Neurofibromatosis Type 1 Mutations Research Articles

Topical delivery of mitogen-activated protein kinase inhibitor binimetinib prevents the development of cutaneous neurofibromas in neurofibromatosis type 1 mutant mice

Cutaneous neurofibromas (cNFs) are a hallmark of patients with the neurofibromatosis type 1 (NF1) genetic disorder. These benign nerve sheath tumors, which can amount to thousands, develop from puberty onward, often cause pain and are considered by patients to be the primary burden of the disease. Mutations of NF1, encoding a negative regulator of the RAS signaling pathway, in the Schwann cell (SCs) lineage are considered to be at the origin of cNFs. The mechanisms governing cNFs development are poorly understood, and therapeutics to reduce cNFs are missing, mainly due to the lack of appropriate animal models. To address this, we designed the Nf1-KO mouse model that develops cNFs. Using this model, we found that cNFs development is a singular event and goes through 3 successive stages: initiation, progression, and stabilization characterized by changes in the proliferative and MAPK activities of tumor SCs. We found that skin trauma accelerated the development of cNFs and further used this model to explore the efficacy of the MEK inhibitor binimetinib to cure these tumors. We showed that while topically delivered binimetinib has a selective and minor effect on mature cNFs, the same drug prevents their development over long periods.

Germline Neurofibromin 1 mutation enhances the anti-tumour immune response and decreases juvenile myelomonocytic leukaemia tumourigenicity.

Juvenile myelomonocytic leukaemia (JMML) is an aggressive paediatric leukaemia characterized by mutations in five canonical RAS pathway genes, including the NF1 gene. JMML is driven by germline NF1 gene mutations, with additional somatic aberrations resulting in the NF1 biallelic inactivation, leading to disease progression. Germline mutations in the NF1 gene alone primarily cause benign neurofibromatosis type 1 (NF1) tumours rather than malignant JMML, yet the underlying mechanism remains unclear. Here, we demonstrate that with reduced NF1 gene dose, immune cells are promoted in anti-tumour immune response. Comparing the biological properties of JMML and NF1 patients, we found that not only JMML but also NF1 patients driven by NF1 mutations could increase monocytes generation. But monocytes cannot further malignant development in NF1 patients. Utilizing haematopoietic and macrophage differentiation from iPSCs, we revealed that NF1 mutations or knockout (KO) recapitulated the classical haematopoietic pathological features of JMML with reduced NF1 gene dose. NF1 mutations or KO promoted the proliferation and immune function of NK cells and iMacs derived from iPSCs. Moreover, NF1-mutated iNKs had a high capacity to kill NF1-KO iMacs. NF1-mutated or KO iNKs administration delayed leukaemia progression in a xenograft animal model. Our findings demonstrate that germline NF1 mutations alone cannot directly drive JMML development and suggest a potential cell immunotherapy for JMML patients.

Abstract 5170: STING inflames NF1 malignancies for immunotherapy

Abstract Introduction: Neurofibromatosis Type 1 (NF1) is caused by mutations in the NF1 gene that encodes neurofibromin, a RAS GTPase-Activating Protein. Inactivating NF1 mutations result in hyperactivation of RAS-mediated signaling. NF1 patients develop benign tumors on the skin and along nerves in the spinal cord and brain, and ~10% of these progress to Malignant Peripheral Nerve Sheath Tumors (MPNST). Attempts to inhibit RAS-signaling to treat MPNST have not worked in clinical trials. Surgical removal is the only cure for MPNST, which is challenging due to large tumor size and/or proximity to nerves. MPNSTs often recur, metastasize, and respond poorly to chemo- and radiotherapy. As a result, MPNSTs are the leading cause of death in NF1 patients. Immune Checkpoint Blockade (ICB) is an approach to treat inoperable, undruggable cancers. Immune checkpoint proteins (ICPs) terminate normal immune responses to prevent collateral tissue damage. Cancer cells hijack this mechanism and express ICPs to avoid immune detection. ICB disrupts this process, enhancing antitumor immunity. Monoclonal antibodies (mABs) that disrupt the interaction between Programmed Cell Death Receptor 1 (PD-1) and its ligand Programmed Cell Death Ligand 1 (PD-L1) are a widely used ICB therapy. Having a T cell-enriched hot tumor microenvironment (TME) is required for successful ICB. However, MPNSTs lack a T cell-inflamed TME and respond poorly to ICB therapy. Activation of the protein “stimulator of interferon genes” (STING) enhances anti-tumor immunity via induction of pro-inflammatory cytokines, thus increasing T cell infiltration into the TME. We hypothesized that reprogramming the MPNST TME by STING pathway activation would turn cold MPNSTs into hot tumors amenable to ICB. Methods: We treated mouse MPNSTs with STING agonist or STING agonist + anti-PD-1/anti-PD-L1 mAb. Tumor size was measured throughout treatment. The mice were sacrificed and tumor tissue was analyzed for STING pathway activation, T cell infiltration, cell proliferation, and apoptosis. MPNST allograft tumors in athymic mice were controls. Results: STING pathway activation and increased T cell presence was observed in STING agonist-treated MPNSTs compared to vehicle-treated. MPNSTs treated with STING agonist alone or STING agonist + PD-1/PD-L1 mAbs showed less tumor growth relative to vehicle. Importantly, STING agonist + PD-1/PD-L1 mAb-treated tumors showed significant cell death increase while cell proliferation remained unchanged. Interestingly, tumors in athymic mice continued to grow despite treatment suggesting the antitumor effects seen in immunocompetent mice were mediated by T cells. Conclusions: Our data show that MPNSTs can become T cell-rich tumors by activating STING signaling. Reprogramming the TME made MPNSTs susceptible to immune destruction by ICB therapy. Our studies support this novel treatment strategy for MPNST, an aggressive, deadly tumor for which no molecular therapy currently exists. Citation Format: Nipunika Somatilaka, Laasya Madana, Ali Sadek, Renee M. McKay, Lu Q. Le. STING inflames NF1 malignancies for immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5170.

