Since miRNA may regulate central nervoussystem functions such as cognitive function and reward feedback, we hypothesizedthat with the extension of disease course, changes in miRNA-451a, miRNA-34a-5p, andmiRNA-221-3p expression may cause the deterioration of the central nervous system.Studies have shown that reduced BDNF plays an important role in depression andsuicidal behavior (34). This evidence concerns the gene BDNF and major depressive disorder.