A significant inverse correlation between the FA values of the body of the corpus callosum and SLC6A4 DNA methylation at CpG3 was observed for patients with MDD (Pearson's correlation: r=−0.493, P=0.003; Table 4 and Figure 3), in conjunction with a marginally significant inverse correlation at CpG4 (Pearson's correlation: r=−0.438, P=0.01; Table 4). This evidence concerns the gene SLC6A4 and major depressive disorder.