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Mirceta M, Shum N, Schmidt MHM, Pearson CE. Fragile sites, chromosomal lesions, tandem repeats, and disease. Front Genet 2022; 13:985975. [PMID: 36468036 PMCID: PMC9714581 DOI: 10.3389/fgene.2022.985975] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 09/02/2022] [Indexed: 09/16/2023] Open
Abstract
Expanded tandem repeat DNAs are associated with various unusual chromosomal lesions, despiralizations, multi-branched inter-chromosomal associations, and fragile sites. Fragile sites cytogenetically manifest as localized gaps or discontinuities in chromosome structure and are an important genetic, biological, and health-related phenomena. Common fragile sites (∼230), present in most individuals, are induced by aphidicolin and can be associated with cancer; of the 27 molecularly-mapped common sites, none are associated with a particular DNA sequence motif. Rare fragile sites ( ≳ 40 known), ≤ 5% of the population (may be as few as a single individual), can be associated with neurodevelopmental disease. All 10 molecularly-mapped folate-sensitive fragile sites, the largest category of rare fragile sites, are caused by gene-specific CGG/CCG tandem repeat expansions that are aberrantly CpG methylated and include FRAXA, FRAXE, FRAXF, FRA2A, FRA7A, FRA10A, FRA11A, FRA11B, FRA12A, and FRA16A. The minisatellite-associated rare fragile sites, FRA10B, FRA16B, can be induced by AT-rich DNA-ligands or nucleotide analogs. Despiralized lesions and multi-branched inter-chromosomal associations at the heterochromatic satellite repeats of chromosomes 1, 9, 16 are inducible by de-methylating agents like 5-azadeoxycytidine and can spontaneously arise in patients with ICF syndrome (Immunodeficiency Centromeric instability and Facial anomalies) with mutations in genes regulating DNA methylation. ICF individuals have hypomethylated satellites I-III, alpha-satellites, and subtelomeric repeats. Ribosomal repeats and subtelomeric D4Z4 megasatellites/macrosatellites, are associated with chromosome location, fragility, and disease. Telomere repeats can also assume fragile sites. Dietary deficiencies of folate or vitamin B12, or drug insults are associated with megaloblastic and/or pernicious anemia, that display chromosomes with fragile sites. The recent discovery of many new tandem repeat expansion loci, with varied repeat motifs, where motif lengths can range from mono-nucleotides to megabase units, could be the molecular cause of new fragile sites, or other chromosomal lesions. This review focuses on repeat-associated fragility, covering their induction, cytogenetics, epigenetics, cell type specificity, genetic instability (repeat instability, micronuclei, deletions/rearrangements, and sister chromatid exchange), unusual heritability, disease association, and penetrance. Understanding tandem repeat-associated chromosomal fragile sites provides insight to chromosome structure, genome packaging, genetic instability, and disease.
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Affiliation(s)
- Mila Mirceta
- Program of Genetics and Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, ON, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Natalie Shum
- Program of Genetics and Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, ON, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Monika H. M. Schmidt
- Program of Genetics and Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, ON, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Christopher E. Pearson
- Program of Genetics and Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, ON, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, ON, Canada
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2
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Gall-Duncan T, Sato N, Yuen RKC, Pearson CE. Advancing genomic technologies and clinical awareness accelerates discovery of disease-associated tandem repeat sequences. Genome Res 2022; 32:1-27. [PMID: 34965938 PMCID: PMC8744678 DOI: 10.1101/gr.269530.120] [Citation(s) in RCA: 33] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Accepted: 11/29/2021] [Indexed: 11/25/2022]
Abstract
Expansions of gene-specific DNA tandem repeats (TRs), first described in 1991 as a disease-causing mutation in humans, are now known to cause >60 phenotypes, not just disease, and not only in humans. TRs are a common form of genetic variation with biological consequences, observed, so far, in humans, dogs, plants, oysters, and yeast. Repeat diseases show atypical clinical features, genetic anticipation, and multiple and partially penetrant phenotypes among family members. Discovery of disease-causing repeat expansion loci accelerated through technological advances in DNA sequencing and computational analyses. Between 2019 and 2021, 17 new disease-causing TR expansions were reported, totaling 63 TR loci (>69 diseases), with a likelihood of more discoveries, and in more organisms. Recent and historical lessons reveal that properly assessed clinical presentations, coupled with genetic and biological awareness, can guide discovery of disease-causing unstable TRs. We highlight critical but underrecognized aspects of TR mutations. Repeat motifs may not be present in current reference genomes but will be in forthcoming gapless long-read references. Repeat motif size can be a single nucleotide to kilobases/unit. At a given locus, repeat motif sequence purity can vary with consequence. Pathogenic repeats can be "insertions" within nonpathogenic TRs. Expansions, contractions, and somatic length variations of TRs can have clinical/biological consequences. TR instabilities occur in humans and other organisms. TRs can be epigenetically modified and/or chromosomal fragile sites. We discuss the expanding field of disease-associated TR instabilities, highlighting prospects, clinical and genetic clues, tools, and challenges for further discoveries of disease-causing TR instabilities and understanding their biological and pathological impacts-a vista that is about to expand.
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Affiliation(s)
- Terence Gall-Duncan
- Program of Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1L7, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Nozomu Sato
- Program of Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1L7, Canada
| | - Ryan K C Yuen
- Program of Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1L7, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Christopher E Pearson
- Program of Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1L7, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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3
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Schröder C, Horsthemke B, Depienne C. GC-rich repeat expansions: associated disorders and mechanisms. MED GENET-BERLIN 2021; 33:325-335. [PMID: 38835438 PMCID: PMC11006399 DOI: 10.1515/medgen-2021-2099] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 11/12/2021] [Indexed: 06/06/2024]
Abstract
Noncoding repeat expansions are a well-known cause of genetic disorders mainly affecting the central nervous system. Missed by most standard technologies used in routine diagnosis, pathogenic noncoding repeat expansions have to be searched for using specific techniques such as repeat-primed PCR or specific bioinformatics tools applied to genome data, such as ExpansionHunter. In this review, we focus on GC-rich repeat expansions, which represent at least one third of all noncoding repeat expansions described so far. GC-rich expansions are mainly located in regulatory regions (promoter, 5' untranslated region, first intron) of genes and can lead to either a toxic gain-of-function mediated by RNA toxicity and/or repeat-associated non-AUG (RAN) translation, or a loss-of-function of the associated gene, depending on their size and their methylation status. We herein review the clinical and molecular characteristics of disorders associated with these difficult-to-detect expansions.
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Affiliation(s)
- Christopher Schröder
- Institute of Human Genetics, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Bernhard Horsthemke
- Institute of Human Genetics, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Christel Depienne
- Institute of Human Genetics, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
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Forman TE, Dennison BJC, Fantauzzo KA. The Role of RNA-Binding Proteins in Vertebrate Neural Crest and Craniofacial Development. J Dev Biol 2021; 9:34. [PMID: 34564083 PMCID: PMC8482138 DOI: 10.3390/jdb9030034] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 08/23/2021] [Accepted: 08/25/2021] [Indexed: 12/11/2022] Open
Abstract
Cranial neural crest (NC) cells delaminate from the neural folds in the forebrain to the hindbrain during mammalian embryogenesis and migrate into the frontonasal prominence and pharyngeal arches. These cells generate the bone and cartilage of the frontonasal skeleton, among other diverse derivatives. RNA-binding proteins (RBPs) have emerged as critical regulators of NC and craniofacial development in mammals. Conventional RBPs bind to specific sequence and/or structural motifs in a target RNA via one or more RNA-binding domains to regulate multiple aspects of RNA metabolism and ultimately affect gene expression. In this review, we discuss the roles of RBPs other than core spliceosome components during human and mouse NC and craniofacial development. Where applicable, we review data on these same RBPs from additional vertebrate species, including chicken, Xenopus and zebrafish models. Knockdown or ablation of several RBPs discussed here results in altered expression of transcripts encoding components of developmental signaling pathways, as well as reduced cell proliferation and/or increased cell death, indicating that these are common mechanisms contributing to the observed phenotypes. The study of these proteins offers a relatively untapped opportunity to provide significant insight into the mechanisms underlying gene expression regulation during craniofacial morphogenesis.
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Affiliation(s)
| | | | - Katherine A. Fantauzzo
- Department of Craniofacial Biology, School of Dental Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA; (T.E.F.); (B.J.C.D.)
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5
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Monckton DG. The Contribution of Somatic Expansion of the CAG Repeat to Symptomatic Development in Huntington's Disease: A Historical Perspective. J Huntingtons Dis 2021; 10:7-33. [PMID: 33579863 PMCID: PMC7990401 DOI: 10.3233/jhd-200429] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The discovery in the early 1990s of the expansion of unstable simple sequence repeats as the causative mutation for a number of inherited human disorders, including Huntington's disease (HD), opened up a new era of human genetics and provided explanations for some old problems. In particular, an inverse association between the number of repeats inherited and age at onset, and unprecedented levels of germline instability, biased toward further expansion, provided an explanation for the wide symptomatic variability and anticipation observed in HD and many of these disorders. The repeats were also revealed to be somatically unstable in a process that is expansion-biased, age-dependent and tissue-specific, features that are now increasingly recognised as contributory to the age-dependence, progressive nature and tissue specificity of the symptoms of HD, and at least some related disorders. With much of the data deriving from affected individuals, and model systems, somatic expansions have been revealed to arise in a cell division-independent manner in critical target tissues via a mechanism involving key components of the DNA mismatch repair pathway. These insights have opened new approaches to thinking about how the disease could be treated by suppressing somatic expansion and revealed novel protein targets for intervention. Exciting times lie ahead in turning these insights into novel therapies for HD and related disorders.
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Affiliation(s)
- Darren G. Monckton
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
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Pozo-Palacios J, Llamos-Paneque A, Rivas C, Onofre E, López-Cáceres A, Villareal J. Experiences of the Molecular Diagnosis of Fragile X Syndrome in Ecuador. Front Psychiatry 2021; 12:716311. [PMID: 34966298 PMCID: PMC8710471 DOI: 10.3389/fpsyt.2021.716311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 11/03/2021] [Indexed: 12/01/2022] Open
Abstract
Fragile X syndrome (FXS) is the most common cause of hereditary intellectual disability and the second most common cause of intellectual disability of genetic etiology. This complex neurodevelopmental disorder is caused by an alteration in the CGG trinucleotide expansion in fragile X mental retardation gene 1 (FMR1) leading to gene silencing and the subsequent loss of its product: fragile X mental retardation protein 1 (FMRP). Molecular diagnosis is based on polymerase chain reaction (PCR) screening followed by Southern blotting (SB) or Triplet primer-PCR (TP-PCR) to determine the number of CGG repeats in the FMR1 gene. We performed, for the first time, screening in 247 Ecuadorian male individuals with clinical criteria to discard FXS. Analysis was carried out by the Genetics Service of the Hospital de Especialidades No. 1 de las Fuerzas Armadas (HE-1), Ecuador. The analysis was performed using endpoint PCR for CGG fragment expansion analysis of the FMR1 gene. Twenty-two affected males were identified as potentially carrying the full mutation in FMR1 and thus diagnosed with FXS that is 8.1% of the sample studied. The average age at diagnosis of the positive cases was 13 years of age, with most cases from the geographical area of Pichincha (63.63%). We confirmed the familial nature of the disease in four cases. The range of CGG variation in the population was 12-43 and followed a modal distribution of 27 repeats. Our results were similar to those reported in the literature; however, since it was not possible to differentiate between premutation and mutation cases, we can only establish a molecular screening approach to identify an expanded CGG repeat, which makes it necessary to generate national strategies to optimize molecular tests and establish proper protocols for the diagnosis, management, and follow-up of patients, families, and communities at risk of presenting FXS.
