FGF4 and major depressive disorder: However, growth hormone (GH), fibroblast growth factor 4 (FGF-4), transforming growth factor 1β (TGF-1β), and endocrine gland-derived vascular endothelial growth factor (EG-VEGF), all of which are involved in intestinal mucosal repair, are underexpressed in patients with MDD compared to HCs (Fig. 1E).