Individual variations in color vision and its molecular biology
by
Kitahara K.
Department of Ophthalmology,
Jikei University School of Medicine, Tokyo, Japan.
Nippon Ganka Gakkai Zasshi. 1998 Dec;102(12):837-49.
ABSTRACTIndividual variations in normal color vision and congenital red-green color vision defects in Japanese males were investigated using both psychophysics and molecular biology techniques. 1. Normal color vision. We studied 72 Japanese males who were diagnosed as having normal color vision using the Ishihara plates test and Nagel model I anomaloscope. The structure of the gene arrays of the X-linked L- and M-pigment genes was determined using quantitative PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism). We found the following variations of the number of M-pigment genes: 27 (38%) of these men had only one M-pigment gene, 29 (40%) had two, 13 (18%) had three and 3 (4%) had four. Two common polymorphisms were found at amino acid residue 180 of both L- and M-opsin, of the total 56 (78%) were Ser and the other 16 (23%) were Ala in the L-pigment and of the total 65 (90%) were Ala and the other 7 (10%) were Ser in the M-pigment. The Rayleigh match midpoints fell within the normal range, however there were two fairly distinct groups with consistent differences in each group. The mean values of the proportion of red in a mixture of red and green were 0.564 +/- 0.026 (mean +/- standard deviation). Correlation was found only between the Rayleigh match midpoint and the polymorphism at residue 180 of L-pigment. In order to estimate the variations of L/M cone ratio in the retinae the spectral sensitivities using heterochromatic flicker method were measured. Using the hypothesis that the luminosity function is proportional to the sum of L- and M-cone spectral sensitivity (k L (lambda) + M (lambda)), the constant k values were obtained. The k values for the subjects with Ser180 and Ala180 L-pigment were 1.89 +/- 1.44 and 1.85 +/- 1.02 respectively. Furthermore, in order to study the variation of information processing system, the spectral sensitivities for 1 degree, 200-ms test flash on a white background were measured. Using the hypothesis that the spectral sensitivity is proportional to the difference of L- and M-cone spectral sensitivity (L (lambda) - k' M (lambda)), the k' values were obtained. The k' values for the subjects with Ser180 and Ala180 L-pigment were 1.38 +/- 0.06 and 1.49 +/- 0.07 respectively. As a result, it was suggested that there are individual variations in both the L/M cone ratio and the color opponent system. 2. Congenital red-green color vision deficiencies. We studied the structure of the gene arrays of the X-linked L- and M-pigment genes and investigated the relationship between genotype and phenotype in 21 Japanese males comprising 4 protanopia, 6 protanomaly, 7 deuteranopia and 4 deuteranomaly. All of the protan subjects had 5' L-M fusion gene with/without the M gene. All of the deutan subjects had a normal L gene with/without 5' M-L fusion gene. Genotype agreed with phenotype in 8 of 10 protan subjects and 10 of 11 deutan subjects. Two of them were diagnosed as abnormal trichromatism in spite of having only one gene. One of them was diagnosed as dichromatism in spite of having two genes that encoded spectrally different pigments. As a result, it was felt that the diagnosis of dichromacy and abnormal trichromacy with an anomaloscope has limitations.Colour-blindness
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