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Pathogenic neurofibromatosis type 1 (NF1) RNA splicing resolved by targeted RNAseq

ABSTRACT: Neurofibromatosis type 1 (NF1) is caused by loss-of-function variants in the NF1 gene. Approximately 10% of these variants affect RNA splicing and are either missed by conventional DNA diagnostics or are misinterpreted by in silico splicing predictions. Therefore, a targeted RNAseq-based approach was designed to detect pathogenic RNA splicing and associated pathogenic DNA variants. For this method RNA was extracted from lymphocytes, followed by targeted RNAseq. Next, an in-house developed tool (QURNAs) was used to calculate the enrichment score (ERS) for each splicing event. This method was thoroughly tested using two different patient cohorts with known pathogenic splice-variants in NF1. In both cohorts all 56 normal reference transcript exon splice junctions, 24 previously described and 45 novel non-reference splicing events were detected. Additionally, all expected pathogenic splice-variants were detected. Eleven patients with NF1 symptoms were subsequently tested, three of which have a known NF1 DNA variant with a putative effect on RNA splicing. This effect could be confirmed for all 3. The other eight patients were previously without any molecular confirmation of their NF1-diagnosis. A deep-intronic pathogenic splice variant could now be identified for two of them (25%). These results suggest that targeted RNAseq can be successfully used to detect pathogenic RNA splicing variants in NF1.

SUBMITTER: Koster R

PROVIDER: S-EPMC8593033 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Pathogenic Neurofibromatosis type 1 (NF1) RNA splicing resolved by targeted RNAseq

Project description:Neurofibromatosis type 1 (NF1) is caused by loss-of-function variants in the NF1 gene. Approximately 10% of these variants affect RNA splicing and are either missed by conventional DNA diagnostics or are misinterpreted by in silico splicing predictions. Therefore, a targeted RNAseq-based approach was designed to detect pathogenic RNA splicing and associated pathogenic DNA variants. an in-house developed tool (QURNAS) was used to calculate the enrichment score (ERS) for each splicing event. RNA enrichment of NF1 and SPRED1 was done using SPET (NUGEN - NF1 only) and using SureSelect (Agilent - NF1 and SPRED1).

| EGAS00001005530 | EGA

Five novel NF1 gene pathogenic variants in 10 different Chinese families with neurofibromatosis type 1.

Project description:BackgroundNeurofibromatosis type 1 (NF1) is an autosomal dominant disorder with equal sex incidence that is characterized by neurofibromas, café-au-lait macules, axillary freckling, optic pathway tumor, distinctive osseous lesion, and iris Lisch nodules. Inactivating variants in the NF1 gene have been identified to be correlated with NF1. This tumor suppressor gene is located at 17q11.2.MethodsTen affected NF1 probands and their available relatives from 10 unrelated Chinese families with neurofibromatosis type 1 were clinically studied. All of these probands mainly complained of osseous lesions. PCR was used to analyze and sequence the variants. We collected both laboratory and radiological information.ResultsWe detected five novel pathogenic variants including two de novo variants in these 10 families: one missense variant, p.Cys709Arg(c.2125T>C), in exon 18 and four frameshift variants: p.Leu1459Profs*2(c.4436dupT) in exon 34; p.Lys99Argfs*4(c.296delA) in exon 4; p.Leu762Cysfs*2(c.2283delA) in exon 19; and p.Leu1522Ilefs*53(c.4562_4563dupAT) in exon 34.ConclusionNovel pathogenic variants in the NF1 gene in these families correlated with the phenotype and genotype and explained the clinical manifestations of these patients. The results help us to understand the genetic basis of patients with neurofibromatosis type 1 in China. Our study expands the pathogenic variant spectrum of the NF1 gene and may be helpful in genetic counseling and prenatal genetic diagnosis.

| S-EPMC6732320 | biostudies-literature

Somatic neurofibromatosis type 1 (NF1) inactivation characterizes NF1-associated pilocytic astrocytoma.

