This genomic sequence represents the 5\' regulatory region of the solute carrier family 6 member 4 (SLC6A4) gene on chromosome 17. It includes the gene promoter and a polymorphic region known as 5-HTTLPR, which is located approximately 1 kb upstream of the major transcription start site. The polymorphic region is composed of 16 tandemly-repeated units in the long (L) allele, where each repeat unit is 20-23 bps in length. Deletion of repeat units 6-8 results in a short (S) allele. Single nucleotide polymorphisms, including rs25531 and rs25532, have also been identified in this region. The 5-HTTLPR region has both positive- and negative-acting cis-regulatory components in SLC6A4 promoter activity assays, and the L and S alleles also display allele-dependent promoter activity. Due to the role of the SLC6A4 gene in serotonin reuptake, a large number of studies have associated the 5-HTTLPR, rs25531 and rs25532 polymorphisms with a variety of mood, behavioral and stress-related psychopathologies. However, these associations are complex and may be population-dependent, and/or related to epigenetic processes or other known polymorphisms, including the STin2 variable number tandem repeat (VNTR) that overlaps an enhancer element in an SLC6A4 intron. This genomic sequence also includes an accessible chromatin region used in a lentiviral ReSE (repressive ability of silencer elements) screen that assays for cell survival based on transcriptional repression of an apoptosis-inducing fusion protein. That subregion was identified as a functional silencer in phorbol 12-myristate 13-acetate-treated (for megakaryocytic differentiation) K562 erythroleukemia cells. [provided by RefSeq, Apr 2023]