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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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2
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Straub D, Schmitt LM, Boggs AE, Horn PS, Dominick KC, Gross C, Erickson CA. A sensitive and reproducible qRT-PCR assay detects physiological relevant trace levels of FMR1 mRNA in individuals with Fragile X syndrome. Sci Rep 2023; 13:3808. [PMID: 36882476 PMCID: PMC9992378 DOI: 10.1038/s41598-023-29786-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 02/10/2023] [Indexed: 03/09/2023] Open
Abstract
Fragile X syndrome (FXS) is the most common inherited intellectual disability. FXS is caused by a trinucleotide repeat expansion in the 5' untranslated region of the FMR1 gene, which leads to gene methylation, transcriptional silencing, and lack of expression of Fragile X Messenger Riboprotein (FMRP). Currently available FXS therapies are inefficient, and the disease severity is highly variable, making it difficult to predict disease trajectory and treatment response. We and others have recently shown that a subset of full-mutation, fully-methylated (FM-FM) males with FXS express low amounts of FMRP which could contribute to phenotypic variability. To better understand the underlying mechanisms, we developed a sensitive qRT-PCR assay to detect FMR1 mRNA in blood. This assay reproducibly detects trace amounts of FMR1 mRNA in a subset of FM-FM males, suggesting that current Southern Blot and PCR determination of FM-FM status is not always associated with complete transcriptional silencing. The functional relevance of trace-level FMR1 mRNA is confirmed by showing a positive correlation with cognitive function; however, phenotypic variability is not fully explained by FMR1 expression. These results corroborate the need for better molecular assays for FXS diagnosis and encourage studies to elucidate the factors contributing to the phenotypic variability of FXS.
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Affiliation(s)
- Devan Straub
- Division of Child and Adolescent Psychiatry, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA
| | - Lauren M Schmitt
- Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA
- Department of Pediatrics, University of Cincinnati College of Medicine, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA
| | - Anna E Boggs
- Division of Child and Adolescent Psychiatry, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA
| | - Paul S Horn
- Department of Pediatrics, University of Cincinnati College of Medicine, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA
- Division of Neurology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH, 45229-3039, USA
| | - Kelli C Dominick
- Division of Child and Adolescent Psychiatry, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati College of Medicine, Stetson Building Suite 3200, 260 Stetson Street, Cincinnati, OH, 45267-0559, USA
| | - Christina Gross
- Department of Pediatrics, University of Cincinnati College of Medicine, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA
- Division of Neurology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH, 45229-3039, USA
| | - Craig A Erickson
- Division of Child and Adolescent Psychiatry, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA.
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati College of Medicine, Stetson Building Suite 3200, 260 Stetson Street, Cincinnati, OH, 45267-0559, USA.
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Baker EK, Arpone M, Bui M, Kraan CM, Ling L, Francis D, Hunter MF, Rogers C, Field MJ, Santa María L, Faundes V, Curotto B, Morales P, Trigo C, Salas I, Alliende AM, Amor DJ, Godler DE. Tissue mosaicism, FMR1 expression and intellectual functioning in males with fragile X syndrome. Am J Med Genet A 2023; 191:357-369. [PMID: 36349505 PMCID: PMC10952635 DOI: 10.1002/ajmg.a.63027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Revised: 09/13/2022] [Accepted: 10/13/2022] [Indexed: 11/10/2022]
Abstract
Fragile X syndrome (FXS) is caused by hypermethylation of the FMR1 promoter due to the full mutation expansion (full mutation [FM]: CGG ≥ 200 repeats) and silencing of FMR1. Assessment of mosaicism for active-unmethylated alleles has prognostic utility. This study examined relationships between FMR1 methylation in different tissues with FMR1 messenger ribonucleic acid (mRNA) and intellectual functioning in 87 males with FXS (1.89-43.17 years of age). Methylation sensitive Southern blot (mSB) and Methylation Specific-Quantitative Melt Aanalysis (MS-QMA) were used to examine FMR1 methylation. FMR1 mRNA levels in blood showed strong relationships with FMR1 methylation assessed using MS-QMA in blood (n = 68; R2 = 0.597; p = 1.4 × 10-10 ) and buccal epithelial cells (BEC) (n = 62; R2 = 0.24; p = 0.003), with these measures also showing relationships with intellectual functioning scores (p < 0.01). However, these relationships were not as strong for mSB, with ~40% of males with only FM alleles that were 100% methylated and non-mosaic by mSB, showing methylation mosaicism by MS-QMA. This was confirmed through presence of detectable levels of FMR1 mRNA in blood. In summary, FMR1 methylation levels in blood and BEC examined by MS-QMA were significantly associated with FMR1 mRNA levels and intellectual functioning in males with FXS. These relationships were not as strong for mSB, which underestimated prevalence of mosaicism.
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Affiliation(s)
- Emma K. Baker
- Diagnosis and Development, Murdoch Children's Research InstituteRoyal Children's HospitalMelbourneVictoriaAustralia
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health SciencesUniversity of MelbourneParkvilleVictoriaAustralia
- School of Psychology and Public HealthLa Trobe UniversityBundooraVictoriaAustralia
| | - Marta Arpone
- Diagnosis and Development, Murdoch Children's Research InstituteRoyal Children's HospitalMelbourneVictoriaAustralia
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health SciencesUniversity of MelbourneParkvilleVictoriaAustralia
- Brain and Mind, Murdoch Children's Research InstituteRoyal Children's HospitalParkvilleVictoriaAustralia
| | - Minh Bui
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global HealthUniversity of MelbourneMelbourneVictoriaAustralia
| | - Claudine M. Kraan
- Diagnosis and Development, Murdoch Children's Research InstituteRoyal Children's HospitalMelbourneVictoriaAustralia
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health SciencesUniversity of MelbourneParkvilleVictoriaAustralia
| | - Ling Ling
- Diagnosis and Development, Murdoch Children's Research InstituteRoyal Children's HospitalMelbourneVictoriaAustralia
| | - David Francis
- Victorian Clinical Genetics Services and Murdoch Children's Research InstituteThe Royal Children's HospitalMelbourneVictoriaAustralia
| | - Mathew F. Hunter
- Monash GeneticsMonash HealthClaytonVictoriaAustralia
- Department of PaediatricsMonash UniversityClaytonVictoriaAustralia
| | - Carolyn Rogers
- Genetics of Learning Disability ServiceHunter GeneticsWaratahNew South WalesAustralia
| | - Michael J. Field
- Genetics of Learning Disability ServiceHunter GeneticsWaratahNew South WalesAustralia
| | - Lorena Santa María
- Molecular and Cytogenetics LaboratoryINTA University of ChileSantiagoChile
| | - Víctor Faundes
- Molecular and Cytogenetics LaboratoryINTA University of ChileSantiagoChile
| | - Bianca Curotto
