For instance, some studies in MDD patients have yielded evidence of a relationship between brain volume and genetic factors, including particularly brain-derived neurotrophic factor (BDNF) and methylenetetrahydrofolate reductase (MTHFR)/catechol-O-methyltransferase (COMT) polymorphisms[14–18]. The gene discussed is BDNF; the disease is major depressive disorder.