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FY Demirci, AL Radak, BW Rigatti, TS Mah, MB Gorin, AH Milam; Histopathology of a Retina With X-Linked Cone-Rod Dystrophy Caused by a Mutation in the RPGR Exon ORF15 . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2723.
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Purpose: To evaluate the retina of a patient donor with X-linked cone-rod dystrophy caused by a mutation in the RPGR exon ORF15. Methods: Direct PCR sequencing from leucocyte genomic DNA from an X-linked cone dystrophy individual identified a 1-nt insertion in ORF15, resulting in a frameshift leading to altered amino acid structure and early termination. The eye of this 60 year-old affected male donor was fixed within 2 hours of death through the eye donor program sponsored by the Foundation Fighting Blindness with the assistance of the Eye Bank of Western Pennsylvania (now known as CORE). The retina from this patient was processed for histopathologic examination and immunocytochemistry. Results: Grossly the macula was atrophic with a bull's eye appearance, but the remaining retina appeared normal with no bone spicule pigmentation. Microscopically, the RPE was absent in focal areas of the macula and the remaining RPE cells were depigmented or hyperpigmented. Cones and rods were missing from the fovea and reduced in number with shortened outer segments elsewhere in the macula. Neurons in the inner nuclear and ganglion cell layers were also reduced in the macula. Immunohistochemistry demonstrated some loss of cones elsewhere in the retina and the remaining cones had shortened outer segments. The rods were near normal in number but their outer segments were also shortened. Conclusion: The macular pathology observed in this patient is consistent with X-linked cone-rod dystrophy. The abnormalities observed in both the cone and rod photoreceptors confirm the importance of the RPGR gene product in the normal function of both cell types, but leaves unresolved how various mutations in the same gene can lead to significantly different clinical phenotypes. We hypothesize that variations in the multiple splice variants of the RPGR transcript in the different photoreceptor types may account for some of these different clinical patterns.
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