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Huang R, Yang X, Zhou H, Fu F, Cheng K, Wang Y, Ma C, Li R, Jing X, Han J, Zhen L, Pan M, Li D, Liao C. Prenatal Diagnosis of Talipes Equinovarus by Ultrasound and Chromosomal Microarray Analysis: A Chinese Single-Center Retrospective Study. Genes (Basel) 2022; 13. [PMID: 36140741 DOI: 10.3390/genes13091573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Revised: 08/24/2022] [Accepted: 08/29/2022] [Indexed: 12/03/2022] Open
Abstract
Background: There are few studies on the detection rate by chromosomal microarray analysis (CMA) of the prenatal diagnosis of talipes equinovarus (TE) compared to conventional karyotyping. We aimed to explore the molecular etiology of fetal TE and examine the detection rate by CMA, which provides more information for the clinical screening and genetic counseling of TE. Methods: In this retrospective study, pregnancies diagnosed with fetal TE were enrolled and clinical data for all cases were retrieved from our medical record database, including demographic data for pregnancies, ultrasound findings, karyotype/CMA results, and pregnant and perinatal outcomes. Results: Among the 164 patients, 17 (10.4%) clinically significant variants were detected by CMA. In 148 singleton pregnancies, the diagnostic rate of clinically significant variants was significantly higher in the non-isolated TE group than in the isolated TE group (10/37, 27.0% vs. 6/111, 5.4%, P < 0.001). In twin pregnancies, 1 (6.3%) pathogenic copy number variant was present in the other 16 twin pregnancies. Conclusions: This study demonstrates that CMA is useful for the prenatal genetic diagnosis of fetal TE. Fetal TE with the associated structural malformation correlates with a higher probability of clinically significant variants. This data may aid prenatal diagnosis and genetic counseling for fetal TE.
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van den Akker PC, Bolling MC, Pasmooij AMG. Revertant Mosaicism in Genodermatoses: Natural Gene Therapy Right before Your Eyes. Biomedicines 2022; 10:2118. [PMID: 36140224 PMCID: PMC9495737 DOI: 10.3390/biomedicines10092118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 08/23/2022] [Accepted: 08/23/2022] [Indexed: 11/19/2022] Open
Abstract
Revertant mosaicism (RM) is the intriguing phenomenon in which nature itself has successfully done what medical science is so eagerly trying to achieve: correcting the effect of disease-causing germline variants and thereby reversing the disease phenotype back to normal. RM was molecularly confirmed for the first time in a genodermatosis in 1997, the genetic skin condition junctional epidermolysis bullosa (EB). At that time, RM was considered an extraordinary phenomenon. However, several important discoveries have changed this conception in the past few decades. First, RM has now been identified in all major subtypes of EB. Second, RM has also been identified in many other genodermatoses. Third, a theoretical mathematical exercise concluded that reverse mutations should be expected in all patients with a recessive subtype of EB or any other genodermatosis. This has shifted the paradigm from RM being an extraordinary phenomenon to it being something that every physician working in the field of genodermatoses should be looking for in every patient. It has also raised hope for new treatment options in patients with genodermatoses. In this review, we summarize the current knowledge on RM and discuss the perspectives of RM for the future treatment of patients with genodermatoses.
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Liehr T, Schreyer I, Kuechler A, Manolakos E, Singer S, Dufke A, Wilhelm K, Jančušková T, Čmejla R, Othman MAK, Al-Rikabi AH, Mrasek K, Ziegler M, Kankel S, Kreskowski K, Weise A. Parental origin of deletions and duplications - about the necessity to check for cryptic inversions. Mol Cytogenet 2018. [PMID: 29541160 PMCID: PMC5845138 DOI: 10.1186/s13039-018-0369-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Background Copy number variants (CNVs) are the genetic bases for microdeletion/ microduplication syndromes (MMSs). Couples with an affected child and desire to have further children are routinely tested for a potential parental origin of a specific CNV either by molecular karyotyping or by two color fluorescence in situ hybridization (FISH), yet. In the latter case a critical region probe (CRP) is combined with a control probe for identification of the chromosome in question. However, CNVs can arise also due to other reasons, like a recombination-event based on a submicroscopic, cryptic inversion in one of the parents. Results Seventy-four patients with different MMSs and overall 81 CNVs were studied here by a novel three color FISH approach. The way how three locus-specific probes are selected (one is the CRP and two are flanking it in a distance of 5-10 Mb) enables to detect or exclude two possible parental conditions as origins of the CNV seen in the index: (i) direct parental origin of the CNV (deletion or duplication) or (ii) a parental cryptic inversion. Thus, for overall 51/81 CNVs (63%) a parental origin could be determined. 36/51 (70.5%) inherited the CNV directly from one of the parents, but 15/51 (29.5%) were due to an exclusively by three color FISH detectable parental inversion. A 2:1 ratio of maternal versus paternal inheritance was found. Also almost two times more male than female were among the index patients. Conclusion The new, here suggested three color FISH approach is suited for more comprehensive parental studies of patients with MMS. The detection rate for parental origin was increased by 140% in this study. Still, for 30/81 cases (37%) no reason for the ‘de novo’ MMS in the affected index patient could be found by the here suggested FISH-probe set. Electronic supplementary material The online version of this article (10.1186/s13039-018-0369-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Thomas Liehr
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
| | - Isolde Schreyer
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany.,2Center for Ambulant Medicine, Jena University Hospital, Jena, Germany
| | - Alma Kuechler
- 3Institut für Humangenetik, Universitätsklinikum Essen, Essen, Germany
| | | | - Sylke Singer
