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Hou F, Mao A, Shan S, Li Y, Meng W, Zhan J, Nie W, Jin H. Evaluating the clinical utility of a long-read sequencing-based approach in genetic testing of fragile-X syndrome. Clin Chim Acta 2023; 551:117614. [PMID: 38375623 DOI: 10.1016/j.cca.2023.117614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 10/19/2023] [Accepted: 10/22/2023] [Indexed: 02/21/2024]
Abstract
BACKGROUND Fragile X syndrome (FXS) arises from the FMR1 CGG expansion. Comprehensive genetic testing for FMR1 CGG expansions, AGG interruptions, and microdeletions is essential to provide genetic counseling for females carrying premutation alleles. However, conventional PCR-based FMR1 assays mainly focus on CGG repeats, and could detect AGG interruption only in males. METHODS The clinical utility of a long-read sequencing-based assay termed comprehensive analysis of FXS (CAFXS) was evaluated in 238 high-risk samples by comparing to conventional PCR assays. RESULTS PCR assays identified five premuation and three full mutation categories alleles in all the samples, and CAFXS successfully called all the FMR1 CGG expansion. CAFXS identified 24-bp microdeletions upstream to the trinucleotide region with 30 CGG repeats, which was miscalled by the length-based PCR methods. CAFXS also identified a 187-bp deletion in about 1/7 of the sequencing reads in a male patient with mosaic full mutation alleles. CAFXS allowed for precise constructing the FMR1 CGG repeat and AGG interruption pattern in all the samples, and identified a novel and alternative CGA interruption in one normal female sample. CONCLUSIONS CAFXS represents a more comprehensive and accurate approach for FXS genetic testing that potentially enables more informed genetic counseling compared to PCR-based methods.
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Affiliation(s)
- Fei Hou
- Department of Prenatal Diagnosis, Jinan Maternal and Child Health Hospital, Jinan 250001, Shandong Province, China
| | - Aiping Mao
- Berry Genomics Corporation, Beijing 102200, China
| | - Shan Shan
- Department of Prenatal Diagnosis, Jinan Maternal and Child Health Hospital, Jinan 250001, Shandong Province, China
| | - Yan Li
- Department of Prenatal Diagnosis, Jinan Maternal and Child Health Hospital, Jinan 250001, Shandong Province, China
| | - Wanli Meng
- Berry Genomics Corporation, Beijing 102200, China
| | - Jiahan Zhan
- Berry Genomics Corporation, Beijing 102200, China
| | - Wenying Nie
- Department of Prenatal Diagnosis, Jinan Maternal and Child Health Hospital, Jinan 250001, Shandong Province, China
| | - Hua Jin
- Department of Prenatal Diagnosis, Jinan Maternal and Child Health Hospital, Jinan 250001, Shandong Province, China.
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2
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Liang Q, Liu Y, Liu Y, Duan R, Meng W, Zhan J, Xia J, Mao A, Liang D, Wu L. Comprehensive Analysis of Fragile X Syndrome: Full Characterization of the FMR1 Locus by Long-Read Sequencing. Clin Chem 2022; 68:1529-1540. [PMID: 36171182 DOI: 10.1093/clinchem/hvac154] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Accepted: 07/21/2022] [Indexed: 11/14/2022]
Abstract
BACKGROUND Fragile X syndrome (FXS) is the most frequent cause of inherited X-linked intellectual disability. Conventional FXS genetic testing methods mainly focus on FMR1 CGG expansions and fail to identify AGG interruptions, rare intragenic variants, and large gene deletions. METHODS A long-range PCR and long-read sequencing-based assay termed comprehensive analysis of FXS (CAFXS) was developed and evaluated in Coriell and clinical samples by comparing to Southern blot analysis and triplet repeat-primed PCR (TP-PCR). RESULTS CAFXS accurately detected the number of CGG repeats in the range of 93 to at least 940 with mass fraction of 0.5% to 1% in the background of normal alleles, which was 2-4-fold analytically more sensitive than TP-PCR. All categories of mutations detected by control methods, including full mutations in 30 samples, were identified by CAFXS for all 62 clinical samples. CAFXS accurately determined AGG interruptions in all 133 alleles identified, even in mosaic alleles. CAFXS successfully identified 2 rare intragenic variants including the c.879A > C variant in exon 9 and a 697-bp microdeletion flanking upstream of CGG repeats, which disrupted primer annealing in TP-PCR assay. In addition, CAFXS directly determined the breakpoints of a 237.1-kb deletion and a 774.0-kb deletion encompassing the entire FMR1 gene in 2 samples. CONCLUSIONS Long-read sequencing-based CAFXS represents a comprehensive assay for identifying FMR1 CGG expansions, AGG interruptions, rare intragenic variants, and large gene deletions, which greatly improves the genetic screening and diagnosis for FXS.
