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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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Brand BA, Blesson AE, Smith-Hicks CL. The Impact of X-Chromosome Inactivation on Phenotypic Expression of X-Linked Neurodevelopmental Disorders. Brain Sci 2021; 11:brainsci11070904. [PMID: 34356138 PMCID: PMC8305405 DOI: 10.3390/brainsci11070904] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Revised: 06/16/2021] [Accepted: 06/20/2021] [Indexed: 12/20/2022] Open
Abstract
Nearly 20% of genes located on the X chromosome are associated with neurodevelopmental disorders (NDD) due to their expression and role in brain functioning. Given their location, several of these genes are either subject to or can escape X-chromosome inactivation (XCI). The degree to which genes are subject to XCI can influence the NDD phenotype between males and females. We provide a general review of X-linked NDD genes in the context of XCI and detailed discussion of the sex-based differences related to MECP2 and FMR1, two common X-linked causes of NDD that are subject to XCI. Understanding the effects of XCI on phenotypic expression of NDD genes may guide the development of stratification biomarkers in X-linked disorders.
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Affiliation(s)
- Boudewien A Brand
- Center for Autism and Related Disorders, Kennedy Krieger Institute, Baltimore, MD 21205, USA; (B.A.B.); (A.E.B.)
| | - Alyssa E Blesson
- Center for Autism and Related Disorders, Kennedy Krieger Institute, Baltimore, MD 21205, USA; (B.A.B.); (A.E.B.)
| | - Constance L. Smith-Hicks
- Department of Neurology and Developmental Medicine, Kennedy Krieger Institute, Baltimore, MD 21205, USA
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA
- Correspondence:
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Bland KM, Aharon A, Widener EL, Song MI, Casey ZO, Zuo Y, Vidal GS. FMRP regulates the subcellular distribution of cortical dendritic spine density in a non-cell-autonomous manner. Neurobiol Dis 2021; 150:105253. [PMID: 33421563 PMCID: PMC7878418 DOI: 10.1016/j.nbd.2021.105253] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Revised: 12/15/2020] [Accepted: 01/04/2021] [Indexed: 01/18/2023] Open
Abstract
Fragile X syndrome (FXS) is the most common form of intellectual disability that arises from the dysfunction of a single gene-Fmr1. The main neuroanatomical correlate of FXS is elevated dendritic spine density on cortical pyramidal neurons, which has been modeled in Fmr1-/Y mice. However, the cell-autonomous contribution of Fmr1 on cortical dendritic spine density has not been assessed. Even less is known about the role of Fmr1 in heterozygous female mosaic mice, which are a putative model for human Fmr1 full mutation carriers (i.e., are heterozygous for the full Fmr1-silencing mutation). In this neuroanatomical study, spine density in cortical pyramidal neurons of Fmr1+/- and Fmr1-/Y mice was studied at multiple subcellular compartments, layers, and brain regions. Spine density in Fmr1+/- mice is higher than WT but lower than Fmr1-/Y. Not all subcellular compartments in layer V Fmr1+/- and Fmr1-/Y cortical pyramidal neurons are equally affected: the apical dendrite, a key subcellular compartment, is principally affected over basal dendrites. Within apical dendrites, spine density is differentially affected across branch orders. Finally, identification of FMRP-positive and FMRP-negative neurons within Fmr1+/- permitted the study of the cell-autonomous effect of Fmr1 on spine density. Surprisingly, layer V cortical pyramidal spine density between FMRP-positive and FMRP-negative neurons does not differ, suggesting that the regulation of the primary neuroanatomical defect of FXS-elevated spine density-is non-cell-autonomous.
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Affiliation(s)
- Katherine M Bland
- Department of Biology, James Madison University, Harrisonburg, VA 22801, United States
| | - Adam Aharon
- Department of Molecular, Cell and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, United States
| | - Eden L Widener
- Department of Biology, James Madison University, Harrisonburg, VA 22801, United States
| | - M Irene Song
- Department of Biology, James Madison University, Harrisonburg, VA 22801, United States
| | - Zachary O Casey
- Department of Biology, James Madison University, Harrisonburg, VA 22801, United States
| | - Yi Zuo
- Department of Molecular, Cell and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, United States.
| | - George S Vidal
- Department of Biology, James Madison University, Harrisonburg, VA 22801, United States.
