1
|
Urine-Derived Epithelial Cell Lines: A New Tool to Model Fragile X Syndrome (FXS). Cells 2020; 9:cells9102240. [PMID: 33027907 PMCID: PMC7600987 DOI: 10.3390/cells9102240] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 09/29/2020] [Accepted: 10/02/2020] [Indexed: 02/08/2023] Open
Abstract
Fragile X syndrome (FXS) is an X-linked neurodevelopmental condition associated with intellectual disability and behavioral problems due to the lack of the Fragile X mental retardation protein (FMRP), which plays a crucial role in synaptic plasticity and memory. A desirable in vitro cell model to study FXS would be one that can be generated by simple isolation and culture method from a collection of a non-invasive donor specimen. Currently, the various donor-specific cells can be isolated mainly from peripheral blood and skin biopsy. However, they are somewhat invasive methods for establishing cell lines from the primary subject material. In this study, we characterized a cost-effective and straightforward method to derive epithelial cell lines from urine samples collected from participants with FXS and healthy controls (TD). The urine-derived cells expressed epithelial cell surface markers via fluorescence-activated cell sorting (FACS). We observed inter, and the intra-tissue CGG mosaicism in the PBMCs and the urine-derived cells from participants with FXS potentially related to the observed variations in the phenotypic and clinical presentation FXS. We characterized these urine-derived epithelial cells for FMR1 mRNA and FMRP expression and observed some expression in the lines derived from full mutation mosaic participants. Further, FMRP expression was localized in the cytoplasm of the urine-derived epithelial cells of healthy controls. Deficient FMRP expression was also observed in mosaic males, while, as expected, no expression was observed in cells derived from participants with a hypermethylated full mutation.
Collapse
|
2
|
Budimirovic DB, Schlageter A, Filipovic-Sadic S, Protic DD, Bram E, Mahone EM, Nicholson K, Culp K, Javanmardi K, Kemppainen J, Hadd A, Sharp K, Adayev T, LaFauci G, Dobkin C, Zhou L, Brown WT, Berry-Kravis E, Kaufmann WE, Latham GJ. A Genotype-Phenotype Study of High-Resolution FMR1 Nucleic Acid and Protein Analyses in Fragile X Patients with Neurobehavioral Assessments. Brain Sci 2020; 10:E694. [PMID: 33008014 PMCID: PMC7601415 DOI: 10.3390/brainsci10100694] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 09/25/2020] [Accepted: 09/25/2020] [Indexed: 01/04/2023] Open
Abstract
Fragile X syndrome (FXS) is caused by silencing of the FMR1 gene, which encodes a protein with a critical role in synaptic plasticity. The molecular abnormality underlying FMR1 silencing, CGG repeat expansion, is well characterized; however, delineation of the pathway from DNA to RNA to protein using biosamples from well characterized patients with FXS is limited. Since FXS is a common and prototypical genetic disorder associated with intellectual disability (ID) and autism spectrum disorder (ASD), a comprehensive assessment of the FMR1 DNA-RNA-protein pathway and its correlations with the neurobehavioral phenotype is a priority. We applied nine sensitive and quantitative assays evaluating FMR1 DNA, RNA, and FMRP parameters to a reference set of cell lines representing the range of FMR1 expansions. We then used the most informative of these assays on blood and buccal specimens from cohorts of patients with different FMR1 expansions, with emphasis on those with FXS (N = 42 total, N = 31 with FMRP measurements). The group with FMRP data was also evaluated comprehensively in terms of its neurobehavioral profile, which allowed molecular-neurobehavioral correlations. FMR1 CGG repeat expansions, methylation levels, and FMRP levels, in both cell lines and blood samples, were consistent with findings of previous FMR1 genomic and protein studies. They also demonstrated a high level of agreement between blood and buccal specimens. These assays further corroborated previous reports of the relatively high prevalence of methylation mosaicism (slightly over 50% of the samples). Molecular-neurobehavioral correlations confirmed the inverse relationship between overall severity of the FXS phenotype and decrease in FMRP levels (N = 26 males, mean 4.2 ± 3.3 pg FMRP/ng genomic DNA). Other intriguing findings included a significant relationship between the diagnosis of FXS with ASD and two-fold lower levels of FMRP (mean 2.8 ± 1.3 pg FMRP/ng genomic DNA, p = 0.04), in particular observed in younger age- and IQ-adjusted males (mean age 6.9 ± 0.9 years with mean 3.2 ± 1.2 pg FMRP/ng genomic DNA, 57% with severe ASD), compared to FXS without ASD. Those with severe ID had even lower FMRP levels independent of ASD status in the male-only subset. The results underscore the link between FMR1 expansion, gene methylation, and FMRP deficit. The association between FMRP deficiency and overall severity of the neurobehavioral phenotype invites follow up studies in larger patient cohorts. They would be valuable to confirm and potentially extend our initial findings of the relationship between ASD and other neurobehavioral features and the magnitude of FMRP deficit. Molecular profiling of individuals with FXS may have important implications in research and clinical practice.