- Institut für Medizinische Genetik und angewandte Genomik, Tübingen, Germany
| | - Andreas Dufke
- Institut für Medizinische Genetik und angewandte Genomik, Tübingen, Germany
| | - Kathleen Wilhelm
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
| | | | - Radek Čmejla
- 6Synlab czech s.r.o., synlab genetics s.r.o, Praha, Czech Republic
| | - Moneeb A K Othman
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
| | - Ahmed H Al-Rikabi
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
| | - Kristin Mrasek
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
| | - Monika Ziegler
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
| | - Stefanie Kankel
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
| | - Katharina Kreskowski
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
| | - Anja Weise
- 1Jena University Hospital, Institute of Human Genetics, Friedrich Schiller University, Postfach D-07740, Jena, Germany
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van den Akker PC, Pasmooij AMG, Joenje H, Hofstra RMW, te Meerman GJ, Jonkman MF. A "late-but-fitter revertant cell" explains the high frequency of revertant mosaicism in epidermolysis bullosa. PLoS One 2018; 13:e0192994. [PMID: 29470523 PMCID: PMC5823395 DOI: 10.1371/journal.pone.0192994] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2017] [Accepted: 02/03/2018] [Indexed: 12/20/2022] Open
Abstract
Revertant mosaicism, or "natural gene therapy", is the phenomenon in which germline mutations are corrected by somatic events. In recent years, revertant mosaicism has been identified in all major types of epidermolysis bullosa, the group of heritable blistering disorders caused by mutations in the genes encoding epidermal adhesion proteins. Moreover, revertant mosaicism appears to be present in all patients with a specific subtype of recessive epidermolysis bullosa. We therefore hypothesized that revertant mosaicism should be expected at least in all patients with recessive forms of epidermolysis bullosa. Naturally corrected, patient-own cells are of extreme interest for their promising therapeutic potential, and their presence in all patients would open exciting, new treatment perspectives to those patients. To test our hypothesis, we determined the probability that single nucleotide reversions occur in patients' skin using a mathematical developmental model. According to our model, reverse mutations are expected to occur frequently (estimated 216x) in each patient's skin. Reverse mutations should, however, occur early in embryogenesis to be able to drive the emergence of recognizable revertant patches, which is expected to occur in only one per ~10,000 patients. This underestimate, compared to our clinical observations, can be explained by the "late-but-fitter revertant cell" hypothesis: reverse mutations arise at later stages of development, but provide revertant cells with a selective growth advantage in vivo that drives the development of recognizable healthy skin patches. Our results can be extrapolated to any other organ with stem cell division numbers comparable to skin, which may offer novel future therapeutic options for other genetic conditions if these revertant cells can be identified and isolated.
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Affiliation(s)
- Peter C. van den Akker
- University of Groningen, University Medical Center Groningen, Department of Genetics, Groningen, the Netherlands
- University of Groningen, University Medical Center Groningen, Department of Dermatology, Groningen, the Netherlands
| | - Anna M. G. Pasmooij
- University of Groningen, University Medical Center Groningen, Department of Dermatology, Groningen, the Netherlands
| | - Hans Joenje
- Department of Clinical Genetics and the Cancer Center Amsterdam/VUmc Institute for Cancer and Immunology, VU University Medical Center, Amsterdam, the Netherlands
| | - Robert M. W. Hofstra
- Department of Clinical Genetics, Erasmus Medical Center, Rotterdam, the Netherlands
| | - Gerard J. te Meerman
- University of Groningen, University Medical Center Groningen, Department of Genetics, Groningen, the Netherlands
| | - Marcel F. Jonkman
- University of Groningen, University Medical Center Groningen, Department of Dermatology, Groningen, the Netherlands
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Gagic M, Markovic MK, Kecmanovic M, Keckarevic D, Mladenovic J, Dackovic J, Milic-Rasic V, Romac S. Analysis of PMP22 duplication and deletion using a panel of six dinucleotide tandem repeats. Clin Chem Lab Med 2017; 54:773-80. [PMID: 26479344 DOI: 10.1515/cclm-2015-0602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 09/10/2015] [Indexed: 11/15/2022]
Abstract
BACKGROUND Charcot-Marie-Tooth type 1A (CMT1A) is the most common type of hereditary motor and sensory neuropathies (HMSN), caused by the duplication of the 17p11.2 region that includes the PMP22 gene. Reciprocal deletion of the same region is the main cause of hereditary neuropathy with liability to pressure palsies (HNPP). CMT1A accounts for approximately 50% of HMSN patients. Diagnostics of CMT1A and HNPP are based on quantitative analysis of the affected region or RFLP detection of breakage points. The aim of this study was to improve the sensitivity and efficiency of CMT1A and HNPP genetic diagnostics by introducing analysis of six STR markers (D17S261-D17S122-D17S839-D17S1358-D17S955-D17S921) spanning the duplicated region. METHODS Forty-six CMT1A and seven HNPP patients, all genetically diagnosed by RFLP analysis, were tested for duplication or deletion using six STR markers. RESULTS In all CMT1A and HNPP patients, microsatellite analysis comprising six STR markers confirmed the existence of a duplication or deletion. In 89% (41/46) CMT1A patients the confirmation was based on detecting three alleles on at least one locus. In the remaining 11% (5) CMT1A patients, duplication was also confirmed based on two peaks with clear dosage difference for at least two different markers. All HNPP patients (7/7) displayed only one allele for each analyzed locus. CONCLUSIONS Microsatellite analysis using six selected STR loci showed a high level of sensitivity and specificity for genetic diagnostics of CMT1A and HNPP. The results here strongly suggest STR marker analysis as a method of choice in PMP22 duplication/deletion testing.
