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Nelson N, Feurstein S, Niaz A, Truong J, Holien JK, Lucas S, Fairfax K, Dickinson J, Bryan TM. Functional genomics for curation of variants in telomere biology disorder associated genes: A systematic review. Genet Med 2023; 25:100354. [PMID: 36496180 DOI: 10.1016/j.gim.2022.11.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 11/28/2022] [Accepted: 11/30/2022] [Indexed: 12/12/2022] Open
Abstract
PURPOSE Patients with an underlying telomere biology disorder (TBD) have variable clinical presentations, and they can be challenging to diagnose clinically. A genomic diagnosis for patients presenting with TBD is vital for optimal treatment. Unfortunately, many variants identified during diagnostic testing are variants of uncertain significance. This complicates management decisions, delays treatment, and risks nonuptake of potentially curative therapies. Improved application of functional genomic evidence may reduce variants of uncertain significance classifications. METHODS We systematically searched the literature for published functional assays interrogating TBD gene variants. When possible, established likely benign/benign and likely pathogenic/pathogenic variants were used to estimate the assay sensitivity, specificity, positive predictive value, negative predictive value, and odds of pathogenicity. RESULTS In total, 3131 articles were screened and 151 met inclusion criteria. Sufficient data to enable a PS3/BS3 recommendation were available for TERT variants only. We recommend that PS3 and BS3 can be applied at a moderate and supportive level, respectively. PS3/BS3 application was limited by a lack of assay standardization and limited inclusion of benign variants. CONCLUSION Further assay standardization and assessment of benign variants are required for optimal use of the PS3/BS3 criterion for TBD gene variant classification.
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Affiliation(s)
- Niles Nelson
- The Menzies Institute for Medical Research, College of Health and Medicine, The University of Tasmania, Hobart, Tasmania, Australia; Department of Molecular Medicine, The Royal Hobart Hospital, Hobart, Tasmania, Australia; Department of Molecular Haematology, The Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia.
| | - Simone Feurstein
- Section of Hematology, Oncology, and Rheumatology, Department of Internal Medicine, Heidelberg University Hospital, Heidelberg, Germany
| | - Aram Niaz
- Children's Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, New South Wales, Australia
| | - Jia Truong
- School of Science, STEM College, RMIT University, Bundoora, Victoria, Australia
| | - Jessica K Holien
- School of Science, STEM College, RMIT University, Bundoora, Victoria, Australia
| | - Sionne Lucas
- The Menzies Institute for Medical Research, College of Health and Medicine, The University of Tasmania, Hobart, Tasmania, Australia
| | - Kirsten Fairfax
- The Menzies Institute for Medical Research, College of Health and Medicine, The University of Tasmania, Hobart, Tasmania, Australia
| | - Joanne Dickinson
- The Menzies Institute for Medical Research, College of Health and Medicine, The University of Tasmania, Hobart, Tasmania, Australia
| | - Tracy M Bryan
- Children's Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, New South Wales, Australia
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Revy P, Kannengiesser C, Bertuch AA. Genetics of human telomere biology disorders. Nat Rev Genet 2023; 24:86-108. [PMID: 36151328 DOI: 10.1038/s41576-022-00527-z] [Citation(s) in RCA: 43] [Impact Index Per Article: 43.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/11/2022] [Indexed: 01/24/2023]
Abstract
Telomeres are specialized nucleoprotein structures at the ends of linear chromosomes that prevent the activation of DNA damage response and repair pathways. Numerous factors localize at telomeres to regulate their length, structure and function, to avert replicative senescence or genome instability and cell death. In humans, Mendelian defects in several of these factors can result in abnormally short or dysfunctional telomeres, causing a group of rare heterogeneous premature-ageing diseases, termed telomeropathies, short-telomere syndromes or telomere biology disorders (TBDs). Here, we review the TBD-causing genes identified so far and describe their main functions associated with telomere biology. We present molecular aspects of TBDs, including genetic anticipation, phenocopy, incomplete penetrance and somatic genetic rescue, which underlie the complexity of these diseases. We also discuss the implications of phenotypic and genetic features of TBDs on fundamental aspects related to human telomere biology, ageing and cancer, as well as on diagnostic, therapeutic and clinical approaches.
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Affiliation(s)
- Patrick Revy
- INSERM UMR 1163, Laboratory of Genome Dynamics in the Immune System, Equipe Labellisée Ligue Nationale contre le Cancer, Paris, France.
- Université Paris Cité, Imagine Institute, Paris, France.
| | - Caroline Kannengiesser
- APHP Service de Génétique, Hôpital Bichat, Paris, France
- Inserm U1152, Université Paris Cité, Paris, France
| | - Alison A Bertuch
- Departments of Paediatrics and Molecular & Human Genetics, Baylor College of Medicine, Houston, TX, USA
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3
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Arthur JW, Pickett HA, Barbaro PM, Kilo T, Vasireddy RS, Beilharz TH, Powell DR, Hackett EL, Bennetts B, Curtin JA, Jones K, Christodoulou J, Reddel RR, Teo J, Bryan TM. A novel cause of DKC1-related bone marrow failure: Partial deletion of the 3' untranslated region. EJHAEM 2021; 2:157-166. [PMID: 35845273 PMCID: PMC9175968 DOI: 10.1002/jha2.165] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/22/2020] [Revised: 01/03/2021] [Accepted: 01/07/2021] [Indexed: 12/11/2022]
Abstract
Telomere biology disorders (TBDs), including dyskeratosis congenita (DC), are a group of rare inherited diseases characterized by very short telomeres. Mutations in the components of the enzyme telomerase can lead to insufficient telomere maintenance in hematopoietic stem cells, resulting in the bone marrow failure that is characteristic of these disorders. While an increasing number of genes are being linked to TBDs, the causative mutation remains unidentified in 30‐40% of patients with DC. There is therefore a need for whole genome sequencing (WGS) in these families to identify novel genes, or mutations in regulatory regions of known disease‐causing genes. Here we describe a family in which a partial deletion of the 3′ untranslated region (3′ UTR) of DKC1, encoding the protein dyskerin, was identified by WGS, despite being missed by whole exome sequencing. The deletion segregated with disease across the family and resulted in reduced levels of DKC1 mRNA in the proband. We demonstrate that the DKC1 3′ UTR contains two polyadenylation signals, both of which were removed by this deletion, likely causing mRNA instability. Consistent with the major function of dyskerin in stabilization of the RNA subunit of telomerase, hTR, the level of hTR was also reduced in the proband, providing a molecular basis for his very short telomeres. This study demonstrates that the terminal region of the 3′ UTR of the DKC1 gene is essential for gene function and illustrates the importance of analyzing regulatory regions of the genome for molecular diagnosis of inherited disease.
