NF1 microdeletions in neurofibromatosis type 1: from genotype to phenotype

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 ～1.0 Mb microdeletion type, designated as type‐3, with breakpoints in the paralogous regions middle NF1‐REP‐b and distal NF1‐REP–c. © 2010 Wiley‐Liss, Inc.     

Recurrent NF1 gene mutation in a patient with oligosymptomatic neurofibromatosis type 1 (NF1)

We report a 21-year-old male with symptomatic optic glioma who does not fulfill the diagnosis of neurofibromatosis 1 (NF1) according to standard NIH criteria. Analysis of the NF1 gene revealed a recurrent mutation in exon 37 (C6792A or Y2264X). This nonsense mutation causes skipping of exon 37 during the splicing process and is predicted to result in a protein shortened by 34 amino acid residues. The mutation was detected in all tissues examined (blood lymphocytes, oral mucosa, and dermal fibroblasts). The same mutation was previously found in 3 patients with clinically confirmed NF1. To our knowledge, this is the first report of an adult patient carrying a putative (non-mosaic) NF1 gene mutation in multiple tissues but not fulfilling the NIH criteria for the clinical diagnosis of NF1. Am. J. Med. Genet. 86:328–330, 1999.     

Objective assessment of nasality in Flemish adults with neurofibromatosis type 1

When characterizing the speech of a patient with neurofibromatosis type 1 (NF1), hypernasality is often mentioned. As few studies applied technically assisted evaluations of nasality in NF1 patients, the aim of the present study was to document the nasal resonance of adults with NF1 using nasometry. The nasometric data obtained from the NF1 patients were compared with the nasalance scores of a healthy control group and with normative data. The final study group consisted of 24 adult NF1 patients and 16 controls, all living in the East Flemish part of Belgium. Nasalance scores were obtained while the participants sustained three vowels (/a:/, /i./, and /u./) and one consonant (/m/) and read three standard nasalance passages. Despite the inter- and intra-subject variability, we observed that NF1 patients as a group exhibited higher mean nasalance scores than controls. This finding was especially clear in males. Potential genotype-phenotype correlations between NF1 mutation type and hypernasality were examined but could not be demonstrated. Conversely, comparison of the nasometric data obtained from the NF1 patients with magnetic resonance imaging findings showed some degree of interesting correlation. We conclude that, notwithstanding the small sample size for some analyses, nasality is an area of interest in the NF1 population. As altered nasality influences speech intelligibility, nasality requires attention during follow-up visits, particularly when it concerns a male NF1 patient.     

Analysis of NF1 gene mutations in two sporadic patients with neurofibromatosis type 1CSCD

Objective: To detect mutations of the NF1 gene in two sporadic cases with neurofibromatosis type 1 (NF1) and explore their molecular mechanisms. Methods: Clinical data of the two patients was collected. Genomic DNA was extracted from peripheral blood samples. Specific primers were designed to exclude pseudogenes. PCR was performed to amplify all coding exons of the NF1 gene. PCR products were directly sequenced. Results: Two novel mutations of the NF1 gene (c. 1019-1020delCT in exon 9 and c. 7189G> A in exon 48) were respectively identified in the two patients but not among their unaffected parents or 100 healthy controls. Conclusion: Mutations of the NF1 gene may have predisposed to the NF1 in the two patients. © 2018 MeDitorial Ltd. All rights reserved.     

Molecular analysis of neurofibromatosis type 1 mutations.

We have examined a panel of 115 unrelated NF1 individuals for mutation in the 3' region of the NF1 gene, using Southern blotting and polymerase chain reaction amplification of exons followed by single-strand conformation polymorphism (SSCP) analysis. We found only 2 unequivocal mutations: a 571 bp deletion which removed exon 6 and resulted in a frameshift in exon 7, and a 2 bp deletion in exon 1. A third sequence variation detected by SSCP was predicted to cause a lysine-arginine substitution in exon 6. This is a conservative change, and since the affected individual is a new mutation whose parents are not available, we cannot be sure of its biological significance. We detected mutations in at most 3% of individuals, from an analysis which covered 17% of the coding sequence by SSCP and a larger region by Southern blotting. This relative failure to detect mutations accords with the experience of others. Even allowing for the incomplete sensitivity of the methods used, the results suggest that the majority of NF1 mutations lie elsewhere in the coding sequence or outside it.     

