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Govers BM, van Huet RAC, Roosing S, Keijser S, Los LI, den Hollander AI, Klevering BJ. The genetics and disease mechanisms of rhegmatogenous retinal detachment. Prog Retin Eye Res 2023; 97:101158. [PMID: 36621380 DOI: 10.1016/j.preteyeres.2022.101158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 12/20/2022] [Accepted: 12/23/2022] [Indexed: 01/07/2023]
Abstract
Rhegmatogenous retinal detachment (RRD) is a sight threatening condition that warrants immediate surgical intervention. To date, 29 genes have been associated with monogenic disorders involving RRD. In addition, RRD can occur as a multifactorial disease through a combined effect of multiple genetic variants and non-genetic risk factors. In this review, we provide a comprehensive overview of the spectrum of hereditary disorders involving RRD. We discuss genotype-phenotype correlations of these monogenic disorders, and describe genetic variants associated with RRD through multifactorial inheritance. Furthermore, we evaluate our current understanding of the molecular disease mechanisms of RRD-associated genetic variants on collagen proteins, proteoglycan versican, and the TGF-β pathway. Finally, we review the role of genetics in patient management and prevention of RRD. We provide recommendations for genetic testing and prophylaxis of at-risk patients, and hypothesize on novel therapeutic approaches beyond surgical intervention.
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Affiliation(s)
- Birgit M Govers
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, the Netherlands; Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Ramon A C van Huet
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Susanne Roosing
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, the Netherlands; Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Sander Keijser
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Leonoor I Los
- Department of Ophthalmology, University Medical Center Groningen, Groningen, the Netherlands
| | - Anneke I den Hollander
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, the Netherlands; AbbVie, Genomics Research Center, Cambridge, MA, USA
| | - B Jeroen Klevering
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, the Netherlands.
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Ashkenazy N, Sengillo JD, Iyer PG, Negron CI, Yannuzzi NA, Berrocal AM. Phenotypic expansion of KCNJ13-associated snowflake vitreoretinal degeneration. Ophthalmic Genet 2023; 44:505-508. [PMID: 36440807 DOI: 10.1080/13816810.2022.2149816] [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: 04/19/2022] [Revised: 10/26/2022] [Accepted: 11/15/2022] [Indexed: 11/29/2022]
Abstract
INTRODUCTION An 18-year old highly myopic woman presented with bilateral retinoschisis associated with a unilateral macular hole in the right eye and vitreomacular traction in the left eye. METHODS Genetic studies disclosed a heterozygous pathogenic variant in the KCNJ13 gene was identified (c.484C>T (p.Arg162Trp)), consistent with a diagnosis of snowflake vitreoretinal degeneration (SVD). RESULTS While there were no corneal guttata, juvenile cataracts, or perivascular sheathing in this case, salient features of SVD included a fibrillar vitreous structure, crystalline retinopathy, and flattened optic nerves. The patient developed a FTMH in the left eye at 17 months follow up, followed by a rhegmatogenous retinal detachment (RRD) requiring 2 surgical repairs. CONCLUSION This case expands on the spectrum of clinical features in SVD, including retinoschisis and FTMH. It also characterizes optical coherence tomography findings in this rare disease entity. We emphasize the importance of using panel-based genetic testing to clinically distinguish and further define atypical vitreoretinopathies.
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Affiliation(s)
- Noy Ashkenazy
- Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Jesse D Sengillo
- Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA
| | - Prashanth G Iyer
- Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA
- Department of Ophthalmology, Tufts Medical Center, Boston, Massachusetts, USA
| | - Catherin I Negron
- Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA
| | - Nicolas A Yannuzzi
- Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA
| | - Audina M Berrocal
- Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA
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Schroeder M, Peter VG, Gränse L, Andréasson S, Rivolta C, Kjellström U. A novel phenotype associated with the R162W variant in the KCNJ13 gene. Ophthalmic Genet 2022; 43:500-507. [PMID: 35477418 DOI: 10.1080/13816810.2022.2068041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
BACKGROUND Pathogenic variants in KCNJ13 have been associated with both autosomal dominant Snowflake vitreoretinal degeneration (SVD) and autosomal recessive Leber congenital amaurosis. SVD is characterized by aberrant vitreoretinal interface leading to increased risk of retinal detachment, crystalline retinal snowflake deposits, optic disc abnormalities, early-onset cataract, and cornea guttae. Reduced dark adaptation and reduced scotopic rod b-waves have also been described. We report a novel phenotype associated with the R162W variant in KCNJ13. METHODS Four affected members of a Swedish family were included. Three of them were examined with best corrected visual acuity, Goldmann perimetry, full-field-and multifocal electroretinography, optical coherence tomography, fundus color photographs, fundus autofluorescence images, slit lamp inspection, and genetic testing. The fourth subject only managed genetic testing. RESULTS All subjects carry the pathogenic missense variant; c.484C>T (NM_002242.4), R162W, in KCNJ13. ERG measurements revealed reduced macular-as well as general retinal function. Two of the subjects had a history of retinal detachment and the two younger subjects demonstrated early onset cataract. They all had structural macular changes and slightly gliotic optic discs. CONCLUSION In this family, the R162W variant in KCNJ13, previously described in association with SVD, causes a somewhat novel phenotype including macular dystrophy and moderate reduction of general retinal function as the main features combined with disc abnormalities, retinal detachment, and presenile cataract that has been described before. In times of up-coming gene-based therapies, it is important to report new genotype-phenotype associations to improve the possibilities to identify future treatment candidates.
