NF1 mutations and molecular testing

Neurofibromatosis 1 is a progressive autosomal dominant condition caused by mutations in the NF1 gene on chromosome 17. The condition shows clinical variable expressivity, with varying features even between family members who share the same mutation. Furthermore, it is impossible to precisely predict the severity and course of the condition, a source of frustration for families and physicians. Neurofibromatosis 1 is also heterogeneous at the mutation level, with more than 300 independent mutations having been reported in this gene. The mutation data have accumulated slowly owing to the variability of the mutation types and the size and complexity of the gene. This is also reflected in the lack of a simple, inexpensive, highly accurate DNA-based test for neurofibromatosis 1 at present. This article reviews current NF1 mutation spectrum and testing, discussing and illustrating mutation mechanisms and pathogenetic effects, as well as factors affecting DNA testing and interpretation/diagnosis.     

Recent progress toward understanding the molecular biology of von Recklinghausen neurofibromatosis.

The gene for von Recklinghausen neurofibromatosis (NF1) was recently identified by positional cloning and found to code for a large, ubiquitously expressed protein. This protein has both structural and functional similarity to a family of proteins with guanosine triphosphatase-activating properties, involved in the regulation of the protooncogene ras. One of the postulated functions of the NF1 gene product may relate to its ability to regulate ras-mediated cell proliferation. Selective pharmacotherapy directed at downregulating ras may be of benefit to patients with NF1.     

Spinal neurofibromatosis in a family with classical neurofibromatosis type 1 and a novel NF1 gene mutation

Familial spinal neurofibromatosis (FSNF) is a rare form of neurofibromatosis type 1 (NF1) characterized by multiple, histologically proven neurofibromas of the spinal roots leaving no intact segments and associated neurofibromas of major peripheral nerves. It is sometimes associated with other NF1 stigmata. Most patients have NF1 gene mutations. We describe a patient who fulfilled the diagnostic criteria for spinal neurofibromatosis and belonged to a family in which other affected members exhibited classical NF1 stigmata. A novel missense (c.7109 T > A; p.Val2370Asp) mutation in exon 39 of the NF1 gene was present in the affected family members. The family displayed extreme phenotypic variability in the spectrum of NF1. To our knowledge, this is the first patient with spinal neurofibromatosis in the context of classical NF1 with an NF1 gene mutation. The term FSNF is inaccurate as this condition simply reflects the typical autosomal dominant pattern of NF1 inheritance with phenotypoc variability and does not encompass patients with sporadic disease or those in the context of a classical NF1 phenotype as reported in the present family. The term could be replaced by “spinal neurofibromatosis”.     

Loss of neurofibromatosis 1 (NF1) gene expression in NF1-associated pilocytic astrocytomas

The critical role of the neurofibromatosis 1 (NF1) gene as a tumour suppressor has been clearly demonstrated for malignancies arising in NF1 patients. However, little is known about the more common benign tumours, such as the pilocytic astrocytoma. Most NF1-associated astrocytomas are benign and clinically non-progressive, though aggressive tumours are occasionally encountered. In this study, eight pilocytic astrocytomas from six individuals affected with NF1 were analysed for NF1 expression. All eight tumours demonstrated loss of neurofibromin expression by immunohistochemistry, which was confirmed in one case using Western blot analysis. Microsatellite analysis showed loss of a single NF1 allele (LOH) in two of four NF1-associated tumours. These results demonstrate that, in contrast to sporadic astrocytomas, loss of NF1 expression is an important primary genetic event in the pathogenesis of NF1-associated pilocytic astrocytomas.     

Neurofibromatosis 1 and neurofibromatosis 2: a twenty first century perspective

Historically, neurofibromatosis 1 (NF1) has been inextricably linked with neurofibromatosis 2 (NF2). Both are inherited autosomal-dominant neurocutaneous disorders that have high de novo mutation rates and carry a high risk of tumour formation. However, they are clinically and genetically distinct diseases and should be considered as seperate entities. NF1 is a common disease that mainly affects the skin and peripheral nervous system and causes characteristic bony dysplasia. By contrast, NF2 is a rare disorder with a relative paucity of skin manifestations and high-grade malignancy is unusual. Neurological symptoms are the predominant problem and the cardinal sign is bilateral vestibular schwannomas. In this Review, I discuss the pertinent diagnostic, clinical, and genetic symptoms of NF1 and NF2. I also examine the current views on the pathogenesis of these neurocutaneous disorders in the wake of advances in molecular genetics and the development of mouse models of disease.     

