Functional variation in the 3′ untranslated region of the serotonin transporter in human and rhesus macaque

Association of serotonin system-related genes with homicidal behavior and criminal aggression in a prison population of Pakistani Origin

The serotonin transporter (SLC6A4), 5-HT_2A (HTR2A) and 5-HT_2B (HTR2B) recepter genes, express proteins that are important regulators of serotonin reuptake and signaling, and thereby may contribute to the pathogenesis of aggressive criminal behavior. 370 sentenced murderers in Pakistani prisons and 359 men without any history of violence or criminal delinquency were genotyped for six candidate polymorphisms in SLC6A4, HTR2A and HTR2B genes. An association of higher expressing L/L and L_A/L_A variants of the 5-HTTLPR polymorphism was observed with homicidal behavior (bi-allelic: OR = 1.29, p = 0.016, tri-allelic: OR = 1.32, p = 0.015) and in the murderer group only with response to verbal abuse (OR = 2.11, p = 0.015), but not with other measures of self-reported aggression. L/L and L_A/L_A genotypes of the 5-HTTLPR polymorphism were associated with higher aggression scores on STAX1 scale of aggression compared to lower expressing genotypes (S/S, S/L_G, L_G/L_G) in prison inmates. No associations were apparent for other serotonergic gene polymorphisms analyzed. Using the Braineac and GTEx databases, we demonstrated significant eQTL based functional effects for rs25531 in HTTLPR and other serotonergic polymorphisms analyzed in different brain regions and peripheral tissues. In conclusion, these findings implicate SLC6A4* HTTLPR as a major genetic determinant associated with criminal aggression. Future studies are needed to replicate this finding and establish the biologic intermediate phenotypes mediating this relationship.

SNP rs2240688 in CD133 gene on susceptibility and clinicopathological features of hepatocellular carcinoma

Background

CD133 is one of the important cancer stem cells (CSCs) markers of hepatocellular carcinoma (HCC). The aim of this study was to explore the relationship between CD133 single-nucleotide polymorphisms (SNPs) and risk factors associated with HCC susceptibility and clinicopathological features in HCC cases and healthy controls from the Guangxi region of southern China.

Methods

A case control study was conducted, including 565 HCC patients and 561 control subjects. The genotyping of rs2240688 was performed using the SNaPshot method. Unconditional logistic regression was used to correct for gender, age, and other confounding factors. Odds ratio (OR) and its 95% confidence interval (CI) were calculated to analyze the relationship between allele and genotype frequency and the risk of HCC.

Results

The distribution frequencies of CD133 alleles and genotypes in the HCC case group and the control group were statistically significant (P<0.05). The CA heterozygous (P=0.003, OR =1.463, 95% CI: 1.134–1.887) and CC homozygous genotypes (P=0.036, OR =1.910, 95% CI: 1.044–3.493), as well as C carrier status (P=0.004, OR =1.465, 95% CI: 1.136–1.889) and C alleles (P=0.004, OR =1.465, 95% CI: 1.136–1.889), were associated with an increased risk of HCC. Additionally, in the subgroup analysis of CD133 rs2240688 polymorphism and clinical characteristics, the results showed that the genotype distribution of CD133 rs2240688 was significantly different in genotype distribution of metastasis and alanine aminotransferase (ALT).

Conclusions

the expression of miRNA binding site rs2240688 of tumor stem cell marker gene CD133 in HCC may be a promising marker for the prediction of HCC, but larger studies are still needed.

The behavioral genetics of nonhuman primates: Status and prospects

The complexity and diversity of primate behavior have long attracted the attention of ethologists, psychologists, behavioral ecologists, and neuroscientists. Recent studies have advanced our understanding of the nature of genetic influences on differences in behavior among individuals within species. A number of analyses have focused on the genetic analysis of behavioral reactions to specific experimental tests, providing estimates of the degree of genetic control over reactivity, and beginning to identify the genes involved. Substantial progress is also being made in identifying genetic factors that influence the structure and function of the primate brain. Most of the published studies on these topics have examined either cercopithecines or chimpanzees, though a few studies have addressed these questions in other primate species. One potentially important line of research is beginning to identify the epigenetic processes that influence primate behavior, thus revealing specific cellular and molecular mechanisms by which environmental experiences can influence gene expression or gene function relevant to behavior. This review summarizes many of these studies of non-human primate behavioral genetics. The primary focus is on analyses that address the nature of the genes and genetic processes that affect differences in behavior among individuals within non-human primate species. Analyses of between species differences and potential avenues for future research are also discussed.

