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Pacot L, Girish M, Knight S, Spurlock G, Varghese V, Ye M, Thomas N, Pasmant E, Upadhyaya M. Correlation between large rearrangements and patient phenotypes in NF1 deletion syndrome: an update and review. BMC Med Genomics 2024; 17:73. [PMID: 38448973 PMCID: PMC10919053 DOI: 10.1186/s12920-024-01843-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Accepted: 03/01/2024] [Indexed: 03/08/2024] Open
Abstract
About 5-10% of neurofibromatosis type 1 (NF1) patients exhibit large genomic germline deletions that remove the NF1 gene and its flanking regions. The most frequent NF1 large deletion is 1.4 Mb, resulting from homologous recombination between two low copy repeats. This "type-1" deletion is associated with a severe clinical phenotype in NF1 patients, with several phenotypic manifestations including learning disability, a much earlier development of cutaneous neurofibromas, an increased tumour risk, and cardiovascular malformations. NF1 adjacent co-deleted genes could act as modifier loci for the specific clinical manifestations observed in deleted NF1 patients. Furthermore, other genetic modifiers (such as CNVs) not located at the NF1 locus could also modulate the phenotype observed in patients with large deletions. In this study, we analysed 22 NF1 deletion patients by genome-wide array-CGH with the aim (1) to correlate deletion length to observed phenotypic features and their severity in NF1 deletion syndrome, and (2) to identify whether the deletion phenotype could also be modulated by copy number variations elsewhere in the genome. We then review the role of co-deleted genes in the 1.4 Mb interval of type-1 deletions, and their possible implication in the main clinical features observed in this high-risk group of NF1 patients.
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Affiliation(s)
- Laurence Pacot
- Fédération de Génétique et Médecine Génomique, Hôpital Cochin, DMU BioPhyGen, AP-HP, Centre-Université Paris Cité, Paris, France
- Institut Cochin, Inserm U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France
| | - Milind Girish
- School of Clinical Medicine, University of Cambridge, Cambridge, UK
| | - Samantha Knight
- School of Clinical Medicine, University of Cambridge, Cambridge, UK
| | | | - Vinod Varghese
- All Wales Medical Genomics Service, Cardiff, Great Britain
| | - Manuela Ye
- Institut Cochin, Inserm U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France
| | - Nick Thomas
- School of Clinical Medicine, University of Cambridge, Cambridge, UK
| | - Eric Pasmant
- Fédération de Génétique et Médecine Génomique, Hôpital Cochin, DMU BioPhyGen, AP-HP, Centre-Université Paris Cité, Paris, France.
- Institut Cochin, Inserm U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France.
| | - Meena Upadhyaya
- Division of Cancer and Genetics, Institute of Medical Genetics, Cardiff University, Heath Park, CF14 4XN, Cardiff, UK
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Pacot L, Ye M, Nectoux J, Laurendeau I, Briand-Suleau A, Coustier A, Maillard T, Barbance C, Orhant L, Vaucouleur N, Blanché H, Parfait B, Wolkenstein P, Vidaud M, Vidaud D, Pasmant E. Droplet Digital PCR for Fast and Accurate Characterization of NF1 Locus Deletions: Confirmation of the Predominant Maternal Origin of Type-1 Deletions. J Mol Diagn 2024; 26:150-157. [PMID: 38008284 DOI: 10.1016/j.jmoldx.2023.11.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 10/09/2023] [Accepted: 11/07/2023] [Indexed: 11/28/2023] Open
Abstract
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.
