SEVERITY OF COLOR-VISION DEFECTS - ELECTRORETINOGRAPHIC (ERG), MOLECULAR AND BEHAVIORAL-STUDIES

Earlier research on phenotype/genotype relationships in color vision h as shown imperfect predictability of color matching from the photopigm ent spectral sensitivities inferred from molecular genetic analysis. W e previously observed that not all of the genes of the X-chromosome li nked photopigment gene locus are expressed in the retina. Since sequen ce analysis of DNA does not necessarily reveal which of the genes are expressed into photopigments, we used ERG spectral sensitivities and a daptation measurements,to assess expressed photopigment complement. Ma ny deuteranomalous subjects had L, M, and L-M hybrid genes. The ERG re sults showed that M pigment is not present in measurable quantities in deutan subjects. Using these results to determine gene expression imp roved the correlations between inferred pigment separation and color m atching. Furthermore, we found a subject who had normal L and M genes and normal proximal promoter sequences, yet he had a single photopigme nt (M) by ERG and tested as a protanope. These results demonstrate the utility of ERG measurements in studies of molecular genetics of color vision deficiencies, and further support the conclusion that not all genes are expressed in color deficient subjects. In particular, deuter anomaly requires a presently unknown mechanism of selective expression which excludes normal M genes and allows expression of L-M hybrid gen es in one cone type, and the normal L in another. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.