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Neurofibromatosis type-1 is a genetic disorder caused by loss-of-function variants in the tumor-suppressor NF1. Approximately 4% to 11% of neurofibromatosis type-1 patients have a NF1 locus complete deletion resulting from nonallelic homologous recombination between low copy repeats. Codeleted genes probably account for the more severe phenotype observed in NF1-deleted patients. This genotype-phenotype correlation highlights the need for a detailed molecular description. A droplet digital PCR (ddPCR) set along the NF1 locus was designed to delimitate the three recurrent NF1 deletion breakpoints. The ddPCR was tested in 121 samples from nonrelated NF1-deleted patients. Classification based on ddPCR versus multiplex ligation-dependent probe amplification (MLPA) was compared. In addition, microsatellites were analyzed to identify parental origin of deletions. ddPCR identified 77 type-1 (64%), 20 type-2 (16%), 7 type-3 (6%), and 17 atypical deletions (14%). The results were comparable with MLPA, except for three atypical deletions misclassified as type-2 using MLPA, for which the SUZ12 gene was not deleted. A significant maternal bias (25 of 30) in the origin of deletions was identified. This study proposes a fast and efficient ddPCR quantification to allow fine NF1 deletion classification. It indicates that ddPCR can be implemented easily into routine diagnosis to complement the techniques dedicated to NF1 point variant identification. This new tool may help unravel the genetic basis conditioning phenotypic variability in NF1-deleted patients and offer tailored genetic counseling., Competing Interests: Disclosure Statement None declared., (Copyright © 2024 Association for Molecular Pathology and American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Background: Neurofibromatosis type 1 (NF1) is characterized by the highly variable and unpredictable development of benign peripheral nerve sheath tumours: cutaneous (cNFs), subcutaneous (scNFs) and plexiform (pNFs) neurofibromas., Objectives: To identify neurofibroma modifier genes, in order to develop a database of patients with NF1., Methods: All patients were phenotypically evaluated by a medical practitioner using a standardized questionnaire and the causal NF1 variant identified. We enrolled 1333 patients with NF1 who were genotyped for > 7 million common variants., Results: A genome-wide association case-only study identified a significant association with 9q21.33 in the pNF phenotype in the discovery cohort. Twelve, three and four regions suggestive of association at the P ≤ 1 × 10-6 threshold were identified for pNFs, cNFs and scNFs, respectively. Evidence of replication was observed for 4, 2 and 6 loci, including 168 candidate modifier protein-coding genes. Among the candidate modifier genes, some were implicated in the RAS-mitogen-activated protein kinase pathway, cell-cycle control and myelination. Using an original CRISPR/Cas9-based functional assay, we confirmed GAS1 and SPRED2 as pNF and scNF candidate modifiers, as their inactivation specifically affected NF1-mutant Schwann cell growth., Conclusions: Our study may shed new light on the pathogenesis of NF1-associated neurofibromas and will, hopefully, contribute to the development of personalized care for patients with this deleterious and life-threatening condition., Competing Interests: Conflicts of interest The authors declare no conflicts of interest., (© The Author(s) 2023. Published by Oxford University Press on behalf of British Association of Dermatologists. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Differential diagnosis between constitutional mismatch repair deficiency (CMMRD) and neurofibromatosis type 1 (NF1 ) is crucial as treatment and surveillance differ. We report the case of a girl with a clinical diagnosis of sporadic NF1 who developed a glioblastoma. Immunohistochemistry for MMR proteins identified PMS2 loss in tumour and normal cells and WES showed the tumour had an ultra-hypermutated phenotype, supporting the diagnosis of CMMRD. Germline analyses identified two variants (one pathogenic variant and one classified as variant(s) of unknown significance) in the PMS2 gene and subsequent functional assays on blood lymphocytes confirmed the diagnosis of CMMRD. The large plexiform neurofibroma of the thigh and the freckling were however more compatible with NF1. Indeed, a NF1 PV (variant allele frequencies of 20%, 3% and 9% and in blood, skin and saliva samples, respectively) was identified confirming a mosaicism for NF1. Retrospective analysis of a French cohort identified NF1 mosaicism in blood DNA in 2 out of 22 patients with CMMRD, underlining the existence of early postzygotic PV of NF1 gene in patients with CMMRD whose tumours have been frequently reported to exhibit somatic NF1 mutations. It highlights the potential role of this pathway in the pathogenesis of CMMRD-associated gliomas and argues in favour of testing MEK inhibitors in this context., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease with complete penetrance but highly variable expressivity. In most patients, Next Generation Sequencing (NGS) technologies allow the identification of a loss-of-function pathogenic variant in the NF1 gene, a negative regulator of the RAS-MAPK pathway. We describe the 5-year diagnosis wandering of a patient with a clear NF1 clinical diagnosis, but no molecular diagnosis using standard molecular technologies. The patient presented with a typical NF1 phenotype but NF1 targeted NGS, NF1 transcript analysis, MLPA, and array comparative genomic hybridization failed to reveal a genetic aberration. After 5 years of unsuccessful investigations, trio WGS finally identified a de novo mosaic (VAF ~ 14%) 24.6 kb germline deletion encompassing the promoter and first exon of NF1. This case report illustrates the relevance of WGS to detect structural variants including copy number variants that would be missed by alternative approaches. The identification of the causal pathogenic variant allowed a tailored genetic counseling with a targeted non-invasive prenatal diagnosis by detecting the deletion in plasmatic cell-free DNA from the proband's pregnant partner. This report clearly highlights the need to make WGS a clinically accessible test, offering a tremendous opportunity to identify a molecular diagnosis for otherwise unsolved cases., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Individuals with the three base pair deletion NM_000267.3(NF1):c.2970_2972del p.(Met992del) have been recognised to present with a milder neurofibromatosis type 1 (NF1) phenotype characterised by café-au-lait macules (CALs) and intertriginous freckling, as well as a lack of cutaneous, subcutaneous and plexiform neurofibromas and other NF1-associated complications. Examining large cohorts of patients over time with this specific genotype is important to confirm the presentation and associated risks of this variant across the lifespan. Forty-one individuals with the in-frame NF1 deletion p.Met992del were identified from 31 families. Clinicians completed a standardised clinical questionnaire for each patient and the resulting data were collated and compared to published cohorts. Thirteen patients have been previously reported, and updated clinical information has been obtained for these individuals. Both CALs and intertriginous freckling were present in the majority of individuals (26/41, 63%) and the only confirmed features in 11 (27%). 34/41 (83%) of the cohort met NIH diagnostic criteria. There was a notable absence of all NF1-associated tumour types (neurofibroma and glioma). Neurofibroma were observed in only one individual-a subcutaneous lesion (confirmed histologically). Nineteen individuals were described as having a learning disability (46%). This study confirms that individuals with p.Met992del display a mild tumoural phenotype compared to those with 'classical', clinically diagnosed NF1, and this appears to be the case longitudinally through time as well as at presentation. Learning difficulties, however, appear to affect a significant proportion of NF1 subjects with this phenotype. Knowledge of this genotype-phenotype association is fundamental to accurate prognostication for families and caregivers., (© 2021. The Author(s).)

