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Zhuang Y, Zhang R, Li M, Zou Y, Jiang S, Zhang Y, Liu S, Yu B. A Novel Ectodysplasin a Gene mutation of X-Linked Hypohidrotic Ectodermal Dysplasia. Clin Cosmet Investig Dermatol 2024; 17:1505-1517. [PMID: 38952411 PMCID: PMC11215660 DOI: 10.2147/ccid.s451125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Accepted: 06/06/2024] [Indexed: 07/03/2024]
Abstract
Introduction Hypohidrotic ectodermal dysplasia (HED) is a genetic disorder that influences structures of ectodermal origin, such as teeth, hair, and sweat glands. Compared with autosomal recessive and dominant modes of inheritance, the X-linked HED (XLHED) characterized by Hypodontia/Oligodontia teeth, Absent/sparse hair, Anhidrosis/hypohidrosis, and characteristic facial features, is the most frequent and its primary cause is the mutation of ectodysplasin A (EDA) gene. This research aimed to expound the clinical and molecular features of a Chinese male with XLHED and to summarize and compare several previous findings. Methods Genomic DNA was obtained from the peripheral blood of the proband and his family members, then Sanger sequencing was used to perform a mutational analysis of EDA. Real-time quantitative PCR and Western blotting were used to detect EDA expression. The transcriptional activity of NF-κB was detected using a luciferase assay. Results The probandwith XLHED was identified a novel EDA mutation, c.1119G>C(p.M373I), that affected the molecular analysis of transmembrane protein exon8 mutations, inherited from the mother. He showed a severe multiple-tooth loss, with over 20 permanent teeth missing and sparse hair and eyebrows, dry, thin, and itching skin. Furthermore, his sweating function was abnormal to a certain extent. Discussion The functional study showed that this novel mutant led to a significant decrease in the EDA expression level and transcriptional activity of NF-κB. Our findings extend the range of EDA mutations in XLHED patients, which provides the basis and idea for further exploring the pathogenesis of XLHED.
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Affiliation(s)
- Yuan Zhuang
- Dermatological Department, The Affiliated Hospital of QingdaoUniversity, Qingdao, People’s Republic of China
- dermatological department, Women and Children’s hospital, Qingdao University, Qingdao, People’s Republic of China
| | - Ru Zhang
- Medical Genetic Department, The Affiliated Hospital of Qingdao University, Qingdao, People’s Republic of China
- Prenatal Diagnosis Center, The Affiliated Hospital of Qingdao University, Qingdao, People’s Republic of China
| | - Miaomiao Li
- Medical Genetic Department, The Affiliated Hospital of Qingdao University, Qingdao, People’s Republic of China
- Prenatal Diagnosis Center, The Affiliated Hospital of Qingdao University, Qingdao, People’s Republic of China
| | - Yaru Zou
- Dermatological Department, The Affiliated Hospital of QingdaoUniversity, Qingdao, People’s Republic of China
| | - Shui Jiang
- Dermatological Department, The Affiliated Hospital of QingdaoUniversity, Qingdao, People’s Republic of China
| | - Yanan Zhang
- Dermatological Department, The Affiliated Hospital of QingdaoUniversity, Qingdao, People’s Republic of China
| | - Shiguo Liu
- Medical Genetic Department, The Affiliated Hospital of Qingdao University, Qingdao, People’s Republic of China
- Prenatal Diagnosis Center, The Affiliated Hospital of Qingdao University, Qingdao, People’s Republic of China
| | - Bo Yu
- Dermatological Department, The Affiliated Hospital of QingdaoUniversity, Qingdao, People’s Republic of China
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Hu H, Chen C, Shi S, Li B, Duan S. The gene mutations and subtelomeric DNA methylation in immunodeficiency, centromeric instability and facial anomalies syndrome. Autoimmunity 2019; 52:192-198. [PMID: 31476899 DOI: 10.1080/08916934.2019.1657846] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Immunodeficiency, centromeric instability and facial anomalies syndrome (ICF) is a rare autosomal recessive disorder, which is characteristic of a severe impairment of immunity. In the genetic aspect, ICF is featured with mutations primarily located in the specific genes (DNMT3B for ICF1, ZBTB24 for ICF2, CDCA7 for ICF3, and HELLS for ICF4). The subtelomeric region is defined as 500 kb at the terminal of each autosomal arm. And subtelomeric DNA fragments can partially regulate key biological activities, including chromosome movement and localization in the nucleus. In this review, we updated and summarized gene mutations in ICF based on the previous review. In addition, we focused on the correlation between subtelomeric DNA methylation and ICF. The relationship between subtelomeric methylation and telomere length in ICF was also summarized.
