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Patricia T. Y. Stappers, Linda Visser, Frans C. C. Riemslag, Caroline Osterholt, Maria M. van Genderen, Frans P. M. Cremers, Rob W. J. Collin, L. Ingeborgh van den Born; Preservation Of S-cone Function In Patients With Autosomal Recessive NRL Mutations. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4552.
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© ARVO (1962-2015); The Authors (2016-present)
To study the phenotype in patients with autosomal recessive NRL mutations and to investigate whether S-cone function is preserved in a similar manner as in patients with Enhanced S-Cone Syndrome (ESCS).
Three Moroccan patients of 2 different families were enrolled in this study. One patient, from a consanguineous marriage, was analyzed by homozygosity mapping. The other two siblings were included in a targeted next-generation sequencing project. Ophthalmic examination included best-corrected visual acuity, slit-lamp biomicroscopy, funduscopy, Goldmann kinetic perimetry, optical coherence tomography, and fundus autofluorescence. Extended electroretinography (ERG, Rod- and Cone b-wave series) was performed with in addition S-cone-specific ERG testing, using an amber stimulus on a blue background and a blue stimulus on an amber background.
The isolated patient carried a homozygous missense mutation (c.508C>A; p.Arg170Ser) in the NRL gene, whereas the same mutation was identified heterozygously in the two siblings, in combination with a one base-pair deletion (c.654del; p.Cys219ValfsX4) on the other allele. Both mutations have not been reported previously. All three patients had reduced visual acuity with the typical appearance of a clumped pigmentary retinal degeneration. Macular schisis was observed in the oldest patient. ERG under scotopic conditions showed absent responses for low stimulus strengths and reduced responses for high stimulus strengths, with constant b-wave latencies despite increasing stimulus strength. A relatively high amplitude was detected with a blue stimulus on an amber background, while an amber stimulus on a blue background showed reduced responses.
From our findings in ERG testing we conclude that S-cone function is preserved in our patients, thus supporting the idea that the phenotype associated with autosomal recessive NRL mutations shows similarities to ESCS.
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