- Molecular and Cytogenetics LaboratoryINTA University of ChileSantiagoChile
| | - Paulina Morales
- Molecular and Cytogenetics LaboratoryINTA University of ChileSantiagoChile
| | - Cesar Trigo
- Molecular and Cytogenetics LaboratoryINTA University of ChileSantiagoChile
| | - Isabel Salas
- Molecular and Cytogenetics LaboratoryINTA University of ChileSantiagoChile
| | | | - David J. Amor
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health SciencesUniversity of MelbourneParkvilleVictoriaAustralia
- Neurodisability and Rehabilitation, Murdoch Children's Research InstituteRoyal Children's HospitalMelbourneVictoriaAustralia
| | - David E. Godler
- Diagnosis and Development, Murdoch Children's Research InstituteRoyal Children's HospitalMelbourneVictoriaAustralia
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health SciencesUniversity of MelbourneParkvilleVictoriaAustralia
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FAZELI Z, GHADERIAN SMH, NAJMABADI H, OMRANI MD. Understanding the Molecular Basis of Fragile X Syndrome Using Differentiated Mesenchymal Stem Cells. IRANIAN JOURNAL OF CHILD NEUROLOGY 2022; 16:85-95. [PMID: 35222660 PMCID: PMC8753000 DOI: 10.22037/ijcn.v15i4.22070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/08/2018] [Accepted: 02/21/2021] [Indexed: 11/09/2022]
Abstract
OBJECTIVES Fragile X syndrome (FXS) has been known as the most common cause of inherited intellectual disability and autism. This disease results from the loss of fragile X mental retardation protein expression due to the expansion of CGG repeats located on the 5' untranslated region of the fragile X mental retardation 1 (FMR1) gene. MATERIALS & METHODS In the present study, the peripheral blood-mesenchymal stem cells (PB-MSCs) of two female full mutation carriers were differentiated into neuronal cells by the suppression of bone morphogenesis pathway signaling. Then, the expression of genes adjacent to CGG repeats expansion, including SLIT and NTRK-like protein 2 (SLITRK2), SLIT and NTRK-like protein 4 (SLITRK4), methyl CpG binding protein 2 (MECP2), and gamma-aminobutyric acid receptor subunit alpha-3 (GABRA3), were evaluated in these cells using SYBR Green real-time polymerase chain reaction. RESULTS The obtained results indicated that the expression of SLITRK2 and SLITRK4 were upregulated and downregulated in the neuron-like cells differentiated from the PB-MSCs of females with FMR1 full mutation, compared to that of the normal females, respectively. Furthermore, the expression of MECP2 and GABRA3 genes were observed to be related to the phenotypic differences observed in the female FMR1 full mutation carriers. CONCLUSION The observed association of expression of genes located upstream of the FMR1 gene with phenotypic differences in the female carriers could increase the understanding of novel therapeutic targets for patients with mild symptoms of FXS and the patients affected by other FMR1-related disorders.
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Affiliation(s)
- Zahra FAZELI
- Department of Medical Genetics, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | | | - Hossein NAJMABADI
- Genetics Research Center, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran
| | - Mir Davood OMRANI
- Urogenital Stem Cell Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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5
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Parental Reports on Early Autism Behaviors in Their Children with Fragile X Syndrome as a Function of Infant Feeding. Nutrients 2021; 13:nu13082888. [PMID: 34445048 PMCID: PMC8401950 DOI: 10.3390/nu13082888] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 08/13/2021] [Accepted: 08/20/2021] [Indexed: 11/16/2022] Open
Abstract
This study evaluates the prevalence of autistic behaviors in fragile X syndrome as a function of infant diet. Retrospective survey data from the Fragile X Syndrome Nutrition Study, which included data on infant feeding and caregiver-reported developmental milestones for 190 children with fragile X syndrome enrolled in the Fragile X Online Registry with Accessible Database (FORWARD), were analyzed. Exploratory, sex-specific associations were found linking the use of soy-based infant formula with worse autistic behaviors related to language in females and self-injurious behavior in males. These findings prompt prospective evaluation of the effects of soy-based infant formula on disease comorbidities in fragile X syndrome, a rare disorder for which newborn screening could be implemented if there was an intervention. Gastrointestinal problems were the most common reason cited for switching to soy-based infant formula. Thus, these findings also support the study of early gastrointestinal problems in fragile X syndrome, which may underly the development and severity of disease comorbidities. In conjunction with comorbidity data from the previous analyses of the Fragile X Syndrome Nutrition Study, the findings indicate that premutation fragile X mothers should be encouraged to breastfeed.
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6
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Payán-Gómez C, Ramirez-Cheyne J, Saldarriaga W. Variable Expressivity in Fragile X Syndrome: Towards the Identification of Molecular Characteristics That Modify the Phenotype. Appl Clin Genet 2021; 14:305-312. [PMID: 34262328 PMCID: PMC8273740 DOI: 10.2147/tacg.s265835] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 06/21/2021] [Indexed: 12/18/2022] Open
Abstract
Fragile X syndrome (FXS), is an X-linked inherited genetic disease. FXS is the leading cause of inherited intellectual disability and autism in the world. Those affected are characterized by intellectual disability, language deficit, typical facies, and macroorchidism. Alterations in the FMR1 gene have been associated with FXS. The majority of people with this condition have an allele with an expansion of more than 200 repeats in a tract of CGGs within the 5' untranslated region, and this expansion is associated with a hypermethylated state of the gene promoter. FXS has incomplete penetrance and variable expressivity. Intellectual disability is present in 100% of males and 60% of females. Autism spectrum disorder symptoms appear in 50% to 60% of males and 20% of females. Other characteristics such as behavioral and physical alterations have significant variations in presentation frequency. The molecular causes of the variable phenotype in FXS patients are becoming clear: these causes are related to the FMR1 gene itself and to secondary, modifying gene effects. In FXS patients, size and methylation mosaicisms are common. Secondary to mosaicism, there is a variation in the quantity of FMR1 mRNA and the protein coded by the gene Fragile Mental Retardation Protein (FMRP). Potential modifier genes have also been proposed, with conflicting results. Characterizing patients according to CGG expansion, methylation status, concentration of mRNA and FMRP, and genotypification for possible modifier genes in a clinical setting offers an opportunity to identify predictors for treatment response evaluation. When intervention strategies become available to modulate the course of the disease they could be crucial for selecting patients and identifying the best therapeutic intervention. The purpose of this review is to present the information available about the molecular causes of the variability of the expression incomplete penetrance and variable expressivity in FXS and their potential clinical applications.
