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Sato T, Kuniyoshi K, Hayashi T, Nishiwaki H, Mizobuchi K, Kusaka S. Clinical course of two siblings with potassium voltage-gated channel modifier subfamily V member 2 (KCNV2)-associated retinopathy. Doc Ophthalmol 2024; 148:173-182. [PMID: 38630375 DOI: 10.1007/s10633-024-09971-0] [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: 03/15/2023] [Accepted: 03/15/2024] [Indexed: 08/10/2024]
Abstract
BACKGROUND KCNV2-associated retinopathy causes a phenotype reported as "cone dystrophy with nyctalopia and supernormal rod responses (CDSRR; OMIM# 610356)," featuring pathognomonic findings on electroretinography (ERG). Here, we report the clinical courses of two siblings with CDSRR. CASE REPORTS Patient 1: A 3-year-old boy with intermittent exophoria was referred to our hospital. The patient's decimal best-corrected visual acuity (BCVA) at age 6 was 0.7 and 0.7 in the right and left eyes, respectively. Photophobia and night blindness were also observed. Because the ERG showed a delayed and supernormal b-wave with a "squaring (trough-flattened)" a-wave in the DA-30 ERG, and CDSRR was diagnosed. The patient's vision gradually worsened, and faint bilateral bull's eye maculopathy was observed at the age of 27 years, although the fundi were initially unremarkable. Genetic examination revealed a homozygous missense variant, c.529T > C (p.Cys177Arg), in the KCNV2 gene. Patient 2: The second patient was Patient 1's younger sister, who was brought to our hospital at 3 years of age. The patient presented with exotropia, mild nystagmus, photophobia, night blindness, and color vision abnormalities. The patients' decimal BCVA at age 13 was 0.6 and 0.4 in the right and left eyes, respectively, and BCVA gradually decreased until the age of 24 years. The fundi were unremarkable. The siblings had similar ERG findings and the same homozygous missense variant in the KCNV2 gene. CONCLUSIONS The siblings had clinical findings typical of CDSRR. High-intense flash ERG is recommended for identifying pathognomonic "squaring" a-waves in patients with CDSRR.
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Affiliation(s)
- Tomoko Sato
- Department of Ophthalmology, Faculty of Medicine, Kindai University, Osaka-Sayama, Japan
| | - Kazuki Kuniyoshi
- Department of Ophthalmology, Faculty of Medicine, Kindai University, Osaka-Sayama, Japan.
| | - Takaaki Hayashi
- Department of Ophthalmology, The Jikei University School of Medicine, Tokyo, Japan
| | | | - Kei Mizobuchi
- Department of Ophthalmology, The Jikei University School of Medicine, Tokyo, Japan
| | - Shunji Kusaka
- Department of Ophthalmology, Faculty of Medicine, Kindai University, Osaka-Sayama, Japan
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2
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Tyler CW, Likova LT. Brain trauma impacts retinal processing: photoreceptor pathway interactions in traumatic light sensitivity. Doc Ophthalmol 2022; 144:179-190. [PMID: 35445376 PMCID: PMC9192363 DOI: 10.1007/s10633-022-09871-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Accepted: 03/12/2022] [Indexed: 11/21/2022]
Abstract
BACKGROUND Concussion-induced light sensitivity, or traumatic photalgia, is a lifelong debilitating problem for upwards of 50% of mild traumatic brain injury (mTBI) cases, though of unknown etiology. We employed spectral analysis of electroretinographic (ERG) responses to assess retinal changes in mTBI as a function of the degree of photalgia. METHODS The design was a case-control study of the changes in the ERG waveform as a function of level of light sensitivity in individuals who had suffered incidents of mild traumatic brain injury. The mTBI participants were categorized into non-, mild-, and severe-photalgic groups based on their spectral nociophysical settings. Light-adapted ERG responses were recorded from each eye for 200 ms on-off stimulation of three spectral colors (R:red, G:green, and B:blue) and their sum (W:white) at the highest pain-free intensity level for each participant. The requirement of controls for testing hypersensitive individuals at lower light levels was addressed by recording a full light intensity series in the control group. RESULTS Both the b-wave and the photopic negative response (PhNR) were significantly reduced in the non-photalgic mTBI group relative to controls. In the photalgic groups, the main b-wave peak shifted to the timing of the rod b-wave, with reduced amplitude at the timing of the cone response. CONCLUSION These results suggest the interpretation that the primary etiology of the painful light sensitivity in mTBI is release of the rod pathway from cone-mediated inhibition at high light levels, causing overactivation of the rod pathway.
