1
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Curnow E, Wang Y. New Animal Models for Understanding FMRP Functions and FXS Pathology. Cells 2022; 11:1628. [PMID: 35626665 PMCID: PMC9140010 DOI: 10.3390/cells11101628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Revised: 05/03/2022] [Accepted: 05/09/2022] [Indexed: 11/16/2022] Open
Abstract
Fragile X encompasses a range of genetic conditions, all of which result as a function of changes within the FMR1 gene and abnormal production and/or expression of the FMR1 gene products. Individuals with Fragile X syndrome (FXS), the most common heritable form of intellectual disability, have a full-mutation sequence (>200 CGG repeats) which brings about transcriptional silencing of FMR1 and loss of FMR protein (FMRP). Despite considerable progress in our understanding of FXS, safe, effective, and reliable treatments that either prevent or reduce the severity of the FXS phenotype have not been approved. While current FXS animal models contribute their own unique understanding to the molecular, cellular, physiological, and behavioral deficits associated with FXS, no single animal model is able to fully recreate the FXS phenotype. This review will describe the status and rationale in the development, validation, and utility of three emerging animal model systems for FXS, namely the nonhuman primate (NHP), Mongolian gerbil, and chicken. These developing animal models will provide a sophisticated resource in which the deficits in complex functions of perception, action, and cognition in the human disorder are accurately reflected and aid in the successful translation of novel therapeutics and interventions to the clinic setting.
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Affiliation(s)
- Eliza Curnow
- REI Division, Department of ObGyn, University of Washington, Seattle, WA 98195, USA
- Washington National Primate Research Center, University of Washington, Seattle, WA 98195, USA
| | - Yuan Wang
- Program in Neuroscience, Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL 32306, USA
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2
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Bleuzé L, Triaca V, Borreca A. FMRP-Driven Neuropathology in Autistic Spectrum Disorder and Alzheimer's disease: A Losing Game. Front Mol Biosci 2021; 8:699613. [PMID: 34760921 PMCID: PMC8573832 DOI: 10.3389/fmolb.2021.699613] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Accepted: 08/24/2021] [Indexed: 12/28/2022] Open
Abstract
Fragile X mental retardation protein (FMRP) is an RNA binding protein (RBP) whose absence is essentially associated to Fragile X Syndrome (FXS). As an RNA Binding Protein (RBP), FMRP is able to bind and recognize different RNA structures and the control of specific mRNAs is important for neuronal synaptic plasticity. Perturbations of this pathway have been associated with the autistic spectrum. One of the FMRP partners is the APP mRNA, the main protagonist of Alzheimer’s disease (AD), thereby regulating its protein level and metabolism. Therefore FMRP is associated to two neurodevelopmental and age-related degenerative conditions, respectively FXS and AD. Although these pathologies are characterized by different features, they have been reported to share a number of common molecular and cellular players. The aim of this review is to describe the double-edged sword of FMRP in autism and AD, possibly allowing the elucidation of key shared underlying mechanisms and neuronal circuits. As an RBP, FMRP is able to regulate APP expression promoting the production of amyloid β fragments. Indeed, FXS patients show an increase of amyloid β load, typical of other neurological disorders, such as AD, Down syndrome, Parkinson’s Disease, etc. Beyond APP dysmetabolism, the two neurodegenerative conditions share molecular targets, brain circuits and related cognitive deficits. In this review, we will point out the potential common neuropathological pattern which needs to be addressed and we will hopefully contribute to clarifying the complex phenotype of these two neurorological disorders, in order to pave the way for a novel, common disease-modifying therapy.
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Affiliation(s)
- Louis Bleuzé
- University de Rennes 1, Rennes, France.,Humanitas Clinical and Research Center-IRCCS, Rozzano (Mi), Italy
| | - Viviana Triaca
- Institute of Biochemistry and Cell Biology, National Research Council (CNR-IBBC), International Campus A. Buzzati Traverso, Monterotondo, Italy
| | - Antonella Borreca
- Humanitas Clinical and Research Center-IRCCS, Rozzano (Mi), Italy.,Institute of Neuroscience-National Research Council (CNR-IN), Milan, Italy
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3
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Beyond Trinucleotide Repeat Expansion in Fragile X Syndrome: Rare Coding and Noncoding Variants in FMR1 and Associated Phenotypes. Genes (Basel) 2021; 12:genes12111669. [PMID: 34828275 PMCID: PMC8623550 DOI: 10.3390/genes12111669] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 10/20/2021] [Accepted: 10/21/2021] [Indexed: 11/17/2022] Open
Abstract
FMR1 (FMRP translational regulator 1) variants other than repeat expansion are known to cause disease phenotypes but can be overlooked if they are not accounted for in genetic testing strategies. We collected and reanalyzed the evidence for pathogenicity of FMR1 coding, noncoding, and copy number variants published to date. There is a spectrum of disease-causing FMR1 variation, with clinical and functional evidence supporting pathogenicity of five splicing, five missense, one in-frame deletion, one nonsense, and four frameshift variants. In addition, FMR1 deletions occur in both mosaic full mutation patients and as constitutional pathogenic alleles. De novo deletions arise not only from full mutation alleles but also alleles with normal-sized CGG repeats in several patients, suggesting that the CGG repeat region may be prone to genomic instability even in the absence of repeat expansion. We conclude that clinical tests for potentially FMR1-related indications such as intellectual disability should include methods capable of detecting small coding, noncoding, and copy number variants.