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Affiliation(s)
- Laurence Pacot
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France; Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | - Manuela Ye
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France
| | - Juliette Nectoux
- Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | - Ingrid Laurendeau
- Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | - Audrey Briand-Suleau
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France; Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | - Audrey Coustier
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France
| | - Théodora Maillard
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France
| | - Cécile Barbance
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France
| | - Lucie Orhant
- Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | - Nicolas Vaucouleur
- Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | | | - Béatrice Parfait
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France; Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | - Pierre Wolkenstein
- Department of Dermatology, Hôpital Henri Mondor, Assistance Publique-Hôpital Paris, Créteil, France; INSERM, Clinical Investigation Center 1430, Referral Center of Neurofibromatosis, Hôpital Henri Mondor, Assistance Publique-Hôpital Paris, Faculté de Santé Paris Est Créteil, Créteil, France
| | - Michel Vidaud
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France; Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | - Dominique Vidaud
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France; Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France
| | - Eric Pasmant
- Institut Cochin, INSERM U1016, CNRS UMR8104, Université Paris Cité, CARPEM, Paris, France; Fédération de Génétique et Médecine Génomique, DMU BioPhyGen, Assistance Publique-Hôpital Paris, Centre-Université Paris Cité, Hôpital Cochin, Paris, France.
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3
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Kehrer-Sawatzki H, Cooper DN. Classification of NF1 microdeletions and its importance for establishing genotype/phenotype correlations in patients with NF1 microdeletions. Hum Genet 2021; 140:1635-1649. [PMID: 34535841 PMCID: PMC8553723 DOI: 10.1007/s00439-021-02363-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Accepted: 09/01/2021] [Indexed: 01/12/2023]
Abstract
An estimated 5–11% of patients with neurofibromatosis type-1 (NF1) harbour large deletions encompassing the NF1 gene and flanking regions. These NF1 microdeletions are subclassified into type 1, 2, 3 and atypical deletions which are distinguishable from each other by their extent and by the number of genes included within the deletion regions as well as the frequency of mosaicism with normal cells. Most common are type-1 NF1 deletions which encompass 1.4-Mb and 14 protein-coding genes. Type-1 deletions are frequently associated with overgrowth, global developmental delay, cognitive disability and dysmorphic facial features which are uncommon in patients with intragenic pathogenic NF1 gene variants. Further, patients with type-1 NF1 deletions frequently exhibit high numbers of neurofibromas and have an increased risk of malignant peripheral nerve sheath tumours. Genes located within the type-1 NF1 microdeletion interval and co-deleted with NF1 are likely to act as modifiers responsible for the severe disease phenotype in patients with NF1 microdeletions, thereby causing the NF1 microdeletion syndrome. Genotype/phenotype correlations in patients with NF1 microdeletions of different lengths are important to identify such modifier genes. However, these correlations are critically dependent upon the accurate characterization of the deletions in terms of their extent. In this review, we outline the utility as well as the shortcomings of multiplex ligation-dependent probe amplification (MLPA) to classify the different types of NF1 microdeletion and indicate the importance of high-resolution microarray analysis for correct classification, a necessary precondition to identify those genes responsible for the NF1 microdeletion syndrome.
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Affiliation(s)
| | - David N Cooper
- Institute of Medical Genetics, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK
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4
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Büki G, Zsigmond A, Czakó M, Szalai R, Antal G, Farkas V, Fekete G, Nagy D, Széll M, Tihanyi M, Melegh B, Hadzsiev K, Bene J. Genotype-Phenotype Associations in Patients With Type-1, Type-2, and Atypical NF1 Microdeletions. Front Genet 2021; 12:673025. [PMID: 34168676 PMCID: PMC8217751 DOI: 10.3389/fgene.2021.673025] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Accepted: 05/12/2021] [Indexed: 11/23/2022] Open
Abstract