Serotonin transporter variants play a role in anxiety sensitivity in South African adolescents

OBJECTIVES

Anxiety sensitivity (AS) has predictive potential for the development of anxiety disorders. We investigated the role that gene-environment (G × E) interactions, focussing on childhood trauma (CT) and selected SLC6A4 variants, play in modulating levels of AS in a South African adolescent population.

METHODS

All adolescents (n = 951) completed measures for AS and CT. Six SLC6A4 polymorphisms were genotyped. G × E influences on AS levels were assessed using multiple linear regression models. Relevant confounders were included in all analyses.

RESULTS

Xhosa (n = 634) and Coloured (n = 317) participants were analysed independently of one another. The 5-HTTLPR-rs25531 L-G haplotype associated with reduced AS among Xhosa adolescents (P = 0.010). In addition, the rs1042173 CC-genotype protected against increased levels of AS in Xhosa participants who had experienced increased levels of CT (P = 0.038). Coloured males homozygous for the S-allele had significantly increased levels of AS compared to Coloured males with at least one L-allele (P = 0.016).

CONCLUSIONS

This is the first study to be conducted on AS in adolescents from two ethnically diverse populations. Results indicate that the L-G haplotype confers protection against high AS levels in a Xhosa population. Furthermore, increased CT was found to protect against high levels of AS in Xhosa rs1042173 CC-carriers.

The population genomics of rhesus macaques (Macaca mulatta) based on whole-genome sequences

Rhesus macaques (Macaca mulatta) are the most widely used nonhuman primate in biomedical research, have the largest natural geographic distribution of any nonhuman primate, and have been the focus of much evolutionary and behavioral investigation. Consequently, rhesus macaques are one of the most thoroughly studied nonhuman primate species. However, little is known about genome-wide genetic variation in this species. A detailed understanding of extant genomic variation among rhesus macaques has implications for the use of this species as a model for studies of human health and disease, as well as for evolutionary population genomics. Whole-genome sequencing analysis of 133 rhesus macaques revealed more than 43.7 million single-nucleotide variants, including thousands predicted to alter protein sequences, transcript splicing, and transcription factor binding sites. Rhesus macaques exhibit 2.5-fold higher overall nucleotide diversity and slightly elevated putative functional variation compared with humans. This functional variation in macaques provides opportunities for analyses of coding and noncoding variation, and its cellular consequences. Despite modestly higher levels of nonsynonymous variation in the macaques, the estimated distribution of fitness effects and the ratio of nonsynonymous to synonymous variants suggest that purifying selection has had stronger effects in rhesus macaques than in humans. Demographic reconstructions indicate this species has experienced a consistently large but fluctuating population size. Overall, the results presented here provide new insights into the population genomics of nonhuman primates and expand genomic information directly relevant to primate models of human disease.

Polymorphism of rs3813034 in Serotonin Transporter Gene SLC6A4 Is Associated With the Selective Serotonin and Serotonin-Norepinephrine Reuptake Inhibitor Response in Depressive Disorder: Sequencing Analysis of SLC6A4

Selective serotonin and serotonin-norepinephrine reuptake inhibitors (SSRI/SNRI) are commonly used for treating major depression. Regretfully, significant heterogeneity exists regarding the benefits of SSRI/SNRI in individual cases. We previously reported that a polymorphism located in the serotonin transporter linked promoter region (5-HTT LPR) is associated with an interindividual difference in SSRI treatment efficacy. However, this explains only a small part of the variation of this complex phenotype. Other 5-HTT variants in the coding regions, 3' untranslated region (3' UTR), and introns adjacent to each exon could also contribute to treatment response. Therefore, we performed a sequencing analysis of the SLC6A4 gene (coding for 5-HTT) and investigated the association between variants detected in this study and the antidepressant response to SSRI/SNRI in 201 Japanese depressive patients. Seventeen novel mutations were identified by sequencing analysis. We found that the polymorphism G2563T (rs3813034) as a tag single-nucleotide polymorphism of IVS9 A-90G (rs140701), G2356T (rs1042173), and A3641C (rs7224199) is associated with interindividual variability of SSRI/SNRI efficacy at week 6, independent from clinical variables and effect of 5-HTT LPR (P < 0.001 by multiple regression analysis). This polymorphism could help determine individualized SSRI/SNRI treatments for depressive patients in combination with 5-HTT LPR.

