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Capalbo A, Fabiani M, Caroselli S, Poli M, Girardi L, Patassini C, Favero F, Cimadomo D, Vaiarelli A, Simon C, Rienzi LF, Ubaldi FM. Clinical validity and utility of preconception expanded carrier screening for the management of reproductive genetic risk in IVF and general population. Hum Reprod 2021; 36:2050-2061. [PMID: 34021342 DOI: 10.1093/humrep/deab087] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Revised: 03/15/2021] [Indexed: 11/14/2022] Open
Abstract
STUDY QUESTION What is the clinical validity and utility of preconception Expanded Carrier Screening (ECS) application on the management of prospective parents? SUMMARY ANSWER The high detection rate of at-risk couples (ARCs) and the high proportion opting for IVF/preimplantation genetic testing (PGT) treatment demonstrate the clinical utility of ECS in the preconception space in IVF and general population. WHAT IS KNOWN ALREADY About 2-4% of couples are at risk of conceiving a child with an autosomal recessive or X-linked genetic disorder. In recent years, the increasing cost-effectiveness of genetic diagnostic techniques has allowed the creation of ECS panels for the simultaneous detection of multiple recessive disorders. Comprehensive preconception genetic screening holds the potential to significantly improve couple's genetic risk assessment and reproductive planning to avoid detectable inheritable genetic offspring. STUDY DESIGN, SIZE, DURATION A total of 3877 individuals without a family history of genetic conditions were analyzed between January 2017 and January 2020. Of the enrolled individuals, 1212 were gamete donors and 2665 were patients planning on conceiving from both the IVF and the natural conception group. From the non-donor cohort, 1133 were analyzed as individual patients, while the remaining ones were analyzed as couples, for a total of 766 couples. PARTICIPANTS/MATERIALS, SETTING, METHODS A focused ECS panel was developed following American College of Obstetrics and Gynecology ACOG-recommended criteria (prevalence, carrier rate, severity), including highly penetrant severe childhood conditions. Couples were defined at-risk when both partners carried an autosomal recessive pathogenic/likely pathogenic variant (PLP) on the same gene or when the woman was a carrier of an X-linked PLP variant. ARC detection rate defined the clinical validity of the ECS approach. Clinical utility was evaluated by monitoring ARCs reproductive decision making. MAIN RESULTS AND THE ROLE OF CHANCE A total of 402 individuals (10.4%) showed PLP for at least one of the genes tested. Among the 766 couples tested, 173 showed one carrier partner (22.6%), whereas 20 couples (2.6%) were found to be at increased risk. Interestingly, one ARC was identified as a result of cascade testing in the extended family of an individual carrying a pathogenic variant on the Survival Of Motor Neuron 1SMN1 gene. Of the identified ARCs, 5 (0.7%) were at risk for cystic fibrosis, 5 (0.7%) for fragile X syndrome, 4 (0.5%) for spinal muscular atrophy, 4 (0.5%) for Beta-Thalassemia/Sickle Cell Anemia, 1 (0.1%) for Smith-Lemli-Opitz Syndrome and 1 (0.1%) for Duchenne/Becker Dystrophy. Fifteen ARCs were successfully followed up from both the IVF and the natural conception groups. All of these (15/15) modified their reproductive planning by undergoing ART with Preimplantation Genetic Testing for Monogenic disease and Aneuploidies (PGT-M and PGT-A). To date, 6/15 (40%) couples completed their PGT cycle with euploid/unaffected embryos achieving a pregnancy after embryo transfer and three of them have already had an unaffected baby. LIMITATIONS, REASONS FOR CAUTION The use of a limited panel of core gene-disease pairs represents a limitation on the research perspective as it can underestimate the rate of detectable carriers and ARCs in this cohort of prospective parents. Expanding the scope of ECS to a larger panel of conditions is becoming increasingly feasible, thanks to a persistent technological evolution and progressive cataloging of gene-disease associations. WIDER IMPLICATIONS OF THE FINDINGS These results highlight the potential clinical validity and utility of ECS in reducing the risk of a pregnancy affected by a detectable inheritable genetic condition. The steady reduction in the costs of genetic analyses enables the expansion of monogenic testing/screening applications at the preimplantation stage, thus, providing valid decisional support and reproductive autonomy to patients, particularly in the context of IVF. STUDY FUNDING/COMPETING INTEREST(S) No external funding was used for this study. A.C., M.F., S.C., M.P., L.G., and C.P. are employees of Igenomix Italy. C.S. is the head of the scientific board of Igenomix. TRIAL REGISTRATION NUMBER N/A.