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Affiliation(s)
- Qiaowei Liang
- Department of Medical Genetics, Hunan Jiahui Genetics Hospital, Changsha, Hunan, China
| | - Yingdi Liu
- Center for Medical Genetics and Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, China
| | - Yaning Liu
- Department of Medical Genetics, Hunan Jiahui Genetics Hospital, Changsha, Hunan, China
| | - Ranhui Duan
- Center for Medical Genetics and Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, China
| | - Wanli Meng
- Berry Genomics Corporation, Beijing, China
| | | | - Jiahui Xia
- Department of Medical Genetics, Hunan Jiahui Genetics Hospital, Changsha, Hunan, China
| | - Aiping Mao
- Berry Genomics Corporation, Beijing, China
| | - Desheng Liang
- Department of Medical Genetics, Hunan Jiahui Genetics Hospital, Changsha, Hunan, China.,Center for Medical Genetics and Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, China
| | - Lingqian Wu
- Department of Medical Genetics, Hunan Jiahui Genetics Hospital, Changsha, Hunan, China.,Center for Medical Genetics and Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, China
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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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Erbs E, Fenger-Grøn J, Jacobsen CM, Lildballe DL, Rasmussen M. Spontaneous rescue of a FMR1 repeat expansion and review of deletions in the FMR1 non-coding region. Eur J Med Genet 2021; 64:104244. [PMID: 34022415 DOI: 10.1016/j.ejmg.2021.104244] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 04/16/2021] [Accepted: 05/02/2021] [Indexed: 12/07/2022]
Abstract
Fragile X syndrome (FXS) is caused by CGG-repeat expansion in the 5' UTR of FMR1 of >200 repeats. Rarely, FXS is caused by deletions; however, it is not clear whether deletions including only the non-coding region of FMR1 are pathogenic. We report a deletion in the 5' UTR of FMR1 in an unaffected male infant and review 12 reported deletions involving only the non-coding region of FMR1. Genetic testing was requested in a male infant born to a mother harbouring a FMR1 full mutation. The maternal grandmother carried a FMR1 premutation. FMR1 CGG repeats were analysed using repeat-primed PCR. Only a short PCR fragment was amplified and subsequent Sanger sequencing detected an 88 bp deletion in hemizygous form. The deletion included all CGG repeats and flanking sequences but no FMR1 exons. Linkage analysis using STR markers revealed that the deletion had occurred on the allele, which was expanded in the mother and the maternal grandmother. Reverse transcription and quantitative PCR showed normal FMR1 mRNA levels. Grønskov et al. reported a 157 bp deletion of all CGG repeats and flanking sequences in a female without FXS hemizygous for the FMR1 gene due to a deletion on the other X chromosome. Protein expression was unaffected by the deletion. The reported deletion comprises the deletion detected in the male infant. At almost 2 years of age he is unaffected. Based on these observations and the normal FMR1 mRNA level, we conclude that a spontaneous rescue of an FMR1 repeat expansion has occurred.
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Affiliation(s)
- Emilie Erbs
- Department of Clinical Genetics, Lillebaelt Hospital, University Hospital of Southern Denmark, Vejle, Denmark.
