Previous fMRI studies have identified increased activity in dorso-lateral prefrontal cortex (DLPFC) and decreased amygdala activity from the baseline as imaging markers of antidepressant response in patients with MDD. However, these studies have examined MDD as a homogenous group without specifying the type of patient group, and brain regions as a priori hypothesis.We therefore need studies using combined genetics and neuroimaging measures as biomarkers in the prediction and evaluation of clinical response to antidepressants. In this study we attempted to determine imaging clinical efficacy markers in previously defined brain regions (amygdala and prefrontal regions) for two classes of antidepressants (citalopram and quetiapine extended release (XR)) with differential action on serotonin transporter inhibition in a subgroup of MDD patients with high risk allele ( S/Lg) of serotonin transporter gene polymorphism.