No association between genotype of the promoter region of serotonin transporter gene and serotonin transporter binding in human brain measured by pet

The human serotonin transporter (5-HTT) gene has a polymorphism in the 5′-flanking promoter region that is called the serotonin transporter gene-linked polymorphic region (5-HTTLPR). In lymphoblast cell lines, the promoter activity of the 5-HTT gene is dependent on 5-HTTLPR allelic variants. The transcriptional activity of the l allele was more than twice as high as that of the s allele. The s allele is considered to be associated with mood disorders and anxiety-related personality traits. To evaluate the functional differences of 5-HTTLPR in the brain in vivo, we examined the allelic variations of 5-HTTLPR and measured 5-HTT binding in the living human brain using positron emission tomography (PET) with C¹¹-labeled trans-1, 2, 4, 5, 6, 10-β-hexahydro-6-[4-(methylthio) phenyl]pyrrolo[2,1-a]isoquinoline (McN5652) as a ligand. Twenty- seven healthy male subjects participated in this study. Although the human lymphoblast cells with the l/l genotype was reported to produce higher concentrations of both mRNA and protein of 5-HTT than those with the l/s or s/s genotype in a human lymphoblast in vitro study, 5-HTT binding in vivo was not significantly different among subjects with the three genotypes (l/l: 0.842 ± 0.184, l/s: 0.708 ± 0.118, s/s: 0.825 ± 0.209). In conclusion, this study does not support the assumption that the genotype-dependent differences of 5-HTTLPR directly contributes to the regulation of the 5-HTT binding site in the living human brain.