Neurofibromatosis type 1 is a tumor predisposition syndrome inherited in autosomal dominant manner. Besides the intragenic loss-of-function mutations in NF1 gene, large deletions encompassing the NF1 gene and its flanking regions are responsible for the development of the variable clinical phenotype. These large deletions titled as NF1 microdeletions lead to a more severe clinical phenotype than those observed in patients with intragenic NF1 mutations. Around 5-10% of the cases harbor large deletion and four major types of NF1 microdeletions (type 1, 2, 3 and atypical) have been identified so far. They are distinguishable in term of their size and the location of the breakpoints, by the frequency of somatic mosaicism with normal cells not harboring the deletion and by the number of the affected genes within the deleted region. In our study genotype-phenotype analyses have been performed in 17 mostly pediatric patients with NF1 microdeletion syndrome identified by multiplex ligation-dependent probe amplification after systematic sequencing of the NF1 gene. Confirmation and classification of the NF1 large deletions were performed using array comparative genomic hybridization, where it was feasible. In our patient cohort 70% of the patients possess type-1 deletion, one patient harbors type-2 deletion and 23% of our cases have atypical NF1 deletion. All the atypical deletions identified in this study proved to be novel. One patient with atypical deletion displayed mosaicism. In our study NF1 microdeletion patients presented dysmorphic facial features, macrocephaly, large hands and feet, delayed cognitive development and/or learning difficulties, speech difficulties, overgrowth more often than patients with intragenic NF1 mutations. Moreover, neurobehavior problems, macrocephaly and overgrowth were less frequent in atypical cases compared to type-1 deletion. Proper diagnosis is challenging in certain patients since several clinical manifestations show age-dependency. Large tumor load exhibited more frequently in this type of disorder, therefore better understanding of genotype-phenotype correlations and progress of the disease is essential for individuals suffering from neurofibromatosis to improve the quality of their life. Our study presented additional clinical data related to NF1 microdeletion patients especially for pediatric cases and it contributes to the better understanding of this type of disorder.
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Affiliation(s)
- Gergely Büki
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary.,Szentágothai Research Centre, University of Pécs, Pécs, Hungary
| | - Anna Zsigmond
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary
| | - Márta Czakó
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary.,Szentágothai Research Centre, University of Pécs, Pécs, Hungary
| | - Renáta Szalai
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary.,Szentágothai Research Centre, University of Pécs, Pécs, Hungary
| | - Gréta Antal
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary
| | - Viktor Farkas
- 1st Department of Pediatrics, Semmelweis University, Budapest, Hungary
| | - György Fekete
- 2nd Department of Pediatrics, Semmelweis University, Budapest, Hungary
| | - Dóra Nagy
- Department of Medical Genetics, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Márta Széll
- Department of Medical Genetics, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Marianna Tihanyi
- Genetic Laboratory, Szent Rafael Hospital of Zala County, Zalaegerszeg, Hungary
| | - Béla Melegh
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary.,Szentágothai Research Centre, University of Pécs, Pécs, Hungary.,Full member of the European Reference Network on Genetic Tumour Risk Syndromes (ERN GENTURIS) - Project ID No. 739547, Pécs, Hungary
| | - Kinga Hadzsiev
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary.,Szentágothai Research Centre, University of Pécs, Pécs, Hungary
| | - Judit Bene
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary.,Szentágothai Research Centre, University of Pécs, Pécs, Hungary.,Full member of the European Reference Network on Genetic Tumour Risk Syndromes (ERN GENTURIS) - Project ID No. 739547, Pécs, Hungary
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5
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Omar W, Ahmedou AB, Youssef O, Sami R, Abada R, Mohamed R, Mohamed M. Intermittent dysphagia revealing a lateropharyngeal neurofibroma in a child: Case report: A case report. Ann Med Surg (Lond) 2021; 67:102438. [PMID: 34168868 PMCID: PMC8209718 DOI: 10.1016/j.amsu.2021.102438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 05/18/2021] [Accepted: 05/23/2021] [Indexed: 11/05/2022] Open
Abstract
Introduction Neurofibromatosis type 1 (NF1) is an disorder characterised by various phenotypic features like hyperpigmented spots, neurofibromas, Lisch nodules, skeletal abnormalities and tendency to develop neoplasms. Case presentation We present the case of a 12-year-old patient referred by his pediatrician for intermittent dysphagia and a sensation of food attachment, in whom several café-au-lait spots on the body had been found, and a case of type 1 neurofibromatosis in the patient's siblings. The decision was to closely follow-up the patient, the progression of his symptoms and the size of the cervical neurofibroma. The patient's current follow-up has been two years, with a minimal increase in the frequency of episodes of dysphagia, and with Ct-scan performed every year. No major growth of the cervical mass was noted. Discussion Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder characterised by various phenotypic features like hyperpigmented spots, neurofibromas, Lisch nodules, skeletal abnormalities and tendency to develop neoplasms. Conclusion The treatment is not codified and abstention therapeutic may be a wise decision. NF1 shows an autosomal dominant pattern of inheritance and wide phenotypical variability. Neurofibromatosis type 1 is a neurogenetic disorder. The cervical soft tissues may also be the primary site for tumors. The treatment is not codified. Abstention therapeutic may be a wise decision.
