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Walker AJ, Graham C, Greenwood M, Woodall M, Maeshima R, O’Hara-Wright M, Sanz DJ, Guerrini I, Aldossary AM, O’Callaghan C, Baines DL, Harrison PT, Hart SL. Molecular and functional correction of a deep intronic splicing mutation in CFTR by CRISPR-Cas9 gene editing. Mol Ther Methods Clin Dev 2023; 31:101140. [PMID: 38027060 PMCID: PMC10661860 DOI: 10.1016/j.omtm.2023.101140] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Accepted: 10/17/2023] [Indexed: 12/01/2023]
Abstract
Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the CFTR gene. The 10th most common mutation, c.3178-2477C>T (3849+10kb C>T), involves a cryptic, intronic splice site. This mutation was corrected in CF primary cells homozygous for this mutation by delivering pairs of guide RNAs (gRNAs) with Cas9 protein in ribonucleoprotein (RNP) complexes that introduce double-strand breaks to flanking sites to excise the 3849+10kb C>T mutation, followed by DNA repair by the non-homologous end-joining pathway, which functions in all cells of the airway epithelium. RNP complexes were delivered to CF basal epithelial cell by a non-viral, receptor-targeted nanocomplex comprising a formulation of targeting peptides and lipids. Canonical CFTR mRNA splicing was, thus, restored leading to the restoration of CFTR protein expression with concomitant restoration of electrophysiological function in airway epithelial air-liquid interface cultures. Off-target editing was not detected by Sanger sequencing of in silico-selected genomic sites with the highest sequence similarities to the gRNAs, although more sensitive unbiased whole genome sequencing methods would be required for possible translational developments. This approach could potentially be used to correct aberrant splicing signals in several other CF mutations and other genetic disorders where deep-intronic mutations are pathogenic.
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Affiliation(s)
- Amy J. Walker
- Genetics and Genomic Medicine Department, UCL Great Ormond Street Institute of Child Health, London, UK
| | - Carina Graham
- Genetics and Genomic Medicine Department, UCL Great Ormond Street Institute of Child Health, London, UK
| | - Miriam Greenwood
- Genetics and Genomic Medicine Department, UCL Great Ormond Street Institute of Child Health, London, UK
| | - Maximillian Woodall
- Institute for Infection and Immunity, St. George’s, University of London, London, UK
| | - Ruhina Maeshima
- Genetics and Genomic Medicine Department, UCL Great Ormond Street Institute of Child Health, London, UK
| | - Michelle O’Hara-Wright
- Genetics and Genomic Medicine Department, UCL Great Ormond Street Institute of Child Health, London, UK
| | - David J. Sanz
- Department of Physiology, BioSciences Institute, University College Cork, Cork, Ireland
| | - Ileana Guerrini
- Genetics and Genomic Medicine Department, UCL Great Ormond Street Institute of Child Health, London, UK
| | - Ahmad M. Aldossary
- Genetics and Genomic Medicine Department, UCL Great Ormond Street Institute of Child Health, London, UK
| | - Christopher O’Callaghan
- Infection, Immunity & Inflammation Department, UCL Great Ormond Street Institute of Child Health, London, UK
| | - Deborah L. Baines
- Institute for Infection and Immunity, St. George’s, University of London, London, UK
| | - Patrick T. Harrison
- Department of Physiology, BioSciences Institute, University College Cork, Cork, Ireland
| | - Stephen L. Hart
- Genetics and Genomic Medicine Department, UCL Great Ormond Street Institute of Child Health, London, UK
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2
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Roy S, Ghosh S, Ray J, Ray K, Sengupta M. Missing heritability of Wilson disease: a search for the uncharacterized mutations. Mamm Genome 2023; 34:1-11. [PMID: 36462057 DOI: 10.1007/s00335-022-09971-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2022] [Accepted: 11/24/2022] [Indexed: 12/05/2022]
Abstract
Wilson disease (WD), a copper metabolism disorder caused by mutations in ATP7B, manifests heterogeneous clinical features. Interestingly, in a fraction of clinically diagnosed WD patients, mutations in ATP7B appears to be missing. In this review we discuss the plausible explanations of this missing heritability and propose a workflow that can identify the hidden mutations. Mutation analyses of WD generally includes targeted sequencing of ATP7B exons, exon-intron boundaries, and rarely, the proximal promoter region. We propose that variants in the distal cis-regulatory elements and/or deep intronic variants that impact splicing might well represent the hidden mutations. Heterozygous del/ins that remain refractory to conventional PCR-sequencing method may also represent such mutations. In this review, we also hypothesize that mutations in the key copper metabolism genes, like, ATOX1, COMMD1, and SLC31A1, could possibly lead to a WD-like phenotype. In fact, WD does present overlapping symptoms with other rare genetic disorders; hence, the possibility of a misdiagnosis and thus adding to missing heritability cannot be excluded. In this regard, it seems that whole-genome analysis will provide a comprehensive and rapid molecular diagnosis of WD. However, considering the associated cost for such a strategy, we propose an alternative customized screening schema of WD which include targeted sequencing of ATP7B locus as well as other key copper metabolism genes. Success of such a schema has been tested in a pilot study.
