A new subset of deutan colour vision defect associated with an L/M visual pigment gene array of normal order and -71C substitution in the Japanese population

Abstract

In 524 Japanese individuals with deutan colour vision defect, 76 had a normal-order pigment gene array, where the L gene is at the first position and the M gene(s) is located downstream. Of these 76 individuals, 69 had a -71A>C substitution in the M gene without any other mutation. Because the expression of L/M genes is up-regulated by thyroid hormone (T3) in human retinoblastoma WERI cells, we examined the effects of T3 on promoter activity; T3 increased the activity of the -71A promoter 2-fold, but it had no effect on the -71C promoter. Similarly, the -71C promoter was much less activated by T3 than the -71A promoter in HEK293 cells expressing thyroid hormone receptor isoform β2. Such a weak response of the -71C promoter to T3 may cause a decrease in the number of M cones and/or the density of M pigment during the differentiation of M cones. The average Rayleigh match midpoint was 18.9 ± 4.1 in 162 ordinary deuteranomaly individuals, but was 37.3 ± 9.1 in 63 deuteranomaly individuals with -71C. The -71A>C substitution was found to be specific to eastern Asia. These results suggest that there may be a new subset of deuteranomaly associated with -71C in the Japanese (and probably eastern Asian) population(s).

Keywords: deutan; gene; opsin; promoter; thyroid hormone.