Neurofibromatosis Type 1 Mutations Research Articles

Simultaneous Detection of NF1, SPRED1, LZTR1, and NF2 Gene Mutations by Targeted NGS in an Italian Cohort of Suspected NF1 Patients.

Neurofibromatosis type 1 (NF1) displays overlapping phenotypes with other neurocutaneous diseases such as Legius Syndrome. Here, we present results obtained using a next generation sequencing (NGS) panel including NF1, NF2, SPRED1, SMARCB1, and LZTR1 genes on Ion Torrent. Together with NGS, the Multiplex Ligation-Dependent Probe Amplification Analysis (MLPA) method was performed to rule out large deletions/duplications in NF1 gene; we validated the MLPA/NGS approach using Sanger sequencing on DNA or RNA of both positive and negative samples. In our cohort, a pathogenic variant was found in 175 patients; the pathogenic variant was observed in NF1 gene in 168 cases. A SPRED1 pathogenic variant was also found in one child and in a one year old boy, both NF2 and LZTR1 pathogenic variants were observed; in addition, we identified five LZTR1 pathogenic variants in three children and two adults. Six NF1 pathogenic variants, that the NGS analysis failed to identify, were detected on RNA by Sanger. NGS allows the identification of novel mutations in five genes in the same sequencing run, permitting unambiguous recognition of disorders with overlapping phenotypes with NF1 and facilitating genetic counseling and a personalized follow-up.

Clinical characterization of children and adolescents with NF1 microdeletions

PurposeAn estimated 5–11% of patients with neurofibromatosis type 1 (NF1) harbour NF1 microdeletions encompassing the NF1 gene and its flanking regions. The purpose of this study was to evaluate the clinical phenotype in children and adolescents with NF1 microdeletions.MethodsWe retrospectively analysed 30 children and adolescents with NF1 microdeletions pertaining to externally visible neurofibromas. The internal tumour load was determined by volumetry of whole-body magnetic resonance imaging (MRI) in 20 children and adolescents with NF1 microdeletions. Furthermore, the prevalence of global developmental delay, autism spectrum disorder and attention deficit hyperactivity disorder (ADHD) were evaluated.ResultsChildren and adolescents with NF1 microdeletions had significantly more often cutaneous, subcutaneous and externally visible plexiform neurofibromas than age-matched patients with intragenic NF1 mutations. Internal neurofibromas were detected in all 20 children and adolescents with NF1 microdeletions analysed by whole-body MRI. By contrast, only 17 (61%) of 28 age-matched NF1 patients without microdeletions had internal tumours. The total internal tumour load was significantly higher in NF1 microdeletion patients than in NF1 patients without microdeletions. Global developmental delay was observed in 28 (93%) of 30 children with NF1 microdeletions investigated. The mean full-scale intelligence quotient in our patient group was 77.7 which is significantly lower than that of patients with intragenic NF1 mutations. ADHD was diagnosed in 15 (88%) of 17 children and adolescents with NF1 microdeletion. Furthermore, 17 (71%) of the 24 patients investigated had T-scores ≥ 60 up to 75, indicative of mild to moderate autistic symptoms, which are consequently significantly more frequent in patients with NF1 microdeletions than in the general NF1 population. Also, the mean total T-score was significantly higher in patients with NF1 microdeletions than in the general NF1 population.ConclusionOur findings indicate that already at a very young age, NF1 microdeletions patients frequently exhibit a severe disease manifestation which requires specialized long-term clinical care.

In Vitro Effect of Dovitinib (TKI258), a Multi-Target Angiokinase Inhibitor on Aggressive Meningioma Cells