| | - Jesper Fenger-Grøn
- Department of Paediatrics, Lillebaelt Hospital, University Hospital of Southern Denmark, Kolding, Denmark
| | - Cecilie Mondrup Jacobsen
- Department of Clinical Genetics, Lillebaelt Hospital, University Hospital of Southern Denmark, Vejle, Denmark
| | - Dorte Launholt Lildballe
- Department of Clinical Genetics, Lillebaelt Hospital, University Hospital of Southern Denmark, Vejle, Denmark
| | - Maria Rasmussen
- Department of Clinical Genetics, Lillebaelt Hospital, University Hospital of Southern Denmark, Vejle, Denmark; Department of Regional Health Research, University of Southern Denmark, Odense M, Denmark
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Rajaratnam A, Shergill J, Salcedo-Arellano M, Saldarriaga W, Duan X, Hagerman R. Fragile X syndrome and fragile X-associated disorders. F1000Res 2017; 6:2112. [PMID: 29259781 PMCID: PMC5728189 DOI: 10.12688/f1000research.11885.1] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 11/20/2017] [Indexed: 12/26/2022] Open
Abstract
Fragile X syndrome (FXS) is caused by a full mutation on the
FMR1 gene and a subsequent lack of FMRP, the protein product of
FMR1. FMRP plays a key role in regulating the translation of many proteins involved in maintaining neuronal synaptic connections; its deficiency may result in a range of intellectual disabilities, social deficits, psychiatric problems, and dysmorphic physical features. A range of clinical involvement is also associated with the
FMR1 premutation, including fragile X-associated tremor ataxia syndrome, fragile X-associated primary ovarian insufficiency, psychiatric problems, hypertension, migraines, and autoimmune problems. Over the past few years, there have been a number of advances in our knowledge of FXS and fragile X-associated disorders, and each of these advances offers significant clinical implications. Among these developments are a better understanding of the clinical impact of the phenomenon known as mosaicism, the revelation that various types of mutations can cause FXS, and improvements in treatment for FXS.
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Affiliation(s)
| | | | | | - Wilmar Saldarriaga
- MIND Institute, UC Davis Health, Sacramento, CA, USA.,Department of Morphology and Obstetrics & Gynecology, Universidad del Valle, School of Medicine, Cali, Valle del Cauca, Colombia
| | - Xianlai Duan
- MIND Institute, UC Davis Health, Sacramento, CA, USA.,Department of Neurology, The Third Hospital of Changsha, Hunan Sheng, China
| | - Randi Hagerman
- MIND Institute, UC Davis Health, Sacramento, CA, USA.,Department of Pediatrics, University of California, Davis, School of Medicine, Sacramento, CA, USA
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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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Germinal mosaicism for a deletion of the FMR1 gene leading to fragile X syndrome. Eur J Med Genet 2016; 59:459-62. [PMID: 27546052 DOI: 10.1016/j.ejmg.2016.08.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Accepted: 08/09/2016] [Indexed: 11/20/2022]
Abstract
Aberrant CGG trinucleotide amplification within the FMR1 gene, which spans approximately 38 Kb of genomic DNA is almost always what leads to fragile X syndrome (FXS). However, deletions of part or the entire FMR1 gene can also cause FXS. Both CGG amplification-induced silencing and deletions result in the absence of the FMR1 gene product, FMRP. Here, we report a rare case of germinal mosaicism of a deletion encompassing approximately 300 Kb of DNA, which by removing the entire FMR1 gene led to FXS. The male proband, carrying the deletion, presented in clinic with the typical features of FXS. His mother was analyzed by FISH on metaphase chromosomes with cosmid probe c22.3 spanning the FMR1 locus, and she was found not to carry the deletion on 30 analyzed cells from peripheral blood lymphocytes. Prenatal examination of the mother's third pregnancy showed that the male fetus also had the same deletion as the proband. Following this prenatal diagnosis, FISH analysis in the mother was expanded to 400 metaphases from peripheral lymphocytes, and a heterozygous FMR1 deletion was found in three. Although this result could be considered questionable from a diagnostic point of view, it indicates that the deletion is in the ovary's germinal cells.