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.

High-yield identification of pathogenic NF1 variants by skin fibroblast transcriptome screening after apparently normal diagnostic DNA testing.

Neurofibromatosis type 1 (NF1) is caused by inactivating mutations in NF1. Due to the size, complexity, and high mutation rate at the NF1 locus, the identification of causative variants can be challenging.To obtain a molecular diagnosis in 15 individuals meeting diagnostic criteria for NF1, we performed transcriptome analysis (RNA-seq) on RNA obtained from cultured skin fibroblasts. In each case, routine molecular DNA diagnostics had failed to identify a disease-causing variant in NF1.A pathogenic variant or abnormal mRNA splicing was identified in 13 cases: 6 deep intronic variants and 2 transposon insertions causing noncanonical splicing, 3 postzygotic changes, 1 branch point mutation and, in 1 case, abnormal splicing for which the responsible DNA change remains to be identified. These findings helped resolve the molecular findings for an additional 17 individuals in multiple families with NF1, demonstrating the utility of skin-fibroblast-based transcriptome analysis for molecular diagnostics. RNA-seq improves mutation detection in NF1 and provides a powerful complementary approach to DNA-based methods. Importantly, our approach is applicable to other genetic disorders, particularly those caused by a wide variety of variants in a limited number of genes and specifically for individuals in whom routine molecular DNA diagnostics did not identify the causative variant.

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.

Clinical characteristics and in silico analysis of congenital pseudarthrosis of the tibia combined with neurofibromatosis type 1 caused by a novel NF1 mutation.

Congenital pseudarthrosis of the tibia (CPT) is a rare congenital bone malformation, which has a strong relationship with Neurofibromatosis type 1 (NF1). NF1 is an autosomal dominant disease leading to multisystem disorders. Here, we presented the genotypic and phenotypic characteristics of one unique case of a five-generation Chinese family. The proband was CPT accompanied with NF1 due to NF1 mutation. The proband developed severe early-onset CPT combined with NF1 after birth. Appearance photos and X-ray images of the left limb of the proband showed significant bone malformation. Slit-lamp examination showed Lisch nodules in both eyes of the proband. Whole-exome sequencing (WES) and Sanger sequencing confirmed the truncation variant of NF1 (c.871G>T, p. E291*). Sequence conservative and evolutionary conservation analysis indicated that the novel mutation (p.E291*) was highly conserved. The truncated mutation led to the loss of functional domains, including CSRD, GRD, TBD, SEC14-PH, CTD, and NLS. It may explain why the mutation led to a severe clinical feature. Our report expands the genotypic spectrum of NF1 mutations and the phenotypic spectrum of CPT combined with NF1.

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.

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.

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.

