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Winston Lee, Kaspar Schuerch, Yajing Xie, Jana Zernant, Stephen H. Tsang, Janet R. Sparrow, Rando Allikmets; Simultaneous Expression of ABCA4 and GPR143 Mutations: A Complex Phenotypic Manifestation. Invest. Ophthalmol. Vis. Sci. 2016;57(7):3409-3415. doi: 10.1167/iovs.16-19621.
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To describe the complex, overlapping phenotype expressed in a two generation family harboring pathogenic mutations in the ABCA4 and GPR143 genes.
Clinical evaluation of a two generation family included quantitative autofluorescence imaging (qAF, 488-nm excitation) using a modified confocal scanning laser ophthalmoscope equipped with an internal fluorescent reference to account for varying laser power detector sensitivity, spectral-domain optical coherence tomography, and full-field ERG testing. Complete sequencing of the ABCA4 and GPR143 genes was carried out in each individual.
Affected individuals presented with bull's eye lesions and qAF levels above the 95% confidence interval for healthy eyes; full-field ERG revealed no generalized rod dysfunction but mild implicit time delays in cone responses. Complete sequencing of the ABCA4 gene revealed two disease-causing mutations, p.L541P and p.G1961E; and mutational phase was confirmed in each unaffected parent. Further examination in the affected patients revealed a peripheral “mud-splattered” pattern of hypopigmented RPE after which sequencing of GPR143 revealed a novel missense variant, p.Y157C. The GPR143 variant segregated from the father who did not exhibit any indications of retinal disease with the exception of an abnormal near-infrared autofluorescence (NIR-AF) signal distribution in the macula.
An individual carrying both ABCA4 and GPR143 disease-causing mutations can express a complex, overlapping phenotype associated with both Stargardt disease and X-linked ocular albinism (OA1). The absence of OA1-related disease changes (with the exception of NIR-AF changes associated with melanin distribution) in the father may be indicative of mild expressivity or variable gene penetrance.
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