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Affiliation(s)
- Jonathan W Arthur
- Children's Medical Research Institute Faculty of Medicine and Health, University of Sydney Westmead New South Wales Australia
| | - Hilda A Pickett
- Children's Medical Research Institute Faculty of Medicine and Health, University of Sydney Westmead New South Wales Australia
| | - Pasquale M Barbaro
- Children's Medical Research Institute Faculty of Medicine and Health, University of Sydney Westmead New South Wales Australia
| | - Tatjana Kilo
- Haematology Department Children's Hospital at Westmead Westmead New South Wales Australia
| | - Raja S Vasireddy
- Haematology Department Children's Hospital at Westmead Westmead New South Wales Australia
| | - Traude H Beilharz
- Monash Biomedicine Discovery Institute Department of Biochemistry and Molecular Biology, Monash University Clayton Victoria Australia
| | - David R Powell
- Monash Bioinformatics Platform Monash University Clayton Victoria Australia
| | - Emma L Hackett
- Department of Molecular Genetics Children's Hospital Westmead Westmead New South Wales Australia
| | - Bruce Bennetts
- Department of Molecular Genetics Children's Hospital Westmead Westmead New South Wales Australia.,Disciplines of Genetic Medicine and Child and Adolescent Health, Faculty of Medicine and Health University of Sydney Westmead New South Wales Australia
| | - Julie A Curtin
- Haematology Department Children's Hospital at Westmead Westmead New South Wales Australia
| | - Kristi Jones
- Disciplines of Genetic Medicine and Child and Adolescent Health, Faculty of Medicine and Health University of Sydney Westmead New South Wales Australia.,Department of Clinical Genetics Children's Hospital Westmead Westmead New South Wales Australia
| | - John Christodoulou
- Disciplines of Genetic Medicine and Child and Adolescent Health, Faculty of Medicine and Health University of Sydney Westmead New South Wales Australia.,Murdoch Children's Research Institute and Department of Paediatrics Melbourne Medical School Parkville Victoria Australia
| | - Roger R Reddel
- Children's Medical Research Institute Faculty of Medicine and Health, University of Sydney Westmead New South Wales Australia
| | - Juliana Teo
- Haematology Department Children's Hospital at Westmead Westmead New South Wales Australia
| | - Tracy M Bryan
- Children's Medical Research Institute Faculty of Medicine and Health, University of Sydney Westmead New South Wales Australia
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4
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Xu J, Khincha PP, Giri N, Alter BP, Savage SA, Wong JM. Investigation of chromosome X inactivation and clinical phenotypes in female carriers of DKC1 mutations. Am J Hematol 2016; 91:1215-1220. [PMID: 27570172 DOI: 10.1002/ajh.24545] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 07/25/2016] [Accepted: 08/25/2016] [Indexed: 12/15/2022]
Abstract
Dyskeratosis congenita (DC) is an inherited bone marrow failure and cancer susceptibility syndrome caused by germline mutations in telomere biology genes. Germline mutations in DKC1, which encodes the protein dyskerin, cause X-linked recessive DC. Because of skewed X-chromosome inactivation, female DKC1 mutation carriers do not typically develop clinical features of DC. This study evaluated female DKC1 mutation carriers with DC-associated phenotypes to elucidate the molecular features of their mutations, in comparison with unaffected carriers and mutation-negative female controls. All female DKC1 mutation carriers had normal leukocyte subset telomere lengths and similarly skewed X-inactivation in multiple tissue types, regardless of phenotype. We observed dyskerin expression, telomerase RNA accumulation, and pseudouridylation present in all mutation carriers at levels comparable to healthy wild-type controls. Our study suggests that mechanisms in addition to X chromosome inactivation, such as germline mosaicism or epigenetics, may contribute to DC-like phenotypes present in female DKC1 mutation carriers. Future studies are warranted to understand the molecular mechanisms associated with the phenotypic variability in female DKC1 mutation carriers, and to identify those at risk of disease. Am. J. Hematol. 91:1215-1220, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Jialin Xu
- Molecular and Cellular Pharmacology Group, Faculty of Pharmaceutical SciencesUniversity of British ColumbiaVancouver BC Canada
| | - Payal P. Khincha
- Clinical Genetics Branch, Division of Cancer Epidemiology and GeneticsNational Cancer Institute, National Institutes of HealthRockville Maryland
| | - Neelam Giri
- Clinical Genetics Branch, Division of Cancer Epidemiology and GeneticsNational Cancer Institute, National Institutes of HealthRockville Maryland
| | - Blanche P. Alter
- Clinical Genetics Branch, Division of Cancer Epidemiology and GeneticsNational Cancer Institute, National Institutes of HealthRockville Maryland
| | - Sharon A. Savage
- Clinical Genetics Branch, Division of Cancer Epidemiology and GeneticsNational Cancer Institute, National Institutes of HealthRockville Maryland
| | - Judy M.Y. Wong
- Molecular and Cellular Pharmacology Group, Faculty of Pharmaceutical SciencesUniversity of British ColumbiaVancouver BC Canada
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Glousker G, Touzot F, Revy P, Tzfati Y, Savage SA. Unraveling the pathogenesis of Hoyeraal-Hreidarsson syndrome, a complex telomere biology disorder. Br J Haematol 2015; 170:457-71. [PMID: 25940403 DOI: 10.1111/bjh.13442] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Hoyeraal-Hreidarsson (HH) syndrome is a multisystem genetic disorder characterized by very short telomeres and considered a clinically severe variant of dyskeratosis congenita. The main cause of mortality, usually in early childhood, is bone marrow failure. Mutations in several telomere biology genes have been reported to cause HH in about 60% of the HH patients, but the genetic defects in the rest of the patients are still unknown. Understanding the aetiology of HH and its diverse manifestations is challenging because of the complexity of telomere biology and the multiple telomeric and non-telomeric functions played by telomere-associated proteins in processes such as telomere replication, telomere protection, DNA damage response and ribosome and spliceosome assembly. Here we review the known clinical complications, molecular defects and germline mutations associated with HH, and elucidate possible mechanistic explanations and remaining questions in our understanding of the disease.
