With regard to interactions, we found a significant result for the groups (PUD MDD vs. controls) on the NEO FFI Extraversion Scale, and DRD4 exon 3 (Ex3) (Figure 1, F2,389 = 4.22, p = 0.015) accounted for 2.1% of the variance (Table 5). The gene discussed is DRD4; the disease is major depressive disorder.