Clinical features and pathobiology of neurofibromatosis 1

Neurofibromatosis 1 is a progressive multisystem disorder. The hallmark feature is the occurrence of nerve sheath tumors, neurofibromas. Other features include tumors such as optic gliomas and malignant peripheral nerve sheath tumors. There are also nontumor manifestations, such as skeletal dysplasia and learning disabilities. Since the NF1 gene was identified, much has been learned about the molecular genetics of the disorder; recently, this has led to insights about pathogenesis. Ultimately, it is hoped that this will be translated into specific means of treatment. This review describes the various clinical features of neurofibromatosis 1 and considers them in the context of the pathophysiology of the disorder.     

Recent advances in neurofibromatosis type 1

PURPOSE OF REVIEW: The past decade, since the identification of the neurofibromatosis type 1 (NF1) gene, has witnessed great advances in our understanding of the role of the NF1 gene in the molecular pathogenesis of NF1-associated clinical abnormalities. The purpose of this review is to highlight recent advances in defining the molecular etiology of nervous system tumors and learning disabilities. RECENT FINDINGS: Neurofibromas and optic pathway gliomas result from NF1 inactivation in Schwann cells and astrocytes, respectively, but other cellular factors contribute to tumorigenesis. In addition, malignant progression of plexiform neurofibromas to malignant peripheral nerve sheath tumors requires additional genetic changes, including increased expression of growth factor receptors, molecules that are involved in tumor invasion and metastasis, and inactivation of critical cell cycle regulators. In addition, specific types of NF1 gene mutation may be associated with an increased risk for malignancy in individuals with NF1. SUMMARY: Research over the past few years has resulted in a detailed understanding of the molecular genetics of benign and malignant tumors affecting individuals with NF1 as well as the development of refined small animal models for these tumors. In addition, clinical studies have begun to define specific subpopulations of patients at risk for cancer and have identified targeted therapies for NF1-associated tumors, based on basic science research advances.     

Genetic predisposition to peripheral nerve neoplasia: diagnostic criteria and pathogenesis of neurofibromatoses, Carney complex, and related syndromes

Neoplasms of the peripheral nerve sheath represent essential clinical manifestations of the syndromes known as the neurofibromatoses. Although involvement of multiple organ systems, including skin, central nervous system, and skeleton, may also be conspicuous, peripheral nerve neoplasia is often the most important and frequent cause of morbidity in these patients. Clinical characteristics of neurofibromatosis type 1 (NF1) and neurofibromatosis type 2 (NF2) have been extensively described and studied during the last century, and the identification of mutations in the NF1 and NF2 genes by contemporary molecular techniques have created a separate multidisciplinary field in genetic medicine. In schwannomatosis, the most recent addition to the neurofibromatosis group, peripheral nervous system involvement is the exclusive (or almost exclusive) clinical manifestation. Although the majority of cases of schwannomatosis are sporadic, approximately one-third occur in families and a subset of these has recently been associated with germline mutations in the tumor suppressor gene SMARCB1/INI1. Other curious syndromes that involve the peripheral nervous system are associated with predominant endocrine manifestations, and include Carney complex and MEN2b, secondary to inactivating mutations in the PRKAR1A gene in a subset, and activating mutations in RET, respectively. In this review, we provide a concise update on the diagnostic criteria, pathology and molecular pathogenesis of these enigmatic syndromes in relation to peripheral nerve sheath neoplasia.     

Neurofibromatosis Type 1 Association with Moyamoya Disease

The neurofibromatoses are genetic disorders of the nervous system that primarily affect the development and growth of neural (nerve) cell tissues. The neurofibromatoses are classified as neurofibromatosis type 1 (NF1) and neurofibromatosis type 2 (NF2). NF1 is the more common type of the neurofibromatoses. The gene responsible for NF1 is located on the chromosome region 17q11.2 and for familial moyamoya disease on chromosome 17q25. This article reports on a 20-year-old female with neurofibromatosis-1 who developed moyamoya syndrome. More extensive reports and further investigations of such families having this combination will certainly provide a better understanding of this link in the near future.     

Neurofibromatosis type 1 association with moyamoya disease

The neurofibromatoses are genetic disorders of the nervous system that primarily affect the development and growth of neural (nerve) cell tissues. The neurofibromatoses are classified as neurofibromatosis type 1 (NF1) and neurofibromatosis type 2 (NF2). NF1 is the more common type of the neurofibromatoses. The gene responsible for NF1 is located on the chromosome region 17q11.2 and for familial moyamoya disease on chromosome 17q25. This article reports on a 20-year-old female with neurofibromatosis-1 who developed moyamoya syndrome. More extensive reports and further investigations of such families having this combination will certainly provide a better understanding of this link in the near future.     