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Affiliation(s)
- César Payán-Gómez
- Deparment of Biology, Faculty of Natural Sciences, Universidad del Rosario, Bogotá, Colombia
| | - Julian Ramirez-Cheyne
- Health Faculty, Universidad del Valle, Cali, Colombia
- Hospital Universitario del Valle, Cali, Colombia
| | - Wilmar Saldarriaga
- Health Faculty, Universidad del Valle, Cali, Colombia
- Hospital Universitario del Valle, Cali, Colombia
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7
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Kraan CM, Baker EK, Arpone M, Bui M, Ling L, Gamage D, Bretherton L, Rogers C, Field MJ, Wotton TL, Francis D, Hunter MF, Cohen J, Amor DJ, Godler DE. DNA Methylation at Birth Predicts Intellectual Functioning and Autism Features in Children with Fragile X Syndrome. Int J Mol Sci 2020; 21:ijms21207735. [PMID: 33086711 PMCID: PMC7589848 DOI: 10.3390/ijms21207735] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Revised: 10/15/2020] [Accepted: 10/16/2020] [Indexed: 12/12/2022] Open
Abstract
Fragile X syndrome (FXS) is a leading single-gene cause of intellectual disability (ID) with autism features. This study analysed diagnostic and prognostic utility of the Fragile X-Related Epigenetic Element 2 DNA methylation (FREE2m) assessed by Methylation Specific-Quantitative Melt Analysis and the EpiTYPER system, in retrospectively retrieved newborn blood spots (NBS) and newly created dried blood spots (DBS) from 65 children with FXS (~2–17 years). A further 168 NBS from infants from the general population were used to establish control reference ranges, in both sexes. FREE2m analysis showed sensitivity and specificity approaching 100%. In FXS males, NBS FREE2m strongly correlated with intellectual functioning and autism features, however associations were not as strong for FXS females. Fragile X mental retardation 1 gene (FMR1) mRNA levels in blood were correlated with FREE2m in both NBS and DBS, for both sexes. In females, DNAm was significantly increased at birth with a decrease in childhood. The findings support the use of FREE2m analysis in newborns for screening, diagnostic and prognostic testing in FXS.
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Affiliation(s)
- Claudine M Kraan
- Diagnosis and Development, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia; (C.M.K.); (E.K.B.); (M.A.); (L.L.); (D.G.); (L.B.); (D.J.A.)
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville VIC 3052, Australia
| | - Emma K Baker
- Diagnosis and Development, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia; (C.M.K.); (E.K.B.); (M.A.); (L.L.); (D.G.); (L.B.); (D.J.A.)
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville VIC 3052, Australia
- School of Psychology and Public Health, La Trobe University, Bundoora VIC 3086, Australia
| | - Marta Arpone
- Diagnosis and Development, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia; (C.M.K.); (E.K.B.); (M.A.); (L.L.); (D.G.); (L.B.); (D.J.A.)
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville VIC 3052, Australia
- Brain and Mind, Murdoch Children’s Research Institute, Royal Children’s Hospital, Parkville VIC 3052, Australia
| | - Minh Bui
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne VIC 3052, Australia;
| | - Ling Ling
- Diagnosis and Development, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia; (C.M.K.); (E.K.B.); (M.A.); (L.L.); (D.G.); (L.B.); (D.J.A.)
| | - Dinusha Gamage
- Diagnosis and Development, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia; (C.M.K.); (E.K.B.); (M.A.); (L.L.); (D.G.); (L.B.); (D.J.A.)
| | - Lesley Bretherton
- Diagnosis and Development, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia; (C.M.K.); (E.K.B.); (M.A.); (L.L.); (D.G.); (L.B.); (D.J.A.)
| | - Carolyn Rogers
- Genetics of Learning Disability Service (GOLD service), Hunter Genetics, Newcastle NSW 2298, Australia; (C.R.); (M.J.F.)
| | - Michael J Field
- Genetics of Learning Disability Service (GOLD service), Hunter Genetics, Newcastle NSW 2298, Australia; (C.R.); (M.J.F.)
| | - Tiffany L Wotton
- New South Wales Newborn Screening Program, Children’s Hospital at Westmead, Sydney NSW 2145, Australia;
| | - David Francis
- Victorian Clinical Genetics Services, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia;
| | - Matt F Hunter
- Monash Genetics, Monash Health, Clayton, VIC 3168, Australia;
| | - Jonathan Cohen
- Centre for Developmental Disability Health Victoria, Monash University, Doveton VIC 3177, Australia;
- Fragile X Alliance Inc., North Caulfield VIC 3161, Australia
| | - David J Amor
- Diagnosis and Development, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia; (C.M.K.); (E.K.B.); (M.A.); (L.L.); (D.G.); (L.B.); (D.J.A.)
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville VIC 3052, Australia
| | - David E Godler
- Diagnosis and Development, Murdoch Children’s Research Institute, Royal Children’s Hospital, Melbourne VIC 3052, Australia; (C.M.K.); (E.K.B.); (M.A.); (L.L.); (D.G.); (L.B.); (D.J.A.)
- Department of Paediatrics, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville VIC 3052, Australia
- Correspondence: ; Tel.: +613-8341-6496
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FMR1 mRNA from full mutation alleles is associated with ABC-C FX scores in males with fragile X syndrome. Sci Rep 2020; 10:11701. [PMID: 32678152 PMCID: PMC7367290 DOI: 10.1038/s41598-020-68465-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 06/22/2020] [Indexed: 02/08/2023] Open
Abstract
Fragile X syndrome (FXS) is caused by a hypermethylated full mutation (FM) expansion with ≥ 200 CGG repeats, and a decrease in FMR1 mRNA and its protein. However, incomplete silencing from FM alleles has been associated with more severe autism features in FXS males. This study compared scores on the Aberrant Behavior Checklist-Community-FXS version (ABC-CFX) in 62 males affected with FXS (3 to 32 years) stratified based on presence or absence of mosaicism and/or FMR1 mRNA silencing. Associations between ABC-CFX subscales and FMR1 mRNA levels, assessed using real-time PCR relative standard curve method, were also examined. The FXS group mosaic for premutation (PM: 55–199 CGGs) and FM alleles had lower irritability (p = 0.014) and inappropriate speech (p < 0.001) scores compared to males with only FM alleles and complete loss of FMR1 mRNA. The PM/FM mosaic group also showed lower inappropriate speech scores compared to the incomplete silencing (p = 0.002) group. Increased FMR1 mRNA levels were associated with greater irritability (p < 0.001), and lower health-related quality of life scores (p = 0.004), but only in the incomplete silencing FM-only group. The findings suggest that stratification based on CGG sizing and FMR1 mRNA levels may be warranted in future research and clinical trials utilising ABC-CFX subscales as outcome measures.
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Fernández E, Gennaro E, Pirozzi F, Baldo C, Forzano F, Turolla L, Faravelli F, Gastaldo D, Coviello D, Grasso M, Bagni C. FXS-Like Phenotype in Two Unrelated Patients Carrying a Methylated Premutation of the FMR1 Gene. Front Genet 2018; 9:442. [PMID: 30450110 PMCID: PMC6224343 DOI: 10.3389/fgene.2018.00442] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Accepted: 09/14/2018] [Indexed: 12/31/2022] Open
Abstract
Fragile X syndrome (FXS) is mostly caused by two distinct events that occur in the FMR1 gene (Xq27.3): an expansion above 200 repeats of a CGG triplet located in the 5′UTR of the gene, and methylation of the cytosines located in the CpG islands upstream of the CGG repeats. Here, we describe two unrelated families with one FXS child and another sibling presenting mild intellectual disability and behavioral features evocative of FXS. Genetic characterization of the undiagnosed sibling revealed mosaicism in both the CGG expansion size and the methylation levels in the different tissues analyzed. This report shows that in the same family, two siblings carrying different CGG repeats, one in the full-mutation range and the other in the premutation range, present methylation mosaicism and consequent decreased FMRP production leading to FXS and FXS-like features, respectively. Decreased FMRP levels, more than the number of repeats seem to correlate with the severity of FXS clinical phenotypes.