Background: Meningiomas represent ∼30% of primary central nervous system (CNS) tumors. Although advances in surgery and radiotherapy have significantly improved survival, there remains an important subset of patients whose tumors have more aggressive behavior and are refractory to conventional therapy. Recent advances in molecular genetics and epigenetics suggest that this aggressive behavior may be due to the deletion of the DNA repair and tumor suppressor gene, CHEK2, neurofibromatosis Type 2 (NF2) mutation on chromosome 22q12, and genetic abnormalities in multiple RTKs including FGFRs. Management of higher-grade meningiomas, such as anaplastic meningiomas (AM: WHO grade III), is truly challenging and there isn’t an established chemotherapy option. We investigate the effect of active multi tyrosine receptor kinase inhibitor Dovitinib at stopping AM cell growth in in vitro with either frequent codeletion or mutated CHEK2 and NF2 gene.Methods: Treatment effects were assessed using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, western blot analysis, caspases assay, and DNA fragmentation assay.Results: Treatment of CH157MN and IOMM-Lee cells with Dovitinib suppressed multiple angiokinases—mainly FGFRs, leading to suppression of downstream signaling by RAS–RAF–MAPK molecules and PI3K–AKT molecules which are involved in cell proliferation, cell survival, and tumor invasion. Furthermore, Dovitinib induced apoptosis via downregulation of survival proteins (Bcl-XL), and over-expression of apoptotic factors (Bax and caspase-3) regardless of CHEK2 and NF2 mutation status.Conclusions: This study establishes the groundwork for the development of Dovitinib as a therapeutic agent for high-grade AM with either frequent codeletion or mutated CHEK2 and NF2, an avenue with high translational potential.

Mosaic Neurofibromatosis Type 1 With Multiple Cutaneous Diffuse and Plexiform Neurofibromas of the Lower Leg

Neurofibromatosis type 1 (NF1) is an autosomal dominant hereditary disease with complete penetrance and a very variable phenotype. Recent research has shown that postzygotic NF1 gene mutations occur to a far greater extent than previously thought. The phenotype of affected individuals reflects the time of somatic mutation and the phenotype is correspondingly diverse. This report describes histological and genetic findings in a case of mosaic NF1, the clinical control of which documents almost stationary skin findings over a period of 9 years. The 55-year-old female first presented for advice on a strip of nodular skin tumours of the calf skin. She had no hallmarks of NF1. It was only 9 years later that she had the skin tumours removed, all of which were partially diffuse and partially plexiform neurofibroma. The genetic examination showed an atypical large deletion of the NF1 gene in the skin tumours, but not in overlying skin or blood. Segmental NF1 is a distinct type of mosaic/somatic NF1 mutation. The phenotype of diffuse and plexiform skin neurofibromas can resemble cutaneous neurofibroma. Surgical therapy for segmental neurofibromatosis does not differ from the concepts for treating nerve sheath tumours in NF1 patients with a germline NF1 mutation.

SAT-222 Aggressive Phenotype Pheochromocytoma Associated with NF-1 and BRCA Mutation

IntroductionPheochromocytomas are catecholamine-secreting tumors of the adrenal medulla that occur sporadically or with familial association. Familial predilection occurs in those with multiple endocrine neoplasia type 2, von Hippel-Lindau disease, and neurofibromatosis Type 1 (NF-1). To date, more than 21 gene mutations have been identified that are involved in the development of pheochromocytomas. However, co-existence of two different mutations such as NF-1 and BRCA gene mutations with pheochromocytoma has not been well described.Clinical CaseA 40 year-old woman with NF-1 and recently diagnosed left breast invasive ductal carcinoma, estrogen positive, progesterone positive, HER-2 negative BRCA2 positive breast cancer and right breast lobular carcinoma in situ underwent staging CT scan. A 2.7 cm left adrenal incidentaloma with heterogeneous texture and 69–100 HU was discovered. Symptom review revealed chronic headaches and increasing frequency of anxiousness and irritability. She had no personal or family history of hypertension. Laboratory analysis showed elevated catecholamine levels included plasma normetanephrine of 2.8 nmol/L (normal <0.9), metanephrine of 0.9 nmol/L (normal <0.5), 24 hour urine metanephrine 498 mcg/24 hr (normal <180) and 24 hour urine normetanephrine of 1,152 mcg/24 hr (normal <451). Findings were consistent with adrenal pheochromocytoma.She was immediately started on phenoxybenzamine and encouraged to increase fluid intake to expand intravascular volume before surgery. She underwent laparoscopic left partial adrenalectomy fourteen days later. Surgical pathology revealed a 3.0 cm pheochromocytoma in a background of nodular hyperplasia of the medulla, described as an aggressive tumor phenotype based on morphological features.ConclusionsIt has been estimated that 1.5–14% of adrenal incidentalomas are pheochromocytomas. While only 3% of NF-1 patients have pheochromocytomas, 20–50% of NF-1 patients with concurrent hypertension have underlying chromaffin tumors. This association is significant when compared to the pheochromocytoma incidence of 0.1% in all hypertensive individuals. Interestingly, germline mutations of BRCA-1 associated protein-1 gene have been reported in patients with paragangliomas, therefore it may be plausible to consider interactions between NF-1 and breast cancer BRCA-2 gene mutations, resulting in an unusual and more aggressive pheochromocytoma phenotype, even when detected at an early stage, as in this case. It is also important to recognize and adequately treat pheochromocytoma prior to having surgery to avoid possible intraoperative hypertensive crisis, a concept that was underscored in this particular case when the patient was relatively asymptomatic and entirely normotensive preoperatively.