Early prediction of functional prognosis in neurofibromatosis type 2 patients based on genotype–phenotype correlation with targeted deep sequencing

Regardless of treatment, the clinical progression of neurofibromatosis type 2 (NF2), particularly in terms of hearing, swallowing, and gait, tend to worsen throughout the patients’ lives. We performed a retrospective analysis of functional outcomes in Japanese NF2 patients to predict their functional prognosis. We analyzed genotype–phenotype correlation based on genetic data from a cohort of 57 patients with a mean follow-up of 14.5 ± 6.0 years. Their functional outcomes, including hearing, swallowing, and ambulation, were reviewed. Performing a targeted deep sequencing, germline NF2 mutations were identified in 28 patients (49.1%), and mosaic NF2 was identified in 20 patients (20, 35.0%). The functional preservation period and outcome differed significantly depending on clinical/genetic factors. Among these factors, “Truncating”, “Mosaic”, and “Age of symptom onset ≥ 25” had the most significant effects on functional disability. By applying a combination of an NF2 mutation type/location, and age of symptom onset, we classified different degrees of functional preservation and progression, schwannoma growth rate and total interventions per year per patient. The prediction of detailed functional outcomes in NF2 patients can plan better strategies for life-long disease management and social integration.

A multicenter, open-label, single-arm, phase 1 dose-escalation study to evaluate the safety, tolerability, and anti-tumor activity of FCN-159 in adults with neurofibromatosis type 1.

3011 Background: Neurofibromatosis type 1 (NF1) is an autosomal-dominant genetic disease that increases susceptibility to malignant tumors. Up to 50% of patients with NF1 present with plexiform neurofibroma (PN). Surgery, a common treatment strategy for patients with PN, has limited efficacy. NF1 is caused by mutations in the gene that encodes neurofibromin; the NF1 mutation then leads to tumorigenesis via dysregulation of the Ras/Raf/MEK/ERK pathway. FCN-159 is anti-tumorigenic via highly potent, selective inhibition of MEK1/2. This study aims to assess the safety of FCN-159 in patients with NF1-related PN. Methods: This is a multicenter, open-label, single-arm, phase 1 dose-escalation and phase 2 dose-expansion study (NCT04954001). Patients with NF1-related PN that was not completely resectable or not suitable for surgery were enrolled in the study; they received FCN-159 monotherapy continuously in 28-day cycles. Here, we report safety and clinical efficacy data from adults enrolled in phase 1. Results: As of the data cutoff of December 1, 2021, 19 adults from 3 hospitals in China have been enrolled in the phase 1 dose-escalation study, 3 in 4 mg, 4 in 6 mg, 8 in 8 mg, and 4 in 12 mg. The most common neurofibroma-related complications were disfigurement and pain, occurring in 10 patients (52.6%) and 4 patients (21.1%) at baseline, respectively. Four patients experienced dose-limiting toxicity; G3 folliculitis was reported in 1 patient (16.7%) receiving the 8-mg dose and 3 (100%) patients receiving the 12-mg dose. The maximum tolerated dose was determined to be 8 mg. Study-drug-related treatment-emergent adverse events (TEAEs) were observed in all 19 patients (100%); the majority were grade 1 or 2 in severity. Nine (47.4%) patients reported grade 3 study drug-related TEAEs; 4 patients experienced paronychia and 5 experienced folliculitis, which were the most common causes of dose reduction (42.1%) and drug interruption (21.2%). One patient experienced a serious adverse event of rhegmatogenous retinal detachment, but this was considered unrelated to the study drug as it was preexisting at baseline. Of the 16 patients with at least 1 post-baseline tumor assessment, all (100%) had reduced tumor size and 6 (37.5%) had a reduction in tumor size of > 20%. Three out of 6 patients with a second tumor assessment result had further tumor shrinkage; tumor volumes in the remaining 3 patients were similar to those at first assessment. The largest reduction in tumor size was 84.2%. Conclusions: Overall, FCN-159 at 8 mg is well tolerated, with easy to manage adverse events, and showed promising anti-neurofibroma activity in phase 1; this warrants further investigation in a phase 2 study on efficacy and safety in this indication. Clinical trial information: NCT04954001.

Mutation of PTPN11 (Encoding SHP-2) Promotes MEK Activation and Malignant Progression in Neurofibromin-Deficient Cells in a Manner Sensitive to BRAP Mutation.

Germline mutations of NF1 cause neurofibromatosis type 1 (NF1) through the activation of the RAS signaling pathway, and some NF1 patients develop malignant peripheral nerve sheath tumors (MPNSTs). Here, we established subclones of the human NF1-MPNST cell line sNF96.2 that manifest increased tumorigenic activity and increased phosphorylation of the protein kinases MEK and Akt relative to the parental cells. Genomic DNA sequencing identified 14 additional heterozygous mutations within the coding regions of 13 cancer- and other disease-related genes in these subclones. One of these genes, PTPN11, encodes SHP-2, and the forced expression of the identified G503V mutant of SHP-2 increased both tumorigenic activity and MEK phosphorylation in parental sNF96.2 cells, suggesting that the combination of PTPN11 and NF1 mutations induces the pathological activation of the RAS pathway. These effects of SHP-2 (G503V) were inhibited by the coexpression of the G370A mutant of BRAP, which was also detected in the highly malignant subclones, and this inhibition was accompanied by the calpain-dependent cleavage of SHP-2 (G503V). The cleavage of SHP-2 (G503V) and suppression of MEK phosphorylation mediated by BRAP (G370A) were not detected in NF1-intact (HeLa) cells. Tumor promotion by SHP-2 (G503V) and its suppression by BRAP (G370A) may serve as a basis for the development of new treatment strategies for NF1.