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Affiliation(s)
- Shubhrajit Roy
- S. N. Pradhan Centre for Neurosciences, University of Calcutta, Kolkata, India
- Post-doctoral Fellow, Physiology Department, Johns Hopkins University, Baltimore, USA
| | - Sampurna Ghosh
- Department of Genetics, University of Calcutta, 35 Ballygunge Circular Road, Kolkata, 700019, India
- Department of Biochemistry, Microbiology and Immunology, University of Saskatchewan, Saskatoon, Canada
| | - Jharna Ray
- S. N. Pradhan Centre for Neurosciences, University of Calcutta, Kolkata, India
| | - Kunal Ray
- Ramakrishna Mission Vivekananda Educational and Research Institute, Narendrapur, Kolkata, 700 103, India.
| | - Mainak Sengupta
- Department of Genetics, University of Calcutta, 35 Ballygunge Circular Road, Kolkata, 700019, India.
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3
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Splicing mutations in the CFTR gene as therapeutic targets. Gene Ther 2022; 29:399-406. [PMID: 35650428 PMCID: PMC9385490 DOI: 10.1038/s41434-022-00347-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 05/07/2022] [Accepted: 05/12/2022] [Indexed: 11/08/2022]
Abstract
The marketing approval, about ten years ago, of the first disease modulator for patients with cystic fibrosis harboring specific CFTR genotypes (~5% of all patients) brought new hope for their treatment. To date, several therapeutic strategies have been approved and the number of CFTR mutations targeted by therapeutic agents is increasing. Although these drugs do not reverse the existing disease, they help to increase the median life expectancy. However, on the basis of their CFTR genotype, ~10% of patients presently do not qualify for any of the currently available CFTR modulator therapies, particularly patients with splicing mutations (~12% of the reported CFTR mutations). Efforts are currently made to develop therapeutic agents that target disease-causing CFTR variants that affect splicing. This highlights the need to fully identify them by scanning non-coding regions and systematically determine their functional consequences. In this review, we present some examples of CFTR alterations that affect splicing events and the different therapeutic options that are currently developed and tested for splice switching.
