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Sung Pyo Park, In Hwan Hong, Winston Lee, Marcela Marsiglia, Takeshi Kitamura, Stephen Tsang, Stanley Chang; Cellular Imaging Demonstrates Genetic Mosaicism in Heterozygous Carriers of an X-Linked Ciliopathy Gene. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3448.
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The purpose of this study was to evaluate structural characteristics in 5 female obligate carriers of XLRP by using multimodal non-invasive imaging methods, including AO-SLO.
Five patients and 18 controls having similar age and refractive error with patients were investigated. The XLRP carrier state was diagnosed by clinical and genetic analyses. All participants underwent a complete ophthalmic examination that included fundus color photography, IR and FAF imaing, SD-OCT and ERG. High resolution image of cone cells and direct measurement of the number of cones were investigated by AO-SLO equipped with a dual liquid crystal on silicon modulator. For the number of cones, we acquired 2 kinds of parameters: cone count by manual estimation and cone density by automated estimation.
3 patients were confirmed with mutations in RPGR gene and the rest of the patients were diagnosed as carriers by clinical investigation and pedigree analysis. Regarding AO-SLO examination, compared to normal eyes, some images of each XLRP patient showed normal appearance of cone cell with a compact arrangement. However, cone cells in several areas showed irregular pattern and were of variable asymmetrical sizes and shapes. There were some dark areas where the cone cells were damaged or lost so that less compact distribution of cone cells than controls was noted. Statistical analysis between 5 carriers and controls revealed that the number of cone cells in these images was significantly decreased. When we compared the average number of cone cells counted using either method, among total 60 areas obtained from 5 carriers, overall 29 areas showed cone counts or densities lower than 1 standard deviation from the controls and the agreement between the 2 different methods was up to 82.8%.
In all carriers, qualitative and quantitative analyses by AO-SLO imaging revealed a mosaic pattern of cone disruption, even in the absence of visual symptoms, normal visual acuity, normal macular thickness and mildly subnormal full-field cone ERG findings. Since the technique is sensitive to the level of a single cone, the ability to visualize the cone cells in vivo should be especially useful in other retinal diseases. Further investigation of XLRP carriers may yield insight into how cone structures change over time and ultimately enable understanding of the role of RPGR and RP2 in live human patients.
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