Dissecting the clinical phenotype associated with mosaic type-2 NF1 microdeletions

Patients with large deletions of the NF1 gene and its flanking regions (termed NF1 microdeletions) generally exhibit more severe clinical manifestations of neurofibromatosis type-1 (NF1). Here, we have investigated the clinical phenotype displayed by eight patients harbouring mosaic type-2 NF1 microdeletions. These patients did not exhibit facial dysmorphism, attention deficit hyperactivity disorder, delayed cognitive development and/or learning disabilities, cognitive impairment, congenital heart disease, hyperflexibility of joints, large hands and feet, muscular hypotonia or bone cysts. All these features have previously been reported to be disproportionately associated with germline (i.e. non-mosaic) type-1 NF1 microdeletions as compared with the general NF1 population. Plexiform neurofibromas were also less prevalent in patients with mosaic type-2 NF1 microdeletions as compared with patients carrying constitutional (germline) type-1 NF1 microdeletions. Five of the eight patients with mosaic type-2 deletions investigated here had 20-250 cutaneous neurofibromas, but only one of them exhibited a high load of cutaneous neurofibromas (N?>?1,000). By contrast, a previous study indicated a high burden of cutaneous neurofibromas (N?>?1,000) in 50?% of adult patients with germline type-1 NF1 deletions. Patients with germline type-1 NF1 microdeletions have been reported to have an increased lifetime risk of 16-26?% for a malignant peripheral nerve sheath tumour (MPNST). In this study, one of the eight investigated mosaic type-2 microdeletion patients developed an MPNST. We conclude that patients with mosaic type-2 NF1 microdeletions may also be at an increased risk of MPNSTs despite their generally milder disease manifestations as compared with germline type-1 NF1 microdeletions.     

A mouse embryonic stem cell model of Schwann cell differentiation for studies of the role of neurofibromatosis type 1 in Schwann cell development and tumor formation

The neurofibromatosis Type 1 (NF1) gene functions as a tumor suppressor gene. One known function of neurofibromin, the NF1 protein product, is to accelerate the slow intrinsic GTPase activity of Ras to increase the production of inactive rasGDP, with wide-ranging effects on p21ras pathways. Loss of neurofibromin in the autosomal dominant disorder NF1 is associated with tumors of the peripheral nervous system, particularly neurofibromas, benign lesions in which the major affected cell type is the Schwann cell (SC). NF1 is the most common cancer predisposition syndrome affecting the nervous system. We have developed an in vitro system for differentiating mouse embryonic stem cells (mESC) that are NF1 wild type (+/+), heterozygous (+/-), or null (-/-) into SC-like cells to study the role of NF1 in SC development and tumor formation. These mES-generated SC-like cells, regardless of their NF1 status, express SC markers correlated with their stage of maturation, including myelin proteins. They also support and preferentially direct neurite outgrowth from primary neurons. NF1 null and heterozygous SC-like cells proliferate at an accelerated rate compared to NF1 wild type; this growth advantage can be reverted to wild type levels using an inhibitor of MAP kinase kinase (Mek). The mESC of all NF1 types can also be differentiated into neuron-like cells. This novel model system provides an ideal paradigm for studies of the role of NF1 in cell growth and differentiation of the different cell types affected by NF1 in cells with differing levels of neurofibromin that are neither transformed nor malignant.     

Developmental regulation of a neuron-specific neurofibromatosis 1 isoform.

We have identified a protein isoform of the neurofibromatosis 1 (NF1) gene (neurofibromin) containing the alternatively spliced exon 9a that is expressed in forebrain neurons. Exon 9a neurofibromin is localized in the cytoplasm, sediments in a P100 fraction, and is expressed throughout the soma and processes in cortical neurons in vitro. Expression of exon 9a neurofibromin is developmentally regulated, with expression first detected after postnatal day 2. The identification of this novel protein isoform with restricted neuronal expression suggests novel functions for neurofibromin in the postmitotic brain that are perhaps relevant to the learning disabilities observed in children with NF1.     