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Affiliation(s)
- A Capalbo
- Igenomix Italy, Marostica, Italy.,Igenomix Foundation, INCLIVA, Valencia, Spain
| | | | | | - M Poli
- Igenomix Italy, Marostica, Italy
| | | | | | | | - D Cimadomo
- GeneraLife, Center for Reproductive Medicine, Clinica Valle Giulia, Rome, Italy
| | - A Vaiarelli
- GeneraLife, Center for Reproductive Medicine, Clinica Valle Giulia, Rome, Italy
| | - C Simon
- Igenomix Italy, Marostica, Italy.,Igenomix Foundation, INCLIVA, Valencia, Spain.,Department of Obstetrics and Gynecology, University of Valencia, Valencia, Spain.,Department of Obstetrics and Gynecology BIDMC, Harvard University, Cambridge, MA, USA
| | - L F Rienzi
- GeneraLife, Center for Reproductive Medicine, Clinica Valle Giulia, Rome, Italy
| | - F M Ubaldi
- GeneraLife, Center for Reproductive Medicine, Clinica Valle Giulia, Rome, Italy
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Sihombing NRB, Winarni TI, Utari A, van Bokhoven H, Hagerman RJ, Faradz SMH. Surveillance and prevalence of fragile X syndrome in Indonesia. Intractable Rare Dis Res 2021; 10:11-16. [PMID: 33614370 PMCID: PMC7882090 DOI: 10.5582/irdr.2020.03101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Fragile X syndrome (FXS) is the most prevalent inherited cause of intellectual disability (ID) and autism spectrum disorder (ASD). Many studies have been conducted over the years, however, in Indonesia there is relatively less knowledge on the prevalence of FXS. We reviewed all studies involving FXS screening and cascade testing of the high-risk population in Indonesia for two decades, to elucidate the prevalence, as well as explore the presence of genetic clusters of FXS in Indonesia. The prevalence of FXS in the ID population of Indonesia ranged between 0.9-1.9%, while in the ASD population, the percentage was higher (6.15%). A screening and cascade testing conducted in a small village on Java Island showed a high prevalence of 45% in the ID population, suggesting a genetic cluster. The common ancestry of all affected individuals was suggestive of a founder effect in the region. Routine screening and subsequent cascade testing are essential, especially in cases of ID and ASD of unknown etiology in Indonesia.
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Affiliation(s)
- Nydia Rena Benita Sihombing
- Division of Human Genetics, Center for Biomedical Research (CEBIOR), Faculty of Medicine, Diponegoro University/Diponegoro National Hospital, Semarang, Indonesia
| | - Tri Indah Winarni
- Division of Human Genetics, Center for Biomedical Research (CEBIOR), Faculty of Medicine, Diponegoro University/Diponegoro National Hospital, Semarang, Indonesia
| | - Agustini Utari
- Division of Human Genetics, Center for Biomedical Research (CEBIOR), Faculty of Medicine, Diponegoro University/Diponegoro National Hospital, Semarang, Indonesia
- Department of Pediatrics, Faculty of Medicine, Diponegoro University, Semarang, Indonesia
| | - Hans van Bokhoven
- Department of Human Genetics, Donders Institute for Brain, Cognition, and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Randi J Hagerman
- MIND Institute, UC Davis Health, University of California, Davis, California, USA
| | - Sultana MH Faradz
- Division of Human Genetics, Center for Biomedical Research (CEBIOR), Faculty of Medicine, Diponegoro University/Diponegoro National Hospital, Semarang, Indonesia
- Address correspondence to:Sultana MH Faradz, Center for Biomedical Research (CEBIOR), Faculty of Medicine, Diponegoro University, Jl. Prof. Soedarto SH no. 1, Semarang (50275), Central-Java, Indonesia. E-mail:
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Liu Q, Tong Y, Wang K. Genome-wide detection of short tandem repeat expansions by long-read sequencing. BMC Bioinformatics 2020; 21:542. [PMID: 33371889 PMCID: PMC7768641 DOI: 10.1186/s12859-020-03876-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 11/13/2020] [Indexed: 12/04/2022] Open
Abstract
