With regard to interactions, we received a significant result for the groups (PUD MDD vs. controls) on the NEO FFI Conscientiousness Scale, and DRD4 exon 3 (Ex3) (Figure 2, F2,389 = 5.24, p = 0.006) accounted for 2.6% of the variance (Table 5). Here, DRD4 is linked to major depressive disorder.