correlations can provide prognostic guidance and aid in organ-specific surveillance.

Genotypes and clinical intervention of patients with neurofibromatosis type 1 associated dystrophic scoliosis.

To analyze the genotypic characteristics of patients with neurofibromatosis type 1 (NF1) associated dystrophic scoliosis and to summarize the outcomes of the surgical treatment of these patients. Exome sequencing (ES) combined with multiplex ligation-dependent probe amplification (MLPA) was used for genotypic identification. All patients underwent surgical treatments for spinal deformities, and the outcomes of the surgery was summarized by analyzing the clinical and imaging parameters before and after the surgery. Fourteen patients (six males and eight females) were clinically diagnosed as NF1 associated dystrophic scoliosis with common symptoms including café-au-lait spots, paravertebral tumors, and dystrophic scoliosis. NF1 mutations were detected in 12 (85.7%) patients, including four nonsense mutations, three splicing mutations, three frameshift mutations, and two exon deletions. The first surgical procedure included growing-rod surgery in 10 patients and posterior spinal fusion in four patients. The follow-up duration was 2.3 years (1.0-10.3 years), and the Cobb angle of the main curve improved from 61.5° (30°-125°) pre-operatively to 14.5° (0°-42°) at the last follow-up, with an average correction rate of 74.0% (44-100%). Instrumentation-related complications occurred in four patients during the follow-up period. In patients with dystrophic scoliosis who met the clinical diagnostic criteria for NF1, the mutation detection rate of ES combined with MLPA was 85.7%. There was no mutation hotspot in NF1 gene, molecular diagnosis could offer information about genetic counseling, prenatal diagnosis and eugenics. Surgical treatment according to patient's age and severity could effectively correct the spinal deformities.

Questions on surgical treatment of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a hereditary tumor syndrome caused by a mutation in tumor suppressor gene NF1. The disease occurs with a frequency of 1:3000 of the population. Typical manifestations of NF1 are multiple cutaneous, subcutaneous and plexiform neurofibromas, which cause serious cosmetic defects in the appearance of patients. Since an effective method for the treatment of NF1 has not yet been introduced into clinical practice, which makes it possible to completely get rid of multiple neoplasms, surgical removal or the use of photodestruction methods remains the method of choice for the treatment of cutaneous and subcutaneous neurofibromas. However, plexiform neurofibromas infiltratively grow into the surrounding tissues, so their complete excision is often impossible. Therefore, surgical excision is indicated for localized forms of plexiform neurofibromas and in emergency situations when they are located near vital structures or in the presence of a mass effect. Moreover, excision of cutaneous and subcutaneous neurofibromas may initiate formation and growth of new tumors. This is due to the degranulation of mast cells in response to tumor damage, since the pathology of the immune system plays an important role in the development of neurofibromas. In order to avoid dissemination of tumors, it is also important to adhere to the principles of antiblastic surgery. Therefore, the most promising is the complex treatment of NF1 with the combined use of a classical approach, surgical laser, ketotifen, and an inhibitor of mitogen-activated kinase. This method can be recommended for the treatment of malignant peripheral nerve sheath tumors, as well as sporadic neoplasms, the resistance of which is caused by a somatic mutation in the NF1 gene. The goal of NF1 treatment is to improve the quality of life of the patient as a whole and reduce pain using an integrated multidisciplinary approach.

Functional restoration of mouse Nf1 nonsense alleles in differentiated cultured neurons.

Neurofibromatosis type 1 (NF1), one of the most common autosomal dominant genetic disorders, is caused by mutations in the NF1 gene. NF1 patients have a wide variety of manifestations with a subset at high risk for the development of tumors in the central nervous system (CNS). Nonsense mutations that result in the synthesis of truncated NF1 protein (neurofibromin) are strongly associated with CNS tumors. Therapeutic nonsense suppression with small molecule drugs is a potentially powerful approach to restore the expression of genes harboring nonsense mutations. Ataluren is one such drug that has been shown to restore full-length functional protein in several models of nonsense mutation diseases, as well as in patients with nonsense mutation Duchenne muscular dystrophy. To test ataluren's potential applicability to NF1 nonsense mutations associated with CNS tumors, we generated a homozygous Nf1R683X/R683X-3X-FLAG mouse embryonic stem (mES) cell line which recapitulates an NF1 patient nonsense mutation (c.2041 C > T; p.Arg681X). We differentiated Nf1R683X/R683X-3X-FLAG mES cells into cortical neurons in vitro, treated the cells with ataluren, and demonstrated that ataluren can promote readthrough of the nonsense mutation at codon 683 of Nf1 mRNA in neural cells. The resulting full-length protein is able to reduce the cellular level of hyperactive phosphorylated ERK (pERK), a RAS effector normally suppressed by the NF1 protein.