BACKGROUND Short tandem repeat (STR), or "microsatellite", is a tract of DNA in which a specific motif (typically < 10 base pairs) is repeated multiple times. STRs are abundant throughout the human genome, and specific repeat expansions may be associated with human diseases. Long-read sequencing coupled with bioinformatics tools enables the estimation of repeat counts for STRs. However, with the exception of a few well-known disease-relevant STRs, normal ranges of repeat counts for most STRs in human populations are not well known, preventing the prioritization of STRs that may be associated with human diseases. RESULTS In this study, we extend a computational tool RepeatHMM to infer normal ranges of 432,604 STRs using 21 long-read sequencing datasets on human genomes, and build a genomic-scale database called RepeatHMM-DB with normal repeat ranges for these STRs. Evaluation on 13 well-known repeats show that the inferred repeat ranges provide good estimation to repeat ranges reported in literature from population-scale studies. This database, together with a repeat expansion estimation tool such as RepeatHMM, enables genomic-scale scanning of repeat regions in newly sequenced genomes to identify disease-relevant repeat expansions. As a case study of using RepeatHMM-DB, we evaluate the CAG repeats of ATXN3 for 20 patients with spinocerebellar ataxia type 3 (SCA3) and 5 unaffected individuals, and correctly classify each individual. CONCLUSIONS In summary, RepeatHMM-DB can facilitate prioritization and identification of disease-relevant STRs from whole-genome long-read sequencing data on patients with undiagnosed diseases. RepeatHMM-DB is incorporated into RepeatHMM and is available at https://github.com/WGLab/RepeatHMM .
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Affiliation(s)
- Qian Liu
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, Children's Hospital of Philadelphia, Philadelphia, PA, 19104, USA
| | - Yao Tong
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, Children's Hospital of Philadelphia, Philadelphia, PA, 19104, USA
| | - Kai Wang
- Raymond G. Perelman Center for Cellular and Molecular Therapeutics, Children's Hospital of Philadelphia, Philadelphia, PA, 19104, USA.
- Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA.
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Lian DS, Chen XY, Zeng HS, Wang YY. Capillary electrophoresis based on nucleic acid analysis for diagnosing inherited diseases. Clin Chem Lab Med 2020; 59:249-266. [PMID: 32374277 DOI: 10.1515/cclm-2020-0186] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Accepted: 04/04/2020] [Indexed: 11/15/2022]
Abstract
Most hereditary diseases are incurable, but their deterioration could be delayed or stopped if diagnosed timely. It is thus imperative to explore the state-of-the-art and high-efficient diagnostic techniques for precise analysis of the symptoms or early diagnosis of pre-symptoms. Diagnostics based on clinical presentations, hard to distinguish different phenotypes of the same genotype, or different genotypes displaying similar phenotypes, are incapable of pre-warning the disease status. Molecular diagnosis is ahead of harmful phenotype exhibition. However, conventional gold-standard molecular classifications, such as karyotype analysis, Southern blotting (SB) and sequencing, suffer drawbacks like low automation, low throughput, prolonged duration, being labor intensive and high cost. Also, deficiency in flexibility and diversity is observed to accommodate the development of precise and individualized diagnostics. The aforementioned pitfalls make them unadaptable to the increasing clinical demand for detecting and interpreting numerous samples in a rapid, accurate, high-throughput and cost-effective manner. Nevertheless, capillary electrophoresis based on genetic information analysis, with advantages of automation, high speed, high throughput, high efficiency, high resolution, digitization, versatility, miniature and cost-efficiency, coupled with flexible-designed PCR strategies in sample preparation (PCR-CE), exhibit an excellent power in deciphering cryptic molecular information of superficial symptoms of genetic diseases, and can analyze in parallel a large number of samples in a single PCR-CE, thereby providing an alternative, accurate, customized and timely diagnostic tool for routine screening of clinical samples on a large scale. Thus, the present study focuses on CE-based nucleic acid analysis used for inherited disease diagnosis. Also, the limitations and challenges of this PCR-CE for diagnosing hereditary diseases are discussed.
