TGFB1 and major depressive disorder: The causal factors considered in this article are only those that are modifiable by a therapeutic intervention, and they are cerebrovascular impairment, circadian rhythm abnormalities, depression, diabetes mellitus, hyperlipidemia, hypertension, being underweight, malnutrition including deficiencies of folate and vitamin D, metabolic syndrome, mitochondrial abnormalities, TGF-β deficiency, and WNT/β-catenin deficiency.