Project description:Low-grade brain tumors (pilocytic astrocytomas) arising in the neurofibromatosis type 1 (NF1) inherited cancer predisposition syndrome are hypothesized to result from a combination of germline and acquired somatic NF1 tumor suppressor gene mutations. However, genetically engineered mice (GEM) in which mono-allelic germline Nf1 gene loss is coupled with bi-allelic somatic (glial progenitor cell) Nf1 gene inactivation develop brain tumors that do not fully recapitulate the neuropathological features of the human condition. These observations raise the intriguing possibility that, while loss of neurofibromin function is necessary for NF1-associated low-grade astrocytoma development, additional genetic changes may be required for full penetrance of the human brain tumor phenotype. To identify these potential cooperating genetic mutations, we performed whole-genome sequencing (WGS) analysis of three NF1-associated pilocytic astrocytoma (PA) tumors. We found that the mechanism of somatic NF1 loss was different in each tumor (frameshift mutation, loss of heterozygosity, and methylation). In addition, tumor purity analysis revealed that these tumors had a high proportion of stromal cells, such that only 50%-60% of cells in the tumor mass exhibited somatic NF1 loss. Importantly, we identified no additional recurrent pathogenic somatic mutations, supporting a model in which neuroglial progenitor cell NF1 loss is likely sufficient for PA formation in cooperation with a proper stromal environment.

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Two Novel NF1 Pathogenic Variants Causing the Creation of a New Splice Site in Patients With Neurofibromatosis Type I.

Project description:Neurofibromatosis type I (NF1) is one of the most common autosomal dominant disorders, since the estimated incidence is one in 3,500 births. In this study, we present bioinformatical and functional characterization of two novel splicing NF1 variants, detected in NF1 patients. Patient 1, carrying NF1:c.122A>T, which introduces a new exonic 5' donor splice site, was diagnosed with hormone-positive, Her-2-negative breast cancer at the age of 47. She had an atypical presentation of NF1, with few café-au-lait spots and no Lisch nodules. Patient developed a hemothorax due to subclavian artery rupture, which has previously been described as an extremely rare complication of NF1. Patient 2, carrying NF1:c.7395-17T>G that creates a new intronic 3' acceptor splice site, had quite a typical clinical presentation of NF1: formations on her tongue in the region of her left metacarpal bones and on her left foot, plexiform neurofibroma in her pelvis, several café-au-lait spots, and axillary freckling. She was also diagnosed with cognitive impairment. In the report, we are presenting two novel variants which were successfully classified based on NGS and mRNA analysis. Based on results of mRNA analysis, both variants were classified as likely pathogenic according to ACMG guidelines applying evidence categories PS3, PM2, PP3, and PP1 supporting. By characterizing those two novel NF1 splicing variants, we have confirmed the neurofibromatosis type I phenotype in the two probands.

| S-EPMC6714493 | biostudies-literature

Neurofibromatosis type 1 (Nf1)-mutant mice exhibit increased sleep fragmentation.

Project description:Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder in which affected children and adults are at a higher risk of sleep disorders. In an effort to identify potential sleep disturbances in a small animal model, we used a previously reported Nf1 conditional knockout (Nf1CKO ) mouse strain. In contrast to Nf1 mutant flies, the distribution of vigilance states was intact in Nf1CKO mice. However, Nf1CKO mice exhibited increased non-REM sleep (NREM)-to-wake and wake-to-NREM transitions. This sleep disruption was accompanied by decreased bout durations during awake and NREM sleep states under both light and dark conditions. Moreover, Nf1CKO mice have higher percentage delta power during awake and NREM sleep states under all light conditions. Taken together, Nf1CKO mice phenocopy some of the sleep disturbances observed in NF1 patients and provide a tractable platform to explore the molecular mechanisms governing sleep abnormalities in NF1.

| S-EPMC6609510 | biostudies-literature

An Illustrative Case of Neurofibromatosis Type 1 and NF1 Microdeletion.

Project description:We report on a patient with NF1 microdeletion and clinical manifestations that fulfill the diagnostic criteria for neurofibromatosis type 1 but also presenting features reminiscent of Proteus syndrome.

| S-EPMC2957849 | biostudies-literature

Somatic neurofibromatosis type 1 (NF1) inactivation events in cutaneous neurofibromas of a single NF1 patient.