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Affiliation(s)
- Dong-Sheng Lian
- Guangzhou Women and Children's Medical Center of Guangzhou Medical University, NO. 9 at Jinsui Rd., Tianhe District, Guangzhou, Guangdong, P.R. China.,Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, P.R. China
| | - Xiang-Yuan Chen
- Guangzhou Women and Children's Medical Center of Guangzhou Medical University, NO. 9 at Jinsui Rd., Tianhe District, Guangzhou, Guangdong, P.R. China
| | - Hua-Song Zeng
- Guangzhou Women and Children's Medical Center of Guangzhou Medical University, NO. 9 at Jinsui Rd., Tianhe District, Guangzhou, Guangdong, P.R. China
| | - Yan-Yi Wang
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, P.R. China
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Sihombing NRB, Cai S, Wong DPW, Guan M, Chong SSC, Faradz SMH, Winarni TI. Repeat expansion and methylation-sensitive triplet-primed polymerase chain reaction for fragile X mental retardation 1 gene screening in institutionalised intellectually disabled individuals. Singapore Med J 2020; 62:143-148. [PMID: 31989181 DOI: 10.11622/smedj.2020009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
INTRODUCTION Fragile X syndrome (FXS) is the most prevalent X-linked intellectual disability (ID) and a leading genetic cause of autism, characterised by cognitive and behavioural impairments. The hyperexpansion of a CGG repeat in the fragile X mental retardation 1 (FMR1) gene leads to abnormal hypermethylation, resulting in the lack or absence of its protein. Tools for establishing the diagnosis of FXS have been extensively developed, including assays based on triplet-primed polymerase chain reaction (TP-PCR) for detection and quantification of the CGG trinucleotide repeat expansion, as well as determination of the methylation status of the alleles. This study aimed to utilise a simple, quick and affordable method for high sensitivity and specificity screening and diagnosis of FXS in institutionalised individuals with ID. METHODS A total of 109 institutionalised individuals at the Center for Social Rehabilitation of Intellectual Disability Kartini, Temanggung, Central Java, Indonesia, were screened in a three-step process using FastFrax™ Identification, Sizing and Methylation Status Kits. RESULTS Two samples that were classified as indeterminate with respect to the 41-repeat control at the identification step were subsequently determined to be non-expanded by both sizing and methylation status analyses. Two samples classified as expanded at the identification step were determined to carry full mutation expansions > 200 repeats that were fully methylated using sizing and methylation status analyses, respectively, yielding a disease prevalence of 1.83%. CONCLUSION Repeat expansion and methylation-specific TP-PCR is practical, effective and inexpensive for the diagnosis of FXS, especially in high-risk populations of individuals with ID of undetermined aetiology.