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4
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Zeidler S, Severijnen LA, de Boer H, van der Toorn EC, Ruivenkamp CAL, Bijlsma EK, Willemsen R. A missense variant in the nuclear export signal of the FMR1 gene causes intellectual disability. Gene 2020; 768:145298. [PMID: 33181255 DOI: 10.1016/j.gene.2020.145298] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 10/14/2020] [Accepted: 11/04/2020] [Indexed: 11/15/2022]
Abstract
Fragile X syndrome (FXS) is the most common monogenetic cause of intellectual disability and autism spectrum disorders. Mostly, FXS is caused by transcriptional silencing of the FMR1 gene due to a repeat expansion in the 5' UTR, and consequently lack of the protein product FMRP. However, in rare cases FXS is caused by other types of variants in the FMR1 gene. We describe a missense variant in the FMR1 gene, identified through whole-exome sequencing, in a boy with intellectual disability and behavioral problems. The variant is located in the FMRP's nuclear export signal (NES). We performed expression and localization studies of the variant in hair roots and HEK293 cells. Our results show normal expression but significant retention of the FMRP in the cells' nucleus. This finding suggests a possible FMRP reduction at its essential functional sites in the dendrites and the synaptic compartments and possible interference of other cellular processes in the nucleus. Together, this might lead to a FXS phenotype in the boy.
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Affiliation(s)
- Shimriet Zeidler
- Department of Clinical Genetics, Erasmus MC, Rotterdam, The Netherlands.
| | | | - Helen de Boer
- Department of Clinical Genetics, Erasmus MC, Rotterdam, The Netherlands
| | | | - Claudia A L Ruivenkamp
- Department of Clinical Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Emilia K Bijlsma
- Department of Clinical Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Rob Willemsen
- Department of Clinical Genetics, Erasmus MC, Rotterdam, The Netherlands
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5
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Sitzmann AF, Hagelstrom RT, Tassone F, Hagerman RJ, Butler MG. Rare FMR1 gene mutations causing fragile X syndrome: A review. Am J Med Genet A 2017; 176:11-18. [PMID: 29178241 DOI: 10.1002/ajmg.a.38504] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Revised: 09/21/2017] [Accepted: 09/24/2017] [Indexed: 12/16/2022]
Abstract
Fragile X syndrome (FXS) is the most common inherited form of intellectual disability, typically due to CGG-repeat expansions in the FMR1 gene leading to lack of expression. We identified a rare FMR1 gene mutation (c.413G>A), previously reported in a single patient and reviewed the literature for other rare FMR1 mutations. Our patient at 10 years of age presented with the classical findings of FXS including intellectual disability, autism, craniofacial findings, hyperextensibility, fleshy hands, flat feet, unsteady gait, and seizures but without the typical CGG-repeat expansion. He had more features of FXS than the previously reported patient with the same mutation. Twenty individuals reported previously with rare missense or nonsense mutations or other coding disturbances of the FMR1 gene ranged in age from infancy to 50 years; most were verbal with limited speech, had autism and hyperactivity, and all had intellectual disability. Four of the 20 individuals had a mutation within exon 15, three within exon 5, and two within exon 2. The FMR1 missense mutation (c.413G>A) is the same as in a previously reported male where it was shown that there was preservation of the post-synaptic function of the fragile X mental retardation protein (FMRP), the encoded protein of the FMR1 gene was preserved. Both patients with this missense mutation had physical, cognitive, and behavioral features similarly seen in FXS.
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Affiliation(s)
- Adam F Sitzmann
- Departments of Psychiatry & Behavioral Sciences and Pediatrics, University of Kansas Medical Center, Kansas City, Kansas
| | - Robert T Hagelstrom
- Human Genetics Laboratory, Munroe-Meyer Institute, University of Nebraska Medical Center, Omaha, Nebraska
| | - Flora Tassone
- Department of Biochemistry and Molecular Medicine, University of California-Davis Medical Center, Sacramento, California.,MIND Institute, University of California-Davis Medical Center, Sacramento, California
| | - Randi J Hagerman
- MIND Institute, University of California-Davis Medical Center, Sacramento, California.,Department of Pediatrics, University of California-Davis Medical Center, Sacramento, California
| | - Merlin G Butler
- Departments of Psychiatry & Behavioral Sciences and Pediatrics, University of Kansas Medical Center, Kansas City, Kansas
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6
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Intragenic FMR1 disease-causing variants: a significant mutational mechanism leading to Fragile-X syndrome. Eur J Hum Genet 2017; 25:423-431. [PMID: 28176767 DOI: 10.1038/ejhg.2016.204] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Revised: 12/07/2016] [Accepted: 12/14/2016] [Indexed: 11/09/2022] Open
Abstract
Fragile-X syndrome (FXS) is a frequent genetic form of intellectual disability (ID). The main recurrent mutagenic mechanism causing FXS is the expansion of a CGG repeat sequence in the 5'-UTR of the FMR1 gene, therefore, routinely tested in ID patients. We report here three FMR1 intragenic pathogenic variants not affecting this sequence, identified using high-throughput sequencing (HTS): a previously reported hemizygous deletion encompassing the last exon of FMR1, too small to be detected by array-CGH and inducing decreased expression of a truncated form of FMRP protein, in three brothers with ID (family 1) and two splice variants in boys with sporadic ID: a de novo variant c.990+1G>A (family 2) and a maternally inherited c.420-8A>G variant (family 3). After clinical reevaluation, the five patients presented features consistent with FXS (mean Hagerman's scores=15). We conducted a systematic review of all rare non-synonymous variants previously reported in FMR1 in ID patients and showed that six of them are convincing pathogenic variants. This study suggests that intragenic FMR1 variants, although much less frequent than CGG expansions, are a significant mutational mechanism leading to FXS and demonstrates the interest of HTS approaches to detect them in ID patients with a negative standard work-up.