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Affiliation(s)
- Juan Pozo-Palacios
- Facultad de Ciencias Médicas, Escuela de Medicina, Universidad de Cuenca, Cuenca, Ecuador
| | - Arianne Llamos-Paneque
- Medical Genetic Services, Hospital de las Fuerzas Armadas, Quito, Ecuador.,Sciences of Life Faculty, School of Dentistry, International University of Ecuador, Quito, Ecuador
| | - Christian Rivas
- Medical Genetic Services, Hospital de las Fuerzas Armadas, Quito, Ecuador
| | - Emily Onofre
- Medical Genetic Services, Hospital de las Fuerzas Armadas, Quito, Ecuador
| | - Andrea López-Cáceres
- Neurodesarrollo Quito, Quito, Ecuador.,Fundación Santa Fe de Bogotá, Bogotá, Colombia
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Kim K, Hessl D, Randol JL, Espinal GM, Schneider A, Protic D, Aydin EY, Hagerman RJ, Hagerman PJ. Association between IQ and FMR1 protein (FMRP) across the spectrum of CGG repeat expansions. PLoS One 2019; 14:e0226811. [PMID: 31891607 PMCID: PMC6938341 DOI: 10.1371/journal.pone.0226811] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Accepted: 12/05/2019] [Indexed: 12/20/2022] Open
Abstract
Fragile X syndrome, the leading heritable form of intellectual disability, is caused by hypermethylation and transcriptional silencing of large (CGG) repeat expansions (> 200 repeats) in the 5′ untranslated region of the fragile X mental retardation 1 (FMR1) gene. As a consequence of FMR1 gene silencing, there is little or no production of FMR1 protein (FMRP), an important element in normal synaptic function. Although the absence of FMRP has long been known to be responsible for the cognitive impairment in fragile X syndrome, the relationship between FMRP level and cognitive ability (IQ) is only imprecisely understood. To address this issue, a high-throughput, fluorescence resonance energy transfer (FRET) assay has been used to quantify FMRP levels in dermal fibroblasts, and the relationship between FMRP and IQ measures was assessed by statistical analysis in a cohort of 184 individuals with CGG-repeat lengths spanning normal (< 45 CGGs) to full mutation (> 200 CGGs) repeat ranges in fibroblasts. The principal findings of the current study are twofold: i) For those with normal CGG repeats, IQ is no longer sensitive to further increases in FMRP above an FMRP threshold of ~70% of the mean FMRP level; below this threshold, IQ decreases steeply with further decreases in FMRP; and ii) For the current cohort, a mean IQ of 85 (lower bound for the normal IQ range) is attained for FMRP levels that are only ~35% of the mean FMRP level among normal CGG-repeat controls. The current results should help guide expectations for efforts to induce FMR1 gene activity and for the levels of cognitive function expected for a given range of FMRP levels.
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Affiliation(s)
- Kyoungmi Kim
- UC Davis MIND Institute, UC Davis Health, Sacramento, California, United States of America
- Department of Public Health Sciences, University of California, Davis, School of Medicine, Davis, California, United States of America
| | - David Hessl
- UC Davis MIND Institute, UC Davis Health, Sacramento, California, United States of America
- Department of Psychiatry and Behavioral Sciences, University of California, Davis, School of Medicine, Sacramento, California, United States of America
| | - Jamie L. Randol
- Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Davis, California, United States of America
| | - Glenda M. Espinal
- Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Davis, California, United States of America
| | - Andrea Schneider
- UC Davis MIND Institute, UC Davis Health, Sacramento, California, United States of America
- Department of Pediatrics, University of California, Davis, School of Medicine, Sacramento, California, United States of America
| | - Dragana Protic
- UC Davis MIND Institute, UC Davis Health, Sacramento, California, United States of America
| | - Elber Yuksel Aydin
- UC Davis MIND Institute, UC Davis Health, Sacramento, California, United States of America
| | - Randi J. Hagerman
- UC Davis MIND Institute, UC Davis Health, Sacramento, California, United States of America
- Department of Pediatrics, University of California, Davis, School of Medicine, Sacramento, California, United States of America
| | - Paul J. Hagerman
- UC Davis MIND Institute, UC Davis Health, Sacramento, California, United States of America
- Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Davis, California, United States of America
- * E-mail:
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Horga A, Woodward CE, Mills A, Pareés I, Hargreaves IP, Brown RM, Bugiardini E, Brooks T, Manole A, Remzova E, Rahman S, Reilly MM, Houlden H, Sweeney MG, Brown GK, Polke JM, Gago F, Parton MJ, Pitceathly RDS, Hanna MG. Differential phenotypic expression of a novel PDHA1 mutation in a female monozygotic twin pair. Hum Genet 2019; 138:1313-1322. [PMID: 31673819 PMCID: PMC6874639 DOI: 10.1007/s00439-019-02075-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Accepted: 10/18/2019] [Indexed: 01/27/2023]
Abstract
Pyruvate dehydrogenase complex (PDC) deficiency caused by mutations in the X-linked PDHA1 gene has a broad clinical presentation, and the pattern of X-chromosome inactivation has been proposed as a major factor contributing to its variable expressivity in heterozygous females. Here, we report the first set of monozygotic twin females with PDC deficiency, caused by a novel, de novo heterozygous missense mutation in exon 11 of PDHA1 (NM_000284.3: c.1100A>T). Both twins presented in infancy with a similar clinical phenotype including developmental delay, episodes of hypotonia or encephalopathy, epilepsy, and slowly progressive motor impairment due to pyramidal, extrapyramidal, and cerebellar involvement. However, they exhibited clear differences in disease severity that correlated well with residual PDC activities (approximately 60% and 20% of mean control values, respectively) and levels of immunoreactive E1α subunit in cultured skin fibroblasts. To address whether the observed clinical and biochemical differences could be explained by the pattern of X-chromosome inactivation, we undertook an androgen receptor assay in peripheral blood. In the less severely affected twin, a significant bias in the relative activity of the two X chromosomes with a ratio of approximately 75:25 was detected, while the ratio was close to 50:50 in the other twin. Although it may be difficult to extrapolate these results to other tissues, our observation provides further support to the hypothesis that the pattern of X-chromosome inactivation may influence the phenotypic expression of the same mutation in heterozygous females and broadens the clinical and genetic spectrum of PDC deficiency.
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Affiliation(s)
- Alejandro Horga
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
- Neuromuscular Diseases Unit, Department of Neurology, Hospital Clínico San Carlos, IdISSC, Madrid, Spain
| | - Catherine E Woodward
- Neurogenetics Unit, The National Hospital for Neurology and Neurosurgery, London, UK
| | - Alberto Mills
- Area of Pharmacology, Department of Biomedical Sciences, School of Medicine and Health Sciences, University of Alcalá, Alcalá de Henares, Spain
| | - Isabel Pareés
- Sobell Department of Motor Neuroscience and Movement Disorders, UCL Queen Square Institute of Neurology, London, UK
| | - Iain P Hargreaves
- Neurometabolic Unit, The National Hospital for Neurology and Neurosurgery, London, UK
| | - Ruth M Brown
- Oxford Medical Genetics Laboratories, The Churchill Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
| | - Enrico Bugiardini
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
| | - Tony Brooks
- UCL Genomics, UCL Great Ormond Street Institute of Child Health, University College London, London, UK
| | - Andreea Manole
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
| | - Elena Remzova
- Neurometabolic Unit, The National Hospital for Neurology and Neurosurgery, London, UK
| | - Shamima Rahman
- Metabolic Unit, Great Ormond Street Hospital for Children NHS Foundation Trust and UCL Great Ormond Street Institute of Child Health, London, UK
| | - Mary M Reilly
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
| | - Henry Houlden
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
| | - Mary G Sweeney
- Neurogenetics Unit, The National Hospital for Neurology and Neurosurgery, London, UK
| | - Garry K Brown
- Oxford Medical Genetics Laboratories, The Churchill Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
| | - James M Polke
- Neurogenetics Unit, The National Hospital for Neurology and Neurosurgery, London, UK
| | - Federico Gago
- Area of Pharmacology, Department of Biomedical Sciences, School of Medicine and Health Sciences, University of Alcalá, Alcalá de Henares, Spain
| | - Matthew J Parton
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK
| | - Robert D S Pitceathly
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK.
| | - Michael G Hanna
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology and The National Hospital for Neurology and Neurosurgery, London, UK.
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Abu Diab M, Eiges R. The Contribution of Pluripotent Stem Cell (PSC)-Based Models to the Study of Fragile X Syndrome (FXS). Brain Sci 2019; 9:brainsci9020042. [PMID: 30769941 PMCID: PMC6406836 DOI: 10.3390/brainsci9020042] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2019] [Revised: 02/11/2019] [Accepted: 02/13/2019] [Indexed: 02/06/2023] Open
Abstract
Fragile X syndrome (FXS) is the most common heritable form of cognitive impairment. It results from a deficiency in the fragile X mental retardation protein (FMRP) due to a CGG repeat expansion in the 5′-UTR of the X-linked FMR1 gene. When CGGs expand beyond 200 copies, they lead to epigenetic gene silencing of the gene. In addition, the greater the allele size, the more likely it will become unstable and exhibit mosaicism for expansion size between and within tissues in affected individuals. The timing and mechanisms of FMR1 epigenetic gene silencing and repeat instability are far from being understood given the lack of appropriate cellular and animal models that can fully recapitulate the molecular features characteristic of the disease pathogenesis in humans. This review summarizes the data collected to date from mutant human embryonic stem cells, induced pluripotent stem cells, and hybrid fusions, and discusses their contribution to the investigation of FXS, their key limitations, and future prospects.
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Affiliation(s)
- Manar Abu Diab
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center, Jerusalem 91031, Israel.
- School of Medicine, Hebrew University of Jerusalem, Jerusalem 9112102, Israel.
| | - Rachel Eiges
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center, Jerusalem 91031, Israel.
- School of Medicine, Hebrew University of Jerusalem, Jerusalem 9112102, Israel.
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10
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Jiraanont P, Kumar M, Tang HT, Espinal G, Hagerman PJ, Hagerman RJ, Chutabhakdikul N, Tassone F. Size and methylation mosaicism in males with Fragile X syndrome. Expert Rev Mol Diagn 2018; 17:1023-1032. [PMID: 28929824 DOI: 10.1080/14737159.2017.1377612] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND Size and methylation mosaicism are a common phenomenon in Fragile X syndrome (FXS). Here, the authors report a study on twelve fragile X males with atypical mosaicism, seven of whom presented with autism spectrum disorder. METHODS A combination of Southern Blot and PCR analysis was used for CGG allele sizing and methylation. FMR1 mRNA and FMRP expression were measured by qRT-PCR and by Homogeneous Time Resolved Fluorescence methodology, respectively. RESULTS DNA analysis showed atypical size- or methylation-mosaicism with both, full mutation and smaller (normal to premutation) alleles, as well as a combination of methylated and unmethylated alleles. Four individuals carried a deletion of the CGG repeat and portions of the flanking regions. The extent of methylation among the participants was reflected in the lower FMR1 mRNA and FMRP expression levels detected in these subjects. CONCLUSION Decreased gene expression is likely the main contributor to the cognitive impairment observed in these subjects; although the presence of a normal allele did not appear to compensate for the presence of the full mutation, it correlated with better cognitive function in some but not all of the reported cases emphasizing the complexity of the molecular and clinical profile in FXS.