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Affiliation(s)
| | | | | | | | - Samuel Siong-Chuan Chong
- Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | | | - Tri Indah Winarni
- Center for Biomedical Research (CEBIOR), Faculty of Medicine, Diponegoro University, Semarang, Indonesia
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Joachim A, Ruttkowski B, Palmieri N. Microsatellite Analysis of Geographically Close Isolates of Cystoisospora suis. Front Vet Sci 2019; 6:96. [PMID: 31001546 PMCID: PMC6454066 DOI: 10.3389/fvets.2019.00096] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Accepted: 03/08/2019] [Indexed: 12/30/2022] Open
Abstract
Microsatellites are short repetitive DNA sequences of 2–6 repeats interspersed in the genome that display a rapid mutation rate and consequently show high variation between individuals or populations. They have been used to characterize population diversity and structure and the level of variation between different isolates of a number of different organisms, including apicomplexan protozoa. Currently nothing is known about the genetic variability and population structure of Cystoisospora suis (Apicomplexa: Coccidia), the causative agent of piglet coccidiosis, and we made use of the recently available genome of C. suis (strain Wien-I) to amplify microsatellite regions (ca. 300–550 bp) and evaluate the applicability of fluorescence-labeled primers to investigate amplicon length variation at high resolution using capillary electrophoresis (CE). Two phenotypically characterized isolates (Wien-I, toltrazuril susceptible; Holl 1 toltrazuril resistant) and six field isolates from Europe were compared by conventional PCR followed by agar-gel electrophoresis, Sanger sequencing, and CE (fluorescence labeling and fragment length analysis) to evaluate the applicability of the method. Four primer pairs could be identified that amplified bands of the expected size and were labeled for CE analysis. High resolution CE for size determination of PCR amplicons proved to be a reliable and simple method. It revealed high diversity of the analyzed strains, with marked differences even between two strains from neighboring swine farms. In follow-up studies, adaptation of the PCR assay to multiplexing and amplification of small DNA quantities will provide a cost-effective tool to analyse field strains to reveal geographic diversity that could be mapped to phenotypic traits.
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Affiliation(s)
- Anja Joachim
- Institute of Parasitology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Bärbel Ruttkowski
- Institute of Parasitology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Nicola Palmieri
- Institute of Parasitology, University of Veterinary Medicine Vienna, Vienna, Austria
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Liu Q, Zhang P, Wang D, Gu W, Wang K. Interrogating the "unsequenceable" genomic trinucleotide repeat disorders by long-read sequencing. Genome Med 2017; 9:65. [PMID: 28720120 PMCID: PMC5514472 DOI: 10.1186/s13073-017-0456-7] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 06/30/2017] [Indexed: 12/26/2022] Open
Abstract
Microsatellite expansion, such as trinucleotide repeat expansion (TRE), is known to cause a number of genetic diseases. Sanger sequencing and next-generation short-read sequencing are unable to interrogate TRE reliably. We developed a novel algorithm called RepeatHMM to estimate repeat counts from long-read sequencing data. Evaluation on simulation data, real amplicon sequencing data on two repeat expansion disorders, and whole-genome sequencing data generated by PacBio and Oxford Nanopore technologies showed superior performance over competing approaches. We concluded that long-read sequencing coupled with RepeatHMM can estimate repeat counts on microsatellites and can interrogate the “unsequenceable” genomic trinucleotide repeat disorders.
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Affiliation(s)
- Qian Liu
- Institute for Genomic Medicine, Columbia University, New York, NY, 10032, USA
| | - Peng Zhang
- Nextomics Biosciences, Wuhan, Hubei, 430000, China
| | - Depeng Wang
- Nextomics Biosciences, Wuhan, Hubei, 430000, China
| | - Weihong Gu
- China-Japan Friendship Hospital, Beijing, 100029, China
| | - Kai Wang
- Institute for Genomic Medicine, Columbia University, New York, NY, 10032, USA. .,Department of Biomedical Informatics, Columbia University, New York, NY, 10032, USA.
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Lim GXY, Yeo M, Koh YY, Winarni TI, Rajan-Babu IS, Chong SS, Faradz SMH, Guan M. Validation of a commercially available test that enables the quantification of the numbers of CGG trinucleotide repeat expansion in FMR1 gene. PLoS One 2017; 12:e0173279. [PMID: 28278294 PMCID: PMC5344422 DOI: 10.1371/journal.pone.0173279] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 02/13/2017] [Indexed: 11/26/2022] Open
Abstract
In the present study, we evaluated a commercially available TP-PCR-based assay, the FastFraXTMFMR1 Sizing kit, as a test in quantifying the number of CGG repeats in the FMR1 gene. Based on testing with well characterized DNA samples from Coriell, the kit yielded size results within 3 repeats of those obtained by common consensus (n = 14), with the exception of one allele. Furthermore, based on data obtained using all Coriell samples with or without common consensus (n = 29), the Sizing kit was 97.5% in agreement with existing approaches. Additionally, the kit generated consistent size information in repeatability and reproducibility studies (CV 0.39% to 3.42%). Clinical performance was established with 198 archived clinical samples, yielding results of 100% sensitivity (95% CI, 91.03% to 100%) and 100% specificity (95% CI, 97.64% to 100%) in categorizing patient samples into the respective normal, intermediate, premutation and full mutation genotypes.