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Affiliation(s)
- Galina Glousker
- Department of Genetics, The Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem, Israel
| | - Fabien Touzot
- INSERM UMR 1163, Laboratory of Genome Dynamics in the Immune System, Paris Descartes - Sorbonne Paris Cité University, Imagine Institute, Paris, France
| | - Patrick Revy
- INSERM UMR 1163, Laboratory of Genome Dynamics in the Immune System, Paris Descartes - Sorbonne Paris Cité University, Imagine Institute, Paris, France
| | - Yehuda Tzfati
- Department of Genetics, The Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem, Israel
| | - Sharon A Savage
- Clinical Genetics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA
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Genetic mosaics and the germ line lineage. Genes (Basel) 2015; 6:216-37. [PMID: 25898403 PMCID: PMC4488662 DOI: 10.3390/genes6020216] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Revised: 03/27/2015] [Accepted: 04/07/2015] [Indexed: 12/26/2022] Open
Abstract
Genetic mosaics provide information about cellular lineages that is otherwise difficult to obtain, especially in humans. De novo mutations act as cell markers, allowing the tracing of developmental trajectories of all descendants of the cell in which the new mutation arises. De novo mutations may arise at any time during development but are relatively rare. They have usually been observed through medical ascertainment, when the mutation causes unusual clinical signs or symptoms. Mutational events can include aneuploidies, large chromosomal rearrangements, copy number variants, or point mutations. In this review we focus primarily on the analysis of point mutations and their utility in addressing questions of germ line versus somatic lineages. Genetic mosaics demonstrate that the germ line and soma diverge early in development, since there are many examples of combined somatic and germ line mosaicism for de novo mutations. The occurrence of simultaneous mosaicism in both the germ line and soma also shows that the germ line is not strictly clonal but arises from at least two, and possibly multiple, cells in the embryo with different ancestries. Whole genome or exome DNA sequencing technologies promise to expand the range of studies of genetic mosaics, as de novo mutations can now be identified through sequencing alone in the absence of a medical ascertainment. These technologies have been used to study mutation patterns in nuclear families and in monozygotic twins, and in animal model developmental studies, but not yet for extensive cell lineage studies in humans.
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Angrisani A, Vicidomini R, Turano M, Furia M. Human dyskerin: beyond telomeres. Biol Chem 2014; 395:593-610. [PMID: 24468621 DOI: 10.1515/hsz-2013-0287] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Accepted: 01/24/2014] [Indexed: 12/15/2022]
Abstract
Human dyskerin is an evolutively conserved protein that participates in diverse nuclear complexes: the H/ACA snoRNPs, that control ribosome biogenesis, RNA pseudouridylation, and stability of H/ACA snoRNAs; the scaRNPs, that control pseudouridylation of snRNAs; and the telomerase active holoenzyme, which safeguards telomere integrity. The biological importance of dyskerin is further outlined by the fact that its deficiency causes the X-linked dyskeratosis congenita disease, while its over-expression characterizes several types of cancers and has been proposed as prognostic marker. The role of dyskerin in telomere maintenance has widely been discussed, while its functions as H/ACA sno/scaRNP component has been so far mostly overlooked and represent the main goal of this review. Here we summarize how increasing evidence indicates that the snoRNA/microRNA pathways can be interlaced, and that dyskerin-dependent RNA pseudouridylation represents a flexible mechanism able to modulate RNA function in different ways, including modulation of splicing, change of mRNA coding properties, and selective regulation of IRES-dependent translation. We also propose a speculative model that suggests that the dynamics of pre-assembly and nuclear import of H/ACA RNPs are crucial regulatory steps that can be finely controlled in the cytoplasm in response to developmental, differentiative and stress stimuli.
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Fong YW, Ho JJ, Inouye C, Tjian R. The dyskerin ribonucleoprotein complex as an OCT4/SOX2 coactivator in embryonic stem cells. eLife 2014; 3. [PMID: 25407680 PMCID: PMC4270071 DOI: 10.7554/elife.03573] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Accepted: 11/19/2014] [Indexed: 01/06/2023] Open
Abstract
Acquisition of pluripotency is driven largely at the transcriptional level by activators OCT4, SOX2, and NANOG that must in turn cooperate with diverse coactivators to execute stem cell-specific gene expression programs. Using a biochemically defined in vitro transcription system that mediates OCT4/SOX2 and coactivator-dependent transcription of the Nanog gene, we report the purification and identification of the dyskerin (DKC1) ribonucleoprotein complex as an OCT4/SOX2 coactivator whose activity appears to be modulated by a subset of associated small nucleolar RNAs (snoRNAs). The DKC1 complex occupies enhancers and regulates the expression of key pluripotency genes critical for self-renewal in embryonic stem (ES) cells. Depletion of DKC1 in fibroblasts significantly decreased the efficiency of induced pluripotent stem (iPS) cell generation. This study thus reveals an unanticipated transcriptional role of the DKC1 complex in stem cell maintenance and somatic cell reprogramming. DOI:http://dx.doi.org/10.7554/eLife.03573.001 The stem cells found in an embryo are able to develop into any of the cell types found in the body of the animal: an ability called pluripotency. When a cell becomes a specialized cell type, such as a nerve cell or a muscle cell, it loses this ability. However, mature cells can be reprogrammed back to a pluripotent state by artificially introducing certain proteins (known as ‘reprogramming factors’) into the mature cells. A core group of reprogramming factors are known to activate networks of genes that are normally only expressed in stem cells, and by doing so trigger and maintain a pluripotent state. Other proteins help these core factors to regulate these networks of genes. In 2011, researchers discovered that a protein complex called XPC—which is normally involved in DNA repair—also helps two core reprogramming factors to activate an important gene related to pluripotency. Now, Fong et al., including several of the researchers involved in the 2011 work, have identified another unexpected partner for the same two core reprogramming factors. The protein complex, called DKC1, has a number of known functions related to the processing of RNA molecules. This complex has also been linked to a fatal, rare human disorder called dyskeratosis congenita—a condition that affects many parts