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4
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Di Scipio M, Tavares E, Deshmukh S, Audo I, Green-Sanderson K, Zubak Y, Zine-Eddine F, Pearson A, Vig A, Tang CY, Mollica A, Karas J, Tumber A, Yu CW, Billingsley G, Wilson MD, Zeitz C, Héon E, Vincent A. Phenotype Driven Analysis of Whole Genome Sequencing Identifies Deep Intronic Variants that Cause Retinal Dystrophies by Aberrant Exonization. Invest Ophthalmol Vis Sci 2021; 61:36. [PMID: 32881472 PMCID: PMC7443117 DOI: 10.1167/iovs.61.10.36] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Purpose To demonstrate the effectiveness of combining retinal phenotyping and focused variant filtering from genome sequencing (GS) in identifying deep intronic disease causing variants in inherited retinal dystrophies. Methods Affected members from three pedigrees with classical enhanced S-cone syndrome (ESCS; Pedigree 1), congenital stationary night blindness (CSNB; Pedigree 2), and achromatopsia (ACHM; Pedigree 3), respectively, underwent detailed ophthalmologic evaluation, optical coherence tomography, and electroretinography. The probands underwent panel-based genetic testing followed by GS analysis. Minigene constructs (NR2E3, GPR179 and CNGB3) and patient-derived cDNA experiments (NR2E3 and GPR179) were performed to assess the functional effect of the deep intronic variants. Results The electrophysiological findings confirmed the clinical diagnosis of ESCS, CSNB, and ACHM in the respective pedigrees. Panel-based testing revealed heterozygous pathogenic variants in NR2E3 (NM_014249.3; c.119-2A>C; Pedigree 1) and CNGB3 (NM_019098.4; c.1148delC/p.Thr383Ilefs*13; Pedigree 3). The GS revealed heterozygous deep intronic variants in Pedigrees 1 (NR2E3; c.1100+1124G>A) and 3 (CNGB3; c.852+4751A>T), and a homozygous GPR179 variant in Pedigree 2 (NM_001004334.3; c.903+343G>A). The identified variants segregated with the phenotype in all pedigrees. All deep intronic variants were predicted to generate a splice acceptor gain causing aberrant exonization in NR2E3 [89 base pairs (bp)], GPR179 (197 bp), and CNGB3 (73 bp); splicing defects were validated through patient-derived cDNA experiments and/or minigene constructs and rescued by antisense oligonucleotide treatment. Conclusions Deep intronic mutations contribute to missing heritability in retinal dystrophies. Combining results from phenotype-directed gene panel testing, GS, and in silico splice prediction tools can help identify these difficult-to-detect pathogenic deep intronic variants.
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Affiliation(s)
- Matteo Di Scipio
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Erika Tavares
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Shriya Deshmukh
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Isabelle Audo
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France.,CHNO des Quinze-Vingts, INSERM-DGOS CIC1423, Paris, France.,University College London Institute of Ophthalmology, London, United Kingdom
| | - Kit Green-Sanderson
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Yuliya Zubak
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Fayçal Zine-Eddine
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Alexander Pearson
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Anjali Vig
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Chen Yu Tang
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Antonio Mollica
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Jonathan Karas
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Anupreet Tumber
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, Canada
| | - Caberry W Yu
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Gail Billingsley
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada
| | - Michael D Wilson
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
| | - Christina Zeitz
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Elise Héon
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada.,Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, Canada.,Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Canada
| | - Ajoy Vincent
- Genetics and Genomic Biology, The Hospital for Sick Children, Toronto, Canada.,Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, Canada.,Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Canada
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5
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Alvarez MEV, Chivers M, Borovska I, Monger S, Giannoulatou E, Kralovicova J, Vorechovsky I. Transposon clusters as substrates for aberrant splice-site activation. RNA Biol 2020; 18:354-367. [PMID: 32965162 PMCID: PMC7951965 DOI: 10.1080/15476286.2020.1805909] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Transposed elements (TEs) have dramatically shaped evolution of the exon-intron structure and significantly contributed to morbidity, but how recent TE invasions into older TEs cooperate in generating new coding sequences is poorly understood. Employing an updated repository of new exon-intron boundaries induced by pathogenic mutations, termed DBASS, here we identify novel TE clusters that facilitated exon selection. To explore the extent to which such TE exons maintain RNA secondary structure of their progenitors, we carried out structural studies with a composite exon that was derived from a long terminal repeat (LTR78) and AluJ and was activated by a C > T mutation optimizing the 5ʹ splice site. Using a combination of SHAPE, DMS and enzymatic probing, we show that the disease-causing mutation disrupted a conserved AluJ stem that evolved from helix 3.3 (or 5b) of 7SL RNA, liberating a primordial GC 5ʹ splice site from the paired conformation for interactions with the spliceosome. The mutation also reduced flexibility of conserved residues in adjacent exon-derived loops of the central Alu hairpin, revealing a cross-talk between traditional and auxilliary splicing motifs that evolved from opposite termini of 7SL RNA and were approximated by Watson-Crick base-pairing already in organisms without spliceosomal introns. We also identify existing Alu exons activated by the same RNA rearrangement. Collectively, these results provide valuable TE exon models for studying formation and kinetics of pre-mRNA building blocks required for splice-site selection and will be useful for fine-tuning auxilliary splicing motifs and exon and intron size constraints that govern aberrant splice-site activation.
