Differential role of serotonergic polymorphisms in alcohol and heroin dependence

Neuropharmacological and Neurogenetic Correlates of Opioid Use Disorder (OUD) As a Function of Ethnicity: Relevance to Precision Addiction Medicine

BACKGROUND

Over 100 people die daily from opioid overdose and $78.5B per year is spent on treatment efforts, however, the real societal cost is multifold greater. Alternative strategies to eradicate/manage drug misuse and addiction need consideration. The perception of opioid addiction as a social/criminal problem has evolved to evidence-based considerations of them as clinical disorders with a genetic basis. We present evaluations of the genetics of addiction with ancestryspecific risk profiles for consideration.

OBJECTIVE

Studies of gene variants associated with predisposition to substance use disorders (SUDs) are monolithic, and exclude many ethnic groups, especially Hispanics and African Americans. We evaluate gene polymorphisms that impact brain reward and predispose individuals to opioid addictions, with a focus on the disparity of research which includes individuals of African and Hispanic descent.

METHODOLOGY

PubMed and Google Scholar were searched for: Opioid Use Disorder (OUD), Genome- wide association studies (GWAS); genetic variants; polymorphisms, restriction fragment length polymorphisms (RFLP); genomics, epigenetics, race, ethnic group, ethnicity, ancestry, Caucasian/ White, African American/Black, Hispanic, Asian, addictive behaviors, reward deficiency syndrome (RDS), mutation, insertion/deletion, and promotor region.

RESULTS

Many studies exclude non-White individuals. Studies that include diverse populations report ethnicity-specific frequencies of risk genes, with certain polymorphisms specifically associated with Caucasian and not African-American or Hispanic susceptibility to OUD or SUDs, and vice versa.

CONCLUSION

To adapt precision medicine-based addiction management in a blended society, we propose that ethnicity/ancestry-informed genetic variations must be analyzed to provide real precision- guided therapeutics with the intent to attenuate this uncontrollable fatal epidemic.

Association of the DRD4 exon III and 5-HTTLPR VNTR polymorphisms with substance abuse in Jordanian Arab population

Genetic variations in the dopamine D4 receptor (DRD4) gene and the serotonin transporter (SLC6A4) gene are involved in the aetiology of substance abuse disorder (SUD). The main aim of this study is to evaluate the genetic association of DRD4 (48 bp-VNTR) and SLC6A4 (rs25531 and 5-HTTLPR VNTR) gene polymorphisms with SUD susceptibility among the Jordanian Arab population. This study included 500 SUD patients and 500 healthy matched controls. The VNTR Genetic polymorphisms of DRD4 and SLC6A4 genes were genotyped using conventional polymerase chain reaction (PCR). While, the rs25531 SNP was genotyped using PCR-restriction fragment length polymorphism (PCR-RFLP) technique. The genetic association was analysed using different statistical analyses including chi-square, Fisher exact test and one way ANOVA test. The DRD4 exon III VNTR polymorphism was associated with SUD significantly in case of alleles 4, 7 and genotype 7/7 (P = 0.004, 0.0005 and 0.01, respectively). While, there was no genetic association between the 5-HTTLPR (LL, LS, SS), rs25331 (AA, AG, GG) and tri-allelic (SASA, LASG, LASA, LALG, LALA) genotypes (P = 0.26, 0.71 and 0.52, respectively) and SUD. Moreover, using multinomial regression analysis, the homozygous 7/7 and 2/2 VNTR genotypes of DRD4 gene were nominally significantly associated with a lower risk of addiction (OR = 0.285 with P = 0.003 and OR = 0.447 with P = 0.031, respectively) after adjusting for other covariates. Our findings showed that 4 and 7 repeats and the genotype 7/7 of DRD4 exon III VNTRs polymorphism are involved in the aetiology of SUD among Jordanian population in compared to the 5-HTTLPR polymorphisms.