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Affiliation(s)
- Poonnada Jiraanont
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA.,b Research Center for Neuroscience, Institute of Molecular Biosciences , Mahidol University , Nakornpathom , Thailand
| | - Madhur Kumar
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA
| | - Hiu-Tung Tang
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA
| | - Glenda Espinal
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA
| | - Paul J Hagerman
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA.,c M.I.N.D. Institute , University of California Davis Medical Center , Sacramento , CA , USA
| | - Randi J Hagerman
- c M.I.N.D. Institute , University of California Davis Medical Center , Sacramento , CA , USA.,d Department of Pediatrics , University of California, Davis Medical Center , Sacramento , CA , USA
| | - Nuanchan Chutabhakdikul
- b Research Center for Neuroscience, Institute of Molecular Biosciences , Mahidol University , Nakornpathom , Thailand
| | - Flora Tassone
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA.,c M.I.N.D. Institute , University of California Davis Medical Center , Sacramento , CA , USA
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11
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Dahlhaus R. Of Men and Mice: Modeling the Fragile X Syndrome. Front Mol Neurosci 2018; 11:41. [PMID: 29599705 PMCID: PMC5862809 DOI: 10.3389/fnmol.2018.00041] [Citation(s) in RCA: 84] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Accepted: 01/31/2018] [Indexed: 12/26/2022] Open
Abstract
The Fragile X Syndrome (FXS) is one of the most common forms of inherited intellectual disability in all human societies. Caused by the transcriptional silencing of a single gene, the fragile x mental retardation gene FMR1, FXS is characterized by a variety of symptoms, which range from mental disabilities to autism and epilepsy. More than 20 years ago, a first animal model was described, the Fmr1 knock-out mouse. Several other models have been developed since then, including conditional knock-out mice, knock-out rats, a zebrafish and a drosophila model. Using these model systems, various targets for potential pharmaceutical treatments have been identified and many treatments have been shown to be efficient in preclinical studies. However, all attempts to turn these findings into a therapy for patients have failed thus far. In this review, I will discuss underlying difficulties and address potential alternatives for our future research.
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Affiliation(s)
- Regina Dahlhaus
- Institute for Biochemistry, Emil-Fischer Centre, University of Erlangen-Nürnberg, Erlangen, Germany
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12
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Mor-Shaked H, Eiges R. Reevaluation of FMR1 Hypermethylation Timing in Fragile X Syndrome. Front Mol Neurosci 2018; 11:31. [PMID: 29467618 PMCID: PMC5808132 DOI: 10.3389/fnmol.2018.00031] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 01/24/2018] [Indexed: 12/27/2022] Open
Abstract
Fragile X syndrome (FXS) is one of the most common heritable forms of cognitive impairment. It results from a fragile X mental retardation protein (FMRP) protein deficiency caused by a CGG repeat expansion in the 5'-UTR of the X-linked FMR1 gene. Whereas in most individuals the number of CGGs is steady and ranges between 5 and 44 units, in patients it becomes extensively unstable and expands to a length exceeding 200 repeats (full mutation). Interestingly, this disease is exclusively transmitted by mothers who carry a premutation allele (55-200 CGG repeats). When the CGGs reach the FM range, they trigger the spread of abnormal DNA methylation, which coincides with a switch from active to repressive histone modifications. This results in epigenetic gene silencing of FMR1 presumably by a multi-stage, developmentally regulated process. The timing of FMR1 hypermethylation and transcription silencing is still hotly debated. There is evidence that hypermethylation varies considerably between and within the tissues of patients as well as during fetal development, thus supporting the view that FMR1 silencing is a post-zygotic event that is developmentally structured. On the other hand, it may be established in the female germ line and transmitted to the fetus as an integral part of the mutation. This short review summarizes the data collected to date concerning the timing of FMR1 epigenetic gene silencing and reassess the evidence in favor of the theory that gene inactivation takes place by a developmentally regulated process around the 10th week of gestation.
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Affiliation(s)
- Hagar Mor-Shaked
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center, Jerusalem, Israel.,Hebrew University Medical School, Jerusalem, Israel
| | - Rachel Eiges
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center, Jerusalem, Israel.,Hebrew University Medical School, Jerusalem, Israel
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13
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von Kopylow K, Spiess AN. Human spermatogonial markers. Stem Cell Res 2017; 25:300-309. [PMID: 29239848 DOI: 10.1016/j.scr.2017.11.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Revised: 11/06/2017] [Accepted: 11/13/2017] [Indexed: 12/22/2022] Open
Abstract
In this review, we provide an up-to-date compilation of published human spermatogonial markers, with focus on the three nuclear subtypes Adark, Apale and B. In addition, we have extended our recently published list of putative spermatogonial markers with protein expression and RNA-sequencing data from the Human Protein Atlas and supported these by literature evidence. Most importantly, we have put substantial effort in acquiring a comprehensive list of new and potentially interesting markers by refiltering the raw data of 15 published germ cell expression datasets (four human, eleven rodent) and subsequent building of intersections to acquire a robust, cross-species set of spermatogonia-enriched or -specific transcripts.
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Affiliation(s)
- Kathrein von Kopylow
- Department of Andrology, University Hospital Hamburg-Eppendorf, Hamburg, Germany.
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14
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Constantin L. The Role of MicroRNAs in Cerebellar Development and Autism Spectrum Disorder During Embryogenesis. Mol Neurobiol 2016; 54:6944-6959. [PMID: 27774573 DOI: 10.1007/s12035-016-0220-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 10/12/2016] [Indexed: 02/03/2023]
Abstract
MicroRNAs (miRNAs) are a class of small non-coding RNA molecules with wide-ranging and subtle effects on protein production. Their activity during the development of the cerebellum provides a valuable exemplar of how non-coding molecules may assist the development and function of the central nervous system and drive neurodevelopmental disorders. Three distinct aspects of miRNA contribution to early cerebellar development will here be reviewed. Aspects are the establishment of the cerebellar anlage, the generation and maturation of at least two principal cell types of the developing cerebellar microcircuit, and the etiology and early progression of autism spectrum disorder. It will be argued here that the autism spectrum is an adept model to explore miRNA impact on the cognitive and affective processes that descend from the developing cerebellum.
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Affiliation(s)
- Lena Constantin
- School of Biomedical Sciences, The University of Queensland, St Lucia, QLD, 4072, Australia. .,Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD, 4072, Australia.
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15
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Mor-Shaked H, Eiges R. Modeling Fragile X Syndrome Using Human Pluripotent Stem Cells. Genes (Basel) 2016; 7:genes7100077. [PMID: 27690107 PMCID: PMC5083916 DOI: 10.3390/genes7100077] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 09/02/2016] [Accepted: 09/12/2016] [Indexed: 02/06/2023] Open
Abstract
Fragile X syndrome (FXS) is the most common heritable form of cognitive impairment. It results from a loss-of-function mutation by a CGG repeat expansion at the 5′ untranslated region of the X-linked fragile X mental retardation 1 (FMR1) gene. Expansion of the CGG repeats beyond 200 copies results in protein deficiency by leading to aberrant methylation of the FMR1 promoter and the switch from active to repressive histone modifications. Additionally, the CGGs become increasingly unstable, resulting in high degree of variation in expansion size between and within tissues of affected individuals. It is still unclear how the FMR1 protein (FMRP) deficiency leads to disease pathology in neurons. Nor do we know the mechanisms by which the CGG expansion results in aberrant DNA methylation, or becomes unstable in somatic cells of patients, at least in part due to the lack of appropriate animal or cellular models. This review summarizes the current contribution of pluripotent stem cells, mutant human embryonic stem cells, and patient-derived induced pluripotent stem cells to disease modeling of FXS for basic and applied research, including the development of new therapeutic approaches.
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Affiliation(s)
- Hagar Mor-Shaked
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center Affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel.
| | - Rachel Eiges
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center Affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel.
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16
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Cascade Screening for Fragile X Syndrome/CGG Repeat Expansions in Children Attending Special Education in Sri Lanka. PLoS One 2015; 10:e0145537. [PMID: 26694146 PMCID: PMC4687912 DOI: 10.1371/journal.pone.0145537] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Accepted: 12/04/2015] [Indexed: 01/08/2023] Open
Abstract
Fragile X syndrome (FXS) is the commonest cause of inherited mental retardation and clinically presents with learning, emotional and behaviour problems. FXS is caused by expansion of cytosine-guanine-guanine (CGG) repeats present in the 5’ untranslated region of the FMR1 gene. The aim of this study was to screen children attending special education institutions in Sri Lanka to estimate the prevalence of CGG repeat expansions. The study population comprised a representative national sample of 850 children (540 males, 310 females) with 5 to 18 years of age from moderate to severe mental retardation of wide ranging aetiology. Screening for CGG repeat expansion was carried out on DNA extracted from buccal cells using 3’ direct triplet primed PCR followed by melting curve analysis. To identify the expanded status of screened positive samples, capillary electrophoresis, methylation specific PCR and Southern hybridization were carried out using venous blood samples. Prevalence of CGG repeat expansions was 2.2%. Further classification of the positive samples into FXS full mutation, pre-mutation and grey zone gave prevalence of 1.3%, 0.8% and 0.1% respectively. All positive cases were male. No females with FXS were detected in our study may have been due to the small sample size.
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Russ J, Liu EY, Wu K, Neal D, Suh E, Irwin DJ, McMillan CT, Harms MB, Cairns NJ, Wood EM, Xie SX, Elman L, McCluskey L, Grossman M, Van Deerlin VM, Lee EB. Hypermethylation of repeat expanded C9orf72 is a clinical and molecular disease modifier. Acta Neuropathol 2015; 129:39-52. [PMID: 25388784 DOI: 10.1007/s00401-014-1365-0] [Citation(s) in RCA: 84] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 11/04/2014] [Accepted: 11/04/2014] [Indexed: 12/12/2022]
Abstract
C9orf72 promoter hypermethylation inhibits the accumulation of pathologies which have been postulated to be neurotoxic. We tested here whether C9orf72 hypermethylation is associated with prolonged disease in C9orf72 mutation carriers. C9orf72 methylation was quantified from brain or blood using methylation-sensitive restriction enzyme digest-qPCR in a cross-sectional cohort of 118 C9orf72 repeat expansion carriers and 19 non-carrier family members. Multivariate regression models were used to determine whether C9orf72 hypermethylation was associated with age at onset, disease duration, age at death, or hexanucleotide repeat expansion size. Permutation analysis was performed to determine whether C9orf72 methylation is heritable. We observed a high correlation between C9orf72 methylation across tissues including cerebellum, frontal cortex, spinal cord and peripheral blood. While C9orf72 methylation was not significantly different between ALS and FTD and did not predict age at onset, brain and blood C9orf72 hypermethylation was associated with later age at death in FTD (brain: β = 0.18, p = 0.006; blood: β = 0.15, p < 0.001), and blood C9orf72 hypermethylation was associated with longer disease duration in FTD (β = 0.03, p = 0.007). Furthermore, C9orf72 hypermethylation was associated with smaller hexanucleotide repeat length (β = -16.69, p = 0.033). Finally, analysis of pedigrees with multiple mutation carriers demonstrated a significant association between C9orf72 methylation and family relatedness (p < 0.0001). C9orf72 hypermethylation is associated with prolonged disease in C9orf72 repeat expansion carriers with FTD. The attenuated clinical phenotype associated with C9orf72 hypermethylation suggests that slower clinical progression in FTD is associated with reduced expression of mutant C9orf72. These results support the hypothesis that expression of the hexanucleotide repeat expansion is associated with a toxic gain of function.
