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C. Friedburg, M. Schambeck, M. Bonin, S. Kohl, B. Wissinger, B. Lorenz; Ocular Phenotype in 3 Young Siblings With a Homozygous KCNV2-Mutation Followed for 14 Years. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3683.
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© ARVO (1962-2015); The Authors (2016-present)
To present the ocular phenotype from early childhood to teens in 3 siblings with a novel homozygous mutation in the KCNV2-gene reported to cause cone dystrophy with supernormal rod electroretinograms (ERGs).
Patients were observed over 14 years, presenting first at 2 months to 5 years of age. According to age-related capacities clinical investigation included visual acuity, orthoptics, retinoscopy, slitlamp and fundus examination, color vision testing (Lanthony Panel D15 and Nagel Anomaloscope), Goldmann visual fields (VF), 2-color-threshold perimetry (2CTP), fundus photography, fundus autofluorescence (FAF), optical coherence tomography (OCT), and Ganzfeld -ERGs (ISCEV standard). Whole genome homozygosity mapping was done applying the Affymetrix 100K SNP array. PCR amplified genomic DNA fragments were screened for mutations by direct DNA sequencing.
Presenting with congenital nystagmus and initially hyperopic astigmatism, the two older siblings developed excessive myopia associated with circumpapillary myopic atrophy. The youngest had no nystagmus up to the age of 22 months. Visual acuities in all three ranged from 20/200 to 20/70. Only minor irregularities of the macular RPE were visible but FAF demonstrated a 1 PD diameter central hyperfluorescent ring. Colors were misjudged along the protan/deutan or later the achromatic axes. OCTs were normal. VF initially appeared normal, later a central scotoma was present. In scotopic 2CTP, rod sensitivity was reduced by 2 log units; in photopic 2CTP, sensitivity to red and blue stimuli was lower by 2 and 1 log units, repectively. Scotopic ERG b-waves were markedly delayed. Some of the amplitudes were "supernormal", the amplitude-versus-flash intensity function was consistently steeper. Photopic ERG b-waves were smaller than a-waves. The whole genome SNP analysis of the family revealed a region of marker homozygosity on chromosome 9p24. Subsequent mutation analysis showed a homozygous Gly461Arg mutation in KCNV2 in all three subjects.
The disease first imposed as an early-onset incomplete cone dysfunction. Onset of nystagmus was variable. Progressive axial myopia may be one sign to differentiate the disease from incomplete achromatopsia. More obvious signs of a progressive disorder were the central hyperfluorescent ring in FAF and a consistent delay of scotopic b-waves. "Supernormal" b-waves may not necessarily been seen.
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