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Schon K, Spasic-Boskovic O, Brugger K, Graves TD, Abbs S, Park SM, Ambegaonkar G, Armstrong R. Mosaicism for a pathogenic MFN2 mutation causes minimal clinical features of CMT2A in the parent of a severely affected child. Neurogenetics 2017; 18:49-55. [PMID: 28063088 DOI: 10.1007/s10048-016-0504-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Accepted: 12/07/2016] [Indexed: 10/26/2022]
Abstract
Charcot-Marie-Tooth disease (CMT) refers to a genetically heterogeneous group of disorders which cause a peripheral motor and sensory neuropathy. The overall prevalence is 1 in 2500 individuals. Mutations in the MFN2 gene are the commonest cause for the axonal (CMT2) type. We describe a Caucasian 5-year old girl affected by CMT2A since the age of 2 years. She presented with unsteady gait, in-turning of the feet and progressive foot deformities. Nerve conduction studies suggested an axonal neuropathy and molecular testing identified a previously reported pathogenic variant c.1090C > T, p.(Arg364Trp) in the MFN2 gene. This variant was also detected in a mosaic state in blood and saliva by Sanger sequencing in her subjectively healthy father. Next generation sequencing showed that the level of mosaicism was 21% in blood and 24% in saliva. A high recurrence risk was given because the father had proven somatic mosaicism and an affected child implying gonadal mosaicism. The parents were referred for pre-implantation genetic diagnosis. To the best of our knowledge, this is the first reported case of somatic mosaicism for MFN2. This study has important implications for genetic counselling in families with CMT2A.
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Daly AF, Yuan B, Fina F, Caberg JH, Trivellin G, Rostomyan L, de Herder WW, Naves LA, Metzger D, Cuny T, Rabl W, Shah N, Jaffrain-Rea ML, Zatelli MC, Faucz FR, Castermans E, Nanni-Metellus I, Lodish M, Muhammad A, Palmeira L, Potorac I, Mantovani G, Neggers SJ, Klein M, Barlier A, Liu P, Ouafik L, Bours V, Lupski JR, Stratakis CA, Beckers A. Somatic mosaicism underlies X-linked acrogigantism syndrome in sporadic male subjects. Endocr Relat Cancer 2016; 23:221-33. [PMID: 26935837 PMCID: PMC4877443 DOI: 10.1530/erc-16-0082] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Accepted: 03/01/2016] [Indexed: 12/15/2022]
Abstract
Somatic mosaicism has been implicated as a causative mechanism in a number of genetic and genomic disorders. X-linked acrogigantism (XLAG) syndrome is a recently characterized genomic form of pediatric gigantism due to aggressive pituitary tumors that is caused by submicroscopic chromosome Xq26.3 duplications that include GPR101 We studied XLAG syndrome patients (n= 18) to determine if somatic mosaicism contributed to the genomic pathophysiology. Eighteen subjects with XLAG syndrome caused by Xq26.3 duplications were identified using high-definition array comparative genomic hybridization (HD-aCGH). We noted that males with XLAG had a decreased log2ratio (LR) compared with expected values, suggesting potential mosaicism, whereas females showed no such decrease. Compared with familial male XLAG cases, sporadic males had more marked evidence for mosaicism, with levels of Xq26.3 duplication between 16.1 and 53.8%. These characteristics were replicated using a novel, personalized breakpoint junction-specific quantification droplet digital polymerase chain reaction (ddPCR) technique. Using a separate ddPCR technique, we studied the feasibility of identifying XLAG syndrome cases in a distinct patient population of 64 unrelated subjects with acromegaly/gigantism, and identified one female gigantism patient who had had increased copy number variation (CNV) threshold for GPR101 that was subsequently diagnosed as having XLAG syndrome on HD-aCGH. Employing a combination of HD-aCGH and novel ddPCR approaches, we have demonstrated, for the first time, that XLAG syndrome can be caused by variable degrees of somatic mosaicism for duplications at chromosome Xq26.3. Somatic mosaicism was shown to occur in sporadic males but not in females with XLAG syndrome, although the clinical characteristics of the disease were similarly severe in both sexes.
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Affiliation(s)
- Adrian F Daly
- Department of Endocrinology, Centre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium
| | - Bo Yuan
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TexasUSA
| | - Frederic Fina
- Assistance Publique Hôpitaux de Marseille (AP-HM), Hôpital Nord, Service de Transfert d'Oncologie Biologique, Marseille, France Laboratoire de Biologie Médicale, and Aix-Marseille UniversitéInserm, CRO2 UMR_S 911, Marseille, France
| | - Jean-Hubert Caberg
- Department of Human Genetics, Centre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium
| | - Giampaolo Trivellin
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), Bethesda, Maryland, USA
| | - Liliya Rostomyan
- Department of Endocrinology, Centre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium
| | - Wouter W de Herder
- Section of Endocrinology, Department of Medicine, Erasmus University Medical Center Rotterdam and Pituitary Center Rotterdam, Rotterdam, The Netherlands
| | - Luciana A Naves
- Department of Endocrinology, University of Brasilia, Brasilia, Brazil
| | - Daniel Metzger
- Endocrinology and Diabetes Unit, BC Children's Hospital, Vancouver, British Columbia, Canada
| | - Thomas Cuny
- Department of Endocrinology, University Hospital, Nancy, France
| | - Wolfgang Rabl
- Kinderklinik, Technische Universität München, Munich, Germany
| | - Nalini Shah
- Department of Endocrinology, KEM Hospital, Mumbai, India
| | - Marie-Lise Jaffrain-Rea
- Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, L'Aquila and Neuromed Institute, IRCCS, Pozzilli, Italy
| | - Maria Chiara Zatelli
- Section of Endocrinology, Department of Medical Sciences, University of Ferrara, Ferrara, Italy
| | - Fabio R Faucz
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), Bethesda, Maryland, USA
| | - Emilie Castermans
- Department of Human Genetics, Centre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium
| | - Isabelle Nanni-Metellus
- Assistance Publique Hôpitaux de Marseille (AP-HM), Hôpital Nord, Service de Transfert d'Oncologie Biologique, Marseille, France
| | - Maya Lodish
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), Bethesda, Maryland, USA
| | - Ammar Muhammad
- Section of Endocrinology, Department of Medicine, Erasmus University Medical Center Rotterdam and Pituitary Center Rotterdam, Rotterdam, The Netherlands
| | - Leonor Palmeira
- Department of Endocrinology, Centre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium
| | - Iulia Potorac