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Affiliation(s)
| | - Martin Chivers
- School of Medicine, University of Southampton, Southampton, UK
| | - Ivana Borovska
- Slovak Academy of Sciences, Institute of Molecular Physiology and Genetics, Bratislava, Slovak Republic
| | - Steven Monger
- Computational Genomics Laboratory, Victor Chang Cardiac Research Institute, Darlinghurst, Australia
| | - Eleni Giannoulatou
- Computational Genomics Laboratory, Victor Chang Cardiac Research Institute, Darlinghurst, Australia.,St. Vincent's Clinical School, University of New South Wales, Sydney, Australia
| | - Jana Kralovicova
- School of Medicine, University of Southampton, Southampton, UK.,Slovak Academy of Sciences, Institute of Molecular Physiology and Genetics, Bratislava, Slovak Republic
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6
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Understanding human DNA variants affecting pre-mRNA splicing in the NGS era. ADVANCES IN GENETICS 2019; 103:39-90. [PMID: 30904096 DOI: 10.1016/bs.adgen.2018.09.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Pre-mRNA splicing, an essential step in eukaryotic gene expression, relies on recognition of short sequences on the primary transcript intron ends and takes place along transcription by RNA polymerase II. Exonic and intronic auxiliary elements may modify the strength of exon definition and intron recognition. Splicing DNA variants (SV) have been associated with human genetic diseases at canonical intron sites, as well as exonic substitutions putatively classified as nonsense, missense or synonymous variants. Their effects on mRNA may be modulated by cryptic splice sites associated to the SV allele, comprehending exon skipping or shortening, and partial or complete intron retention. As splicing mRNA outputs result from combinatorial effects of both intrinsic and extrinsic factors, in vitro functional assays supported by computational analyses are recommended to assist SV pathogenicity assessment for human Mendelian inheritance diseases. The increasing use of next-generating sequencing (NGS) targeting full genomic gene sequence has raised awareness of the relevance of deep intronic SV in genetic diseases and inclusion of pseudo-exons into mRNA. Finally, we take advantage of recent advances in sequencing and computational technologies to analyze alternative splicing in cancer. We explore the Catalog of Somatic Mutations in Cancer (COSMIC) to describe the proportion of splice-site mutations in cis and trans regulatory elements. Genomic data from large cohorts of different cancer types are increasingly available, in addition to repositories of normal and somatic genetic variations. These are likely to bring new insights to understanding the genetic control of alternative splicing by mapping splicing quantitative trait loci in tumors.
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7
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Bergougnoux A, Délétang K, Pommier A, Varilh J, Houriez F, Altieri JP, Koenig M, Férec C, Claustres M, Lalau G, Bienvenu T, Audrézet MP, Pagin A, Girodon E, Raynal C, Taulan-Cadars M. Functional characterization and phenotypic spectrum of three recurrent disease-causing deep intronic variants of the CFTR gene. J Cyst Fibros 2018; 18:468-475. [PMID: 30389601 DOI: 10.1016/j.jcf.2018.10.012] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 10/15/2018] [Accepted: 10/17/2018] [Indexed: 01/01/2023]
Abstract
BACKGROUND The CFTR genotype remains incomplete in 1% of Cystic Fibrosis (CF) cases, because only one or no disease-causing variants is detected after extended analysis. This fraction is probably higher in CFTR-Related Disorders (CFTR-RD). Deep-intronic CFTR variants are putative candidates to fill this gap. However, the recurrence, phenotypic spectrum and full molecular characterization of newly reported variants are unknown. METHODS Minigenes and analysis of CFTR transcripts in nasal epithelial cells were used to determine the impact on CFTR splicing of intronic variants that we previously identified by next generation sequencing of the whole CFTR locus. Phenotypic data were collected in 19 patients with CF and CFTR-RD, in whom one of the deep intronic variants has been detected. RESULTS Three deep-intronic variants promoted the inclusion of pseudo-exons (PE) in the CFTR transcript, hindering the synthesis of a functional protein. The c.2989-313A > T variant, detected in four patients with CF or CFTR-RD from three different families, led to the inclusion of a 118 bp PE. The c.3469-1304C > G variant promoted the inclusion of a 214 bp-PE and was identified in five patients with CF from four families. Haplotype analysis confirmed that this variant was associated with one CF chromosome of African origin. The most represented variant in our cohort was the c.3874-4522A > G, detected in 10 patients with various phenotypes, from male infertility to CF with pancreatic insufficiency. CONCLUSION These three deep intronic CFTR variants are associated with a large phenotypic spectrum, including typical CF. They should be included in CF diagnostic testing and carrier screening strategies.