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Affiliation(s)
- Marion Schroeder
- Department of Ophthalmology and Clinical Sciences Lund, Lund University, Skane University Hospital, Lund, Sweden
| | - Virginie G Peter
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland.,Department of Ophthalmology, University of Basel, Basel, Switzerland
| | - Lotta Gränse
- Department of Ophthalmology and Clinical Sciences Lund, Lund University, Skane University Hospital, Lund, Sweden
| | - Sten Andréasson
- Department of Ophthalmology and Clinical Sciences Lund, Lund University, Skane University Hospital, Lund, Sweden
| | - Carlo Rivolta
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland.,Department of Ophthalmology, University of Basel, Basel, Switzerland
| | - Ulrika Kjellström
- Department of Ophthalmology and Clinical Sciences Lund, Lund University, Skane University Hospital, Lund, Sweden
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Cheung R, Ly A, Katalinic P, Coroneo MT, Chang A, Kalloniatis M, Madigan MC, Nivison-Smith L. Visualisation of peripheral retinal degenerations and anomalies with ocular imaging. Semin Ophthalmol 2022; 37:554-582. [DOI: 10.1080/08820538.2022.2039222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- Rene Cheung
- School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
| | - Angelica Ly
- Centre for Eye Health, University of New South Wales, Sydney, Australia
| | - Paula Katalinic
- Centre for Eye Health, University of New South Wales, Sydney, Australia
| | - Minas Theodore Coroneo
- Department of Ophthalmology, Prince of Wales Clinical School, Faculty of Medicine, The University of New South Wales, Sydney, Australia
| | - Andrew Chang
- Sydney Institute of Vision Science, Sydney, Australia
- Save Sight Institute, The University of Sydney, Sydney, Australia
| | - Michael Kalloniatis
- School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
- Centre for Eye Health, University of New South Wales, Sydney, Australia
| | - Michele C. Madigan
- School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
- Save Sight Institute, The University of Sydney, Sydney, Australia
| | - Lisa Nivison-Smith
- School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
- Centre for Eye Health, University of New South Wales, Sydney, Australia
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Jiao X, Ma Z, Lei J, Liu P, Cai X, Shahi PK, Chan CC, Fariss R, Pattnaik BR, Dong L, Hejtmancik JF. Retinal Development and Pathophysiology in Kcnj13 Knockout Mice. Front Cell Dev Biol 2022; 9:810020. [PMID: 35096838 PMCID: PMC8790323 DOI: 10.3389/fcell.2021.810020] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 12/10/2021] [Indexed: 11/22/2022] Open
Abstract
Purpose: We constructed and characterized knockout and conditional knockout mice for KCNJ13, encoding the inwardly rectifying K+ channel of the Kir superfamily Kir7.1, mutations in which cause both Snowflake Vitreoretinal Degeneration (SVD) and Retinitis pigmentosa (RP) to further elucidate the pathology of this disease and to develop a potential model system for gene therapy trials. Methods: A Kcnj13 knockout mouse line was constructed by inserting a gene trap cassette expressing beta-galactosidase flanked by FRT sites in intron 1 with LoxP sites flanking exon two and converted to a conditional knockout by FLP recombination followed by crossing with C57BL/6J mice having Cre driven by the VMD2 promoter. Lentiviral replacement of Kcnj13 was driven by the EF1a or VMD2 promoters. Results: Blue-Gal expression is evident in E12.5 brain ventricular choroid plexus, lens, neural retina layer, and anterior RPE. In the adult eye expression is seen in the ciliary body, RPE and choroid. Adult conditional Kcnj13 ko mice show loss of photoreceptors in the outer nuclear layer, inner nuclear layer thinning with loss of bipolar cells, and thinning and disruption of the outer plexiform layer, correlating with Cre expression in the overlying RPE which, although preserved, shows morphological disruption. Fundoscopy and OCT show signs of retinal degeneration consistent with the histology, and photopic and scotopic ERGs are decreased in amplitude or extinguished. Lentiviral based replacement of Kcnj13 resulted in increased ERG c- but not a- or b- wave amplitudes. Conclusion: Ocular KCNJ13 expression starts in the choroid, lens, ciliary body, and anterior retina, while later expression centers on the RPE with no/lower expression in the neuroretina. Although KCNJ13 expression is not required for survival of the RPE, it is necessary for RPE maintenance of the photoreceptors, and loss of the photoreceptor, outer plexiform, and outer nuclear layers occur in adult KCNJ13 cKO mice, concomitant with decreased amplitude and eventual extinguishing of the ERG and signs of retinitis pigmentosa on fundoscopy and OCT. Kcnj13 replacement resulting in recovery of the ERG c- but not a- and b-waves is consistent with the degree of photoreceptor degeneration seen on histology.
