Serotonin transporter promoter gene polymorphism and long-term outcome of antidepressant treatment

Objective: This study investigates the relationship between the serotonin transporter linked polymorphic region (5-HTTLPR) and the long-term outcome of antidepressant treatment. Methods: One hundred and twenty-eight patients with major depressive disorder were evaluated for long-term outcome (up to 3 years) of antidepressant treatment. The severity and improvement of depression were assessed with the Clinical Global Impression scale. The genotypes of 5-HTTLPR in the patients were determined using polymerase chain reaction. Results: During the long-term treatment of antidepressants (1-3 years of treatment), clinical improvement of depressive symptoms was more significant for carriers of the long (I) allele [I/I and I/short (s) genotypes] than for those possessing the s/s genotype (P=0.025 at 1 year, P=0.005 at 2 years, P=0.005 at 3 years). A response to treatment was also significantly more frequent in carriers of the I allele than in those with the s/s genotype (P=0.015). Conclusion: These findings show that patients with major depressive disorder possessing the 5-HTTLPR I allele may exhibit a better long-term outcome when treated with antidepressants.