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18
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Avitzour M, Mor-Shaked H, Yanovsky-Dagan S, Aharoni S, Altarescu G, Renbaum P, Eldar-Geva T, Schonberger O, Levy-Lahad E, Epsztejn-Litman S, Eiges R. FMR1 epigenetic silencing commonly occurs in undifferentiated fragile X-affected embryonic stem cells. Stem Cell Reports 2014; 3:699-706. [PMID: 25418717 PMCID: PMC4235235 DOI: 10.1016/j.stemcr.2014.09.001] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2014] [Revised: 08/28/2014] [Accepted: 09/01/2014] [Indexed: 12/14/2022] Open
Abstract
Fragile X syndrome (FXS) is the most common heritable form of cognitive impairment. It results from epigenetic silencing of the X-linked FMR1 gene by a CGG expansion in its 5′-untranslated region. Taking advantage of a large set of FXS-affected human embryonic stem cell (HESC) lines and isogenic subclones derived from them, we show that FMR1 hypermethylation commonly occurs in the undifferentiated state (six of nine lines, ranging from 24% to 65%). In addition, we demonstrate that hypermethylation is tightly linked with FMR1 transcriptional inactivation in undifferentiated cells, coincides with loss of H3K4me2 and gain of H3K9me3, and is unrelated to CTCF binding. Taken together, these results demonstrate that FMR1 epigenetic gene silencing takes place in FXS HESCs and clearly highlights the importance of examining multiple cell lines when investigating FXS and most likely other epigenetically regulated diseases. FMR1 epigenetic gene silencing commonly occurs in the undifferentiated FXS cells FXS HESCs are heterogeneous for repeat size and methylation levels This study underscores the importance of multiple HESC lines in disease modeling
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Affiliation(s)
- Michal Avitzour
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Hagar Mor-Shaked
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Shira Yanovsky-Dagan
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Shira Aharoni
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Gheona Altarescu
- Zohar PGD Lab, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Paul Renbaum
- Zohar PGD Lab, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Talia Eldar-Geva
- IVF Unit, Department of Obstetrics and Gynecology, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Oshrat Schonberger
- IVF Unit, Department of Obstetrics and Gynecology, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Ephrat Levy-Lahad
- Zohar PGD Lab, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Silvina Epsztejn-Litman
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel
| | - Rachel Eiges
- Stem Cell Research Laboratory, Medical Genetics Institute, Shaare Zedek Medical Center affiliated with the Hebrew University School of Medicine, Jerusalem 91031, Israel.
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19
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Liu EY, Russ J, Wu K, Neal D, Suh E, McNally AG, Irwin DJ, Van Deerlin VM, Lee EB. C9orf72 hypermethylation protects against repeat expansion-associated pathology in ALS/FTD. Acta Neuropathol 2014; 128:525-41. [PMID: 24806409 PMCID: PMC4161616 DOI: 10.1007/s00401-014-1286-y] [Citation(s) in RCA: 132] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 04/24/2014] [Accepted: 04/25/2014] [Indexed: 12/13/2022]
Abstract
Hexanucleotide repeat expansions of C9orf72 are the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal degeneration. The mutation is associated with reduced C9orf72 expression and the accumulation of potentially toxic RNA and protein aggregates. CpG methylation is known to protect the genome against unstable DNA elements and to stably silence inappropriate gene expression. Using bisulfite cloning and restriction enzyme-based methylation assays on DNA from human brain and peripheral blood, we observed CpG hypermethylation involving the C9orf72 promoter in cis to the repeat expansion mutation in approximately one-third of C9orf72 repeat expansion mutation carriers. Promoter hypermethylation of mutant C9orf72 was associated with transcriptional silencing of C9orf72 in patient-derived lymphoblast cell lines, resulting in reduced accumulation of intronic C9orf72 RNA and reduced numbers of RNA foci. Furthermore, demethylation of mutant C9orf72 with 5-aza-deoxycytidine resulted in increased vulnerability of mutant cells to oxidative and autophagic stress. Promoter hypermethylation of repeat expansion carriers was also associated with reduced accumulation of RNA foci and dipeptide repeat protein aggregates in human brains. These results indicate that C9orf72 promoter hypermethylation prevents downstream molecular aberrations associated with the hexanucleotide repeat expansion, suggesting that epigenetic silencing of the mutant C9orf72 allele may represent a protective counter-regulatory response to hexanucleotide repeat expansion.
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Affiliation(s)
- Elaine Y. Liu
- Translational Neuropathology Research Laboratory, Perelman School of Medicine at the University of Pennsylvania, 605B Stellar Chance Laboratories, 422 Curie Blvd, Philadelphia, PA 19104, USA. Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA
| | - Jenny Russ
- Translational Neuropathology Research Laboratory, Perelman School of Medicine at the University of Pennsylvania, 605B Stellar Chance Laboratories, 422 Curie Blvd, Philadelphia, PA 19104, USA. Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA
| | - Kathryn Wu
- Translational Neuropathology Research Laboratory, Perelman School of Medicine at the University of Pennsylvania, 605B Stellar Chance Laboratories, 422 Curie Blvd, Philadelphia, PA 19104, USA. Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA
| | - Donald Neal
- Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA
| | - Eunran Suh
- Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA
| | - Anna G. McNally
- Translational Neuropathology Research Laboratory, Perelman School of Medicine at the University of Pennsylvania, 605B Stellar Chance Laboratories, 422 Curie Blvd, Philadelphia, PA 19104, USA. Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA
| | - David J. Irwin
- Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA. Department of Neurology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA
| | - Vivianna M. Van Deerlin
- Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, USA
| | - Edward B. Lee
- Translational Neuropathology Research Laboratory, Perelman School of Medicine at the University of Pennsylvania, 605B Stellar Chance Laboratories, 422 Curie Blvd, Philadelphia, PA 19104, USA
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Pretto D, Yrigollen CM, Tang HT, Williamson J, Espinal G, Iwahashi CK, Durbin-Johnson B, Hagerman RJ, Hagerman PJ, Tassone F. Clinical and molecular implications of mosaicism in FMR1 full mutations. Front Genet 2014; 5:318. [PMID: 25278957 PMCID: PMC4166380 DOI: 10.3389/fgene.2014.00318] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 08/25/2014] [Indexed: 12/27/2022] Open
Abstract
Expansions of more than 200 CGG repeats (full mutation) in the FMR1 gene give rise to fragile X syndrome (FXS) through a process that generally involves hypermethylation of the FMR1 promoter region and gene silencing, resulting in absence of expression of the encoded protein, FMRP. However, mosaicism with alleles differing in size and extent of methylation often exist within or between tissues of individuals with FXS. In the current work, CGG-repeat lengths and methylation status were assessed for eighteen individuals with FXS, including 13 mosaics, for which peripheral blood cells (PBMCs) and primary fibroblast cells were available. Our results show that for both PBMCs and fibroblasts, FMR1 mRNA and FMRP expression are directly correlated with the percent of methylation of the FMR1 allele. In addition, Full Scale IQ scores were inversely correlated with the percent methylation and positively correlated with higher FMRP expression. These latter results point toward a positive impact on cognition for full mutation mosaics with lower methylation compared to individuals with fully methylated, full mutation alleles. However, we did not observe a significant reduction in the number of seizures, nor in the severity of hyperactivity or autism spectrum disorder, among individuals with mosaic genotypes in the presentation of FXS. These observations suggest that low, but non-zero expression of FMRP may be sufficient to positively impact cognitive function in individuals with FXS, with methylation mosaicism (lowered methylation fraction) contributing to a more positive clinical outcome.
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Affiliation(s)
- Dalyir Pretto
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Carolyn M Yrigollen
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Hiu-Tung Tang
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - John Williamson
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Glenda Espinal
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Chris K Iwahashi
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Blythe Durbin-Johnson
- Department of Public Health Sciences, School of Medicine, University of California at Davis Davis, CA, USA
| | - Randi J Hagerman
- Department of Pediatrics, School of Medicine, University of California at Davis Davis, CA, USA ; MIND Institute, UC Davis Medical Center Sacramento, CA, USA
| | - Paul J Hagerman
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA ; Department of Pediatrics, School of Medicine, University of California at Davis Davis, CA, USA
| | - Flora Tassone
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA ; Department of Pediatrics, School of Medicine, University of California at Davis Davis, CA, USA
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21
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Biancalana V, Glaeser D, McQuaid S, Steinbach P. EMQN best practice guidelines for the molecular genetic testing and reporting of fragile X syndrome and other fragile X-associated disorders. Eur J Hum Genet 2014; 23:417-25. [PMID: 25227148 PMCID: PMC4666582 DOI: 10.1038/ejhg.2014.185] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Revised: 07/09/2014] [Accepted: 07/10/2014] [Indexed: 01/25/2023] Open
Abstract
Different mutations occurring in the unstable CGG repeat in 5' untranslated region of FMR1 gene are responsible for three fragile X-associated disorders. An expansion of over ∼200 CGG repeats when associated with abnormal methylation and inactivation of the promoter is the mutation termed ‘full mutation' and is responsible for fragile X syndrome (FXS), a neurodevelopmental disorder described as the most common cause of inherited intellectual impairment. The term ‘abnormal methylation' is used here to distinguish the DNA methylation induced by the expanded repeat from the ‘normal methylation' occurring on the inactive X chromosomes in females with normal, premutation, and full mutation alleles. All male and roughly half of the female full mutation carriers have FXS. Another anomaly termed ‘premutation' is characterized by the presence of 55 to ∼200 CGGs without abnormal methylation, and is the cause of two other diseases with incomplete penetrance. One is fragile X-associated primary ovarian insufficiency (FXPOI), which is characterized by a large spectrum of ovarian dysfunction phenotypes and possible early menopause as the end stage. The other is fragile X-associated tremor/ataxia syndrome (FXTAS), which is a late onset neurodegenerative disorder affecting males and females. Because of the particular pattern and transmission of the CGG repeat, appropriate molecular testing and reporting is very important for the optimal genetic counselling in the three fragile X-associated disorders. Here, we describe best practice guidelines for genetic analysis and reporting in FXS, FXPOI, and FXTAS, including carrier and prenatal testing.