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Affiliation(s)
- Esperanza Fernández
- Center for Human Genetics, KU Leuven, Leuven, Belgium.,VIB & KU Leuven Center for Brain & Disease Research, Leuven, Belgium
| | - Elena Gennaro
- Laboratorio di Genetica Umana, Ospedali Galliera, Genoa, Italy
| | - Filomena Pirozzi
- Center for Human Genetics, KU Leuven, Leuven, Belgium.,VIB & KU Leuven Center for Brain & Disease Research, Leuven, Belgium
| | - Chiara Baldo
- Laboratorio di Genetica Umana, Ospedali Galliera, Genoa, Italy
| | - Francesca Forzano
- Clinical Genetics Department, Borough Wing Guy's Hospital, Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom.,S.S.D. Genetica Medica, Ospedali Galliera, Genoa, Italy
| | - Licia Turolla
- U.O.S. Genetica Medica, Azienda ULSS 2, Treviso, Italy
| | - Francesca Faravelli
- Clinical Genetics Department, Great Ormond Street Hospital, London, United Kingdom
| | - Denise Gastaldo
- Department of Fundamental Neurosciences, University of Lausanne, Lausanne, Switzerland
| | | | - Marina Grasso
- Laboratorio di Genetica Umana, Ospedali Galliera, Genoa, Italy
| | - Claudia Bagni
- Center for Human Genetics, KU Leuven, Leuven, Belgium.,VIB & KU Leuven Center for Brain & Disease Research, Leuven, Belgium.,Department of Fundamental Neurosciences, University of Lausanne, Lausanne, Switzerland.,Department of Biomedicine and Prevention, University of Rome Tor Vergata, Rome, Italy
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10
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Esanov R, Andrade NS, Bennison S, Wahlestedt C, Zeier Z. The FMR1 promoter is selectively hydroxymethylated in primary neurons of fragile X syndrome patients. Hum Mol Genet 2018; 25:4870-4880. [PMID: 28173181 DOI: 10.1093/hmg/ddw311] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 08/17/2016] [Accepted: 09/02/2016] [Indexed: 12/13/2022] Open
Abstract
Fragile X syndrome (FXS) results from a repeat expansion mutation near the FMR1 gene promoter and is the most common form of heritable intellectual disability and autism. Full mutations larger than 200 CGG repeats trigger FMR1 heterochromatinization and loss of gene expression, which is primarily responsible for the pathological features of FXS . In contrast, smaller pre-mutations of 55–200 CGG are associated with FMR1 overexpression and Fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative condition. While the role of 5-methylcytosine (5mC) in FMR1 gene silencing has been studied extensively, the role of 5-hydroxymethylation (5hmC), a newly discovered epigenetic mark produced through active DNA demethylation, has not been previously investigated in FXS neurons. Here, we used two complementary epigenetic assays, 5hmC sensitive restriction digest and ten-eleven translocation-assisted bisulfite pyrosequencing, to quantify FMR1 5mC and 5hmC levels. We observed increased levels of 5hmC at the FMR1 promoter in FXS patient brains with full-mutations relative to pre-mutation carriers and unaffected controls. In addition, we found that 5hmC enrichment at the FMR1 locus in FXS cells is specific to neurons by utilizing a nuclei sorting technique to separate neuronal and glial DNA fractions from post-mortem brain tissues. This FMR1 5hmC enrichment was not present in cellular models of FXS including fibroblasts, lymphocytes and reprogrammed neurons, indicating they do not fully recapitulate this epigenetic feature of disease. Future studies could investigate the potential to leverage this epigenetic pathway to restore FMR1 expression and discern whether levels of 5hmC correlate with phenotypic severity.
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Affiliation(s)
- Rustam Esanov
- Department of Psychiatry & Behavioral Sciences, Center for Therapeutic Innovation, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Nadja S Andrade
- Department of Psychiatry & Behavioral Sciences, Center for Therapeutic Innovation, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Sarah Bennison
- Department of Psychiatry & Behavioral Sciences, Center for Therapeutic Innovation, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Claes Wahlestedt
- Department of Psychiatry & Behavioral Sciences, Center for Therapeutic Innovation, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Zane Zeier
- Department of Psychiatry & Behavioral Sciences, Center for Therapeutic Innovation, University of Miami Miller School of Medicine, Miami, FL 33136, USA
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11
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Choi M, Genereux DP, Goodson J, Al-Azzawi H, Allain SQ, Simon N, Palasek S, Ware CB, Cavanaugh C, Miller DG, Johnson WC, Sinclair KD, Stöger R, Laird CD. Epigenetic memory via concordant DNA methylation is inversely correlated to developmental potential of mammalian cells. PLoS Genet 2017; 13:e1007060. [PMID: 29107996 PMCID: PMC5690686 DOI: 10.1371/journal.pgen.1007060] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Revised: 11/16/2017] [Accepted: 10/08/2017] [Indexed: 11/25/2022] Open
Abstract
In storing and transmitting epigenetic information, organisms must balance the need to maintain information about past conditions with the capacity to respond to information in their current and future environments. Some of this information is encoded by DNA methylation, which can be transmitted with variable fidelity from parent to daughter strand. High fidelity confers strong pattern matching between the strands of individual DNA molecules and thus pattern stability over rounds of DNA replication; lower fidelity confers reduced pattern matching, and thus greater flexibility. Here, we present a new conceptual framework, Ratio of Concordance Preference (RCP), that uses double-stranded methylation data to quantify the flexibility and stability of the system that gave rise to a given set of patterns. We find that differentiated mammalian cells operate with high DNA methylation stability, consistent with earlier reports. Stem cells in culture and in embryos, in contrast, operate with reduced, albeit significant, methylation stability. We conclude that preference for concordant DNA methylation is a consistent mode of information transfer, and thus provides epigenetic stability across cell divisions, even in stem cells and those undergoing developmental transitions. Broader application of our RCP framework will permit comparison of epigenetic-information systems across cells, developmental stages, and organisms whose methylation machineries differ substantially or are not yet well understood.