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Affiliation(s)
- Christopher W Tyler
- Smith-Kettlewell Eye Research Institute, 2318 Fillmore Street, San Francisco, 94115, USA.
- Division of Optometry and Vision Science, School of Health Sciences, City University of London, London, UK.
| | - Lora T Likova
- Smith-Kettlewell Eye Research Institute, 2318 Fillmore Street, San Francisco, 94115, USA
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3
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Rashwan R, Hunt DM, Carvalho LS. The role of voltage-gated ion channels in visual function and disease in mammalian photoreceptors. Pflugers Arch 2021; 473:1455-1468. [PMID: 34255151 DOI: 10.1007/s00424-021-02595-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 05/31/2021] [Accepted: 06/10/2021] [Indexed: 12/26/2022]
Abstract
Light activation of the classical light-sensing retinal neurons, the photoreceptors, results in a graded change in membrane potential that ultimately leads to a reduction in neurotransmitter release to the post-synaptic retinal neurons. Photoreceptors show striking powers of adaptation, and for visual processing to function optimally, they must adjust their gain to remain responsive to different levels of ambient light intensity. The presence of a tightly controlled balance of inward and outward currents modulated by several different types of ion channels is what gives photoreceptors their remarkably dynamic operating range. Part of the resetting and modulation of this operating range is controlled by potassium and calcium voltage-gated channels, which are involved in setting the dark resting potential and synapse signal processing, respectively. Their essential contribution to visual processing is further confirmed in patients suffering from cone dystrophy with supernormal rod response (CDSRR) and congenital stationary night blindness type 2 (CSNB2), both conditions that lead to irreversible vision loss. This review will discuss these two types of voltage-gated ion channels present in photoreceptors, focussing on their structure and physiology, and their role in visual processing. It will also discuss the use and benefits of knockout mouse models to further study the function of these channels and what routes to potential treatments could be applied for CDSRR and CSNB2.
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Affiliation(s)
- Rabab Rashwan
- Lions Eye Institute, Nedlands, Western Australia, 6009, Australia
- Department of Microbiology and Immunology, Faculty of Medicine, Minia University, Minia, Egypt
| | - David M Hunt
- Lions Eye Institute, Nedlands, Western Australia, 6009, Australia
- Centre for Ophthalmology and Vision Science, The University of Western Australia, Perth, Western Australia, 6009, Australia
- School of Biological Sciences, University of Western Australia, Nedlands, Western Australia, 6009, Australia
| | - Livia S Carvalho
- Lions Eye Institute, Nedlands, Western Australia, 6009, Australia.
- Centre for Ophthalmology and Vision Science, The University of Western Australia, Perth, Western Australia, 6009, Australia.
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4
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Esteves-Leandro J, Torres-Costa S, Estrela-Silva S, Santos-Silva R, Brandão E, Grangeia A, Fernandes S, Oliveira R, Falcão-Reis F, Rocha-Sousa A. Cone dystrophy with supernormal rod responses: A rare KCNV2 gene variant. Eur J Ophthalmol 2021; 32:664-672. [PMID: 33706576 DOI: 10.1177/11206721211000000] [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: 11/17/2022]
Abstract
PURPOSE To describe the clinical, electrophysiological, and genetic findings of three Portuguese families with a rare variant in the KCNV2 gene resulting in "cone dystrophy with supernormal rod responses" (CDSRR). METHODS Retrospective clinical revision of five individuals from three unrelated families with CDSRR. Ophthalmological examination was described in all patients and included color vision testing, fundus photography, fundus autofluorescence (FAF) imaging, spectral domain-optical coherence tomography (SD-OCT), pattern electroretinogram (ERG), and full-field ERG. The mutational screening of the KCNV2 gene was performed with Sanger and Next Generation Sequencing. RESULTS All patients showed childhood-onset photophobia and progressive visual acuity loss with varying degrees of severity. In multimodal imaging, various degrees of retinal pigment epithelium disturbances and outer retinal atrophy, which tend to be worst with advancing age, were observed. Molecular screening identified a rare presumed truncating variant (p.Glu209Ter) in homozygosity in two families and in compound heterozygosity in a third family. Three patients showed ERG changes characteristic of CDSRR, however, two patients presented with incomplete electrophysiological features of the disease. CONCLUSION A rare variant in the KCNV2 gene was identified in five patients from three Portuguese families. This variant often leads to a severe and progressive form of retinopathy. Considerable variability in the ERG responses among patients with this KCNV2 variant was observed.