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Jiménez-Barrón LT, O'Rawe JA, Wu Y, Yoon M, Fang H, Iossifov I, Lyon GJ. Genome-wide variant analysis of simplex autism families with an integrative clinical-bioinformatics pipeline. Cold Spring Harb Mol Case Stud 2016; 1:a000422. [PMID: 27148569 PMCID: PMC4850892 DOI: 10.1101/mcs.a000422] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Autism spectrum disorders (ASDs) are a group of developmental disabilities that affect social interaction and communication and are characterized by repetitive behaviors. There is now a large body of evidence that suggests a complex role of genetics in ASDs, in which many different loci are involved. Although many current population-scale genomic studies have been demonstrably fruitful, these studies generally focus on analyzing a limited part of the genome or use a limited set of bioinformatics tools. These limitations preclude the analysis of genome-wide perturbations that may contribute to the development and severity of ASD-related phenotypes. To overcome these limitations, we have developed and utilized an integrative clinical and bioinformatics pipeline for generating a more complete and reliable set of genomic variants for downstream analyses. Our study focuses on the analysis of three simplex autism families consisting of one affected child, unaffected parents, and one unaffected sibling. All members were clinically evaluated and widely phenotyped. Genotyping arrays and whole-genome sequencing were performed on each member, and the resulting sequencing data were analyzed using a variety of available bioinformatics tools. We searched for rare variants of putative functional impact that were found to be segregating according to de novo, autosomal recessive, X-linked, mitochondrial, and compound heterozygote transmission models. The resulting candidate variants included three small heterozygous copy-number variations (CNVs), a rare heterozygous de novo nonsense mutation in MYBBP1A located within exon 1, and a novel de novo missense variant in LAMB3. Our work demonstrates how more comprehensive analyses that include rich clinical data and whole-genome sequencing data can generate reliable results for use in downstream investigations.
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Affiliation(s)
- Laura T Jiménez-Barrón
- Stanley Institute for Cognitive Genomics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA;; Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico
| | - Jason A O'Rawe
- Stanley Institute for Cognitive Genomics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA;; Graduate Genetics Program, Stony Brook University, Stony Brook, New York 11794, USA
| | - Yiyang Wu
- Stanley Institute for Cognitive Genomics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA;; Graduate Genetics Program, Stony Brook University, Stony Brook, New York 11794, USA
| | - Margaret Yoon
- Stanley Institute for Cognitive Genomics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
| | - Han Fang
- Stanley Institute for Cognitive Genomics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
| | - Ivan Iossifov
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA;; New York Genome Center, New York, New York 10013, USA
| | - Gholson J Lyon
- Stanley Institute for Cognitive Genomics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA;; Graduate Genetics Program, Stony Brook University, Stony Brook, New York 11794, USA;; Utah Foundation for Biomedical Research, Salt Lake City, Utah 84107, USA
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8
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Sastre A, Campillo NE, Gil C, Martinez A. Therapeutic approaches for the future treatment of Fragile X. Curr Opin Behav Sci 2015. [DOI: 10.1016/j.cobeha.2015.01.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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9
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Santos AR, Kanellopoulos AK, Bagni C. Learning and behavioral deficits associated with the absence of the fragile X mental retardation protein: what a fly and mouse model can teach us. ACTA ACUST UNITED AC 2014; 21:543-55. [PMID: 25227249 PMCID: PMC4175497 DOI: 10.1101/lm.035956.114] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The Fragile X syndrome (FXS) is the most frequent form of inherited mental disability and is considered a monogenic cause of autism spectrum disorder. FXS is caused by a triplet expansion that inhibits the expression of the FMR1 gene. The gene product, the Fragile X Mental Retardation Protein (FMRP), regulates mRNA metabolism in brain and nonneuronal cells. During brain development, FMRP controls the expression of key molecules involved in receptor signaling, cytoskeleton remodeling, protein synthesis and, ultimately, spine morphology. Symptoms associated with FXS include neurodevelopmental delay, cognitive impairment, anxiety, hyperactivity, and autistic-like behavior. Twenty years ago the first Fmr1 KO mouse to study FXS was generated, and several years later other key models including the mutant Drosophila melanogaster, dFmr1, have further helped the understanding of the cellular and molecular causes behind this complex syndrome. Here, we review to which extent these biological models are affected by the absence of FMRP, pointing out the similarities with the observed human dysfunction. Additionally, we discuss several potential treatments under study in animal models that are able to partially revert some of the FXS abnormalities.
