Both let‐7c and let‐7b are involved in the expression regulation of insulin‐like growth factor 1 (IGF‐1) gene in the PI3K‐Akt‐mTOR (phosphatidylinositol trihydroxykinase–protein kinase B‐mammalian target of rapamycin) signaling pathway and are significantly downregulated in patients with major depressive disorder (MDD) as compared to healthy subjects. The gene discussed is IGF1; the disease is major depressive disorder.