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Affiliation(s)
- João Esteves-Leandro
- Department of Ophthalmology, Centro Hospitalar Universitário de São João, Porto, Portugal
| | - Sónia Torres-Costa
- Department of Ophthalmology, Centro Hospitalar Universitário de São João, Porto, Portugal
| | - Sérgio Estrela-Silva
- Department of Ophthalmology, Centro Hospitalar Universitário de São João, Porto, Portugal.,Department of Surgery and Physiology, Faculty of Medicine, University of Porto, Porto, Portugal
| | - Renato Santos-Silva
- Department of Ophthalmology, Centro Hospitalar Universitário de São João, Porto, Portugal.,Department of Surgery and Physiology, Faculty of Medicine, University of Porto, Porto, Portugal
| | - Elisete Brandão
- Department of Ophthalmology, Centro Hospitalar Universitário de São João, Porto, Portugal
| | - Ana Grangeia
- Department of Genetics, Centro Hospitalar Universitário de São João, Porto, Portugal
| | - Susana Fernandes
- Department of Genetics, Centro Hospitalar Universitário de São João, Porto, Portugal.,Institute for Innovation and Health Research (I3S), University of Porto, Porto, Portugal
| | - Renata Oliveira
- Department of Genetics, Centro Hospitalar Universitário de São João, Porto, Portugal
| | - Fernando Falcão-Reis
- Department of Ophthalmology, Centro Hospitalar Universitário de São João, Porto, Portugal.,Department of Surgery and Physiology, Faculty of Medicine, University of Porto, Porto, Portugal
| | - Amândio Rocha-Sousa
- Department of Ophthalmology, Centro Hospitalar Universitário de São João, Porto, Portugal.,Department of Surgery and Physiology, Faculty of Medicine, University of Porto, Porto, Portugal
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Stockman A, Henning GB, Rider AT. Clinical vision and molecular loss: Integrating visual psychophysics with molecular genetics reveals key details of normal and abnormal visual processing. Prog Retin Eye Res 2020; 83:100937. [PMID: 33388434 DOI: 10.1016/j.preteyeres.2020.100937] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2020] [Revised: 12/11/2020] [Accepted: 12/17/2020] [Indexed: 01/08/2023]
Abstract
Over the past two decades we have developed techniques and models to investigate the ways in which known molecular defects affect visual performance. Because molecular defects in retinal signalling invariably alter the speed of visual processing, our strategy has been to measure the resulting changes in flicker sensitivity. Flicker measurements provide not only straightforward clinical assessments of visual performance but also reveal fundamental details about the functioning of both abnormal and normal visual systems. Here, we bring together our past measurements of patients with pathogenic variants in the GNAT2, RGS9, GUCA1A, RPE65, OPA1, KCNV2 and NR2E3 genes and analyse the results using a standard model of visual processing. The model treats flicker sensitivity as the result of the actions of a sequence of simple processing steps, one or more of which is altered by the genetic defect. Our analyses show that most defects slow down the visual response directly, but some speed it up. Crucially, however, other steps in the processing sequence can make compensatory adjustments to offset the abnormality. For example, if the abnormal step slows down the visual response, another step is likely to speed up or attenuate the response to rebalance system performance. Such compensatory adjustments are probably made by steps in the sequence that usually adapt to changing light levels. Our techniques and modelling also allow us to tease apart stationary and progressive effects, and the localised molecular losses help us to unravel and characterise individual steps in the normal and abnormal processing sequences.