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Unraveling unusual X-chromosome patterns during fragile-X syndrome genetic testing. Clin Chim Acta 2018; 476:167-172. [DOI: 10.1016/j.cca.2017.11.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 11/16/2017] [Accepted: 11/19/2017] [Indexed: 01/07/2023]
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Geens M, Seriola A, Barbé L, Santalo J, Veiga A, Dée K, Van Haute L, Sermon K, Spits C. Female human pluripotent stem cells rapidly lose X chromosome inactivation marks and progress to a skewed methylation pattern during culture. Mol Hum Reprod 2016; 22:285-98. [DOI: 10.1093/molehr/gaw004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 01/13/2016] [Indexed: 12/25/2022] Open
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Chaudhary AG, Hussein IR, Abuzenadah A, Gari M, Bassiouni R, Sogaty S, Lary S, Al-Quaiti M, Al Balwi M, Al Qahtani M. Molecular diagnosis of fragile X syndrome using methylation sensitive techniques in a cohort of patients with intellectual disability. Pediatr Neurol 2014; 50:368-76. [PMID: 24630283 DOI: 10.1016/j.pediatrneurol.2013.11.020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 09/04/2013] [Accepted: 11/23/2013] [Indexed: 11/26/2022]
Abstract
BACKGROUND Fragile X syndrome, the most common form of inherited intellectual disability, is caused by expansion of CGG trinucleotide repeat at the 5' untranslated region of the FMR1 gene at Xq27. In affected individuals, the CGG repeat expansion leads to hypermethylation and the gene is transcriptionally inactive. Our aim was to identify fragile X syndrome among children with intellectual disability in Saudi Arabia. PATIENTS AND METHODS The study included 63 patients (53 males, 10 females) presented with intellectual disability, 29 normal subjects, and 23 other family members. DNA samples from six patients previously diagnosed with fragile X syndrome by Southern blot technique were used as positive controls. The method was based on bisulfite treatment of DNA followed by two different techniques. The first technique applied polymerase chain reaction amplification using one set of primers specific for amplifying methylated CpG dinucleotide region; another set designed to amplify the unmethylated CGG repeats. The second technique used the methylation-specific melting curve analysis for detection of methylation status of the FMR1 promoter region. RESULTS Molecular testing using methylation sensitive polymerase chain reaction had shown amplified products in all normal subjects using unmethylated but not methylated primers indicating normal alleles, whereas amplified products were obtained using methylated polymerase chain reaction primers in fragile X syndrome-positive samples and in 9 of 53 males, indicating affected individuals. Molecular testing using melting curve analysis has shown a single low melting peak in all normal males and in (44/53) patients indicating unmethylated FMR1 gene, whereas high melting peak indicating methylated gene was observed in the fragile X syndrome-positive samples and in 9 of 53 patients. We found 100% concordance between results of both techniques and the results of Southern blot analysis. Three samples have shown both methylated and unmethylated alleles, indicating possible mosaicism. No female patients or carriers could be detected by both techniques. CONCLUSION The technique can be applied for the rapid screening for fragile X syndrome among patients with intellectual disability. The impact of mosaicism on clinical severity needs further investigation.
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Affiliation(s)
- Adeel G Chaudhary
- Faculty of Medical Sciences, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
| | - Ibtessam R Hussein
- Center of Excellence in Genomic Medicine Research, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia.
| | - Adel Abuzenadah
- Faculty of Medical Sciences, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
| | - Mamdouh Gari
- Faculty of Medical Sciences, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
| | - Randa Bassiouni
- Pediatric Hospital, Ministry of Health, Al Taif, Kingdom of Saudi Arabia
| | | | - Sahira Lary
- Faculty of Science, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
| | - Maha Al-Quaiti
- Center of Excellence in Genomic Medicine Research, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
| | - Mohammed Al Balwi
- King Abdulaziz Medical City for National Guard Health Affairs, and King Saud bin Abdulaziz University for Health Sciences, Riyadh, Kingdom of Saudi Arabia
| | - Mohammed Al Qahtani
- Faculty of Medical Sciences, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
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Politte LC, McDougle CJ. Phase II and III drugs for the treatment of fragile X syndrome. Expert Opin Orphan Drugs 2012. [DOI: 10.1517/21678707.2013.750240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Chaste P, Betancur C, Gérard-Blanluet M, Bargiacchi A, Kuzbari S, Drunat S, Leboyer M, Bourgeron T, Delorme R. High-functioning autism spectrum disorder and fragile X syndrome: report of two affected sisters. Mol Autism 2012; 3:5. [PMID: 22738402 PMCID: PMC3444384 DOI: 10.1186/2040-2392-3-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Accepted: 06/08/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability (ID), as well as the most frequent monogenic cause of autism spectrum disorder (ASD). Men with FXS exhibit ID, often associated with autistics features, whereas women heterozygous for the full mutation are typically less severely affected; about half have a normal or borderline intelligence quotient (IQ). Previous findings have shown a strong association between ID and ASD in both men and women with FXS. We describe here the case of two sisters with ASD and FXS but without ID. One of the sisters presented with high-functioning autism, the other one with pervasive developmental disorder not otherwise specified and low normal IQ. METHODS The methylation status of the mutated FMR1 alleles was examined by Southern blot and methylation-sensitive polymerase chain reaction. The X-chromosome inactivation was determined by analyzing the methylation status of the androgen receptor at Xq12. RESULTS Both sisters carried a full mutation in the FMR1 gene, with complete methylation and random X chromosome inactivation. We present the phenotype of the two sisters and other family members. CONCLUSIONS These findings suggest that autistic behaviors and cognitive impairment can manifest as independent traits in FXS. Mutations in FMR1, known to cause syndromic autism, may also contribute to the etiology of high-functioning, non-syndromic ASD, particularly in women. Thus, screening for FXS in patients with ASD should not be limited to those with comorbid ID.