Novel patient-derived xenograft and cell line models for therapeutic screening in NF2-associated schwannoma.

Treatment of schwannomas in patients with neurofibromatosis type 2 (NF2) is extremely unsatisfactory, and innovative therapeutic approaches are urgently needed. However, the lack of clinically relevant NF2-associated schwannoma models has severely hampered drug discovery in this rare disease. Here we report the first establishment and characterization of patient-derived xenograft (PDX) and cell line models of NF2-associated schwannoma, which recapitulates the morphological and histopathological features of patient tumors, retain patient NF2 mutations, and maintain gene expression profiles resembling patient tumor profiles with the preservation of multiple key signaling pathways commonly dysregulated in human schwannomas. Using gene expression profiling, we identified elevated PI3K/AKT/mTOR networks in human NF2-associated vestibular schwannomas. Using high-throughput screening of 157 inhibitors targeting the PI3K/AKT/mTOR pathways in vitro, we identified a dozen inhibitors (such as BEZ235, LY2090314, and AZD8055) with significant growth-suppressive effects. Interestingly, we observed that three cell lines displayed differential therapeutic responses to PI3K/AKT/mTOR inhibitors. Furthermore, we demonstrated that two orally bioavailable inhibitors, AZD8055 and PQR309, suppressed NF2-associated schwannoma growth both in vitro and in vivo. In conclusion, our novel patient-derived models of NF2-associated schwannoma closely mimic the phenotypes and genotypes of patient tumors, making them reliable preclinical tools for testing novel personalized therapies. © 2022 The Pathological Society of Great Britain and Ireland.

Detection of malignant peripheral nerve sheath tumors in patients with neurofibromatosis using aneuploidy and mutation identification in plasma.

Malignant peripheral nerve sheath tumors (MPNST) are the deadliest cancer that arises in individuals diagnosed with neurofibromatosis and account for nearly 5% of the 15,000 soft tissue sarcomas diagnosed in the United States each year. Comprised of neoplastic Schwann cells, primary risk factors for developing MPNST include existing plexiform neurofibromas (PN), prior radiotherapy treatment, and expansive germline mutations involving the entire NF1 gene and surrounding genes. PN develop in nearly 30-50% of patients with neurofibromatosis type 1 (NF1) and most often grow rapidly in the first decade of life. One of the most important aspects of clinical care for NF1 patients is monitoring PN for signs of malignant transformation to MPNST that occurs in 10-15% of patients. We perform aneuploidy analysis on ctDNA from 883 ostensibly healthy individuals and 28 patients with neurofibromas, including 7 patients with benign neurofibroma, 9 patients with PN and 12 patients with MPNST. Overall sensitivity for detecting MPNST using genome wide aneuploidy scoring was 33%, and analysis of sub-chromosomal copy number alterations (CNAs) improved sensitivity to 50% while retaining a high specificity of 97%. In addition, we performed mutation analysis on plasma cfDNA for a subset of patients and identified mutations in NF1, NF2, RB1, TP53BP2, and GOLGA2. Given the high throughput and relatively low sequencing coverage required by our assay, liquid biopsy represents a promising technology to identify incipient MPNST.