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Affiliation(s)
- Wydadi Omar
- ENT, Head and Neck Surgery Department, Ibn Rochd UniversityHospital, Faculty of Medicine and Pharmacy, Hassan II, Casablanca, Morocco
| | - Ahmed Brahim Ahmedou
- ENT, Head and Neck Surgery Department, Ibn Rochd UniversityHospital, Faculty of Medicine and Pharmacy, Hassan II, Casablanca, Morocco
| | - Oukessou Youssef
- ENT, Head and Neck Surgery Department, Ibn Rochd UniversityHospital, Faculty of Medicine and Pharmacy, Hassan II, Casablanca, Morocco
| | - Rouadi Sami
- ENT, Head and Neck Surgery Department, Ibn Rochd UniversityHospital, Faculty of Medicine and Pharmacy, Hassan II, Casablanca, Morocco
| | - Redallah Abada
- ENT, Head and Neck Surgery Department, Ibn Rochd UniversityHospital, Faculty of Medicine and Pharmacy, Hassan II, Casablanca, Morocco
| | - Roubal Mohamed
- ENT, Head and Neck Surgery Department, Ibn Rochd UniversityHospital, Faculty of Medicine and Pharmacy, Hassan II, Casablanca, Morocco
| | - Mahtar Mohamed
- ENT, Head and Neck Surgery Department, Ibn Rochd UniversityHospital, Faculty of Medicine and Pharmacy, Hassan II, Casablanca, Morocco
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Serra G, Antona V, Corsello G, Zara F, Piro E, Falsaperla R. NF1 microdeletion syndrome: case report of two new patients. Ital J Pediatr 2019; 45:138. [PMID: 31703719 PMCID: PMC6839219 DOI: 10.1186/s13052-019-0718-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2019] [Accepted: 09/16/2019] [Indexed: 01/24/2023] Open
Abstract
Background 17q11.2 microdeletions, which include the neurofibromatosis type 1 (NF1) gene region, are responsible for the NF1 microdeletion syndrome, observed in 4.2% of all NF1 patients. Large deletions of the NF1 gene and its flanking regions are associated with a more severe NF1 phenotype than the NF1 general population. Case presentation We hereby describe the clinical and molecular features of two girls (aged 2 and 4 years, respectively), with non-mosaic atypical deletions. Patient 1 showed fifteen café-au-lait spots and axillary freckling, as well as a Lisch nodule in the left eye, strabismus, high-arched palate, malocclusion, severe kyphoscoliosis, bilateral calcaneovalgus foot, mild generalized hypotonia, hyperactivity and deficits of speech-related abilities. NF1 genomic rearrangements through multiplex ligation-dependent probe amplification (MLPA) detected an heterozygous deletion of the whole NF1 gene. Array comparative genomic hybridization (a-CGH) analysis defined a 17q11.2 deletion of about 1 Mb (breakpoints at positions 29,124,299 and 30,151,654), which involved different genes (partially CRLF3, ATAD5, TEFM, ADAP2, RNF135, OMG, EVI2B, EVI2A, RAB11FIP4), including NF1. Patient 2 showed growth and developmental delay, supravalvular pulmonary stenosis, twenty-five café-au-lait spots, axillary freckling, craniofacial dysmorphic features, short neck with pterygium, limb abnormalities and foci of neural dysplasia on brain magnetic resonance imaging (MRI). MLPA detected an heterozygous deletion of NF1, which was detailed by a-CGH indicating the positions 29,124,299 and 30,326,958 as its breakpoints, and which included aside from the genes deleted in Patient 1 also COPRS, UTP6 and partially SUZ12. Fluorescent in situ hybridization (FISH) analysis of the parents documented a de novo origin of the deletions in both cases. Conclusions The present report will likely provide further insights and a better characterization of NF1 microdeletion syndrome.
