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”.     

A new nonsense mutation in the NF1 gene with neurofibromatosis–Noonan syndrome phenotype

Purpose

Neurofibromatosis–Noonan syndrome is a rare autosomal dominant disorder which combines neurofibromatosis type 1 (NF1) features with Noonan syndrome. NF1 gene mutations are reported in the majority of these patients.

Method

Sequence analysis of the established genes for Noonan syndrome revealed no mutation; a heterozygous NF1 point mutation c.7549C>T in exon 51, creating a premature stop codon (p.R2517X), had been demonstrated.

Result

Neurofibromatosis–Noonan syndrome recently has been considered a subtype of NF1 and caused by different NF1 mutations.

Conclusion

We report the case of a 14-year-old boy with neurofibromatosis type 1 with Noonan-like features, who complained of headache with triventricular hydrocephaly and a heterozygous NF1 point mutation c.7549C>T in exon 51.     

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.     

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.     

Phenotype-genotype study in 154 French NF2 mutation carriers

INTRODUCTION: Germline mutations in the NF2 gene are responsible for 80 p.cent of neurofibromatosis type 2 typical cases. Mutations are mainly truncating mutations or deletions, missense mutations having been reported in few cases. An important phenotypic variability is observed among gene carriers. To assess whether the phenotypic variability of neurofibromatosis 2 could be linked to genotype, clinical data of 154 patients whose NF2 germline alteration had been identified in our laboratory have been collected. METHODS: A retrospective questionnaire was sent to the physicians in charge of these patients. Statistical analyses regarding genotypic and phenotypic data were performed by comparisons of average values and correlation tests. RESULTS: In French patients, type of mutation was correlated neither with patients' sex, nor with disease occurrence mode (de novo or inherited mutation). Disease associated with missense mutations occurred later, with a less severe symptomatology. Patients with nonsense or frameshift mutations were more frequently affected with meningiomas and spinal tumours, in addition to VIII nerve schwannomas, an observation that underlies the genetic determination of the number and type of NF2-related tumours. CONCLUSION: Results from the literature as well as from our study tend to show that only few correlations exist between genotype and phenotype in the NF2 disease. It also recognizes that missense mutations have a lower level of evolution, severity and mortality risk. Nonsense and frameshift mutations seem to be associated with a higher number of meningiomas and spinal tumours. Therefore, NF2 gene screening keeps its indications in both typical and moderate forms of the disease. Mutations are responsible of 80 p.cent of typical forms; in moderate forms, identification of a missense mutation seems linked to a lower disease evolution. In any case, assessment and supervision should be identical. Finally, in a small number of cases, the NF2 gene appears to be implicated in clinical forms different from those defined by NIH and it might be of interest to enlarge the clinical features suggestive of the disease.     

Recent developments in neurofibromatosis type 1

PURPOSE OF REVIEW: This review summarizes the recent clinical and genetic developments in neurofibromatosis type 1 (NF1) and provides an insight into the possible underlying pathomechanisms. RECENT FINDINGS: NF1, or von Recklinghausen disease, is one of the most common hereditary neurocutaneous disorders in humans. Clinically, NF1 is characterized by café-au-lait spots, freckling, skin neurofibroma, plexiform neurofibroma, bony defects, Lisch nodules and tumors of the central nervous system. The responsible gene, NF1, encodes a 2818 amino acid protein (neurofibromin). Pathological mutations range from single nucleotide substitutions to large-scale genomic deletions dispersed throughout the gene. In addition to the conventional mutation screening methods, a DNA chip microarray-based technology, combinational sequence-based hybridization, has been introduced to expedite mutation detection. Functional analysis has become more amenable following the development of the following: (1) primary Schwann cell cultures from NF1 patients; (2) mouse models; (3) proteomic technologies; and (4) mRNA silencing by RNA interference. These studies have shown that neurofibromin plays a role in adenylate cyclase and AKT-mTOR mediated pathways. It also appears to affect Ras-GTPase activating protein activity through the phosphorylation of protein kinase C which impacts on cell motility by binding with actin in the cytoskeleton. SUMMARY: Recent advances in the clinical features and molecular genetics of NF1 will be discussed together with insights into the underlying pathomechanisms of NF1.     