Contribution of whole genome sequencing in the molecular diagnosis of mosaic partial deletion of the NF1 gene in neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease with complete penetrance but highly variable expressivity. In most patients, Next Generation Sequencing (NGS) technologies allow the identification of a loss-of-function pathogenic variant in the NF1 gene, a negative regulator of the RAS-MAPK pathway. We describe the 5-year diagnosis wandering of a patient with a clear NF1 clinical diagnosis, but no molecular diagnosis using standard molecular technologies. The patient presented with a typical NF1 phenotype but NF1 targeted NGS, NF1 transcript analysis, MLPA, and array comparative genomic hybridization failed to reveal a genetic aberration. After 5years of unsuccessful investigations, trio WGS finally identified a de novo mosaic (VAF ~ 14%) 24.6kb germline deletion encompassing the promoter and first exon of NF1. This case report illustrates the relevance of WGS to detect structural variants including copy number variants that would be missed by alternative approaches. The identification of the causal pathogenic variant allowed a tailored genetic counseling with a targeted non-invasive prenatal diagnosis by detecting the deletion in plasmatic cell-free DNA from the proband's pregnant partner. This report clearly highlights the need to make WGS a clinically accessible test, offering a tremendous opportunity to identify a molecular diagnosis for otherwise unsolved cases.

Intragenic inversions in NF1 gene as pathogenic mechanism in neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1), an autosomal dominant disorder characterized by skin pigmentary lesions and multiple cutaneous neurofibromas, is caused by neurofibromin 1 (NF1) loss of function variants. Currently, a molecular diagnosis is frequently established using a multistep protocol based on cDNA and gDNA sequence analysis and/or Multiplex Ligation-dependent Probe Amplification (MLPA) assay on genomic DNA, providing an overall detection rate of about 95-97%. The small proportion of clinically diagnosed patients, which at present do not obtain a molecular confirmation likely are mosaic, as their pathogenic variant may remain undetected due to low sensitivity of low coverage NGS approaches, or they may carry a type of pathogenic variant refractory to currently used technologies. Here, we report two unrelated patients presenting with two different inversions that disrupt the NF1 coding sequence, resulting in an NF1 phenotype. In one subject, the inversion was associated with microdeletions spanning a few NF1 exons at both breakpoints, while in the other the rearrangement did not cause exon loss, thus testing negative by MLPA assay. Considering the high proportion of repeated regions within the NF1 sequence, we propose that intragenic structural rearrangements should be considered as possible pathogenic mechanisms in patients fulfilling the NIH diagnostic criteria of NF1 but lacking of molecular confirmation and in patients with NF1 intragenic microdeletions.

Prospects for the treatment of neurofibromatosis type 1: A review

Neurofibromatosis type 1 (NF1) is an autosomal dominant hereditary tumor syndrome with a prevalence of 1:3000 in human population. About 50% of NF1 cases are sporadic due to newly emerging germline mutations in NF1 gene. Protein product of NF1 is a neurofibromin, which inhibits RAS-RAF-MEK-ERK system. The prevalence of NF1 is increasing as patients are fertile. Therefore, it is important to use rapid diagnostic methods for NF1 mutations in NF1 families for prenatal prophylaxis. Mutations in NF1 gene play roles in sporadic carcinogenesis and in development of cancer resistance to chemotherapy. Specific for NF1 are multiple subcutaneous and cutaneous neurofibromas, age spots, skeletal abnormalities, mental retardation, tumors of the brain and optic nerves. Half of patients with NF1 develop plexiform neurofibromas, which disfigure them or compress vital organs. The difficulty in treating NF1 is due to involvement of immune system, since a large number of degranulating mast cells are found in neurofibromas. Mast cells secrete cytokines that dont provide a proper anti-tumor immune response, but initiate formation and growth of new neurofibromas. Therefore, long-term administration of ketotiphen was proposed for treatment of NF1 patients. Surgical removal of neurofibromas causes relapses and induction of the growth of new tumors; therefore, it is necessary to develop an effective therapy for NF1. The effectiveness of complex therapy of NF1 with use of ketotiphen, Lydase and Aevit, as well as monotherapy with an ATP-independent inhibitor of mitogen-activated protein kinase, has been described. For widespread clinical implementation of these methods, it is necessary to conduct studies on large sample of patients, as well as to make medicines available for patients. Gene therapy may become promising in the treatment of NF1, which requires identification of the type of mutation in NF1 gene in each individual and the use of specific microRNAs.

