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Hnoonual A, Plong-On O, Worachotekamjorn J, Charalsawadi C, Limprasert P. Clinical and molecular characteristics of FMR1 microdeletion in patient with fragile X syndrome and review of the literature. Clin Chim Acta 2024; 553:117728. [PMID: 38142803 DOI: 10.1016/j.cca.2023.117728] [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: 09/18/2023] [Revised: 12/09/2023] [Accepted: 12/16/2023] [Indexed: 12/26/2023]
Abstract
BACKGROUND Fragile X syndrome (FXS) is mainly caused by FMR1 CGG repeat expansions. Other types of mutations, particularly deletions, are also responsible for FXS phenotypes, however these mutations are often missed by routine clinical testing. MATERIALS AND METHODS Molecular diagnosis in cases of suspected FXS was a combination of PCR and Southern blot. Measurement of the FMRP protein level was useful for detecting potentially deleterious impact. RESULTS PCR analysis and Southern blot revealed a case with premutation and suspected deletion alleles. Sanger sequencing showed that the deletion involved 313 bp upstream of repeats and some parts of CGG repeat tract, leaving transcription start site. FMRP was detected in 5.5 % of blood lymphocytes. CONCLUSION According to our review of case reports, most patients carrying microdeletion and full mutation had typical features of FXS. To our knowledge, our case is the first to describe mosaicism of a premutation and microdeletion in the FMR1 gene. The patient was probably protected from the effects of the deletion by mosaicism with premutation allele, leading to milder phenotype. It is thus important to consider appropriate techniques for detecting FMR1 variants other than repeat expansions which cannot be detected by routine FXS diagnosis.
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Affiliation(s)
- Areerat Hnoonual
- Department of Pathology, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand; Genomic Medicine Center, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand
| | - Oradawan Plong-On
- Department of Pathology, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand
| | | | - Chariyawan Charalsawadi
- Department of Pathology, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand; Genomic Medicine Center, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand
| | - Pornprot Limprasert
- Department of Pathology, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand; Genomic Medicine Center, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand.
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Elhawary NA, AlJahdali IA, Abumansour IS, Azher ZA, Falemban AH, Madani WM, Alosaimi W, Alghamdi G, Sindi IA. Phenotypic variability to medication management: an update on fragile X syndrome. Hum Genomics 2023; 17:60. [PMID: 37420260 DOI: 10.1186/s40246-023-00507-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Accepted: 07/03/2023] [Indexed: 07/09/2023] Open
Abstract
This review discusses the discovery, epidemiology, pathophysiology, genetic etiology, molecular diagnosis, and medication-based management of fragile X syndrome (FXS). It also highlights the syndrome's variable expressivity and common comorbid and overlapping conditions. FXS is an X-linked dominant disorder associated with a wide spectrum of clinical features, including but not limited to intellectual disability, autism spectrum disorder, language deficits, macroorchidism, seizures, and anxiety. Its prevalence in the general population is approximately 1 in 5000-7000 men and 1 in 4000-6000 women worldwide. FXS is associated with the fragile X messenger ribonucleoprotein 1 (FMR1) gene located at locus Xq27.3 and encodes the fragile X messenger ribonucleoprotein (FMRP). Most individuals with FXS have an FMR1 allele with > 200 CGG repeats (full mutation) and hypermethylation of the CpG island proximal to the repeats, which silences the gene's promoter. Some individuals have mosaicism in the size of the CGG repeats or in hypermethylation of the CpG island, both produce some FMRP and give rise to milder cognitive and behavioral deficits than in non-mosaic individuals with FXS. As in several monogenic disorders, modifier genes influence the penetrance of FMR1 mutations and FXS's variable expressivity by regulating the pathophysiological mechanisms related to the syndrome's behavioral features. Although there is no cure for FXS, prenatal molecular diagnostic testing is recommended to facilitate early diagnosis. Pharmacologic agents can reduce some behavioral features of FXS, and researchers are investigating whether gene editing can be used to demethylate the FMR1 promoter region to improve patient outcomes. Moreover, clustered regularly interspaced palindromic repeats (CRISPR)/Cas9 and developed nuclease defective Cas9 (dCas9) strategies have promised options of genome editing in gain-of-function mutations to rewrite new genetic information into a specified DNA site, are also being studied.