神经纤维瘤病1型基因32、33号外显子突变的检测

目的检测中国人神经纤维瘤病１型（ＮＦ１）基因３２、３３外显子突变。方法应用聚合酶链反应－单链构象多态性（ＰＣＲＳＳＣＰ）法分析１４个ＮＦ１家系６２名成员及３０名正常对照外周血白细胞ＤＮＡ的ＮＦ１基因３２、３３号外显子。结果３个家系（２１．４％）、４例ＮＦ１患者（１１．１％）ＮＦ１基因３２号外显子的ＤＮＡＳＳＣＰ发生泳动变位,可能为ＮＦ１基因３２号外显子发生突变。家系中其他成员及正常对照无此现象。通过３种不同的ＳＳＣＰ实验条件,未发现３３号外显子异常泳动变位。结论３２号外显子可能为中国人ＮＦ１基因突变热点之一。本研究方法对ＮＦ１症状前诊断和产前诊断有重要应用价值。     

The spectrum of somatic and germline NF1 mutations in NF1 patients with spinal neurofibromas

Neurofibromatosis type 1 (NF1) is a common inherited complex multi-system disorder associated with the growth of various benign and malignant tumors. About 40% of NF1 patients develop spinal tumors, of whom some have familial spinal neurofibromatosis (FSNF), a variant form of NF1 in which patients present with multiple bilateral spinal tumors but have few other clinical features of the disease. We have studied 22 spinal neurofibromas derived from 14 unrelated NF1 patients. Seven of these patients satisfied the diagnostic criteria of NF1 while the remaining seven had only few features of NF1. The latter group defined as FSNF harbored significantly higher number of missense or missense and splice-site germline mutations compared to the group with classical NF1. This is the first study to describe NF1 somatic mutations in spinal neurofibromas. Loss-of-heterozygosity (LOH) was identified in 8/22 of the spinal tumors, 75% of LOH observed was found to result from mitotic recombination, suggesting that this may represent a frequent mutational mechanisms in these benign tumors. No evidence for LOH of the TP53 gene was found in these tumors.     

Diagnosis of neurofibromatosis type 1 using RFLPs tightly linked to gene

This study reports the results of a linkage analysis in nine families with members who had neurofibromatosis type 1 (NF1), using five restriction fragment length polymorphisms (RFLPs) tightly linked to the NF1 locus. The purpose of this analysis was to determine whether the at-risk individuals were carrying the NF1 allele and whether the nine families would be informative for prenatal testing. The families included 25 patients with NF1, 3 individuals at risk for NF1, and 11 unaffected subjects, with a total of 39 family members and 12 matings. In 6 matings two or more flanking probes were informative, in 3 matings only one probe was informative, and in the other 3 no probe was informative. DNA linkage analysis showed with more than 98% probability that the 3 at-risk individuals did not carry the NF1 mutation. No recombination events were observed. In 6 families it will be possible to do a DNA prenatal diagnosis if this type of test is requested. The NF1 gene has been identified and direct testing for the NF1 mutation is now possible. Linkage testing, however, will probably remain useful and complementary to direct analysis of the NF1 gene to reveal intragenic recombination events and for diagnosis in families in which the detection of mutation is difficult.     

How does the Schwann cell lineage form tumors in NF1?

Neurofibromas are benign tumors of peripheral nerve that occur sporadically or in patients with the autosomal dominant tumor predisposition syndrome neurofibromatosis type 1 (NF1). Multiple neurofibroma subtypes exist which differ in their site of occurrence, their association with NF1, and their tendency to undergo transformation to become malignant peripheral nerve sheath tumors (MPNSTs), the most common malignancy associated with NF1. Most NF1 patients carry a constitutional mutation of the NF1 tumor suppressor gene. Neurofibromas develop in these patients when an unknown cell type in the Schwann cell lineage loses its remaining functional NF1 gene and initiates a complex series of interactions with other cell types; these interactions may be influenced by aberrant expression of growth factors and growth factor receptors and the action of modifier genes. Cells within certain neurofibroma subtypes subsequently accumulate additional mutations affecting the p19(ARF)-MDM2-TP53 and p16INK4A-Rb signaling cascades, mutations of other as yet unidentified genes, and amplification of growth factor receptor genes, resulting in their transformation into MPNSTs. These observations have been validated using a variety of transgenic and knockout mouse models that recapitulate neurofibroma and MPNST pathogenesis. A new generation of mouse models is also providing important new insights into the identity of the cell type in the Schwann cell lineage that gives rise to neurofibromas. Our improving understanding of the mechanisms underlying the pathogenesis of neurofibromas and MPNSTs raises intriguing new questions about the origin and pathogenesis of these neoplasms and establishes models for the development of new therapies targeting these neoplasms.     

神经鞘瘤中NF2基因外显子2突变及意义

目的 :研究神经鞘瘤中 型多发神经纤维瘤病基因 (NF2 )外显子 2的突变及其意义。方法 :用 PCR- SS-CP、 DNA测序检测 36例神经鞘瘤 (听神经瘤 16例 ,其它 2 0例 )中 NF2基因外显子 2的突变。结果 :我们共发现 4例突变 ,均为听神经瘤 ,其中移码突变 2例、反义突变 2例。结论 :NF2基因外显子 2的突变可能是听神经瘤发生中的关键因素。     

A novel neurofibromin (NF1) interaction with the leucine‐rich pentatricopeptide repeat motif‐containing protein links neurofibromatosis type 1 and the french canadian variant of leigh's syndrome in a common molecular complex