Studying longitudinal trajectories in animal models of psychiatric illness and their translation to the human condition

Many forms of psychopathology and/or psychiatric illness can occur through the pathways of altered environmental sensitivity, impulsivity, social functioning, and anxious responding. While these traits are also heritable, environmental conditions are known to play a critical role. The genetic factors that contribute to these traits may be adaptive in certain contexts, but can - under the environmental conditions commonly faced among modern humans - also be key moderators of risk for psychopathological outcomes. This article will discuss how animal studies inform us of the various environmental mechanisms through which prenatal or early postnatal environmental challenge can produce long-term effects on behavior and will briefly address how pre-copulatory, pre-natal and early postnatal epigenetic effects can contribute to persistent alterations in offspring behavior. Its main focus will be how nonhuman primate studies have helped us to understand how genetic vulnerability factors can moderate responses to early environmental factors, suggesting pathways through which early stress might produce long-term effects, thus pointing to systems that might moderate risk for psychiatric illnesses in humans.

Neurogenetics of aggressive behavior: studies in primates

Aggressive behavior can have adaptive value in certain environmental contexts, but when extreme or executed inappropriately, can also lead to maladaptive outcomes. Neurogenetic studies performed in nonhuman primates have shown that genetic variation that impacts reward sensitivity, impulsivity, and anxiety can contribute to individual differences in aggressive behavior. Genetic polymorphisms in the coding or promoter regions of the Mu-Opioid Receptor (OPRM1), Corticotropin Releasing Hormone (CRH), Monoamine Oxidase A (MAOA), Dopamine D4 Receptor (DRD4), and Serotonin Transporter (SLC6A4) genes have been shown to be functionally similar in humans and rhesus macaques and have been demonstrated to contribute to individual differences in aggression. This body of literature suggests mechanisms by which genetic variation that promotes aggressivity could simultaneously increase evolutionary success while making modern humans more vulnerable to psychopathology.

The evolutionary history of SLC6A4 and the role of plasticity in Macaca

Serotonin has been repeatedly indicated as a biological marker of behavior. In particular, the serotonin transporter gene, SLC6A4, has been the focus of a large body of research. Interestingly, both rhesus macaques (Macaca mulatta) and humans have independently evolved a number of shared polymorphisms for this gene, which is indicative of parallel evolution between the two species. However, little is known about the evolution of this gene, particularly within macaques. Although there are several hypotheses as to the adaptive values of various polymorphisms, few authors have gone beyond theoretical discussion. Here, we examined the genetic variation in SLC6A4 within and between several species of macaques and investigate whether selection has played a significant role in its evolutionary history. In addition, we assayed the promoter region polymorphism, 5-HTTLPR, which is known to play a significant role in regulating both serotonin turnover and behavior. In examining the distribution of the 5-HTTLPR polymorphism, we identified significant differences between Indian and Chinese populations of Macaca mulatta; furthermore, we discovered its presence in Macaca cyclopis, which has not been described before. In regard to the evolutionary history of SLC6A4, we found little evidence for selection and conclude that SLC6A4 largely evolved through neutral processes, possibly due to its potential role in regulating behavioral plasticity. However, we also found very low levels of linkage between the coding regions and 5-HTTLPR. Because we limited evolutionary analyses to the coding regions, it is possible that the promoter region shows a distinct evolutionary history from SLC6A4.

Large-scale polymorphism discovery in macaque G-protein coupled receptors

BACKGROUND

G-protein coupled receptors (GPCRs) play an inordinately large role in human health. Variation in the genes that encode these receptors is associated with numerous disorders across the entire spectrum of disease. GPCRs also represent the single largest class of drug targets and associated pharmacogenetic effects are modulated, in part, by polymorphisms. Recently, non-human primate models have been developed focusing on naturally-occurring, functionally-parallel polymorphisms in candidate genes. This work aims to extend those studies broadly across the roughly 377 non-olfactory GPCRs. Initial efforts include resequencing 44 Indian-origin rhesus macaques (Macaca mulatta), 20 Chinese-origin rhesus macaques, and 32 cynomolgus macaques (M. fascicularis).