Collapse
Affiliation(s)
- Dejan B. Budimirovic
- Departments of Psychiatry and Neurogenetics, Fragile X Clinic, Kennedy Krieger Institute, Baltimore, MD 21205, USA;
- Department of Psychiatry & Behavioral Sciences-Child Psychiatry, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
| | - Annette Schlageter
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| | - Stela Filipovic-Sadic
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| | - Dragana D. Protic
- Departments of Psychiatry and Neurogenetics, Fragile X Clinic, Kennedy Krieger Institute, Baltimore, MD 21205, USA;
- School of Medicine, University of Belgrade, 11000 Belgrade, Serbia
| | - Eran Bram
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| | - E. Mark Mahone
- Department of Neuropsychology, Kennedy Krieger Institute, Baltimore, MD 21205, USA;
| | - Kimberly Nicholson
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| | - Kristen Culp
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| | - Kamyab Javanmardi
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| | - Jon Kemppainen
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| | - Andrew Hadd
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| | - Kevin Sharp
- Department of Pediatrics, Rush University Medical Center, Chicago, IL 60612, USA; (K.S.); (L.Z.); (E.B.-K.)
| | - Tatyana Adayev
- Institute for Basic Research in Developmental Disabilities, Staten Island, NY 10314, USA; (T.A.); (G.L.); (C.D.); (W.T.B.)
| | - Giuseppe LaFauci
- Institute for Basic Research in Developmental Disabilities, Staten Island, NY 10314, USA; (T.A.); (G.L.); (C.D.); (W.T.B.)
| | - Carl Dobkin
- Institute for Basic Research in Developmental Disabilities, Staten Island, NY 10314, USA; (T.A.); (G.L.); (C.D.); (W.T.B.)
| | - Lili Zhou
- Department of Pediatrics, Rush University Medical Center, Chicago, IL 60612, USA; (K.S.); (L.Z.); (E.B.-K.)
| | - William Ted Brown
- Institute for Basic Research in Developmental Disabilities, Staten Island, NY 10314, USA; (T.A.); (G.L.); (C.D.); (W.T.B.)
| | - Elizabeth Berry-Kravis
- Department of Pediatrics, Rush University Medical Center, Chicago, IL 60612, USA; (K.S.); (L.Z.); (E.B.-K.)