Loss‐of‐function mutations and deletions in the neurofibromin tumor suppressor gene (NF1) cause neurofibromatosis type 1 (NF‐1), the most common inherited syndrome of the nervous system in humans, with a birth incidence of 1:3,000. The most visible features of NF‐1 are the neoplastic manifestations caused by the loss of Ras‐GTPase‐activating protein (Ras‐GAP) activity mediated through the GAP‐related domain (GRD) of neurofibromin (NF1), the protein encoded by NF1. However, the syndrome is also characterized by cognitive dysfunction and a number of developmental abnormalities. The molecular etiology of many of these nonneoplastic phenotypes remains unknown. Here we show that the tubulin‐binding domain (TBD) of NF1 is a binding partner of the leucine‐rich pentatricopeptide repeat motif‐containing (LRPPRC) protein. These two proteins complex with Kinesin 5B, hnRNP A2, Staufen1, and Myelin Basic Protein (MBP) mRNA, likely in RNA granules. This interaction is of interest in that it links NF‐1 with Leigh's syndrome, French Canadian variant (LSFC), an autosomal recessive neurodegenerative disorder that arises from mutations in the LRPPRC gene. Our findings provide clues to how loss or mutation of NF1 and LRPPRC may contribute to the manifestations of NF‐1 and LSFC. © 2013 Wiley Periodicals, Inc.     

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.     

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.     

Novel mutations in the NF1 gene in Czech patients with neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is one of the most common inherited human disorders, with an estimated incidence of 1 per 3500 births. In most cases, the disease is caused either by mutation in the NF1 gene, or by a particular or complete deletion of the NF1 gene. The NF1 gene exhibits one of the highest mutation rates of any human disorder. In this experimental study of the NF1 gene, we screened the mutational spectrum of 22 unrelated patients from the Czech Republic using the denaturing high-performance liquid chromatography (DHPLC) and multiplex ligation-dependent probe amplification (MLPA) methods. We found NF1 mutations in 17 patients: 15 causal mutations were detected with the use of the DHPLC method (15/20, 75%). With the MPLA method, we also confirmed and specified two large deletions that were previously genotyped by microsatellite markers. Twelve of the above-mentioned mutations were newly found: c.1_2delATinsCC, c.1185+1G>C, c.1757_1760delCTAG, c.1642-7A>G, c.2329 T>G, c.2816delA, c.3738_3741delGTTT, c.4733 C>T, c.5220delT, c.6473_6474insGAAG, ex14_49del, ex28_49del. We present this study as a first effectual step in the routine diagnosis of the NF1 in patients from the Czech Republic.     

Restored plasticity in a mouse model of neurofibromatosis type 1 via inhibition of hyperactive ERK and CREB

Patients with neurofibromatosis type 1 (NF1), resulting from neurofibromin gene mutations, frequently suffer from deficits in learning and spatial memory. Mice heterozygous for functional deletion of the NF1 gene (NF1(+/-) mice) also exhibit compromised spatial learning, and deficits in early-stage hippocampal long-term potentiation (LTP). Neurofibromin is a multifunctional protein which acts in part as an inhibitory constraint on Ras signalling, and the deficits in early-stage LTP and spatial learning have been linked to Ras hyperactivation. However, the downstream targets of Ras hyperactivation that lead to cognitive disruption are unknown. The levels of activity of signalling molecules potentially downstream of Ras were therefore studied in NF1(+/-) mice. Elevated phospho-ERK (pERK) levels were observed in the hippocampi from NF1(+/-) mice, while phospho-Akt/PKB (pAkt) and phospho-eIF4E (peIF4E) levels were unchanged relative to wild-type mice. Hippocampal levels of phospho-CREB (pCREB) were also increased, suggesting potential changes in late-phase LTP in NF1(+/-) mice. Indeed, LTP was found to be impaired for at least 4 h following induction in NF1(+/-) mice, linking neurofibromin function with the long-term maintenance of LTP. Remarkably, U0126, an inhibitor of ERK activation, at doses which reduced the hyperactive pERK levels in NF1(+/-) mice to the levels observed in control mice, caused a reduction in the deficits in early-phase LTP and completely rescued the long-term LTP deficits. In contrast to the abundant evidence that reductions in ERK activity lead to impaired plasticity, these data indicate that ERK hyperactivation in a partial model of type 1 neurofibromatosis leads to deficits in long-lasting hippocampal plasticity.     

Molecular study in von Recklinghausen neurofibromatosis (NF1)

The von Recklinghausen neurofibromatosis (NF1) gene has been mapped to the pericentromeric region of chromosome 17 and various DNA markers have been identified in this region. We have performed a genetic analysis using an anonymous DNA marker, HHH202 (D17S33), tightly linked to the NF1 gene in seven NF1 Italian families. Only one family was fully informative for the HHH202/RsaI polymorphism. In this family this marker can be used for presymptomatic and prenatal diagnosis. However, it is necessary to use additional flanking markers in order to increase informativeness and to obtain better diagnostic accuracy.