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Affiliation(s)
- Ana Rita Santos
- VIB Center for the Biology of Disease, 3000 Leuven, Belgium Center for Human Genetics, KU Leuven, 3000 Leuven, Belgium Leuven Institute for Neurodegenerative Diseases (LIND), KU Leuven, 3000 Leuven, Belgium
| | - Alexandros K Kanellopoulos
- VIB Center for the Biology of Disease, 3000 Leuven, Belgium Center for Human Genetics, KU Leuven, 3000 Leuven, Belgium Leuven Institute for Neurodegenerative Diseases (LIND), KU Leuven, 3000 Leuven, Belgium
| | - Claudia Bagni
- VIB Center for the Biology of Disease, 3000 Leuven, Belgium Center for Human Genetics, KU Leuven, 3000 Leuven, Belgium Leuven Institute for Neurodegenerative Diseases (LIND), KU Leuven, 3000 Leuven, Belgium Department of Biomedicine and Prevention, University of Rome "Tor Vergata" 00133, Rome, Italy
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10
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Handt M, Epplen A, Hoffjan S, Mese K, Epplen JT, Dekomien G. Point mutation frequency in the FMR1 gene as revealed by fragile X syndrome screening. Mol Cell Probes 2014; 28:279-83. [PMID: 25171808 DOI: 10.1016/j.mcp.2014.08.003] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Revised: 08/18/2014] [Accepted: 08/18/2014] [Indexed: 01/05/2023]
Abstract
Fragile X syndrome (FXS) is a common cause of intellectual disability, developmental delay and autism spectrum disorders. This syndrome is due to a functional loss of the FMR1 gene product FMRP, and, in most cases, it is caused by CGG repeat expansion in the FMR1 promoter. Yet, also other FMR1 mutations may cause a FXS-like phenotype. Since standard molecular testing does not include the analysis of the FMR1 coding region, the prevalence of point mutations causing FXS is not well known. Here, high resolution melting (HRM) was used to screen for FMR1 gene mutations in 508 males with clinical signs of mental retardation and developmental delay, but without CGG and GCC repeat expansions in the FMR1 gene and AFF2 genes, respectively. Sequence variations were identified by HRM analysis and verified by direct DNA sequencing. Two novel missense mutations (p.Gly482Ser in one patient and p.Arg534His in two unrelated patients), one intronic and two 3'-untranslated region (UTR) variations were identified in the FMR1 gene. Missense mutations in the FMR1 gene might account for a considerable proportion of cases in male patients with FXS-related symptoms, such as those linked to mental retardation and developmental delay.
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Affiliation(s)
- Maximilian Handt
- Faculty of Health, Witten/Herdecke University, Alfred-Herrhausen-Straße 50, 58448 Witten, Germany
| | - Andrea Epplen
- Human Genetics, Ruhr-University, Universitätsstraße 150, 44801 Bochum, Germany
| | - Sabine Hoffjan
- Human Genetics, Ruhr-University, Universitätsstraße 150, 44801 Bochum, Germany
| | - Kemal Mese
- Faculty of Health, Witten/Herdecke University, Alfred-Herrhausen-Straße 50, 58448 Witten, Germany
| | - Jörg T Epplen
- Faculty of Health, Witten/Herdecke University, Alfred-Herrhausen-Straße 50, 58448 Witten, Germany; Human Genetics, Ruhr-University, Universitätsstraße 150, 44801 Bochum, Germany
| | - Gabriele Dekomien
- Human Genetics, Ruhr-University, Universitätsstraße 150, 44801 Bochum, Germany.
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11
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Fragile X syndrome due to a missense mutation. Eur J Hum Genet 2014; 22:1185-9. [PMID: 24448548 DOI: 10.1038/ejhg.2013.311] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Revised: 11/05/2013] [Accepted: 11/20/2013] [Indexed: 11/08/2022] Open
Abstract
Fragile X syndrome is a common inherited form of intellectual disability and autism spectrum disorder. Most patients exhibit a massive CGG-repeat expansion mutation in the FMR1 gene that silences the locus. In over two decades since the discovery of FMR1, only a single missense mutation (p.(Ile304Asn)) has been reported as causing fragile X syndrome. Here we describe a 16-year-old male presenting with fragile X syndrome but without the repeat expansion mutation. Rather, we find a missense mutation, c.797G>A, that replaces glycine 266 with glutamic acid (p.(Gly266Glu)). The Gly266Glu FMR protein abolished many functional properties of the protein. This patient highlights the diagnostic utility of FMR1 sequencing.
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12
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Nelson DL, Orr HT, Warren ST. The unstable repeats--three evolving faces of neurological disease. Neuron 2013; 77:825-43. [PMID: 23473314 PMCID: PMC3608403 DOI: 10.1016/j.neuron.2013.02.022] [Citation(s) in RCA: 155] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/20/2013] [Indexed: 01/08/2023]
Abstract
Disorders characterized by expansion of an unstable nucleotide repeat account for a number of inherited neurological diseases. Here, we review examples of unstable repeat disorders that nicely illustrate three of the major pathogenic mechanisms associated with these diseases: loss of function typically by disrupting transcription of the mutated gene, RNA toxic gain of function, and protein toxic gain of function. In addition to providing insight into the mechanisms underlying these devastating neurological disorders, the study of these unstable microsatellite repeat disorders has provided insight into very basic aspects of neuroscience.