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Affiliation(s)
- Haochang Hu
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
| | - Chujia Chen
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
| | - Shanping Shi
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
| | - Bin Li
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
| | - Shiwei Duan
- Medical Genetics Center, School of Medicine, Ningbo University, Ningbo, Zhejiang, China
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Lin Y, Yin W, Bian Z. Mutation detection and prenatal diagnosis of XLHED pedigree. PeerJ 2017; 5:e3691. [PMID: 28875069 PMCID: PMC5578367 DOI: 10.7717/peerj.3691] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 07/25/2017] [Indexed: 01/08/2023] Open
Abstract
BACKGROUND The phenotypic characters of X -linked Hypohidrotic Ectodermal Dysplasia (XLHED) are the dysplasia of epithelial- and mesenchymal-derived organs. Ectodysplasin (EDA) is the causative gene of XLHED. METHODS The current study reported a large Chinese XLHED pedigree. The genomic DNA of adult and fetus was extracted from peripheral blood and shed chorion cell respectively. The nucleotide variation in EDA gene was screened through direct sequencing the coding sequence. The methylation state of EDA gene's promoter was evaluated by pyrosequencing. RESULTS This Chinese XLHED family had two male patients and three carriers. All of them were with a novel EDA frameshift mutation. The mutation, c.172-173insGG, which leads to an immediate premature stop codon in exon one caused severe structural changes of EDA. Prenatal diagnosis suggested that the fetus was a female carrier. The follow-up observation of this child indicated that she had mild hypodontia of deciduous teeth at age six. The methylation level of EDA gene's promoter was not related to carriers' phenotype changes in this family. DISCUSSION We reported a new frameshift mutation of EDA gene in a Chinese family. Prenatal diagnosis can help to predict the disease status of the fetus.
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Affiliation(s)
- Yao Lin
- The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, Wuhan University, Wuhan, Hubei, China.,Department of Endodontics, Xiamen Stomatology Hospital, Xiamen, Fujian, China
| | - Wei Yin
- The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, Wuhan University, Wuhan, Hubei, China
| | - Zhuan Bian
- The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) & Key Laboratory of Oral Biomedicine Ministry of Education, Wuhan University, Wuhan, Hubei, China
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Sterlin D, Velasco G, Moshous D, Touzot F, Mahlaoui N, Fischer A, Suarez F, Francastel C, Picard C. Genetic, Cellular and Clinical Features of ICF Syndrome: a French National Survey. J Clin Immunol 2016; 36:149-59. [PMID: 26851945 DOI: 10.1007/s10875-016-0240-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 01/31/2016] [Indexed: 12/22/2022]
Abstract
PURPOSE Autosomal recessive deficiencies of DNMT3B or ZBTB24 account for two-thirds of cases of immunodeficiency, centromeric instability and facial dysmorphism (ICF syndrome). This primary immunodeficiency (PID) is characterized mainly by an antibody deficiency, facial abnormalities and centromeric instability. We analyzed the national cohort of patients with ICF syndrome with the aim of providing a more detailed description of the phenotype and management of patients with ICF syndrome. METHODS Demographic, genetic, immunological, and clinical features were recorded for each patient. RESULTS In the French cohort, seven of the nine patients carried DNMT3B mutations, six of which had never been described before. One patient had compound heterozygous ZBTB24 mutations. All patients were found to lack CD19(+)CD27(+) memory B cells. This feature is a major diagnostic criterion for both ICF1 and ICF2. Patients suffered both bacterial and viral infections, and three patients developed bronchiectasis. Autoimmune manifestations (hepatitis, nephritis and thyroiditis) not previously reported in ICF1 patients were also detected in two of our ICF1 patients. The mode of treatment and outcome of the French patients are reported, by genetic defect, and compared with those for 68 previously reported ICF patients. Immunoglobulin (Ig) replacement treatment was administered to all nine French patients. One ICF1 patient presented severe autoimmune manifestations and pancytopenia and underwent allogeneic hematopoietic stem cell transplantation (HSCT), but she died from unknown causes 6 years post-transplant. CONCLUSION Autoimmune signs are uncommon in ICF syndrome, but, when present, they affect patient outcome and require immunosuppressive treatment. The long-term outcome of ICF patients has been improved by the combination of IgG replacement and antibiotic prophylaxis.
