Extended Phenotypic Characteristics of NR2E3-related Enhanced S-cone Syndrome

Abstract

 

Purpose

 

To evaluate a cohort of patients to enhance the phenotypic description of NR2E3-related enhanced S-cone syndrome (ESCS).

 

Methods

 

Eight patients (seven families; Age range: 11 - 56 years) with characteristic full-field electroretinographic (ERG) features of ESCS were screened for mutations in the NR2E3 gene. All underwent detailed ophthalmological evaluation, which included distance and color vision testing, contrast sensitivity measurement, fundus photography and Goldmann visual field (GVF) perimetry. Fundus autofluorescence (AF) imaging and optical coherence tomography (OCT) were performed in 7 cases.

 

Results

 

Two pathogenic mutations in NR2E3 were identified in 7 cases; one pathogenic mutation was identified in case 8. The dim-light scotopic ERGs (DA0.002) were non-recordable in all cases. The mixed rod-cone ERGs (DA2.29) were simplifed and delayed in all cases; a- and b-wave amplitudes were subnormal in all except case 8 (aged 11 years). Single flash photopic ERGs (LA2.29) were delayed and had similar waveform morphology as DA2.29 ERGs in all cases; LA2.29 ERG b-wave amplitudes were sub/low-normal in all except case 8. Photopic flicker amplitude was smaller than LA2.29 ERG a-wave in all cases. Best corrected vision (BCVA) ranged from 20/20 to 20/200 (median: 20/50). BCVA was 20/30 or better in three cases (Ages: 11, 21 and 57 years); two of whom had normal contrast sensitivity. Color vision was normal in the tritan axis in all cases; red-green deficits were noted in 6 cases. The classical ESCS fundus description of mid-peripheral nummular pigment clumping or yellowish retinal deposition was noted only in 6 cases. GVF showed mid-peripheral field deficits to I4e target in 15/16 eyes. The OCT showed schitic changes at the fovea in three cases; 2 improved on carbonic anhydrase inhibitors. Retinal structural disorganization within and/or beyond the vascular arcades were noted in all tested. Hyper-intense AF was noted within the arcades in all tested, but the pattern was variable.

 

Conclusions

 

The strict genotype-ERG phenotype correlation in ESCS is reconfirmed. The classical fundus changes are found in only 75% of cases. The OCT abnormalities observed in this series enhance the description of NR2E3-related ESCS, and can be a useful adjunct to direct ERG testing and genetic screening in atypical cases. This study also demonstrates early field constriction in ESCS.

 

Keywords: 494 degenerations/dystrophies • 509 electroretinography: clinical • 539 genetics