Clinical Pharmacogenomics of Antidepressant Response

The study includes two components：(1) cross-sectional (Study I), and (2) longitudinal treatment trial (Study II). The cross-sectional component will include all subjects initially recruited for the parent project. Genotyping characteristics will be compared with clinical status (i.e., recovered vs symptomatic). The treatment trial component (one) will include a subset of the subjects (n = 400) who remain significantly depressed. They will be randomly assigned to 8-weeks of treatment with either citalopram or paroxetine. With such a design, we wish to test the following hypotheses： Ⅰ. Depressed patients with the short variant of the serotonin transporter (5HTTLPR) will respond faster and better to antidepressants compared to their counterparts with the long variant. Concurrently, patients with the 5-HTT Stin2 12/12 allele will also show better response as compared to those with the 10/12 allele. Ⅱ. Depressed patients who are homozygous for deficient or less active CYP2D6 or CYP2C19 enzyme(s) will be more likely to show treatment emergent side effects compared to subjects with the wildtype alleles. Specifically, in Study II, CYP2D6 polymorphism will predict PAR but not CIT side effects and CYP2C19 polymorphism will be associated with CIT but not PAR side effects.