Association of serotonin and GABA pathway gene polymorphisms with alcohol dependence: A preliminary study

BACKGROUND

Alcohol dependence (AD), characterized by profound disruptions in specific circuits of the brain is influenced by both environmental, which play a significant role in developing addiction and genetic factors, which make some individuals more susceptible to disruptions. Various polymorphisms in the neurotransmitter genes are reported to increase the risk of developing dependence. The present study aimed to identify association of serotonin and GABA polymorphisms with AD in Indian subjects.

METHOD

The study group comprised of 141 AD cases recruited as per DSM IV TR criteria from the outpatient Department of Psychiatry and 110 volunteers from the general population. Clinical and family history was noted and 5 ml blood drawn for genetic studies. Polymorphisms 5-HTTLPR and STin2 of serotonin and rs2279020 and rs3219151 of the GABA pathway were analyzed and results correlated with age at first use quantity consumed, duration of use, dependence and age at onset of dependence.

RESULTS

The marker frequencies were similar between cases and controls except for rs3219151. 5-HTTLPR was significantly associated with high AUDIT scores and alcohol intake (p < 0.0001), GABA_A rs2279020 and rs3219151 with age at first use (p < 0.0001); rs2279020 with higher AUDIT score (p = 0.002) and rs3219151 with quantity (p = 0.0001). High frequency of GABRA6 rs3219151 TT genotype in AD and its association with lower age at first use, higher intake/day, and higher duration of dependence appears to confer risk.

CONCLUSIONS

This preliminary study, though on a smaller sample size, suggests an association of 5-HTTLPR and GABA_A receptor polymorphisms with AD in our population.

Serotonin transporter gene polymorphisms may be associated with poststroke neurological recovery after escitalopram use

OBJECTIVE

Selective serotonin reuptake inhibitors (SSRIs) putatively improve neurological recovery after stroke. We aimed to investigate whether serotonin transporter (SERT) gene polymorphisms are related to the responsiveness to SSRIs in the poststroke neurological recovery.

METHODS

This was a post hoc analysis of the EMOTION study (ClinicalTrials.gov NCT01278498), a randomised, placebo-controlled, double-blind trial examining the efficacy of escitalopram on emotional and neurological disturbances after acute stroke. Patients with no/minimal disability initially (modified Rankin Scale (mRS) 0-1) were excluded. Of the participants, 301 underwent genetic studies of the STin2 (a variable number tandem repeat (VNTR) in intron 2) (STin2 12/10 and STin2 12/12 genotypes) and 5-HTTLPR (a variable-length repeat in the promoter region) polymorphisms of SERT. We explored whether neurological function (National Institutes of Health Stroke Scale (NIHSS) score and mRS) at 3 months would differ according to SERT polymorphisms within each treatment arm (escitalopram and placebo).

RESULTS

Among the escitalopram users (n=159), neurological function in subjects with STin2 12/10 (n=29) improved significantly more than that in STin2 12/12 carriers (n=130) at 3 months. After adjusting for age, initial NIHSS and depression, STin2 12/10 independently predicted a good clinical outcome (mRS 0-1) (OR 2.99, 95% CI 1.04 to 8.58) at 3 months. However, differences between STin2 polymorphisms were not shown in the placebo group (n=142). 5-HTTLPR polymorphisms were not associated with neurological recovery in any treatment group.

CONCLUSION

STin2 VNTR polymorphisms may be associated with poststroke neurological recovery after SSRI therapy. Further studies are needed to identify the role of serotonin in neurological recovery after stroke.

Association between serotonin transporter gene polymorphism and recurrent aphthous stomatitis

Background:

Anxiety-related traits have been attributed to sequence variability in the genes coding for serotonin transmission in  the brain. Two alleles, termed long (L) and short (S) differing by 44 base pairs, are found in a polymorphism identified in the promoter region of serotonin transporter gene. The presence of the short allele  and SS and LS genotypes is found to be associated with the reduced expression of this gene decreasing the uptake of serotonin in the brain leading to various anxiety-related traits. Recurrent aphthous stomatitis (RAS) is an oral mucosal disease with varied etiology including the presence of stress, anxiety, and genetic influences. The present study aimed to determine this serotonin transporter gene polymorphism in patients with RAS and compare it with normal individuals.

