Rationale: Serotonin transporter (5-HTT) gene polymorphisms are linked with antidepressant response to selective serotonin reuptake inhibitor drugs (SSRIs), though the favorable allelic variant differs by ethnic group (Caucasian versus Korean or Japanese). In Caucasian patients, response also is linked to measures of platelet 5-HTT function.
Objectives: Here, we study both 5-HTT gene polymorphisms and 5-HTT function as determinants of antidepressant response to SSRIs in Korean patients.
Methods: We enrolled 99 patients with major depression and 48 control subjects. For statistical power, both samples were enriched with the l/l 5-HTTLPR polymorphism, which is uncommon in Koreans. Patients were treated with fluoxetine or sertraline. Response was assessed at 6 weeks. Subjects were genotyped for s/l polymorphism in the 5-HTT promoter region (5-HTTLPR). Platelet 5-HTT activity was determined as maximal uptake rate (Vmax) and affinity constant (Km).
Results: Response was differentially associated with the s allele of 5-HTTLPR, which also was significantly associated with Vmax. These associations are opposite to those reported in Caucasian populations. Responders had significantly higher Vmax and Km than nonresponders. In Koreans as well as Caucasians, high Vmax is related to antidepressant response to SSRIs, though the 5-HTTLPR polymorphism associations with both response and function differ by ethnicity.
Conclusions: Both ethnicity and function must be considered in evaluating candidate gene biomarkers of response to SSRIs in depression.