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Affiliation(s)
- Valérie Biancalana
- Laboratoire Diagnostic Génétique, Faculté de Médecine-CHRU, Strasbourg, France
| | | | - Shirley McQuaid
- National Centre for Medical Genetics, Our Lady's Children's Hospital, Crumlin, Dublin, Ireland
| | - Peter Steinbach
- Institute of Human Genetics, University Hospital of Ulm, Ulm, Germany
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22
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Jorge P, Mota-Freitas MM, Santos R, Silva ML, Soares G, Fortuna AM. A 26-Year Experience in Chorionic Villus Sampling Prenatal Genetic Diagnosis. J Clin Med 2014; 3:838-48. [PMID: 26237480 PMCID: PMC4449647 DOI: 10.3390/jcm3030838] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2014] [Revised: 06/20/2014] [Accepted: 06/23/2014] [Indexed: 12/04/2022] Open
Abstract
This report describes the trends of chorionic villus sampling (CVS) referred for prenatal genetic diagnosis in the past two and a half decades in a Portuguese Center. Our cohort of 491 CVS was mostly performed by the transcervical method at the 12th gestational week. Data collected within the framework of this study relate to the following: sampling method, referral reason versus abnormality and incidence of procedure-related pregnancy loss, that declined to about 0.5% over the last 15 years. The year 2000 represented a change in referral reasons for chorionic tissue collection, shifting from almost exclusively for cytogenetic testing to an increasing number of molecular tests for monogenic disorders. Herein, success rates as well as cytogenetic and/or molecular DNA results are presented. These latter include not only tests for several monogenic disorders, but also aneuploidy and maternal cell contamination screening. This retrospective analysis reiterates that CVS is a safe and reliable first trimester technique for prenatal diagnosis in high genetic risk pregnancies.
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Affiliation(s)
- Paula Jorge
- Center of Medical Genetics Doutor Jacinto Magalhães, Oporto Hospital Center, C.H.P., EPE, Praça Pedro Nunes, 88, 4099-028 Porto, Portugal.
- Unit for Multidisciplinary Research in Biomedicine, UMIB, ICBAS-UP, Rua Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal.
| | - Maria Manuela Mota-Freitas
- Center of Medical Genetics Doutor Jacinto Magalhães, Oporto Hospital Center, C.H.P., EPE, Praça Pedro Nunes, 88, 4099-028 Porto, Portugal.
- Unit for Multidisciplinary Research in Biomedicine, UMIB, ICBAS-UP, Rua Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal.
| | - Rosário Santos
- Center of Medical Genetics Doutor Jacinto Magalhães, Oporto Hospital Center, C.H.P., EPE, Praça Pedro Nunes, 88, 4099-028 Porto, Portugal.
- Unit for Multidisciplinary Research in Biomedicine, UMIB, ICBAS-UP, Rua Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal.
| | - Maria Luz Silva
- Center of Medical Genetics Doutor Jacinto Magalhães, Oporto Hospital Center, C.H.P., EPE, Praça Pedro Nunes, 88, 4099-028 Porto, Portugal.
| | - Gabriela Soares
- Center of Medical Genetics Doutor Jacinto Magalhães, Oporto Hospital Center, C.H.P., EPE, Praça Pedro Nunes, 88, 4099-028 Porto, Portugal.
| | - Ana Maria Fortuna
- Center of Medical Genetics Doutor Jacinto Magalhães, Oporto Hospital Center, C.H.P., EPE, Praça Pedro Nunes, 88, 4099-028 Porto, Portugal.
- Unit for Multidisciplinary Research in Biomedicine, UMIB, ICBAS-UP, Rua Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal.
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23
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Usdin K, Hayward BE, Kumari D, Lokanga RA, Sciascia N, Zhao XN. Repeat-mediated genetic and epigenetic changes at the FMR1 locus in the Fragile X-related disorders. Front Genet 2014; 5:226. [PMID: 25101111 PMCID: PMC4101883 DOI: 10.3389/fgene.2014.00226] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Accepted: 06/29/2014] [Indexed: 01/01/2023] Open
Abstract
The Fragile X-related disorders are a group of genetic conditions that include the neurodegenerative disorder, Fragile X-associated tremor/ataxia syndrome (FXTAS), the fertility disorder, Fragile X-associated primary ovarian insufficiency (FXPOI) and the intellectual disability, Fragile X syndrome (FXS). The pathology in all these diseases is related to the number of CGG/CCG-repeats in the 5′ UTR of the Fragile X mental retardation 1 (FMR1) gene. The repeats are prone to continuous expansion and the increase in repeat number has paradoxical effects on gene expression increasing transcription on mid-sized alleles and decreasing it on longer ones. In some cases the repeats can simultaneously both increase FMR1 mRNA production and decrease the levels of the FMR1 gene product, Fragile X mental retardation 1 protein (FMRP). Since FXTAS and FXPOI result from the deleterious consequences of the expression of elevated levels of FMR1 mRNA and FXS is caused by an FMRP deficiency, the clinical picture is turning out to be more complex than once appreciated. Added complications result from the fact that increasing repeat numbers make the alleles somatically unstable. Thus many individuals have a complex mixture of different sized alleles in different cells. Furthermore, it has become apparent that the eponymous fragile site, once thought to be no more than a useful diagnostic criterion, may have clinical consequences for females who inherit chromosomes that express this site. This review will cover what is currently known about the mechanisms responsible for repeat instability, for the repeat-mediated epigenetic changes that affect expression of the FMR1 gene, and for chromosome fragility. It will also touch on what current and future options are for ameliorating some of these effects.
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Affiliation(s)
- Karen Usdin
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda MD, USA
| | - Bruce E Hayward
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda MD, USA
| | - Daman Kumari
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda MD, USA
| | - Rachel A Lokanga
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda MD, USA
| | - Nicholas Sciascia
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda MD, USA
| | - Xiao-Nan Zhao
- Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda MD, USA
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Pretto DI, Mendoza-Morales G, Lo J, Cao R, Hadd A, Latham GJ, Durbin-Johnson B, Hagerman R, Tassone F. CGG allele size somatic mosaicism and methylation in FMR1 premutation alleles. J Med Genet 2014; 51:309-18. [PMID: 24591415 DOI: 10.1136/jmedgenet-2013-102021] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BACKGROUND Greater than 200 CGG repeats in the 5'UTR of the FMR1 gene lead to epigenetic silencing and lack of the FMR1 protein, causing fragile X Syndrome. Individual carriers of a premutation (PM) allele with 55-200 CGG repeats are typically unmethylated and can present with clinical features defined as FMR1-associated conditions. METHODS Blood samples from 17 male PM carriers were assessed clinically and molecularly by Southern blot, western blot, PCR and QRT-PCR. Blood and brain tissue from an additional 18 PM males were also similarly examined. Continuous outcomes were modelled using linear regression and binary outcomes were modelled using logistic regression. RESULTS Methylated alleles were detected in different fractions of blood cells in all PM cases (n=17). CGG repeat numbers correlated with percent of methylation and mRNA levels and, especially in the upper PM range, with greater number of clinical involvements. Inter-tissue/intra-tissue somatic instability and differences in percent methylation were observed between blood and fibroblasts (n=4) and also observed between blood and different brain regions in three of the 18 PM cases examined. CGG repeat lengths in lymphocytes remained unchanged over a period of time ranging from 2 to 6 years, three cases for whom multiple samples were available. CONCLUSIONS In addition to CGG size instability, individuals with a PM expanded allele can exhibit methylation and display more clinical features likely due to RNA toxicity and/or FMR1 silencing. The observed association between CGG repeat length and percent of methylation with the severity of the clinical phenotypes underscores the potential value of methylation in affected PM to further understand penetrance, inform diagnosis and expand treatment options.
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Affiliation(s)
- Dalyir I Pretto
- Department of Biochemistry and Molecular Medicine, University of California Davis, School of Medicine, Sacramento, California, USA
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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: 95] [Impact Index Per Article: 9.5] [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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Peterson SE, Loring JF. Genomic instability in pluripotent stem cells: implications for clinical applications. J Biol Chem 2013; 289:4578-84. [PMID: 24362040 DOI: 10.1074/jbc.r113.516419] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Human pluripotent stem cells (hPSCs) are known to acquire genomic changes as they proliferate and differentiate. Despite concerns that these changes will compromise the safety of hPSC-derived cell therapy, there is currently scant evidence linking the known hPSC genomic abnormalities with malignancy. For the successful use of hPSCs for clinical applications, we will need to learn to distinguish between innocuous genomic aberrations and those that may cause tumors. To minimize any effects of acquired mutations on cell therapy, we strongly recommend that cells destined for transplant be monitored throughout their preparation using a high-resolution method such as SNP genotyping.
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Affiliation(s)
- Suzanne E Peterson
- From the Department of Chemical Physiology and Center for Regenerative Medicine, The Scripps Research Institute, La Jolla, California 92037
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Huang W, Luo S, Ou J, Zhu F, Xia Y, Xue J, Pan Q, Wu L, Duan R. Correlation betweenFMR1expression and clinical phenotype in discordant dichorionic–diamniotic monozygotic twin sisters with the fragile x mutation. J Med Genet 2013; 51:159-64. [DOI: 10.1136/jmedgenet-2013-101978] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Gerhardt J, Tomishima MJ, Zaninovic N, Colak D, Yan Z, Zhan Q, Rosenwaks Z, Jaffrey SR, Schildkraut CL. The DNA replication program is altered at the FMR1 locus in fragile X embryonic stem cells. Mol Cell 2013; 53:19-31. [PMID: 24289922 DOI: 10.1016/j.molcel.2013.10.029] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 09/04/2013] [Accepted: 10/23/2013] [Indexed: 01/17/2023]
Abstract
Fragile X syndrome (FXS) is caused by a CGG repeat expansion in the FMR1 gene that appears to occur during oogenesis and during early embryogenesis. One model proposes that repeat instability depends on the replication fork direction through the repeats such that (CNG)n hairpin-like structures form, causing DNA polymerase to stall and slip. Examining DNA replication fork progression on single DNA molecules at the endogenous FMR1 locus revealed that replication forks stall at CGG repeats in human cells. Furthermore, replication profiles of FXS human embryonic stem cells (hESCs) compared to nonaffected hESCs showed that fork direction through the repeats is altered at the FMR1 locus in FXS hESCs, such that predominantly the CCG strand serves as the lagging-strand template. This is due to the absence of replication initiation that would typically occur upstream of FMR1, suggesting that altered replication origin usage combined with fork stalling promotes repeat instability during early embryonic development.
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Affiliation(s)
- Jeannine Gerhardt
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | - Mark J Tomishima
- SKI Stem Cell Research Facility, Sloan-Kettering Institute, New York, NY 10065, USA
| | - Nikica Zaninovic
- Center for Reproductive Medicine and Infertility, Weill Cornell Medical College, New York, NY 10065, USA
| | - Dilek Colak
- Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065, USA
| | - Zi Yan
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Qiansheng Zhan
- Center for Reproductive Medicine and Infertility, Weill Cornell Medical College, New York, NY 10065, USA
| | - Zev Rosenwaks
- Center for Reproductive Medicine and Infertility, Weill Cornell Medical College, New York, NY 10065, USA
| | - Samie R Jaffrey
- Department of Pharmacology, Weill Cornell Medical College, New York, NY 10065, USA
| | - Carl L Schildkraut
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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Sharony R, Shtorch A, Amiel A, Guetta E, Peleg L, Pras E, Ries-Levavi L. Three peaks in the polymerase chain reaction fragile X analysis. J Med Screen 2012; 19:112-5. [DOI: 10.1258/jms.2012.012029] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Objective To report and discuss the observation of three fragments on polymerase chain reaction (PCR) in routine carrier screening for fragile X. Methods From 2005 through 2010, 34,500 women underwent prenatal screening for fragile X. PCR was carried out to amplify the repeat segment. The resulting fragments were scanned by a genetic analyser. Results Three PCR peaks representing three different-sized fragments were found in 25 of the 34,500 women (1:1380 or 0.072%). Karyotype analysis was performed in 16 subjects. Full triple X was found in three women, while two had triple X mosaicism. Of the 16 karyotyped women, five (31%) had a finding of XXX (full or mosaic). Conclusions Triple X (full or mosaic) is the most frequently encountered mechanism responsible for three peaks on fragile X PCR testing.