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Affiliation(s)
- David L. Nelson
- Department of Molecular and Human Genetics, Baylor College
of Medicine, Houston, TX 77030
| | - Harry T. Orr
- Department of Laboratory Medicine and Pathology, University
of Minnesota, Minneapolis, MN 55455
| | - Stephen T. Warren
- Department of Human Genetics, Emory University School of
Medicine, Atlanta, GA 30322
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13
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Abstract
Fragile X syndrome is a common cause of inherited intellectual disability. It is caused by lack of the FMR1 gene product FMRP. The most frequent cause is the expansion of a CGG repeat located in the 5'UTR of FMR1. Alleles with 200 or more repeats become hypermethylated and transcriptionally silent. Only few patients with intragenic point mutations in FMR1 have been reported and, currently, routine analysis of patients referred for fragile X syndrome includes solely analysis for repeat expansion and methylation status. We identified a substitution in exon 2 of FMR1, c.80C>A, causing a nonsense mutation p.Ser27X, in a patient with classical clinical symptoms of fragile X syndrome. The mother who carried the mutation in heterozygous form presented with mild intellectual impairment. We conclude that further studies including western blot and DNA sequence analysis of the FMR1 gene should be performed in patients with typical symptoms of fragile X syndrome in whom no CGG repeat expansion is detected.
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14
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Collins SC, Bray SM, Suhl JA, Cutler DJ, Coffee B, Zwick ME, Warren ST. Identification of novel FMR1 variants by massively parallel sequencing in developmentally delayed males. Am J Med Genet A 2010; 152A:2512-20. [PMID: 20799337 PMCID: PMC2946449 DOI: 10.1002/ajmg.a.33626] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Fragile X syndrome (FXS), the most common inherited form of developmental delay, is typically caused by CGG-repeat expansion in FMR1. However, little attention has been paid to sequence variants in FMR1. Through the use of pooled-template massively parallel sequencing, we identified 130 novel FMR1 sequence variants in a population of 963 developmentally delayed males without CGG-repeat expansion mutations. Among these, we identified a novel missense change, p.R138Q, which alters a conserved residue in the nuclear localization signal of FMRP. We have also identified three promoter mutations in this population, all of which significantly reduce in vitro levels of FMR1 transcription. Additionally, we identified 10 noncoding variants of possible functional significance in the introns and 3'-untranslated region of FMR1, including two predicted splice site mutations. These findings greatly expand the catalog of known FMR1 sequence variants and suggest that FMR1 sequence variants may represent an important cause of developmental delay.
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Affiliation(s)
- Stephen C. Collins
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Steven M. Bray
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Joshua A. Suhl
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - David J. Cutler
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Bradford Coffee
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Michael E. Zwick
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Stephen T. Warren
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
- Departments of Biochemistry and Pediatrics, Emory University School of Medicine, Atlanta, GA 30322, USA
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15
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Collins SC, Coffee B, Benke PJ, Berry-Kravis E, Gilbert F, Oostra B, Halley D, Zwick ME, Cutler DJ, Warren ST. Array-based FMR1 sequencing and deletion analysis in patients with a fragile X syndrome-like phenotype. PLoS One 2010; 5:e9476. [PMID: 20221430 PMCID: PMC2832695 DOI: 10.1371/journal.pone.0009476] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2010] [Accepted: 02/11/2010] [Indexed: 11/18/2022] Open
Abstract
Background Fragile X syndrome (FXS) is caused by loss of function mutations in the FMR1 gene. Trinucleotide CGG-repeat expansions, resulting in FMR1 gene silencing, are the most common mutations observed at this locus. Even though the repeat expansion mutation is a functional null mutation, few conventional mutations have been identified at this locus, largely due to the clinical laboratory focus on the repeat tract. Methodology/Principal Findings To more thoroughly evaluate the frequency of conventional mutations in FXS-like patients, we used an array-based method to sequence FMR1 in 51 unrelated males exhibiting several features characteristic of FXS but with normal CGG-repeat tracts of FMR1. One patient was identified with a deletion in FMR1, but none of the patients were found to have other conventional mutations. Conclusions/Significance These data suggest that missense mutations in FMR1 are not a common cause of the FXS phenotype in patients who have normal-length CGG-repeat tracts. However, screening for small deletions of FMR1 may be of clinically utility.
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Affiliation(s)
- Stephen C. Collins
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Brad Coffee
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Paul J. Benke
- Joe DiMaggio Children's Hospital, Hollywood, Florida, United States of America
| | - Elizabeth Berry-Kravis
- Departments of Pediatrics and Neurological Sciences, Rush University Medical Center, Chicago, Illinois, United States of America
| | - Fred Gilbert
- Department of Pediatrics, Weill Cornell Medical College, New York, New York, United States of America
| | - Ben Oostra
- Department of Clinical Genetics, Erasmus University, Rotterdam, The Netherlands
| | - Dicky Halley
- Department of Clinical Genetics, Erasmus University, Rotterdam, The Netherlands
| | - Michael E. Zwick
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - David J. Cutler
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Stephen T. Warren
- Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, United States of America
- Departments of Pediatrics and Biochemistry, Emory University School of Medicine, Atlanta, Georgia, United States of America
- * E-mail:
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16
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Abstract
The fragile X syndrome results from expansions as well as deletions of the repeating CGG.CCG DNA sequence in the 5'-untranslated region of the FMR1 gene on the X chromosome. The relative frequency of disease cases promoted by these two types of mutations cannot be ascertained at present because the routine clinical assay monitors only expansions. At least 30 articles have been reviewed that document the involvement of deletions of part or all of the CGG.CCG repeats along with varying extents of DNA flanking regions as well as very small mutations including single base pair changes. Studies of deletion mutants of CGG.CCG tracts in Escherichia coli plasmids revealed a similar spectrum of mutagenic products. The triplet repeat tract in a non-B conformation is the mutagen, not the sequence per se in the right-handed B helix. Hence, molecular investigations in a simple model organism may generate useful initial information toward therapeutic strategies for this disease.