RESULTS

Using the Agilent target enrichment system, capture baits were designed for GPCRs off the human and rhesus exonic sequence. Using next generation sequencing technologies, nearly 25,000 SNPs were identified in coding sequences including over 14,000 non-synonymous and more than 9,500 synonymous protein-coding SNPs. As expected, regions showing the least evolutionary constraint show greater rates of polymorphism and greater numbers of higher frequency polymorphisms. While the vast majority of these SNPs are singletons, roughly 1,750 non-synonymous and 2,900 synonymous SNPs were found in multiple individuals.

CONCLUSIONS

In all three populations, polymorphism and divergence is highly concentrated in N-terminal and C-terminal domains and the third intracellular loop region of GPCRs, regions critical to ligand-binding and signaling. SNP frequencies in macaques follow a similar pattern of divergence from humans and new polymorphisms in primates have been identified that may parallel those seen in humans, helping to establish better non-human primate models of disease.

Serotonin transporter and receptor genes significantly impact nicotine dependence through genetic interactions in both European American and African American smokers

BACKGROUND

Pharmacologic studies implicate a significant role of genes encoding the serotonin transporter (SLC6A4) and the 5-HT3AB subunits HTR3A and HTR3B in nicotine dependence (ND). However, whether they are involved in ND remains largely unknown.

METHODS

Here, we examined the impact of variations in the three genes on ND in 1366 individuals from 402 African American (AA) and 671 individuals from 200 European American (EA) families. The ND of each smoker was assessed with smoking quantity (SQ), heaviness of smoking index (HSI), and Fagerström test for nicotine dependence (FTND).

RESULTS

Association analysis revealed marginal association of rs10160548 in HTR3A with SQ and HSI in AA, 5-HTTLPR in SLC6A4 with FTND in EA, and rs11606194 in HTR3B with SQ and FTND in the pooled sample. Haplotype-based association analysis revealed a few major haplotypes in HTR3A that were significantly associated with ND in the AA, EA, and pooled samples. However, none of these associations remained significant after correcting for multiple testing except for a haplotype G-C-C-T-A-T formed by SNPs rs1150226, rs1062613, rs33940208, rs1985242, rs2276302, and rs10160548 in HTR3A for the AA sample. Considering biological functions of the three genes, we examined interactive effects of variants in the three genes, which revealed significant interactions among rs1062613 and rs10160548 in HTR3A, rs1176744 in HTR3B, and 5-HTTLPR and rs1042173 in SLC6A4 in affecting ND in the three samples.

CONCLUSIONS

We conclude that SLC6A4, HTR3A and HTR3B play a significant role in ND through genetic interactions.

Characterization of single-nucleotide variation in Indian-origin rhesus macaques (Macaca mulatta)

BACKGROUND

Rhesus macaques are the most widely utilized nonhuman primate model in biomedical research. Previous efforts have validated fewer than 900 single nucleotide polymorphisms (SNPs) in this species, which limits opportunities for genetic studies related to health and disease. Extensive information about SNPs and other genetic variation in rhesus macaques would facilitate valuable genetic analyses, as well as provide markers for genome-wide linkage analysis and the genetic management of captive breeding colonies.

RESULTS

We used the available rhesus macaque draft genome sequence, new sequence data from unrelated individuals and existing published sequence data to create a genome-wide SNP resource for Indian-origin rhesus monkeys. The original reference animal and two additional Indian-origin individuals were resequenced to low coverage using SOLiD™ sequencing. We then used three strategies to validate SNPs: comparison of potential SNPs found in the same individual using two different sequencing chemistries, and comparison of potential SNPs in different individuals identified with either the same or different sequencing chemistries. Our approach validated approximately 3 million SNPs distributed across the genome. Preliminary analysis of SNP annotations suggests that a substantial number of these macaque SNPs may have functional effects. More than 700 non-synonymous SNPs were scored by Polyphen-2 as either possibly or probably damaging to protein function and these variants now constitute potential models for studying functional genetic variation relevant to human physiology and disease.

CONCLUSIONS

Resequencing of a small number of animals identified greater than 3 million SNPs. This provides a significant new information resource for rhesus macaques, an important research animal. The data also suggests that overall genetic variation is high in this species. We identified many potentially damaging non-synonymous coding SNPs, providing new opportunities to identify rhesus models for human disease.