- Departments of Pediatrics, Neurological Sciences and Biochemistry, Rush University Medical Center, Chicago, IL 60612, USA
| | - Walter E. Kaufmann
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA;
- Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115, USA
| | - Gary J. Latham
- Asuragen, Inc., Austin, TX 78744, USA; (A.S.); (S.F.-S.); (E.B.); (K.N.); (K.C.); (K.J.); (J.K.); (A.H.)
| |
Collapse
|
3
|
Ramos C, Ocampos M, Barbato IT, Graça Bicalho MD, Nisihara R. Molecular analysis of FMR1 gene in a population in Southern Brazil: Comparison of four methods. Pract Lab Med 2020; 21:e00162. [PMID: 32426440 PMCID: PMC7225725 DOI: 10.1016/j.plabm.2020.e00162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2019] [Revised: 02/04/2020] [Accepted: 03/24/2020] [Indexed: 12/01/2022] Open
Abstract
Objectives Fragile X syndrome (FXS) is caused by expansion of the number of cytosine-guanine-guanine (CGG) repeats in the regulatory region of the gene fragile X mental retardation 1 (FMR1). The molecular diagnoses of FXS can be performed using two tests based on two different techniques, namely polymerase chain reaction (PCR) and Southern blotting (SB). However, both of these techniques have limitations. The purpose of this study was to evaluate the performance of the commercial FragilEase™ PCR kit for FXS diagnosis comparing to other laboratory methods. Design and methods: This study had a retrospective design. We analyzed the performance of the FragilEase™ PCR kit using 90 DNA samples from patients with clinical suspicion of FXS or a family history of the syndrome using capillary electrophoresis and compared with the results obtained for the same samples using PCR, SB, and AmplideX FMR1 PCR. Results FragilEase™ PCR kit displayed high concordance with the results obtained using PCR, SB, and AmplideX FMR1 PCR regarding the detection of normal, intermediate/gray zone, premutation, and full mutation alleles, as well as female homozygosity and mosaicism. The replicate sizes found using the FragilEase™ PCR assay varied on average by two CGG repeats. Conclusion FragilEase™ PCR, as well as other commercially available kits, efficiently detect FMR1 mutations and simplify the workflow in laboratories that performing FXS diagnoses. Southern Blot is the gold standard for FXS diagnosis, however, is a time-consuming method and requires a large amount of DNA. PCR determines the number of CGG repeats, however, it does not differentiate homozygous alleles in women. Commercial PCR-based kits aimed to simplify the workflow in FXS diagnosis with high accuracy.
Collapse
Affiliation(s)
- Cinthia Ramos
- Post Graduate Program in Gynecology and Obstetrics, Universidade Federal do Paraná, Curitiba, Brazil
- Department of Genetics, Federal University of Paraná, Curitiba, Brazil
| | - Maristela Ocampos
- Neurogene Laboratory of Human Citogenetics and Molecular Genetics, Florianópolis, Brazil
| | - Ingrid Tremel Barbato
- Neurogene Laboratory of Human Citogenetics and Molecular Genetics, Florianópolis, Brazil
| | - Maria da Graça Bicalho
- Post Graduate Program in Gynecology and Obstetrics, Universidade Federal do Paraná, Curitiba, Brazil
- Department of Genetics, Federal University of Paraná, Curitiba, Brazil
| | - Renato Nisihara
- Post Graduate Program in Gynecology and Obstetrics, Universidade Federal do Paraná, Curitiba, Brazil
- Department of Medicine, Positivo University, Curitiba, Paraná, Brazil
- Corresponding author.Department of Medicine, Positivo University, R. Prof. Pedro Viriato Parigot de Souza, 5300, Curitiba, 81280-330, Brazil.