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Affiliation(s)
- Minseung Choi
- Department of Biology, University of Washington, Seattle, Washington, United States of America
- Department of Computer Science, Princeton University, Princeton, New Jersey, United States of America
| | - Diane P. Genereux
- Broad Institute of Massachusetts Institute of Technology and Harvard University, Cambridge, Massachusetts, United States of America
| | - Jamie Goodson
- Department of Pathology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Haneen Al-Azzawi
- School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, United Kingdom
| | - Shannon Q. Allain
- Department of Biology, University of Washington, Seattle, Washington, United States of America
| | - Noah Simon
- Department of Biostatistics, University of Washington, Seattle, Washington, United States of America
| | - Stan Palasek
- Department of Mathematics, Princeton University, Princeton, New Jersey, United States of America
| | - Carol B. Ware
- Department of Comparative Medicine, University of Washington School of Medicine, Seattle, Washington, United States of America
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, United States of America
| | - Chris Cavanaugh
- Department of Comparative Medicine, University of Washington School of Medicine, Seattle, Washington, United States of America
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, United States of America
| | - Daniel G. Miller
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, United States of America
- Department of Pediatrics, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Winslow C. Johnson
- Department of Biology, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America
| | - Kevin D. Sinclair
- School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, United Kingdom
| | - Reinhard Stöger
- School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, United Kingdom
| | - Charles D. Laird
- Department of Biology, University of Washington, Seattle, Washington, United States of America
- Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America
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12
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Aliaga SM, Slater HR, Francis D, Du Sart D, Li X, Amor DJ, Alliende AM, Santa Maria L, Faundes V, Morales P, Trigo C, Salas I, Curotto B, Godler DE. Identification of Males with Cryptic Fragile X Alleles by Methylation-Specific Quantitative Melt Analysis. Clin Chem 2016; 62:343-52. [DOI: 10.1373/clinchem.2015.244681] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2015] [Accepted: 12/02/2015] [Indexed: 01/13/2023]
Abstract
Abstract
BACKGROUND
FMR1 full mutations (FMs) (CGG expansion >200) in males mosaic for a normal (<45 CGG) or gray-zone (GZ) (45–54 CGG) allele can be missed with the standard 2-step fragile X syndrome (FXS) testing protocols, largely because the first-line PCR tests showing a normal or GZ allele are not reflexed to the second-line test that can detect FM.
METHODS
We used methylation-specific quantitative melt analysis (MS-QMA) to determine the prevalence of cryptic FM alleles in 2 independent cohorts of male patients (994 from Chile and 2392 from Australia) referred for FXS testing from 2006 to 2013. All MS-QMA–positive cases were retested with commercial triplet primed PCR, methylation-sensitive Southern blot, and a methylation-specific EpiTYPER-based test.
RESULTS
All 38 FMs detected with the standard 2-step protocol were detected with MS-QMA. However, MS-QMA identified methylation mosaicism in an additional 15% and 11% of patients in the Chilean and Australian cohorts, respectively, suggesting the presence of a cryptic FM. Of these additional patients, 57% were confirmed to carry cryptic expanded alleles in blood, buccal mucosa, or saliva samples. Further confirmation was provided by identifying premutation (CGG 55–199) alleles in mothers of probands with methylation-sensitive Southern blot. Neurocognitive assessments showed that low-level mosaicism for cryptic FM alleles was associated with cognitive impairment or autism.
CONCLUSIONS
A substantial number of mosaic FM males who have cognitive impairment or autism are not diagnosed with the currently recommended 2-step testing protocol and can be identified with MS-QMA as a first-line test.
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Affiliation(s)
- Solange M Aliaga
- Cyto-molecular Diagnostic Research Laboratory, Victorian Clinical Genetics Services and Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia
- Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia
- Cytogenetics and Molecular Laboratory, Institute of Nutrition and Food Technology, University of Chile, Santiago, Chile
| | - Howard R Slater
- Cyto-molecular Diagnostic Research Laboratory, Victorian Clinical Genetics Services and Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia
- Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia
| | - David Francis
- Cyto-molecular Diagnostic Research Laboratory, Victorian Clinical Genetics Services and Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia
| | - Desiree Du Sart
- Cyto-molecular Diagnostic Research Laboratory, Victorian Clinical Genetics Services and Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia
| | - Xin Li
- Cyto-molecular Diagnostic Research Laboratory, Victorian Clinical Genetics Services and Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia
| | - David J Amor
- Cyto-molecular Diagnostic Research Laboratory, Victorian Clinical Genetics Services and Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia
- Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia
| | - Angelica M Alliende
- Centre for Diagnosis and Treatment of Fragile X Syndrome, INTA University of Chile, Santiago, Chile
| | - Lorena Santa Maria
- Cytogenetics and Molecular Laboratory, Institute of Nutrition and Food Technology, University of Chile, Santiago, Chile
- Centre for Diagnosis and Treatment of Fragile X Syndrome, INTA University of Chile, Santiago, Chile
| | - Víctor Faundes
- Cytogenetics and Molecular Laboratory, Institute of Nutrition and Food Technology, University of Chile, Santiago, Chile
- Centre for Diagnosis and Treatment of Fragile X Syndrome, INTA University of Chile, Santiago, Chile
| | - Paulina Morales
- Cytogenetics and Molecular Laboratory, Institute of Nutrition and Food Technology, University of Chile, Santiago, Chile
- Centre for Diagnosis and Treatment of Fragile X Syndrome, INTA University of Chile, Santiago, Chile
| | - Cesar Trigo
- Centre for Diagnosis and Treatment of Fragile X Syndrome, INTA University of Chile, Santiago, Chile
| | - Isabel Salas
- Centre for Diagnosis and Treatment of Fragile X Syndrome, INTA University of Chile, Santiago, Chile
| | - Bianca Curotto
- Cytogenetics and Molecular Laboratory, Institute of Nutrition and Food Technology, University of Chile, Santiago, Chile
- Centre for Diagnosis and Treatment of Fragile X Syndrome, INTA University of Chile, Santiago, Chile
| | - David E Godler
- Cyto-molecular Diagnostic Research Laboratory, Victorian Clinical Genetics Services and Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia
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13
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Bhattacharyya A, Zhao X. Human pluripotent stem cell models of Fragile X syndrome. Mol Cell Neurosci 2015; 73:43-51. [PMID: 26640241 DOI: 10.1016/j.mcn.2015.11.011] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 11/03/2015] [Accepted: 11/25/2015] [Indexed: 01/18/2023] Open
Abstract
Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and autism. The causal mutation in FXS is a trinucleotide CGG repeat expansion in the FMR1 gene that leads to human specific epigenetic silencing and loss of Fragile X Mental Retardation Protein (FMRP) expression. Human pluripotent stem cells (PSCs), including human embryonic stem cells (ESCs) and particularly induced PSCs (iPSCs), offer a model system to reveal cellular and molecular events underlying human neuronal development and function in FXS. Human FXS PSCs have been established and have provided insight into the epigenetic silencing of the FMR1 gene as well as aspects of neuronal development.
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Affiliation(s)
- Anita Bhattacharyya
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, United States.
| | - Xinyu Zhao
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, United States.
