Novel 5-HTTLPR Allele Associates with Higher Serotonin Transporter Binding in Putamen: A [11C] DASB Positron Emission Tomography Study

Background The serotonin transporter (5-HTT)-linked polymorphic region (5-HTTLPR) has two frequent alleles, designated long (L), and short (S). The S allele is associated with lower levels of 5-HTT mRNA and lower 5-HTT expression in human cell lines. A functional single nucleotide variant was detected within L, designated LA and LG. Only LA is associated with high levels of in vitro 5-HTT expression, whereas LG is low expressing and more similar to S. We examined the possible influence of the long (A/G) variant on 5-HTT density in the living human brain using 3-(11)C-amino-4-(2-dimethylaminomethylphenyl-sulfanyl) benzonitrile ([11C]DASB) positron emission tomography. Methods The 5-HTT binding potential (5-HTT BP), an index of 5-HTT density, was found in 43 healthy subjects genotyped for 5-HTTLPR long (A/G), and in an ethnically homogenous subsample of 30 Caucasian-Canadians. Results The LA/LA was associated with higher 5-HTT BP in putamen (p = .026, not corrected). This association became stronger in the Caucasian subsample (p = .004) and was significant even after correcting for multiple comparisons. Conclusions The 5-HTTLPR long (A/G) polymorphism influences 5-HTT density leading to higher putamen 5-HTT BP in healthy LA/LA carriers of Caucasian ancestry. This finding extends the role of this polymorphism from in vitro reports of higher 5-HTT expression with the LA/LA genotype into in vivo brains of healthy human subjects.