SLC6A4 and Anxiety: Further support for the aforementioned is reflected in findings of gene x gene and gene x gene x environment interactions which are indicative of significant interaction effects of the BDNF Val66Met polymorphism and the serotonin transporter gene (SLC6A4) on anxiety-related traits (e.g. neuroticism and harm avoidance) (Arias et al., 2012; Terracciano et al., 2010) and depressive symptoms and disorder (Gutiérrez et al., 2015; Kaufman et al., 2006).