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14
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Zeier Z, Esanov R, Belle KC, Volmar CH, Johnstone AL, Halley P, DeRosa BA, Khoury N, van Blitterswijk M, Rademakers R, Albert J, Brothers SP, Wuu J, Dykxhoorn DM, Benatar M, Wahlestedt C. Bromodomain inhibitors regulate the C9ORF72 locus in ALS. Exp Neurol 2015; 271:241-50. [PMID: 26099177 DOI: 10.1016/j.expneurol.2015.06.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Revised: 06/05/2015] [Accepted: 06/16/2015] [Indexed: 12/13/2022]
Abstract
A hexanucleotide repeat expansion residing within the C9ORF72 gene represents the most common known cause of amyotrophic lateral sclerosis (ALS) and places the disease among a growing family of repeat expansion disorders. The presence of RNA foci, repeat-associated translation products, and sequestration of RNA binding proteins suggests that toxic RNA gain-of-function contributes to pathology while C9ORF72 haploinsufficiency may be an additional pathological factor. One viable therapeutic strategy for treating expansion diseases is the use of small molecule inhibitors of epigenetic modifier proteins to reactivate expanded genetic loci. Indeed, previous studies have established proof of this principle by increasing the drug-induced expression of expanded (and abnormally heterochromatinized) FMR1, FXN and C9ORF72 genes in respective patient cells. While epigenetic modifier proteins are increasingly recognized as druggable targets, there have been few screening strategies to address this avenue of drug discovery in the context of expansion diseases. Here we utilize a semi-high-throughput gene expression based screen to identify siRNAs and small molecule inhibitors of epigenetic modifier proteins that regulate C9ORF72 RNA in patient fibroblasts, lymphocytes and reprogrammed motor neurons. We found that several bromodomain small molecule inhibitors increase the expression of C9ORF72 mRNA and pre-mRNA without affecting repressive epigenetic signatures of expanded C9ORF72 alleles. These data suggest that bromodomain inhibition increases the expression of unexpanded C9ORF72 alleles and may therefore compensate for haploinsufficiency without increasing the production of toxic RNA and protein products, thereby conferring therapeutic value.
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Affiliation(s)
- Zane Zeier
- Center for Therapeutic Innovation and Department of Psychiatry & Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Rustam Esanov
- Center for Therapeutic Innovation and Department of Psychiatry & Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Kinsley C Belle
- John P. Hussman Institute for Human Genomics and The Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, USA
| | - Claude-Henry Volmar
- Center for Therapeutic Innovation and Department of Psychiatry & Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Andrea L Johnstone
- Center for Therapeutic Innovation and Department of Psychiatry & Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Paul Halley
- Center for Therapeutic Innovation and Department of Psychiatry & Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Brooke A DeRosa
- John P. Hussman Institute for Human Genomics and The Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, USA
| | - Nathalie Khoury
- Center for Therapeutic Innovation and Department of Psychiatry & Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | | | | | | | - Shaun P Brothers
- Center for Therapeutic Innovation and Department of Psychiatry & Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA
| | - Joanne Wuu
- Department of Neurology, University of Miami Miller School of Medicine, USA
| | - Derek M Dykxhoorn
- John P. Hussman Institute for Human Genomics and The Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, USA
| | - Michael Benatar
- Department of Neurology, University of Miami Miller School of Medicine, USA
| | - Claes Wahlestedt
- Center for Therapeutic Innovation and Department of Psychiatry & Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
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15
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Schaefer TL, Davenport MH, Erickson CA. Emerging pharmacologic treatment options for fragile X syndrome. APPLICATION OF CLINICAL GENETICS 2015; 8:75-93. [PMID: 25897255 PMCID: PMC4396424 DOI: 10.2147/tacg.s35673] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Fragile X syndrome (FXS) is the most common single gene cause of intellectual disability and autism spectrum disorder. Caused by a silenced fragile X mental retardation 1 gene and the subsequent deficiency in fragile X mental retardation protein, patients with FXS experience a range of physical, behavioral, and intellectual debilitations. The FXS field, as a whole, has recently met with some challenges, as several targeted clinical trials with high expectations of success have failed to elucidate significant improvements in a variety of symptom domains. As new clinical trials in FXS are planned, there has been much discussion about the use of the commonly used clinical outcome measures, as well as study design considerations, patient stratification, and optimal age range for treatment. The evidence that modification of these drug targets and use of these failed compounds would prove to be efficacious in human clinical study were rooted in years of basic and translational research. There are questions arising as to the use of the mouse models for studying FXS treatment development. This issue is twofold: many of the symptom domains and molecular and biochemical changes assessed and indicative of efficacy in mouse model study are not easily amenable to clinical trials in people with FXS because of the intolerability of the testing paradigm or a lack of noninvasive techniques (prepulse inhibition, sensory hypersensitivity, startle reactivity, or electrophysiologic, biochemical, or structural changes in the brain); and capturing subtle yet meaningful changes in symptom domains such as sociability, anxiety, and hyperactivity in human FXS clinical trials is challenging with the currently used measures (typically parent/caregiver rating scales). Clinicians, researchers, and the pharmaceutical industry have all had to take a step back and critically evaluate the way we think about how to best optimize future investigations into pharmacologic FXS treatments. As new clinical trials are coming down the drug discovery pipeline, it is clear that the field is moving in a direction that values the development of molecular biomarkers, less subjective quantitative measures of symptom improvement, and rating scales developed specifically for use in FXS in conjunction with drug safety. While summarizing preclinical evidence, where applicable, and discussing challenges in FXS treatment development, this review details both completed clinical trials for the targeted and symptomatic treatment of FXS and introduces novel projects on the cusp of clinical trial investigation.
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Affiliation(s)
- Tori L Schaefer
- Division of Child and Adolescent Psychiatry, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Matthew H Davenport
- Division of Child and Adolescent Psychiatry, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Craig A Erickson
- Division of Child and Adolescent Psychiatry, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
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16
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Loomis EW, Sanz LA, Chédin F, Hagerman PJ. Transcription-associated R-loop formation across the human FMR1 CGG-repeat region. PLoS Genet 2014; 10:e1004294. [PMID: 24743386 PMCID: PMC3990486 DOI: 10.1371/journal.pgen.1004294] [Citation(s) in RCA: 158] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 02/21/2014] [Indexed: 11/24/2022] Open
Abstract
Expansion of a trinucleotide (CGG) repeat element within the 5′ untranslated region (5′UTR) of the human FMR1 gene is responsible for a number of heritable disorders operating through distinct pathogenic mechanisms: gene silencing for fragile X syndrome (>200 CGG) and RNA toxic gain-of-function for FXTAS (∼55–200 CGG). Existing models have focused almost exclusively on post-transcriptional mechanisms, but co-transcriptional processes could also contribute to the molecular dysfunction of FMR1. We have observed that transcription through the GC-rich FMR1 5′UTR region favors R-loop formation, with the nascent (G-rich) RNA forming a stable RNA:DNA hybrid with the template DNA strand, thereby displacing the non-template DNA strand. Using DNA:RNA (hybrid) immunoprecipitation (DRIP) of genomic DNA from cultured human dermal fibroblasts with both normal (∼30 CGG repeats) and premutation (55<CGG<200 repeats) alleles, we provide evidence for FMR1 R-loop formation in human genomic DNA. Using a doxycycline (DOX)-inducible episomal system in which both the CGG-repeat and transcription frequency can be varied, we further show that R-loop formation increases with higher expression levels. Finally, non-denaturing bisulfite mapping of the displaced single-stranded DNA confirmed R-loop formation at the endogenous FMR1 locus and further indicated that R-loops formed over CGG repeats may be prone to structural complexities, including hairpin formation, not commonly associated with other R-loops. These observations introduce a new molecular feature of the FMR1 gene that is directly affected by CGG-repeat expansion and is likely to be involved in the associated cellular dysfunction. Expansion of a CGG-repeat element within the human FMR1 gene is responsible for multiple human diseases, including fragile X syndrome and fragile X-associated tremor/ataxia syndrome (FXTAS). These diseases occur in separate ranges of repeat length and are characterized by profoundly different molecular mechanisms. Fragile X syndrome results from FMR1 gene silencing, whereas FXTAS is associated with an increase in transcription and toxicity of the CGG-repeat-containing mRNA. This study introduces a previously unknown molecular feature of the FMR1 locus, namely the co-transcriptional formation of three-stranded R-loop structures upon re-annealing of the nascent FMR1 transcript to the template DNA strand. R-loops are involved in the normal function of human CpG island promoters in that they contribute to protecting these sequences from DNA methylation. However, excessive R-loop formation can lead to activation of the DNA damage response and result in genomic instability. We used antibody recognition and chemical single-stranded DNA footprinting to show that R-loops form at the FMR1 locus with increasing frequency and greater structural complexity as the CGG-repeat length increases. This discovery provides a missing piece of both the complex FMR1 molecular puzzle and the diseases resulting from CGG-repeat expansion.