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Affiliation(s)
- A Bergougnoux
- CHU de Montpellier, Laboratoire de Génétique Moléculaire, Montpellier, France; Université de Montpellier, Laboratoire de Génétique de Maladies Rares, EA7402 Montpellier, France.
| | - K Délétang
- Université de Montpellier, Laboratoire de Génétique de Maladies Rares, EA7402 Montpellier, France
| | - A Pommier
- Université de Montpellier, Laboratoire de Génétique de Maladies Rares, EA7402 Montpellier, France
| | - J Varilh
- Université de Montpellier, Laboratoire de Génétique de Maladies Rares, EA7402 Montpellier, France
| | - F Houriez
- AP-HP, HUPC, Hôpital Cochin, Laboratoire de Génétique et Biologie Moléculaires, Paris, France
| | - J P Altieri
- CHU de Montpellier, Laboratoire de Génétique Moléculaire, Montpellier, France
| | - M Koenig
- CHU de Montpellier, Laboratoire de Génétique Moléculaire, Montpellier, France; Université de Montpellier, Laboratoire de Génétique de Maladies Rares, EA7402 Montpellier, France
| | - C Férec
- Inserm, UMR1078 Génétique, Génomique Fonctionnelle et Biotechnologies, France; Univ Brest, EFS, IBSAM, Brest, France; CHU de Brest, Laboratoire de Génétique Moléculaire, Brest, France
| | - M Claustres
- Université de Montpellier, Laboratoire de Génétique de Maladies Rares, EA7402 Montpellier, France
| | - G Lalau
- Service de Toxicologie et Génopathies, Institut de Biochimie et Biologie Moléculaire, Centre Hospitalier Régional Universitaire, Lille, France
| | - T Bienvenu
- AP-HP, HUPC, Hôpital Cochin, Laboratoire de Génétique et Biologie Moléculaires, Paris, France
| | - M P Audrézet
- CHU de Brest, Laboratoire de Génétique Moléculaire, Brest, France
| | - A Pagin
- Service de Toxicologie et Génopathies, Institut de Biochimie et Biologie Moléculaire, Centre Hospitalier Régional Universitaire, Lille, France
| | - E Girodon
- AP-HP, HUPC, Hôpital Cochin, Laboratoire de Génétique et Biologie Moléculaires, Paris, France
| | - C Raynal
- CHU de Montpellier, Laboratoire de Génétique Moléculaire, Montpellier, France
| | - M Taulan-Cadars
- Université de Montpellier, Laboratoire de Génétique de Maladies Rares, EA7402 Montpellier, France
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8
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Sanz DJ, Hollywood JA, Scallan MF, Harrison PT. Cas9/gRNA targeted excision of cystic fibrosis-causing deep-intronic splicing mutations restores normal splicing of CFTR mRNA. PLoS One 2017; 12:e0184009. [PMID: 28863137 PMCID: PMC5581164 DOI: 10.1371/journal.pone.0184009] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 08/16/2017] [Indexed: 12/27/2022] Open
Abstract
Cystic Fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene. CRISPR mediated, template-dependent homology-directed gene editing has been used to correct the most common mutation, c.1521_1523delCTT / p.Phe508del (F508del) which affects ~70% of individuals, but the efficiency was relatively low. Here, we describe a high efficiency strategy for editing of three different rare CFTR mutations which together account for about 3% of individuals with Cystic Fibrosis. The mutations cause aberrant splicing of CFTR mRNA due to the creation of cryptic splice signals that result in the formation of pseudoexons containing premature stop codons c.1679+1634A>G (1811+1.6kbA>G) and c.3718-2477C>T (3849+10kbC>T), or an out-of-frame 5' extension to an existing exon c.3140-26A>G (3272-26A>G). We designed pairs of Cas9 guide RNAs to create targeted double-stranded breaks in CFTR either side of each mutation which resulted in high efficiency excision of the target genomic regions via non-homologous end-joining repair. When evaluated in a mini-gene splicing assay, we showed that targeted excision restored normal splicing for all three mutations. This approach could be used to correct aberrant splicing signals or remove disruptive transcription regulatory motifs caused by deep-intronic mutations in a range of other genetic disorders.
