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Crandall E. Peeler, Kari Branham, Sarwar Zahid, William Rhoades, Naheed Khan, K. Thiran Jayasundera, John R. Heckenlively; Patients with ABCA4 Mutations and a Cone Dystrophy-like ERG. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4554.
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Patients with mutations in ABCA4 may present with rod-cone, cone-rod, or normal ERG patterns. We describe the clinical phenotype in 10 patients who exhibit a cone dystrophy ERG pattern and were also found to have ABCA4 mutations.
A retrospective chart review was performed of patients with one or more mutations in ABCA4 to identify those with a cone dystrophy phenotype. Clinical data included visual acuity (VA), Goldmann visual fields (GVF), full-field electroretinography (ffERG), fundus ophthalmoscopy, and fluorescein angiography (FA). Central scotoma sizes from the GVFs were quantified using digital planimetry. ERGs were characterized as typical for cone dystrophy if the photopic B-wave amplitude was more than 2SD below the mean and the scotopic rod ERG was within the normal range in both eyes. Fundus photos were evaluated by two retinal dystrophy specialists, with special attention to the distribution of flecks and atrophy. FA images were assessed for the presence or absence of a dark choroid or a peri-papillary dark ring.
Cone dystrophy ERG patterns were found in 12% (N=10) of our total population with one or more mutations in ABCA4. Seven female and three male patients ranged in age at first visit from 9 to 55 years. Visual acuity from 20 eyes ranged from 20/20 to CF with a mean of 20/104 (calculated using logMAR). Right eye photopic B-wave amplitudes ranged from 25 µV to 91 µV (N = 10; average = 69 µV; range = 15-55% of normal mean), while scotopic B-wave amplitudes ranged from 150 µV to 292 µV (N = 10; average = 257 µV; range = 55-107% of normal mean). Seven of 10 patients exhibited central scotomata with the I4e target, with an average size of 12.75 cm2 (N = 30; range = 0.8 to 52.4 cm2). All patients exhibited fundus flecks and atrophy, to varying degrees. Six patients had a dark choroid and 4 patients had dark rings in both eyes on FA.
Mutations in ABCA4 are most commonly associated with Stargardt disease, but have also been reported as a cause of retinitis pigmentosa or a cone-rod dystrophy. Our data suggest that patients with isolated cone abnormalities on ERG testing may also have causative mutations in ABCA4, in addition to classical funduscopic and FA findings of Stargardt disease such as flecks, atrophy, a dark choroid, and a dark ring. This indicates that FA and subsequent ABCA4 mutation screening is warranted in the isolated cone dystrophy population.
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