CHARACTERIZATION OF ENHANCED S–CONE SYNDROME (ESCS).

Abstract

Abstract: : Purpose: To assess phenotypic variation in Enhanced S–cone Syndrome (ESCS), a rare genetically determined cause of night blindness related to mutation in NR2E3. A single histopathological report determined a retina devoid of rods, and a degenerate cone population principally containing short–wavelength sensitive pigment (Milam et al., 2002). Methods: We have ascertained 16 ESCS patients. In addition to conventional ERG recording, most received extended ERGs, including the use of long duration stimuli with a small LED based Ganzfeld stimulator providing blue, green or orange stimulus or background. Additional investigations included PERG (16/16), multi–focal ERG (4/16) and fundus autofluorescence imaging (AF, 7/16). Results: Clinical presentation was variable, but usually with long–standing night blindness and/or maculopathy. All patients had pathognomonic ERG changes: the rod specific ERG was undetectable; the ERGs to a Standard single flash had a similar waveform under photopic and scotopic conditions; and the 30Hz flicker ERG was of lower amplitude than the single flash photopic ERG a–wave. ERG amplitudes showed high variability across patients related to the severity of degeneration. The older patients tended to have the more severe abnormalities. Most patients showed abnormally large S–cone ERGs with minimal responses to L/M cone stimulation. PERG, when present, could be profoundly delayed. There was evidence for probable OFF– pathway function in at least 7/14 patients. AF imaging showed lack of autofluorescence outside the arcades in severely affected cases. Sparing in the tritan axis on color contrast sensitivity testing was found in 7/9 patients. Eight were tested and positive for NR2E3 mutation. Conclusions: There is marked variation in phenotype between patients with ESCS, which may in part be related to age. There was evidence of probable OFF– pathway function in some patients, an attribute not usually associated with S–cones.

Keywords: electrophysiology: clinical • retinal degenerations: hereditary • retina