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Affiliation(s)
| | - Minli Yeo
- The BioFactory Pte Ltd, Singapore, Singapore
| | | | - Tri Indah Winarni
- Division of Human Genetics, Center for Biomedical Research, Faculty of Medicine, Diponegoro University, Semarang, Indonesia
| | - Indhu-Shree Rajan-Babu
- Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Samuel S. Chong
- Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
- Khoo Teck Puat–National University Children’s Medical Institute, National University Health System, Singapore, Singapore
- Department of Laboratory Medicine, National University Hospital, Singapore, Singapore
| | - Sultana M. H. Faradz
- Division of Human Genetics, Center for Biomedical Research, Faculty of Medicine, Diponegoro University, Semarang, Indonesia
| | - Ming Guan
- The BioFactory Pte Ltd, Singapore, Singapore
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Molecular Correlates and Recent Advancements in the Diagnosis and Screening of FMR1-Related Disorders. Genes (Basel) 2016; 7:genes7100087. [PMID: 27754417 PMCID: PMC5083926 DOI: 10.3390/genes7100087] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 10/06/2016] [Accepted: 10/08/2016] [Indexed: 12/12/2022] Open
Abstract
Fragile X syndrome (FXS) is the most common monogenic cause of intellectual disability and autism. Molecular diagnostic testing of FXS and related disorders (fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor/ataxia syndrome (FXTAS)) relies on a combination of polymerase chain reaction (PCR) and Southern blot (SB) for the fragile X mental retardation 1 (FMR1) CGG-repeat expansion and methylation analyses. Recent advancements in PCR-based technologies have enabled the characterization of the complete spectrum of CGG-repeat mutation, with or without methylation assessment, and, as a result, have reduced our reliance on the labor- and time-intensive SB, which is the gold standard FXS diagnostic test. The newer and more robust triplet-primed PCR or TP-PCR assays allow the mapping of AGG interruptions and enable the predictive analysis of the risks of unstable CGG expansion during mother-to-child transmission. In this review, we have summarized the correlation between several molecular elements, including CGG-repeat size, methylation, mosaicism and skewed X-chromosome inactivation, and the extent of clinical involvement in patients with FMR1-related disorders, and reviewed key developments in PCR-based methodologies for the molecular diagnosis of FXS, FXTAS and FXPOI, and large-scale (CGG)n expansion screening in newborns, women of reproductive age and high-risk populations.
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Cascade Screening for Fragile X Syndrome/CGG Repeat Expansions in Children Attending Special Education in Sri Lanka. PLoS One 2015; 10:e0145537. [PMID: 26694146 PMCID: PMC4687912 DOI: 10.1371/journal.pone.0145537] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Accepted: 12/04/2015] [Indexed: 01/08/2023] Open
Abstract
Fragile X syndrome (FXS) is the commonest cause of inherited mental retardation and clinically presents with learning, emotional and behaviour problems. FXS is caused by expansion of cytosine-guanine-guanine (CGG) repeats present in the 5’ untranslated region of the FMR1 gene. The aim of this study was to screen children attending special education institutions in Sri Lanka to estimate the prevalence of CGG repeat expansions. The study population comprised a representative national sample of 850 children (540 males, 310 females) with 5 to 18 years of age from moderate to severe mental retardation of wide ranging aetiology. Screening for CGG repeat expansion was carried out on DNA extracted from buccal cells using 3’ direct triplet primed PCR followed by melting curve analysis. To identify the expanded status of screened positive samples, capillary electrophoresis, methylation specific PCR and Southern hybridization were carried out using venous blood samples. Prevalence of CGG repeat expansions was 2.2%. Further classification of the positive samples into FXS full mutation, pre-mutation and grey zone gave prevalence of 1.3%, 0.8% and 0.1% respectively. All positive cases were male. No females with FXS were detected in our study may have been due to the small sample size.
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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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