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Affiliation(s)
- Andrew Stockman
- UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, England, UK.
| | - G Bruce Henning
- UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, England, UK
| | - Andrew T Rider
- UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, England, UK
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Zele AJ, Dey A, Adhikari P, Feigl B. Melanopsin hypersensitivity dominates interictal photophobia in migraine. Cephalalgia 2020; 41:217-226. [PMID: 33040593 DOI: 10.1177/0333102420963850] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
PURPOSE To define the melanopsin and cone luminance retinogeniculate pathway contributions to photophobia in healthy controls and migraineurs. METHODS Healthy controls and migraineurs were categorized according to the International Classification of Headache Disorders criteria. Photophobia was measured under full-field illumination using electromyography in response to narrowband lights spanning the melanopsin and cone luminance action spectra. Migraineurs were tested during their interictal headache-free period. Melanopsin-mediated post-illumination pupil responses quantified intrinsically photosensitive Retinal Ganglion Cell (ipRGC) function. RESULTS A model combining the melanopsin and cone luminance action spectra best described photophobia thresholds in controls and migraineurs; melanopsin contributions were ∼1.5× greater than cone luminance. In the illumination range causing photophobia, migraineurs had lower photophobia thresholds (∼0.55 log units; p < 0.001) and higher post-illumination pupil response amplitudes (p = 0.03) than controls. CONCLUSION Photophobia is driven by melanopsin and cone luminance inputs to the cortex via the retino-thalamocortical pathway. In migraineurs, lower photophobia thresholds reflect hypersensitivity of ipRGC and cone luminance pathways, with the larger and prolonged post-illumination pupil response amplitude indicative of a supranormal melanopsin response. Our findings inform artificial lighting strategies incorporating luminaires with low melanopsin excitation and photopic luminance to limit the lighting conditions leading to photophobia.
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Affiliation(s)
- Andrew J Zele
- Centre for Vision and Eye Research, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.,School of Optometry and Vision Science, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Ashim Dey
- Centre for Vision and Eye Research, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.,School of Biomedical Sciences, Queensland University of Technology (QUT), Brisbane, Australia
| | - Prakash Adhikari
- Centre for Vision and Eye Research, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.,School of Optometry and Vision Science, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Beatrix Feigl
- Centre for Vision and Eye Research, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Queensland, Australia.,School of Biomedical Sciences, Queensland University of Technology (QUT), Brisbane, Australia.,Queensland Eye Institute, Brisbane, Queensland, Australia
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The Role of the Voltage-Gated Potassium Channel Proteins Kv8.2 and Kv2.1 in Vision and Retinal Disease: Insights from the Study of Mouse Gene Knock-Out Mutations. eNeuro 2019; 6:eN-NWR-0032-19. [PMID: 30820446 PMCID: PMC6393689 DOI: 10.1523/eneuro.0032-19.2019] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2019] [Revised: 02/01/2019] [Accepted: 02/04/2019] [Indexed: 11/21/2022] Open
Abstract
Mutations in the KCNV2 gene, which encodes the voltage-gated K+ channel protein Kv8.2, cause a distinctive form of cone dystrophy with a supernormal rod response (CDSRR). Kv8.2 channel subunits only form functional channels when combined in a heterotetramer with Kv2.1 subunits encoded by the KCNB1 gene. The CDSRR disease phenotype indicates that photoreceptor adaptation is disrupted. The electroretinogram (ERG) response of affected individuals shows depressed rod and cone activity, but what distinguishes this disease is the supernormal rod response to a bright flash of light. Here, we have utilized knock-out mutations of both genes in the mouse to study the pathophysiology of CDSRR. The Kv8.2 knock-out (KO) mice show many similarities to the human disorder, including a depressed a-wave and an elevated b-wave response with bright light stimulation. Optical coherence tomography (OCT) imaging and immunohistochemistry indicate that the changes in six-month-old Kv8.2 KO retinae are largely limited to the outer nuclear layer (ONL), while outer segments appear intact. In addition, there is a significant increase in TUNEL-positive cells throughout the retina. The Kv2.1 KO and double KO mice also show a severely depressed a-wave, but the elevated b-wave response is absent. Interestingly, in all three KO genotypes, the c-wave is totally absent. The differential response shown here of these KO lines, that either possess homomeric channels or lack channels completely, has provided further insights into the role of K+ channels in the generation of the a-, b-, and c-wave components of the ERG.