Somatic instability of the NF2 gene in schwannomatosis

CONTEXT: Schwannomatosis is a newly described form of neurofibromatosis of unclear pathogenesis. PATIENT AND METHODS: We studied the NF2 locus on chromosome 22 in 7 tumor specimens resected from a 36-year-old man with schwannomatosis of the right ulnar nerve. RESULTS: Unrelated truncating NF2 gene mutations were detected in 4 tumor specimens. None of the NF2 mutations were present in the blood specimen. Loss of heterozygosity at the NF2 locus was seen in all tumors, and in every case the same allele was lost. Loss of distal chromosome 22 markers was variable. Fluorescence in situ hybridization results were consistent with monosomy 22 in 4 tumors and mitotic recombination or nondisjunction in 1. CONCLUSIONS: Molecular analysis of tumor specimens distinguishes schwannomatosis from other forms of neurofibromatosis. Further work is needed to understand the natural history and molecular biology of this condition.     

Clinical spectrum of neurofibromatosis type 1 among children in a tertiary care center

Objectives:To identify the clinical and neuroradiological features of neurofibromatosis type 1 and the risk of malignancy in a pediatric age group.Methods:This observational retrospective cohort study was conducted at King Saud University Medical City, Riyadh, Kingdom of Saudi Arabia, for the patients with neurofibromatosis type 1 who were seen and had follow up from January 2000 to January 2019.Results:A total of 50 children were included. Approximately 90% of patients presented with café-au-lait macules, and 34% had skin-fold freckling. Moreover, 42% of the participants had a first-degree relative with neurofibromatosis type 1, and about a quarter presented with associated epilepsy. About 90% of the neuroradiological features were consistent with those of neurofibromatosis type 1. About 52% of the patients had one or multiple types of tumors, and 34% presented with optic pathway glioma.Conclusion:This study described clinical spectrum of neurofibromatosis type 1 among children. It showed also a higher percentage of tumors than previous studies.

Neurofibromatosis type 1 (NF1) is an autosomal dominant neurocutaneous disorder, that affects 1 in 3500 people worldwide.1 The NF1 is a complex disorder involving multiple body systems, such as the integumentary, visual, skeletal, and central nervous system (CNS); hence, it has different clinical manifestations. This condition is mainly characterized by cutaneous pigmented spots referred to as cafe-au-lait macules.2 The diagnosis of NF1 is mainly based on the criteria established by the National Institutes of Health (NIH) in 1988.3 Based on these criteria, patients are diagnosed with NF1 if they meet ≥2 of the following criteria: 6 or more cafe-au-lait macules with a diameter measuring >5 mm in prepubertal individuals and >15 mm in postpubertal individuals, 2 or more neurofibromas of any type or one plexiform neurofibroma, axillary or inguinal freckling (Crowe’s sign), optic pathway glioma (OPG), 2 or more Lisch nodules, dysplasia of the sphenoid wing or thinning of the long bone cortex (-/+ pseudarthrosis), and a first-degree relative with NF1 fulfilling the above mentioned criteria. The diagnostic criteria were revised in 1997 and were continuously used without modifications.4 Moreover, patients with NF1 have a higher risk of malignancies than individuals in the general population, with an estimated prevalence of 5%, and these malignancies are usually detected during childhood.1There are no available data on the radiologic features and the signs and symptoms at the time of clinical presentation, which are essential for the clinical knowledge of physicians in identifying patients with such condition. In addition, there is a lack of information about clinical outcomes, including the risk of malignancy, among patients with NF1. Therefore, the current study aimed to evaluate the different clinical manifestations and the radiological features of NF1 among pediatric patients. Moreover, the outcomes, which are essential for urgent interventions that can improve life expectancy, were assessed.     

Neurocognitive dysfunction in children with neurofibromatosis type 1

The cognitive dysfunction associated with neurofibromatosis type 1 (NF1) is an intriguing aspect of this phenotypically heterogeneous genetic neurocutaneous disorder. A broad range of both nonverbal and verbal learning disabilities are evident in approximately 30% to 65% of children with NF1. Deficits in IQ, executive function, attention, and motor skills have also been documented. Current challenges lie in discovering the underlying multifactorial etiologies of the cognitive abnormalities found in NF1. Likely answers lie in neuroanatomic correlates as seen on neuroimaging as well as in molecular and genetic advances into the role of neurofibromin, the protein product of the NF1 gene. The development of NF1 animal models with learning and memory difficulties similar to those seen in humans demonstrates promising preliminary evidence that medical treatment of cognitive abnormalities may one day be possible.     

