A replication study confirmed the EDAR gene to be a major contributor to population differentiation regarding head hair thickness in Asia

Hair morphology is a highly divergent phenotype among human populations. We recently reported that a nonsynonymous SNP in the ectodysplasin A receptor (EDAR 1540T/C) is associated with head hair fiber thickness in an ethnic group in Thailand (Thai-Mai) and an Indonesian population. However, these Southeast Asian populations are genetically and geographically close, and thus the genetic contribution of EDAR to hair morphological variation in the other Asian populations has remained unclear. In this study, we examined the association of 1540T/C with hair morphology in a Japanese population (Northeast Asian). As observed in our previous study, 1540T/C showed a significant association with hair cross-sectional area (P = 2.7 x 10(-6)) in Japanese. When all populations (Thai-Mai, Indonesian, and Japanese) were combined, the association of 1540T/C was stronger (P = 3.8 x 10(-10)) than those of age, sex, and population. These results indicate that EDAR is the genetic determinant of hair thickness as well as a strong contributor to hair fiber thickness variation among Asian populations.