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Affiliation(s)
- Robert D Wells
- Center for Genome Research, Institute of Biosciences and Technology, Texas A&M Health Science Center, Texas Medical Center, Houston, Texas 77030-3303, USA.
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17
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Kosmider B, Wells RD. Fragile X repeats are potent inducers of complex, multiple site rearrangements in flanking sequences in Escherichia coli. DNA Repair (Amst) 2007; 6:1850-63. [PMID: 17851139 DOI: 10.1016/j.dnarep.2007.07.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 06/27/2007] [Accepted: 07/12/2007] [Indexed: 01/02/2023]
Abstract
(CGG.CCG)n repeats induce the formation of complex, multiple site rearrangements and/or gross deletions in flanking DNA sequences in Escherichia coli plasmids. DNA sequence analyses of mutant clones revealed the influence of (a) the length (24, 44 or 73 repeats), (b) the orientation of the CGG.CCG region relative to the unidirectional origin, and (c) its transcription status. Complex rearrangements had occurred in the mutant clones since some products contained deletions, inversions and insertions and some products had only gross deletions. Furthermore, the CGG.CCG repeats repeatedly induced, up to 22 times, the formation of identical (to the bp) mutagenic products indicating the powerful nature of the complex processes involved. Also, the mutations were bidirectional from the CGG.CCG tract. The healed junctions had CG-rich microhomologies of 1-6bp, CG-rich regions and putative cruciforms and slipped structures. Hence, the fragile X syndrome mutagenic spectrum has been found, at least in part, in our model system.
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Affiliation(s)
- Beata Kosmider
- Center for Genome Research, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Texas Medical Center, 2121 W. Holcombe Blvd., Houston, TX 77030-3303, USA
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18
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Han XD, Powell BR, Phalin JL, Chehab FF. Mosaicism for a full mutation, premutation, and deletion of the CGG repeats results in 22% FMRP and elevated FMR1 mRNA levels in a high-functioning fragile X male. Am J Med Genet A 2006; 140:1463-71. [PMID: 16761284 DOI: 10.1002/ajmg.a.31291] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The molecular basis in the majority of fragile X patients results from expansion of the CGG repeats in the FMR1 gene causing its transcriptional silencing and deficiency of its encoded protein FMRP. In this communication, we report on a male patient who lacks the characteristic physical features of fragile X and carries a fully methylated mutation, a premutation, a non-methylated full mutation, and a microdeletion encompassing the entire CGG repeat region and 42 bp of upstream flanking sequence. Southern blot analysis revealed that the methylated full mutation accounted for only 10% of his genotype while the premutation/non-methylated full mutation and the microdeletion constituted 37% and 53%, respectively. Immunofluorescent staining of FMRP demonstrated the presence of 22% FMRP in his peripheral blood leukocytes and quantitative RT-PCR revealed a 3.6-fold elevation of FMR1 mRNA levels. Developmental assessments indicated that while he has a learning disability, he does not have mental retardation. Because previous reports had noted that 28% FMRP expression is associated with a characteristic fragile X phenotype, we propose that in our patient the association of 22% FMRP levels with normal physical features and a high-functioning status may have resulted from increased FMRP stability by a mechanism that takes into account the CGG microdeletion and elevated mRNA levels.
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Affiliation(s)
- Xiao-Dong Han
- Department of Laboratory Medicine, University of California-San Francisco, 185 Berry Street, San Francisco, CA 94107, USA
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19
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Vincent JB, Thevarkunnel S, Kolozsvari D, Paterson AD, Roberts W, Scherer SW. Association and transmission analysis of the FMR1 IVS10 + 14C-T variant in autism. Am J Med Genet B Neuropsychiatr Genet 2004; 125B:54-6. [PMID: 14755444 DOI: 10.1002/ajmg.b.20088] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Evidence from the high male to female ratio of individuals with autism as well as suggestive linkage data have implicated the possible involvement of X chromosomal loci in the aetiology of autism. Studies of the FMR1 gene on Xq27 have shown that occasionally individuals, and particularly females, with the [CGG] repeat expansion and methylation mutation may present with autistic symptoms. However, molecular studies suggest that such mutations are not a major cause of autism. Previously, we have screened autism probands for mutations in regions of the FMR1 gene downstream of the [CGG] repeat and identified an intronic variant in the FMR1 gene, IVS10 + 14C-T, which was present at a significantly higher frequency in autistic individuals compared to controls individuals. We have now investigated this variant in a further 136 autism families and 186 control individuals. We have established that the variant is significantly more frequent among East Asian individuals within our affected and control groups (P < 0.0001) and although we observed a trend of higher transmission frequency of the rare allele to affected individuals, there was no significant evidence in either family-based or case/control association studies for this variant in autism (P > 0.05).