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Affiliation(s)
- Gregorio Serra
- Department of Sciences for Health Promotion and Mother and Child Care "G. D'Alessandro", University of Palermo, Palermo, Italy
| | - Vincenzo Antona
- Department of Sciences for Health Promotion and Mother and Child Care "G. D'Alessandro", University of Palermo, Palermo, Italy
| | - Giovanni Corsello
- Department of Sciences for Health Promotion and Mother and Child Care "G. D'Alessandro", University of Palermo, Palermo, Italy
| | - Federico Zara
- Laboratory of Neurogenetics and Neuroscience, Institute G. Gaslini, Genoa, Italy
| | - Ettore Piro
- Department of Sciences for Health Promotion and Mother and Child Care "G. D'Alessandro", University of Palermo, Palermo, Italy.
| | - Raffaele Falsaperla
- Unit of Pediatrics and Pediatric Emergency, University Hospital "Policlinico-Vittorio Emanuele", Catania, Italy
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Emerging genotype-phenotype relationships in patients with large NF1 deletions. Hum Genet 2017; 136:349-376. [PMID: 28213670 PMCID: PMC5370280 DOI: 10.1007/s00439-017-1766-y] [Citation(s) in RCA: 141] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2016] [Accepted: 02/08/2017] [Indexed: 02/07/2023]
Abstract
The most frequent recurring mutations in neurofibromatosis type 1
(NF1) are large deletions encompassing the NF1
gene and its flanking regions (NF1
microdeletions). The majority of these deletions encompass 1.4-Mb and are associated
with the loss of 14 protein-coding genes and four microRNA genes. Patients with
germline type-1 NF1 microdeletions frequently
exhibit dysmorphic facial features, overgrowth/tall-for-age stature, significant
delay in cognitive development, large hands and feet, hyperflexibility of joints and
muscular hypotonia. Such patients also display significantly more cardiovascular
anomalies as compared with patients without large deletions and often exhibit
increased numbers of subcutaneous, plexiform and spinal neurofibromas as compared
with the general NF1 population. Further, an extremely high burden of internal
neurofibromas, characterised by >3000 ml tumour volume, is encountered
significantly, more frequently, in non-mosaic NF1
microdeletion patients than in NF1 patients lacking such deletions. NF1 microdeletion patients also have an increased risk of
malignant peripheral nerve sheath tumours (MPNSTs); their lifetime MPNST risk is
16–26%, rather higher than that of NF1 patients with intragenic NF1 mutations (8–13%). NF1 microdeletion patients, therefore, represent a high-risk group for
the development of MPNSTs, tumours which are very aggressive and difficult to treat.
Co-deletion of the SUZ12 gene in addition to
NF1 further increases the MPNST risk in
NF1 microdeletion patients. Here, we summarise
current knowledge about genotype–phenotype relationships in NF1 microdeletion patients and discuss the potential role of the genes
located within the NF1 microdeletion interval
whose haploinsufficiency may contribute to the more severe clinical
phenotype.
