Five candidate genes (LYPD1, HMBS, HEBP2, SETD3, and ECM2) capable of distinguishing BD from MDD were obtained by a crossover in the Venn diagram (Fig. 7D), and the PPI network was constructed using these five candidate genes, among which Physical Interactions made up 77.64%, and Co-expression made up 8.01%. The gene discussed is HMBS; the disease is major depressive disorder.