POLYMORPHISM IN SEROTONIN TRANSPORTER GENE ASSOCIATED WITH SUSCEPTIBILITY TO MAJOR DEPRESSION

Background The serotonin transporter of the brain provides the primary target for the action of selective antidepressant drugs. We set out t o identify polymorphisms of the serotonin transporter gene and to find out whether there was a relation between any such polymorphisms and t he occurrence of affective disorder. Methods A comparison of a polymor phic region of the human serotonin transporter gene was carried out be tween two groups. The study group comprised 83 patients (39 unipolar d epressive disorder, 44 bipolar disorder) with major affective disorder . The control group comprised 122 anonymous blood donors, and 71 volun teers who had been screened for psychiatric disorders. Findings We det ected three novel alleles of the variable-number-tandem-repeat (VNTR) region (STin2.9, STin2.10, and STin2.12) containing nine, ten and 12 c opies of the VNTR element, respectively. The frequencies of the differ ent forms of the allele in the control group were compared with those in the affective disorder group. There was a significant difference be tween the control and affective disorder groups, largely explained by the excess of the STin2.9 allele in the unipolar group (chi(2)=10.05, p<0.004 [Bonferroni corrected]). The presence of the allele with nine copies of the repeat was significantly associated with risk of unipola r disorder (odds ratio=6.95 [95% CI 1.8-27.2]). Interpretation This as sociation, for an obvious candidate gene, may provide a critical start ing point for an understanding of the likely polygenic contributions t owards susceptibility to affective disorder.