Clinical presentation and genetic analyses of neurofibromatosis type 1 in independent patients with monoallelic double de novo closely spaced mutations in the NF1 gene.

Neurofibromatosis type 1 (NF1) belongs to RASopathies, a group of syndromes caused by germline mutations in Ras/MAPK pathway genes. Most NF1 patients exhibit single inactivating pathogenic variants within the NF1 gene. We performed extensive genetic analyses in two NF1 families disclosing the first two cases of double de novo monoallelic NF1 variants. Both index patients described in this study had classical NF1. Probands were born from fathers in their late 30s and presented closely spaced double mutations (<100 bp) in NF1 regions showing an excess of somatic mutations. Closely spaced multiple mutations have been reported in RAS/MAPK signaling genes but never in NF1. Mutagenesis is a quasi‐random process in humans, therefore two causative variants in the same gene, moreover in the same allele are exceptional. Here, we discuss possible mechanisms for this ultrarare event. Our findings confirm the possibility of a higher risk of concurrent de novo variants in NF1.

Neurofibromatosis from Head to Toe: What the Radiologist Needs to Know.

Neurofibromatosis type 1 (NF1) and neurofibromatosis type 2 (NF2) are autosomal dominant inherited neurocutaneous disorders or phakomatoses secondary to mutations in the NF1 and NF2 tumor suppressor genes, respectively. Although they share a common name, NF1 and NF2 are distinct disorders with a wide range of multisystem manifestations that include benign and malignant tumors. Imaging plays an essential role in diagnosis, surveillance, and management of individuals with NF1 and NF2. Therefore, it is crucial for radiologists to be familiar with the imaging features of NF1 and NF2 to allow prompt diagnosis and appropriate management. Key manifestations of NF1 include café-au-lait macules, axillary or inguinal freckling, neurofibromas or plexiform neurofibromas, optic pathway gliomas, Lisch nodules, and osseous lesions such as sphenoid dysplasia, all of which are considered diagnostic features of NF1. Other manifestations include focal areas of signal intensity in the brain, low-grade gliomas, interstitial lung disease, various abdominopelvic neoplasms, scoliosis, and vascular dysplasia. The various NF1-associated abdominopelvic neoplasms can be categorized by their cellular origin: neurogenic neoplasms, interstitial cells of Cajal neoplasms, neuroendocrine neoplasms, and embryonal neoplasms. Malignant peripheral nerve sheath tumors and intracranial tumors are the leading contributors to mortality in NF1. Classic manifestations of NF2 include schwannomas, meningiomas, and ependymomas. However, NF2 may have shared cutaneous manifestations with NF1. Lifelong multidisciplinary management is critical for patients with either disease. The authors highlight the genetics and molecular pathogenesis, clinical and pathologic features, imaging manifestations, and multidisciplinary management and surveillance of NF1 and NF2. Online supplemental material is available for this article. ©RSNA, 2022.

Genotype-Phenotype Correlations in Neurofibromatosis Type 1: Identification of Novel and Recurrent NF1 Gene Variants and Correlations with Neurocognitive Phenotype.

Neurofibromatosis type 1 (NF1) is one of the most common genetic tumor predisposition syndrome, caused by mutations in the NF1. To date, few genotype-phenotype correlations have been discerned in NF1, due to a highly variable clinical presentation. We aimed to study the molecular spectrum of NF1 and genotype-phenotype correlations in a monocentric study cohort of 85 NF1 patients (20 relatives, 65 sporadic cases). Clinical data were collected at the time of the mutation analysis and reviewed for accuracy in this investigation. An internal phenotypic categorization was applied. The 94% of the patients enrolled showed a severe phenotype with at least one systemic complication and a wide range of associated malignancies. Spine deformities were the most common complications in this cohort. We also reported 66 different NF1 mutations, of which 7 are novel mutations. Correlation analysis identified a slight significant inverse correlation between age at diagnosis and delayed acquisition of psychomotor skills with residual multi-domain cognitive impairment. Odds ratio with 95% confidence interval showed a higher prevalence of learning disabilities in patients carrying frameshift mutations. Overall, our results aim to offer an interesting contribution to studies on the genotype–phenotype of NF1 and in genetic management and counselling.

