Two distinct variable number tandem repeats (VNTRs) within the human serotonin transporter gene (SLC6A4) have been implicated as predisposing factors for CNS disorders. The first termed linked polymorphic region (LPR) located in the 5' promoter exists as two common alleles, short (s) and long (l) of a repeated 22 or 23bp element. The second VNTR in intron 2 (Stin2) exists as three common allelic variants containing 9, 10, or 12 copies of a repeated 16 or 17 bp element. Both of these VNTRs have previously been demonstrated to act as transcriptional regulators based on copy number and sequence. These two VNTR domains often correlate with the same clinical conditions.