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Zobor D, Kohl S, Wissinger B, Zrenner E, Jägle H. Rod and cone function in patients with KCNV2 retinopathy. PLoS One 2012; 7:e46762. [PMID: 23077521 PMCID: PMC3471896 DOI: 10.1371/journal.pone.0046762] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Accepted: 09/10/2012] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND To investigate rod and cone function and disease mechanisms in patients with KCNV2 retinopathy. METHODOLOGY/PRINCIPAL FINDINGS Psychophysical examinations as well as detailed electrophysiological examinations with Ganzfeld and multifocal electroretinogram (ERG) were performed to study response dynamics. Additionally, fundus photography, autofluorescence imaging and spectral domain OCTs were carried out for morphological characterization. Molecular genetic analysis revealed compound heterozygosity in five patients and homozygosity for the KCNV2 gene in one patient. The mutations resulted in complete absence of Kv8.2 subunits in three patients (no protein group, NOP), while the other three patients expressed mutant Kv8.2 subunits resulting in altered Kv2.1/Kv8.2 heteromeric or residual Kv2.1 homomeric potassium channel function (altered protein group, ALP). Although more advanced morphological changes were visible in the NOP group, a clear functional difference between the two groups could not be observed. All patients showed characteristic dynamics of the b-wave intensity-response function, however, scotopic b-wave response amplitudes were within normal limits. We also observed severely reduced oscillatory potentials. CONCLUSIONS/SIGNIFICANCE A specific genotype-phenotype correlation in retinal function could not be demonstrated. KCNV2 mutations cause a unique form of retinal disorder illustrating the importance of K(+)-channels for the resting potential, activation and deactivation of photoreceptors, while phototransduction remains unchanged. The reduced oscillatory potentials further suggest an altered function of the inner retina. Besides the characteristically steep amplitude-versus-intensity relationship, flicker responses at intermediate frequencies (5-15 Hz) are significantly reduced and shifted in phase.
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Affiliation(s)
- Ditta Zobor
- Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany.
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"Cone dystrophy with supernormal rod electroretinogram": a comprehensive genotype/phenotype study including fundus autofluorescence and extensive electrophysiology. Retina 2010; 30:51-62. [PMID: 19952985 DOI: 10.1097/iae.0b013e3181bfe24e] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE The purpose of this study was to characterize the clinical, electrophysiologic, and genetic features in "cone dystrophy with supernormal rod electroretinogram (ERG)." METHODS Twenty-four cases between 5 and 59 years of age were ascertained. Full-field ERGs, incorporating the international standards, were used to derive intensity-ERG response functions. ON-OFF ERGs were performed. Fundus autofluorescence imaging was performed on 15 subjects. Deoxyribonucleic acid was available in 18 cases and was screened for a mutation in KCNV2. RESULTS Photophobia and nyctalopia were common. Autofluorescence was variable but often showed a ring-like area of high density that in middle-aged individuals, usually surrounded by an area of macular retinal pigment epithelial atrophy. Scotopic ERG amplitudes overlapped with the normal range but had characteristic a- and b-wave intensity-response functions; all had a broadened a-wave to the brightest flash. Photopic ERGs were abnormal; there was a delay in some ON and most OFF responses. Mutations in KCNV2 were detected in 18 cases, including 4 with novel mutations. CONCLUSION Individuals with mutations in KCNV2 manifest a wide range of macular and autofluorescence abnormalities. A ring-like area of parafoveal high density autofluorescence is common. ERG amplitudes are variable, but the intensity-ERG response functions and bright flash ERG waveforms are pathognomonic.
