ERG variability in X-linked congenital retinoschisis patients with mutations in the RS1 gene and the diagnostic importance of fundus autofluorescence and OCT
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Purpose X-linked congenital retinoschisis (RS) is a relatively frequent retinal dystrophy associated with RS1 gene mutations. A negative electroretinogram (ERG), i.e., a b/a wave ratio <1.0 in the standard combined response, is considered a key diagnostic feature of RS. Only a few cases without a negative ERG have been reported. Methods This study includes 24 RS patients with RS1 mutations. ERGs (according to ISCEV standards, n = 23), ON-OFF-responses (n = 9), fundus autofluorescence (FAF, n = 8), and optical coherence tomography (OCT, n = 6) were performed. Results The mean age at examination was 22.6 years (0.5–53.2 years), and median visual acuity was 0.3 (no light perception to 0.6). A negative ERG was found in 13 of 23 patients (56.5%), of whom one patient presented a negative ERG at the 2-year follow-up, with an initial b/a wave ratio >1.0. Another patient had a b/a wave ratio of 0.96 in one eye and 1.02 in the fellow eye. In 10 of 23 patients, the b/a wave ratio ranged from 1.03 to 1.34. Single-flash cone and 30 Hz flicker responses were always reduced. FAF and OCT were pathologic in all patients tested. FAF was increased in the fovea. OCT revealed foveal schisis to various degrees and thinning of the retina in an older patient. Conclusions Although ERG abnormalities were detected in all patients tested, more than 40% of patients with RS1 mutations did not have a negative ERG. In clinically suspected RS a combination of ERG, FAF, OCT, and molecular-genetic testing is advised to verify the diagnosis.
KeywordsFull-field ERG Fundus autofluorescence Negative ERG Optical coherence tomography RS1 gene X-linked congenital retinoschisis
Supported in part by the Deutsche Forschungsgemeinschaft, Bonn, Germany (grant numbers KE 442/11-1,2 and WE 1259/12-3). The authors acknowledge the help of W. Berger and his group for performing mutational analysis in three of our patients, already published in The Retinoschisis Consortium, Group 5, 1998 .
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