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Mussotter T, Bengesser K, Högel J, Cooper DN, Kehrer-Sawatzki H. Population-specific differences in gene conversion patterns between human SUZ12 and SUZ12P are indicative of the dynamic nature of interparalog gene conversion. Hum Genet 2014; 133:383-401. [PMID: 24385046 DOI: 10.1007/s00439-013-1410-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Accepted: 12/08/2013] [Indexed: 11/29/2022]
Abstract
Nonallelic homologous gene conversion (NAHGC) resulting from interparalog recombination without crossover represents an important influence on the evolution of duplicated sequences in the human genome. In 17q11.2, different paralogous sequences mediate large NF1 deletions by nonallelic homologous recombination with crossover (NAHR). Among these paralogs are SUZ12 and its pseudogene SUZ12P which harbour the breakpoints of type-2 (1.2-Mb) NF1 deletions. Such deletions are caused predominantly by mitotic NAHR since somatic mosaicism with normal cells is evident in most patients. Investigating whether SUZ12 and SUZ12P have also been involved in NAHGC, we observed gene conversion tracts between these paralogs in both Africans (AFR) and Europeans (EUR). Since germline type-2 NF1 deletions resulting from meiotic NAHR are very rare, the vast majority of the gene conversion tracts in SUZ12 and SUZ12P are likely to have resulted from mitotic recombination during premeiotic cell divisions of germ cells. A higher number of gene conversion tracts were noted within SUZ12 and SUZ12P in AFR as compared to EUR. Further, the distinctive signature of NAHGC (a high number of SNPs per paralog and a high number of shared SNPs between paralogs), a characteristic of many actively recombining paralogs, was observed in both SUZ12 and SUZ12P but only in AFR and not in EUR. A novel polymorphic 2.3-kb deletion in SUZ12P was identified which exhibited a high allele frequency in EUR. We postulate that this interparalog structural difference, together with low allelic recombination rates, could have caused a reduction in NAHGC between SUZ12 and SUZ12P during human evolution.
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Affiliation(s)
- Tanja Mussotter
- Institute of Human Genetics, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany
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9
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Kehrer-Sawatzki H, Vogt J, Mußotter T, Kluwe L, Cooper DN, Mautner VF. Dissecting the clinical phenotype associated with mosaic type-2 NF1 microdeletions. Neurogenetics 2012; 13:229-36. [PMID: 22581253 DOI: 10.1007/s10048-012-0332-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Accepted: 04/26/2012] [Indexed: 12/30/2022]
Abstract
Patients with large deletions of the NF1 gene and its flanking regions (termed NF1 microdeletions) generally exhibit more severe clinical manifestations of neurofibromatosis type-1 (NF1). Here, we have investigated the clinical phenotype displayed by eight patients harbouring mosaic type-2 NF1 microdeletions. These patients did not exhibit facial dysmorphism, attention deficit hyperactivity disorder, delayed cognitive development and/or learning disabilities, cognitive impairment, congenital heart disease, hyperflexibility of joints, large hands and feet, muscular hypotonia or bone cysts. All these features have previously been reported to be disproportionately associated with germline (i.e. non-mosaic) type-1 NF1 microdeletions as compared with the general NF1 population. Plexiform neurofibromas were also less prevalent in patients with mosaic type-2 NF1 microdeletions as compared with patients carrying constitutional (germline) type-1 NF1 microdeletions. Five of the eight patients with mosaic type-2 deletions investigated here had 20-250 cutaneous neurofibromas, but only one of them exhibited a high load of cutaneous neurofibromas (N > 1,000). By contrast, a previous study indicated a high burden of cutaneous neurofibromas (N > 1,000) in 50% of adult patients with germline type-1 NF1 deletions. Patients with germline type-1 NF1 microdeletions have been reported to have an increased lifetime risk of 16-26% for a malignant peripheral nerve sheath tumour (MPNST). In this study, one of the eight investigated mosaic type-2 microdeletion patients developed an MPNST. We conclude that patients with mosaic type-2 NF1 microdeletions may also be at an increased risk of MPNSTs despite their generally milder disease manifestations as compared with germline type-1 NF1 microdeletions.
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