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Affiliation(s)
- Xiaodong Jiao
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Zhiwei Ma
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Jingqi Lei
- Genetic Engineering Core, National Eye Institute, National Institute of Health, Bethesda, MD, United States
| | - Pinghu Liu
- Genetic Engineering Core, National Eye Institute, National Institute of Health, Bethesda, MD, United States
| | - Xiaoyu Cai
- Genetic Engineering Core, National Eye Institute, National Institute of Health, Bethesda, MD, United States
| | - Pawan K Shahi
- Departments of Pediatrics and Ophthalmology and Visual Sciences and the McPherson Eye Research Institute, University of Wisconsin, Madison, AL, United States
| | - Chi-Chao Chan
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Robert Fariss
- Imaging Core, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
| | - Bikash R Pattnaik
- Departments of Pediatrics and Ophthalmology and Visual Sciences and the McPherson Eye Research Institute, University of Wisconsin, Madison, AL, United States
| | - Lijin Dong
- Genetic Engineering Core, National Eye Institute, National Institute of Health, Bethesda, MD, United States
| | - J Fielding Hejtmancik
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD, United States
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Muftuoglu IK, Al-Sheikh M, J S, Rasheed MA, Singh SR, Chhablani J. Imaging in inherited retinal disorders. Eur J Ophthalmol 2021; 31:1656-1676. [PMID: 33525895 DOI: 10.1177/1120672121990578] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Inherited retinal diseases, which results from mutations in over 260 identified genes, affect more than 2 million people globally. The diseases mostly cause severe vision loss in young working population and have severe impact on social economic status of the population. Advances in retinal imaging techniques along with developments in gene identification and cell biology techniques have yielded to a better understanding of the genetic and biochemical mechanisms causing these diseases. Retinal imaging along with through ophthalmological examination is essential to make an accurate diagnosis, to decrease the burden of unneccessary anciliary tests and to select the potential patients that can get benefit from the gene treatment. The purpose of the review is to yield an update on inherited retinal diseases by highlighting microstructural changes in retina and to summarize the retinal changes detected by currently available multimodal imaging techniques.
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Affiliation(s)
- Ilkay Kilic Muftuoglu
- Department of Ophthalmology, Istanbul Training and Research Hospital, Istanbul, Turkey
| | - Mayss Al-Sheikh
- Department of Ophthalmology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Sushma J
- LV Prasad Eye Institute, Hyderabad, Telangana, India
| | | | - Sumit Randhir Singh
- Jacobs Retina Center at Shiley Eye Center, University of California, San Diego, La Jolla, CA, USA
| | - Jay Chhablani
- UPMC Eye Center, University of Pittsburgh, Pittsburgh, PA, USA
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Podobnik M, Frohnhöfer HG, Dooley CM, Eskova A, Nüsslein-Volhard C, Irion U. Evolution of the potassium channel gene Kcnj13 underlies colour pattern diversification in Danio fish. Nat Commun 2020; 11:6230. [PMID: 33277491 PMCID: PMC7718271 DOI: 10.1038/s41467-020-20021-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Accepted: 11/06/2020] [Indexed: 12/20/2022] Open
Abstract
The genetic basis of morphological variation provides a major topic in evolutionary developmental biology. Fish of the genus Danio display colour patterns ranging from horizontal stripes, to vertical bars or spots. Stripe formation in zebrafish, Danio rerio, is a self-organizing process based on cell-contact mediated interactions between three types of chromatophores with a leading role of iridophores. Here we investigate genes known to regulate chromatophore interactions in zebrafish that might have evolved to produce a pattern of vertical bars in its sibling species, Danio aesculapii. Mutant D. aesculapii indicate a lower complexity in chromatophore interactions and a minor role of iridophores in patterning. Reciprocal hemizygosity tests identify the potassium channel gene obelix/Kcnj13 as evolved between the two species. Complementation tests suggest evolutionary change through divergence in Kcnj13 function in two additional Danio species. Thus, our results point towards repeated and independent evolution of this gene during colour pattern diversification.
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Affiliation(s)
- Marco Podobnik
- Max Planck Institute for Developmental Biology, Max-Planck-Ring 5, 72076, Tübingen, Germany
| | - Hans Georg Frohnhöfer
- Max Planck Institute for Developmental Biology, Max-Planck-Ring 5, 72076, Tübingen, Germany
| | - Christopher M Dooley
- Max Planck Institute for Developmental Biology, Max-Planck-Ring 5, 72076, Tübingen, Germany
- Max Planck Institute for Heart and Lung Research, Ludwigstrasse 43, 61231, Bad Nauheim, Germany
| | - Anastasia Eskova
- Max Planck Institute for Developmental Biology, Max-Planck-Ring 5, 72076, Tübingen, Germany
- IBM Research and Development, Schönaicher Straße 220, 71032, Böblingen, Germany
| | | | - Uwe Irion
- Max Planck Institute for Developmental Biology, Max-Planck-Ring 5, 72076, Tübingen, Germany.
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Toms M, Dubis AM, Lim WS, Webster AR, Gorin MB, Moosajee M. Missense variants in the conserved transmembrane M2 protein domain of KCNJ13 associated with retinovascular changes in humans and zebrafish. Exp Eye Res 2019; 189:107852. [PMID: 31647904 PMCID: PMC6899441 DOI: 10.1016/j.exer.2019.107852] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 10/02/2019] [Accepted: 10/19/2019] [Indexed: 01/27/2023]
Abstract
Mutations in KCNJ13 are associated with two retinal disorders; Leber congenital amaurosis (LCA) and snowflake vitreoretinal degeneration (SVD). We describe a novel fibrovascular proliferation in the retina of two affected members of a KCNJ13-related LCA family with a homozygous c.458C > T, p.(Thr153Ile) missense mutation. Optical coherence tomography retinal imaging of the kcnj13 mutant zebrafish (obelixtd15 c.502T > C, p.[Phe168Leu]) revealed a late onset retinal degeneration at 12 months, with retinal thinning and associated retinovascular changes, including increased vessel calibre and vitreous deposits. Both human and zebrafish variants are missense and located within the conserved transmembrane M2 protein domain, suggesting that disruption of this region may contribute to retinovascular changes as an additional feature to the previously described LCA phenotype. Close monitoring of other patients with similar mutations may be required to minimise the ensuing retinal damage.