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Affiliation(s)
- Reuven Sharony
- Vice Chairman, The Genetic Institute and Ob/Gyn Department, Meir Medical Center, Kfar Saba, Israel; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Atalia Shtorch
- Head of the molecular lab, The Genetic Institute, Meir Medical Center, Kfar Saba, Israel
| | - Aliza Amiel
- Head of the cytogenetic lab, The Genetic Institute, Meir Medical Center, Kfar Saba, Israel; The Life Science Faculty, Bar Ilan University, Ramat Gan, Israel
| | - Esther Guetta
- Head of the cytogenetic unit, The Genetic Institute, Sheba Medical Center, Ramat Gan, Israel
| | - Leah Peleg
- Head of the Genetic Lab, The Genetic Institute, Sheba Medical Center, Ramat Gan, Israel
| | - Elon Pras
- Head of the Genetic Institute; The Genetic Institute, Sheba Medical Center, Ramat Gan, Israel; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Liat Ries-Levavi
- Head of the Molecular unit, The Genetic Institute, Sheba Medical Center, Ramat Gan, Israel
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Godler DE, Slater HR, Bui QM, Storey E, Ono MY, Gehling F, Inaba Y, Francis D, Hopper JL, Kinsella G, Amor DJ, Hagerman RJ, Loesch DZ. Fragile X Mental Retardation 1 (FMR1) Intron 1 Methylation in Blood Predicts Verbal Cognitive Impairment in Female Carriers of Expanded FMR1 Alleles: Evidence from a Pilot Study. Clin Chem 2012; 58:590-8. [DOI: 10.1373/clinchem.2011.177626] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Abstract
BACKGROUND
Cognitive status in females with mutations in the FMR1 (fragile X mental retardation 1) gene is highly variable. A biomarker would be of value for predicting which individuals were liable to develop cognitive impairment and could benefit from early intervention. A detailed analysis of CpG sites bridging exon 1 and intron 1 of FMR1, known as fragile X–related epigenetic element 2 (FREE2), suggests that a simple blood test could identify these individuals.
METHODS
Study participants included 74 control females (<40 CGG repeats), 62 premutation (PM) females (55–200 CGG repeats), and 18 full-mutation (FM) females assessed with Wechsler intelligence quotient (IQ) tests. We used MALDI-TOF mass spectrometry to determine the methylation status of FREE2 CpG sites that best identified low-functioning (IQ <70) FM females (>200 CGG repeats), compared the results with those for Southern blot FMR1 activation ratios, and related these assessments to the level of production of the FMR1 protein product in blood.
RESULTS
A methylation analysis of intron 1 CpG sites 10–12 showed the highest diagnostic sensitivity (100%) and specificity (98%) of all the molecular measures tested for detecting females with a standardized verbal IQ of <70 among the study participants. In the group consisting of only FM females, methylation of these sites was significantly correlated with full-scale IQ, verbal IQ, and performance IQ. Several verbal subtest scores showed strong correlation with the methylation of these sites (P = 1.2 × 10−5) after adjustment for multiple measures.
CONCLUSIONS
The data suggest that hypermethylation of the FMR1 intron 1 sites in blood is predictive of cognitive impairment in FM females, with implications for improved fragile X syndrome diagnostics in young children and screening of the newborn population.
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Affiliation(s)
- David E Godler
- Victorian Clinical Genetics Services, Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
| | - Howard R Slater
- Victorian Clinical Genetics Services, Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
- Department of Paediatrics, University of Melbourne, Melbourne, Australia
| | - Quang M Bui
- Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Carlton, Australia
| | - Elsdon Storey
- Van Cleef Roet Centre for Nervous Diseases, Department of Medicine, Monash University, Melbourne, Australia
| | - Michele Y Ono
- UC Davis MIND Institute, Sacramento, CA
- Department of Pediatrics, University of California, Davis, School of Medicine, Sacramento, CA
| | - Freya Gehling
- Victorian Clinical Genetics Services, Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
| | - Yoshimi Inaba
- Victorian Clinical Genetics Services, Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
| | - David Francis
- Victorian Clinical Genetics Services, Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
| | - John L Hopper
- Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Carlton, Australia
| | - Glynda Kinsella
- School of Psychological Science, La Trobe University, Melbourne, Australia
| | - David J Amor
- Victorian Clinical Genetics Services, Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
- Department of Paediatrics, University of Melbourne, Melbourne, Australia
| | - Randi J Hagerman
- UC Davis MIND Institute, Sacramento, CA
- Department of Pediatrics, University of California, Davis, School of Medicine, Sacramento, CA
| | - Danuta Z Loesch
- School of Psychological Science, La Trobe University, Melbourne, Australia
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Clinical utility gene card for: fragile X mental retardation syndrome, fragile X-associated tremor/ataxia syndrome and fragile X-associated primary ovarian insufficiency. Eur J Hum Genet 2011; 19:ejhg201155. [PMID: 21540884 DOI: 10.1038/ejhg.2011.55] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
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The first case described: monozygotic twin sisters with the fragile X premutation but with a different phenotype for premature ovarian failure. Fertil Steril 2011; 95:2431.e13-5. [PMID: 21300345 DOI: 10.1016/j.fertnstert.2011.01.039] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Revised: 01/06/2011] [Accepted: 01/07/2011] [Indexed: 01/19/2023]
Abstract
OBJECTIVE To describe the first case of monozygotic twin sisters with fragile X premutation and discordance for premature ovarian failure (POF). DESIGN A descriptive case study. SETTING Academic center. PATIENT(S) Monozygotic twin sisters with fragile X premutation and discordance for POF. INTERVENTION(S) Serum laboratory testing, fragile X premutation screening, zygosity testing, X-inactivation ratio and Southern blot studies. MAIN OUTCOME MEASURE(S) Incidence of POF in this twin cohort. RESULT(S) Zygosity analysis using polymerase chain reaction of 15 polymorphic markers via capillary gel electrophoresis in these patients confirmed their monozygosity. X-inactivation studies were performed using the human androgen receptor (HUMARA) gene and revealed similar X-inactivation ratios for both the patient and her sister (11:89 and 12:88, respectively) from peripheral serum samples. Southern blot evaluation of the proband and her sister revealed a similar methylation pattern in which the premutation allele was unmethylated much more than the normal allele. The contribution of the premutation on the active allele as determined by Southern blot analysis was consistent between sisters. CONCLUSION(S) The inactivation ratio studies and subsequent Southern blot analysis do not show differences between the patients; therefore, we are unable to identify a causative mechanism for the identical sisters' discordant phenotypes. It is possible that the inactivation ratios observed from the peripheral blood specimens obtained from the sisters do not represent the allele expression and skewing present at the level of the ovary.
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López Castel A, Nakamori M, Tomé S, Chitayat D, Gourdon G, Thornton CA, Pearson CE. Expanded CTG repeat demarcates a boundary for abnormal CpG methylation in myotonic dystrophy patient tissues. Hum Mol Genet 2010; 20:1-15. [PMID: 21044947 DOI: 10.1093/hmg/ddq427] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Myotonic dystrophy (DM1) affects multiple organs, shows age-dependent progression and is caused by CTG expansions at the DM1 locus. We determined the DM1 CpG methylation profile and CTG length in tissues from DM1 foetuses, DM1 adults, non-affected individuals and transgenic DM1 mice. Analysis included CTCF binding sites upstream and downstream of the CTG tract, as methylation-sensitive CTCF binding affects chromatinization and transcription of the DM1 locus. In humans, in a given foetus, expansions were largest in heart and smallest in liver, differing by 40-400 repeats; in adults, the largest expansions were in heart and cerebral cortex and smallest in cerebellum, differing by up to 5770 repeats in the same individual. Abnormal methylation was specific to the mutant allele. In DM1 adults, heart, liver and cortex showed high-to-moderate methylation levels, whereas cerebellum, kidney and skeletal muscle were devoid of methylation. Methylation decreased between foetuses and adults. Contrary to previous findings, methylation was not restricted to individuals with congenital DM1. The expanded repeat demarcates an abrupt boundary of methylation. Upstream sequences, including the CTCF site, were methylated, whereas the repeat itself and downstream sequences were not. In DM1 mice, expansion-, tissue- and age-specific methylation patterns were similar but not identical to those in DM1 individuals; notably in mice, methylation was present up- and downstream of the repeat, but greater upstream. Thus, in humans, the CpG-free expanded CTG repeat appears to maintain a highly polarized pattern of CpG methylation at the DM1 locus, which varies markedly with age and tissues.
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Affiliation(s)
- Arturo López Castel
- Genetics and Genome Biology, Department of Pediatrics, The Hospital for Sick Children, and Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
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Abstract
Development from separate parental germ cells through fertilization and proceeding to a fully functioning adult animal occurs through an intricate program of transcriptional and chromatin changes. Epigenetic alterations such as DNA methylation are an important part of this process. This review looks at the role of DNA methylation in early embryonic development, as well as how this epigenetic mark affects stem cell differentiation and tissue-specific gene expression in somatic cells.
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Affiliation(s)
- Theresa M Geiman
- Laboratory of Cancer Prevention, National Cancer Institute-Frederick, SAIC-Frederick, MD 21702, USA.
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Godler DE, Tassone F, Loesch DZ, Taylor AK, Gehling F, Hagerman RJ, Burgess T, Ganesamoorthy D, Hennerich D, Gordon L, Evans A, Choo KH, Slater HR. Methylation of novel markers of fragile X alleles is inversely correlated with FMRP expression and FMR1 activation ratio. Hum Mol Genet 2010; 19:1618-32. [PMID: 20118148 DOI: 10.1093/hmg/ddq037] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The fragile X syndrome (FXS) is caused by silencing of the fragile X mental retardation gene (FMR1) and the absence of its product, fragile X mental retardation protein (FMRP), resulting from CpG island methylation associated with large CGG repeat expansions (more than 200) termed full mutation (FM). We have identified a number of novel epigenetic markers for FXS using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), naming the most informative fragile X-related epigenetic element 1 (FREE1) and 2 (FREE2). Methylation of both regions was correlated with that of the FMR1 CpG island detected using Southern blot (FREE1 R = 0.97; P < 0.00001, n = 23 and FREE2 R = 0.93; P < 0.00001, n = 23) and negatively correlated with lymphocyte expression of FMRP (FREE1 R = -0.62; P = 0.01, n = 15 and FREE2 R = -0.55; P = 0.03, n = 15) in blood of partially methylated 'high functioning' FM males. In blood of FM carrier females, methylation of both markers was inversely correlated with the FMR1 activation ratio (FREE1 R = -0.93; P < 0.0001, n = 12 and FREE2 R = -0.95; P < 0.0001, n = 9). In a sample set of 49 controls, 18 grey zone (GZ 40-54 repeats), 22 premutation (PM 55-170 repeats) and 22 (affected) FXS subjects, the FREE1 methylation pattern was consistent between blood and chorionic villi as a marker of methylated FM alleles and could be used to differentiate FXS males and females from controls, as well as from carriers of GZ/PM alleles, but not between GZ and PM alleles and controls. Considering its high-throughput and specificity for pathogenic FM alleles, low cost and minimal DNA requirements, FREE MALDI-TOF MS offers a unique tool in FXS diagnostics and newborn population screening.
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Affiliation(s)
- David Eugeny Godler
- Chromosome and Chromatin Research Laboratory, The Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Victoria 3052, Australia.