- Department of Endocrinology, Centre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium Department of Human GeneticsCentre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium
| | - Giovanna Mantovani
- Endocrinology and Diabetology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
| | - Sebastian J Neggers
- Section of Endocrinology, Department of Medicine, Erasmus University Medical Center Rotterdam and Pituitary Center Rotterdam, Rotterdam, The Netherlands
| | - Marc Klein
- Department of Endocrinology, University Hospital, Nancy, France
| | - Anne Barlier
- Laboratory of Molecular Biology, APHM, Hopital la Conception, Aix Marseille Universite, Marseilles, France CRNSCRN2M-UMR 7286, Marseille, France
| | - Pengfei Liu
- Assistance Publique Hôpitaux de Marseille (AP-HM), Hôpital Nord, Service de Transfert d'Oncologie Biologique, Marseille, France
| | - L'Houcine Ouafik
- Laboratoire de Biologie Médicale, and Aix-Marseille Université, Inserm, CRO2 UMR_S 911, Marseille, France
| | - Vincent Bours
- Department of Human Genetics, Centre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium
| | - James R Lupski
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, USA
| | - Constantine A Stratakis
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), Bethesda, Maryland, USA
| | - Albert Beckers
- Department of Endocrinology, Centre Hospitalier Universitaire de Liege, University of Liege, Liege, Belgium
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Liehr T. Entstehungsmechanismen von Zellmosaiken. MED GENET-BERLIN 2014. [DOI: 10.1007/s11825-014-0007-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Zusammenfassung
Zellmosaike bilden sich im Zusammenhang mit „nondisjunction“, Translokationen (balanciert oder unbalanciert), nichthomologem „crossing over“ oder sonstigen chromosomalen oder subchromosomalen „rearrangements“ aus, aber auch durch kompletten oder gewebsspezifischen Chimärismus. Am bekanntesten und häufigsten nachgewiesen sind Zellmosaike, die auf Aneuploidien beruhen, während über die Häufigkeit von submikroskopischen, nur molekulargenetisch oder zytogenetisch nachweisbaren, aber niedriggradigen Zellmosaiken nur wenig bekannt ist. Als Grundlage für die Entstehung von Zellmosaiken gelten „Trisomic“- und/oder „Monosomic-rescue“-Vorgänge. Auch „replikative Fehler“ oder „Endoreduplikation“ einzelner oder mehrere Chromosomen, Isochromosomenbildung oder postzygotisches „non-homologous crossing-over“ werden als Entstehungsmechanismen von Zellmosaiken in der Literatur genannt. Insgesamt ist jedoch festzustellen, dass praktisch alle bekannten Modelle zur Mosaikentstehung bislang auf der deskriptiven Ebene verharren. Ein grundlegendes Verständnis über die tatsächlich z. B. beim Trisomic oder Monosomic rescue ablaufenden Vorgänge ist derzeit mangels Daten nicht vorhanden.
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Affiliation(s)
- Thomas Liehr
- Aff1 Institute of Human Genetics Jena Universitätsklinik, Friedrich-Schiller-Universität Kollegiengasse 10 07743 Jena Deutschland
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9
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Abstract
Chromosomal abnormalities, including microdeletions and microduplications, have long been associated with abnormal developmental outcomes. Early discoveries relied on a common clinical presentation and the ability to detect chromosomal abnormalities by standard karyotype analysis or specific assays such as fluorescence in situ hybridization. Over the past decade, the development of novel genomic technologies has allowed more comprehensive, unbiased discovery of microdeletions and microduplications throughout the human genome. The ability to quickly interrogate large cohorts using chromosome microarrays and, more recently, next-generation sequencing has led to the rapid discovery of novel microdeletions and microduplications associated with disease, including very rare but clinically significant rearrangements. In addition, the observation that some microdeletions are associated with risk for several neurodevelopmental disorders contributes to our understanding of shared genetic susceptibility for such disorders. Here, we review current knowledge of microdeletion/duplication syndromes, with a particular focus on recurrent rearrangement syndromes.
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Affiliation(s)
- Corey T Watson
- Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, NY 10029.,Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029
| | - Tomas Marques-Bonet
- Institut de Biologia Evolutiva, Universitat Pompeu Fabra/CSIC, 08003 Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain.,Centro Nacional de Análisis Genómico, 08023 Barcelona, Spain
| | - Andrew J Sharp
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029
| | - Heather C Mefford
- Department of Pediatrics, University of Washington, Seattle, Washington 98195
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Liehr T, Karamysheva T, Merkas M, Brecevic L, Hamid AB, Ewers E, Mrasek K, Kosyakova N, Weise A. Somatic mosaicism in cases with small supernumerary marker chromosomes. Curr Genomics 2010; 11:432-9. [PMID: 21358988 PMCID: PMC3018724 DOI: 10.2174/138920210793176029] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 05/30/2010] [Accepted: 06/01/2010] [Indexed: 11/22/2022] Open
Abstract
Somatic mosaicism is something that is observed in everyday lives of cytogeneticists. Chromosome instability is one of the leading causes of large-scale genome variation analyzable since the correct human chromosome number was established in 1956. Somatic mosaicism is also a well-known fact to be present in cases with small supernumerary marker chromosomes (sSMC), i.e. karyotypes of 47,+mar/46. In this study, the data available in the literature were collected concerning the frequency mosaicism in different subgroups of patients with sSMC. Of 3124 cases with sSMC 1626 (52%) present with somatic mosaicism. Some groups like patients with Emanuel-, cat-eye- or i(18p)- syndrome only tend rarely to develop mosaicism, while in Pallister-Killian syndrome every patient is mosaic. In general, acrocentric and non-acrocentric derived sSMCs are differently susceptible to mosaicism; non-acrocentric derived ones are hereby the less stable ones. Even though, in the overwhelming majority of the cases, somatic mosaicism does not have any detectable clinical effects, there are rare cases with altered clinical outcomes due to mosaicism. This is extremely important for prenatal genetic counseling. Overall, as mosaicism is something to be considered in at least every second sSMC case, array-CGH studies cannot be offered as a screening test to reliably detect this kind of chromosomal aberration, as low level mosaic cases and cryptic mosaics are missed by that.