| |
Collapse
|
4
|
Significantly Elevated FMR1 mRNA and Mosaicism for Methylated Premutation and Full Mutation Alleles in Two Brothers with Autism Features Referred for Fragile X Testing. Int J Mol Sci 2019; 20:ijms20163907. [PMID: 31405222 PMCID: PMC6721168 DOI: 10.3390/ijms20163907] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 08/04/2019] [Accepted: 08/07/2019] [Indexed: 11/26/2022] Open
Abstract
Although fragile X syndrome (FXS) is caused by a hypermethylated full mutation (FM) expansion with ≥200 cytosine-guanine-guanine (CGG) repeats, and a decrease in FMR1 mRNA and its protein (FMRP), incomplete silencing has been associated with more severe autism features in FXS males. This study reports on brothers (B1 and B2), aged 5 and 2 years, with autistic features and language delay, but a higher non-verbal IQ in comparison to typical FXS. CGG sizing using AmplideX PCR only identified premutation (PM: 55–199 CGGs) alleles in blood. Similarly, follow-up in B1 only revealed PM alleles in saliva and skin fibroblasts; whereas, an FM expansion was detected in both saliva and buccal DNA of B2. While Southern blot analysis of blood detected an unmethylated FM, methylation analysis with a more sensitive methodology showed that B1 had partially methylated PM alleles in blood and fibroblasts, which were completely unmethylated in buccal and saliva cells. In contrast, B2 was partially methylated in all tested tissues. Moreover, both brothers had FMR1 mRNA ~5 fold higher values than those of controls, FXS and PM cohorts. In conclusion, the presence of unmethylated FM and/or PM in both brothers may lead to an overexpression of toxic expanded mRNA in some cells, which may contribute to neurodevelopmental problems, including elevated autism features.
Collapse
|
5
|
Jiraanont P, Kumar M, Tang HT, Espinal G, Hagerman PJ, Hagerman RJ, Chutabhakdikul N, Tassone F. Size and methylation mosaicism in males with Fragile X syndrome. Expert Rev Mol Diagn 2018; 17:1023-1032. [PMID: 28929824 DOI: 10.1080/14737159.2017.1377612] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND Size and methylation mosaicism are a common phenomenon in Fragile X syndrome (FXS). Here, the authors report a study on twelve fragile X males with atypical mosaicism, seven of whom presented with autism spectrum disorder. METHODS A combination of Southern Blot and PCR analysis was used for CGG allele sizing and methylation. FMR1 mRNA and FMRP expression were measured by qRT-PCR and by Homogeneous Time Resolved Fluorescence methodology, respectively. RESULTS DNA analysis showed atypical size- or methylation-mosaicism with both, full mutation and smaller (normal to premutation) alleles, as well as a combination of methylated and unmethylated alleles. Four individuals carried a deletion of the CGG repeat and portions of the flanking regions. The extent of methylation among the participants was reflected in the lower FMR1 mRNA and FMRP expression levels detected in these subjects. CONCLUSION Decreased gene expression is likely the main contributor to the cognitive impairment observed in these subjects; although the presence of a normal allele did not appear to compensate for the presence of the full mutation, it correlated with better cognitive function in some but not all of the reported cases emphasizing the complexity of the molecular and clinical profile in FXS.
Collapse
Affiliation(s)
- Poonnada Jiraanont
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA.,b Research Center for Neuroscience, Institute of Molecular Biosciences , Mahidol University , Nakornpathom , Thailand
| | - Madhur Kumar
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA
| | - Hiu-Tung Tang
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA
| | - Glenda Espinal
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA
| | - Paul J Hagerman
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA.,c M.I.N.D. Institute , University of California Davis Medical Center , Sacramento , CA , USA
| | - Randi J Hagerman
- c M.I.N.D. Institute , University of California Davis Medical Center , Sacramento , CA , USA.,d Department of Pediatrics , University of California, Davis Medical Center , Sacramento , CA , USA
| | - Nuanchan Chutabhakdikul
- b Research Center for Neuroscience, Institute of Molecular Biosciences , Mahidol University , Nakornpathom , Thailand
| | - Flora Tassone
- a Department of Biochemistry and Molecular Medicine , University of California, School of Medicine , Davis , CA , USA.,c M.I.N.D. Institute , University of California Davis Medical Center , Sacramento , CA , USA
| |
Collapse
|
6
|
