Evidence for a combined genetic effect of the 5-HT1A receptor and serotonin transporter genes in the clinical outcome of major depressive patients treated with citalopram

In the context of a long-term follow-up study, we analysed the possible implication of the 5-HT_1A receptor gene (HTR1A) -1018C/G polymorphism in the clinical outcome of major depressive patients treated with citalopram. We had previously reported an association between variation on the SERT gene (SLC6A4) and clinical remission after citalopram treatment. In the present 12-week follow-up study, the combined effect of HTR1A and SLC6A4 genes in clinical outcome and response to citalopram was also evaluated. The sample consisted of 130 patients, all of Spanish origin, who were diagnosed as having a current major depressive episode according to DSM-IV criteria. A 21-item Hamilton Depression Rating Scale was used to assess severity of symptoms at the beginning and during the follow-up to determine the outcome and remission status at week 12. Patients were genotyped for HTR1A gene and, in addition, for two polymorphisms at the CYP2C19 gene, which together account for the 87% of the Caucasian poor metabolizer phenotype. Data were analysed adjusting for the effect of poor metabolizers in clinical response. No independent effect was found for the 5-HT_1A receptor gene in relation to clinical outcome or remission after citalopram treatment. However, a combined genetic effect of HTR1A and SLC6A4 genes was found to influence the clinical outcome of patients [F(4,102) = 2.89, p= 0.02]. When considering the remission status, an increase of patients carrying the risk genotype combination (S/S-G/G) was found among those subjects who did not reach remission (Fisher’s exact test = 0.009). Our results suggest that the combined effect of the serotonin transporter and the 5-HT_1A receptor genes could be related to the clinical outcome of depressive patients treated with citalopram.