Cancer-related gene expression profiles in NF1-associated pilocytic astrocytomas

BACKGROUND: Individuals affected with neurofibromatosis 1 (NF1) develop juvenile pilocytic astrocytomas (JPA) at an increased frequency, suggesting that the NF1 gene product, neurofibromin, functions as a negative growth regulator for astrocytes. Previously, the authors demonstrated that NF1-associated astrocytomas exhibit deletions and loss of NF1 gene expression on the DNA and protein levels. However, little is known about additional genetic events in clinically and radiographically progressive NF1-associated pilocytic astrocytomas. OBJECTIVE/METHODS: To understand the potential role of cooperating genetic events in the development of these low-grade tumors, the authors used immunohistochemistry and selected confirmatory Western blots to examine nine symptomatic NF1-associated pilocytic astrocytomas for gene products whose expression patterns are altered in fibrillary astrocytomas. RESULTS: The authors demonstrate that p53, p16, retinoblastoma (RB), epidermal growth factor receptor (EGFR), cyclin-dependent kinase 4 (CDK4), platelet-derived growth factor A (PDGF-A) and PDGF receptor alpha (PDGF-Ralpha) protein expression profiles are not altered in NF1-associated pilocytic astrocytomas. Similar to their sporadic counterparts, NF1-associated JPA also strongly expressed PEN5, a marker of post-O2A stage oligodendroglial precursor cells. CONCLUSIONS: These results suggest that NF1-associated pilocytic astrocytomas lack the genetic changes typically associated with the more clinically aggressive fibrillary astrocytomas and lay the foundation for future studies to identify NF1 JPA-specific alterations.     

Ⅱ型神经纤维瘤病分子遗传分析指导临床个体化诊疗的研究

目的 建立临床适用的Ⅱ型神经纤维瘤病(NF2)的分子遗传分析方法,对NF2患者及其后代进行分子遗传诊断,以指导NF2家族的遗传咨询及个体化病情监测、随访及临床干预.方法 以天津医科大学总医院神经外科自2009年1月至2010年1月收治的10例NF2患者为研究对象,收集患者的肿瘤组织标本,原代培养并鉴定术中获取的许旺细胞瘤组织.抽提原代培养的肿瘤性许旺细胞及患者血液的基因组DNA(2例NF2患者已有后代且同意接受基因测序,同时对其后代的血液进行基因组DNA提取),对2例NF2患者亲子二代血液及患者的肿瘤性许旺细胞基因组DNA进行NF2基因测序.制定不同的临床干预及随访计划,结合亲子二代分子遗传检测结果,对NF2家族制定后代的长期随访计划.结果 初步建立NF2许旺细胞瘤组织标本与基因组DNA库.基因测序结果显示肿瘤性许旺细胞与患者血液提取的NF2基因突变位点相同.第一组母女存在完全相同的基因突变位点,第二组母子基因突变位点不完全一致,二组检测到的突变位点均位于靠近外显子的调控区.结论 NF2许旺细胞瘤组织标本及基因组DNA库可以为该病分子遗传研究提供组织及基因组DNA资源.分子遗传分析可以指导临床工作,提前预计后代罹患风险,为高风险人群制定个体化的随访计划.个体化的临床干预可以提高患者的生活质量,延长生存期.

Abstract：

Objective To establish a molecular genetic analysis method applicable clinically for genetic diagnosis of patients with neurofibromatosis type Ⅱ (NF2) and their offsprings, and further guide the genetic counseling of NF2 family, condition monitoring, follow-up as well as clinical intervention of the patients. Methods Ten patients with NF2, admitted to our hospital from January 2009 to January 2010, were chosen;tumorigenic Schwann cells in Schwannoma were isolated and purified for primary culture. Genomic DNA was extracted from tumorigenic Schwann cells and from the blood of 2 patients and their offsprings who agreed to accept gene sequencing;the NF2 gene was sequenced (El-15 and El7 exons and adjacent introns). According to the implication of NF2 gene sequencing, genetic counseling was given to the NF2 family, and the potential NF2 patients in offsprings were followed up in a long-term. Results Schwannoma tissue and genomic DNA bank were established initially. Totallysame NF2 gene mutations were detected in genomic DNA extracted both from tumorigenic Schwann cells and blood cells in the same patient. By comparing the genotypes between the patients and the offsprings,consistent NF2 gene mutations were found between a female patient and her daughter aged 3, but not completely consistent gene mutations between another female patient and her son aged 15. All of the mutations in NF2 gene were located in the control region near the exons. Based on the patient's clinical manifestations and symptoms, reasonable plans for clinical interventions and follow-up were developed.Conclusion Schwannoma tissue and genomic DNA bank could supply the bio-resource for genetic molecular testing and treatment studies. Molecular genetic analysis would apply in clinical practice guidance, NF2 risk prediction, and follow-up plan for high-risk NF2 individuals. Early diagnosis and treatment, condition monitoring and long term follow-up and personalized clinical intervention are needed to improve the quality of life and prolong the survival.