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Affiliation(s)
- Thomas Liehr
- Jena University Hospital, Institute of Human Genetics and Anthropology, Jena, Germany
| | | | - Martina Merkas
- Jena University Hospital, Institute of Human Genetics and Anthropology, Jena, Germany
- School of Medicine Zagreb University, Croatian Institute for Brain Research, Zagreb, Croatia
| | - Lukrecija Brecevic
- School of Medicine Zagreb University, Croatian Institute for Brain Research, Zagreb, Croatia
| | - Ahmed B. Hamid
- Jena University Hospital, Institute of Human Genetics and Anthropology, Jena, Germany
| | - Elisabeth Ewers
- Jena University Hospital, Institute of Human Genetics and Anthropology, Jena, Germany
| | - Kristin Mrasek
- Jena University Hospital, Institute of Human Genetics and Anthropology, Jena, Germany
| | - Nadezda Kosyakova
- Jena University Hospital, Institute of Human Genetics and Anthropology, Jena, Germany
| | - Anja Weise
- Jena University Hospital, Institute of Human Genetics and Anthropology, Jena, Germany
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11
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Weise A, Mrasek K, Ewers E, Mkrtchyan H, Kosyakova N, Liehr T. Diagnostic applications of fluorescence in situ hybridization. Expert Opin Med Diagn 2009; 3:453-60. [PMID: 23485212 DOI: 10.1517/17530050902841948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND Fluorescence in situ hybridization (FISH) assays are indispensable in diagnostics and research. Routine application of this so-called molecular cytogenetic technique on human chromosomes started in 1986. Since then, a huge variety of different approaches for chromosomal differentiation based on FISH has been described. It was established to characterize marker chromosomes identified in conventional banding analysis as well as cryptic rearrangements not resolved by standard cytogenetics. OBJECTIVE/METHOD Even though molecular cytogenetics, like banding cytogenetics for almost 40 years, is often called dead now, it offers unique possibilities of single cell analysis. Thus, a review is presented here on the available diagnostic-relevant FISH methods and probe sets applied in routine pre- and postnatal clinical as well as tumor cytogenetics. CONCLUSION Molecular cytogenetics is a fast, straightforward and reliable tool that is indispensable in cytogenetic diagnostics. It is and will continue to be of high clinical impact in diagnostics, especially in the overwhelming majority of routine cytogenetic laboratories that cannot afford and do not need high-throughput chip-based platforms for their daily work.
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Affiliation(s)
- Anja Weise
- Institut für Humangenetik und Anthropologie, Postfach, D 07740 Jena, Germany +0049 3641 935530 ; +0049 3641 935502 ;
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Abstract
There is growing appreciation that the human genome contains significant numbers of structural rearrangements, such as insertions, deletions, inversions, and large tandem repeats. Recent studies have defined approximately 5% of the human genome as structurally variant in the normal population, involving more than 800 independent genes. We present a detailed review of the various structural rearrangements identified to date in humans, with particular reference to their influence on human phenotypic variation. Our current knowledge of the extent of human structural variation shows that the human genome is a highly dynamic structure that shows significant large-scale variation from the currently published genome reference sequence.
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Affiliation(s)
- Andrew J Sharp
- Department of Genome Sciences, University of Washington, Howard Hughes Medical Institute, Seattle, Washington 98195, USA
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13
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Uzel G, Tng E, Rosenzweig SD, Hsu AP, Shaw JM, Horwitz ME, Linton GF, Anderson SM, Kirby MR, Oliveira JB, Brown MR, Fleisher TA, Law SKA, Holland SM. Reversion mutations in patients with leukocyte adhesion deficiency type-1 (LAD-1). Blood 2007; 111:209-18. [PMID: 17875809 PMCID: PMC2200806 DOI: 10.1182/blood-2007-04-082552] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Leukocyte adhesion deficiency type-1 (LAD-1) is an autosomal recessive immunodeficiency caused by mutations in the beta2 integrin, CD18, that impair CD11/CD18 heterodimer surface expression and/or function. Absence of functional CD11/CD18 integrins on leukocytes, particularly neutrophils, leads to their incapacity to adhere to the endothelium and migrate to sites of infection. We studied 3 LAD-1 patients with markedly diminished neutrophil CD18 expression, each of whom had a small population of lymphocytes with normal CD18 expression (CD18(+)). These CD18(+) lymphocytes were predominantly cytotoxic T cells, with a memory/effector phenotype. Microsatellite analyses proved patient origin of these cells. Sequencing of T-cell subsets showed that in each patient one CD18 allele had undergone further mutation. Interestingly, all 3 patients were young adults with inflammatory bowel disease. Somatic reversions of inherited mutations in primary T-cell immunodeficiencies are typically associated with milder clinical phenotypes. We hypothesize that these somatic revertant CD18(+) cytotoxic T lymphocytes (CTLs) may have altered immune regulation. The discovery of 3 cases of reversion mutations in LAD-1 at one center suggests that this may be a relatively common event in this rare disease.
