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M.C. Cheung, M. Wang, K.E. McTaggart, I.M. MacDonald, J.L. Duncan; Detection of Localized Retinal Dysfunction in Choroideremia Carriers . Invest. Ophthalmol. Vis. Sci. 2003;44(13):524.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the cause of severe unilateral vision loss in an obligate female choroideremia carrier. Methods: Genetic testing, multifocal electroretinogram (mfERG), optical coherence tomography (OCT), full field ERG (ERG), fluorescein angiography (FA), Humphrey visual fields (HVF), fundus photography, and histology were used to study a family with choroideremia. MfERG amplitudes and latencies for 103 responses from a stimulus area approximately 40° in diameter were compared to control values from 27 normal eyes. Results: Molecular analysis identified a deletion in exons 9-15 of the choroideremia gene in this family. In a female carrier with unilateral severe central vision loss, mfERG showed severely reduced P1 amplitudes of the first order response with minimal delay in latencies compared to controls. OCT showed attenuation in the macula compared to the contralateral eye. These findings correlated with (1) a prominent band of retinal pigment epithelium (RPE) and choroidal atrophy in the macula seen on examination and FA, (2) a dense central scotoma on HVF testing, and (3) decreased scotopic and photopic amplitudes on ERG. In contrast, studies of the contralateral eye showed equatorial RPE pigment clumping characteristic of choroideremia carriers. The mfERG of this eye showed a mild reduction in P1 amplitudes that correlated with an area of mildly reduced HVF sensitivity, despite normal findings on OCT and ERG. The mfERG of another female carrier in the family with normal vision showed no reduction in amplitudes or delay in latencies. Studies of the affected son were characteristic for advanced choroideremia. Histologic studies of the eyes of his maternal grandmother showed patchy areas of RPE, choriocapillaris, and photoreceptor loss. Conclusions: The mfERG demonstrated macular retinal dysfunction in a female choroideremia carrier with unilateral severe central vision loss. MfERG may be a sensitive tool to measure functional abnormalities in choroideremia carriers. Mosaic inactivation of the normal gene may cause patchy expression of the mutation in the macula leading to severe vision loss in choroideremia carriers.
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