Analysis of CpG C-to-T mutations in neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a dominant disorder caused by mutations in the NF1 gene; approximately 100 NF1 gene mutations have been published. The CpG C-to-T transition is a frequent mutation mechanism in genetic disorders. To estimate its frequency in NF1, we employed a PCR-restriction digestion method to examine 17 CpGs in 65 patients, and also screened for a CpG nonsense transition (R1947X) that occurs in 1-2% of patients. The analysis revealed disease-related CpG C-to-T transitions (including a nonsense mutation that may be as frequent as R1947X) as well as a benign variant and another mutation at a CpG. Four patients showed CpG mutations in analysis of 18 sites (17 surveyed by restriction digest, plus the R1947X assay), including three C-to-T transitions and one C-to-G transversion. These 18 sites represent one-fifth of the 91 CpGs at which a C-to-T transition would result in a nonsense or nonconservative missense mutation. Thus, it is feasible that the CpG mutation rate at NF1 might be similar to that seen in other disorders with a high mutation rate, and that recurrent NF1 mutations may frequently reside at CpG sites. Hum Mutat 11:411, 1998. © 1998 Wiley-Liss, Inc.     

Severe Thoracic and Spinal Bone Abnormalities in neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant, multi-system, neurocutaneous disorder that predisposes to the development of benign and malignant tumors. Classical skeletal abnormalities encompass sphenoid wing dysplasia, congenital bowing of the long bones and vertebral osteopathy associated with non-dystrophic or dystrophic scoliosis found in about 10% of NF1 patients. We report a 17-year-old boy affected by NF1 with extreme severe spinal and thoracic malformations affecting bone and lung tissues, including hypoplasia of the right lung, unilateral costal agenesis and severe dystrophic scoliosis characterized by association of hemivertebra, fusion of adjacent vertebral bodies and defective pedicles. At birth, he presented an acute respiratory distress requiring invasive ventilator support. The diagnosis of NF1 was confirmed at age 5 by the identification of a de novo heterozygous mutation c.4537C > T, p.Arg1513* in NF1. Trio-based Whole Exome Sequencing (WES) was performed to exclude coexistence of a second hit but no clearly other pathogenic variant has been identified. Until now, only one similar NF1 patient suffering from the same association of severe scoliosis and chest deformity leading to respiratory insufficiency was described. The severe prenatal NF1-related scoliosis could explain the lung abnormal development by absence of mechanical constraints. Severe Thoracic and Spinal Bone Abnormalities may be part of the NF1 bone phenotype and should be taken into account to allow adequate genetic counseling.     

Growth in neurofibromatosis 1 microdeletion patients

Microdeletions of the entire NF1 gene and surrounding genomic region occur in about 5% of patients with neurofibromatosis 1 (NF1). NF1 microdeletion patients usually have more cutaneous and plexiform neurofibromas and a higher risk of developing malignant peripheral nerve sheath tumors than other people with NF1. Somatic overgrowth has also been observed in NF1 microdeletion patients, an observation that is remarkable because most NF1 patients are smaller than average for age and sex. We studied longitudinal measurements of height, weight, and head circumference in 56 patients with NF1 microdeletions and 226 NF1 patients with other kinds of mutations. Although children with NF1 microdeletions were much taller than non‐deletion NF1 patients at all ages after 2 years, the lengths of deletion and nondeletion NF1 patients were similar in early infancy. NF1 microdeletion patients tended to be heavier than other NF1 patients, but height or weight more than 3 standard deviations above the mean for age and sex was infrequent in children with NF1 microdeletions. Head circumference and age of puberty were similar in deletion and non‐deletion NF1 patients. The pattern of growth differs substantially in deletion and non‐deletion NF1 patients, but the pathogenic basis for this difference is unknown.     

Increased dental caries in people with neurofibromatosis 1

Neurofibromatosis 1 (NF1) is an autosomal dominant disease that is associated with multiple café-au-lait spots and neurofibromas. Low bone mineral density is frequent in people with NF1, and focal bony abnormalities are characteristic but uncommon features. Dental abnormalities can occur in association with oral neurofibromas but have not otherwise been described in people with NF1. Questionnaires regarding dental caries were sent to families that included at least one individual with NF1. Siblings with NF1 reported significantly more dental caries (mean +/- SD, 8.1 +/- 6.6) than siblings without NF1 in these families (5.5 +/- 5.8, p = 0.019). Our findings suggest that dental caries occur more frequently than expected among people with NF1 and that individuals with this condition may require a modified dental care program.     

The spectrum of NF1 mutations in Korean patients with neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant disorders in humans. NF1 is caused by mutations in the NF1 gene which consists of 57 exons and encodes a GTPase activating protein (GAP), neurofibromin. To date, more than 640 different NF1 mutations have been identified and registered in the Human Gene Mutation Database (HGMD). In order to assess the NF1 mutational spectrum in Korean NF1 patients, we screened 23 unrelated Korean NF1 patients for mutations in the coding region and splice sites of the NF1 gene. We have identified 21 distinct NF1 mutations in 22 patients. The mutations included 10 single base substitutions (3 missense and 7 nonsense), 10 splice site mutations, and 1 single base deletion. Eight mutations have been previously identified and thirteen mutations were novel. The mutations are evenly distributed across exon 3 through intron 47 of the NF1 gene and no mutational hot spots were found. This analysis revealed a wide spectrum of NF1 mutations in Korean patients. A genotype- phenotype correlation analysis suggests that there is no clear relationship between specific NF1 mutations and clinical features of the disease.     