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Tau GZ, Peterson BS. Normal development of brain circuits. Neuropsychopharmacology 2010; 35:147-68. [PMID: 19794405 PMCID: PMC3055433 DOI: 10.1038/npp.2009.115] [Citation(s) in RCA: 825] [Impact Index Per Article: 58.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/11/2009] [Revised: 07/22/2009] [Accepted: 07/23/2009] [Indexed: 01/05/2023]
Abstract
Spanning functions from the simplest reflex arc to complex cognitive processes, neural circuits have diverse functional roles. In the cerebral cortex, functional domains such as visual processing, attention, memory, and cognitive control rely on the development of distinct yet interconnected sets of anatomically distributed cortical and subcortical regions. The developmental organization of these circuits is a remarkably complex process that is influenced by genetic predispositions, environmental events, and neuroplastic responses to experiential demand that modulates connectivity and communication among neurons, within individual brain regions and circuits, and across neural pathways. Recent advances in neuroimaging and computational neurobiology, together with traditional investigational approaches such as histological studies and cellular and molecular biology, have been invaluable in improving our understanding of these developmental processes in humans in both health and illness. To contextualize the developmental origins of a wide array of neuropsychiatric illnesses, this review describes the development and maturation of neural circuits from the first synapse through critical periods of vulnerability and opportunity to the emergent capacity for cognitive and behavioral regulation, and finally the dynamic interplay across levels of circuit organization and developmental epochs.
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Affiliation(s)
- Gregory Z Tau
- Division of Child and Adolescent Psychiatry, Columbia University and the New York State Psychiatric Institute, New York, NY, USA.
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Brouwer J, Willemsen R, Oostra B. The FMR1 gene and fragile X-associated tremor/ataxia syndrome. Am J Med Genet B Neuropsychiatr Genet 2009; 150B:782-98. [PMID: 19105204 PMCID: PMC4320942 DOI: 10.1002/ajmg.b.30910] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The CGG-repeat present in the 5'UTR of the FMR1 gene is unstable upon transmission to the next generation. The repeat is up to 55 CGGs long in the normal population. In fragile X patients, a repeat length exceeding 200 CGGs (full mutation: FM) generally leads to methylation of the repeat and the promoter region, which is accompanied by silencing of the FMR1 gene. The gene product FMRP is involved in regulation of transport and translation of certain mRNA in the dendrite, thereby affecting synaptic plasticity. This is central to learning and memory processes. The absence of FMRP seen in FM is the cause of the mental retardation seen in fragile X patients. The premutation (PM) is defined as 55-200 CGGs. Female PM carriers are at risk of developing primary ovarian insufficiency. Recently it was discovered that elderly PM carriers might develop a progressive neurodegenerative disorder called fragile X-associated tremor/ataxia syndrome. Although arising from the mutations in the same gene, distinct mechanisms lead to fragile X syndrome (absence of FMRP) and FXTAS (toxic RNA gain of function). The pathogenic mechanisms thought to underlie these disorders are discussed, with a specific emphasis on FXTAS. This review gives insight on the implications of all possible repeat length categories seen in fragile X families.
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Affiliation(s)
- J.R. Brouwer
- Department of Clinical Genetics, ErasmusMC, Rotterdam, The Netherlands
| | - R. Willemsen
- Department of Clinical Genetics, ErasmusMC, Rotterdam, The Netherlands
| | - B.A. Oostra
- Department of Clinical Genetics, ErasmusMC, Rotterdam, The Netherlands
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Instability and chromatin structure of expanded trinucleotide repeats. Trends Genet 2009; 25:288-97. [PMID: 19540013 DOI: 10.1016/j.tig.2009.04.007] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Revised: 04/29/2009] [Accepted: 04/30/2009] [Indexed: 12/16/2022]
Abstract
Trinucleotide repeat expansion underlies at least 17 neurological diseases. In affected individuals, the expanded locus is characterized by dramatic changes in chromatin structure and in repeat tract length. Interestingly, recent studies show that several chromatin modifiers, including a histone acetyltransferase, a DNA methyltransferase and the chromatin insulator CTCF can modulate repeat instability. Here, we propose that the unusual chromatin structure of expanded repeats directly impacts their instability. We discuss several potential models for how this might occur, including a role for DNA repair-dependent epigenetic reprogramming in increasing repeat instability, and the capacity of epigenetic marks to alter sense and antisense transcription, thereby affecting repeat instability.
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Nolin SL, Ding XH, Houck GE, Brown WT, Dobkin C. Fragile X full mutation alleles composed of few alleles: Implications for CGG repeat expansion. Am J Med Genet A 2007; 146A:60-5. [DOI: 10.1002/ajmg.a.32087] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Pearson CE, Nichol Edamura K, Cleary JD. Repeat instability: mechanisms of dynamic mutations. Nat Rev Genet 2005; 6:729-42. [PMID: 16205713 DOI: 10.1038/nrg1689] [Citation(s) in RCA: 656] [Impact Index Per Article: 34.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Disease-causing repeat instability is an important and unique form of mutation that is linked to more than 40 neurological, neurodegenerative and neuromuscular disorders. DNA repeat expansion mutations are dynamic and ongoing within tissues and across generations. The patterns of inherited and tissue-specific instability are determined by both gene-specific cis-elements and trans-acting DNA metabolic proteins. Repeat instability probably involves the formation of unusual DNA structures during DNA replication, repair and recombination. Experimental advances towards explaining the mechanisms of repeat instability have broadened our understanding of this mutational process. They have revealed surprising ways in which metabolic pathways can drive or protect from repeat instability.
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Affiliation(s)
- Christopher E Pearson
- Program of Genetics and Genomic Biology, The Hospital for Sick Children, 15-312, TMDT, 101 College Street, East Tower, Toronto, Ontario M5G 1L7, Canada.
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41
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Nichol Edamura K, Leonard MR, Pearson CE. Role of replication and CpG methylation in fragile X syndrome CGG deletions in primate cells. Am J Hum Genet 2005; 76:302-11. [PMID: 15625623 PMCID: PMC1196375 DOI: 10.1086/427928] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2004] [Accepted: 12/08/2004] [Indexed: 01/22/2023] Open
Abstract
Instability of the fragile X CGG repeat involves both maternally derived expansions and deletions in the gametes of full-mutation males. It has also been suggested that the absence of aberrant CpG methylation may enhance repeat deletions through an unknown process. The effect of CGG tract length, DNA replication direction, location of replication initiation, and CpG methylation upon CGG stability were investigated using an SV40 primate replication system. Replication-dependant deletions with 53 CGG repeats were observed when replication was initiated proximal to the repeat, with CGG as the lagging-strand template. When we initiated replication further from the repeat, while maintaining CGG as the lagging-strand template or using CCG as the lagging-strand template, significant instability was not observed. CpG methylation of the unstable template stabilized the repeat, decreasing both the frequency and the magnitude of deletion events. Furthermore, CpG methylation slowed the efficiency of replication for all templates. Interestingly, replication forks displayed no evidence of a block at the CGG repeat tract, regardless of replication direction or CpG methylation status. Templates with 20 CGG repeats were stable under all circumstances. These results reveal that CGG deletions occur during replication and are sensitive to replication-fork dynamics, tract length, and CpG methylation.
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Affiliation(s)
- Kerrie Nichol Edamura
- Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Program of Molecular and Medical Genetics, University of Toronto, Toronto
| | - Michelle R. Leonard
- Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Program of Molecular and Medical Genetics, University of Toronto, Toronto
| | - Christopher E. Pearson
- Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Program of Molecular and Medical Genetics, University of Toronto, Toronto
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42
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Kovtun IV, Thornhill AR, McMurray CT. Somatic deletion events occur during early embryonic development and modify the extent of CAG expansion in subsequent generations. Hum Mol Genet 2004; 13:3057-68. [PMID: 15496421 DOI: 10.1093/hmg/ddh325] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Alterations in trinucleotide repeat length during transmission are important in the pathophysiology of Huntington's disease (HD). However, it is not well understood where, when and by what mechanism expansion occurs. We have followed the fate of CAG repeats during development in mice that can [hHD(-/+)/Msh2(+/+)] or cannot [hHD(-/+)/Msh2(-/-)] expand their repeats. Here we show that long repeats are shortened during somatic replication early in the embryo of the progeny. Our data point to different mechanisms for expansion and deletion. Deletions arise during replication, do not depend on the presence of Msh2 and are largely restricted to early development. In contrast, expansions depend on strand break repair, require the presence of Msh2 and occur later in development. Overall, these results suggest that deletions in early development serve as a safeguard of the genome and protect against expansion of the disease-range repeats during transmission.
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Affiliation(s)
- I V Kovtun
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic and Foundation, Rochester, MN 55905, USA
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43
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Gorbunova V, Seluanov A, Mittelman D, Wilson JH. Genome-wide demethylation destabilizes CTG.CAG trinucleotide repeats in mammalian cells. Hum Mol Genet 2004; 13:2979-89. [PMID: 15459182 DOI: 10.1093/hmg/ddh317] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Many neurological diseases, including myotonic dystrophy, Huntington's disease and several spinocerebellar ataxias, result from intergenerational increases in the length of a CTG.CAG repeat tract. Although the basis for intergenerational repeat expansion is unclear, repeat tracts are especially unstable during germline development and production of gametes. Mammalian development is characterized by waves of genome-wide demethylation and remethylation. To test whether changes in methylation status might contribute to trinucleotide repeat instability, we examined the effects of DNA methyltransferase inhibitors on trinucleotide repeat stability in mammalian cells. Using a selectable genetic system for detection of repeat contractions in CHO cells, we showed that the rate of contractions increased >1000-fold upon treatment with the DNA methyltransferase inhibitor 5-aza-deoxycytidine (5-aza-CdR). The link between DNA demethylation and repeat instability was strengthened by similar results obtained with hydralazine treatment, which inhibits expression of DNA methyltransferase. In human cells from myotonic dystrophy patients, treatment with 5-aza-CdR strongly destabilized repeat tracts in the DMPK gene, with a clear bias toward expansion. The bias toward expansion events and changes in repeat length that occur in jumps, rather than by accumulation of small changes, are reminiscent of the intergenerational repeat instability observed in human patients. The dramatic destabilizing effect of DNA methyltransferase inhibitors supports the hypothesis that changes in methylation patterns during epigenetic reprogramming may trigger the intergenerational repeat expansions that lead to disease.
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Affiliation(s)
- Vera Gorbunova
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
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44
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Rifé M, Nadal A, Milà M, Willemsen R. Immunohistochemical FMRP studies in a full mutated female fetus. Am J Med Genet A 2004; 124A:129-32. [PMID: 14699609 DOI: 10.1002/ajmg.a.20342] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Fragile X syndrome (FXS) is the most common form of inherited mental retardation. Clinical manifestations are due to the absence of the FMRP protein. Affected patients have widely variable phenotypes which are more variable in females than males, presumable due to X inactivation. We report the expression pattern of FMRP in cerebral cortex and ovary in a control and a full-mutated female fetus. FMRP was expressed in mutated and control fetal tissues, although at different levels and patterns. Control fetal cerebral cortex showed FMRP expression in almost all cells, whereas the full mutation carrier showed FMRP positivity in roughly 50% of cortical cells without any specific pattern. In the ovary samples, FMRP expression was seen in all germ cells surrounded by FMRP-negative paragranulosa and interstitial cells. The Müllerian epithelium of the fetal Fallopian tube was continuously positive in the control case, whereas the full mutation carrier showed a discontinuous patchy pattern. Expression of homologue proteins FXR1P and FXR2P showed no differences between control and full mutation fetuses. The pattern of FMRP expression in full mutation carrier females is in agreement with a random X-inactivation in maturing fetal tissues. Immunohistochemical results on cerebral tissues provide a clue for the variation of mental affection among female carriers, depending not only on the number of cells devoid of FMRP, but also on the ultimate destination of those cells in sensitive or more silent location for a proper cerebral development.
