Medical College of Wisconsin, Milwaukee, Wisconsin
Commercial Relationships: M.L. Wagner Schuman, None; J. Rha, None; A.M. Dubis, None; K. Stepien, None; J. Neitz, None; M. Neitz, None; J. Carroll, None.
Support: NIH Grants EY01931, EY17607, EY09303, Research to Prevent Blindness,Fight for Sight, E. Matilda Ziegler Foundation for the Blind,RD & Linda Peters Foundation,Gene & Ruth Posner Foundation
Purpose:The effects of missense and nonsense mutations in rhodopsin on rod photoreceptor viability are well documented, however, little is known about the effects of such mutations in cone opsin on cone viability. The purpose of this study is to determine whether cone photoreceptor viability depends on expression of cone pigment using an dichromatic subject whose dichromacy is caused by a nonsense mutation in his middle (M) wavelength cone pigment gene. During development, photoreceptors that express the mutant opsin gene will not produce pigment. The corresponding mutation in rods, in which functional rhodopsin is not produced results in a loss of rod photoreceptors.
Methods:The subject (JS) was identified as a dichromat by performance on standard color vision tests. Genetic analysis included real time quantitative PCR to estimate the relative numbers of L and M opsin genes, and the genes were directly sequenced. The subject's cone mosaic was imaged using an adaptive optics ophthalmoscope. A standard ophthalmic examination was completed including visual fields, autoflorescence imaging, OCT, and dilated fundus exam.
Results:Color vision test results on subject JS were consistent with deuteranopia. Real time quantitative PCR results indicated that JS had one L and one M opsin gene, and the sequencing data was consistent with this finding. A nucleotide substitution in the M opsin gene changed codon 149 from TGG (Tryptophan) to TGA (termination). OCT images revealed no significant differences from normal. Ophthalmic examination was normal. Adaptive optics imaging revealed decreased density and regularity as compared to normal trichromats and single-gene dichromats. Ophthalmic examination was unremarkable.
Conclusions:These results suggest that the failure to express opsin within cones leads to early cell death and during foveal development the surviving cones fill in the available space. The consequence for vision of the death of the M cone submosaic appears to be limited to a color vision deficiency.
Keywords: color pigments and opsins photoreceptors imaging/image analysis: non-clinical
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