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S. Muraki, H. Ueyama, S. Tanabe, S. Yamade, M. Ohji; Analysis of L-Cone/M-Cone Visual Pigment Genes in Japanese Color-Vision Deficient Men With a Normal Array. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1647.
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We have studied L-cone/M-cone visual pigment genes in Japanese men with congenital color-vision deficiency and found that some subjects had a normal array of one L gene followed by an M gene(s). In this study, we analyzed the L and M genes in the subjects with a normal array to determine the causes of their color-vision deficient phenotype.
Genomic DNA was extracted from 531 Japanese men with congenital color-vision deficiency (148 protans and 383 deutans). The promoter and exon 5 of the L/M genes were amplified to estimate the gene numbers and L/M gene ratios, respectively. When there was more than one gene and both the L and M genes were detected, the first gene and downstream genes of an array were amplified separately by long-range polymerase chain reaction and the products were analyzed for exon 5. Promoter activity was assessed by transfection using a luciferase reporter plasmid and a human retinoblastoma cell line, WERI-Rb1.
Among the 531 subjects, we identified 61 (8 protan, 53 deutan) subjects (11.5%) with a normal L/M gene array. Among the 8 protan subjects, 3 had a missense mutation in the L gene at the first position of the array; the other 5 had no missense mutations in the promoter or exons. In those 5 subjects, every portion of introns 1-5 was amplified and sequenced, and no significant mutations were found. Among the 53 deutan subjects, 2 had a missense mutation and 1 had a deletion in the M gene at the second position of the array. In the remaining 50 subjects, 47 had an A-71C substitution in the promoter of the M gene; the other 3 had no missense mutations in the promoter or exons. Every portion of intron 1-5 in 3 subjects, who had been randomly selected from the 47 subjects with -71C, was amplified and sequenced, and no common mutations were found. Promoter activity of the downstream gene promoter with -71C was 30-40% of that of the promoter with -71A, which was comparable to the promoter activity of the first gene promoter.
We found 5 missense mutations and 1 deletion believed to be closely related to color-vision deficiency. In the 47 deutan subjects with the substitution A-71C, no mutations in tight linkage with the substitution were found in introns 1-5. The low activity of the promoter with -71C compared to that with -71A suggested that the substitution itself might have caused the color-vision deficient phenotype.
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