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Affiliation(s)
- M Rifé
- Servei de Genètica, Centre de Diagnòstic Biomèdic, Hospital Clínic, Barcelona, Spain
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45
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Abstract
Descriptive studies have established that the developmental events responsible for the assembly of neural systems and circuitry are conserved across mammalian species. However, primates are unique regarding the time during which histogenesis occurs and the extended postnatal period during which myelination of pathways and circuitry formation occur and are then subsequently modified, particularly in the cerebral cortex. As in lower mammals, the framework for subcortical-cortical connectivity in primates is established before midgestation and already begins to remodel before birth. Association systems, responsible for modulating intracortical circuits that integrate information across functional domains, also form before birth, but their growth and reorganization extend into puberty. There are substantial differences across species in the patterns of development of specific neurochemical systems. The complexity is even greater when considering that the development of any particular cellular component may differ among cortical areas in the same primate species. Developmental and behavioral neurobiologists, psychologists, and pediatricians are challenged with understanding how functional maturation relates to the evolving anatomical organization of the human brain during childhood, and moreover, how genetic and environmental perturbations affect the adaptive changes exhibited by neural circuits in response to developmental disruption.
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Affiliation(s)
- Pat Levitt
- John F. Kennedy Center for Research on Human Development, Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37203, USA
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46
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Vincent JB, Paterson AD, Strong E, Petronis A, Kennedy JL. The unstable trinucleotide repeat story of major psychosis. AMERICAN JOURNAL OF MEDICAL GENETICS 2003; 97:77-97. [PMID: 10813808 DOI: 10.1002/(sici)1096-8628(200021)97:1<77::aid-ajmg11>3.0.co;2-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
New hopes for cloning susceptibility genes for schizophrenia and bipolar affective disorder followed the discovery of a novel type of DNA mutation, namely unstable DNA. One class of unstable DNA, trinucleotide repeat expansion, is the causal mutation in myotonic dystrophy, fragile X mental retardation, Huntington disease and a number of other rare Mendelian neurological disorders. This finding has led researchers in psychiatric genetics to search for unstable DNA sites as susceptibility factors for schizophrenia and bipolar affective disorder. Increased severity and decreased age at onset of disease in successive generations, known as genetic anticipation, was reported for undifferentiated psychiatric diseases and for myotonic dystrophy early in the twentieth century, but was initially dismissed as the consequence of ascertainment bias. Because unstable DNA was demonstrated to be a molecular substrate for genetic anticipation in the majority of trinucleotide repeat diseases including myotonic dystrophy, many recent studies looking for genetic anticipation have been performed for schizophrenia and bipolar affective disorder with surprisingly consistent positive results. These studies are reviewed, with particular emphasis placed on relevant sampling and statistical considerations, and concerns are raised regarding the interpretation of such studies. In parallel, molecular genetic investigations looking for evidence of trinucleotide repeat expansion in both schizophrenia and bipolar disorder are reviewed. Initial studies of genome-wide trinucleotide repeats using the repeat expansion detection technique suggested possible association of large CAG/CTG repeat tracts with schizophrenia and bipolar affective disorder. More recently, three loci have been identified that contain large, unstable CAG/CTG repeats that occur frequently in the population and seem to account for the majority of large products identified using the repeat expansion detection method. These repeats localize to an intron in transcription factor gene SEF2-1B at 18q21, a site named ERDA1 on 17q21 with no associated coding region, and the 3' end of a gene on 13q21, SCA8, that is believed to be responsible for a form of spinocerebellar ataxia. At present no strong evidence exists that large repeat alleles at either SEF2-1B or ERDA1 are involved in the etiology of schizophrenia or bipolar disorder. Preliminary evidence suggests that large repeat alleles at SCA8 that are non-penetrant for ataxia may be a susceptibility factor for major psychosis. A fourth, but much more infrequently unstable CAG/CTG repeat has been identified within the 5' untranslated region of the gene, MAB21L1, on 13q13. A fifth CAG/CTG repeat locus has been identified within the coding region of an ion transporter, KCNN3 (hSKCa3), on 1q21. Although neither large alleles nor instability have been observed at KCNN3, this repeat locus has been extensively analyzed in association and family studies of major psychosis, with conflicting findings. Studies of polyglutamine containing genes in major psychosis have also shown some intriguing results. These findings, reviewed here, suggest that, although a major role for unstable trinucleotides in psychosis is unlikely, involvement at a more modest level in a minority of cases cannot be excluded, and warrants further investigation.
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Affiliation(s)
- J B Vincent
- Department of Genetics at the Hospital for Sick Children, Toronto, Canada
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47
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Abstract
Human monozygotic (MZ) twins estimated to occur once in 250 live births, result from an errant decision by embryonic cell(s) to develop as separate embryos. They are considered genetically identical and any phenotypic discordance between them has been used to implicate the role of environment. More recent literature, however, has questioned these assumptions but the frequency and the nature of any genetic discordance between MZ twins remains poorly understood. We will review published cases of phenotypic and genetic discordance between monozygotic twins to argue that not all discordance between such twins is due to differences in environment. The causes of reduced concordance between MZ twins remains poorly understood. They represent among the challenging aspects of the genetics of complex multi-factorial traits and diseases. A number of questions regarding the published results on MZ twins merit a re-assessment in the light of modern molecular insight of the human genome. Such an assessment is needed in directing future studies on MZ twins. In particular, we will deal with the origin, development, genetic and epigenetic factors that may have implications in discordance of the MZ twin pairs.
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Affiliation(s)
- S M Singh
- Molecular Genetics Unit, Department of Biology and Division of Medical Genetics, The University of Western Ontario, London, Ontario, Canada.
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48
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Wöhrle D, Salat U, Hameister H, Vogel W, Steinbach P. Demethylation, reactivation, and destabilization of human fragile X full-mutation alleles in mouse embryocarcinoma cells. Am J Hum Genet 2001; 69:504-15. [PMID: 11462172 PMCID: PMC1235481 DOI: 10.1086/322739] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2001] [Accepted: 06/19/2001] [Indexed: 12/14/2022] Open
Abstract
The major causes of fragile X syndrome are mutational expansion of the CGG repeat in the FMR1 gene, hypermethylation, and transcriptional silencing. Most fragile X embryos develop somatic mosaicism of disease-causing "full" expansions of different lengths. Homogeneity of the mosaic patterns among multiple tissues in the same individual indicates that these previously unstable expansions acquire mitotic stability early in fetal life. Since mitotic stability is found strictly associated with hypermethylation in adult tissues, current theory has fixed the time of instability to developmental stages when fully expanded CGG repeats exist in an unmethylated state. We used murine embryocarcinoma (EC) cells (PC13) as a model system of pluripotent embryonic cells. Hypermethylated and unmethylated full expansions on human fragile X chromosomes were transferred from murine A9 hybrids into EC cells, by means of microcell fusion. As demonstrated in the present study for the first time, even full expansion alleles that were fully methylated and stable in the donors' fibroblasts and in A9 became demethylated, reactivated, and destabilized in undifferentiated EC hybrids. When destabilized expansions were reintroduced from EC cells into A9, instability was reversed to stability. Our results strongly support the idea that fully expanded alleles are initially unstable and unmethylated in the human embryo and gain stability upon genetic or epigenetic change of the embryonic cells.
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Affiliation(s)
- D Wöhrle
- Department of Human Genetics, University Hospital of Ulm, 89073 Ulm, Germany
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49
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Salat U, Bardoni B, Wöhrle D, Steinbach P. Increase of FMRP expression, raised levels of FMR1 mRNA, and clonal selection in proliferating cells with unmethylated fragile X repeat expansions: a clue to the sex bias in the transmission of full mutations? J Med Genet 2000; 37:842-50. [PMID: 11073538 PMCID: PMC1734474 DOI: 10.1136/jmg.37.11.842] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Fragile X syndrome is a triplet repeat disorder caused by expansions of a CGG repeat in the fragile X mental retardation gene (FMR1) to more than 220 triplets (full mutation) that usually coincide with hypermethylation and transcriptional silencing. The disease phenotype results from deficiency or loss of FMR1 protein (FMRP) and occurs in both sexes. The underlying full mutations arise exclusively on transmission from a mother who carries a premutation allele (60-200 CGGs). While the absolute requirement of female transmission could result from different mechanisms, current evidence favours selection or contraction processes acting at gametogenesis of pre- and full mutation males. To address these questions experimentally, we used a model system of cultured fibroblasts from a male who presented heterogeneous unmethylated expansions in the pre- and full mutation size range. On continual cell proliferation to 30 doublings we re-examined the behaviour of the expanded repeats on Southern blots and also determined the expression of the FMR1 gene by FMRP immunocytochemistry, western analysis, and RT-PCR. With increasing population doublings, expansion patterns changed and showed accumulation of shorter alleles. The FMRP levels were below normal but increased continuously while the cells that were immunoreactive for FMRP accumulated. The level of FMR1 mRNA was raised with even higher levels of mRNA measured at higher passages. Current results support the theory of a selection advantage of FMRP positive over FMRP deficient cells. During extensive proliferation of spermatogonia in fragile X males, this selection mechanism would eventually replace all full mutations by shorter alleles allowing more efficient FMRP translation. At the proliferation of oogonia of carrier females, the same mechanism would, in theory, favour transmission of any expanded FMR1 allele on inactive X chromosomes.
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Affiliation(s)
- U Salat
- Department of Human Genetics, University Hospital, 89070 Ulm, Germany.
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50
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Reiss AL, Eliez S, Schmitt JE, Patwardhan A, Haberecht M. Brain imaging in neurogenetic conditions: realizing the potential of behavioral neurogenetics research. MENTAL RETARDATION AND DEVELOPMENTAL DISABILITIES RESEARCH REVIEWS 2000; 6:186-97. [PMID: 10982496 DOI: 10.1002/1098-2779(2000)6:3<186::aid-mrdd6>3.0.co;2-9] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Behavioral neurogenetics research is a new method of scientific inquiry that focuses on investigation of neurodevelopmental dysfunction associated with specific genetic conditions. This research method provides a powerful tool for scientific inquiry into human gene-brain-behavior linkages that complements more traditional research approaches. In particular, the use of specific genetic conditions as models of common behavioral and cognitive disorders occurring in the general population can reveal insights into neurodevelopmental pathways that might otherwise be obscured or diluted when investigating more heterogeneous, behaviorally defined subject groups. In this paper, we review five genetic conditions that commonly give rise to identifiable neurodevelopmental and neuropsychiatric disability in children: fragile X syndrome, velo-cardio-facial syndrome, Williams syndrome, Turner syndrome, and Klinefelter syndrome. While emphasis is placed on describing the brain morphology associated with these conditions as revealed by neuroimaging studies, we also include information pertaining to molecular genetic, postmortem, and neurobehavioral investigations to illustrate how behavioral neurogenetics research can contribute to an improved understanding of brain disorders in childhood.
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Affiliation(s)
- A L Reiss
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, California, USA
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