of the body, including the skin and bone marrow. Fong et al. found that when embryonic stems cells from mice are depleted of the DKC1 complex, the activation of important pluripotency-related genes by two of the core reprogramming factors is markedly reduced. The XPC and DKC1 protein complexes were found to interact in pluripotent cells, and together they can activate a pluripotency-related gene to a greater extent than either can individually. Fong et al. propose that DKC1 binds to XPC, which in turn binds to two of the core reprogramming factors. The DKC1 complex also binds to RNA molecules, and Fong et al. found that when the DKC1 complex binds to certain RNAs it is more able to help reprogramming factors activate pluripotency-related genes. On the other hand, other RNA molecules seem to inhibit the complex's ability to activate these genes. Mutations identified in people with dyskeratosis congenita can prevent the DKC1 complex from binding to a subset of human RNA molecules. Moreover, the activity of stem cells is impaired in people with this developmental condition. As such, one of the next challenges will be to investigate if these mutations and RNA binding could be linked to problems with the activation of genes related to pluripotency in stem cells. DOI:http://dx.doi.org/10.7554/eLife.03573.002
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Affiliation(s)
- Yick W Fong
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Jaclyn J Ho
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Carla Inouye
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Robert Tjian
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
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Marrone A, Dokal I. Dyskeratosis congenita: a disorder of telomerase deficiency and its relationship to other diseases. ACTA ACUST UNITED AC 2014. [DOI: 10.1586/17469872.1.3.463] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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10
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Evolutionary conservation and expression of human RNA-binding proteins and their role in human genetic disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 825:1-55. [PMID: 25201102 DOI: 10.1007/978-1-4939-1221-6_1] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
RNA-binding proteins (RBPs) are effectors and regulators of posttranscriptional gene regulation (PTGR). RBPs regulate stability, maturation, and turnover of all RNAs, often binding thousands of targets at many sites. The importance of RBPs is underscored by their dysregulation or mutations causing a variety of developmental and neurological diseases. This chapter globally discusses human RBPs and provides a brief introduction to their identification and RNA targets. We review RBPs based on common structural RNA-binding domains, study their evolutionary conservation and expression, and summarize disease associations of different RBP classes.
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Tümpel S, Rudolph KL. The role of telomere shortening in somatic stem cells and tissue aging: lessons from telomerase model systems. Ann N Y Acad Sci 2012; 1266:28-39. [DOI: 10.1111/j.1749-6632.2012.06547.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Mason PJ, Bessler M. The genetics of dyskeratosis congenita. Cancer Genet 2011; 204:635-45. [PMID: 22285015 PMCID: PMC3269008 DOI: 10.1016/j.cancergen.2011.11.002] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2011] [Revised: 11/11/2011] [Accepted: 11/13/2011] [Indexed: 01/18/2023]
Abstract
Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome associated with characteristic mucocutaneous features and a variable series of other somatic abnormalities. The disease is heterogeneous at the genetic and clinical levels. Determination of the genetic basis of DC has established that the disease is caused by a number of genes, all of which encode products involved in telomere maintenance, either as part of telomerase or as part of the shelterin complex that caps and protects telomeres. There is overlap at the genetic and clinical levels with other, more common conditions, including aplastic anemia (AA), pulmonary fibrosis (PF), and liver cirrhosis. Although part of the spectrum of disorders known to be associated with DC, it has emerged that mutations in telomere maintenance genes can lead to the development of AA and PF in the absence of other DC features. Here we discuss the genetics of DC and its relationship to disease presentation.
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Affiliation(s)
- Philip J Mason
- Division of Hematology, Department of Pediatrics, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, USA.
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Wang Y, Busin R, Reeves C, Bezman L, Raymond G, Toomer CJ, Watkins PA, Snowden A, Moser A, Naidu S, Bibat G, Hewson S, Tam K, Clarke JTR, Charnas L, Stetten G, Karczeski B, Cutting G, Steinberg S. X-linked adrenoleukodystrophy: ABCD1 de novo mutations and mosaicism. Mol Genet Metab 2011; 104:160-6. [PMID: 21700483 DOI: 10.1016/j.ymgme.2011.05.016] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 05/25/2011] [Accepted: 05/25/2011] [Indexed: 11/23/2022]
Abstract
X-linked adrenoleukodystrophy (X-ALD) is a progressive peroxisomal disorder affecting adrenal glands, testes and myelin stability that is caused by mutations in the ABCD1 (NM_000033) gene. Males with X-ALD may be diagnosed by the demonstration of elevated very long chain fatty acid (VLCFA) levels in plasma. In contrast, only 80% of female carriers have elevated plasma VLCFA; therefore targeted mutation analysis is the most effective means for carrier detection. Amongst 489 X-ALD families tested at Kennedy Krieger Institute, we identified 20 cases in which the ABCD1 mutation was de novo in the index case, indicating that the mutation arose in the maternal germ line and supporting a new mutation rate of at least 4.1% for this group. In addition, we identified 10 cases in which a de novo mutation arose in the mother or the grandmother of the index case. In two of these cases studies indicated that the mothers were low level gonosomal mosaics. In a third case biochemical, molecular and pedigree analysis indicated the mother was a gonadal mosaic. To the best of our knowledge mosaicism has not been previously reported in X-ALD. In addition, we identified one pedigree in which the maternal grandfather was mosaic for the familial ABCD1 mutation. Less than 1% of our patient population had evidence of gonadal or gonosomal mosaicism, suggesting it is a rare occurrence for this gene and its associated disorders. However, the residual maternal risk for having additional ovum carrying the mutant allele identified in an index case that appears to have a de novo mutation is at least 13%.
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Affiliation(s)
- Ying Wang
- DNA Diagnostic Laboratory, Johns Hopkins University School of Medicine, CMSC1004, 600 N. Wolfe Street, Baltimore, MD 21287, USA.