Ciaccio C, Fontana L, Milani D, Tabano S, Miozzo M, Esposito S. Fragile X syndrome: a review of clinical and molecular diagnoses. Ital J Pediatr 2017; 43:39. [PMID: 28420439 PMCID: PMC5395755 DOI: 10.1186/s13052-017-0355-y] [Citation(s) in RCA: 90] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2016] [Accepted: 04/07/2017] [Indexed: 12/24/2022] Open
Abstract
Background Fragile X Syndrome (FXS) is the second cause of intellectual disability after Down syndrome and the most prevalent cause of intellectual disability in males, affecting 1:5000–7000 men and 1:4000–6000 women. It is caused by an alteration of the FMR1 gene, which maps at the Xq27.3 band: more than 99% of individuals have a CGG expansion (>200 triplets) in the 5′ UTR of the gene, and FMR1 mutations and duplication/deletion are responsible for the remaining (<1%) molecular diagnoses of FXS. The aim of this review was to gather the current clinical and molecular knowledge about FXS to provide clinicians with a tool to guide the initial assessment and follow-up of FXS and to offer to laboratory workers and researchers an update about the current diagnostic procedures. Discussion FXS is a well-known condition; however, most of the studies thus far have focused on neuropsychiatric features. Unfortunately, some of the available studies have limitations, such as the paucity of patients enrolled or bias due to the collection of the data in a single-country population, which may be not representative of the average global FXS population. In recent years, insight into the adult presentation of the disease has progressively increased. Pharmacological treatment of FXS is essentially symptom based, but the growing understanding of the molecular and biological mechanisms of the disease are paving the way to targeted therapy, which may reverse the effects of FMRP deficiency and be a real cure for the disease itself, not just its symptoms. Conclusions The clinical spectrum of FXS is wide, presenting not only as an isolated intellectual disability but as a multi-systemic condition, involving predominantly the central nervous system but potentially affecting any apparatus. Given the relative high frequency of the condition and its complex clinical management, FXS appears to have an important economic and social burden.
Collapse
Affiliation(s)
- Claudia Ciaccio
- Pediatric Highly Intensive Care Unit, Department of Pathophysiology and Transplantation, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via Commenda 9, 20122, Milan, Italy
| | - Laura Fontana
- Division of Pathology, Department of Pathophysiology and Transplantation, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Donatella Milani
- Pediatric Highly Intensive Care Unit, Department of Pathophysiology and Transplantation, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via Commenda 9, 20122, Milan, Italy
| | - Silvia Tabano
- Division of Pathology, Department of Pathophysiology and Transplantation, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Monica Miozzo
- Division of Pathology, Department of Pathophysiology and Transplantation, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Susanna Esposito
- Pediatric Clinic, Department of Surgical and Biomedical Sciences, Università degli Studi di Perugia, Piazza Lucio Severi 1, Loc. S. Andrea delle Fratte, 06132, Perugia, Italy.
| |
Collapse
|
7
|
Gonçalves TF, dos Santos JM, Gonçalves AP, Tassone F, Mendoza-Morales G, Ribeiro MG, Kahn E, Boy R, Pimentel MMG, Santos-Rebouças CB. Finding FMR1 mosaicism in Fragile X syndrome. Expert Rev Mol Diagn 2016; 16:501-7. [PMID: 26716517 DOI: 10.1586/14737159.2016.1135739] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVE Almost all patients with Fragile X Syndrome (FXS) exhibit a CGG repeat expansion (full mutation) in the Fragile Mental Retardation 1 gene (FMR1). Here, the authors report five unrelated males with FXS harboring a somatic full mutation/deletion mosaicism. METHODS Mutational profiles were only elucidated by using a combination of molecular approaches (CGG-based PCR, Sanger sequencing, MS-MLPA, Southern blot and mPCR). RESULTS Four patients exhibited small deletions encompassing the CGG repeats tract and flanking regions, whereas the remaining had a larger deletion comprising at least exon 1 and part of intron 1 of FMR1 gene. The presence of a 2-3 base pairs microhomology in proximal and distal non-recurrent breakpoints without scars supports the involvement of microhomology mediated induced repair (MMBIR) mechanism in three small deletions. CONCLUSION The authors data highlights the importance of using different research methods to elucidate atypical FXS mutational profiles, which are clinically undistinguishable and may have been underestimated.
