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D. Nagy, S. Kohl, E. Zrenner, B. Wissinger, H. Jägle; Detailed Functional and Morphological Analysis in Patients With Cone Dystrophy With Supernormal Rod Response Due to Mutations in the Kcnv2 Gene. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4757.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate detailed phenotype characteristics and disease mechanism in patients with cone dystrophy with supernormal rod response (CDSRR) with known alterations of the KCNV2 gene locus.
Eight patients (3 female, 5 male; mean age: 31, range: 27 to 59 years) with known mutations of the KCNV2 gene were examined. Besides psychophysical examinations (visual acuity, visual field, color vision, dark adaptation) a detailed electrophysiological examination was performed including extended Ganzfeld ERG recordings with the Espion E2 (Diagnosys LCC) and multifocal ERG (mfERG) using the VERIS system (Electro-Diagnostic Imaging Inc.). Where possible, fundus photography, autofluorescence imaging and spectral domain OCT imaging was carried out for a detailed morphological characterization.
Molecular genetic examinations revealed compound heterozygosity in seven and homozygosity for mutations in the KCNV2 gene in one patient. Two new mutations were identified. Visual acuity was markedly reduced (mean VA: 0.15, range between 0.02 and 0.5) in all patients, visual field testing revealed a central scotoma with normal outer boundaries. Color vision disturbances and elevated dark adaptation thresholds were found in every case, even if night blindness was not present. Ganzfeld ERG recordings showed normal to supernormal mixed rod-cone response amplitudes with markedly prolonged implicit times. Most interestingly, b/a-ratios were significantly higher in all of the cases (mean 2.55, range 1.9 to 3.49), even though the b-wave amplitude was within normal ranges in some patients. Responses to high intensity flashes showed supernormal b-wave amplitudes and prolonged implicit times in all patients. Photopic responses and mfERG responses showed reduced amplitudes and prolonged implicit times. Fundus morphology revealed macular atrophy and normal periphery in all patients; progression of the disease could not be observed.
We describe novel mutations in the KCNV2 gene causing CDSRR. Our cases and previous descriptions of this retinal dystrophy, however, not always show supernormal rod b-wave response amplitudes. More typical features of the disease are the significantly larger mixed rod-cone response b/a-ratio and the marked prolongation of implicit times, which are present in every patient. These characteristics seem essential and unique in retinal dystrophies due to mutations in the KCNV2 gene.
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