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Affiliation(s)
- Nasser A Elhawary
- Department of Medical Genetics, College of Medicine, Umm Al-Qura University, Mecca, 21955, Saudi Arabia.
| | - Imad A AlJahdali
- Department of Community Medicine, College of Medicine, Umm Al-Qura University, Mecca, Saudi Arabia
| | - Iman S Abumansour
- Department of Medical Genetics, College of Medicine, Umm Al-Qura University, Mecca, 21955, Saudi Arabia
| | - Zohor A Azher
- Department of Medical Genetics, College of Medicine, Umm Al-Qura University, Mecca, 21955, Saudi Arabia
| | - Alaa H Falemban
- Department of Pharmacology and Toxicology, College of Medicine, Umm Al-Qura University, Mecca, 24382, Saudi Arabia
| | - Wefaq M Madani
- Department of Hematology and Immunology, Faculty of Medicine, Umm Al-Qura University, Mecca, Saudi Arabia
| | - Wafaa Alosaimi
- Department of Hematology, Maternity and Children Hospital, Mecca, Saudi Arabia
| | - Ghydda Alghamdi
- Department of Medical Genetics, College of Medicine, Umm Al-Qura University, Mecca, 21955, Saudi Arabia
| | - Ikhlas A Sindi
- Department of Biology, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia
- Preparatory Year Program, Batterjee Medical College, Jeddah, 21442, Saudi Arabia
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Cogram P, Fernández-Beltrán LC, Casarejos MJ, Sánchez-Yepes S, Rodríguez-Martín E, García-Rubia A, Sánchez-Barrena MJ, Gil C, Martínez A, Mansilla A. The inhibition of NCS-1 binding to Ric8a rescues fragile X syndrome mice model phenotypes. Front Neurosci 2022; 16:1007531. [PMID: 36466176 PMCID: PMC9709425 DOI: 10.3389/fnins.2022.1007531] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2022] [Accepted: 09/26/2022] [Indexed: 01/01/2024] Open
Abstract
Fragile X syndrome (FXS) is caused by the loss of function of Fragile X mental retardation protein (FMRP). FXS is one of the leading monogenic causes of intellectual disability (ID) and autism. Although it is caused by the failure of a single gene, FMRP that functions as an RNA binding protein affects a large number of genes secondarily. All these genes represent hundreds of potential targets and different mechanisms that account for multiple pathological features, thereby hampering the search for effective treatments. In this scenario, it seems desirable to reorient therapies toward more general approaches. Neuronal calcium sensor 1 (NCS-1), through its interaction with the guanine-exchange factor Ric8a, regulates the number of synapses and the probability of the release of a neurotransmitter, the two neuronal features that are altered in FXS and other neurodevelopmental disorders. Inhibitors of the NCS-1/Ric8a complex have been shown to be effective in restoring abnormally high synapse numbers as well as improving associative learning in FMRP mutant flies. Here, we demonstrate that phenothiazine FD44, an NCS-1/Ric8a inhibitor, has strong inhibition ability in situ and sufficient bioavailability in the mouse brain. More importantly, administration of FD44 to two different FXS mouse models restores well-known FXS phenotypes, such as hyperactivity, associative learning, aggressive behavior, stereotype, or impaired social approach. It has been suggested that dopamine (DA) may play a relevant role in the behavior and in neurodevelopmental disorders in general. We have measured DA and its metabolites in different brain regions, finding a higher metabolic rate in the limbic area, which is also restored with FD44 treatment. Therefore, in addition to confirming that the NCS-1/Ric8a complex is an excellent therapeutic target, we demonstrate the rescue effect of its inhibitor on the behavior of cognitive and autistic FXS mice and show DA metabolism as a FXS biochemical disease marker.