Analysis of NF1 gene mutations among eleven sporadic patients with neurofibromatosis type 1CSCD

Objective: To explore the genetic etiology for 11 sporadic patients with neurofibromatosis type 1. Methods: Chip targeting capture and high-throughput sequencing were employed to detect potential mutations of NF1 and NF2 genes among the 11 patients. The data was filtered through multiple mutational databases and in-house whole exome sequence database. Sanger sequencing was used for analysis of family members of the patients. Results: Eleven pathogenic variants were found among the 11 patients, which included two splicing mutations, one missense mutation, two nonsense mutations, and six frame-shifting mutations. None of the mutations was recorded by the public database or the in-house database generated from 1775 samples through whole exome sequencing. None of the unaffected parents carried the same mutation. Seven mutations were associated with neurofibromatosis type 1 previously, while the remaining four were discovered for the first time. Prenatal diagnosis of two high-risk pregnancies suggested that neither fetus has inherited the NF1 mutation from their affected parents. Conclusion: Identification of causative mutations in patients with sporadic-type neurofibromatosis type 1 has provided a basis for genetic counseling. The four novel mutations have enriched the spectrum of NF1 gene mutations. © 2018 MeDitorial Ltd. All rights reserved.     

Magnetic resonance findings and ophthalmologic abnormalities are correlated in patients with neurofibromatosis type 1 (NF1)

In subjects with neurofibromatosis type 1 (NF1), we show that a reduction in the visual field is the most sensitive indicator of gliomas along the optic pathway. Therefore, we conclude that a visual field evaluation is the most sensitive clinical test among those evaluated to predict the presence of optic pathway pathology on an MRI examination. These data may contribute to the establishment of more precise guidelines for the evaluation and treatment of children with NF1. Am. J. Med. Genet. 93:269–272, 2000. © 2000 Wiley‐Liss, Inc.     

Somatic NF1 mutation spectra in a family with neurofibromatosis type 1: toward a theory of genetic modifiers

Neurofibromatosis type 1 (NF1), an autosomal dominantly-inherited disorder, is mainly characterized by the occurrence of multiple dermal neurofibromas and is caused by mutations in the NF1 gene, a tumor suppressor gene. The variable expressivity of the disease and the lack of a genotype/phenotype correlation prevents any prediction of patient outcome and points to the action of genetic factors in addition to stochastic factors modifying the severity of the disease. The analysis of somatic NF1 gene mutations in neurofibromas from NF1 patients revealed that each neurofibroma results from an individual second hit mutation, indicating that factors that influence somatic mutation rates may be regarded as potential modifiers of NF1. A mutational screen of numerous neurofibromas from two NF1 patients presented here revealed a predominance of point mutations, small deletions, and insertions as second hit mutations in both patients. Seven novel mutations are reported. Together with the results of studies that showed LOH as the predominant second hit in neurofibromas of other patients, our results suggest that in different patients different factors may influence the somatic mutation rate and thereby the severity of the disease.     

No evidence for linkage to the type 1 or type 2 neurofibromatosis loci in Noonan syndrome families

A linkage analysis has been performed on 6 two-generation families with classical Noonan syndrome to determine whether the shydrome is linked to neurofibromatosis type 1 on chromosome 17q or to neurofibromatosis type 2 on chromosome 22q. A significantly negative location score was obtained between 10cM centromeric to and 15 cM telomeric from the neurofibromatosis type 1 locus. A significantly negative lod score was obtained with a marker mapping within the region where neurofibromatosis type 2 is thought to be located. These data indicate that Noonan syndrome is not tightly linked to either neurofibromatosis type 1 or type 2. © 1993 Wiley-Liss, Inc.     

Identification of forty-five novel and twenty-three known NF1 mutations in Chinese patients with neurofibromatosis type 1

Neurofibromatosis type 1 (NF1), characterized by skin neurofibromas and an excess of café-au-lait spots, is due to mutations in the neurofibromin (NF1) gene. Identifying the genetic defect in individuals with the disease represents a significant challenge because the gene is extremely large with a high incidence of sporadic mutations across the entire gene ranging from single nucleotide substitutes to large deletions. In the present study, we have used a combination of techniques (heteroduplex analysis, sequencing, loss of heterozygosity and quantification of gene dosage) to define the genetic defect in 68 individuals from a cohort of 107 NF1 Taiwanese patients of Chinese origin. Fifty-eight were initially identified using heteroduplex analytical techniques and confirmed by sequence analysis. A further five were identified by direct sequence analysis alone. The reminders were shown to carry large deletions in the NF1 gene by demonstrating loss of heterozygosity that was confirmed by gene dosage measurements using quantitative-PCR techniques. Mis-sense, non-sense, frame-shift or splice-site mutations were identified across the entire gene of which the majority (45/68) were novel in nature. The detection rate with the various analytical techniques and the types of mutation detected are consistent with published data involving both individuals and large cohort studies from other ethnic backgrounds.     