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Affiliation(s)
- Gulbu Uzel
- Laboratory of Clinical Infectious Diseases, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH), Bethesda, MD, USA.
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14
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Sharp AJ, Hansen S, Selzer RR, Cheng Z, Regan R, Hurst JA, Stewart H, Price SM, Blair E, Hennekam RC, Fitzpatrick CA, Segraves R, Richmond TA, Guiver C, Albertson DG, Pinkel D, Eis PS, Schwartz S, Knight SJL, Eichler EE. Discovery of previously unidentified genomic disorders from the duplication architecture of the human genome. Nat Genet 2006; 38:1038-42. [PMID: 16906162 DOI: 10.1038/ng1862] [Citation(s) in RCA: 437] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Accepted: 07/20/2006] [Indexed: 01/29/2023]
Abstract
Genomic disorders are characterized by the presence of flanking segmental duplications that predispose these regions to recurrent rearrangement. Based on the duplication architecture of the genome, we investigated 130 regions that we hypothesized as candidates for previously undescribed genomic disorders. We tested 290 individuals with mental retardation by BAC array comparative genomic hybridization and identified 16 pathogenic rearrangements, including de novo microdeletions of 17q21.31 found in four individuals. Using oligonucleotide arrays, we refined the breakpoints of this microdeletion, defining a 478-kb critical region containing six genes that were deleted in all four individuals. We mapped the breakpoints of this deletion and of four other pathogenic rearrangements in 1q21.1, 15q13, 15q24 and 17q12 to flanking segmental duplications, suggesting that these are also sites of recurrent rearrangement. In common with the 17q21.31 deletion, these breakpoint regions are sites of copy number polymorphism in controls, indicating that these may be inherently unstable genomic regions.
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Affiliation(s)
- Andrew J Sharp
- Department of Genome Sciences and The Howard Hughes Medical Institute, University of Washington School of Medicine, 1705 NE Pacific St., Seattle, Washington 98195, USA
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15
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Greenberg SA, Walsh RJ. Molecular diagnosis of inheritable neuromuscular disorders. Part I: Genetic determinants of inherited disease and their laboratory detection. Muscle Nerve 2005; 31:418-30. [PMID: 15704142 DOI: 10.1002/mus.20278] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Understanding of the genetic basis of inheritable neuromuscular disorders has grown rapidly over the last decade, resulting in improved classification and understanding of their pathogenesis. A consequence of these advances has been the development of genetic tests of blood specimens for the diagnosis of many of these diseases. For many patients, these blood tests have eliminated the need for other more invasive diagnostic tests such as muscle or nerve biopsy, and for some patients, reduced exposure to immunosuppressive medication and its complications. The first part of this review focuses on the nature of genetic disorders, the laboratory methods used in the performance of genetic tests, and general practical aspects of their use and interpretation. The second part discusses the applicability of these tests to the range of neuromuscular disorders.
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Affiliation(s)
- Steven A Greenberg
- Department of Neurology, Division of Neuromuscular Disease, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, Massachusetts 02115, USA.
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16
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Slater H, Bruno D, Ren H, La P, Burgess T, Hills L, Nouri S, Schouten J, Choo KHA. Improved testing for CMT1A and HNPP using multiplex ligation-dependent probe amplification (MLPA) with rapid DNA preparations: comparison with the interphase FISH method. Hum Mutat 2004; 24:164-71. [PMID: 15241798 DOI: 10.1002/humu.20072] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP) are the two most common peripheral neuropathies, with incidences of about 1 in 2,500. Several techniques can be used to detect the typical 1.5-Mb duplication or deletion associated with these respective conditions, but none combines simplicity with high sensitivity. MLPA is a new technique for measuring sequence dosage. We have assessed its performance for the detection of the specific 1.5-Mb duplication/deletion by prospectively testing 50 patients referred with differential diagnoses of CMT or HNPP. Probes were designed to evaluate the TEKT3, PMP22, and COX10 genes within the CMT1A/HNPP region. We have compared the results with our existing fluorescence in situ hybridization (FISH) assay, which was performed in parallel. There was concordance of results for 49 patients. Of note, one patient showed an intermediate multiplex ligation-dependent probe amplification (MLPA) result with an abnormal FISH result, which is consistent with mosaicism. The assay works equally well with either purified DNA or rapid DNA preparations made by direct cell lysis. The use of the latter significantly reduces the cost of the assay. MLPA is a sensitive, specific, robust, and cost-effective technique suitable for fast, high-throughput testing and offers distinct advantages over other testing methods.
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Affiliation(s)
- Howard Slater
- Genetic Health Services Victoria and Murdoch Childrens Research Institute, University of Melbourne Department of Paediatrics, Royal Children's Hospital, Parkville, Australia.
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17
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Abstract
There are increasing reports of multiple different types of somatic mosaicism detected in patients with inherited and non-inherited disorders. The characteristics of several of the major types of mosaicism will be outlined, and contrasted with somatic mosaicism, which is the focus of this article. This review examines examples of somatic mosaicism due to differences in DNA sequence arising from in vivo site specific reversion to normal of inherited mutations in humans. While several known mechanisms of reversion are evident in a number of these examples, they are not in some others. The possible significance of the role of selection, particularly in view of recent results of gene therapy, is discussed.
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Affiliation(s)
- R Hirschhorn
- Medicine, Cell Biology & Pediatrics, New York University School of Medicine, 550 First Ave CD612, New York, NY 10016, USA.