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Affiliation(s)
- John B Vincent
- Program in Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.
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20
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Clarke NF, Mowat D, Kooy RF, Reyniers E, Willemsen R. Fragile X syndrome phenotype with normalFMR1 gene studies. ACTA ACUST UNITED AC 2004; 129A:326-8. [PMID: 15326639 DOI: 10.1002/ajmg.a.30194] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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21
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Wang TS, Hsieh LJ, Hsu TY, Chung CH, Li SY. DNA damage and repair in lymphoblastoid cell lines from normal donors and fragile X syndrome patients. Arch Med Res 2002; 33:128-35. [PMID: 11886710 DOI: 10.1016/s0188-4409(01)00376-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Because lymphocytes from fragile X patients have been reported as hypersensitive to bleomycin-induced chromatid breaks and because the number of trinucleotide repeats in families with fragile X syndrome has a propensity to expand, we have investigated the possibility that fragile X cells may be hypersensitive to DNA damage and have a lower capacity for DNA repair. METHODS Lymphocytes from normal and fragile X syndrome donors were immortalized by Epstein-Barr virus transformation. Characteristics of fragile X syndrome including the folate-sensitive fragile site on chromosome Xq27.3, length of CGG repeat expansion, and FMRP expression in Epstein-Barr virus-transformed lymphoblastoid cell lines were analyzed by standard cytogenetic methods, Southern blot, and Western blot, respectively. Analysis of DNA damage and repair induced by hydrogen peroxide, bleomycin, ethyl methanesulfonate, 4-nitroquinoline-N-oxide, etoposide, and mitomycin C was carried out by single-cell gel electrophoresis assay (known as comet assay). RESULTS Lymphoblastoid cell lines from fragile X donors had a folate-sensitive fragile site on chromosome Xq27.3, no or low FMRP expression, and expansion of the CGG repeat. Results of comet assay showed that fragile X cells were not more sensitive to mutagen-induced DNA strand breaks and did not have lower DNA repair capacity in comparison with normal cells. Furthermore, one fragile X cell line showed hyposensitivity to DNA strand breaks induced by hydrogen peroxide, bleomycin, and ethyl methansulfonate. CONCLUSIONS The results of this study do not support the notion that CGG trinucleotide expansion in fragile X syndrome is caused by permanent deficiency in DNA repair.
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Affiliation(s)
- Tsu Shing Wang
- Department of Life Sciences, Chung Shan Medical University, Taichung 402, Taiwan, Republic of China (ROC).
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22
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Abstract
The clinical features of the Fragile X mental retardation syndrome are linked to the absence of the set of protein isoforms, derived from alternative splicing of the Fragile X mental retardation gene 1 (FMR1), and collectively termed FMRP. FMRP is an RNA binding protein that is part of a ribonucleoprotein particle associated to actively translating polyribosomes, and which can shuttle between nucleus and cytoplasm. Two highly homologous human proteins, FXR1P and FXR2P, share the same domain structure as FMRP, and probably similar functions. The properties of FMRP suggested that it is involved in nuclear export, cytoplasmic transport, and/or translational control of target mRNAs. In particular, it may play a role in regulation of protein synthesis at postsynaptic sites of dendrites, and in maturation of dendritic spines. Efforts are underway to identify the putative specific mRNA targets of FMRP, and study the effect of FMRP absence on the corresponding proteins. Other approaches have led to the identification of proteins that interact with FMRP. Some of them discriminate between FMRP and the homologous FXR1/2P proteins, and may thus be important for defining unique functions of FMRP that are deficient in Fragile X patients. The physiological functions of FMRP are notably approached through the study of a FMR1 knock-out mouse model. The recent identification in Drosophila melanogaster of genes encoding homologs of FMRP/FXRP and of their interacting proteins, open the way to use of Drosophila genetics to study FMRP function.
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Affiliation(s)
- B Bardoni
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Strasbourg, France
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23
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Abstract
Although many pediatric neurologic disorders, such as epilepsy and mental retardation, are the result of a combination of genetic and environmental factors, many others are the result of mutations of single genes. Most of these single gene traits are inherited in autosomal dominant, autosomal recessive, or X-linked fashion. The diversity of mutations that are responsible for these diseases produces variability in phenotypic expression. However, there are other important features of many neurologic disorders that cannot be explained by standard models of mendelian inheritance. This review focuses on recently described mechanisms, such as genomic imprinting, germline mosaicism, mitochondrial inheritance, and triplet repeat expansion. The diagnostic evaluation, prognostic significance, and recurrence risk for specific neurogenetic disorders is correlated with these underlying disease mechanisms.
