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J Mol Neurosci. 2005;27(2):219-24.

Allelic association analysis of the functional insertion/deletion polymorphism in the promoter region of the serotonin transporter gene in bipolar affective disorder.

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PROGENE (LIM 23), Institute of Psychiatry, University of São Paulo Medical School, São Paulo, Brazil, and Section of General Hospital Psychiatry, Institute of Psychiatry, King's College London, UK.


The human serotonin transporter gene (5-HTT) is a candidate for the pathogenesis of mood disorders, including bipolar disorder (BPD). The 5-HTT gene has a 44-bp insertion/deletion polymorphism within the promoter region (5-HTTLPR) with 2 allelic forms, the long (l) and the short (s) variants, which affect transcriptional rates of the 5-HTT gene. Association between the low-activity s variant and BPD has been suggested but remains controversial, as replication has not been consistent. In the present study, we examined the frequency of this polymorphism in a group of 266 Brazilian BPD patients and 306 control subjects. Genotyping for the 5-HTTLPR was performed using PCR. The allele frequencies were found to differ between BPD patients and controls (p=0.03), with a higher frequency of the l allele in the patients compared with the controls (60.5% vs 54.4%). The distribution of genotypes also differed significantly between cases and controls (chi2=10.4, 2 df, p=0.005), with higher frequency of heterozygous l/s genotype in the BPD patient group (52.6% vs 44%). Because prior evidence from gene expression studies indicated that l/s and s/s genotypes are not distinguishable biochemically, we compared the distribution of the l/l genotype and the combined group l/s plus s/s between case and controls, but there was no significant difference (chi2=0.22). Likewise, a logistic regression model considering a dominant role for the s variant was not significant (OR=0.92, 95% CI 0.64-1.32). Our results suggest that the low-activity s variant does not influence susceptibility to BPD in our population.

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