COVID-19 in people with neurofibromatosis 1, neurofibromatosis 2, or schwannomatosis

PurposePeople with pre-existing conditions may be more susceptible to severe COVID-19 when infected by SARS-CoV-2. The relative risk and severity of SARS-CoV-2 infection in people with rare diseases such as neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), or schwannomatosis (SWN) is unknown.MethodsWe investigated the proportions of people with NF1, NF2, or SWN in the National COVID Cohort Collaborative (N3C) electronic health record data set who had a positive test result for SARS-CoV-2 or COVID-19.ResultsThe cohort sizes in N3C were 2501 (NF1), 665 (NF2), and 762 (SWN). We compared these with N3C cohorts of patients with other rare diseases (98-9844 individuals) and the general non-NF population of 5.6 million. The site- and age-adjusted proportion of people with NF1, NF2, or SWN who had a positive test result for SARS-CoV-2 or COVID-19 (collectively termed positive cases) was not significantly higher than in individuals without NF or other selected rare diseases. There were no severe outcomes reported in the NF2 or SWN cohorts. The proportion of patients experiencing severe outcomes was no greater for people with NF1 than in cohorts with other rare diseases or the general population.ConclusionHaving NF1, NF2, or SWN does not appear to increase the risk of being SARS-CoV-2 positive or of being a patient with COVID-19 or of developing severe complications from SARS-CoV-2.     

Variable expression of neurofibromatosis 1 in monozygotic twins

Neurofibromatosis 1 (NF1) is a common autosomal dominant disorder with high penetrance but extreme variability of expression. Monozygotic (MZ) twins with NF1 who have phenotypic discordances are a useful tool in evaluating which traits are influenced by non-hereditary influences such as second hit somatic events, environmental agents, epigenetic modification, or post-zygotic mutations. We evaluated nine sets of MZ twins and one set of MZ triplets, ages 4-18 years, for NF1 features and calculated probandwise concordance (P(C)) for each feature. MZ twins were highly concordant in numbers of café-au-lait spots (P(C) = 0.89) and cutaneous neurofibromas. IQ scores were within 10 points for all twin pairs tested, and similar patterns of learning disabilities and speech disorders were observed. Twin pairs showed significant discordance for tumors, particularly plexiform neurofibromas (P(C) = 0.40) and malignant peripheral nerves sheath tumors (MPNST), as expected if post-natal second-hit events were contributing to these features. One set of twins was concordant for multiple, large paraspinal neurofibromas, suggesting that there may be more hereditary factors involved in production of paraspinal neurofibromas. Four sets were concordant for pectus deformities of the chest (P(C) = 0.80). Three sets of twins were discordant for scoliosis (P(C) = 0.40); an additional set was concordant for scoliosis but differed in presence of dystrophic features and need for surgery. Our data suggest there are additional non-hereditary factors modifying the NF1 phenotype and causing discordancies between MZ twins. Future studies may focus on differences in epigenetic changes or somatic mosaicism which have been documented for other disease genes in MZ twins.     

一例散发1型神经纤维瘤病患者的NF1基因嵌合突变分析

目的 对1例散发1型神经纤维瘤病患者的NF1基因进行嵌合突变分析.方法 提取先证者外周血基因组RNA,PCR扩增NF1基因编码区序列并进行序列测定;找到突变后,基因组DNA途径证实突变,并对先证者儿子的NF1基因相应外显子也进行序列分析;针对NF1基因第51外显子已发现的突变,取先证者全血淋巴细胞、口腔上皮细胞和尿路上皮细胞基因组DNA进行PCR扩增,PCR产物T克隆及测序.结果 先证者的临床表现符合1型神经纤维瘤病.先证者外周血RNA途径检测出无义突变c.7911C＞T(p.Q2510X);基因组DNA途径证实患者外周血淋巴细胞、口腔上皮细胞和尿路上皮细胞中均有该突变,尿路上皮细胞中该突变测序信号较弱;在PCR产物的T克隆-测序中,来自先证者的血液、口腔上皮、尿液上皮细胞无义突变c.7911C＞T(p.Q2510X)突变体的重组菌分别占总数的42％、36％、12％.其儿子、正常对照不存在上述突变.结论 先证者在胚胎早期发生了NF1基因突变,使其体内部分细胞带有NF1基因突变,导致形成全身嵌合的1型神经纤维瘤病.