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Affiliation(s)
- David J. Sanz
- Department of Physiology, BioSciences Institute, University College Cork, Cork, Ireland
| | - Jennifer A. Hollywood
- Department of Physiology, BioSciences Institute, University College Cork, Cork, Ireland
- School of Microbiology, University College Cork, Cork, Ireland
| | | | - Patrick T. Harrison
- Department of Physiology, BioSciences Institute, University College Cork, Cork, Ireland
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9
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Deep intronic mutations and human disease. Hum Genet 2017; 136:1093-1111. [DOI: 10.1007/s00439-017-1809-4] [Citation(s) in RCA: 178] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Accepted: 05/05/2017] [Indexed: 12/22/2022]
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10
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Palhais B, Dembic M, Sabaratnam R, Nielsen KS, Doktor TK, Bruun GH, Andresen BS. The prevalent deep intronic c. 639+919 G>A GLA mutation causes pseudoexon activation and Fabry disease by abolishing the binding of hnRNPA1 and hnRNP A2/B1 to a splicing silencer. Mol Genet Metab 2016; 119:258-269. [PMID: 27595546 DOI: 10.1016/j.ymgme.2016.08.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 08/25/2016] [Accepted: 08/26/2016] [Indexed: 11/21/2022]
Abstract
Fabry disease is an X-linked recessive inborn disorder of the glycosphingolipid metabolism, caused by total or partial deficiency of the lysosomal α-galactosidase A enzyme due to mutations in the GLA gene. The prevalent c.639+919 G>A mutation in GLA leads to pathogenic insertion of a 57bp pseudoexon sequence from intron 4, which is responsible for the cardiac variant phenotype. In this study we investigate the splicing regulatory mechanism leading to GLA pseudoexon activation. Splicing analysis of GLA minigenes revealed that pseudoexon activation is influenced by cell-type. We demonstrate that the wild-type sequence harbors an hnRNP A1 and hnRNP A2/B1-binding exonic splicing silencer (ESS) overlapping the 5'splice site (5'ss) that prevents pseudoexon inclusion. The c.639+919 G>A mutation disrupts this ESS allowing U1 snRNP recognition of the 5'ss. We show that the wild-type GLA 5'ss motif with the ESS is also able to inhibit inclusion of an unrelated pseudoexon in the FGB gene, and that also in the FGB context inactivation of the ESS by the c.639+919 G>A mutation causes pseudoexon activation, underscoring the universal nature of the ESS. Finally, we demonstrate that splice switching oligonucleotide (SSO) mediated blocking of the pseudoexon 3'ss and 5'ss effectively restores normal GLA splicing. This indicates that SSO based splicing correction may be a therapeutic alternative in the treatment of Fabry disease.