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Affiliation(s)
- Erick W. Loomis
- Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Davis, California, United States of America
| | - Lionel A. Sanz
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, California, United States of America
- The Genome Center, University of California, Davis, Davis, California, United States of America
| | - Frédéric Chédin
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, California, United States of America
- The Genome Center, University of California, Davis, Davis, California, United States of America
| | - Paul J. Hagerman
- Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Davis, California, United States of America
- MIND Institute, University of California, Davis, Health System, Sacramento, California, United States of America
- * E-mail:
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17
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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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18
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Genereux DP, Laird CD. Why do fragile X carrier frequencies differ between Asian and non-Asian populations? Genes Genet Syst 2014; 88:211-24. [PMID: 24025249 DOI: 10.1266/ggs.88.211] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Asian and non-Asian populations have been reported to differ substantially in the distribution of fragile X alleles into the normal (< 55 CGG repeats), premutation (55-199 CGG repeats), and full-mutation (> 199 CGG repeats) size classes. Our statistical analyses of data from published general-population studies confirm that Asian populations have markedly lower frequencies of premutation alleles, reminiscent of earlier findings for expanded alleles at the Huntington's Disease locus. To examine historical and contemporary factors that may have shaped and now sustain allele-frequency differences at the fragile X locus, we develop a population-genetic/epigenetic model, and apply it to these published data. We find that founder-haplotype effects likely contribute to observed frequency differences via substantially lower mutation rates in Asian populations. By contrast, any premutation frequency differences present in founder populations would have disappeared in the several millennia since initial establishment of these groups. Differences in the reproductive fitness of female premutation carriers arising from fragile X primary ovarian insufficiency (FXPOI) and from differences in mean maternal age may also contribute to global variation in carrier frequencies.
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19
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Elli FM, de Sanctis L, Bollati V, Tarantini L, Filopanti M, Barbieri AM, Peverelli E, Beck-Peccoz P, Spada A, Mantovani G. Quantitative analysis of methylation defects and correlation with clinical characteristics in patients with pseudohypoparathyroidism type I and GNAS epigenetic alterations. J Clin Endocrinol Metab 2014; 99:E508-17. [PMID: 24423294 DOI: 10.1210/jc.2013-3086] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
CONTEXT Pseudohypoparathyroidism type I (PHP-I) includes two main subtypes, PHP-Ia and -Ib. About 70% of PHP-Ia patients, who show Albright hereditary osteodystrophy (AHO) associated with resistance toward multiple hormones (PTH/TSH/GHRH/gonadotropins), carry heterozygous mutations in the α-subunit of the stimulatory G protein (Gsα) exons 1-13, encoded by the guanine nucleotide binding-protein α-stimulating activity polypeptide 1 (GNAS), whereas the majority of PHP-Ib patients, who classically display hormone resistance limited to PTH and TSH with no AHO sign, have methylation defects in the imprinted GNAS cluster. Recently methylation defects have been detected also in patients with PHP and different degrees of AHO, indicating a molecular overlap between the two forms. OBJECTIVES The objectives of the study were to collect patients with the following characteristics: clinical PHP-I (with or without AHO), no mutation in Gsα coding sequence, but the presence of GNAS methylation alterations and to investigate the existence of correlations between the degree of the epigenetic defect and the severity of the disease. PATIENTS AND METHODS We quantified GNAS methylation alterations by both PCR-pyrosequencing and methylation specific-multiplex ligation-dependent probe amplification assay in genomic DNA from 63 patients with PHP-I and correlated these findings with clinical parameters (age at diagnosis; calcium, phosphorus, PTH, TSH levels; presence or absence of each AHO sign). RESULTS By both approaches, the degree of the imprinting defect did not correlate with the onset of the disease, the severity of endocrine resistances, or with the presence/absence of specific AHO signs. CONCLUSIONS Similar molecular alterations may lead to a broad spectrum of diseases, from isolated PTH resistance to complete PHP-Ia, and the degree of methylation alterations does not reflect or anticipate the severity and the type of different PHP/AHO manifestations.
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Affiliation(s)
- Francesca M Elli
- Department of Clinical Sciences and Community Health (F.M.E., M.F., A.M.B., E.P., P.B.-P., A.S., G.M.), Endocrinology and Diabetology Unit, University of Milan, Fondazione Istituto di Ricovero e Cura a Carattere Scientifico, Ca' Granda Ospedale Maggiore Policlinico, and Center of Molecular and Genetic Epidemiology (V.B., L.T.), Department of Clinical Sciences and Community Health, Università di Milano and Fondazione Cà Granda Istituto di Ricovero e Cura a Carattere Scientifico, Ospedale Maggiore Policlinico, 20122 Milan, Italy; and Department of Public Health and Pediatrics (L.d.S.), University of Turin, and Regina Margherita Children's Hospital, 10126 Turin, Italy
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Fragile X syndrome: a preclinical review on metabotropic glutamate receptor 5 (mGluR5) antagonists and drug development. Psychopharmacology (Berl) 2014; 231:1217-26. [PMID: 24232444 DOI: 10.1007/s00213-013-3330-3] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Accepted: 10/14/2013] [Indexed: 10/26/2022]
Abstract
RATIONALE Fragile X syndrome (FXS) is considered the leading inherited cause of intellectual disability and autism. In FXS, the fragile X mental retardation 1 (FMR1) gene is silenced and the fragile X mental retardation protein (FMRP) is not expressed, resulting in the characteristic features of the syndrome. Despite recent advances in understanding the pathophysiology of FXS, there is still no cure for this condition; current treatment is symptomatic. Preclinical research is essential in the development of potential therapeutic agents. OBJECTIVES This review provides an overview of the preclinical evidence supporting metabotropic glutamate receptor 5 (mGluR5) antagonists as therapeutic agents for FXS. RESULTS According to the mGluR theory of FXS, the absence of FMRP leads to enhanced glutamatergic signaling via mGluR5, which leads to increased protein synthesis and defects in synaptic plasticity including enhanced long-term depression. As such, efforts to develop agents that target the underlying pathophysiology of FXS have focused on mGluR5 modulation. Animal models, particularly the Fmr1 knockout mouse model, have become invaluable in exploring therapeutic approaches on an electrophysiological, behavioral, biochemical, and neuroanatomical level. Two direct approaches are currently being investigated for FXS treatment: reactivating the FMR1 gene and compensating for the lack of FMRP. The latter approach has yielded promising results, with mGluR5 antagonists showing efficacy in clinical trials. CONCLUSIONS Targeting mGluR5 is a valid approach for the development of therapeutic agents that target the underlying pathophysiology of FXS. Several compounds are currently in development, with encouraging results.