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Salah SB, Kamei S, Sénéćhal A, Lopez S, Bazalgette C, Bazalgette C, Eliaou CM, Zanlonghi X, Hamel CP. Novel KCNV2 mutations in cone dystrophy with supernormal rod electroretinogram. Am J Ophthalmol 2008; 145:1099-106. [PMID: 18400204 DOI: 10.1016/j.ajo.2008.02.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2007] [Revised: 01/26/2008] [Accepted: 02/02/2008] [Indexed: 10/22/2022]
Abstract
PURPOSE To describe patients with cone dystrophy and supernormal rod electroretinogram (ERG) and search for mutations in the recently described KCNV2 gene. DESIGN Clinical and molecular study. METHODS Patients from three families originating from France, Morocco, and Algeria had standard ophthalmologic examination and color vision analysis, Goldmann perimetry, International Society for Clinical Electrophysiology of Vision (ISCEV) protocol in accordance with ERG testing, autofluorescence evaluation, and optical coherence tomography 3 scanning. The two coding exons of KCNV2 were polymerase chain reaction amplified and sequenced. RESULTS All patients had the characteristic features of supernormal, delayed rod ERG responses at the highest levels of stimulation and markedly reduced cone responses. In the French family, two affected sisters were compound heterozygotes for the recurrent c.1381G>A (Gly461Arg) mutation and for a novel c.442G>T (Glu148Stop) mutation. In the Moroccan family, affected members were homozygotes for the novel c.1404delC mutation (His468fsX503) and in the Algerian family, the proband was homozygote for the novel c.1001delC mutation (Ala334fsX453). In the three families, parents were unaffected heterozygote carriers. None of the mutations were present in 50 control chromosomes. CONCLUSIONS The three novel truncative mutations are likely to be null mutations leading to loss of function, with no difference in the phenotype presentation. Amino acid changes are found exclusively in the N-terminal fragment of the protein and in the P-loop, indicating the importance of those regions for the function of the KCNV2 protein.
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Thiagalingam S, McGee TL, Weleber RG, Sandberg MA, Trzupek KM, Berson EL, Dryja TP. Novel mutations in the KCNV2 gene in patients with cone dystrophy and a supernormal rod electroretinogram. Ophthalmic Genet 2008; 28:135-42. [PMID: 17896311 DOI: 10.1080/13816810701503681] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
PURPOSE To identify mutations in KCNV2 in patients with a form of cone dystrophy characterized by a supernormal rod electroretinogram (ERG). METHODS The 2 exons and flanking intron DNA of KCNV2 from 8 unrelated patients were PCR amplified and sequenced. RESULTS We found 1 frameshift, 2 nonsense, 1 non-stop, and 6 missense mutations. Every patient had one or two mutations identified. Of the missense mutations, 4 affected residues were in the amino terminal region of the protein, and two in the pore region. CONCLUSIONS KCNV2 mutations account for most if not all cases of cone dystrophy with a supernormal rod ERG.
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Affiliation(s)
- Sureka Thiagalingam
- Ocular Molecular Genetics Institute, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114, USA
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Wu H, Cowing JA, Michaelides M, Wilkie SE, Jeffery G, Jenkins SA, Mester V, Bird AC, Robson AG, Holder GE, Moore AT, Hunt DM, Webster AR. Mutations in the gene KCNV2 encoding a voltage-gated potassium channel subunit cause "cone dystrophy with supernormal rod electroretinogram" in humans. Am J Hum Genet 2006; 79:574-9. [PMID: 16909397 PMCID: PMC1559534 DOI: 10.1086/507568] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2006] [Accepted: 07/06/2006] [Indexed: 11/03/2022] Open
Abstract
"Cone dystrophy with supernormal rod electroretinogram (ERG)" is an autosomal recessive disorder that causes lifelong visual loss combined with a supernormal ERG response to a bright flash of light. We have linked the disorder to a 0.98-cM (1.5-Mb) region on chromosome 9p24, flanked by rs1112534 and rs1074449, using homozygosity mapping in one large consanguineous pedigree. Analysis of one gene within this region, KCNV2, showed a homozygous nonsense mutation. Mutations were also found in 17 alleles of 10 other unrelated families with the same disorder. In situ hybridization demonstrated KCNV2 expression in human rod and cone photoreceptors. The precise function of KCNV2 in human photoreceptors remains to be determined, although this work suggests that mutations might perturb or abrogate I(KX), the potassium current within vertebrate photoreceptor inner segments, which has been shown to set their resting potential and voltage response.