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Affiliation(s)
- Delphine Sterlin
- Study Center for Primary Immunodeficiencies, Necker-Enfants Malades Hospital, Assistance Publique Hôpitaux de Paris (APHP), University Paris Descartes, 149 rue de Sevres, 75015, Paris, France
| | - Guillaume Velasco
- CNRS UMR7216, Epigenetics and Cell Fate, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - Despina Moshous
- Pediatric Immuno-Hematology Unit, Necker Children's Hospital, APHP, Université Paris Descartes, Paris, France.,INSERM UMR1163, Imagine Institute, Necker Medical School, Sorbonne Paris Cité, University Paris Descartes, Paris, France
| | - Fabien Touzot
- Pediatric Immuno-Hematology Unit, Necker Children's Hospital, APHP, Université Paris Descartes, Paris, France.,INSERM UMR1163, Imagine Institute, Necker Medical School, Sorbonne Paris Cité, University Paris Descartes, Paris, France.,Laboratory of Molecular Mechanisms of Hematologic Disorders and Therapeutic Implications, INSERM UMR1163, Imagine Institut, Necker Medical School, University Paris Descartes, Paris, France.,Biotherapy Department, Necker-Enfants Malades Hospital, APHP, University Paris Descartes, Paris, France
| | - Nizar Mahlaoui
- Pediatric Immuno-Hematology Unit, Necker Children's Hospital, APHP, Université Paris Descartes, Paris, France.,French National Reference Center for Primary Immune Deficiencies (CEREDIH), Necker - Enfants Malades Hospital, Assistance Publique Hôpitaux de Paris, Paris, France
| | - Alain Fischer
- Pediatric Immuno-Hematology Unit, Necker Children's Hospital, APHP, Université Paris Descartes, Paris, France.,INSERM UMR1163, Imagine Institute, Necker Medical School, Sorbonne Paris Cité, University Paris Descartes, Paris, France.,College de France, Paris, France.,French National Reference Center for Primary Immune Deficiencies (CEREDIH), Necker - Enfants Malades Hospital, Assistance Publique Hôpitaux de Paris, Paris, France
| | - Felipe Suarez
- Adult Hematology Unit, Necker Children's Hospital, APHP, University Paris Descartes, Paris, France.,French National Reference Center for Primary Immune Deficiencies (CEREDIH), Necker - Enfants Malades Hospital, Assistance Publique Hôpitaux de Paris, Paris, France.,INSERM UMR1163 and CNRS ERL8254, Imagine Institute, Necker Medical School, Sorbonne Paris Cité, University Paris Descartes, Paris, France
| | - Claire Francastel
- CNRS UMR7216, Epigenetics and Cell Fate, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - Capucine Picard
- Study Center for Primary Immunodeficiencies, Necker-Enfants Malades Hospital, Assistance Publique Hôpitaux de Paris (APHP), University Paris Descartes, 149 rue de Sevres, 75015, Paris, France. .,Pediatric Immuno-Hematology Unit, Necker Children's Hospital, APHP, Université Paris Descartes, Paris, France. .,Laboratory of the Human Genetics of Infectious Diseases, INSERM UMR1163, Imagine Institute, Necker Medical School, Sorbonne Paris Cité, University Paris Descartes, Paris, France. .,French National Reference Center for Primary Immune Deficiencies (CEREDIH), Necker - Enfants Malades Hospital, Assistance Publique Hôpitaux de Paris, Paris, France.