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Affiliation(s)
- Patricia Cogram
- Department of Genetics, Institute of Ecology and Biodiversity (IEB), Faculty of Sciences, Universidad de Chile, Santiago, Chile
- FRAXA-DVI, FRAXA Research Foundation, Santiago, Chile
| | - Luis C. Fernández-Beltrán
- Department of Neurobiology, Instituto Ramón y Cajal de Investigación Sanitaria, Hospital Universitario Ramón y Cajal, Madrid, Spain
| | - María José Casarejos
- Department of Neurobiology, Instituto Ramón y Cajal de Investigación Sanitaria, Hospital Universitario Ramón y Cajal, Madrid, Spain
| | - Sonia Sánchez-Yepes
- Department of Neurobiology, Instituto Ramón y Cajal de Investigación Sanitaria, Hospital Universitario Ramón y Cajal, Madrid, Spain
| | - Eulalia Rodríguez-Martín
- Department of Immunology, Instituto Ramón y Cajal de Investigación Sanitaria, Hospital Universitario Ramón y Cajal, Madrid, Spain
| | - Alfonso García-Rubia
- Centro de Investigaciones Biológicas Margarita Salas-CSIC, Madrid, Spain
- Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos III, Madrid, Spain
| | | | - Carmen Gil
- Centro de Investigaciones Biológicas Margarita Salas-CSIC, Madrid, Spain
| | - Ana Martínez
- Centro de Investigaciones Biológicas Margarita Salas-CSIC, Madrid, Spain
- Centro de Investigación Biomédica en Red en Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos III, Madrid, Spain
| | - Alicia Mansilla
- Department of Neurobiology, Instituto Ramón y Cajal de Investigación Sanitaria, Hospital Universitario Ramón y Cajal, Madrid, Spain
- Department of Biology Systems, Universidad de Alcala, Madrid, Spain
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Kingdom R, Wright CF. Incomplete Penetrance and Variable Expressivity: From Clinical Studies to Population Cohorts. Front Genet 2022; 13:920390. [PMID: 35983412 PMCID: PMC9380816 DOI: 10.3389/fgene.2022.920390] [Citation(s) in RCA: 63] [Impact Index Per Article: 31.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Accepted: 06/09/2022] [Indexed: 12/20/2022] Open
Abstract
The same genetic variant found in different individuals can cause a range of diverse phenotypes, from no discernible clinical phenotype to severe disease, even among related individuals. Such variants can be said to display incomplete penetrance, a binary phenomenon where the genotype either causes the expected clinical phenotype or it does not, or they can be said to display variable expressivity, in which the same genotype can cause a wide range of clinical symptoms across a spectrum. Both incomplete penetrance and variable expressivity are thought to be caused by a range of factors, including common variants, variants in regulatory regions, epigenetics, environmental factors, and lifestyle. Many thousands of genetic variants have been identified as the cause of monogenic disorders, mostly determined through small clinical studies, and thus, the penetrance and expressivity of these variants may be overestimated when compared to their effect on the general population. With the wealth of population cohort data currently available, the penetrance and expressivity of such genetic variants can be investigated across a much wider contingent, potentially helping to reclassify variants that were previously thought to be completely penetrant. Research into the penetrance and expressivity of such genetic variants is important for clinical classification, both for determining causative mechanisms of disease in the affected population and for providing accurate risk information through genetic counseling. A genotype-based definition of the causes of rare diseases incorporating information from population cohorts and clinical studies is critical for our understanding of incomplete penetrance and variable expressivity. This review examines our current knowledge of the penetrance and expressivity of genetic variants in rare disease and across populations, as well as looking into the potential causes of the variation seen, including genetic modifiers, mosaicism, and polygenic factors, among others. We also considered the challenges that come with investigating penetrance and expressivity.
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Affiliation(s)
| | - Caroline F. Wright
- Institute of Biomedical and Clinical Science, Royal Devon & Exeter Hospital, University of Exeter Medical School, Exeter, United Kingdom
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