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Affiliation(s)
- Maria Toms
- UCL Institute of Ophthalmology, London, UK
| | - Adam M Dubis
- UCL Institute of Ophthalmology, London, UK; Moorfields Eye Hospital NHS Foundation Trust, London, UK
| | - Wei Sing Lim
- Moorfields Eye Hospital NHS Foundation Trust, London, UK
| | - Andrew R Webster
- UCL Institute of Ophthalmology, London, UK; Moorfields Eye Hospital NHS Foundation Trust, London, UK
| | - Michael B Gorin
- Department of Ophthalmology, Jules Stein Eye Institute, David Geffen School of Medicine, UCLA Los Angeles, USA
| | - Mariya Moosajee
- UCL Institute of Ophthalmology, London, UK; Moorfields Eye Hospital NHS Foundation Trust, London, UK.
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Kondo H, Fujimoto K, Imagawa M, Oku K, Matsushita I, Hayashi T, Nagata T. Electroretinograms of eyes with Stickler syndrome. Doc Ophthalmol 2019; 140:233-243. [DOI: 10.1007/s10633-019-09739-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Accepted: 11/20/2019] [Indexed: 10/25/2022]
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LEBER CONGENITAL AMAUROSIS WITH LARGE RETINAL PIGMENT CLUMPS CAUSED BY COMPOUND HETEROZYGOUS MUTATIONS IN KCNJ13. Retin Cases Brief Rep 2018; 11:221-226. [PMID: 27203561 DOI: 10.1097/icb.0000000000000326] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE To describe a patient with mutations in KCNJ13 presenting particular clinical features. METHODS Standard ophthalmic examination, fundus autofluorescence, spectral domain optical coherence tomography, full-field electroretinography. The 3 exons of KCNJ13 were polymerase chain reaction amplified and Sanger sequenced. PATIENTS A 31-year-old man with Leber congenital amaurosis. RESULTS Patient had nystagmus since childhood, best-corrected visual acuity limited to 20/400 OD and 20/200 OS, and had cataracts extracted in both eyes. There were clumpy pigment deposits mostly in macular area, causing an uneven line of retinal pigment epithelium on spectral domain optical coherence tomography. In retinal parts devoid of pigment deposits around the optic disk and in periphery, retinal thickness was increased and hyperreflective formations were present either in the inner nuclear layer or in the outer nuclear layer. The patient was compound heterozygous for new mutations in KCNJ13 which encodes the Kir 7.1 potassium channel, c.314G>T (p.Ser105Ile) in exon 2 and c.655C>T (p.Gln219*) in exon 3. Both mutations were absent from databases. CONCLUSION KCNJ13 mutations are responsible for early-onset retinal dystrophy, featuring remarkable clumpy pigment deposits at the level of the retinal pigment epithelium, suggesting dysfunction and disorganization of this tissue. Parts of the retina remain relatively preserved anatomically but are increased in thickness. This distinct fundus appearance should help in identifying the "KCNJ13 retinal dystrophy" to orient the molecular diagnosis.
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Johnston T, Chandra A, Hewitt AW. Current Understanding of the Genetic Architecture of Rhegmatogenous Retinal Detachment. Ophthalmic Genet 2016; 37:121-9. [PMID: 26757352 DOI: 10.3109/13816810.2015.1033557] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Rhegmatogenous retinal detachment (RRD) is a common and potentially blinding surgical retinal disease. While the precise molecular mechanisms leading to RRD are poorly understood, there is an increasing body of literature supporting the role of heritable factors in the pathogenesis of the condition. Much work has been undertaken investigating genes important in syndromic forms of RRD (e.g., Stickler, Wagner Syndrome, etc.) and research pertaining to genetic investigations of idiopathic or non-syndromic RRD has also recently been reported. To date, at least 12 genetic loci have been implicated in the development of syndromes of which RRD is a feature. A recent GWAS identified five loci implicated in the development of idiopathic RRD.This article provides an overview of the genetic mechanisms of both syndromic and idiopathic RRD. The genetics of predisposing conditions, such as myopia and lattice degeneration, are also discussed.