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Walne AJ, Dokal I. Telomerase dysfunction and dyskeratosis congenita. Cytotechnology 2011; 45:13-22. [PMID: 19003239 DOI: 10.1007/s10616-004-5121-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2004] [Accepted: 09/21/2004] [Indexed: 01/04/2023] Open
Abstract
Dyskeratosis congenita (DC) is a multi system bone marrow failure syndrome characterized by muco-cutaneous abnormalities and an increased predisposition to malignancy. It exhibits considerable clinical and genetic heterogeneity. X-linked recessive, autosomal dominant and autosomal recessive forms of the disease are recognized. The X-linked recessive form is due to mutations in dyskerin, which is a component of both small nucleolar ribonuclear protein particles and the telomerase complex. Autosomal dominant DC is due to mutations in the RNA component of telomerase, TERC. As dyskerin and TERC are both components of the telomerase complex and all patients with DC have short telomeres it appears that the principal pathology in DC relates to telomerase dysfunction. The gene or genes involved in the recessive form of DC remain elusive, though genes whose products are required for telomere maintenance remain strong candidates. The study of DC has highlighted the critical role of telomerase and the consequences, including premature aging and malignancy, of its dysfunction.
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Affiliation(s)
- Amanda J Walne
- Department of Haematology, Division of Investigative Science, Faculty of Medicine, Imperial College London, Hammersmith Hospital, Du Cane Road, London, W12 ONN, United Kingdom,
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Gu BW, Fan JM, Bessler M, Mason PJ. Accelerated hematopoietic stem cell aging in a mouse model of dyskeratosis congenita responds to antioxidant treatment. Aging Cell 2011; 10:338-48. [PMID: 21241452 DOI: 10.1111/j.1474-9726.2011.00674.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Mutations in DKC1, encoding telomerase associated protein dyskerin, cause X-linked dyskeratosis congenita (DC), a bone marrow (BM) failure, and cancer susceptibility syndrome. Decreased accumulation of telomerase RNA resulting in excessive telomere shortening and premature cellular senescence is thought to be the primary cause of disease in X-linked DC. Affected tissues are those that require constant renewal by stem cell activity. We previously showed that in Dkc1(Δ15) mice, which contain a mutation that is a copy of a human mutation causing DC, mutant cells have a telomerase-dependent proliferative defect and increased accumulation of DNA damage in the first generation before the telomeres are short. We now demonstrate the presence of the growth defect in Dkc1(Δ15) mouse embryonic fibroblasts in vitro and show that accumulation of DNA damage and levels of reactive oxygen species increase with increasing population doublings. Treatment with the antioxidant, N-acetyl cysteine (NAC), partially rescued the growth disadvantage of mutant cells in vitro and in vivo. Competitive BM repopulation experiments showed that the Dkc1(Δ15) mutation is associated with a functional stem cell defect that becomes more severe with increasing age, consistent with accelerated senescence, a hallmark of DC hematopoiesis. This stem cell phenotype was partially corrected by NAC treatment. These results suggest that a pathogenic Dkc1 mutation accelerates stem cell aging, that increased oxidative stress might play a role in the pathogenesis of X-linked DC, and that some manifestations of DC may be prevented or delayed by antioxidant treatment.
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Affiliation(s)
- Bai-Wei Gu
- Division of Hematology, Department of Internal Medicine, Washington University School of Medicine, St Louis, MO, USA
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Somatic gene mutation and human disease other than cancer: An update. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2010; 705:96-106. [DOI: 10.1016/j.mrrev.2010.04.002] [Citation(s) in RCA: 147] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Revised: 03/29/2010] [Accepted: 04/08/2010] [Indexed: 12/24/2022]
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Baran I, Nalcaci R, Kocak M. Dyskeratosis congenita: clinical report and review of the literature. Int J Dent Hyg 2010; 8:68-74. [PMID: 20096085 DOI: 10.1111/j.1601-5037.2009.00364.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Dyskeratosis congenita (DKC) is an inherited disorder that usually presents in males, consisting of the triad of leukoplakia of the mucous membranes, nails dystrophy and skin pigmentation. Oral and dental abnormalities may also be present. Most cases are X-linked autosomal dominant, but recessive forms have also been reported. This study describes herein a case in which the classic triad of signs was present, along with the development of leukoplakia in the buccal mucosa. Our patient, a 25-year-old man, presented with several characteristic systemic features of this condition, together with the following oral features: hypodontia, delayed dental eruption, short blunt roots, extensive caries, gingival inflammation and bleeding, loss of alveolar bone and buccal mucosa with leukoplakia and irregular ulcers. The patient was given full preventive care. The primary teeth were extracted under local anaesthesia. After establishing optimal oral health, oral hygiene instructions were given to the patient and he was rehabilitated with fixed and removable partial denture. Prosthetic treatments were carried out after establishing optimal oral health. This treatment option appears beneficial in this patient, resulting in rehabilitation of occlusion and less mechanical irritation to the oral mucosa.
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Affiliation(s)
- I Baran
- Department of Prosthetic Dentistry, Faculty of Dentistry, Kirikkale University, Kirikkale, Turkey.
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A pathogenic dyskerin mutation impairs proliferation and activates a DNA damage response independent of telomere length in mice. Proc Natl Acad Sci U S A 2008; 105:10173-8. [PMID: 18626023 DOI: 10.1073/pnas.0803559105] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Telomeres are nucleoprotein structures that cap the ends of chromosomes, protecting them from exonucleases and distinguishing them from double-stranded breaks. Their integrity is maintained by telomerase, an enzyme consisting of a reverse transcriptase, TERT and an RNA template, TERC, and other components, including the pseudouridine synthase, dyskerin, the product of the DKC1 gene. When telomeres become critically short, a p53-dependent pathway causing cell cycle arrest is induced that can lead to senescence, apoptosis, or, rarely to genomic instability and transformation. The same pathway is induced in response to DNA damage. DKC1 mutations in the disease dyskeratosis congenita are thought to act via this mechanism, causing growth defects in proliferative tissues through telomere shortening. Here, we show that pathogenic mutations in mouse Dkc1 cause a growth disadvantage and an enhanced DNA damage response in the context of telomeres of normal length. We show by genetic experiments that the growth disadvantage, detected by disparities in X-inactivation patterns in female heterozygotes, depends on telomerase. Hemizygous male mutant cells showed a strikingly enhanced DNA damage response via the ATM/p53 pathway after treatment with etoposide with a significant number of DNA damage foci colocalizing with telomeres in cytological preparations. We conclude that dyskerin mutations cause slow growth independently of telomere shortening and that this slow growth is the result of the induction of DNA damage. Thus, dyskerin interacts with telomerase and affects telomere maintenance independently of telomere length.