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Velasco G, Walton EL, Sterlin D, Hédouin S, Nitta H, Ito Y, Fouyssac F, Mégarbané A, Sasaki H, Picard C, Francastel C. Germline genes hypomethylation and expression define a molecular signature in peripheral blood of ICF patients: implications for diagnosis and etiology. Orphanet J Rare Dis 2014; 9:56. [PMID: 24742017 PMCID: PMC4022050 DOI: 10.1186/1750-1172-9-56] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Accepted: 04/11/2014] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Immunodeficiency Centromeric Instability and Facial anomalies (ICF) is a rare autosomal recessive disease characterized by reduction in serum immunoglobulins with severe recurrent infections, facial dysmorphism, and more variable symptoms including mental retardation. ICF is directly related to a genomic methylation defect that mainly affects juxtacentromeric heterochromatin regions of certain chromosomes, leading to chromosomal rearrangements that constitute a hallmark of this syndrome upon cytogenetic testing. Mutations in the de novo DNA methyltransferase DNMT3B, the protein ZBTB24 of unknown function, or loci that remain to be identified, lie at its origin. Despite unifying features, common or distinguishing molecular signatures are still missing for this disease. METHOD We used the molecular signature that we identified in a mouse model for ICF1 to establish transcriptional biomarkers to facilitate diagnosis and understanding of etiology of the disease. We assayed the expression and methylation status of a set of genes whose expression is normally restricted to germ cells, directly in whole blood samples and epithelial cells of ICF patients. RESULTS We report that DNA hypomethylation and expression of MAEL and SYCE1 represent robust biomarkers, easily testable directly from uncultured cells to diagnose the most prevalent sub-type of the syndrome. In addition, we identified the first unifying molecular signatures for ICF patients. Of importance, we validated the use of our biomarkers to diagnose a baby born to a family with a sick child. Finally, our analysis revealed unsuspected complex molecular signatures in two ICF patients suggestive of a novel genetic etiology for the disease. CONCLUSIONS Early diagnosis of ICF syndrome is crucial since early immunoglobulin supplementation can improve the course of disease. However, ICF is probably underdiagnosed, especially in patients that present with incomplete phenotype or born to families with no affected relatives. The specific and robust biomarkers identified in this study could be introduced into routine clinical immunology or neurology departments to facilitate testing of patients with suspected ICF syndrome. In addition, as exemplified by two patients with a combination of molecular defects never described before, our data support the search for new types of mutations at the origin of ICF syndrome.
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Affiliation(s)
- Guillaume Velasco
- Université Paris Diderot-Paris7, CNRS UMR7216, Epigénétique et Destin Cellulaire, Case Courrier 7042; 35, rue Hélène Brion, 75205 Paris, France.
