Within the central 5-HT system, the serotonin transporter (5-HTT) is thought to regulate the magnitude and duration of serotonergic signaling by governing the reuptake of serotonin from the synaptic junction. The transporter is encoded by a single gene, the solute ligand carrier family 6 (neurotransmitter transporter, serotonin) member A4 (SLC6A4), on chromosome 17q11.1-q12, the promoter region of which contains a 44-bp insertion/deletion polymorphism, also known as the 5-HTTLPR. Research suggests that the long (l) allele of this polymorphic region is more than twice as active as the short (s) allele (Heils et al., 1996; Lesch et al., 1996), resulting in increased transcription of the serotonin transporter, and the potential for increased reuptake of serotonin from the synaptic cleft, and overall lower levels of serotonin in the synapse (Murphy et al., 2001), though not all studies have reported this functional relationship in humans (Shioe et al., 2003; Willeit et al., 2000). The 5-HTTLPR has been linked to alcohol abuse, schizophrenia, depression, bipolar disorder, and smoking, though with inconsistent results (Serretti, Calati, Mandelli, & De, 2006). Based on the literature, it seems