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Affiliation(s)
- C Cunniff
- Department of Pediatrics, Obstetrics and Gynecology, University of Arizona College of Medicine and the Steele Memorial Children's Research Center, Tucson 85724-5073, USA
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24
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Abstract
Taxonomic features of fragile X syndrome (FXS) associated with the fragile X mutation have evolved over several decades. Males are more severely impacted cognitively than females, but both show declines in IQ scores as they age. Although many males with FXS exhibit autistic-like features, autism does not occur more frequently in males with FXS than among males with mental retardation (MR). FXS is caused by inactivation of the FMR1 gene located on Xq27.3. FMRP, the protein produced by FMR1, has been detected in most organs and in brain. In cells, it is located primarily in cytoplasm and contains motifs found in RNA-binding proteins. The FMRP N-terminal contains a functional nuclear localization signal which permits the protein to shuttle between cytoplasm and nucleus. FMR1 knockout mice show subtle behavioral and visual-spatial difficulties. Analysis of their brain tissue suggests absence of FMRP impairs synaptic maturation. Individuals with the fragile premutation produce FMRP, and the phenotype associated with the premutation has been controversial. However, there seems to be a higher incidence of premature ovarian failure in women with the premutation than is found in the general female population. This may be related to unusual increases in mRNA levels in premutation carriers.
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Affiliation(s)
- B Bardoni
- Institute of Medical Genetics at the Pavia Faculty of Medicine, Italy
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25
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Limprasert P, Saechan V, Ruangdaraganon N, Sura T, Vasiknanote P, Jaruratanasirikul S, Brown WT. Haplotype analysis at the FRAXA locus in Thai subjects. ACTA ACUST UNITED AC 2001. [DOI: 10.1002/1096-8628(20010122)98:3<224::aid-ajmg1096>3.0.co;2-r] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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26
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Eficacia de un test clínico como preselección de niños con sospecha de síndrome X frágil. An Pediatr (Barc) 2001. [DOI: 10.1016/s1695-4033(01)77538-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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28
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Milà M, Castellví-Bel S, Sánchez A, Barceló A, Badenas C, Mallolas J, Estivill X. Rare variants in the promoter of the fragile X syndrome gene (FMR1). Mol Cell Probes 2000; 14:115-9. [PMID: 10799273 DOI: 10.1006/mcpr.2000.0293] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Fragile X syndrome, the most common form of familial mental retardation, is mainly caused by the expansion of an unstable region of CGG repeats in the 5' untranslated region of the FMR1 (Fragile X Mental Retardation-1) gene. Molecular tools to detect an abnormal CGG expansion in FMR1 include Southern blot hybridization and PCR amplification. Southern blotting with the StB12.3 probe and Eco RI/Eag I double digestion is widely used as a routine test for fragile X syndrome diagnosis in laboratories around the world. A patient with mental retardation of unknown origin showed absence of digestion for Eag I due to a -149C-->G substitution in the CpG island of the FMR1 gene, which destroys that restriction enzyme site. Screening for other changes around that region also detected a -154insGGC in a patient with a phenotype highly suggestive of fragile X syndrome but without CGG expansion. Expression studies did not show any abnormal changes in FMR1 function. In summary, we have identified two different changes (a C to G substitution at -149 and a GGC insertion at -154) in the promoter of the FMR1 gene. These are the first variants described in the promoter of the FMR1 gene.
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Affiliation(s)
- M Milà
- Servei de Genètica, Hospital Clínic, Barcelona, Catalunya, Spain.
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29
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Vasiliev GV, Merkulov VM, Kobzev VF, Merkulova TI, Ponomarenko MP, Kolchanov NA. Point mutations within 663-666 bp of intron 6 of the human TDO2 gene, associated with a number of psychiatric disorders, damage the YY-1 transcription factor binding site. FEBS Lett 1999; 462:85-8. [PMID: 10580097 DOI: 10.1016/s0014-5793(99)01513-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Single base mutations G-->A at position 663 and G-->T at position 666 of intron 6 of the human tryptophan oxygenase gene (TDO2) are associated with a variety of psychiatric disorders [Comings, D.E. et al. (1996) Pharmacogenetics 6, 307-318]. Binding of rat liver nuclear extract proteins to synthetic double-strand oligonucleotides corresponding to three allelic states of the region between 651 bp and 680 bp of human TDO2 intron 6 has been studied by gel shift assay. It has been demonstrated that to each allelic state of the region there corresponds a specific set of proteins that interacts with it. With the aid of computer analysis and using specific anti-YY-1 antibodies it has been shown that both mutations damage the YY-1 transcription factor binding site.
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Affiliation(s)
- G V Vasiliev
- Institute of Cytology and Genetics, Russian Academy of Sciences, Novosibirsk, Russia
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30
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Abstract
The fragile X syndrome is characterised by mental retardation, behavioural features, and physical features, such as a long face with large protruding ears and macro-orchidism. In 1991, after identification of the fragile X mental retardation (FMR1) gene, the cytogenetic marker (a fragile site at Xq27.3) became replaced by molecular diagnosis. The fragile X syndrome was one of the first examples of a "novel" class of disorders caused by a trinucleotide repeat expansion. In the normal population, the CGG repeat varies from six to 54 units. Affected subjects have expanded CGG repeats (>200) in the first exon of the FMR1 gene (the full mutation). Phenotypically normal carriers of the fragile X syndrome have a repeat in the 43 to 200 range (the premutation). The cloning of the FMR1 gene led to the characterisation of its protein product FMRP, encouraged further clinical studies, and opened up the possibility of more accurate family studies and fragile X screening programmes.
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Affiliation(s)
- B B de Vries
- Department of Clinical Genetics, University Hospital Dijkzigt and Erasmus University, Rotterdam, The Netherlands
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