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Weemaes CMR, van Tol MJD, Wang J, van Ostaijen-ten Dam MM, van Eggermond MCJA, Thijssen PE, Aytekin C, Brunetti-Pierri N, van der Burg M, Graham Davies E, Ferster A, Furthner D, Gimelli G, Gennery A, Kloeckener-Gruissem B, Meyn S, Powell C, Reisli I, Schuetz C, Schulz A, Shugar A, van den Elsen PJ, van der Maarel SM. Heterogeneous clinical presentation in ICF syndrome: correlation with underlying gene defects. Eur J Hum Genet 2013; 21:1219-25. [PMID: 23486536 PMCID: PMC3798845 DOI: 10.1038/ejhg.2013.40] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Revised: 01/30/2013] [Accepted: 02/06/2013] [Indexed: 11/09/2022] Open
Abstract
Immunodeficiency with centromeric instability and facial anomalies (ICF) syndrome is a primary immunodeficiency, predominantly characterized by agammaglobulinemia or hypoimmunoglobulinemia, centromere instability and facial anomalies. Mutations in two genes have been discovered to cause ICF syndrome: DNMT3B and ZBTB24. To characterize the clinical features of this syndrome, as well as genotype-phenotype correlations, we compared clinical and genetic data of 44 ICF patients. Of them, 23 had mutations in DNMT3B (ICF1), 13 patients had mutations in ZBTB24 (ICF2), whereas for 8 patients, the gene defect has not yet been identified (ICFX). While at first sight these patients share the same immunological, morphological and epigenetic hallmarks of the disease, systematic evaluation of all reported informative cases shows that: (1) the humoral immunodeficiency is generally more pronounced in ICF1 patients, (2) B- and T-cell compartments are both involved in ICF1 and ICF2, (3) ICF2 patients have a significantly higher incidence of intellectual disability and (4) congenital malformations can be observed in some ICF1 and ICF2 cases. It is expected that these observations on prevalence and clinical presentation will facilitate mutation-screening strategies and help in diagnostic counseling.
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Affiliation(s)
- Corry MR Weemaes
- Department of Pediatric Infectious Diseases and Immunology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
| | - Maarten JD van Tol
- Department of Pediatrics, Leiden University Medical Center, Leiden, The Netherlands
| | - Jun Wang
- Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | | | - Marja CJA van Eggermond
- Department of Immunohaematology and Blood Transfusion, Leiden University Medical Center, Leiden, The Netherlands
| | - Peter E Thijssen
- Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Caner Aytekin
- Department of Pediatric Immunology, Dr Sami Ulus Maternity and Children's Research and Educational Hospital, Ankara, Turkey
| | | | - Mirjam van der Burg
- Department of Immunology, Erasmus Medical Center, Rotterdam, The Netherlands
| | - E Graham Davies
- Centre for Immunodeficiency, Great Ormond Street Hospital and Institute of Child Health, London, UK
| | - Alina Ferster
- Department of Pediatrics, Haemato-Oncology Unit, Hôpital Universitaire des Enfants Reine Fabiola, Université Libre de Bruxelles, Brussels, Belgium
| | | | - Giorgio Gimelli
- Laboratorio di Citogenetica, Instituto G Gaslini, Genova, Italy
| | - Andy Gennery
- Department of Paediatric Immunology, Newcastle Upon Tyne Hospital, NHS Foundation Trust, United Kingdom and Institute of Cellular Medicine, Newcastle University, Newcastle Upon Tyne, UK
| | - Barbara Kloeckener-Gruissem
- Institute of Medical Molecular Genetics, University of Zurich, Zurich, Switzerland
- Department of Biology, ETHZ, Zurich, Switzerland
| | - Stephan Meyn
- Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Cynthia Powell
- Department of Pediatrics, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Ismail Reisli
- Department of Pediatric Immunology and Allergy, Necmettin Erbakan University, Meram Medical Faculty, Konya, Turkey
| | - Catharina Schuetz
- Department of Pediatrics and Adolescent Medicine, University Hospital Ulm, Ulm, Germany
| | - Ansgar Schulz
- Department of Pediatrics and Adolescent Medicine, University Hospital Ulm, Ulm, Germany
| | - Andrea Shugar
- Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Peter J van den Elsen
- Department of Immunohaematology and Blood Transfusion, Leiden University Medical Center, Leiden, The Netherlands
- Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands
