Bradyopsia is a rare retinal disorder, first described in 3 unrelated Dutch families.1 Patients with bradyopsia have difficulty tracking moving objects and adapting to sudden changes in luminance levels owing to a defect in the photoreceptor deactivation mechanism within the phototransduction cascades. Homozygous mutations in either the regulator G-protein signaling 9 (RGS9) or RGS9 anchor protein (R9AP) gene that encode the photoreceptor GTPase accelerating protein and its anchor protein, respectively, have been identified in patients with bradyopsia.2 We report a case of bradyopsia in an Asian man with characteristic electrophysiological and genetic findings. This study was approved by the institutional review board of the Singapore Eye Research Institute.
Full-field electroretinogram findings. The scotopic responses (rod derived) were normal in each eye. The dark-adapted maximal flash responses (rod and cone combined) were normal but only for the initial flash (arrows). The maximal a- and b-wave amplitudes of the subsequent flashes were markedly reduced with a 20-second interstimulus interval (ISI) but normal with an ISI of 60 seconds. The dark-adapted cone system response (long-wavelength stimulation under scotopic condition) indicated the presence of cone system function (asterisks). The photopic single-flash and 30-Hz flicker responses (cone derived), however, were undetectable in each eye. OD indicates right eye; OS, left eye.
Compound heterozygous mutation in the R9AP gene. The unaffected father was heterozygous for the 2–base pair (bp) deletion (c.277-278delAT). The mother showed a normal sequence owing to the amplification of only 1 allele of R9AP. The affected patient was seemingly homozygous for the 2-bp deletion owing to the amplification of only his paternal copy of the R9AP gene. The + and − symbols denote the normal sequence and the deletion of the entire gene, respectively. The 2-bp deletion (c.277-278delAT) mutation is denoted by the letter m. Circles indicate females; squares, males; and filled symbol, affected individual.
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