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease with complete penetrance but high variable expressivity. NF1 is caused by loss-of-function mutations in the NF1 gene, a negative regulator of the RAS-MAPK pathway. The NF1 gene has one of the highest mutation rates in human disorders, which may explain the outbreak of independent de novo variants in the same family. Here, we report the co-occurrence of pathogenic variants in the NF1 and SPRED1 genes in six families with NF1 and Legius syndrome, using next-generation sequencing. In five of these families, we observed the co-occurrence of two independent NF1 variants. All NF1 variants were classified as pathogenic, according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG-AMP) guidelines. In the sixth family, one sibling inherited a complete deletion of the NF1 gene from her mother and carried a variant of unknown significance in the SPRED1 gene. This variant was also present in her brother, who was diagnosed with Legius syndrome, a differential diagnosis of NF1. This work illustrates the complexity of molecular diagnosis in a not-so-rare genetic disease.

Neurofibromatosis type 1 (NF1) is a common tumor predisposition syndrome in which glioma is one of the prevalent tumors. Gliomagenesis in NF1 results in a heterogeneous spectrum of low- to high-grade neoplasms occurring during the entire lifespan of patients. The pattern of genetic and epigenetic alterations of glioma that develops in NF1 patients and the similarities with sporadic glioma remain unknown. Here, we present the molecular landscape of low- and high-grade gliomas in patients affected by NF1 (NF1-glioma). We found that the predisposing germline mutation of the NF1 gene was frequently converted to homozygosity and the somatic mutational load of NF1-glioma was influenced by age and grade. High-grade tumors harbored genetic alterations of TP53 and CDKN2A, frequent mutations of ATRX associated with Alternative Lengthening of Telomere, and were enriched in genetic alterations of transcription/chromatin regulation and PI3 kinase pathways. Low-grade tumors exhibited fewer mutations that were over-represented in genes of the MAP kinase pathway. Approximately 50% of low-grade NF1-gliomas displayed an immune signature, T lymphocyte infiltrates, and increased neo-antigen load. DNA methylation assigned NF1-glioma to LGm6, a poorly defined Isocitrate Dehydrogenase 1 wild-type subgroup enriched with ATRX mutations. Thus, the profiling of NF1-glioma defined a distinct landscape that recapitulates a subset of sporadic tumors.

Background: To limit risks of miscarriages associated with invasive procedures of current prenatal diagnosis practice, we aim to develop a personalized medicine-based protocol for non-invasive prenatal diagnosis (NIPD) of monogenic disorders relying on the detection of paternally inherited mutations in maternal blood using droplet digital PCR (ddPCR)., Methods: This study included four couples at risk of transmitting paternal neurofibromatosis type 1 (NF1) mutations and four couples at risk of transmitting compound heterozygous CFTR mutations. NIPD was performed between 8 and 15 weeks of gestation, in parallel to conventional invasive diagnosis. We designed specific hydrolysis probes to detect the paternal mutation and to assess the presence of cell-free fetal DNA by ddPCR. Analytical performances of each assay were determined from paternal sample, an then fetal genotype was inferred from maternal plasma sample., Results: Presence or absence of the paternal mutant allele was correctly determined in all the studied plasma DNA samples., Conclusions: We report an NIPD protocol suitable for implementation in an experienced laboratory of molecular genetics. Our proof-of-principle results point out a high accuracy for early detection of paternal NF1 and CFTR mutations in cell-free DNA, and open new perspectives for extending the technology to NIPD of many other monogenic diseases.

Neurofibromatosis type 1 (NF1) is a frequent autosomal dominant genetic disorder that predisposes to the development of benign and malignant tumors. Mutation of the NF1 gene affects the RAS-MAPK signaling pathway and leads to a dysfunction in cell proliferation and induces tumor development. Epidemiology of cancer in children with NF1 is very different from the general pediatric population, which requires regular and specific monitoring. Neurofibroma is the most frequent benign tumor. It can be very invalidating depending on the size and location of the tumor. Currently, there is no specific treatment for these tumors. The most frequent malignancies in children with NF1 are leukemias, rhabdomyosarcomas, malignant peripheral nerve sheath tumors and gliomas. The treatment of these tumors should consider the risk of second cancers induced by radio- and chemotherapy. We report on the case of a 5-year-old boy with NF1 developing two tumors., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)

Moyamoya syndrome (MMS) is the most common cerebral vasculopathy among children with neurofibromatosis type 1 (NF1). In this study, we clinically, radiologically, and genetically examined a cohort that was not previously described, comprising European children with NF1 and MMS. The NF1 genotyping had been registered. This study included 18 children. The mean age was 2.93 ± 3.03 years at the NF1 diagnosis and 7.43 ± 4.27 years at the MMS diagnosis. In seven patients, MMS was diagnosed before or at the same time as NF1. Neuroimaging was performed in 10 patients due to clinical symptoms, including headache (n = 6), cerebral infarction (n = 2), and complex partial seizures (n = 2). The remaining eight children (47%) had MMS diagnosed incidentally. Sixteen children were characterized molecularly. The features of MMS were similar between patients with and without NF1. Additionally, the NF1 phenotype and genotype were similar between children with and without MMS. Interestingly, three children experienced tumors with malignant histology or behavior. The presence of two first cousins in our cohort suggested that there may be potential genetic factors, not linked to NF1, with an additional role respect of NF1 might play a role in MMS pathogenesis. The incidental diagnosis of MMS, and the observation that, among children with NF1, those with MMS were clinically indistinguishable from those without MMS, suggested that it might be worthwhile to add an angiographic sequence to brain MRIs requested for children with NF1. A MMS diagnosis may assist in properly addressing an NF1 diagnosis in very young children who do not fulfill diagnostic criteria., (© 2017 Wiley Periodicals, Inc.)