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Affiliation(s)
- Pauline Chaste
- Human Genetics and Cognitive Functions, Institut Pasteur, Paris, France.
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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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Wang X, Soloway PD, Clark AG. Paternally biased X inactivation in mouse neonatal brain. Genome Biol 2010; 11:R79. [PMID: 20663224 PMCID: PMC2926790 DOI: 10.1186/gb-2010-11-7-r79] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2010] [Revised: 05/10/2010] [Accepted: 07/27/2010] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND X inactivation in female eutherian mammals has long been considered to occur at random in embryonic and postnatal tissues. Methods for scoring allele-specific differential expression with a high degree of accuracy have recently motivated a quantitative reassessment of the randomness of X inactivation. RESULTS After RNA-seq data revealed what appeared to be a chromosome-wide bias toward under-expression of paternal alleles in mouse tissue, we applied pyrosequencing to mouse brain cDNA samples from reciprocal cross F1 progeny of divergent strains and found a small but consistent and highly statistically significant excess tendency to under-express the paternal X chromosome. CONCLUSIONS The bias toward paternal X inactivation is reminiscent of marsupials (and extraembryonic tissues in eutherians), suggesting that there may be retained an evolutionarily conserved epigenetic mark driving the bias. Allelic bias in expression is also influenced by the sampling effect of X inactivation and by cis-acting regulatory variation (eQTL), and for each gene we quantify the contributions of these effects in two different mouse strain combinations while controlling for variability in Xce alleles. In addition, we propose an efficient method to identify and confirm genes that escape X inactivation in normal mice by directly comparing the allele-specific expression ratio profile of multiple X-linked genes in multiple individuals.
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Affiliation(s)
- Xu Wang
- Deptartment of Molecular Biology and Genetics, Cornell University, 227 Biotechnology Building, Ithaca, NY 14853, USA
- Cornell Center for Comparative and Population Genomics, 130 Biotechnology Building, Cornell University, Ithaca, NY 14853, USA
| | - Paul D Soloway
- Division of Nutritional Sciences, College of Agriculture and Life Sciences, 211 Weill Hall, Cornell University, Ithaca, NY 14853, USA
| | - Andrew G Clark
- Deptartment of Molecular Biology and Genetics, Cornell University, 227 Biotechnology Building, Ithaca, NY 14853, USA
- Cornell Center for Comparative and Population Genomics, 130 Biotechnology Building, Cornell University, Ithaca, NY 14853, USA
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Martínez R, Bonilla-Henao V, Ramos I, Sobrino F, Lucas M, Pintado E. May anomalous X chromosome methylation be responsible for the spontaneous abortion of a male foetus? J Genet 2009; 87:261-4. [PMID: 19147911 DOI: 10.1007/s12041-008-0040-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- R Martínez
- Departamento de Bioquimica Médica y Biología Molecular, Facultad de Medicina, Avda. Sanchez Pizjuán, 4 E-41009, Sevilla, Spain
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Paradas C, Solano F, Carrillo F, Fernández C, Bautista J, Pintado E, Lucas M. Highly skewed inactivation of the wild-type X-chromosome in asymptomatic female carriers of spinal and bulbar muscular atrophy (Kennedy’s disease). J Neurol 2008; 255:853-7. [DOI: 10.1007/s00415-008-0766-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2007] [Revised: 05/23/2007] [Accepted: 10/05/2007] [Indexed: 10/22/2022]
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Butler MG, Theodoro MF, Bittel DC, Kuipers PJ, Driscoll DJ, Talebizadeh Z. X-chromosome inactivation patterns in females with Prader-Willi syndrome. Am J Med Genet A 2007; 143A:469-75. [PMID: 17036338 PMCID: PMC5459689 DOI: 10.1002/ajmg.a.31506] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Prader-Willi syndrome (PWS) is a complex neurodevelopmental disorder caused by loss of paternally expressed genes from the 15q11-q13 region generally due to a paternally-derived deletion of the 15q11-q13 region or maternal disomy 15 (UPD). Maternal disomy 15 is usually caused by maternal meiosis I non-disjunction associated with advanced maternal age and after fertilization with a normal sperm leading to trisomy 15, a lethal condition unless trisomy rescue occurs with loss of the paternal chromosome 15. To further characterize the pathogenesis of maternal disomy 15 process in PWS, the status of X-chromosome inactivation was calculated to determine whether non-random skewing of X-inactivation is present indicating a small pool of early embryonic cells. We studied X-chromosome inactivation in 25 females with PWS-UPD, 35 with PWS-deletion, and 50 controls (with similar means, medians, and age ranges) using the polymorphic androgen receptor (AR) gene assay. A significant positive correlation (r = 0.5, P = 0.01) was seen between X-chromosome inactivation and age for only the UPD group. Furthermore, a significantly increased level (P = 0.02) of extreme X-inactivation skewness (>90%) was detected in our PWS-UPD group (24%) compared to controls (4%). This observation could indicate that trisomy 15 occurred at conceptus with trisomy rescue in early pregnancy leading to extreme skewness in several PWS-UPD subjects. Extreme X-inactivation skewness may also lead to additional risks for X-linked recessive disorders in PWS females with UPD and extreme X-chromosome skewness.