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8
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Gonçalves TF, dos Santos JM, Gonçalves AP, Tassone F, Mendoza-Morales G, Ribeiro MG, Kahn E, Boy R, Pimentel MMG, Santos-Rebouças CB. Finding FMR1 mosaicism in Fragile X syndrome. Expert Rev Mol Diagn 2016; 16:501-7. [PMID: 26716517 DOI: 10.1586/14737159.2016.1135739] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVE Almost all patients with Fragile X Syndrome (FXS) exhibit a CGG repeat expansion (full mutation) in the Fragile Mental Retardation 1 gene (FMR1). Here, the authors report five unrelated males with FXS harboring a somatic full mutation/deletion mosaicism. METHODS Mutational profiles were only elucidated by using a combination of molecular approaches (CGG-based PCR, Sanger sequencing, MS-MLPA, Southern blot and mPCR). RESULTS Four patients exhibited small deletions encompassing the CGG repeats tract and flanking regions, whereas the remaining had a larger deletion comprising at least exon 1 and part of intron 1 of FMR1 gene. The presence of a 2-3 base pairs microhomology in proximal and distal non-recurrent breakpoints without scars supports the involvement of microhomology mediated induced repair (MMBIR) mechanism in three small deletions. CONCLUSION The authors data highlights the importance of using different research methods to elucidate atypical FXS mutational profiles, which are clinically undistinguishable and may have been underestimated.
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Affiliation(s)
| | | | | | - Flora Tassone
- b Department of Biochemistry and Molecular Medicine , UC Davis School of Medicine, University of California, Davis , Sacramento , CA , USA.,c Davis MIND Institute , Sacramento , CA , USA
| | - Guadalupe Mendoza-Morales
- b Department of Biochemistry and Molecular Medicine , UC Davis School of Medicine, University of California, Davis , Sacramento , CA , USA
| | - Márcia Gonçalves Ribeiro
- d Clinical Genetics Service , IPPMG, Federal University of Rio de Janeiro , Rio de Janeiro , Brazil
| | - Evelyn Kahn
- d Clinical Genetics Service , IPPMG, Federal University of Rio de Janeiro , Rio de Janeiro , Brazil
| | - Raquel Boy
- e Pedro Ernesto University Hospital , State University of Rio de Janeiro , Rio de Janeiro , Brazil
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9
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Abstract
Fragile X syndrome (FXS), a trinucleotide repeat disorder, is the most common heritable form of cognitive impairment. Since the discovery of the FMR1 gene in 1991, great strides have been made in the field of molecular diagnosis for FXS. Cytogenetic analysis, which was the method of diagnosis in the early 1990, was replaced by Southern blot and PCR analysis albeit with some limitations. In the past few years many PCR-based methodologies, able to amplify large full mutation expanded alleles, with or without methylation, have been proposed. Reviewed here are the advantages, disadvantages and limitations of the most recent developments in the field of FXS diagnosis.
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Affiliation(s)
- Flora Tassone
- a Department of Biochemistry and Molecular Medicine , University of California, Davis, School of Medicine , Davis , CA 95616 , USA.,b MIND Institute , University of California Davis Medical Center , Sacramento , CA 95817 , USA
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10
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Luo S, Huang W, Xia Q, Du Q, Wu L, Duan R. Mutational analyses of the FMR1 gene in Chinese pediatric population of fragile x suspects: low tolerance for point mutation. J Child Neurol 2015; 30:803-6. [PMID: 24963073 DOI: 10.1177/0883073814538508] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 05/07/2014] [Indexed: 11/17/2022]
Abstract
CGG repeat expansion is the most common cause of fragile X syndrome. Numerous efforts have been made to identify novel mutations in patients with intellectual disability, developmental delay, and/or autism. To evaluate the mutational spectrum in the at-risk Chinese population, 60 pediatric patients presenting fragile X traits but normal-sized CGG repeats were sequenced for all 17 exons and regulatory regions in FMR1. A c.879A>C mutation, reported to alter a neighboring splicing, was detected in a severely retarded male and his normal mother. However, the exon junction appears unaffected. A 237-kb deletion covering the entire FMR1 was identified to cause moderate intellectual disability and marked hyperactivity in an 8-year-old boy. The 5' and 3' breakpoints were buried in the surrounding long interspersed and short interspersed elements, respectively. In general, missense mutations do not commonly cause fragile X syndrome, whereas deletions should be considered with caution in patient referrals presenting with developmental delay and/or ordinary retardation.