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Betsalel OT, van de Kamp JM, Martínez-Muñoz C, Rosenberg EH, de Brouwer APM, Pouwels PJW, van der Knaap MS, Mancini GMS, Jakobs C, Hamel BCJ, Salomons GS. Detection of low-level somatic and germline mosaicism by denaturing high-performance liquid chromatography in a EURO-MRX family with SLC6A8 deficiency. Neurogenetics 2008; 9:183-90. [DOI: 10.1007/s10048-008-0125-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2007] [Accepted: 02/25/2008] [Indexed: 11/28/2022]
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The coding/non-coding overlapping architecture of the gene encoding the Drosophila pseudouridine synthase. BMC Mol Biol 2007; 8:15. [PMID: 17328797 PMCID: PMC1821038 DOI: 10.1186/1471-2199-8-15] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Accepted: 02/28/2007] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In eukaryotic cells, each molecule of H/ACA small nucleolar RNA (snoRNA) assembles with four evolutionarily conserved core proteins to compose a specific ribonucleoprotein particle. One of the four core components has pseudouridine synthase activity and catalyzes the conversion of a selected uridine to pseudouridine. Members of the pseudouridine synthase family are highly conserved. In addition to catalyzing pseudouridylation of target RNAs, they carry out a variety of essential functions related to ribosome biogenesis and, in mammals, to telomere maintenance. To investigate further the molecular mechanisms underlying the expression of pseudouridine synthase genes, we analyzed the transcriptional activity of the Drosophila member of this family in great detail. RESULTS The Drosophila gene for pseudouridine synthase, minifly/Nop60b (mfl), encodes two novel mRNAs ending at a downstream poly(A) site. One species is characterized only by an extended 3'-untranslated region (3'UTR), while a minor mRNA encodes a variant protein that represents the first example of an alternative subform described for any member of the family to date. The rare spliced variant is detected mainly in females and is predicted to have distinct functional properties. We also report that a cluster comprising four isoforms of a C/D box snoRNA and two highly related copies of a small ncRNA gene of unknown function is intron-encoded at the gene-variable 3'UTRs. Because this arrangement, the alternative 3' ends allow mfl not only to produce two distinct protein subforms, but also to release different ncRNAs. Intriguingly, accumulation of all these intron-encoded RNAs was found to be sex-biased and quantitatively modulated throughout development and, within the ovaries, the ncRNAs of unknown function were found not ubiquitously expressed. CONCLUSION Our results expand the repertoire of coding/non-coding transcripts derived from the gene encoding Drosophila pseudouridine synthase. This gene exhibits a complex and interlaced organization, and its genetic information may be expressed as different protein subforms and/or ncRNAs that may potentially contribute to its biological functions.
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Abstract
Dyskeratosis congenita is an inherited disorder that usually presents in males, consisting of the triad of leukoplakia of the mucous membranes, nail dystrophy and skin pigmentation. Whilst most cases are X-linked, autosomal dominant and recessive forms have been reported. The significance of the condition lies in premature mortality arising from either bone marrow failure or malignant change within the areas of leukoplakia. Various mucocutaneous and non-mucocutaneous manifestations have been reported. The syndrome arises from an inherited defect within the DKC1 gene that codes for the protein dyskerin in the X-linked recessive form of the disorder, whereas mutations in the RNA component of telomerase (TERC) result in the autosomal dominant form of the condition. The identification of a white patch within the mouth of a child in the absence of any other obvious cause should arouse suspicion of this rare condition. Greater understanding of the molecular biology surrounding this syndrome should lead to improvements in diagnosis, monitoring of disease progression and therapy.
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Affiliation(s)
- T P B Handley
- Unit of Oral Surgery and Medicine, University of Dundee, Park Place, Dundee DD1 4HR, and Department of Oral and Maxillofacial Surgery, Monklands Hospital, Airdre, UK
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Vulliamy TJ, Marrone A, Knight SW, Walne A, Mason PJ, Dokal I. Mutations in dyskeratosis congenita: their impact on telomere length and the diversity of clinical presentation. Blood 2005; 107:2680-5. [PMID: 16332973 DOI: 10.1182/blood-2005-07-2622] [Citation(s) in RCA: 239] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The two genes mutated in the bone marrow failure syndrome dyskeratosis congenita (DC) both encode components of the telomerase complex responsible for maintaining the ends of chromosomes in stem cells and in the germ line. In reviewing the mutation profile that is found in DC, we describe 9 novel mutations in the DKC1 gene and 3 novel TERC mutations responsible for the X-linked and autosomal dominant forms of the disease, respectively, but find that two thirds of the families do not have mutations in either of these genes. In a significant subset of these uncharacterized families, the index case presents with severe disease previously defined as the Hoyeraal Hreidarsson (HH) syndrome. The diverse clinical phenotype seen in patients with X-linked DC is not explained by the different amino acid substitutions: Presentation of the recurrent A353V substitution ranges from classic DC to the severe HH variant. However, we do see that patients with HH have significantly shorter telomeres than those with a relatively mild presentation. In the new families described with TERC mutations, there is further evidence of disease anticipation associated with shorter telomeres in the younger generations. This study highlights the considerable genetic and phenotypic diversity of DC.
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Affiliation(s)
- Tom J Vulliamy
- Department of Haematology, Hammersmith Hospital, Du Cane Rd, London, W12 ONN, United Kingdom.
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23
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Meier UT. The many facets of H/ACA ribonucleoproteins. Chromosoma 2005; 114:1-14. [PMID: 15770508 PMCID: PMC4313906 DOI: 10.1007/s00412-005-0333-9] [Citation(s) in RCA: 215] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2004] [Revised: 01/31/2005] [Accepted: 02/01/2005] [Indexed: 10/25/2022]
Abstract
The H/ACA ribonucleoproteins (RNPs) are known as one of the two major classes of small nucleolar RNPs. They predominantly guide the site-directed pseudouridylation of target RNAs, such as ribosomal and spliceosomal small nuclear RNAs. In addition, they process ribosomal RNA and stabilize vertebrate telomerase RNA. Taken together, the function of H/ACA RNPs is essential for ribosome biogenesis, pre-mRNA splicing, and telomere maintenance. Every cell contains 100-200 different species of H/ACA RNPs, each consisting of the same four core proteins and one function-specifying H/ACA RNA. Most of these RNPs reside in nucleoli and Cajal bodies and mediate the isomerization of specific uridines to pseudouridines. Catalysis of the reaction is mediated by the putative pseudouridylase NAP57 (dyskerin, Cbf5p). Unexpectedly, mutations in this housekeeping enzyme are the major determinants of the inherited bone marrow failure syndrome dyskeratosis congenita. This review details the many diverse functions of H/ACA RNPs, some yet to be uncovered, with an emphasis on the role of the RNP proteins. The multiple functions of H/ACA RNPs appear to be reflected in the complex phenotype of dyskeratosis congenita.