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Affiliation(s)
- Timothy Johnston
- a Centre for Eye Research Australia, University of Melbourne, Department of Ophthalmology, Royal Victorian Eye and Ear Hospital , Melbourne , Victoria , Australia and
| | - Aman Chandra
- a Centre for Eye Research Australia, University of Melbourne, Department of Ophthalmology, Royal Victorian Eye and Ear Hospital , Melbourne , Victoria , Australia and
| | - Alex W Hewitt
- a Centre for Eye Research Australia, University of Melbourne, Department of Ophthalmology, Royal Victorian Eye and Ear Hospital , Melbourne , Victoria , Australia and.,b School of Medicine, Menzies Research Institute Tasmania, University of Tasmania , Hobart , Tasmania , Australia
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12
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Abstract
Genetic studies have linked alterations in Kir7.1 channel to diverse pathologies. We summarize functional relevance of Kir7.1 channel in retinal pigment epithelium (RPE), regulation of channel function by various cytoplasmic metabolites, and mutations that cause channelopathies. At the apical membrane of RPE, K(+) channels contribute to subretinal K(+) homeostasis and support Na(+)/K(+) pump and Na(+)-K(+)-2Cl(-) cotransporter function by providing a pathway for K(+) secretion. Electrophysiological studies have established that barium- and cesium-sensitive inwardly rectifying K(+) (Kir) channels make up a major component of the RPE apical membrane K(+) conductance. Native human RPE expresses transcripts for Kir1.1, Kir2.1, Kir2.2, Kir3.1, Kir3.4, Kir4.2, and Kir6.1, albeit at levels at least 50-fold lower than Kir7.1. Kir7.1 is structurally similar to other Kir channels, consisting of 2 trans-membrane domains, a pore-forming loop that contains the selectivity filter, and 2 cytoplasmic polar tails. Within the cytoplasmic structure, clusters of amino acid sequences form regulatory domains that interact with cellular metabolites and control the opening and closing of the channel. Recent evidence indicated that intrinsic sequence motifs present in Kir7.1 control surface expression. Mutant Kir7.1 channels are associated with inherited eye pathologies such as Snowflake Vitreoretinal Degeneration (SVD) and Lebers Congenital Amaurosis (LCA16). Based on the current evidence, mutations implicated in channelopathies have the potential to be used for genetic testing to diagnose blindness due to Kir7.1.
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Affiliation(s)
- Mohit Kumar
- a Departments of Biotechnology and Bioinformatics ; NIIT University ; Neemrana , Rajasthan , India
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Khan AO, Bergmann C, Neuhaus C, Bolz HJ. A distinct vitreo-retinal dystrophy with early-onset cataract from recessive KCNJ13 mutations. Ophthalmic Genet 2014; 36:79-84. [PMID: 25475713 DOI: 10.3109/13816810.2014.985846] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE To document a distinct vitreo-retinal dystrophy with early-onset cataract as related to recessive KCNJ13 mutations. METHODS A retrospective case series (two patients from two families) Results: A 12-year-old Saudi Arabian girl with nystagmus since birth was referred because of recent decreased vision. Parents were first cousins and a younger sister had been diagnosed with retinal dystrophy. Examination revealed total white cataract in the right eye. In the left eye, there were posterior cortical lenticular opacities and an unusual retina fundus dystrophic appearance notable for fibrosis over the optic disc and clumped pigmentation. After right eye cataract surgery, the posterior pole of the left eye was seen as similar to that of the right eye and electroretinography revealed severe cone-rod dysfunction, with only subnormal scotopic tracings recordable in both eyes. Next-generation sequencing of retinal dystrophy genes revealed homozygosity for a novel missense mutation in KCNJ13 (c.359T > C; p.Ile120Thr [NM_002242.4]), which co-segregated with the disease. Direct KCNJ13 sequencing for an unrelated 33-year-old Saudi Arabian male with similar clinical findings but early-adult-onset rather than juvenile cataract revealed the same homozygous mutation. CONCLUSIONS Juvenile or early-adult-onset cataract in the setting of a congenital vitreo-retinal dystrophy notable for fibrosis over the disc and clumped pigmentation in the posterior pole is a unique phenotype that suggests recessive KCNJ13 mutations.
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Affiliation(s)
- Arif O Khan
- Division of Pediatric Ophthalmology, King Khaled Eye Specialist Hospital , Riyadh , Saudi Arabia
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Abstract
Fuchs' corneal dystrophy (FCD) is a common late-onset genetic disorder of the corneal endothelium. It causes loss of endothelial cell density and excrescences in the Descemet membrane, eventually progressing to corneal edema, necessitating corneal transplantation. The genetic basis of FCD is complex and heterogeneous, demonstrating variable expressivity and incomplete penetrance. To date, three causal genes, ZEB1, SLC4A11 and LOXHD1, have been identified, representing a small proportion of the total genetic load of FCD. An additional four loci have been localized, including a region on chromosome 18 that is potentially responsible for a large proportion of all FCD cases. The elucidation of the causal genes underlying these loci will begin to clarify the pathogenesis of FCD and pave the way for the emergence of nonsurgical treatments.
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Affiliation(s)
- Benjamin W Iliff
- The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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Pattnaik BR, Tokarz S, Asuma MP, Schroeder T, Sharma A, Mitchell JC, Edwards AO, Pillers DAM. Snowflake vitreoretinal degeneration (SVD) mutation R162W provides new insights into Kir7.1 ion channel structure and function. PLoS One 2013; 8:e71744. [PMID: 23977131 PMCID: PMC3747230 DOI: 10.1371/journal.pone.0071744] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Accepted: 07/02/2013] [Indexed: 01/08/2023] Open
Abstract
Snowflake Vitreoretinal Degeneration (SVD) is associated with the R162W mutation of the Kir7.1 inwardly-rectifying potassium channel. Kir7.1 is found at the apical membrane of Retinal Pigment Epithelial (RPE) cells, adjacent to the photoreceptor neurons. The SVD phenotype ranges from RPE degeneration to an abnormal b-wave to a liquid vitreous. We sought to determine how this mutation alters the structure and function of the human Kir7.1 channel. In this study, we expressed a Kir7.1 construct with the R162W mutation in CHO cells to evaluate function of the ion channel. Compared to the wild-type protein, the mutant protein exhibited a non-functional Kir channel that resulted in depolarization of the resting membrane potential. Upon co-expression with wild-type Kir7.1, R162W mutant showed a reduction of IKir7.1 and positive shift in ‘0’ current potential. Homology modeling based on the structure of a bacterial Kir channel protein suggested that the effect of R162W mutation is a result of loss of hydrogen bonding by the regulatory lipid binding domain of the cytoplasmic structure.