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Affiliation(s)
- Merlin G Butler
- Section of Medical Genetics and Molecular Medicine, Children's Mercy Hospitals and Clinics and University of Missouri, Kansas City School of Medicine, Kansas City, Missouri 64108, USA.
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Hanson JE, Madison DV. Presynaptic FMR1 genotype influences the degree of synaptic connectivity in a mosaic mouse model of fragile X syndrome. J Neurosci 2007; 27:4014-8. [PMID: 17428978 PMCID: PMC6672544 DOI: 10.1523/jneurosci.4717-06.2007] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Almost all female and some male fragile X syndrome (FXS) patients are mosaic for expression of the FMR1 gene, yet all research in models of FXS has been in animals uniformly lacking Fmr1 expression. Therefore, we developed a system allowing neuronal genotype to be visualized in vitro in mouse brain slices mosaic for Fmr1 expression. Whole-cell recordings from individual pairs of presynaptic and postsynaptic neurons in organotypic hippocampal slices were used to probe the cell-autonomous effects of Fmr1 genotype in mosaic networks. These recordings revealed that wild-type presynaptic neurons formed synaptic connections at a greater rate than presynaptic neurons lacking normal Fmr1 function in mosaic networks. At the same time, the postsynaptic Fmr1 genotype did not influence the probability that a neuron received synaptic connections. Asymmetric presynaptic function during development of the brain could result in a decreased participation in network function by the portion of neurons lacking FMR1 expression.
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Affiliation(s)
- Jesse E. Hanson
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305
| | - Daniel V. Madison
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305
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Dahl C, Grønskov K, Larsen LA, Guldberg P, Brøndum-Nielsen K. A homogeneous assay for analysis of FMR1 promoter methylation in patients with fragile X syndrome. Clin Chem 2007; 53:790-3. [PMID: 17259243 DOI: 10.1373/clinchem.2006.080762] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
BACKGROUND Fragile X syndrome is caused by the expansion of a CGG trinucleotide repeat at the 5' untranslated region of the fragile X mental retardation 1 gene (FMR1). When expanded to >200 repeats (full mutation), the repeat region and the adjacent promoter CpG island become hypermethylated, rendering FMR1 transcriptionally inactive. Conventional molecular diagnosis of fragile X syndrome involves determination of the CGG repeat number by Southern blot analysis. METHODS A homogeneous methylation-specific melting curve analysis (MS-MCA) assay for methylation status of the FMR1 promoter region was developed on the LightCycler platform. Genomic DNA was treated with sodium bisulfite, and a region containing 8 CpG sites was amplified in the presence of SYBR Green I, using primers that do not differentiate between methylated and unmethylated FMR1 molecules. After amplification, the samples were melted at 0.05 degrees C/s, and fluorescence melting curves were recorded. We studied samples, previously characterized by Southern blot analyses, from 10 female and 10 male donors with normal numbers of CGG trinucleotide repeats, 9 male donors who were premutation carriers, 4 male donors who carried both a premutation and a full mutation, and 25 patients with fragile X syndrome. RESULTS Samples from all 20 male patients with fragile X syndrome showed a high melting peak corresponding to fully methylated FMR1, whereas samples from healthy males showed a single low melting peak corresponding to unmethylated FMR1. Of 24 samples from affected males, 9 (38%) showed 2 melting peaks, suggesting that cellular methylation mosaicism is common in fragile X syndrome. CONCLUSIONS MS-MCA allows rapid and reliable identification of fragile X syndrome in male patients.
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Affiliation(s)
- Christina Dahl
- Institute of Cancer Biology, Danish Cancer Society, Copenhagen, Denmark
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