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Doll CA, Broadie K. Impaired activity-dependent neural circuit assembly and refinement in autism spectrum disorder genetic models. Front Cell Neurosci 2014; 8:30. [PMID: 24570656 PMCID: PMC3916725 DOI: 10.3389/fncel.2014.00030] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 01/21/2014] [Indexed: 01/23/2023] Open
Abstract
Early-use activity during circuit-specific critical periods refines brain circuitry by the coupled processes of eliminating inappropriate synapses and strengthening maintained synapses. We theorize these activity-dependent (A-D) developmental processes are specifically impaired in autism spectrum disorders (ASDs). ASD genetic models in both mouse and Drosophila have pioneered our insights into normal A-D neural circuit assembly and consolidation, and how these developmental mechanisms go awry in specific genetic conditions. The monogenic fragile X syndrome (FXS), a common cause of heritable ASD and intellectual disability, has been particularly well linked to defects in A-D critical period processes. The fragile X mental retardation protein (FMRP) is positively activity-regulated in expression and function, in turn regulates excitability and activity in a negative feedback loop, and appears to be required for the A-D remodeling of synaptic connectivity during early-use critical periods. The Drosophila FXS model has been shown to functionally conserve the roles of human FMRP in synaptogenesis, and has been centrally important in generating our current mechanistic understanding of the FXS disease state. Recent advances in Drosophila optogenetics, transgenic calcium reporters, highly-targeted transgenic drivers for individually-identified neurons, and a vastly improved connectome of the brain are now being combined to provide unparalleled opportunities to both manipulate and monitor A-D processes during critical period brain development in defined neural circuits. The field is now poised to exploit this new Drosophila transgenic toolbox for the systematic dissection of A-D mechanisms in normal versus ASD brain development, particularly utilizing the well-established Drosophila FXS disease model.
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Affiliation(s)
- Caleb A Doll
- Department of Biological Sciences, Vanderbilt University Nashville, TN, USA
| | - Kendal Broadie
- Department of Biological Sciences, Vanderbilt University Nashville, TN, USA ; Kennedy Center for Research on Human Development, Vanderbilt University Nashville, TN, USA
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Kovács T, Kelemen O, Kéri S. Decreased fragile X mental retardation protein (FMRP) is associated with lower IQ and earlier illness onset in patients with schizophrenia. Psychiatry Res 2013; 210:690-3. [PMID: 23333116 DOI: 10.1016/j.psychres.2012.12.022] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2011] [Revised: 09/28/2012] [Accepted: 12/20/2012] [Indexed: 01/11/2023]
Abstract
The purpose of this study was to investigate Fragile X Syndrome (FXS)-related mechanisms in schizophrenia, including CGG triplet expansion, FMR1 mRNA, and fragile X mental retardation protein (FMRP) levels in lymphocytes. We investigated 36 patients with schizophrenia and 30 healthy controls using Southern blot analysis, mRNA assay, and enzyme-linked immunosorbent assay (ELISA). General intellectual functions were assessed with the Wechsler Adult Intelligence Scale-III, and the clinical symptoms were evaluated with the Positive and Negative Syndrome Scale. Results revealed that, relative to healthy controls, CGG triplet size and FMR1 mRNA were unaltered in patients with schizophrenia. However, the FMRP level was significantly reduced in patients compared with controls. We found an association between lower FMRP levels, reduced IQ, and earlier illness onset in schizophrenia. Chlorpromazine-equivalent antipsychotic dose did not correlate with FMRP levels. These results raise the possibility of impaired translation of FMR1 mRNA, altered epigenetic regulation, or increased degradation of FMRP in schizophrenia, which may play a role in dysfunctional neurodevelopmental processes and impaired neuroplasticity.
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Grasso M, Boon EMJ, Filipovic-Sadic S, van Bunderen PA, Gennaro E, Cao R, Latham GJ, Hadd AG, Coviello DA. A novel methylation PCR that offers standardized determination of FMR1 methylation and CGG repeat length without southern blot analysis. J Mol Diagn 2013; 16:23-31. [PMID: 24177047 DOI: 10.1016/j.jmoldx.2013.09.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Revised: 09/05/2013] [Accepted: 09/09/2013] [Indexed: 01/20/2023] Open
Abstract
Fragile X syndrome and associated disorders are characterized by the number of CGG repeats and methylation status of the FMR1 gene for which Southern blot (SB) historically has been required for analysis. This study describes a simple PCR-only workflow (mPCR) to replace SB analysis, that incorporates novel procedural controls, treatment of the DNA in separate control and methylation-sensitive restriction endonuclease reactions, amplification with labeled primers, and two-color amplicon sizing by capillary electrophoresis. mPCR was evaluated in two independent laboratories with 76 residual clinical samples that represented typical and challenging fragile X alleles in both males and females. mPCR enabled superior size resolution and analytical sensitivity for size and methylation mosaicism compared to SB. Full mutation mosaicism was detected down to 1% in a background of 99% normal allele with 50- to 100-fold less DNA than required for SB. A low level of full mutation mosaicism in one sample was detected using mPCR but not observed using SB. Overall, the sensitivity for detection of full mutation alleles was 100% (95% CI: 89%-100%) with an accuracy of 99% (95% CI: 93%-100%). mPCR analysis of DNA from individuals with Klinefelter and Turner syndromes, and DNA from sperm and blood, were consistent with SB. As such, mPCR enables accurate, sensitive, and standardized methods of FMR1 analysis that can harmonize results across different laboratories.
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Affiliation(s)
- Marina Grasso
- Laboratory of Human Genetics, Galliera Hospital, Genoa, Italy.
| | - Elles M J Boon
- Laboratory for Diagnostic Genome Analysis, Department of Clinical Genetics, Leiden University Medical Center (LUMC), Leiden, the Netherlands
| | | | - Patrick A van Bunderen
- Laboratory for Diagnostic Genome Analysis, Department of Clinical Genetics, Leiden University Medical Center (LUMC), Leiden, the Netherlands
| | - Elena Gennaro
- Laboratory of Human Genetics, Galliera Hospital, Genoa, Italy
| | - Ru Cao
- Asuragen, Inc., Austin, Texas
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