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Affiliation(s)
- U Thomas Meier
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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Poulsen L, Møller LB, Plunkett K, Belmont J, Tümer Z, Horn N. X-Linked Menkes Disease: First Documented Report of Germ-Line Mosaicism. ACTA ACUST UNITED AC 2004; 8:286-91. [PMID: 15727253 DOI: 10.1089/gte.2004.8.286] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This work investigated a three-generation Menkes disease family, where germ-line mosaicism was suspected in the maternal grandmother of the index patient. She had given birth to 2 boys who died of suspected Menkes disease on the basis of clinical and photographic evidence. Biochemical analysis of the index patient confirmed the diagnosis of Menkes disease, and DNA analysis established a partial gene deletion (EX11_EX23del), involving exons 11-23 and the 3'-untranslated region (UTR) of ATP7A. A junction fragment was detectable by Southern blot analysis, which enabled carrier analysis. The mother was demonstrated to be a carrier, whereas analysis of lymphoblasts and skin fibroblasts from the maternal grandmother gave no indication of a partial gene deletion. No materials were available from the possibly affected maternal uncles. Further genetic analyses, including biochemical testing of the grandmother and haplotype analysis using four intragenic markers on DNA from selected members of the family, corroborated this finding. The combined results from DNA analyses showed that the grandmother had transmitted three different ATP7A haplotypes to her offspring: (1) the at-risk allele (CA(B))-1 and the deletion; (2) the at-risk allele (CA(B))-1 without deletion; and (3) the second allele (CAB)-2 without deletion. In conclusion, our study demonstrated segregation of Menkes disease within the family investigated that can best be explained by extensive germ-line mosaicism in the maternal grandmother. The finding of germ-line mosaicism has obvious implications for genetic counseling of Menkes disease families.
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Affiliation(s)
- Lena Poulsen
- Medical Genetics Laboratory Center, The John F. Kennedy Institute, Glostrup, Denmark
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25
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Abstract
Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome exhibiting considerable clinical and genetic heterogeneity. X-linked recessive, autosomal dominant and autosomal recessive forms are recognised. The gene mutated in X-linked DC (DKC1) encodes a highly conserved nucleolar protein called dyskerin. Dyskerin associates with the H/ACA class of small nucleolar RNAs which are important in guiding the conversion of uracil to pseudouracil in ribosomal RNA. Dyskerin also associates with the RNA component of telomerase (hTR) which is important in the maintenance of telomeres. Mutations in hTR were recently demonstrated in patients with autosomal dominant DC and in a subset of patients with aplastic anaemia (AA) but without other diagnostic features of DC. This discovery demonstrates that both DC and a subset of AA are due to a defect in telomerase. The link between DC and AA and in turn to defective telomerase suggests that treatments directed at correction of telomerase activity might benefit DC/AA patients who do not respond to conventional therapy.
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Affiliation(s)
- Inderjeet Dokal
- Department of Haematology-Division of Investigative Science, Faculty of Medicine, Imperial College, Hammersmith Hospital, Commonwealth Building, London, UK.
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26
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Laccone F, Jünemann I, Whatley S, Morgan R, Butler R, Huppke P, Ravine D. Large deletions of the MECP2 gene detected by gene dosage analysis in patients with Rett syndrome. Hum Mutat 2004; 23:234-44. [PMID: 14974082 DOI: 10.1002/humu.20004] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/08/2022]
Abstract
MECP2 mutations are responsible for Rett syndrome (RTT). Approximately a quarter of classic RTT cases, however, do not have an identifiable mutation of the MECP2 gene. We hypothesized that larger deletions arising from a deletion prone region (DPR) occur commonly and are not being routinely detected by the current PCR-mediated screening strategies. We developed and applied a quantitative PCR strategy (qPCR) to samples referred for diagnostic assessment from 140 patients among whom RTT was strongly suspected and from a second selected group of 31 girls with classical RTT. Earlier MECP2 mutation screening in both groups of patients had yielded a wild-type result. We identified 10 large deletions (7.1%) within the first group and five deletions in the second group (16.1%). Sequencing of the breakpoints in 11 cases revealed that eight cases had one breakpoint within the DPR. Among seven cases, the breakpoint distant to the DPR involved one of several Alu repeats. Sequence analysis of the junction sequences revealed that eight cases had complex rearrangements. Examination of the MECP2 genomic sequence reveals that it is highly enriched for repeat elements, with the content of Alu repeats rising to 27.8% in intron 2, in which there was an abundance of breakpoints among our patients. Furthermore, a perfect chi sequence, known to be recombinogenic in E. coli, is located in the DPR. We propose that the chi sequence and Alu repeats are potent factors contributing to genomic rearrangement. We suggest that routine mutation screening in MECP2 should include quantitative analysis of the genomic sequences flanking the DPR.
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Affiliation(s)
- Franco Laccone
- Institute of Human Genetics, University of Göttingen, Germany.
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27
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Cuevas-Covarrubias SA, Jiménez-Vaca AL, González-Huerta LM, Valdes-Flores M, Del Refugio Rivera-Vega M, Maya-Nunez G, Kofman-Alfaro SH. Somatic and germinal mosaicism for the steroid sulfatase gene deletion in a steroid sulfatase deficiency carrier. J Invest Dermatol 2002; 119:972-5. [PMID: 12406347 DOI: 10.1046/j.1523-1747.2002.t01-1-00185.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Steroid sulfatase deficiency results in X-linked ichthyosis, an inborn error of metabolism in which the principal molecular defect is the complete deletion of the steroid sulfatase gene and flanking markers. Mosaicism for the steroid sulfatase gene has not yet been reported in X-linked ichthyosis. In this study we describe an X-linked ichthyosis patient with complete deletion of the steroid sulfatase gene and his mother with somatic and germinal mosaicism for this molecular defect. The family (X-linked ichthyosis patient, grandmother, mother, and sister) was analyzed through steroid sulfatase enzyme assay, polymerase chain reaction, DNA markers, and fluorescence in situ hybridization of the steroid sulfatase gene. Steroid sulfatase activity was undetectable in the X-linked ichthyosis patient, very low in the mother, and normal in the grandmother and sister. The X-linked ichthyosis patient showed a 2 Mb deletion of the steroid sulfatase gene and flanking regions from 5'DXS1139 to 3'DXF22S1. The mother showed one copy of the steroid sulfatase gene in 98.5% of oral cells and in 80% of leukocytes. The grandmother and sister showed two copies of the steroid sulfatase gene. The origin of the X chromosome with the deletion of the steroid sulfatase gene corresponded to the grandfather of the proband. We report the first case of somatic and germinal mosaicism of the steroid sulfatase gene in an X-linked ichthyosis carrier and propose DNA slippage as the most plausible mechanism in the genesis of this mosaicism.