The commonest tumors associated with neurofibromatosis type 1 (NF1) are benign peripheral nerve sheath tumors, called neurofibromas. Malignant transformation of neurofibromas into aggressive MPNSTs may occur with a poor patient prognosis. A cooperative role of SUZ12 or EED inactivation, along with NF1, TP53, and CDKN2A loss-of-function, has been proposed to drive progression to MPNSTs. An exome sequencing analysis of eight MPNSTs, one plexiform neurofibroma, and seven cutaneous neurofibromas was undertaken. Biallelic inactivation of the NF1 gene was observed in the plexiform neurofibroma and the MPNSTs, underlining that somatic biallelic NF1 inactivation is likely to be the initiating event for plexiform neurofibroma genesis, although it is unlikely to be sufficient for the subsequent MPNST development. The majority (5/8) of MPNSTs in our analyses demonstrated homozygous or heterozygous deletions of CDKN2A, which may represent an early event following NF1 LOH in the malignant transformation of Schwann cells from plexiform neurofibroma to MPNST. Biallelic somatic alterations of SUZ12 was also found in 4/8 MPNSTs. EED biallelic alterations were detected in 2 of the other four MPNSTs, with one tumor having a homozygous EED deletion. A missense mutation in the chromatin regulator KDM2B was also identified in one MPNST. No TP53 point mutations were found in this study, confirming previous data that TP53 mutations may be relatively rare in NF1-associated MPNSTs. Our study confirms the frequent biallelic inactivation of PRC2 subunits SUZ12 and EED in MPNSTs, and suggests the implication of KDM2B., (© 2017 Wiley Periodicals, Inc.)

Molecular diagnosis of neurofibromatosis type 1 (NF1) is challenging owing to the large size of the tumour suppressor gene NF1, and the lack of mutation hotspots. A somatic alteration of the wild-type NF1 allele is observed in NF1-associated tumours. Genetic heterogeneity in NF1 was confirmed in patients with SPRED1 mutations. Here, we present a targeted next-generation sequencing (NGS) of NF1 and SPRED1 using a multiplex PCR approach (230 amplicons of ∼150 bp) on a PGM sequencer. The chip capacity allowed mixing 48 bar-coded samples in a 4-day workflow. We validated the NGS approach by retrospectively testing 30 NF1-mutated samples, and then prospectively analysed 279 patients in routine diagnosis. On average, 98.5% of all targeted bases were covered by at least 20X and 96% by at least 100X. An NF1 or SPRED1 alteration was found in 246/279 (88%) and 10/279 (4%) patients, respectively. Genotyping throughput was increased over 10 times, as compared with Sanger, with ∼90[euro ] for consumables per sample. Interestingly, our targeted NGS approach also provided quantitative information based on sequencing depth allowing identification of multiexons deletion or duplication. We then addressed the NF1 somatic mutation detection sensitivity in mosaic NF1 patients and tumours.

Neurofibromatosis type 1 (NF1) is caused by dominant loss-of-function mutations of the tumor suppressor NF1 containing 57 constitutive coding exons. A huge number of different pathogenic NF1 alterations has been reported. The aim of the present study was to evaluate the usefulness of a multiplex ligation-dependent probe amplification (MLPA) approach in NF1 patients to detect single and multi-exon NF1 gene copy number variations. A genotype-phenotype correlation was then performed in NF1 patients carrying these types of genetic alterations. Among 565 NF1 index cases from the French NF1 cohort, single and multi-exon deletions/duplications screening identified NF1 partial deletions/duplications in 22 patients (~4%) using MLPA analysis. Eight single exon deletions, 11 multiple exons deletions, 1 complex rearrangement and 2 duplications were identified. All results were confirmed using a custom array-CGH. MLPA and custom array-CGH allowed the identification of rearrangements that were missed by cDNA/DNA sequencing or microsatellite analysis. We then performed a targeted next-generation sequencing of NF1 that allowed confirmation of all 22 rearrangements. No clear genotype-phenotype correlations were found for the most clinically significant disease features of NF1 in patients with single and multi-exons NF1 gene copy number changes.

Background: Neurofibromatosis 1 (NF1) belongs to the autosomal dominant neurocutaneous disorders' group, which mainly includes NF1 and NF2, tuberous sclerosis, von Hippel-Lindau disease and Cerebral Cavernous Malformations (CCMs). NF1 has a major impact on the nervous system, eye, skin, bone or cardiovascular system. Cerebrovascular lesions have been reported in NF1 including aneurysm, pseudoaneurysm, arteriovenous malformations, vascular stenosis or occlusion and Moya moya syndrome., Objective: To report a case of an NF1 patient with multiple CCMs., Observation: A 47-year-old man with café-au-lait skin lesions, countless cutaneous neurofibromas, short stature and scoliosis was admitted for progressive spinal cord compression due to histologically proven neurofibroma. Systematic cerebral MRI screening including gradient echo sequences showed multiple asymptomatic CCMs. Screening of CCM1, CCM2 and CCM3 genes was negative while a deleterious frameshift mutation was identified in NF1 gene., Conclusion: While single CCM can occur in NF1 patients following radiation exposure, they are only rarely reported in non-irradiated NF1 brain. Even if it could be a fortuitous association, plausible links and explanations exist. If cerebral MRI can be systematic in NF1 to detect asymptomatic gliomas, used protocols in neuroradiology do not usually include gradient echo sequences, the most sensitive test for CCM detection, leading possibly to failure to detect these vascular lesions. More reports having this combination and further investigations of NF1 families will certainly provide a better understanding of links between these 2 phakomatoses, as recently reported with "multiple meningiomas" phenotype associated with multiple CCMs in patients with CCM3 gene mutations or café-au-lait skin lesions in CCM1 mutation carriers., (Copyright © 2015. Published by Elsevier B.V.)