New Model Systems and the Development of Targeted Therapies for the Treatment of Neurofibromatosis Type 1-Associated Malignant Peripheral Nerve Sheath Tumors.

Neurofibromatosis Type 1 (NF1) is a common genetic disorder and cancer predisposition syndrome (1:3000 births) caused by mutations in the tumor suppressor gene NF1. NF1 encodes neurofibromin, a negative regulator of the Ras signaling pathway. Individuals with NF1 often develop benign tumors of the peripheral nervous system (neurofibromas), originating from the Schwann cell linage, some of which progress further to malignant peripheral nerve sheath tumors (MPNSTs). Treatment options for neurofibromas and MPNSTs are extremely limited, relying largely on surgical resection and cytotoxic chemotherapy. Identification of novel therapeutic targets in both benign neurofibromas and MPNSTs is critical for improved patient outcomes and quality of life. Recent clinical trials conducted in patients with NF1 for the treatment of symptomatic plexiform neurofibromas using inhibitors of the mitogen-activated protein kinase (MEK) have shown very promising results. However, MEK inhibitors do not work in all patients and have significant side effects. In addition, preliminary evidence suggests single agent use of MEK inhibitors for MPNST treatment will fail. Here, we describe the preclinical efforts that led to the identification of MEK inhibitors as promising therapeutics for the treatment of NF1-related neoplasia and possible reasons they lack single agent efficacy in the treatment of MPNSTs. In addition, we describe work to find targets other than MEK for treatment of MPNST. These have come from studies of RAS biochemistry, in vitro drug screening, forward genetic screens for Schwann cell tumors, and synthetic lethal screens in cells with oncogenic RAS gene mutations. Lastly, we discuss new approaches to exploit drug screening and synthetic lethality with NF1 loss of function mutations in human Schwann cells using CRISPR/Cas9 technology.

Human iPSC-Derived Neurons and Cerebral Organoids Establish Differential Effects of Germline NF1 Gene Mutations.

SummaryNeurofibromatosis type 1 (NF1) is a common neurodevelopmental disorder caused by a spectrum of distinct germline NF1 gene mutations, traditionally viewed as equivalent loss-of-function alleles. To specifically address the issue of mutational equivalency in a disease with considerable clinical heterogeneity, we engineered seven isogenic human induced pluripotent stem cell lines, each with a different NF1 patient NF1 mutation, to identify potential differential effects of NF1 mutations on human central nervous system cells and tissues. Although all mutations increased proliferation and RAS activity in 2D neural progenitor cells (NPCs) and astrocytes, we observed striking differences between NF1 mutations on 2D NPC dopamine levels, and 3D NPC proliferation, apoptosis, and neuronal differentiation in developing cerebral organoids. Together, these findings demonstrate differential effects of NF1 gene mutations at the cellular and tissue levels, suggesting that the germline NF1 gene mutation is one factor that underlies clinical variability.

Genomics, Epigenetics, and Hearing Loss in Neurofibromatosis Type 2.

In this review, we discuss current knowledge about the genetics and epigenetics of vestibular schwannoma (VS) in relation to hearing loss. A multistep and sequential genetic algorithm suitable for the identification of Neurofibromatosis Type 2 (NF2) constitutional and somatic mutations is discussed. A review was performed of the English literature from 1990 to 2019 using PubMed regarding genetics and epigenetics of vestibular schwannoma and NF2. NF2 is a genetic disorder characterized by NF2 mutations that affect the function of a tumor suppressor called merlin. In particular, individuals with NF2 develop bilateral VS that can lead to hearing loss and even deafness. Recent advances in genetic and epigenetic studies have improved our understanding of the genotype-phenotype relationships that affect hearing in NF2 patients. Specific constitutional NF2 mutations including particular truncating, deletion, and missense mutations have been associated with poorer hearing outcomes and more severe clinical manifestations. Epigenetic events, such as DNA methylation and histone modifications, also contribute to the development and progression of hearing loss in NF2 patients. Furthermore, the accumulation of multiple NF2 and non-NF2 genetic and epigenetic abnormalities at the level of the tumor may contribute to worse hearing outcomes. Understanding genetic and epigenetic signatures in individual NF2 patients and particularly in each VS will allow us to develop novel gene therapies and precision medicine algorithms to preserve hearing in NF2 individuals.

