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Paper Chase

Recessive NRL mutations in patients with clumped pigmentary retinal degeneration and relative preservation of blue cone function.

Proc. Natl. Acad. Sci. U.S.A.. Dec 21, 2004;101(51):17819-24.
Nishiguchi KM, Friedman JS, Sandberg MA, Swaroop A, Berson EL, Dryja TP.

Ocular Molecular Genetics Institute and Berman-Gund Laboratory for the Study of Retinal Degenerations, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA.

Abstract:

Mice lacking the transcription factor Nrl have no rod photoreceptors and an increased number of short-wavelength-sensitive cones. Missense mutations in NRL are associated with autosomal dominant retinitis pigmentosa; however, the phenotype associated with the loss of NRL function in humans has not been reported. We identified two siblings who carried two allelic mutations: a predicted null allele (L75fs) and a missense mutation (L160P) altering a highly conserved residue in the domain involved in DNA-binding-site recognition. In vitro luciferase reporter assays demonstrated that the NRL-L160P mutant had severely reduced transcriptional activity compared with the WT NRL protein, consistent with a severe loss of function. The affected patients had night blindness since early childhood, consistent with a severe reduction in rod function. Color vision was normal, suggesting the presence of all cone color types; nevertheless, a comparison of central visual fields evaluated with white-on-white and blue-on-yellow light stimuli was consistent with a relatively enhanced function of short-wavelength-sensitive cones in the macula. The fundi had signs of retinal degeneration (such as vascular attenuation) and clusters of large, clumped, pigment deposits in the peripheral fundus at the level of the retinal pigment epithelium (clumped pigmentary retinal degeneration). Our report presents an unusual clinical phenotype in humans with loss-of-function mutations in NRL.