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Affiliation(s)
- Bikash R. Pattnaik
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
- Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, Wisconsin, United States of America
- McPherson Eye Research Institute, University of Wisconsin, Madison, Wisconsin, United States of America
- * E-mail:
| | - Sara Tokarz
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Matti P. Asuma
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Tyler Schroeder
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Anil Sharma
- Department of Experimental Pathology, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Julie C. Mitchell
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Albert O. Edwards
- Institute for Molecular Biology, University of Oregon, and Oregon Retina, Eugene, Oregon, United States of America
| | - De-Ann M. Pillers
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
- McPherson Eye Research Institute, University of Wisconsin, Madison, Wisconsin, United States of America
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Abstract
PURPOSE To identify early features of Fuchs endothelial dystrophy (FED) in carriers of the rs613872(G) transcription factor 4 gene (TCF4) aged 20 to 21 years. METHODS Prospective cohort study of people aged 20 to 21 years previously enrolled in the Western Australia Pregnancy (Raine) Cohort. Specular microscopy was performed using a noncontact specular microscopy (EM-3000; Tomey, Nagoya, Japan). Individual genotype data were extracted from the genome-wide Illumina 660 Quad Array. Analysis of the association between the rs613872 risk allele in TCF4 and specular microscopic measurements was conducted. RESULTS Association between the rs613872 risk allele and corneal endothelial cell density (CD) as well as the coefficient of variation in cell shape was the main outcome measure. Genotype and specular microscopic data were available for a total of 445 participants (46% women). The median CD was 2851 and 2850 cells per square millimeter in the right and left eyes, respectively. No significant differences between intereye variability in endothelial CD were seen (right eye to left eye correlation = 0.64); however, a significant difference in variability of endothelial CD between men and women was observed (male: OD, 2839 ± 124 cells/mm² and OS, 2845 ± 124 cells/mm² vs. female: OD, 2838 ± 134 cells/mm² and OS, 2842 ± 132 cells/mm²; OD, P = 0.0013 and OS, P = 0.0016). Eleven individuals were homozygous for the rs613872 risk allele. We found no association between rs613872 genotype and CD or coefficient of variation. One of 11 homozygous GG individuals was found to have a gutta in 1 sample field on specular microscopy, whereas 2 of 297 TT individuals also had a gutta each in 1 sample field. CONCLUSIONS We were unable to detect an association between TCF4 rs613872 genotype and the variation in corneal endothelial CD or variation in cell morphology in a healthy young adult population.
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Sergouniotis PI, Davidson AE, Mackay DS, Li Z, Yang X, Plagnol V, Moore AT, Webster AR. Recessive mutations in KCNJ13, encoding an inwardly rectifying potassium channel subunit, cause leber congenital amaurosis. Am J Hum Genet 2011; 89:183-90. [PMID: 21763485 DOI: 10.1016/j.ajhg.2011.06.002] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Revised: 06/03/2011] [Accepted: 06/07/2011] [Indexed: 12/13/2022] Open
Abstract
Inherited retinal degenerations, including retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA), comprise a group of disorders showing high genetic and allelic heterogeneity. The determination of a full catalog of genes that can, when mutated, cause human retinal disease is a powerful means to understand the molecular physiology and pathology of the human retina. As more genes are found, remaining ones are likely to be rarer and/or unexpected candidates. Here, we identify a family in which all known RP/LCA-related genes are unlikely to be associated with their disorder. A combination of homozygosity mapping and exome sequencing identifies a homozygous nonsense mutation, c.496C>T (p.Arg166X), in a gene, KCNJ13, encoding a potassium channel subunit Kir7.1. A screen of a further 333 unrelated individuals with recessive retinal degeneration identified an additional proband, homozygous for a missense mutation, c.722T>C (p.Leu241Pro), in the same gene. The three affected members of the two families have been diagnosed with LCA. All have a distinct and unusual retinal appearance and a similar early onset of visual loss, suggesting both impaired retinal development and progressive retinal degeneration, involving both rod and cone pathways. Examination of heterozygotes revealed no ocular disease. This finding implicates Kir7.1 as having an important role in human retinal development and maintenance. This disorder adds to a small diverse group of diseases consequent upon loss or reduced function of inwardly rectifying potassium channels affecting various organs. The distinct retinal phenotype that results from biallelic mutations in KCNJ13 should facilitate the molecular diagnosis in further families.