Validating indicators of CNS disorders in a swine model of neurological disease.

Genetically modified swine disease models are becoming increasingly important for studying molecular, physiological and pathological characteristics of human disorders. Given the limited history of these model systems, there remains a great need for proven molecular reagents in swine tissue. Here, to provide a resource for neurological models of disease, we validated antibodies by immunohistochemistry for use in examining central nervous system (CNS) markers in a recently developed miniswine model of neurofibromatosis type 1 (NF1). NF1 is an autosomal dominant tumor predisposition disorder stemming from mutations in NF1, a gene that encodes the Ras-GTPase activating protein neurofibromin. Patients classically present with benign neurofibromas throughout their bodies and can also present with neurological associated symptoms such as chronic pain, cognitive impairment, and behavioral abnormalities. As validated antibodies for immunohistochemistry applications are particularly difficult to find for swine models of neurological disease, we present immunostaining validation of antibodies implicated in glial inflammation (CD68), oligodendrocyte development (NG2, O4 and Olig2), and neuron differentiation and neurotransmission (doublecortin, GAD67, and tyrosine hydroxylase) by examining cellular localization and brain region specificity. Additionally, we confirm the utility of anti-GFAP, anti-Iba1, and anti-MBP antibodies, previously validated in swine, by testing their immunoreactivity across multiple brain regions in mutant NF1 samples. These immunostaining protocols for CNS markers provide a useful resource to the scientific community, furthering the utility of genetically modified miniswine for translational and clinical applications.

A Novel Mutation in Neurofibromatosis Type 1 with Optic Glioma

Neurofibromatosis type 1 is an autosomal dominant disorder which is characterized by multiple café-au-lait spots in the body, intertriginous freckles, Lisch nodules, neurofibroma, optic glioma and bone dysplasia. One of the clinical characteristics of Neurofibromatosis type 1 is the risk of benign and malignant tumor development. Optic gliomas, a type of astrocytoma, are the most common central nervous system complication in children with Neurofibromatosis type 1 and are seen in 10–15% of cases. In this case report, a patient with an optic glioma and a mutation that was not previously identified in the NF1 gene is presented in the light of the literature. Identification of new mutations that cause Neurofibromatosis type 1 disease and reporting of clinical findings caused by the mutations will allow a large proportion of genotypephenotype correlation. Early diagnosis has a great importance in terms of followup of patients for malignancies that may develop in the future.

Clinical manifestations and neurofibromatosis type 1 gene mutations of 25 patients with neurofibromatosis type 1 from 10 Chinese pedigrees

This study enrolled 25 patients with neurofibromatosis type 1 (NF1) from 10 Chinese pedigrees. Sanger sequencing analysis and multiplex ligation-dependent probe amplification analysis were used to detect mutations and large fragment losses of the NF1 gene. This study identified 10 NF1 mutations, which comprised six novel and four recurrent mutations. Majority of the mutations can lead to termination codon production, which results in the synthesis of the truncated gene product neurofibromin.

A neurofibromatosis type I patient presenting with four different cancer types including malignant peripheral nerve sheath tumor, gastrointestinal stromal tumor, pancreatic neuroendocrine tumor, and renal cell carcinoma within 1 year

Neurofibromatosis type 1 (NF1) is a germline autosomal dominant disorder caused by the loss-of-function tumor suppressor gene NF1, which encodes neurofibromin protein. When multiple tumors arise within a short time in patients with the germline NF1 mutation, it is important to determine whether the tumors are metastatic or different primary tumors. We, herein, report a 35-year-old female with multiple tumors that were confirmed to be a malignant peripheral nerve sheath tumor, gastrointestinal stromal tumor, renal cell carcinoma, and pancreatic neuroendocrine tumor, and all were treated accordingly. This case further supports that tissue confirmation is important in patients with the NF1 germline mutation.