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Affiliation(s)
- Huimin Wu
- University College London, Institute of Ophthalmology, London, United Kingdom
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13
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Michaelides M, Hardcastle AJ, Hunt DM, Moore AT. Progressive cone and cone-rod dystrophies: phenotypes and underlying molecular genetic basis. Surv Ophthalmol 2006; 51:232-58. [PMID: 16644365 DOI: 10.1016/j.survophthal.2006.02.007] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The cone and cone-rod dystrophies form part of a heterogeneous group of retinal disorders that are an important cause of visual impairment in children and adults. There have been considerable advances made in recent years in our understanding of the pathogenesis of these retinal dystrophies, with many of the chromosomal loci and causative genes having now been identified. Mutations in 12 genes, including GUCA1A, peripherin/RDS, ABCA4 and RPGR, have been described to date; and in many cases detailed functional assessment of the effects of the encoded mutant proteins has been undertaken. This improved knowledge of disease mechanisms has raised the possibility of future treatments for these disorders, for which there are no specific therapies available at the present time.
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Michaelides M, Holder GE, Webster AR, Hunt DM, Bird AC, Fitzke FW, Mollon JD, Moore AT. A detailed phenotypic study of "cone dystrophy with supernormal rod ERG". Br J Ophthalmol 2005; 89:332-9. [PMID: 15722315 PMCID: PMC1772537 DOI: 10.1136/bjo.2004.050567] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AIMS To characterise the detailed phenotype of "cone dystrophy with supernormal rod ERG" in a case series of 10 patients. METHODS 10 affected patients were examined clinically and underwent colour fundus photography, with nine undergoing detailed electrophysiological testing. Five patients were assessed further with fundus autofluorescence (AF) imaging, automated photopic and dark adapted perimetry, and dark adaptometry. Detailed colour vision assessment was performed in six subjects. Blood samples were taken from four patients for DNA extraction and mutation screening of NR2E3 was undertaken. RESULTS The onset of symptoms was in the first and second decades of life. Subjects presented with reduced central vision and marked photophobia. All individuals were myopic and colour vision testing revealed severely reduced colour discrimination predominantly along the red-green axes; tritan colour vision was relatively well preserved. Nyctalopia is a later feature of the disorder. Funduscopy and AF imaging revealed a range of macular appearances. There was electrophysiological evidence of marked macular dysfunction, reduced and delayed cone responses, and supernormal and delayed rod responses. Photopic and dark adapted perimetry revealed central scotomata with widespread peripheral sensitivity loss. No disease causing sequence variants in NR2E3 were identified. CONCLUSIONS The largest case series to date has been described of the clinical, psychophysical and electrophysiological characteristics of this unusual cone dystrophy with supernormal rod responses. Electrophysiological data were consistent with a post-phototransduction, but pre-inner nuclear layer, site of dysfunction. While the definitive diagnosis can only be made with electrophysiological testing, several characteristics that may increase suspicion of this diagnosis are presented.
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Affiliation(s)
- M Michaelides
- Institute of Ophthalmology, University College London, London EC1V 9EL, UK
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Tanimoto N, Usui T, Ichibe M, Takagi M, Hasegawa S, Abe H. PIII and Derived PII Analysis in a Patient with Retinal Dysfunction with Supernormal Scotopic ERG. Doc Ophthalmol 2005; 110:219-26. [PMID: 16328930 DOI: 10.1007/s10633-005-7861-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/16/2005] [Indexed: 10/25/2022]
Abstract
PURPOSE To present electroretinographic (ERG) findings in a patient with retinal dysfunction with supernormal scotopic ERG, and to analyze rod and cone PIII components and rod inner nuclear layer (derived PII) responses. PATIENT A Japanese 11-year-old girl complained of poor visual acuity. There was no parental consanguinity in her family. The corrected visual acuity was 0.7 in both eyes. No abnormal finding was observed in both fundi. METHODS The patient underwent full-field ERGs. Rod and cone a-waves were analyzed using photoreceptor models. The derived PII responses were analyzed using a technique described by Hood and Birch. RESULTS In the photopic ERG, responses to single flash and 30-Hz flicker were attenuated. In the scotopic ERG, b-wave was supernormal in amplitude in response to intense flashes, but smaller than normal and markedly delayed over a lower range of flash intensities. By the PIII analysis, phototransductions (values of S) of both rod and cone were remarkably decreased. The derived PII responses for this patient were larger than the responses for normal subjects, and the onset of the PII responses in this patient are significantly delayed compared to those in normal subjects. CONCLUSIONS The ophthalmological findings in this patient are consistent with previous publications of this disease. Although it has been reported that the sites of disease action were beyond the outer segment (values of S were within the normal range), our results suggest that photoreceptors could be involved in sites of disease action in at least some patients with this disease.