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Yehezkel S, Shaked R, Sagie S, Berkovitz R, Shachar-Bener H, Segev Y, Selig S. Characterization and rescue of telomeric abnormalities in ICF syndrome type I fibroblasts. Front Oncol 2013; 3:35. [PMID: 23450006 PMCID: PMC3584450 DOI: 10.3389/fonc.2013.00035] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Accepted: 02/08/2013] [Indexed: 11/19/2022] Open
Abstract
Mutations in the human DNA methyltransferase 3B (DNMT3B) gene lead to ICF (immunodeficiency, centromeric region instability, and facial anomalies) syndrome type I. We have previously described a telomere-related phenotype in cells from these patients, involving severe hypomethylation of subtelomeric regions, abnormally short telomeres and high levels of telomeric-repeat-containing RNA (TERRA). Here we demonstrate that ICF-patient fibroblasts carry abnormally short telomeres at a low population doubling (PD) and enter senescence prematurely. Accordingly, we attempted to rescue the senescence phenotype by ectopic expression of human telomerase, which led to elongated telomeres with hypomethylated subtelomeres. The senescence phenotype was overcome under these conditions, thus dissociating subtelomeric-DNA hypomethylation per se from the senescence phenotype. In addition, we examined whether the subtelomeric methylation could be restored by expression of a normal copy of full length DNMT3B1 in ICF fibroblasts. Ectopic expression of DNMT3B1 failed to rescue the abnormal hypomethylation at subtelomeres. However, partial rescue of subtelomeric-hypomethylation was achieved by co-expression of DNMT3B1 together with DNA methyltransferase 3-like (DNMT3L), encoding a protein that functions as a stimulator of DNMT3A and DNMT3B. DNMT3B1 and DNMT3L are predominantly expressed during early embryonic development, suggesting that de novo subtelomeric DNA methylation during crucial stages of human embryonic development may be necessary for setting and maintaining normal telomere length.
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Affiliation(s)
- Shiran Yehezkel
- Rambam Health Care Campus and Rappaport Faculty of Medicine and Research Institute, Molecular Medicine Laboratory, Technion-Israel Institute of Technology Haifa, Israel
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Yehezkel S, Segev Y, Viegas-Péquignot E, Skorecki K, Selig S. Hypomethylation of subtelomeric regions in ICF syndrome is associated with abnormally short telomeres and enhanced transcription from telomeric regions. Hum Mol Genet 2008; 17:2776-89. [PMID: 18558631 DOI: 10.1093/hmg/ddn177] [Citation(s) in RCA: 171] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Telomeres and adjacent subtelomeric regions are packaged as heterochromatin in many organisms. The heterochromatic features include DNA methylation, histones H3-Lys9 (Lysine 9) and H4-Lys20 (Lysine 20) methylation and heterochromatin protein1 alpha binding. Subtelomeric DNA is hypomethylated in human sperm and ova, and these regions are subjected to de novo methylation during development. In mice this activity is carried out by DNA methyltransferase 3b (Dnmt3b). Mutations in DNMT3B in humans lead to the autosomal-recessive ICF (immunodeficiency, centromeric region instability, facial anomalies) syndrome. Here we show that, in addition to several satellite and non-satellite repeats, the subtelomeric regions in lymphoblastoid and fibroblast cells of ICF patients are also hypomethylated to similar levels as in sperm. Furthermore, the telomeres are abnormally short in both the telomerase-positive and -negative cells, and many chromosome ends lack detectable telomere fluorescence in situ hybridization signals from either one or both sister-chromatids. In contrast to Dnmt3a/b(-/-) mouse embryonic stem cells, increased telomere sister-chromatid exchange was not observed in ICF cells. Hypomethylation of subtelomeric regions was associated in the ICF cells with advanced telomere replication timing and elevated levels of transcripts emanating from telomeric regions, known as TERRA (telomeric-repeat-containing RNA) or TelRNA. The current findings provide a mechanistic explanation for the abnormal telomeric phenotype observed in ICF syndrome and highlights the link between TERRA/TelRNA and structural telomeric integrity.
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Affiliation(s)
- Shiran Yehezkel
- Department of Nephrology and Laboratory of Molecular Medicine, Rambam Medical Center and Rappaport Faculty of Medicine and Research Institute, Technion, Haifa 31096, Israel
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