Single-nucleotide polymorphisms (SNPs) in TPH2 gene are linked to 5-HT dysfunction (Gao et al., 2012), which have been associated with MDD (Zill et al., 2004; Zhang et al., 2005), and one of the SNPs in the TPH2 gene is associated with amygdala and hippocampal volume (Inoue et al., 2010). The gene discussed is TPH2; the disease is major depressive disorder.