In humans, the reduction of SERT binding in the brain has been suggested as a putative biomarker of depression (Selvaraj et al., 2011; Newberg et al., 2012) since several neuroimaging studies have shown a reduction in SERT binding in different brain areas from drug-naïve depressed patients (Malison et al., 1998; Parsey et al., 2006; Joensuu et al., 2007; Selvaraj et al., 2011; Newberg et al., 2012). Here, SLC6A4 is linked to depressive symptom measurement.