The impact of host immune cells on the development of neurofibromatosis type 1: The abnormal immune system provides an immune microenvironment for tumorigenesis.

The immune system plays an essential role in the development of tumors, which has been demonstrated in multiple types of cancers. Consistent with this, immunotherapies with targets that disrupt these mechanisms and turn the immune system against developing cancers have been proven effective. In neurofibromatosis type 1 (NF1), an autosomal dominant genetic disorder, the understanding of the complex interactions of the immune system is incomplete despite the discovery of the pivotal role of immune cells in the tumor microenvironment. Individuals with NF1 show a loss of the NF1 gene in nonneoplastic cells, including immune cells, and the aberrant immune system exhibits intriguing interactions with NF1. This review aims to provide an update on recent studies showing the bilateral influences of NF1 mutations on immune cells and how the abnormal immune system promotes the development of NF1 and NF1-related tumors. We then discuss the immune receptors major histocompatibility complex class I and II and the PD-L1 mechanism that shield NF1 from immunosurveillance and enable the immune escape of tumor tissues. Clarification of the latest understanding of the mechanisms underlying the effects of the abnormal immune system on promoting the development of NF1 will indicate potential future directions for further studies and new immunotherapies.

NF1-like optic pathway gliomas in children: clinical and molecular characterization of this specific presentation.

BackgroundPediatric neurofibromatosis type 1 (NF1)–associated optic pathway gliomas (OPGs) exhibit different clinico-radiological features, treatment, and outcome compared with sporadic OPGs. While NF1-associated OPGs are caused by complete loss-of-function of the NF1 gene, other genetic alterations of the RAS-MAPK pathway are frequently described in the sporadic cases. We identified a group of patients who presented OPGs with typical radiological features of NF1-associated OPGs but without the NF1 diagnostic criteria. We aim to investigate into the possible molecular mechanisms underlying this “NF1-like” pediatric OPGs presentation.MethodsWe analyzed clinico-radiological features of 16 children with NF1-like OPGs and without NF1 diagnostic criteria. We performed targeted sequencing of the NF1 gene in constitutional samples (n = 16). The RAS-MAPK pathway major genes were sequenced in OPG tumor samples (n = 11); BRAF FISH and IHC analyses were also performed.ResultsIn one patient’s blood and tumor samples, we identified a NF1 nonsense mutation (exon 50: c.7285C>T, p.Arg2429*) with ~8% and ~70% VAFs, respectively, suggesting a mosaic NF1 mutation limited to the brain (segmental NF1). This patient presented signs of neurodevelopmental disorder. We identified a somatic alteration of the RAS-MAPK pathway in eight tumors: four BRAF activating p.Val600Glu mutations, three BRAF:KIAA oncogenic fusions, and one putative gain-of-function complex KRAS indel inframe mutation.ConclusionsNF1-like OPGs can rarely be associated with mosaic NF1 that needs specific constitutional DNA analyses for diagnosis. Further studies are warranted to explore unknown predisposition condition leading to the NF1-like OPG presentation, particularly in patients with the association of a neurodevelopmental disorder.

Malignant peripheral nerve-sheath tumors in an adolescent patient with mosaic localized NF1: A case report.

Malignant peripheral nerve-sheath tumors (MPNSTs) are rare malignancies that are often observed in patients with neurofibromatosis type 1 (NF1). However, the occurrence of MPNST associated with mosaic localized NF1 is extremely rare. Previous reports have revealed that MPNST was associated with mosaic localized NF1 in only three patients who were >40 years of age. The present report details a 16-year-old man who presented with pain and a 3 cm mass on the medial side of the right knee. Magnetic resonance imaging revealed a circumscribed soft tissue tumor located in the subcutaneous tissue. His previous doctor believed that it was benign and conducted a marginal resection. However, postoperative histology results demonstrated spindle cell sarcoma, following which the patient was referred to The Osaka International Cancer Institute. Localized café-au-lait spots were identified in the affected leg, which inferred that the patient had NF1-related MPNST. A wide resection was performed to completely resect the residual tumor; however, a definitive histological diagnosis was challenging due to the small residual tumor. Hence, the genomic mutations of NF1 in the regional café-au-lait spots were analyzed. The result revealed an NF1 microdeletion and a consistently limited expression of NF1 in the tumor sample. Finally, the patient was diagnosed with MPNST with mosaic localized NF1. Local recurrence and distant metastasis were not observed 1.5 years after surgery. In conclusion, the present report presented MPNST in an adolescent patient with mosaic localized NF1. The occurrence of MPNSTs correlated with mosaic localized NF1 is extremely rare. However, it is of high-grade malignancy and therefore, its clinical features should be considered by orthopedists and pathologists.

