Phenotypic Characterization of Patients With Autosomal Recessive Congenital Stationary Night Blindness (AR CSNB)

Abstract

Abstract: : Purpose: Phenotypic characterization of patients with AR CSNB. Methods: Fourteen female patients with a diagnosis of autosomal recessive CSNB were examined. The diagnosis was based on a family history of recessive transmission; stable longstanding night blindness; and the absence of fundus changes suggestive of a progressive retinal degeneration. Each patient underwent refraction, an ophthalmologic examination, and, when possible, electrophysiological testing to incorporate the ISCEV standard ERG and pattern ERG as well as long duration ON–OFF stimulation and S–cone testing. Testing appropriate for age was performed in young children. Results:The patients were aged from 4 to 50 years. Visual acuity ranged from 20/20 to 20/200. Ten patients had high myopia ranging from –6 to –20 diopters. Five had nystagmus. Fundus examination was normal or showed myopic changes with tilted discs recorded in 4 patients. Nine patients had strabismus. Pattern ERG was normal in 5 patients, subnormal in 1, undetectable in 4 (including 3 patients with pronounced nystagmus). PERG was not performed in 4 patients. Maximum ERG was electronegative in all cases with a b/a ratio ranging from 0.3 to 0.8. Oscillatory potentials were subnormal in all patients. The rod–specific ERG was undetectable in 6/10 patients and present but subnormal in 4/10. In 8 cases, the single flash photopic ERG waveform was unusual with a broadened trough and sharply rising peak. Long duration stimulation was performed in 9 patients; 6 had electronegative ON–responses with a relative sparing of the OFF response, similar to the findings in complete X–linked CSNB. All such patients had severe myopia and 3 had nystagmus. One subject had both ON and OFF pathway dysfunction, and was also myopic with a small rotary nystagmus. The ERG findings in this case lay between those of the complete and incomplete forms of XL–CSNB. Conclusions: These findings suggest phenotypic heterogeneity of AR CSNB with a majority resembling those of complete XL CSNB.

Keywords: electroretinography: clinical • retinal degenerations: hereditary • retina: distal (photoreceptors, horizontal cells, bipolar cells)