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Affiliation(s)
- Shiyu Luo
- State Key Laboratory of Medical Genetics, Xiangya School of Medicine, Central South University, Changsha, 410078, Hunan, China
| | - Wen Huang
- State Key Laboratory of Medical Genetics, Xiangya School of Medicine, Central South University, Changsha, 410078, Hunan, China
| | - Qiuping Xia
- State Key Laboratory of Medical Genetics, Xiangya School of Medicine, Central South University, Changsha, 410078, Hunan, China
| | - Qian Du
- State Key Laboratory of Medical Genetics, Xiangya School of Medicine, Central South University, Changsha, 410078, Hunan, China
| | - Lingqian Wu
- State Key Laboratory of Medical Genetics, Xiangya School of Medicine, Central South University, Changsha, 410078, Hunan, China
| | - Ranhui Duan
- State Key Laboratory of Medical Genetics, Xiangya School of Medicine, Central South University, Changsha, 410078, Hunan, China
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Burruss DM, Wood TC, Espinoza L, Dwivedi A, Holden KR. Severe Hunter syndrome (mucopolysaccharidosis II) phenotype secondary to large deletion in the X chromosome encompassing IDS, FMR1, and AFF2 (FMR2). J Child Neurol 2012; 27:786-90. [PMID: 22190500 DOI: 10.1177/0883073811425860] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A 2-year-old boy with an initial diagnosis of Hunter syndrome (mucopolysaccharidosis II) had a more severe phenotype than expected, which warranted further evaluation. The patient had severe infantile global neurodevelopmental delays, macrocephaly with a prominent forehead, coarse facial features with clear corneas, chronic congestion with snoring, wide-spaced teeth, short thick neck, hepatomegaly, an inguinal hernia repaired, early clawhand deformities, and severe generalized hypotonia. X chromosome microarray revealed a large deletion encompassing the genes IDS, FMR1, and AFF2 (FMR2) confirming the diagnoses of both Hunter and fragile X syndromes. This case is also a reminder to clinicians that for optimum patient care, further diagnostic testing is warranted if there is concern that a patient's phenotype is more severe or complex than would be expected for the initial neurogenetic diagnosis.
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Affiliation(s)
- Day M Burruss
- College of Medicine, Medical University of South Carolina, Charleston, SC, USA
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12
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Abstract
Alternate DNA structures that deviate from B-form double-stranded DNA such as G-quadruplex (G4) DNA can be formed by sequences that are widely distributed throughout the human genome. G-quadruplex secondary structures, formed by the stacking of planar quartets composed of four guanines that interact by Hoogsteen hydrogen bonding, can affect cellular DNA replication and transcription, and influence genomic stability. The unique metabolism of G-rich chromosomal regions that potentially form quadruplexes may influence a number of biological processes including immunoglobulin gene rearrangements, promoter activation and telomere maintenance. A number of human diseases are characterized by telomere defects, and it is proposed that G-quadruplex structures which form at telomere ends play an important role in telomere stability. Evidence from cellular studies and model organisms suggests that diseases with known defects in G4 DNA helicases are likely to be perturbed in telomere maintenance and cellular DNA replication. In this minireview, we discuss the connections of G-quadruplex nucleic acids to human genetic diseases and cancer based on the recent literature.
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Affiliation(s)
- Yuliang Wu
- Laboratory of Molecular Gerontology, National Institute on Aging, Baltimore, MD, USA
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The -413C > G substitution in the promoter of the FMR1 gene is not associated with the fragile X syndrome phenotype. Mol Cell Probes 2009; 24:107-9. [PMID: 19836446 DOI: 10.1016/j.mcp.2009.10.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Revised: 09/03/2009] [Accepted: 10/05/2009] [Indexed: 11/15/2022]
Abstract
Most common inherited form of intellectual disability, fragile X syndrome is associated to an expansion of greater than 200 CGG repeats in the 5' untranslated region of the FMR1 gene on the X chromosome which causes transcriptional silencing and deficiency of the encoded protein FMRP. Molecular diagnosis is performed through a combination of PCR to identify fewer than 100-150 repeats and of Southern blot analysis to identify longer alleles and the methylation status of the FMR1 promoter. We present a family with one patient with mild mental retardation who showed an atypical profile at Southern analysis due to the -413C > G transversion located in the FMR1 promoter which had been described as possibly associated with mental retardation. We demonstrated this variant in other four family members along three generations, including the maternal grandfather who did not manifest any pathological feature. Though the -413C > G substitution was not found in a large control series, these findings allowed to exclude its role in determining the disease phenotype.
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