SLC6A4 and major depressive disorder: The interactions between gene polymorphism HSPA1A (rs1008438), SLC6A4 (rs4795541), and BDNF (rs6265), or HSPA1A (rs1043618 and rs1008438), APOE (rs429358), and BDNF (rs6265) demonstrated a significant accumulation effect when associated with MDD (p = 0.016), supporting the idea that MDD may be associated with the interaction of multiple genetic pathways [23], as was seen in other studies [25, 32].