Collapse
Affiliation(s)
| | | | | | - Flora Tassone
- b Department of Biochemistry and Molecular Medicine , UC Davis School of Medicine, University of California, Davis , Sacramento , CA , USA.,c Davis MIND Institute , Sacramento , CA , USA
| | - Guadalupe Mendoza-Morales
- b Department of Biochemistry and Molecular Medicine , UC Davis School of Medicine, University of California, Davis , Sacramento , CA , USA
| | - Márcia Gonçalves Ribeiro
- d Clinical Genetics Service , IPPMG, Federal University of Rio de Janeiro , Rio de Janeiro , Brazil
| | - Evelyn Kahn
- d Clinical Genetics Service , IPPMG, Federal University of Rio de Janeiro , Rio de Janeiro , Brazil
| | - Raquel Boy
- e Pedro Ernesto University Hospital , State University of Rio de Janeiro , Rio de Janeiro , Brazil
| | | | | |
Collapse
|
8
|
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.
Collapse
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
| |
Collapse
|
9
|
Pretto D, Yrigollen CM, Tang HT, Williamson J, Espinal G, Iwahashi CK, Durbin-Johnson B, Hagerman RJ, Hagerman PJ, Tassone F. Clinical and molecular implications of mosaicism in FMR1 full mutations. Front Genet 2014; 5:318. [PMID: 25278957 PMCID: PMC4166380 DOI: 10.3389/fgene.2014.00318] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 08/25/2014] [Indexed: 12/27/2022] Open
Abstract
Expansions of more than 200 CGG repeats (full mutation) in the FMR1 gene give rise to fragile X syndrome (FXS) through a process that generally involves hypermethylation of the FMR1 promoter region and gene silencing, resulting in absence of expression of the encoded protein, FMRP. However, mosaicism with alleles differing in size and extent of methylation often exist within or between tissues of individuals with FXS. In the current work, CGG-repeat lengths and methylation status were assessed for eighteen individuals with FXS, including 13 mosaics, for which peripheral blood cells (PBMCs) and primary fibroblast cells were available. Our results show that for both PBMCs and fibroblasts, FMR1 mRNA and FMRP expression are directly correlated with the percent of methylation of the FMR1 allele. In addition, Full Scale IQ scores were inversely correlated with the percent methylation and positively correlated with higher FMRP expression. These latter results point toward a positive impact on cognition for full mutation mosaics with lower methylation compared to individuals with fully methylated, full mutation alleles. However, we did not observe a significant reduction in the number of seizures, nor in the severity of hyperactivity or autism spectrum disorder, among individuals with mosaic genotypes in the presentation of FXS. These observations suggest that low, but non-zero expression of FMRP may be sufficient to positively impact cognitive function in individuals with FXS, with methylation mosaicism (lowered methylation fraction) contributing to a more positive clinical outcome.
Collapse
Affiliation(s)
- Dalyir Pretto
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Carolyn M Yrigollen
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Hiu-Tung Tang
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - John Williamson
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Glenda Espinal
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Chris K Iwahashi
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA
| | - Blythe Durbin-Johnson
- Department of Public Health Sciences, School of Medicine, University of California at Davis Davis, CA, USA
| | - Randi J Hagerman
- Department of Pediatrics, School of Medicine, University of California at Davis Davis, CA, USA ; MIND Institute, UC Davis Medical Center Sacramento, CA, USA
| | - Paul J Hagerman
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA ; Department of Pediatrics, School of Medicine, University of California at Davis Davis, CA, USA
| | - Flora Tassone
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California at Davis Davis, CA, USA ; Department of Pediatrics, School of Medicine, University of California at Davis Davis, CA, USA
| |
Collapse
|