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Baratz KH, Tosakulwong N, Ryu E, Brown WL, Branham K, Chen W, Tran KD, Schmid-Kubista KE, Heckenlively JR, Swaroop A, Abecasis G, Bailey KR, Edwards AO. E2-2 protein and Fuchs's corneal dystrophy. N Engl J Med 2010; 363:1016-24. [PMID: 20825314 DOI: 10.1056/nejmoa1007064] [Citation(s) in RCA: 193] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
BACKGROUND Fuchs's corneal dystrophy (FCD) is a leading cause of corneal transplantation and affects 5% of persons in the United States who are over the age of 40 years. Clinically visible deposits called guttae develop under the corneal endothelium in patients with FCD. A loss of endothelial cells and deposition of an abnormal extracellular matrix are observed microscopically. In advanced disease, the cornea swells and becomes cloudy because the remaining endothelial cells are not sufficient to keep the cornea dehydrated and clear. Although rare genetic variation that contributes to both early-onset and typical late-onset forms of FCD has been identified, to our knowledge, no common variants have been reported. METHODS We performed a genomewide association study and replicated the most significant observations in a second, independent group of subjects. RESULTS Alleles in the transcription factor 4 gene (TCF4), encoding a member of the E-protein family (E2-2), were associated with typical FCD (P=2.3x10(-26)). The association increased the odds of having FCD by a factor of 30 for persons with two copies of the disease variants (homozygotes) and discriminated between case subjects and control subjects with about 76% accuracy. At least two regions of the TCF4 locus were associated independently with FCD. Alleles in the gene encoding protein tyrosine phosphatase receptor type G (PTPRG) were associated with FCD (P=4.0x10(-7)), but the association did not reach genomewide significance. CONCLUSIONS Genetic variation in TCF4 contributes to the development of FCD. (Funded by the National Eye Institute and others.)
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Affiliation(s)
- Keith H Baratz
- Department of Ophthalmology, Mayo Clinic, Rochester, MN, USA
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Berger W, Kloeckener-Gruissem B, Neidhardt J. The molecular basis of human retinal and vitreoretinal diseases. Prog Retin Eye Res 2010; 29:335-75. [PMID: 20362068 DOI: 10.1016/j.preteyeres.2010.03.004] [Citation(s) in RCA: 394] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
During the last two to three decades, a large body of work has revealed the molecular basis of many human disorders, including retinal and vitreoretinal degenerations and dysfunctions. Although belonging to the group of orphan diseases, they affect probably more than two million people worldwide. Most excitingly, treatment of a particular form of congenital retinal degeneration is now possible. A major advantage for treatment is the unique structure and accessibility of the eye and its different components, including the vitreous and retina. Knowledge of the many different eye diseases affecting retinal structure and function (night and colour blindness, retinitis pigmentosa, cone and cone rod dystrophies, photoreceptor dysfunctions, as well as vitreoretinal traits) is critical for future therapeutic development. We have attempted to present a comprehensive picture of these disorders, including biological, clinical, genetic and molecular information. The structural organization of the review leads the reader through non-syndromic and syndromic forms of (i) rod dominated diseases, (ii) cone dominated diseases, (iii) generalized retinal degenerations and (iv) vitreoretinal disorders, caused by mutations in more than 165 genes. Clinical variability and genetic heterogeneity have an important impact on genetic testing and counselling of affected families. As phenotypes do not always correlate with the respective genotypes, it is of utmost importance that clinicians, geneticists, counsellors, diagnostic laboratories and basic researchers understand the relationships between phenotypic manifestations and specific genes, as well as mutations and pathophysiologic mechanisms. We discuss future perspectives.
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Affiliation(s)
- Wolfgang Berger
- Division of Medical Molecular Genetics and Gene Diagnostics, Institute of Medical Genetics, University of Zurich, Schorenstrasse 16, CH-8603 Schwerzenbach, Switzerland.
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Density of common complex ocular traits in the aging eye: analysis of secondary traits in genome-wide association studies. PLoS One 2008; 3:e2510. [PMID: 18575587 PMCID: PMC2424139 DOI: 10.1371/journal.pone.0002510] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2008] [Accepted: 05/21/2008] [Indexed: 11/19/2022] Open
Abstract
Genetic association studies are identifying genetic risks for common complex ocular traits such as age-related macular degeneration (AMD). The subjects used for discovery of these loci have been largely from clinic-based, case-control studies. Typically, only the primary phenotype (e.g., AMD) being studied is systematically documented and other complex traits (e.g., affecting the eye) are largely ignored. The purpose of this study was to characterize these other or secondary complex ocular traits present in the cases and controls of clinic-based studies being used for genetic study of AMD. The records of 100 consecutive new patients (of any diagnosis) age 60 or older for which all traits affecting the eye had been recorded systematically were reviewed. The average patient had 3.5 distinct diagnoses. A subset of 10 complex traits was selected for further study because they were common and could be reliably diagnosed. The density of these 10 complex ocular traits increased by 0.017 log-traits/year (P = 0.03), ranging from a predicted 2.74 at age 60 to 4.45 at age 90. Trait-trait association was observed only between AMD and primary vitreomacular traction (P = 0.0009). Only 1% of subjects age 60 or older had no common complex traits affecting the eye. Extrapolations suggested that a study of 2000 similar subjects would have sufficient power to detect genetic association with an odds ratio of 2.0 or less for 4 of these 10 traits. In conclusion, the high prevalence of complex traits affecting the aging eye and the inherent biases in referral patterns leads to the potential for confounding by undocumented secondary traits within case-control studies. In addition to the primary trait, other common ocular phenotypes should be systematically documented in genetic association studies so that adjustments for potential trait-trait associations and other bias can be made and genetic risk variants identified in secondary analyses.