Neurofibromatosis type 1 (NF1) is an autosomal dominant, multi-system, neurocutaneous disorder that predisposes to the development of benign and malignant tumors with a birth incidence rate of 1 in 2500-3000. 50% of cases are sporadic. The diagnosis is exclusively based on clinical assessment with clinical diagnostic criteria such as café-au-lait spots, neurofibromas, axillary or groin freckling, Lisch nodules, optic pathway glioma, bony dysplasia and first-degree relative with NF1. We report a family with NF1 in which two members presented atypical clinical features in addition to the classical diagnostic criteria. Three relatives affected by NF1, a father and two of his three sons, are described. The clinical diagnosis was originally worn in all three cases, with the association many spots café-au -lait over the entire body and some axillary freckling as well as first-degree relative. One case presented an Acute Myeloid Leukemia (AML) type 2 at 10 years of age diagnosed before the revelation of bicytopenia associated pallor and isolated asthenia. A second case presented a nephrotic syndrome at 4 years of age due to the association of hydrops with headache and asthenia. Direct sequencing of NF1 led to identify the familial mutation, a previously unreported heterozygous missense mutation c.3443C > A, p.Ala1148Glu in exon 20 which segregated with all three affected patients. The family described in this report confirms the high clinical variability of NF1, even intrafamilial, and raises the question as to whether rare features such as AML and nephrotic syndrome are associated with NF1. Some NF1 patients presenting glomerular diseases or AML have rarely been reported, but due to the small number of cases described the mechanisms underlying these associations are poorly understood. However, it seems important to be aware of the possible occurrence of nephritic syndrome and/or malignant blood diseases in NF1 patients., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)

Purpose: The hallmark of neurofibromatosis type 1 (NF1) is the onset of dermal or plexiform neurofibromas, mainly composed of Schwann cells. Plexiform neurofibromas can transform into malignant peripheral nerve sheath tumors (MPNST) that are resistant to therapies., Experimental Design: The aim of this study was to identify an additional pathway in the NF1 tumorigenesis. We focused our work on Wnt signaling that is highly implicated in cancer, mainly in regulating the proliferation of cancer stem cells. We quantified mRNAs of 89 Wnt pathway genes in 57 NF1-associated tumors including dermal and plexiform neurofibromas and MPNSTs. Expression of two major stem cell marker genes and five major epithelial-mesenchymal transition marker genes was also assessed. The expression of significantly deregulated Wnt genes was then studied in normal human Schwann cells, fibroblasts, endothelial cells, and mast cells and in seven MPNST cell lines., Results: The expression of nine Wnt genes was significantly deregulated in plexiform neurofibromas in comparison with dermal neurofibromas. Twenty Wnt genes showed altered expression in MPNST biopsies and cell lines. Immunohistochemical studies confirmed the Wnt pathway activation in NF1-associated MPNSTs. We then confirmed that the knockdown of NF1 in Schwann cells but not in epithelial cells provoked the activation of Wnt pathway by functional transfection assays. Furthermore, we showed that the protein expression of active β-catenin was increased in NF1-silenced cell lines. Wnt pathway activation was strongly associated to both cancer stem cell reservoir and Schwann-mesenchymal transition., Conclusion: We highlighted the implication of Wnt pathway in NF1-associated tumorigenesis., (©2013 AACR.)

Neurofibromatosis type 1 (NF1) affects about one in 3,500 people in all ethnic groups. Most NF1 patients have private loss-of-function mutations scattered along the NF1 gene. Here, we present an original NF1 investigation strategy and report a comprehensive mutation analysis of 565 unrelated patients from the NF-France Network. A NF1 mutation was identified in 546 of the 565 patients, giving a mutation detection rate of 97%. The combined cDNA/DNA approach showed that a significant proportion of NF1 missense mutations (30%) were deleterious by affecting pre-mRNA splicing. Multiplex ligation-dependent probe amplification allowed the identification of restricted rearrangements that would have been missed if only sequencing or microsatellite analysis had been performed. In four unrelated families, we identified two distinct NF1 mutations within the same family. This fortuitous association points out the need to perform an exhaustive NF1 screening in the case of molecular discordant-related patients. A genotype-phenotype study was performed in patients harboring a truncating (N = 368), in-frame splicing (N = 36), or missense (N = 35) mutation. The association analysis of these mutation types with 12 common NF1 clinical features confirmed a weak contribution of the allelic heterogeneity of the NF1 mutation to the NF1 variable expressivity., (© 2013 WILEY PERIODICALS, INC.)

Background: Neurofibromatosis type 1 (NF1) is a common dominant tumor predisposition syndrome affecting 1 in 3,500 individuals. The hallmarks of NF1 are the development of peripheral nerve sheath tumors either benign (dermal and plexiform neurofibromas) or malignant (MPNSTs)., Results: To comprehensively characterize the role of microRNAs in NF1 tumorigenesis, we analyzed 377 miRNAs expression in a large panel of dermal and plexiform neurofibromas, and MPNSTs. The most significantly upregulated miRNA in plexiform neurofibromas was miR-486-3p that targets the major tumor suppressor gene, PTEN. We confirmed PTEN downregulation at mRNA level. In plexiform neurofibromas, we also report aberrant expression of four miRNAs involved in the RAS-MAPK pathway (miR-370, miR-143, miR-181a, and miR-145). In MPNSTs, significant deregulated miRNAs were involved in PTEN repression (miR-301a, miR-19a, and miR-106b), RAS-MAPK pathway regulation (Let-7b, miR-195, and miR-10b), mesenchymal transition (miR-200c, let-7b, miR-135a, miR-135b, and miR-9), HOX genes expression (miR-210, miR-196b, miR-10a, miR-10b, and miR-9), and cell cycle progression (miR-195, let-7b, miR-20a, miR-210, miR-129-3p, miR-449a, and miR-106b)., Conclusion: We confirmed the implication of PTEN in genesis of plexiform neurofibromas and MPNSTs in NF1. Markedly deregulated miRNAs might have potential diagnostic or prognostic value and could represent novel strategies for effective pharmacological therapies of NF1 tumors.

Here we report on a family with two siblings born to unrelated healthy parents, one with neurofibromatosis type 1 (NF1) and the other with Noonan syndrome (NS). Molecular investigations performed on the NF1 and PTPN11 genes showed two independent de novo mutations as a cause for NF1 in the NF1 proband and NS in her affected brother. Both de novo mutations were potentially of paternal origin, given the advanced paternal age at the time of conception., (Copyright © 2012 Wiley Periodicals, Inc.)

Although neurofibromatosis 1 (NF1) is a common Mendelian disorder with autosomal-dominant inheritance, its expression is highly variable and unpredictable. Many NF1 patients have been genotyped but few allele-phenotype correlations have been identified. NF1 genotype-phenotype correlations are difficult to identify because of the complexity of the NF1 phenotype, its strong age dependency, the relatedness of many clinical features and the huge heterogeneity of pathogenic NF1 mutations. Some NF1 patients with a given NF1 mutation may develop very severe disease while others with the same mutation have only mild symptoms. This phenotypic variability may be due to both modifier genes and environmental factors. Recent targeted strategies have identified several interesting candidate modifier genes.

