Abstract
Purpose :
We describe a novel form of congenital stationary night blindness associated with mutations in the GUCY2D gene.
Methods :
We report clinical and genetic findings of 4 patients from 3 unrelated families who presented with night blindness, normal fundi, full visual fields, and excellent visual acuity. Clinical evaluations included fundus imaging, spectral mode OCT, Goldmann visual fields, formal dark adaptometry, full-field stimulus testing (FST), and full-field electroretinography according to ISCEV standards. All patients underwent whole-exome DNA testing. Plausible causative mutations were identified using standard heuristic algorithms.
Results :
Three unrelated patients presented with complaints of night blindness since early childhood. Visual acuities ranged from 20/15 to 20/25-2. Goldmann visual fields were full to peripheral isopters, and normal or nearly normal centrally. Formal dark adaptometry demonstrated less than 0.5 log units of decrease in scotopic threshold over 20 minutes. FST demonstrated reduced retinal sensitivity to less than or equal to 1/3 of normal. Dilated fundus examination was normal. Spectral mode OCT was normal, or suggested a slight lucency in the outer segment ellipsoid line centrally in three patients. One patient had thinned ONL outside of the fovea. Full-field electroretinography was strikingly abnormal, with reduced photopic responses with increased implicit times, and absent responses to a dim, rod-isolating flash stimulus. Responses to the full-strength dark-adapted flash stimulus closely resembled the scaled responses to photopic single flashes, presumably due to cone activity. Whole-exome DNA analysis identified heterozygous mutations in the GUCY2D gene as the only likely causative mutations (see Table). Subsequently, a sibling of one of the initial patients presented with similar findings, and the same GUCY2D mutations.
Conclusions :
We report a small cohort of patients with a novel night-blindness syndrome associated with mutations in GUCY2D. These findings differ from previous reports of patients with GUCY2D mutations, who have been described with Leber congenital amaurosis or cone-rod dystrophy. In contrast, our patients have excellent visual acuity, normal fundi, and stationary night blindness, with ERG findings suggesting a complete absence of rod function.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.