Comparative genetic approaches to the evolution of human brain and behavior

With advances in genomic technologies, the amount of genetic data available to scientists today is vast. Genomes are now available or planned for 14 different primate species and complete resequencing of numerous human individuals from numerous populations is underway. Moreover, high-throughput deep sequencing is quickly making whole genome efforts within the reach of single laboratories allowing for unprecedented studies. Comparative genetic approaches to the identification of the underlying basis of human brain, behavior, and cognitive ability are moving to the forefront. Two approaches predominate: inter-species divergence comparisons and intra-species polymorphism studies. These methodological differences are useful for different time scales of evolution and necessarily focus on different evolutionary events in the history of primate and hominin evolution. Inter-species divergence is more useful in studying large scale primate, or hominoid, evolution whereas intra-species polymorphism can be more illuminating of recent hominin evolution. These differences in methodological utility also extend to studies of differing genetic substrates; current divergence studies focus primarily on protein evolution whereas polymorphism studies are substrate ambivalent. Some of the issues inherent in these studies can be ameliorated by current sequencing capabilities whereas others remain intractable. New avenues are also being opened that allow for the incorporation of novel substrates and approaches. In the post-genomic era, the study of human evolution, specifically as it relates to the brain, is becoming more complete focusing increasingly on the totality of the system and better conceptualizing the entirety of the genetic changes that have lead to the human phenotype today.

Evolutionary genetics in wild primates: combining genetic approaches with field studies of natural populations

Ecological and evolutionary studies of wild primates hold important keys to understanding both the shared characteristics of primate biology and the genetic and phenotypic differences that make specific lineages, including our own, unique. Although complementary genetic research on nonhuman primates has long been of interest, recent technological and methodological advances now enable functional and population genetic studies in an unprecedented manner. In the past several years, novel genetic data sets have revealed new information about the demographic history of primate populations and the genetics of adaptively important traits. In combination with the rich history of behavioral, ecological, and physiological work on natural primate populations, genetic approaches promise to provide a compelling picture of primate evolution in the past and in the present day.

Association of a polyadenylation polymorphism in the serotonin transporter and panic disorder

BACKGROUND

Genetic markers in the serotonin transporter are associated with panic disorder (PD). The associated polymorphisms do not include the serotonin transporter-linked polymorphic region and display no obvious functional attributes. A common polymorphism (rs3813034) occurs in one of the two reported polyadenylation signals for the serotonin transporter and is in linkage disequilibrium with the PD-associated markers. If functional, rs3813034 might be the risk factor that explains the association of the serotonin transporter and PD.

METHODS

Quantitative polymerase chain reaction on human brain samples (n = 65) and lymphoblast cultures (n = 71) was used to test rs3813034 for effects on expression of the polyadenylation forms of the serotonin transporter. rs3813034 was also tested for association in a sample of PD cases (n = 307) and a control sample (n = 542) that has similar population structure.

RESULTS

The balance of the two polyadenylation forms of the serotonin transporter is associated with rs3813034 in brain (p < .001) and lymphoblasts (p < .001). The balance of the polyadenylation forms is also associated with gender in brain only (p < .05). Association testing of rs3813034 in PD identified a significant association (p = .0068) with a relative risk of 1.56 and 1.81 for the heterozygous and homozygous variant genotypes, respectively.

CONCLUSIONS

rs3813034 is a functional polymorphism in the serotonin transporter that alters the balance of the two polyadenylation forms of the serotonin transporter. rs3813034 is a putative risk factor for PD and other behavioral disorders that involve dysregulation of serotonergic neurotransmission.

Strategies for performing genotype-phenotype association studies in nonhuman primates

Anthropoid primate models offer opportunities to study genetic influence on alcohol consumption and alcohol-related intermediate phenotypes in socially and behaviorally complex animal models that are closely related to humans, and in which functionally equivalent or orthologous genetic variants exist. This review will discuss the methods commonly used for performing candidate gene-based studies in rhesus macaques in order to model how functional genetic variation moderates risk for human psychiatric disorders. Various in silico and in vitro approaches to identifying functional genetic variants for performance of these studies will be discussed. Next, I will provide examples of how this approach can be used for performing candidate gene-based studies and for examining gene by environment interactions. Finally, these approaches will then be placed in the context of how function-guided studies can inform us of genetic variants that may be under selection across species, demonstrating how functional genetic variants that may have conferred selective advantage at some point in the evolutionary history of humans could increase risk for addictive disorders in modern society.