Background: Neurofibromatosis type 1 (NF1) is a tumor predisposition syndrome with a worldwide birth incidence of one in 2500. Genetic factors unrelated to the NF1 locus are thought to influence the number of plexiform neurofibromas (PNFs) in patients with NF1, but no factors have been identified to date., Methods: We used high-resolution array comparative genomic hybridization of tissue from 22 PNFs obtained from 18 NF1 patients to identify modifier genes involved in PNF development. We used a family-based association test for five previously identified cancer-susceptibility tag single-nucleotide polymorphisms (rs1063192, rs2151280, rs2218220, rs10757257, and rs7023329) located in chromosomal region 9p21.3 in 1105 subjects (740 NF1 patients and 365 non-affected relatives) from 306 families. To confirm the functional role of rs2151280, we used real-time quantitative reverse transcription-polymerase chain reaction to analyze the expression of cyclin-dependent kinase inhibitor 2A (CDKN2A), CDKN2B, alternate reading frame (ARF), and antisense noncoding RNA in the INK4 locus (ANRIL) in the peripheral blood of 124 NF1 patients. Relationships between CDKN2A, CDKN2B, ARF, and ANRIL expression and the rs2151280 genotype were tested by the Kruskal-Wallis test. All statistical tests were two-sided., Results: In NF1-associated PNFs, 9p21.3 deletions (including the CDKN2A/B-ANRIL locus) were found as the only recurrent somatic alterations. Single-nucleotide polymorphism rs2151280 (located in ANRIL) was statistically significantly associated with the number of PNFs (P < .001) in NF1 patients. In addition, allele T of rs2151280 was statistically significantly associated with reduced ANRIL transcript levels (P < .001), suggesting that modulation of ANRIL expression mediates PNF susceptibility., Conclusion: Identification of ANRIL as a modifier gene in NF1 may offer clues to the molecular pathogenesis of PNFs, particularly neurofibroma formation, and emphasizes the unanticipated role of large noncoding RNA in activation of critical regulators of tumor development.

Neurofibromatosis type 1 (NF1) patients are at increased risk of developing both benign (neurofibromas) and malignant (malignant peripheral nerve sheath tumors, MPNST) tumors. Molecular data on tumor progression are scarce, and few studies have compared the NF1 locus copy number in these two tumor types. To further explore the role of such NF1 locus rearrangements in NF1 tumorigenesis, and the likely disruption to the associated genes, the NF1 gene region was analyzed in NF1-associated tumors. DNA from three MPNSTs and one neurofibroma, excised from three unrelated NF1 patients, were analyzed using an NF1 region customized array-based comparative genomic hybridization. The somatic NF1 inactivation mutational mechanisms associated with MPNSTs appear to be different from those in benign neurofibromas. Interestingly, the MPNST-associated deletion breakpoints did not involve the paralogous repetitive sequences that are involved in most germline NF1 deletions. The somatic smallest common region of deletion overlap, however, was restricted to approximately the same ~2.2-Mb interval that encompassed most of the genes deleted in NF1 recurrent constitutional deletions. A number of genes in addition to NF1 on 17q (centromere to 17q24.2) may be involved in MPNST development. A larger study is warranted to confirm these findings. As NF1 patients with such germline NF1 deletions do exhibit increased risk of developing MPNST, these present findings emphasize the likely role of at least some of these NF1 flanking genes in MPNST pathobiology.

We investigated the expression of SOX9, a transcription factor linked to the hedgehog pathways, and desert hedgehog, previously shown to be expressed in a malignant peripheral nerve sheath tumor cell line, in neurofibromatosis 1 tumors (neurofibromas and malignant peripheral nerve sheath tumor), and in a group of sporadic spindle cell sarcomas. We found that SOX9 was expressed in Schwann cells from neurofibromatosis 1 tumors, and was significantly up-regulated in malignant peripheral nerve sheath tumor versus neurofibromas at the protein level (P < .0001) and in malignant peripheral nerve sheath tumor and plexiform neurofibroma as compared to diffuse tumors at the mRNA level (P = .002 and P = .009, respectively). SOX9, however, was not a specific feature of malignant peripheral nerve sheath tumor because a significant proportion of spindle cell sarcomas unrelated to neurofibromatosis 1 were also positive. Interestingly, within neurofibromas, SOX9 expression correlated to the histology mostly found in plexiform areas, whereas it was negative or weak in diffuse neurofibroma (P < .0001). In sporadic sarcomas, the proportion of positive cells was actually heterogeneous among cases. Desert hedgehog expression was mostly found in sarcomas (P = .0002), but diffuse staining was only seen in non-neurofibromatosis 1 tumors, whereas malignant peripheral nerve sheath tumor displayed only focal expression. Finally, we found no significant correlation between the expression of SOX9 and desert hedgehog, and neither SOX9 nor desert hedgehog expression was correlated to the histoprognostic grade in sarcomas. Altogether, these results indicate that, although not a specific feature of neurofibromatosis 1 tumors, SOX9 may play a role in the development of malignant peripheral nerve sheath tumor in patients with neurofibromatosis 1 and does not appear to be linked to autocrine stimulation by the desert hedgehog signaling pathway., (Copyright © 2011 Elsevier Inc. All rights reserved.)

In 5-10% of patients, neurofibromatosis type 1 (NF1) results from microdeletions that encompass the entire NF1 gene and a variable number of flanking genes. Two recurrent microdeletion types are found in most cases, with microdeletion breakpoints located in paralogous regions flanking NF1 (proximal NF1-REP-a and distal NF1-REP-c for the 1.4 Mb type-1 microdeletion, and SUZ12 and SUZ12P for the 1.2 Mb type-2 microdeletion). A more severe phenotype is usually associated with NF1 microdeletion patients than in those with intragenic mutations. We characterized NF1 microdeletions in 70 unrelated NF1 microdeleted patients using a high-resolution NF1 custom array comparative genomic hybridization (CGH). Genotype-phenotype correlations were studied in 58 of these microdeletion patients and compared to 389 patients with intragenic truncating NF1 mutations and phenotyped in the same standardized way. Our results confirmed in an unbiased manner the existence of a contiguous gene syndrome with a significantly higher incidence of learning disabilities and facial dysmorphism in microdeleted patients compared to patients with intragenic NF1 mutations. Microdeleted NF1 patients also showed a trend toward significance for childhood overgrowth. High-resolution array-CGH identified a new recurrent approximately 1.0 Mb microdeletion type, designated as type-3, with breakpoints in the paralogous regions middle NF1-REP-b and distal NF1-REP-c.

