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J. Carroll, M. Neitz, J. Neitz; Spectral Sensitivity of Deuteranomalous Photopigments . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1906.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Deuteranomalous trichromacy is the most prevalent class of inherited color vision defect, affecting nearly 5% of men of European ancestry. Individuals with this defect lack functional middle-wavelength-sensitive (M) cone pigment, but are afforded varying degrees of color discrimination by the presence of two spectrally distinct types of long-wavelength-sensitive (L) cone pigment in their retina. In vivo estimates of the affects of amino acid changes on spectral tuning were obtained for L-pigment variants and this information was used to evaluate the distribution of spectral separations of the L pigments among deutans. Methods: The L genes for each deutan were amplified by long-distance polymerase chain reaction (PCR) in two separate reactions-one to amplify the first gene in the X-chromosome pigment gene array and one to amplify all other L genes in the array. Exons 2, 3 and 4 of each L gene were amplified and directly sequenced. The number and ratio of L and M genes in each subject’s array were estimated using real-time quantitative PCR. Spectral sensitivity functions were obtained from each subject using the flicker photometric electroretinogram (ERG). Results: Subjects were grouped based on the identity of polymorphic amino acid positions in their L pigments, and the effect of substitutions at these sites on spectral tuning was estimated. Most of the deutans (57 %) had L pigments that differed only at exon 2 encoded amino acid positions. Examining spectral sensitivity functions from these subjects indicates that on average a shift in lambda max of 2.5 nm is produced by substitutions in exon 2 of an L pigment gene. Previous work has shown that these substitutions produce no measurable spectral shift when present in an M-pigment gene. Substitutions in exon 3 or 4 of the L gene each produce an average shift in lambda max of 3.5 nm. We calculated the spectral separation of each subjects’ L pigments; the range was from 0.5 nm to 10 nm, with an average of 4 nm. Conclusions: Our results provide the first in vivo examination of spectral tuning by amino acid positions encoded by exon 2 of the L gene, and they indicate that there is large variability in the spectral separation of the L pigments among deuteranomalous trichromats.
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