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18
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Abstract
The slow Wallerian degeneration mouse, C57BL/Wld(S), carries a dominant mutation that delays Wallerian degeneration in the distal stump of an injured axon. A highly unusual mutation, an 85-kb tandem triplication in the Wld(S) mouse was identified. Since two duplication cases have been identified before, pulsed field gel electrophoresis (PFGE) can be used to look for the instability of triplication at the chromosomal level. One hundred and eighty chromosomes of Wld(S) from three divergent breeding colonies have been examined and all found to carry the triplication. Thus, the triplication mutation is stable during both mitosis and meiosis, and the previously observed duplication is likely to have been surviving alleles of the original mutation rather than a partial reversion. The triplication has now been shown to be the causative mutation, acting through an Ube4b/Nmnat chimeric gene, indicating the possibility of Wld(S) preventing axon degeneration in diverse pathologies and altering the symptoms. The fact that triplication is stable rules out instability as a source of phenotypic variation. Thus, this result is essential for accurate interpretation of studies the effect of Wld(S) on neurodegenerative phenotypes.
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Affiliation(s)
- Weiqian Mi
- Center for Molecular Medicine (ZMMK) and Institute for Genetics, University of Cologne, Zuelpicher Strasse 47, Germany.
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19
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Thiel CT, Kraus C, Rauch A, Ekici AB, Rautenstrauss B, Reis A. A new quantitative PCR multiplex assay for rapid analysis of chromosome 17p11.2-12 duplications and deletions leading to HMSN/HNPP. Eur J Hum Genet 2003; 11:170-8. [PMID: 12634865 DOI: 10.1038/sj.ejhg.5200920] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2002] [Revised: 10/01/2002] [Accepted: 10/09/2002] [Indexed: 12/15/2022] Open
Abstract
A 1.4-Mb tandem duplication, including the gene for peripheral myelin protein 22 (PMP22) in chromosome 17p11.2-12 is responsible for 70% of the cases of the demyelinating type 1 of Charcot-Marie-Tooth disease or hereditary motor and sensory neuropathy I (CMT1A/HMSN I). A reciprocal deletion of this CMT1A region causes the hereditary neuropathy with liability to pressure palsies (HNPP). The CMT1A duplication increases the PMP22 gene dosage from two to three, the HNPP deletion reduces the gene dosage from two to one. Currently, routine diagnosis of HMSN/HNPP patients is mainly performed with polymorphic markers in-between the repetitive elements flanking the CMT1A region. These show quantitative and/or qualitative changes in case of a CMT1A duplication and a homozygous allele pattern in case of HNPP deletion. In HNPP patients the deletion is usually confirmed by fluorescence in situ hybridisation (FISH). We now developed a reliable, single tube real-time quantitative PCR assay for rapid determination of PMP22 gene dosage directly. This method involves a multiplex reaction using FAM labelled Taqman-probe with TAMRA quencher derived from PMP22 exon 3 and a VIC labelled probe with non-fluorescent quencher from exon 12 of the albumin gene as internal reference. Copy number of the PMP22 gene was determined by the comparative threshold cycle method (deltadeltaCt). Each sample was run in quadruplicate and analysed at two different threshold levels. The level giving the smallest standard deviation was scored. We evaluated this method through the retrospective analysis of 252 HMSN patients with known genotype and could confirm the previous findings in 99% of cases. Two patients were wrongly diagnosed with microsatellite analysis while quantitative real-time PCR identified the correct genotype, as confirmed by FISH. Thus, this method shows superior sensitivity to microsatellite analysis and has the additional advantage of being a fast and uniform assay for quantitative analysis of both CMT1A and HNPP.
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Affiliation(s)
- Christian T Thiel
- Institute of Human Genetics, University of Erlangen-Nuremberg, Schwabachanlage 10, 91054 Erlangen, Germany
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20
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Abstract
Somatic mosaicism -- the presence of genetically distinct populations of somatic cells in a given organism -- is frequently masked, but it can also result in major phenotypic changes and reveal the expression of otherwise lethal genetic mutations. Mosaicism can be caused by DNA mutations, epigenetic alterations of DNA, chromosomal abnormalities and the spontaneous reversion of inherited mutations. In this review, we discuss the human disorders that result from somatic mosaicism, as well as the molecular genetic mechanisms by which they arise. Specifically, we emphasize the role of selection in the phenotypic manifestations of mosaicism.
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Affiliation(s)
- Hagop Youssoufian
- Department of Clinical Discovery, Bristol-Myers Squibb Company, Princeton, New Jersey 08543-4000, USA.
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21
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Abstract
An increasing number of human diseases are recognized to result from recurrent DNA rearrangements involving unstable genomic regions. These are termed genomic disorders, in which the clinical phenotype is a consequence of abnormal dosage of gene(s) located within the rearranged genomic fragments. Both inter- and intrachromosomal rearrangements are facilitated by the presence of region-specific low-copy repeats (LCRs) and result from nonallelic homologous recombination (NAHR) between paralogous genomic segments. LCRs usually span approximately 10-400 kb of genomic DNA, share >or= 97% sequence identity, and provide the substrates for homologous recombination, thus predisposing the region to rearrangements. Moreover, it has been suggested that higher order genomic architecture involving LCRs plays a significant role in karyotypic evolution accompanying primate speciation.
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Affiliation(s)
- Paweł Stankiewicz
- Dept Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030-3498, USA
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22
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Naumann R, Mohm J, Reuner U, Kroschinsky F, Rautenstrauss B, Ehninger G. Early recognition of hereditary motor and sensory neuropathy type 1 can avoid life-threatening vincristine neurotoxicity. Br J Haematol 2001; 115:323-5. [PMID: 11703329 DOI: 10.1046/j.1365-2141.2001.03126.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Hereditary motor and sensory neuropathy type 1 (HMSN-1) is an autosomal dominant disorder, which is usually not associated with neoplastic diseases. The disease predisposes to severe vincristine neurotoxicity. We report a 31-year-old women with recurrent Hodgkin's lymphoma and unrecognized HMSN-1 who developed severe motor neuropathy 3 weeks after the first cycle of treatment including 2 mg of vincristine. HMSN is diagnosed in most cases retrospectively, usually suggested by the observation of foot abnormalities or family history. Recognizing early signs of HMSN, such as areflexia and pes cavus deformity, can prevent severe neurotoxicity of polychemotherapy by avoiding vincristine.