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28
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Abstract
For more than 50 years geneticists have assumed that variations in phenotypic expression are caused by alterations in genotype. Recent evidence shows that 'simple' mendelian disorders or monogenic traits are often far from simple, exhibiting phenotypic variation (variable expressivity) that cannot be explained entirely by a gene or allelic alteration. In certain cases of androgen insensitivity syndrome caused by identical mutations in the androgen receptor gene, phenotypic variability is caused by somatic mosaicism, that is, somatic mutations that occur only in certain androgen-sensitive cells. Recently, more than 30 other genetic conditions that exhibit variable expressivity have been linked to somatic mosaicism. Somatic mutations have also been identified in diseases such as prostate and colorectal cancer. Therefore, the concept of somatic mutations and mosaicism is likely to have far reaching consequences for genetics, in particular in areas such as genetic counseling.
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Affiliation(s)
- B Gottlieb
- Dept. of Biology, John Abbott College, Ste Anne de Bellevue, H9X 3L9, Quebec, Canada.
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29
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Affiliation(s)
- I Dokal
- Department of Haematology, Imperial College School of Medicine, Du Cane Road, London, UK.
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Heiss NS, Bächner D, Salowsky R, Kolb A, Kioschis P, Poustka A. Gene structure and expression of the mouse dyskeratosis congenita gene, dkc1. Genomics 2000; 67:153-63. [PMID: 10903840 DOI: 10.1006/geno.2000.6227] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mutations in the DKC1 gene are responsible for causing X-linked recessive dyskeratosis congenita (DKC) and a more severe allelic variant of the disease, Hoyeraal-Hreidarsson syndrome. Both diseases are characterized by progressive and fatal bone marrow failure. The nucleolar protein dyskerin is the pseudouridine synthase component of the box H+ACA snoRNAs and also interacts with the RNA component (human telomerase, hTR) of the telomerase complex. Dyskerin is therefore thought to function in the processing of pre-rRNA and of the hTR, strengthening the notion that the underlying mechanism of DKC is a premature senescence of cells, especially of the rapidly dividing epithelial and hemopoietic cells. To examine the functions of dyskerin in vivo, it will be necessary to generate mouse models. As a first step, we here provide the genomic structure of the mouse Dkc1 gene and expression analysis of the transcript. Northern hybridizations revealed the tissue-specific expression of an alternative 4.5-kb transcript, in addition to the ubiquitous 2.6-kb transcript. RNA in situ hybridizations on day 10.5-18.5 postconception embryos showed a ubiquitous expression of Dkc1 with a notably higher level of expression confined to the epithelial tissues. In addition, higher level Dkc1 expression was confined to embryonic neural tissues as well as to specific neurons in the cerebellum (Purkinje cells) and the olfactory bulb (mitral cells) of the adult brain. In adult testis, elevated expression was limited to the Leydig cells. The results indicate that some of the pertinent functions of dyskerin may be more tissue-specific than previously thought and are not limited to rapidly dividing cells.
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Affiliation(s)
- N S Heiss
- Department of Molecular Genome Analysis, Deutsches Krebsforschungszentrum (DKFZ), Im Neuenheimer Feld 280, Heidelberg, 69120, Germany.
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Heiss NS, Girod A, Salowsky R, Wiemann S, Pepperkok R, Poustka A. Dyskerin localizes to the nucleolus and its mislocalization is unlikely to play a role in the pathogenesis of dyskeratosis congenita. Hum Mol Genet 1999; 8:2515-24. [PMID: 10556300 DOI: 10.1093/hmg/8.13.2515] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Mutations in the DKC1 gene are responsible for causing the bone marrow failure syndrome, dyskeratosis congenita (DKC; OMIM 305000). The majority of mutations identified to date are missense mutations and are clustered in exons 3, 4 and 11. It is predicted that the corresponding protein dyskerin is a nucleolar phosphoprotein which functions in both pseudo-uridylation and cleavage of precursor rRNA. Dyskerin contains multiple putative nuclear localization signals (NLSs) at the N-terminus (KKHKKKKERKS) and C-terminus [KRKR(X)(17)KKEKKKSKKDKKAK(X)(17)-KKKKKKKKAKEVELVSE]. By fusing dyskerin with the enhanced green fluorescent protein (EGFP) and by following a time course of expression in mammalian cell lines, we showed that full-length dyskerin initially localizes to the nucleoplasm and subsequently accumulates in the nucleoli. A co-localization to the coiled bodies was observed in some cells where dyskerin-EGFP had translocated to the nucleoli. Analysis of a series of mutant constructs indicated that whereas the most C-terminal lysine-rich clusters [KKEKKKS-KKDKKAK(X)(17)KKKKKKKKAKEVELVSE] influence the rate of nucleoplasmic and nucleolar accumulation, the KRKR sequence is primarily responsible for the nuclear import. Nucleolar localization was maintained when either the N- or C-terminal motifs were mutated, but not when all NLSs were removed. We conclude that the intranuclear localization of dyskerin is accomplished by the synergistic effect of a number of NLSs and that the nucleolar localization signals are contained within the NLSs. Further, examination of dyskerin-EGFP fusions mimicking mutations detected in patients indicated that the intracellular mislocalization of dyskerin is unlikely to cause DKC.
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Affiliation(s)
- N S Heiss
- Deutsches Krebsforschungszentrum (DKFZ), Department of Molecular Genome Analysis, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany
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