Sequence variants and haplotype analysis of serotonin transporter gene and association with bipolar affective disorder in Taiwan.

Objectives: Serotonin transporter (SLC6A4) is responsible for serotonin re-uptake into presynaptic terminals, thus fine-tuning brain serotonergic neurotransmission. Current studies have found associations of SLC6A4 polymorphisms with several psychiatric traits including bipolar affective disorder (BPD) in various populations; however, studies with contradictory results were also reported. This study examined the role of SLC6A4 in etiology of BPD in a Taiwanese population.

Methods: Ten markers including two variable number tandem repeat and eight single nucleotide polymorphisms (SNPs) on the SLC6A4 gene were used to study the genetic association with 90 unrelated BPD, type I patients and 103 controls.

Results: Two SNPs were not informative in a Taiwanese population and the other eight polymorphic markers were analyzed by Fisher's exact test and haplotype analysis. No association was detected for any single SLC6A4 marker and BPD. Additional statistic analyses including other factors also showed lack of association between the SLC6A4 gene polymorphisms and BPD. Significant linkage disequilibrium was obtained among eight SLC6A4 markers and eight common haplotypes were constructed that can be found in 95% of the total subjects. The four commonest haplotypes in both patients and controls were identical. However, the fifth commonest haplotype differed in patients and controls and was significantly associated with a protection from BPD.

Conclusions: This study suggested that a particular SLC6A4 haplotype harboring functional sequence variant could play a significant role in BPD etiology in Taiwan. However, due to its modest sample size, the conclusion is not final and should be confirmed in the future studies.