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Affiliation(s)
- Naoyuki Tanimoto
- Division of Ophthalmology and Visual Science, Graduate School of Medical and Dental Sciences, Niigata University, 1-757, Asahimachi, Niigata, 951-8510, Japan.
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Hood DC, Birch DG. Assessing abnormal rod photoreceptor activity with the a-wave of the electroretinogram: applications and methods. Doc Ophthalmol 1998; 92:253-67. [PMID: 9476593 DOI: 10.1007/bf02584080] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The impact of a disease on phototransduction can be assessed by fitting the leading edge of the rod a-wave to high-energy flashes with a quantitative expression. Two parameters of rod receptor activity are obtained, S (sensitivity) and Rm (maximum response). In this study, the meaning of these parameters and examples of conditions that change them were examined. In addition, a new protocol was developed for obtaining these parameters. A set of three to five white flashes were first presented in the dark and then on an adapting field (30 cd/m2). Subtracting the light-adapted responses from the dark-adapted responses yielded isolated rod a-wave responses. A clinical protocol was developed based on a single white flash energy. It is possible to determine whether a disease is producing a change in S and/or Rm with this single flash energy without the use of any equations.
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Affiliation(s)
- D C Hood
- Department of Psychology, Columbia University, New York, NY, USA.
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Hood DC, Cideciyan AV, Halevy DA, Jacobson SG. Sites of disease action in a retinal dystrophy with supernormal and delayed rod electroretinogram b-waves. Vision Res 1996; 36:889-901. [PMID: 8736222 DOI: 10.1016/0042-6989(95)00174-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Delayed rod ERG b-waves in patients with an unusual retinal dystrophy have been attributed by some to an abnormality in receptor cGMP activity. Here the sites of disease action are studied by analyzing rod and cone ERGs using new analytical methods and a wide range of stimulus intensities. Consistent with previous reports, the five patients studied showed rod b-waves that were normal or supernormal in amplitude in response to intense flashes, but smaller than normal and markedly delayed in response to weaker flashes. The cone ERGs, recorded to 29 Hz flicker and to flashes upon a background, were smaller than normal and also showed delays. Models of phototransduction fitted to rod and cone a-waves indicated that the delays in the rod and cone b-waves were not due to the speed or amplification of the transduction process. An analysis of the derived inner nuclear layer (INL) response suggests that the sites of disease action are beyond the outer segment and involve a delay in the activation of INL activity.
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Affiliation(s)
- D C Hood
- Department of Psychology, Columbia University, New York City, NY 10027, USA.
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Simonsen SE, Rosenberg T. Reappraisal of a short-wavelength-sensitive (S-cone) recording technique in routine clinical electroretinography. Doc Ophthalmol 1995; 91:323-32. [PMID: 8899302 DOI: 10.1007/bf01214650] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The recording of blue cone (S-cone) responses as described by Gouras and MacKay was slightly modified and incorporated into our routine ganzfeld electroretinogram protocol. We found a mean S-cone amplitude of 5.0 microV (range 2.9-6.9 microV) and a mean S-cone implicit time of 41.5 msec (range 40-46 msec). Separation between the combined red and green cone (L-M-cone) response and the S-cone response was obtained with blue flash stimuli on a yellow adapting background.
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Affiliation(s)
- S E Simonsen
- National Eye Clinic for the Visually Impaired, Hellerup, Denmark
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