Paper short abstract:

Humans show various responses to the environmental stimulus, “physiological polytypisms.” In this study, we examined an association between the physiological polytypism of response to light stimulus and genetic polymorphism(s), and found that the ratios of melatonin suppression were evidently related to the PER2 haplotypes.

Paper long abstract:

Various responses to the environmental stimulus in the individual level of humans are called “physiological polytypisms.” However, it has been unclear if these are regulated by genetic variations. In this study, we measured ratios of melatonin suppression of 43 Japanese subjects under light-stimulus in constant darkness, and genotyped 6 SNPs in the PER2 gene, which is one of important clock genes related to human circadian rhythm, for the subjects and 145 non-subject Japanese.

Three common haplotypes accounted for more than 95 % of the subjects, and one of the haplotypes had a significantly low sensitive response to light-stimulus (p < 0.01) than the others. The homozygote of the low-sensitive haplotype showed significantly lower rates of melatonin suppression (p < 0.05), and the heterozygotes of the haplotypes varied their ratios. Comparing with the global haplotype frequencies, the low-sensitive haplotype was more frequent in Africans than in non-Africans, and came to the root in the phylogenetic tree.

These results suggest that (1) the physiological polytypisms for light-stimulus is evidently related to the PER2 polymorphisms, and that (2) the haplotype with low-sensitive response is the ancestral type, whereas the other haplotypes with high sensitivity to light are the derived types, suggesting that the high-sensitive haplotypes have spread to the world after out-of-Africa migration of modern humans.