Abstract 1614: Creation of malignant peripheral nerve sheath tumor models deficient for polycomb repressive complex 2 and identification of therapeutic vulnerabilities

Abstract We constructed models of nerve sheath tumors that arise in Neurofibromatosis Type 1 (NF1) patients and conducted therapeutics discovery using synthetic lethal pharmacogenomic screens. Given both plexiform neurofibromas and malignant peripheral nerve sheath tumors (MPNSTs) arise within the Schwann cell lineage, we developed a drug discovery pipeline to identify targeted therapeutics for treating NF1-related neoplasia. Using CRISPR/Cas9, immortalized human Schwann cell lines were created lacking the NF1 gene or NF1 and components of Polycomb Repressive Complex 2 (PRC2), such as SUZ12. ~80% of all MPNST harbor loss of function mutations in PRC2 genes, which is highly suggestive that perturbation of epigenetic homeostasis plays a role in malignant transformation of neurofibromas. Our models mimic the genetics of MPNSTs and allowed us to identify selectively lethal drugs which exploit vulnerabilities specific to these genetic drivers. We describe the identification of these novel drugs, extensive in vivo testing in models of MPNST, and mechanistic studies to explain why they act specifically on MPNSTs. We identified compounds showing selective lethality towards NF1/SUZ12 double mutant cells. These include drugs affecting epigenetic homeostasis, such as HDAC inhibitors (HDACi). Moreover, many of these drugs showed strong synergy when tested in combination with a MEK inhibitor (MEKi) against NF1/SUZ12 deficient human Schwann and MPNST cell lines. We investigated the mechanism of this synergy using genetics, transcriptome, and proteome analysis. Interestingly, these mechanistic studies revealed possible emerging avenues of resistance the cells are utilizing to compensate for and survive therapeutic intervention. For instance, proteomics analysis of PRC2 deficient MPNST cell lines treated with combination therapy of MEKi and HDACi indicates activation of specific survival and stress response pathways. Targeting these pathways in conjunction with the therapeutics we have identified could prevent emergence of resistance and tumor escape. Clinically interesting drug candidates were advanced and tested as single agents and in combination in multiple in vivo models of MPNST (including patient derived and cell line xenografts). The FDA approved drugs vorinostat (HDACi) and selumetinib (MEKi) have shown dramatic efficacy, with combination therapy exhibiting strong synergy in vivo. This includes durable responses in survival studies and the ability to dramatically shrink established tumors, with treated tumors showing markers of apoptosis. The discovery of novel agents effective against several models of MPNST is exciting as there are currently no approved targeted therapies for MPNSTs. Our results implicate targeting of epigenetic homeostasis, in combination with MEKi, as a major vulnerability of MPNSTs deficient for PRC2 activity. Citation Format: Kyle B. Williams, Alex Larsson, Justin Tibbits, Christopher L. Moertel, David A. Largaespada. Creation of malignant peripheral nerve sheath tumor models deficient for polycomb repressive complex 2 and identification of therapeutic vulnerabilities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1614.

Clinical characteristics and genetic testing outcome of suspected hereditary peripheral nerve sheath tumours in a tertiary cancer institution in Singapore

BackgroundPeripheral Nerve Sheath Tumors (PNST) are a diverse group of mostly benign tumours uncommon in the general population. About 5–10% of PNSTs are hereditary, predominantly arising from germline variants in NF1, NF2, SMARCB1, or LZTR1 gene.MethodsWe reviewed the clinical characteristics and genetic testing results of patients referred to the NCIS Adult Cancer Genetics Clinic for suspected hereditary PNST.Results3,001 patients suspected to have various hereditary cancer syndromes were evaluated between year 2000 to March 2021. 13 (0.4%) were clinically diagnosed to have hereditary PNSTs. The majority were male (54%), with a median age at presentation to the genetics clinic of 29 years (range 19–48). 11/13 (85%) patients had multiple PNSTs, 12/13 (92%) had young onset PNSTs, 5/13 (38.5%) had personal and family history of PNST. 11/13 patients (85%) had clinical features of neurofibromatosis type 1 (NF1) including one patient who also fulfilled clinical criteria of neurofibromatosis type 2 (NF2); 2/13 (14%) had multiple schwannomas. Four patients underwent multi-gene panel testing, including one patient with clinical NF1, one patient who met both clinical NF1 and NF2 criteria, and two patients with multiple schwannomas. The patient with clinical features of NF1 was heterozygous for a pathogenic c. 2033dup variant in the NF1 gene. The patient with both NF1/NF2 features was heterozygous for a novel c.732 T > A nonsense variant in the NF2 gene. The two patients with multiple schwannomas were heterozygous for a pathogenic/likely pathogenic variant in the LZTR1 gene and are the first LZTR1-positive schwannomatosis patients reported in Asia.ConclusionHereditary PNSTs are rare referrals to an adult cancer genetics clinic. NF1 is the most common PNST seen. LZTR1 variants may be the underlying cause in Asian patients with multiple schwannomatosis.