The hallmark of neurofibromatosis type 1 is the development of dermal and plexiform neurofibromas. Neurofibromatosis type 1 patients with plexiform neurofibromas are at risk of developing malignant peripheral nerve sheath tumors. We applied a 22,000-oligonucleotide microarray transcriptomic approach to a series of plexiform neurofibromas in comparison with dermal neurofibromas, and results were confirmed with real-time quantitative reverse transcription-polymerase chain reaction. Thirteen genes were upregulated and 10 were downregulated in plexiform neurofibromas. The upregulated genes mainly encode molecules involved in cell adhesion, extracellular matrix, fibrogenesis, and angiogenesis. Several CCN gene family members were dysregulated in neurofibromatosis type 1 tumorigenesis; the angiogenic gene CCN1/CYR61 was specifically upregulated in the plexiform neurofibromas; CCN4/WISP1 was upregulated, and CCN3/NOV and CCN5/WISP2 were downregulated in paired comparisons of plexiform neurofibroma and malignant peripheral nerve sheath tumor from the same patients. CCN1 and CCN3 proteins were detected by immunohistochemistry in neurofibromatosis type 1-associated tumors. Upregulation of S100A8, S100A9, and CD36 was also observed and suggests a role of this pathway in inflammation-associated genesis of plexiform neurofibromas. In summary, a limited number of pathways are potentially involved in plexiform neurofibroma development. Some of the genes identified, particularly CCN1, might be useful diagnostic or prognostic markers or form the basis for novel therapeutic strategies.

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder which displays considerable inter- and intra-familial variability in phenotypic expression. To evaluate the genetic component of variable expressivity in NF1, we examined the phenotypic correlations between affected relatives in 750 NF1 patients from 275 multiplex families collected through the NF-France Network. Twelve NF1-related clinical features, including five quantitative traits (number of café-au-lait spots of small size and of large size, and number of cutaneous, subcutaneous and plexiform neurofibromas) and seven binary ones, were scored. All clinical features studied, with the exception of neoplasms, showed significant familial aggregation after adjusting for age and sex. For most of them, patterns of familial correlations indicated a strong genetic component with no apparent influence of the constitutional NF1 mutation. Heritability estimates of the five quantitative traits ranged from 0.26 to 0.62. Moreover, we investigated for the first time the role of the normal NF1 allele in the variable expression of NF1 through a family-based association study. Nine tag SNPs in NF1 were genotyped in 1132 individuals from 313 NF1 families. No significant deviations of transmission of any of the NF1 variants to affected offspring was found for any of the 12 clinical features examined, based on single marker or haplotype analysis. Taken together, our results provided evidence that genetic modifiers, unlinked to the NF1 locus, contribute to the variable expressivity of the disease.

Objective: Germline loss-of-function mutations in the SPRED1 gene have recently been identified in patients fulfilling the National Institutes of Health (NIH) diagnostic criteria for neurofibromatosis type 1 (NF1) but with no NF1 (neurofibromin 1) mutation found, suggesting a neurofibromatosis type 1-like syndrome., Methods: 61 index cases with NF1 clinical diagnosis but no identifiable NF1 mutation were screened for SPRED1 mutation., Results: We describe one known SPRED1 mutation (c.190C>T leading to p.Arg64Stop) and four novel mutations (c.637C>T leading to p.Gln213Stop, c.2T>C leading to p.Met1Thr, c.46C>T leading to p.Arg16Stop, and c.1048&#95;1060del leading to p.Gly350fs) in five French families. Their NF1-like phenotype was characterised by a high prevalence of café-au-lait spots, freckling, learning disability, and an absence of neurofibromas and Lisch nodules in agreement with the original description. However, we did not observe Noonan-like dysmorphy. It is noteworthy that one patient with the p.Arg16Stop mutation developed a monoblastic acute leukaemia., Conclusions: In our series, SPRED1 mutations occurred with a prevalence of 0.5% in NF1 patients and in 5% of NF1 patients displaying an NF1-like phenotype. SPRED1 mutated patients did not display any specific dermatologic features that were not present in NF1 patients, except for the absence of neurofibromas that seem to be a specific clinical feature of NF1. The exact phenotypic spectrum and the putative complications of this NF1 overlapping syndrome, in particular haematological malignancies, remain to be further characterised. NIH diagnostic criteria for NF1 must be revised in view of this newly characterised Legius syndrome in order to establish a specific genetic counselling.

We describe a large germline deletion removing the NF1 locus, identified by heterozygosity mapping based on microsatellite markers, in an 8-year-old French girl with a particularly severe NF1 contiguous gene syndrome. We used gene-dose mapping with sequence-tagged site real-time PCR to locate the deletion end points, which were precisely characterized by means of long-range PCR and nucleotide sequencing. The deletion is located on chromosome arm 17q and is exactly 7 586 986 bp long. It encompasses the entire NF1 locus and about 100 other genes, including numerous chemokine genes, an attractive in silico-selected cerebrally expressed candidate gene (designated NUFIP2, for nuclear fragile X mental retardation protein interacting protein 2; NM&#95;020772) and four microRNA genes. Interestingly, the centromeric breakpoint is located in intron 4 of the PIPOX gene (pipecolic acid oxidase; NM&#95;016518) and the telomeric breakpoint in intron 5 of the GGNBP2 gene (gametogenetin binding protein 2; NM&#95;024835) coding a transcription factor. As PIPOX and GGNBP2 have the same transcriptional orientation, we postulated, and then confirmed, the existence of a chimeric transcript. This transcript, and/or haploinsufficiency of one or several deleted genes, could explain the clinical severity of the syndrome in this patient.

The severity of neurofibromatosis 1 and its variable expressivity make prenatal diagnosis appealing. We conducted our research to assess patient characteristics associated with the desire for prenatal diagnosis. Between 1995 and 2004, 361 neurofibromatosis 1 adult patients were interviewed about their desire for prenatal diagnosis. Answers were classified in three groups: (1) 'no;' (2) 'uncertain;' (3) 'yes.' Socio-demographical and clinical data were analyzed by logistic multinomial regression for their association with the desire for prenatal diagnosis. Male-to-female sex ratio was 0.93. Mean age at study +/- SD was 33.5 +/- 10. Seven four patients (20.5%) would consider prenatal diagnosis; 240 (66.5%) did not; and 47 (13.0%) were uncertain. In multivariate analysis, compared to the 'no' group, a longer follow-up (OR = 1.25 [1.11-1.41]), a younger age at study time (OR = 1.25 [1.11-1.41]), not having child (OR = 2.46 [1.03-5.97]) and a higher educational level (OR = 5.07 [1.05-24.47]) were independently associated with the 'yes' group. Compared to the 'no' group individuals who were in the 'uncertain' groups were younger (0.95 [0.90-0.99]), less often married (0.11 [0.01-0.89]) and had a longer follow-up (1.26 [1.09-1.46]). There is a significant demand for prenatal diagnosis among neurofibromatosis 1 French patients. This demand is associated with individuals who are younger, have no child, have a longer follow up, and higher level of education., ((c) 2007 Wiley-Liss, Inc.)