Saliva a mirror to oral health in neurofibromatosis type-1 patients

Background Neurofibromatosis (NF) consists of a complex group of syndromes, which occur as a result of inactivation of the various tumor suppressor genes precipitating multiple cutaneous neuromas and schwannomas in the body. Neurofibromatosis type 1 (NF1)/Von Recklinghausen disease/Watson disease affects 1 in 30,000 individuals and is caused by a mutation in the tumor suppressor gene NF1, locus 17 q11.2; this is one of the largest genes in the human genome and is inherited in an autosomal dominant pattern. Case Summary A cross-sectional study was conducted in a family suffering from NF over 3 generations, consisting of 20 members, and those meeting the diagnostic criteria for NF1 according to the National Institutes of Health (Stumpf et al., 1988) were selected. Pedigree analysis, clinical examination, Ramfjord periodontal index, and sialometry were performed for the following parameters: (1) salivary flow rate—whole unstimulated saliva was considered for salivary flow rate, which was measured by asking the patient to spit out saliva into a sterile container and the amount of saliva is quantitatively measured; (2) salivary pH—salivary pH of whole unstimulated saliva was measured by using the pH meter; (3) salivary alpha amylase activity—this was measured by using the starch–saliva–iodine test. Conclusions On clinical examination, all the members of the family showed distinctive osseous lesions at the base of the tongue. Salivary analysis revealed decreased salivary flow rate and increased pH, making the individuals prone to periodontitis caused by decreased clearance and enzymatic activity. Alterations in the salivary glands (acini and ducts) is caused by mutations in the NF1 gene. Neurofibromin is known to play important role in salivary glands cell division and differentiation via the Rho–rock–LIM kinase-2 pathway; hence the defect in neurofibromin results in defective salivary gland cell differentiation, causing nonfunctional cells and making the individual prone to hyposalivation.

Case report of ascending colon cancer and multiple jejunal GISTs in a patient with neurofibromatosis type 1 (NF1)

BackgroundNF1(Neurofibromatosis type 1) is an autosomal dominant genetic disorder. Patients with NF1 have an increased risk of developing benign or malignant tumours, such as gastrointestinal stromal tumours (GISTs). However, the coexistence of NF1, GIST and colon cancer is very rare, and few cases have been reported in the literature.Case presentationWe admitted a case of a 64-year-old man with type 1 neurofibromatosis, GISTs, and ascending colon cancer. This case was characterized by café-au-lait macules, discrete cutaneous neurofibromas, nodular neurofibromas, multiple jejunal tumours, and ascending colon cancer. Laparoscopic exploration revealed ascending colon cancer and multiple jejunal tumours. Laparoscopic right hemicolectomy and local excision of the jejunal tumours were performed successfully. The pathological results confirmed moderate differentiated adenocarcinoma of the ascending colon with multiple jejunal GISTs (low risk, very low risk). Moreover, the immunohistochemistry results of multiple jejunal GISTs suggest that NF1 is positive. Whole-exome sequencing (WES) of colon cancer revealed mutations in more than 20 genes, including KRAS, PIK3CA, APC, SMAD4, etc. The results of whole-exome sequencing (WES) of jejunal GISTs revealed an NF1 mutation and no KIT or PDGFR gene mutation.ConclusionWe report a rare case of simultaneous NF1, GIST and colon adenocarcinoma. For patients with NF1, benign and/or malignant tumours are often combined. Therefore, these patients should undergo regular physical examinations so that early detection and early treatment can be achieved.

Phenotype categorization of neurofibromatosis type I and correlation to NF1 mutation types.