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Audo I, Robson AG, Holder GE, Moore AT. The negative ERG: clinical phenotypes and disease mechanisms of inner retinal dysfunction. Surv Ophthalmol 2008; 53:16-40. [PMID: 18191655 DOI: 10.1016/j.survophthal.2007.10.010] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Inner retinal dysfunction is encountered in a number of retinal disorders, either inherited or acquired, as a primary or predominant defect. Fundus examination is rarely diagnostic in these disorders, although some show characteristic features, and careful electrophysiological assessment of retinal function is needed for accurate diagnosis. The ERG in inner retinal dysfunction typically shows a negative waveform with a preserved a-wave and a selectively reduced b-wave. Advances in retinal physiology and molecular genetics have led to a greater understanding of the pathogenesis of these disorders. This review summarizes current knowledge on normal retinal physiology, the investigative techniques used and the range of clinical disorders in which there is predominantly inner retinal dysfunction.
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Hejtmancik JF, Jiao X, Li A, Sergeev YV, Ding X, Sharma AK, Chan CC, Medina I, Edwards AO. Mutations in KCNJ13 cause autosomal-dominant snowflake vitreoretinal degeneration. Am J Hum Genet 2008; 82:174-80. [PMID: 18179896 DOI: 10.1016/j.ajhg.2007.08.002] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Revised: 08/22/2007] [Accepted: 08/23/2007] [Indexed: 11/19/2022] Open
Abstract
Snowflake vitreoretinal degeneration (SVD, MIM 193230) is a developmental and progressive hereditary eye disorder that affects multiple tissues within the eye. Diagnostic features of SVD include fibrillar degeneration of the vitreous humor, early-onset cataract, minute crystalline deposits in the neurosensory retina, and retinal detachment. A genome-wide scan previously localized the genetic locus for SVD to a 20 Mb region flanked by D2S2158 and D2S2202. This region contains 59 genes, of which 20 were sequenced, disclosing a heterozygous mutation (484C > T, R162W) in KCNJ13, member 13 of subfamily J of the potassium inwardly rectifying channel family in all affected individuals. The mutation in KCNJ13, the gene encoding Kir7.1, was not present in unaffected family members and 210 control individuals. Kir7.1 localized to human retina and retinal pigment epithelium and was especially prevalent in the internal limiting membrane adjacent to the vitreous body. Molecular modeling of this mutation predicted disruption of the structure of the potassium channel in the closed state located immediately adjacent to the cell-membrane inner boundary. Functionally, unlike wild-type Kir7.1 whose overexpression in CHO-K1 cells line produces highly selective potassium current, overexpression of R162W mutant Kir7.1 produces a nonselective cation current that depolarizes transfected cells and increases their fragility. These results indicate that the KCNJ13 R162W mutation can cause SVD and further show that vitreoretinal degeneration can arise through mutations in genes whose products are not structural components of the vitreous.
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Affiliation(s)
- J Fielding Hejtmancik
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, NIH, Bethesda, MD 20892, USA.
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Alvarez BV, Gilmour GS, Mema SC, Martin BT, Shull GE, Casey JR, Sauvé Y. Blindness caused by deficiency in AE3 chloride/bicarbonate exchanger. PLoS One 2007; 2:e839. [PMID: 17786210 PMCID: PMC1950688 DOI: 10.1371/journal.pone.0000839] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Accepted: 08/14/2007] [Indexed: 12/02/2022] Open
Abstract
Background Vision is initiated by phototransduction in the outer retina by photoreceptors, whose high metabolic rate generates large CO2 loads. Inner retina cells then process the visual signal and CO2. The anion exchanger 3 gene (AE3/Slc4a3) encodes full-length AE3 (AE3fl) and cardiac AE3 (AE3c) isoforms, catalyzing plasma membrane Cl−/HCO3− exchange in Müller (AE3fl) and horizontal (AE3c) cells. AE3 thus maintains acid-balance by removing photoreceptor-generated CO2 waste. Methodology/Principal Findings We report that Slc4a3−/− null mice have inner retina defects (electroretinogram b-wave reduction, optic nerve and retinal vessel anomalies). These pathologic features are common to most human vitreoretinal degenerations. Immunobloting analysis revealed that Na+/HCO3− co-transporter (NBC1), and carbonic anhydrase II and CAXIV, protein expression were elevated in Slc4a3−/− mouse retinas, suggesting compensation for loss of AE3. TUNEL staining showed increased numbers of apoptotic nuclei from 4–6 months of age, in Slc4a3−/− mice, indicating late onset photoreceptor death. Conclusions/Significance Identification of Slc4a3 as underlying a previously unrecognized cause of blindness suggests this gene as a new candidate for a subset of hereditary vitreoretinal retinal degeneration.
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Affiliation(s)
- Bernardo V. Alvarez
- Membrane Protein Research Group, Department of Biochemistry, University of Alberta, Edmonton, Canada
- Department of Physiology, University of Alberta, Edmonton, Canada
| | | | - Silvina C. Mema
- Department of Ophthalmology, University of Alberta, Edmonton, Canada
| | - Brent T. Martin
- Department of Physiology, University of Alberta, Edmonton, Canada
| | - Gary E. Shull
- Departments of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Joseph R. Casey
- Membrane Protein Research Group, Department of Biochemistry, University of Alberta, Edmonton, Canada
- Department of Physiology, University of Alberta, Edmonton, Canada
| | - Yves Sauvé
- Department of Physiology, University of Alberta, Edmonton, Canada
- Department of Ophthalmology, University of Alberta, Edmonton, Canada
- * To whom correspondence should be addressed. E-mail:
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