As a component of the apoptosome, a caspase-activating complex, Apaf-1 plays a central role in the mitochondrial caspase activation pathway of apoptosis. We report here the identification of a novel Apaf-1 interacting protein, hepatocellular carcinoma antigen 66 (HCA66) that is able to modulate selectively Apaf-1-dependent apoptosis through its direct association with the CED4 domain of Apaf-1. Expression of HCA66 was able to potentiate Apaf-1, but not receptor-mediated apoptosis, by increasing downstream caspase activity following cytochrome c release from the mitochondria. Conversely, cells depleted of HCA66 were severely impaired for apoptosome-dependent apoptosis. Interestingly, expression of the Apaf-1-interacting domain of HCA66 had the opposite effect of the full-length protein, interfering with the Apaf-1 apoptotic pathway. Using a cell-free system, we showed that reduction of HCA66 expression was associated with a diminished amount of caspase-9 in the apoptosome, resulting in a lower ability of the apoptosome to activate caspase-3. HCA66 maps to chromosome 17q11.2 and is among the genes heterozygously deleted in neurofibromatosis type 1 (NF1) microdeletion syndrome patients. These patients often have a distinct phenotype compared to other NF1 patients, including a more severe tumour burden. Our results suggest that reduced expression of HCA66, owing to haploinsufficiency of HCA66 gene, could render NF1 microdeleted patients-derived cells less susceptible to apoptosis.

Purpose: Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with a complex variety of clinical manifestations. The hallmark of NF1 is the onset of heterogeneous (dermal or plexiform) benign neurofibromas. Plexiform neurofibromas can give rise to malignant peripheral nerve sheath tumors, which are resistant to conventional therapies., Experimental Design: To identify new signaling pathways involved in the malignant transformation of plexiform neurofibromas, we applied a 22,000-oligonucleotide microarray approach to a series of plexiform neurofibromas and malignant peripheral nerve sheath tumors. Changes in the expression of selected genes were then confirmed by real-time quantitative reverse transcription-PCR., Results: We identified two tenascin gene family members that were significantly deregulated in both human NF1-associated tumors and NF1-deficient primary cells: Tenascin C (TNC) was up-regulated whereas tenascin XB (TNXB) was down-regulated during tumor progression. TNC activation is mainly due to the up-regulation of large TNC splice variants. Immunohistochemical studies showed that TNC transcripts are translated into TNC protein in TNC-overexpressing tumors. Aberrant transcriptional activation of TNC seems to be principally mediated by activator protein transcription factor complexes., Conclusion: TNXB and TNC may be involved in the malignant transformation of plexiform neurofibromas. Anti-TNC antibodies, already used successfully in clinical trials to treat malignant human gliomas, may be an appropriate new therapeutic strategy for NF1.

Background: Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with a complex range of clinical symptoms. The hallmark of NF1 is the onset of heterogeneous (dermal or plexiform) benign neurofibromas. Plexiform neurofibromas can give rise to malignant peripheral nerve sheath tumors (MPNSTs), and the underlying molecular mechanisms are largely unknown., Results: To obtain further insight into the molecular pathogenesis of MPNSTs, we used real-time quantitative RT-PCR to quantify the mRNA expression of 489 selected genes in MPNSTs, in comparison with plexiform neurofibromas. The expression of 28 (5.7%) of the 489 genes was significantly different between MPNSTs and plexiform neurofibromas; 16 genes were upregulated and 12 were downregulated in MPNSTs. The altered genes were mainly involved in cell proliferation (MKI67, TOP2A, CCNE2), senescence (TERT, TERC), apoptosis (BIRC5/Survivin, TP73) and extracellular matrix remodeling (MMP13, MMP9, TIMP4, ITGB4). More interestingly, other genes were involved in the Ras signaling pathway (RASSF2, HMMR/RHAMM) and the Hedgehog-Gli signaling pathway (DHH, PTCH2). Several of the down-regulated genes were Schwann cell-specific (L1CAM, MPZ, S100B, SOX10, ERBB3) or mast cell-specific (CMA1, TPSB), pointing to a depletion and/or dedifferentiation of Schwann cells and mast cells during malignant transformation of plexiform neurofibromas., Conclusion: These data suggest that a limited number of signaling pathways, and particularly the Hedgehog-Gli signaling pathway, may be involved in malignant transformation of plexiform neurofibromas. Some of the relevant genes or their products warrant further investigation as potential therapeutic targets in NF1.

Purpose: Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder with a complex variety of clinical symptoms. The hallmark of NF1 is the development of heterogeneous benign neurofibromas, which may appear as dermal neurofibromas or plexiform neurofibromas. NF1 patients with plexiform neurofibromas are at risk of developing malignant peripheral nerve sheath tumors., Experimental Design: To obtain additional insight into the molecular pathogenesis of plexiform neurofibromas, we used real-time quantitative reverse transcription-PCR assays to quantify the mRNA expression of 349 selected genes in plexiform neurofibromas in comparison with dermal neurofibromas and patient-matched malignant peripheral nerve sheath tumors., Results: Thirty genes were significantly up-regulated in plexiform neurofibromas compared with dermal neurofibromas. None were down-regulated. The up-regulated genes mainly encoded transcription factors and growth factors and secreted proteins, cytokines, and their receptors, pointing to a role of paracrine and autocrine signaling defects in the genesis of plexiform neurofibromas. We also identified a gene expression profile, based on MMP9, FLT4/VEGFR3, TNFRSF10B/TRAILR2, SHH, and GLI1, which discriminated those plexiform neurofibromas most likely to undergo malignant transformation., Conclusion: Our study has identified a limited number of signaling pathways that could be involved, when altered, in plexiform neurofibroma development. Some of the up-regulated genes could be useful diagnostic or prognostic markers or form the basis of novel therapeutic strategies.