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Affiliation(s)
- Bruno Palhais
- Department of Biochemistry and Molecular Biology, the Villum Center for Bioanalytical Sciences, University of Southern Denmark, Odense M, Denmark
| | - Maja Dembic
- Department of Biochemistry and Molecular Biology, the Villum Center for Bioanalytical Sciences, University of Southern Denmark, Odense M, Denmark
| | - Rugivan Sabaratnam
- Department of Biochemistry and Molecular Biology, the Villum Center for Bioanalytical Sciences, University of Southern Denmark, Odense M, Denmark
| | - Kira S Nielsen
- Department of Biochemistry and Molecular Biology, the Villum Center for Bioanalytical Sciences, University of Southern Denmark, Odense M, Denmark
| | - Thomas Koed Doktor
- Department of Biochemistry and Molecular Biology, the Villum Center for Bioanalytical Sciences, University of Southern Denmark, Odense M, Denmark
| | - Gitte Hoffmann Bruun
- Department of Biochemistry and Molecular Biology, the Villum Center for Bioanalytical Sciences, University of Southern Denmark, Odense M, Denmark
| | - Brage Storstein Andresen
- Department of Biochemistry and Molecular Biology, the Villum Center for Bioanalytical Sciences, University of Southern Denmark, Odense M, Denmark.
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11
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Straniero L, Soldà G, Costantino L, Seia M, Melotti P, Colombo C, Asselta R, Duga S. Whole-gene CFTR sequencing combined with digital RT-PCR improves genetic diagnosis of cystic fibrosis. J Hum Genet 2016; 61:977-984. [PMID: 27488443 DOI: 10.1038/jhg.2016.101] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Revised: 05/31/2016] [Accepted: 07/07/2016] [Indexed: 11/09/2022]
Abstract
Despite extensive screening, 1-5% of cystic fibrosis (CF) patients lack a definite molecular diagnosis. Next-generation sequencing (NGS) is making affordable genetic testing based on the identification of variants in extended genomic regions. In this frame, we analyzed 23 CF patients and one carrier by whole-gene CFTR resequencing: 4 were previously characterized and served as controls; 17 were cases lacking a complete diagnosis after a full conventional CFTR screening; 3 were consecutive subjects referring to our centers, not previously submitted to any screening. We also included in the custom NGS design the coding portions of the SCNN1A, SCNN1B and SCNN1G genes, encoding the subunits of the sodium channel ENaC, which were found to be mutated in CF-like patients. Besides 2 novel SCNN1B missense mutations, we identified 22 previously-known CFTR mutations, including 2 large deletions (whose breakpoints were precisely mapped), and novel deep-intronic variants, whose role on splicing was excluded by ex-vivo analyses. Finally, for 2 patients, compound heterozygotes for a CFTR mutation and the intron-9c.1210-34TG[11-12]T5 allele-known to be associated with decreased CFTR mRNA levels-the molecular diagnosis was implemented by measuring the residual level of wild-type transcript by digital reverse transcription polymerase chain reaction performed on RNA extracted from nasal brushing.
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Affiliation(s)
- Letizia Straniero
- Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy
| | - Giulia Soldà
- Department of Biomedical Sciences, Humanitas University, Milan, Italy.,Humanitas Clinical and Research Center, Milan, Italy
| | - Lucy Costantino
- Medical Genetics Laboratory, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Manuela Seia
- Medical Genetics Laboratory, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Paola Melotti
- Cystic Fibrosis Center, Azienda Ospedaliera Universitaria Integrata di Verona, Verona, Italy
| | - Carla Colombo
- Cystic Fibrosis Center of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy
| | - Rosanna Asselta
- Department of Biomedical Sciences, Humanitas University, Milan, Italy.,Humanitas Clinical and Research Center, Milan, Italy
| | - Stefano Duga
- Department of Biomedical Sciences, Humanitas University, Milan, Italy.,Humanitas Clinical and Research Center, Milan, Italy
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CADD score has limited clinical validity for the identification of pathogenic variants in noncoding regions in a hereditary cancer panel. Genet Med 2016; 18:1269-1275. [PMID: 27148939 PMCID: PMC5097698 DOI: 10.1038/gim.2016.44] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Accepted: 02/24/2016] [Indexed: 12/18/2022] Open
Abstract
PURPOSE Several in silico tools have been shown to have reasonable research sensitivity and specificity for classifying sequence variants in coding regions. The recently-developed Combined Annotation Dependent Depletion (CADD) method generates predictive scores for single nucleotide variants (SNVs) in all areas of the genome, including non-coding regions. We sought to determine the clinical validity of non-coding variant CADD scores. METHODS We evaluated 12,391 unique SNVs in 624 patient samples submitted for germline mutation testing in a cancer-related gene panel. We compared the distributions of CADD scores of rare SNVs, common SNVs in our patient population, and the null distribution of all possible SNVs stratifying by genomic region. RESULTS The median CADD scores of intronic and nonsynonymous variants were significantly different between rare and common SNVs (p<0.0001). Despite these different distributions, no individual variants could be identified as plausibly causative among rare intronic variants with the highest scores. The ROC AUC for non-coding variants is modest, and the positive predictive value of CADD for intronic variants in panel testing was found to be 0.088. CONCLUSION Focused in-silico scoring systems with much higher predictive value will be necessary for clinical genomic applications.