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Affiliation(s)
- R Naumann
- Department of Medicine I, University Hospital Carl Gustav Carus, Dresden University of Technology, Dresden, Germany.
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23
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Abstract
Cytogenetic imbalance in the newborn is a frequent cause of mental retardation and birth defects. Although aneuploidy accounts for the majority of imbalance, structural aberrations contribute to a significant fraction of recognized chromosomal anomalies. This review describes the major classes of constitutional, structural cytogenetic abnormalities and recent studies that explore the molecular mechanisms that bring about their de novo occurrence. Genomic features flanking the sites of recombination may result in susceptibility to chromosomal rearrangement. One such substrate for recombination is low-copy region-specific repeats. The identification of genome architectural features conferring susceptibility to rearrangements has been accomplished using methods that enable investigation of regions of the genome that are too small to be visualized by traditional cytogenetics and too large to be resolved by conventional gel electrophoresis. These investigations resulted in the identification of previously unrecognized structural cytogenetic anomalies, which are associated with genetic syndromes and allowed for the molecular basis of some chromosomal rearrangements to be delineated.
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Affiliation(s)
- L G Shaffer
- Department of Molecular and Human Genetics, Department of Pediatrics, Baylor College of Medicine, and Texas Children's Hospital, Houston, Texas 77030, USA.
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Helleday T, Arnaudeau C, Jenssen D. A partial hprt gene duplication generated by non-homologous recombination in V79 Chinese hamster cells is eliminated by homologous recombination. J Mol Biol 1998; 279:687-94. [PMID: 9642052 DOI: 10.1006/jmbi.1998.1809] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Here, the sequence in the hprt gene of the duplication mutant SPD8 originating from V79 Chinese hamster cells was determined. The duplication arose after non-homologous recombination between exon 6 and intron 7, resulting in an extra copy of the 3' portion of exon 6, of exon 7 and of flanking intron regions. Only a duplication of exon 7 is present in the mRNA, since the duplicated exon 6 lacks its 5' splice site and is removed during RNA processing. The findings in this study suggest that the non-homologous recombination mechanism which occurred here may have been initiated by endonucleases, rather than by a spontaneous double strand break. Subsequently, 14 spontaneous SPD8 revertants with a functional hprt gene were isolated and characterized using PCR and sequencing. The data revealed that although the SPD8 cell line arose by non-homologous recombination, it reverts spontaneously by homologous recombination. Interestingly, the downstream copy of exon 7 was restored by this process. This was indicated by the presence of a specific mutation, a T-to-G transversion, close to the breakpoint, a characteristic unique to the SPD8 clone. Our results suggest that the spontaneous reversion of this cell line by homologous recombination may involve an exchange, rather than a conversion mechanism.
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Affiliation(s)
- T Helleday
- Department of Genetic and Cellular Toxicology, Wallenberg Laboratory, Stockholm University, Stockholm, S-106 91, Sweden
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25
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Abstract
Abstract
Although many genetic diseases are caused by the presence of point mutations in respective genes, an increasing number of diseases are known to be caused by gene copy number changes. We report the development of a rapid and reliable PCR-based method for quantitation of gene copy number with sufficient sensitivity to detect single copy changes without the use of radioactive or fluorescent labeling. The sensitivity of this technique has been demonstrated by the detection of the DNA duplication or deletion occurring in two inherited peripheral neuropathies, Charcot-Marie-Tooth type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), that are caused by a reciprocal duplication or deletion event on chromosome 17p11.2–12. This method relies on the comparison of the amount of PCR product generated from a potentially duplicated or deleted target sequence with the amount of product generated from a disomic reference gene. The value of this ratio (target PCR product:reference PCR product) indicates whether the target sequence is duplicated, deleted, or unchanged. Using primers from within a duplicated or deleted region (PMP22 gene and EW401) and from within a reference region (NF1 gene), we tested 50 CMT1A, 30 HNPP, and 50 unaffected individuals for the presence of a DNA duplication or deletion. Target:reference ratios of 1.58, 1.02, and 0.56 were detected for the CMT1A, unaffected, and HNPP groups, respectively. Thus, differentiation of the three groups of individuals was on the basis of gene copy number. This technique was successfully used to detect the difference in the X chromosome copy number between males and females (target:reference ratios of 1.1 and 2.3, respectively). This approach to the detection of DNA duplications and deletions is sensitive, accurate, and has potential applications in the quantitation of changes in gene copy number associated with diseases characterized by such chromosomal alterations.
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Shaffer LG, Kennedy GM, Spikes AS, Lupski JR. Diagnosis of CMT1A duplications and HNPP deletions by interphase FISH: Implications for testing in the cytogenetics laboratory. ACTA ACUST UNITED AC 1997. [DOI: 10.1002/(sici)1096-8628(19970331)69:3<325::aid-ajmg20>3.0.co;2-s] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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28
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Abstract
Clinical, neurophysiological and morphological studies on a patient with mosaicism of the 17p11.2 duplication were performed in detail for the first time. Since duplication occurs during paternal meiosis, a somatic reversion is suggested, leading to mosaicism. The proportion of nuclei with duplication varied markedly between 49% in blood cells and 74% in tissue from the sural nerve. Clinically, mild symptoms of a motor and sensory neuropathy were present. However, neurophysiological changes and findings in the sural nerve biopsy were consistent with a typical hereditary motor and sensory neuropathy type 1 (HMSN 1). Differing clinical findings in patients with mosaicism of the 17p11.2 duplication may be explained by a varying degree and/or time of reversion.
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Affiliation(s)
- H Grehl
- Department of Neurology, University Hospital, Erlangen, Germany
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