An NF1 microdeletion is the single most commonly reported mutation in individuals with neurofibromatosis type 1 (NF1). Individuals with an NF1 microdeletion have, as a group, more neurofibromas at a younger age than the group of all individuals with NF1. We report that NF1 microdeletion individuals additionally have a substantially higher lifetime risk for the development of malignant peripheral nerve sheath tumors than individuals with NF1 who do not have an NF1 microdeletion. This should be taken into account in the medical follow-up of individuals with an NF1 microdeletion.

We studied 20 unrelated NF1 patients by Southern blots with seven cDNA probes and loss of heterozygosity (LOH) analysis with four intragenic microsatellites (IVS26-2.3, IVS27AC28.4, IVS27AC33.1, and IVS38GT53.0). Four novel large deletions (178, 184, 236, and 237) have been identified and characterized. The breakpoint of deletion 178 was located in between exons 23-2 and 27b and the sequences downstream of the breakpoint were deleted. For deletion 184, the breakpoint was in between exons 27b and 29, and the region upstream of the breakpoint was deleted. With deletion 236, the breakpoint was in between exons 14 and 18 and the region downstream of the breakpoint was deleted. The breakpoint of deletion 237 was in between exons 38 and 45 and the sequences upstream of the breakpoint were deleted. These deletions were distributed randomly across the NF1 gene and no deletion hot spot was found. Our study suggests that the combination of analyses of loss of heterozygosity, southern blotting and southern blot densitometry can be used as a powerful method to detect large deletions, especially when family record is not available or the patient is a sporadic case., (Copyright 2001 Wiley-Liss, Inc.)

Using a protein truncation assay, we have identified a new mutation in the neurofibromatosis type 1 (NF1) gene that causes a severe defect in NF1 pre-mRNA splicing. The mutation, which consists of a G to A transition at position +1 of the 5' splice site of exon 12a, is associated with the loss of both exons 11 and 12a in the NF1 mRNA. Through the use of in vivo and in vitro splicing assays, we show that the mutation inactivates the 5' splice site of exon 12a, and prevents the definition of exon 12a, a process that is normally required to stimulate the weak 3' splice site of exon 12a. Because the 5' splice site mutation weakens the interaction of splicing factors with the 3' splice site of exon 12a, we propose that exon 11/exon 12a splicing is also compromised, leading to the exclusion of both exons 11 and 12a. Our results provide in vivo support for the importance of the exon definition model during NF1 splicing, and suggest that the NF1 region containing exons 11 and 12a plays an important role in the activity of neurofibromin., (Copyright 2001 Academic Press.)

We studied the NF1 gene in 93 unrelated patients with neurofibromatosis type1, focusing the analysis on four exons that contain the highest number of possible mutations occurring at CpG sites. We used denaturing gradient gel electrophoresis to analyse exons 16, 28, 29 and 49, which contain 45 (25%) of the 183 possible mutations that could occur at the 120 CpG dinucleotides of the coding sequence. Six different mutations were identified, five of which are novel: two truncating mutations, W1810X and 5448insG, located in exon29; two splice defects leading to exon29 skipping, 5206-2A>G and 5546G>A; and one missense mutation, L844F, located in exon16. The already described R1748X mutation located in exon29 was found in two unrelated patients. The 5546G>A and R1748X mutations are located at CpG sites, whereas the W1810X involves a CpNpG site. Four novel polymorphisms, which may be helpful for family studies, were also identified. Overall, all but one mutations were found in exon29, a result which suggests that all the CpG sites of the NF1 coding sequence do not have the same mutability, and that exon29, the most CpG-rich exon, contains mutational hotspots associated with NF1., (Copyright 2000 Wiley-Liss, Inc.)

Neurofibromatosis type 1 (NF1), a genetic disorder with neuroectodermal involvement, demonstrates phenotypic overlap in some patients with Noonan syndrome (NS), ultimately resulting in the so-called neurofibromatosis-Noonan syndrome (NF-NS). A strong association of the two phenotypic traits was recently illustrated by a four-generation family, although NF1 and NS were eventually demonstrated to segregate independently on the basis of polymorphic DNA markers [Bahuau et al., 1996: Am J Med Genet 66:347-355]. Identification of the causal NF1 mutation seemed a prerequisite to further dissecting this singular familial association. Using the protein truncation assay, a nonsense mutation (C2446T-->R816X) of the neurofibromin gene was evidenced. This mutation occurred on a CpG dinucleotide within exon 16 and 5' to the GAP domain-specifying region of the gene. R816X creates a recognition site for endonuclease HphI, absent in 2 individuals with NS only. Screening 184 unrelated NF1 patients, three novel occurrences of the mutation were found in individuals diagnosed with classical NF1. Based on the assumption of genotype-phenotype correlation in these individuals, clinical and molecular analyses of this four-generation family demonstrated that the NF-NS phenotype was additive, being the result of both classical NF1 and NS. This particular observation also suggests the presence of an NS locus on 17q, which might be of interest for further linkage studies.

A large four-generation family with Noonan syndrome (NS) and neurofibromatosis-type 1 (NF1) was studied for clinical association between the two diseases and for linkage analysis with polymorphic DNA markers of the NF1 region in 17q11.2. Nonrandom segregation between NS and NF1 phenotypes was observed. Neurofibromatosis was tightly linked to NF1 markers, whereas Noonan syndrome was found not be allelic to NF1. These results suggest that two mutations at two independent but closely linked loci are the cause of neurofibromatosis-Noonan syndrome (NF-NS) association in this family.

Introduction: Type 1 neurofibromatous tumours (NF) are benign skin tumours which include cutaneous, subcutaneous and plexiform neurofibromas. Plexiform neurofibromas are either diffuse or nodular, the latter form being much more frequent., Case Report: We observed a particular form of neurofibroma in an 18-year-old patient who developed large deep subcutaneous which histology examination revealed to be exclusively nodular plexiform neurofibromas. The patient also had 6 café au lait spots leading to the diagnosis of sporadic NF 1. He did not have acoustic neuronoma, schwannoma or posterior cataract, eliminating NF 2., Comments: In NF 1, subcutaneous neurofibromas develop in 5 p. 100 of the patients. These lesions are termed nodular plexiform neurofibromas when they form long formations along nerve branches. The exclusive nature of the nodular plexiform neurofibromas in our case was exceptional. It could be hypothesized that the particular phenotype in our patient might correspond to a particular anomaly of the NF 1 gene.