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Two novel splicing mutations in the SLC45A2 gene cause Oculocutaneous Albinism Type IV by unmasking cryptic splice sites. J Hum Genet 2015; 60:467-71. [PMID: 26016411 DOI: 10.1038/jhg.2015.56] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Revised: 03/30/2015] [Accepted: 04/26/2015] [Indexed: 11/08/2022]
Abstract
Oculocutaneous albinism (OCA) is characterized by hypopigmentation of the skin, hair and eye, and by ophthalmologic abnormalities caused by a deficiency in melanin biosynthesis. OCA type IV (OCA4) is one of the four commonly recognized forms of albinism, and is determined by mutation in the SLC45A2 gene. Here, we investigated the genetic basis of OCA4 in an Italian child. The mutational screening of the SLC45A2 gene identified two novel potentially pathogenic splicing mutations: a synonymous transition (c.888G>A) involving the last nucleotide of exon 3 and a single-nucleotide insertion (c.1156+2dupT) within the consensus sequence of the donor splice site of intron 5. As computer-assisted analysis for mutant splice-site prediction was not conclusive, we investigated the effects on pre-mRNA splicing of these two variants by using an in vitro minigene approach. Production of mutant transcripts in HeLa cells demonstrated that both mutations cause the almost complete abolishment of the physiologic donor splice site, with the concomitant unmasking of cryptic donor splice sites. To our knowledge, this work represents the first in-depth molecular characterization of splicing defects in a OCA4 patient.
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Functional characterization of two novel splicing mutations in the OCA2 gene associated with oculocutaneous albinism type II. Gene 2013; 537:79-84. [PMID: 24361966 DOI: 10.1016/j.gene.2013.11.102] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 11/10/2013] [Accepted: 11/27/2013] [Indexed: 02/07/2023]
Abstract
Oculocutaneous albinism (OCA) is characterized by hypopigmentation of the skin, hair and eye, and by ophthalmologic abnormalities caused by a deficiency in melanin biosynthesis. OCA type II (OCA2) is one of the four commonly-recognized forms of albinism, and is determined by mutation in the OCA2 gene. In the present study, we investigated the molecular basis of OCA2 in two siblings and one unrelated patient. The mutational screening of the OCA2 gene identified two hitherto-unknown putative splicing mutations. The first one (c.1503+5G>A), identified in an Italian proband and her affected sibling, lies in the consensus sequence of the donor splice site of OCA2 intron 14 (IVS14+5G>A), in compound heterozygosity with a frameshift mutation, c.1450_1451insCTGCCCTGACA, which is predicted to determine the premature termination of the polypeptide chain (p.I484Tfs*19). In-silico prediction of the effect of the IVS14+5G>A mutation on splicing showed a score reduction for the mutant splice site and indicated the possible activation of a newly-created deep-intronic acceptor splice site. The second mutation is a synonymous transition (c.2139G>A, p.K713K) involving the last nucleotide of exon 20. This mutation was found in a young African albino patient in compound heterozygosity with a previously-reported OCA2 missense mutation (p.T404M). In-silico analysis predicted that the mutant c.2139G>A allele would result in the abolition of the splice donor site. The effects on splicing of these two novel mutations were investigated using an in-vitro hybrid-minigene approach that led to the demonstration of the causal role of the two mutations and to the identification of aberrant transcript variants.
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