211 Deep Phenotyping Reveals Germline Determinants of Disease Severity in Neurofibromatosis Type 2

INTRODUCTION: Neurofibromatosis type 2 (NF2) is an autosomal dominant tumor predisposition syndrome with central and peripheral nervous system tumors and non-neoplastic manifestations including peripheral neuropathy. NF2 presents with a large variation in penetrance and severity. Although germline nonsense and frameshift NF2mutations are hypothesized to confer severe disease, the relationship between mutation type and manifestations of this disease is not completely understood. METHODS: Patients (n = 169) with NF2 (Manchester criteria) were enrolled in a Natural History protocol (NCTNCT00598351). Deep phenotypic profiles were created (serially for 5 years) including clinical evaluations, self-reported functional measures, lifetime interventions (surgical, radiation and drug treatments), and imaging (tumor number, type and volume using volumetric MRI of the neuroaxis). Validated germline mutation data (n = 68) was used to examine relationships between genotype and phenotype with attention to NF2 mutation type (indel/large deletion), genomic effect (missense/nonsense/frameshift), predicted protein effect (truncating/non-truncating) and location (exonic/intronic/splice-site). RESULTS: Tumor burden varied greatly between patients (tumor number range 1-165, median 25). We found that cranial meningiomas were a major determinant of total tumor burden. Total tumor burden (number and volume) was associated with worse KPS and decline in KPS over the study protocol (p < 0.001). We found that truncating mutations in exons 11-12 were associated with more severe disease in terms of tumor number on MRI (p = 0.0439). CONCLUSION: This is the first large scale study to deeply phenotype patients with NF2 including longitudinal analysis and demonstrates several previously unrecognized trends related to germline mutations type, imaging findings, and measures of disease severity.

Neurofibromatosis type 1 families with first-degree relatives harbouring distinct NF1 pathogenic variants. Genetic counselling and familial diagnosis: what should be offered?

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder caused by pathogenic variants in NF1. Recently, NF1 testing has been included as a clinical criterion for NF1 diagnosis. Additionally, preconception...

Immune system changes in the pathogenesis of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a hereditary tumor syndrome occurring with a frequency of 1: 3000 of the population. NF1 is caused by germline heterozygous mutations in the NF1 gene, which encodes the oncosuppressor neurofibromin. The disease has a specific progressive course with multiple neurofibromas, in the initiation and growth of which NF1+/ – mast cells, macrophages and lymphocytes play an important role. Accordingly, the deficiency of neurofibromin impairs the differentiation and correct functioning of immune system cells. This is evidenced by the increased risk of leukemia in patients with NF1 and the role of NF1 mutations in the development of sporadic hematological malignancies. The development of neurofibromas is associated with the fact that NF1–/ – Schwann cells stimulate the migration of mast cells into the tumor microenvironment, which actively degranulate. The released cytokines promote neoangiogenesis, inflammation, fibroblast proliferation and the production of excess collagen. Therefore, in the treatment of NF1, the use of ketotifen and a kit/ fms kinase inhibitor is recommended. Macrophages and T-lymphocytes in neurofibromas do not provide an antitumor response, but promote inflammation and tumor growth. They produce STAT3 (signal transducer and activator of transcription 3), TGF-β, EGFR, IL-6, IL-4, and PD-1. Therefore, a promising direction is NF1 therapy with STAT3 inhibitors and immune checkpoint inhibitors that block programmed cell death ligand 1 (PD-L1). Activation of MEK signaling pathways in NF1 leads to PD-L1 stimulation; therefore, MEK inhibitors, which also suppress the RAS/RAF/MEK/ERK system, turned out to be effective in the treatment of NF1. For the treatment of sporadic malignant neoplasms, in the development of which NF1 mutations play a role, the developed methods of NF1 therapy can be used.

Case series of congenital pseudarthrosis of the tibia unfulfilling neurofibromatosis type 1 diagnosis: 21% with somatic NF1 haploinsufficiency in the periosteum.

Up to 84% of patients with congenital pseudarthrosis of the tibia (CPT) present with neurofibromatosis type 1 (NF1) (NF1-CPT). However, the etiology of CPT not fulfilling the NIH diagnostic criteria for NF1 (non-NF1-CPT) is not well understood. Here, we collected the periosteum tissue from the pseudarthrosis (PA) site of 43 non-NF1-CPT patients and six patients with NF1-CPT, together with the blood or oral specimen of trios (probands and unaffected parents). Whole-exome plus copy number variation sequencing, multiplex ligation-dependent probe amplification (MLPA), ultra-high amplicon sequencing, and Sanger sequencing were employed to identify pathogenic variants. The result showed that nine tissues of 43 non-NF1-CPT patients (21%) had somatic mono-allelic NF1 inactivation, and five of six NF1-CPT patients (83.3%) had bi-allelic NF1 inactivation in tissues. However, previous literature involving genetic testing did not reveal somatic mosaicism in non-NF1-CPT patients so far. In NF1-CPT patients, when the results from earlier reports and the present study were combined, 66.7% of them showed somatic NF1 inactivation in PA tissues other than germline inactivation. Furthermore, no diagnostic variants from other known genes (GNAS, AKT1, PDGFRB, and NOTCH3) related to skeletal dysplasia were identified in the nine NF1 positive non-NF1-CPT patients and six NF1-CPT patients. In conclusion, we detected evident somatic mono-allelic NF1 inactivation in the non-NF1-CPT. Thus, for pediatric patients without NF1 diagnosis, somatic mutations in NF1 are important.