Project description:Neurofibromatosis type 1 (NF1) (MIM#162200) is a relatively frequent genetic condition that predisposes to tumor formation. The main types of tumors occurring in NF1 patients are cutaneous and subcutaneous neurofibromas, plexiform neurofibromas, optic pathway gliomas, and malignant peripheral nerve sheath tumors. To search for somatic mutations in cutaneous (dermal) neurofibromas, whole-exome sequencing (WES) was performed on seven spatially separated tumors and two reference tissues (blood and unaffected skin) from a single NF1 patient. Validation of WES findings was done using routine Sanger sequencing or Sequenom IPlex SNP genotyping. Exome sequencing confirmed the existence of a known familial splice-site mutation NM_000267.3:c.3113+1G>A in exon 23 of NF1 gene (HGMD ID CS951480) in blood, unaffected skin, and all tumor samples. In five out of seven analyzed tumors, we additionally detected second-hit mutations in the NF1 gene. Four of them were novel and one was previously observed. Each mutation was distinct, demonstrating the independent origin of each tumor. Only in two of seven tumors we detected an additional somatic mutation that was not associated with NF1. Our study demonstrated that somatic mutations of NF1 are likely the main drivers of cutaneous tumor formation. The study provides evidence for the rareness of single base pair level alterations in the exomes of benign NF1 cutaneous tumors.

| S-EPMC4795057 | biostudies-literature

Clinical spectrum of individuals with pathogenic NF1 missense variants affecting p.Met1149, p.Arg1276, and p.Lys1423: genotype-phenotype study in neurofibromatosis type 1.

Project description:We report 281 individuals carrying a pathogenic recurrent NF1 missense variant at p.Met1149, p.Arg1276, or p.Lys1423, representing three nontruncating NF1 hotspots in the University of Alabama at Birmingham (UAB) cohort, together identified in 1.8% of unrelated NF1 individuals. About 25% (95% confidence interval: 20.5-31.2%) of individuals heterozygous for a pathogenic NF1 p.Met1149, p.Arg1276, or p.Lys1423 missense variant had a Noonan-like phenotype, which is significantly more compared with the "classic" NF1-affected cohorts (all p < .0001). Furthermore, p.Arg1276 and p.Lys1423 pathogenic missense variants were associated with a high prevalence of cardiovascular abnormalities, including pulmonic stenosis (all p < .0001), while p.Arg1276 variants had a high prevalence of symptomatic spinal neurofibromas (p < .0001) compared with "classic" NF1-affected cohorts. However, p.Met1149-positive individuals had a mild phenotype, characterized mainly by pigmentary manifestations without externally visible plexiform neurofibromas, symptomatic spinal neurofibromas or symptomatic optic pathway gliomas. As up to 0.4% of unrelated individuals in the UAB cohort carries a p.Met1149 missense variant, this finding will contribute to more accurate stratification of a significant number of NF1 individuals. Although clinically relevant genotype-phenotype correlations are rare in NF1, each affecting only a small percentage of individuals, together they impact counseling and management of a significant number of the NF1 population.

| S-EPMC6973139 | biostudies-literature

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

Project description: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.

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Impacts of NF1 Gene Mutations and Genetic Modifiers in Neurofibromatosis Type 1.

Project description:Neurofibromatosis type 1 (NF1) is a tumor predisposition genetic disorder that directly affects more than 1 in 3,000 individuals worldwide. It results from mutations of the NF1 gene and shows almost complete penetrance. NF1 patients show high phenotypic variabilities, including cafe-au-lait macules, freckling, or other neoplastic or non-neoplastic features. Understanding the underlying mechanisms of the diversities of clinical symptoms might contribute to the development of personalized healthcare for NF1 patients. Currently, studies have shown that the different types of mutations in the NF1 gene might correlate with this phenomenon. In addition, genetic modifiers are responsible for the different clinical features. In this review, we summarize different genetic mutations of the NF1 gene and related genetic modifiers. More importantly, we focus on the genotype-phenotype correlation. This review suggests a novel aspect to explain the underlying mechanisms of phenotypic heterogeneity of NF1 and provides suggestions for possible novel therapeutic targets to prevent or delay the onset and development of different manifestations of NF1.

| S-EPMC8455870 | biostudies-literature

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