Neurofibromatosis type 1 (NF1) is caused by heterozygous mutation in the NF1 gene. NF1 is one of the most common human genetic diseases. However, the overall genotype-phenotype correlation has not been known, due to a wide spectrum of genotypic and phenotypic heterogeneity. Here we describe the detailed clinical and genetic features of 427 Korean NF1 patients from 389 unrelated families. Long range PCR and sequencing of genomic DNA with multiplex ligation-dependent probe amplification analysis identified 250 different NF1 mutations in 363 families (93%), including 94 novel mutations. With an emphasis on phenotypes requiring medical attention (classified and termed: NF1+), we investigated the correlation of NF1+ and mutation types. NF1+ was more prevalent in patients with truncating/splicing mutations and large deletions than in those with missense mutations (59.6%, 64.3% vs. 36.6%, p = 0.001). This difference was especially significant in the patients younger than age 19 years. The number of items in NF1+ was a higher in the former groups (0.95 ± 0.06, 1.18 ± 0.20 vs. 0.56 ± 0.10, p = 0.002). These results suggest that mutation types are associated not only with higher prevalence of severe phenotypes in NF1 but also with their earlier onset.

Risk of Optic Pathway Glioma in Neurofibromatosis Type 1: No Evidence of Genotype-Phenotype Correlations in A Large Independent Cohort.

The occurrence of optic pathway gliomas (OPGs) in children with neurofibromatosis type 1 (NF1) still raises many questions regarding screening and surveillance because of the lack of robust prognostic factors. Recent studies of an overall cohort of 381 patients have suggested that the genotype may be the main determinant of the development of OPG, with the risk being higher in patients harbouring NF1 mutations in the 5’ tertile and the cysteine/serine-rich domain. In an attempt to confirm this hypothesis, we used strict criteria to select a large independent cohort of 309 NF1 patients with defined constitutional NF1 mutations and appropriate brain images (255 directly enrolled and 54 as a result of a literature search). One hundred and thirty-two patients had OPG and 177 did not. The association of the position (tertiles and functional domains) and type of NF1 mutation with the development of OPG was analysed using the χ2 test and Fisher’s exact probability test; odds ratios (ORs) with 95% confidence intervals were calculated, and Bonferroni’s correction for multiple comparisons was applied; multiple logistic regression was also used to study genotype–phenotype associations further. Our findings show no significant correlation between the site/type of NF1 mutation and the risk of OPG, and thus do not support the hypothesis that certain constitutional mutations provide prognostic information in this regard. In addition, we combined our cohort with a previously described cohort of 381 patients for a total of 690 patients and statistically re-analysed the results. The re-analysis confirmed that there were no correlations between the site (tertile and domain) and the risk of OPG, thus further strengthening our conclusions.

TMOD-23. PRECLINICAL DRUG EVALUATION IN A GENETICALLY ENGINEERED MINIPIG MODEL OF NEUROFIBROMATOSIS TYPE 1

Abstract We have employed gene-editing technology to create a Neurofibromatosis Type 1 (NF1) minipig that replicates the broad spectrum of disease that develops in NF1 patients and meets the National Institute of Health’s diagnostic criteria for NF1. The NF1 boars are fertile and the NF1 mutant allele is transmitted at a Mendelian rate with no reduction in fitness of offspring that inherit this allele. To date, we have observed 100% penetrance of café au lait macules, a phenotype that occurs in nearly every NF1 patient, but has never been demonstrated in any other animal model. The NF1 minipig develops cutaneous neurofibromas and optic pathway glioma, that histologically resemble human tumors. Additionally, we have observed other NF1-associated phenotypes including Lisch nodules, tibial dysplasia, white matter decompaction, hypopigmentation, and freckling of the skin. The FDA has emphasized the need for development and testing of new therapies in large animal disease models prior to human studies. Therefore, we have conducted pharmacological studies in our NF1 swine to look at the pharmacokinetic and pharmacodynamic properties MEK inhibitors, currently in clinical trials for NF1. We have demonstrated that oral administration of the MEK inhibitors results in clinically relevant plasma levels of the drug and inhibition of Ras signaling, and that certain MEK inhibitors can cross the blood brain barrier and have a pharmacodynamic effect, suggesting that they may be effective in treating NF1-associated brain tumors. We envision this large animal model of NF1 will become a standard in the evaluation of the safety and efficacy of new drugs prior to Phase I clinical trials. Further, an NF1 minipig may enable researchers to better understand the biological and genetic mechanisms underlying this complex disease, detect NF1-related tumors earlier, identify biomarkers, discover novel drug targets, and test new drugs and combination therapies for safety and efficacy.