Interestingly, our replication results appeared to be sex or population specific. For example, the SNPs at FRMD4A and RGS17 were replicated only in the male group of the EA sample. An SNP at 7q31.1 was replicated in the total AA sample but not the EA sample. The analysis result suggests that FRMD4A and RGS17 are associated with ND and SI in a sex-specific manner in conjunction with environmental and epigenetic factors. The complex interaction of genetic, environmental, and epigenetic factors may contribute to the disparity of the results for the total and male samples in the replication study. The discrepancy between the results of the EA and AA samples in the replication samples may be secondary to differences in genetic architecture across populations. For example, two ND-associated SNPs, rs1404697 and rs848353 at 7q31.1, are 4.0 kb apart. The two variants are highly correlated in the Korean population (r2 = 0.98) and the European population (r2 = 0.85, HapMap CEU). However, a low correlation was observed in an African population (r2 = 0.013, HapMap YRI). As shown in Table 2, rs848353