Serotonin transporter expression is predicted by early life stress and is associated with disinhibited behavior in infant rhesus macaques

Serotonin transporter (5-HTT) expression patterns may contribute to the risk for adverse psychological outcomes following early life stress. The present study investigated whether two types of early life stress, maternal and social aggression, and a serotonin transporter gene promoter polymorphism (rh5-HTTLPR) predicted lower post-stressor peripheral blood mononuclear cell (PBMC) 5-HTT expression in infant rhesus macaques. We further probed the relationships among these factors and infant behavioral disinhibition within a stressful situation. Fifty-three infants residing with mothers in large, complex social groups were observed over the first 12 postnatal weeks, during which time the rate of aggression received by the infant from their mothers and social group members was recorded. At 90-120 days of age, infants underwent a 25-h maternal separation/biobehavioral assessment, which included standardized behavioral assessments and blood sampling. Infants' rh5-HTTLPR genotypes were determined, and infant 5-HTT expression was quantified from PBMCs collected 8 h after separation. Receipt of aggression from the mother, but not from social group members, was associated with lower post-stressor 5-HTT expression. Lower post-stressor 5-HTT expression, but not receipt of aggression, was associated with disinhibited behavior during assessment. Rh5-HTTLPR genotype was unrelated to any measure. We conclude that 5-HTT regulation is linked with specific, presumably stressful early experiences in infant rhesus macaques. Further, 5-HTT expression predicted behavioral disinhibition, presumably via parallel processes that operate in the brain.

Polymorphisms in the 3' UTR of the serotonin transporter are associated with cognitive flexibility in rhesus macaques

The serotonin system is an important neurophysiological mediator of many behavioral phenotypes. Genetic variation within this system is thought to contribute not only to the natural range of behavioral differences, but also to neuropsychiatric pathologies. Cognitive flexibility, the ability to change patterns of response as reward context shifts, is an important trait that underlies many complex social interactions. Environmental manipulations of the serotonin system have been shown to alter performance on tests measuring cognitive flexibility. Variation at the serotonin transporter promoter region (5HTTLPR) has recently been shown to associate with the performance of rhesus monkeys on an object discrimination reversal learning task [Izquierdo et al., 2007]. Here, we demonstrate that functional genetic variation at the serotonin transporter 3' untranslated region, independent of 5HTTLPR, also associates with performance in an object discrimination reversal learning task in rhesus macaques. The polymorphisms comprising the T:G:T haplotype (T1970, G1991, and T2327) were associated with fewer errors on a reversal learning test and greater levels of cognitive flexibility. We have previously demonstrated that the T:G:T haplotype renders lower levels of gene expression in vitro, paralleling the functionality of human 3' UTR haplotypes, as well as the short allele of 5HTTLPR found in both macaques and humans. The 3' UTR haplotypes are independent and in linkage equilibrium with the 5HTTLPR locus. Together, these data lead to the intriguing possibility that differences observed in human cognitive flexibility, whether naturally or in pathological states, may be associated with genetic variation in the serotonin transporter 3' untranslated region also.

Characterization of a functional polymorphism in the 3' UTR of SLC6A4 and its association with drinking intensity

BACKGROUND

The propensity for severe drinking is hypothesized to be regulated by differential expression of serotonin transporter gene (SLC6A4) in the human brain. The SLC6A4 promoter region 5-HTTLPR has been examined previously as a candidate polymorphic variant associated with severe drinking. In this study, we investigated whether other SLC6A4 single nucleotide polymorphisms (SNPs) are associated with drinking intensity among treatment-seeking alcoholics and whether these polymorphic variants result in differential SLC6A4 expression levels.

METHODS

We analyzed associations of drinking intensity in 275 (78.5% male) treatment-seeking alcoholics of Caucasian and Hispanic origin, with 6 SLC6A4 polymorphisms. Next, to examine the functionality of the SNP that showed a significant association with drinking intensity, we transfected the 2 alleles of rs1042173 into HeLa cell cultures and measured serotonin transporter mRNA and protein expression levels by using qRT-PCR and western blotting techniques.

RESULTS

One of the 6 polymorphisms we examined, rs1042173 in the 3' untranslated region (3'-UTR) of SLC6A4, showed a significant association with drinking intensity. The G allele carriers for rs1042173 were associated with significantly lower drinking intensity (p = 0.0034) compared to T-allele homozygotes. In HeLa cell cultures, the cells transfected with G allele showed a significantly higher mRNA and protein levels than the T allele-transfected cells.

CONCLUSION

These findings suggest that the allelic variations of rs1042173 affect drinking intensity in alcoholics possibly by altering serotonin transporter expression levels. This provides additional support to the hypothesis that SLC6A4 polymorphisms play an important role in regulating propensity for severe drinking.