The serotonin transporter gene (5-HTT) is considered as a candidate gene for BPD as multiple lines of evidence have suggested that it plays an important role in suicide, impulsive behaviour, and emotional liability.ompared with healthy controls, patients with BPD showed higher frequencies of the 10 repeat of the VNTR marker and the S-10 haplotype, and fewer 12 repeat and L A -12 haplotype. These results suggest that the serotonin transporter gene may play a role in the aetiology of BPD.