Materials and Methods:

This study included 20 subjects with various forms of RAS and 20 normal healthy age- and gender-matched individuals. Desquamated oral mucosal cells were collected for DNA extraction and subjected to polymerase chain reaction for studying insertion/deletion in the 5-HTT gene-linked polymorphic region. Cross tabulations followed by Chi-square tests were performed to compare the significance of findings, P < 0.05 was considered statistically significant.

Results:

The LS genotype was the most common genotype found in the subjects with aphthous stomatitis (60%) and controls (40%). The total percentage of LS and SS genotypes and the frequency of S allele were found to be higher in the subjects with aphthous stomatitis as compared to the control group although a statistically significant correlation could not be established, P = 0.144 and 0.371, respectively.

Conclusion:

Within the limitations of this study, occurrence of RAS was not found to be associated with polymorphic promoter region in serotonin transporter gene.

Genetic Polymorphism in the Promoter Region of Serotonin Transporter: Implications for Ethanol Abuse in Children and Adolescents

OBJECTIVES

To provide a review of published literature regarding genetic polymorphism of serotonin transporter gene, named as 5-HTTLPR, and its potential role as a susceptibility marker for ethanol abuse in childhood and adolescence.

METHODS

A literature review of several databases was conducted with the following keywords: 5-HTTLPR, children or adolescents or teenagers, susceptibility, alcohol or ethanol, abuse or misuse.

RESULTS

Alcohol interacts with serotonergic synaptic transmission in several ways, and the reduced availability of serotonin transporters might foster brain dysfunction, driving to alcohol abuse. The initial use of ethanol in children and adolescents is determined primarily by environmental influences, whereas the establishment of drinking patterns is strongly controlled by genetic factors. Functional polymorphic variants in the promoter region of the 5-HTTLPR gene have age-dependent effects in alcohol abuse. This polymorphism, mapped to the 5' region of the SLC6A4, is a variable number of tandem repeats (VNTR) and involves a direct repeat of 20-23 base pairs GC-rich sequences, comprising a short (S) allele, consisting of 14 repeats, and a long (L) allele, with 16 repeats. Additional variants have been described, although their influences on childhood and adolescence ethanol use are not clear.

CONCLUSION

The influence of the 5-HTTLPR allelic variants in children and adolescent misuse of alcohol might be considered for clinical management, preventing long-term behavior problem. Identifying genetic markers associated to the potential alcohol misuse or abuse could be useful in guiding management and formulating effective coping strategies.

A review of 5-HT transporter linked promoter region (5-HTTLPR) polymorphism and associations with alcohol use problems and sexual risk behaviors

Alcohol use and sexual risk behaviors are multidimensional phenomena involving many genetic and environmental factors. 5-HT transporter linked promoter region (5-HTTLPR) polymorphism constitutes an important factor affecting alcohol use problems and risky sexual behaviors. This paper narratively reviews studies on 5-HTTLPR polymorphism and its associations with alcohol use problems and sexual risk behaviors. We searched the electronic databases, PubMed, Ovid, and Google Scholar for articles using MeSH terms. Relevant articles were reviewed and eligible articles were selected for the study. Many studies have reported a significant but moderate association between 5-HTTLPR polymorphism and alcohol use problems. These studies have implicated the presence of at least one S allele to be associated with significant increases in alcohol use problems. Similarly, some studies associate the S allele with increased sexual risk behaviors. Effective alcohol cessation initiatives and STI/HIV prevention programs should be modified to account for 5-HTTLPR polymorphism before planning interventions; genetic effects could moderate the intervention effect.

Association between serotonin transporter gene polymorphisms and heroin dependence: a meta-analytic study

BACKGROUND

Studies have examined the association between heroin dependence and serotonin transporter gene polymorphisms but yielded inconsistent results. The purpose of current study is to determine the overall effect of these polymorphisms on the risk for heroin dependence through a meta-analytic method.

METHODS

A meta-analysis was conducted to examine the association of heroin dependence with two common polymorphisms of serotonin transporter gene, in the promoter (5-hydroxytryptamine transporter-linked promotor region [5-httlpr]) and intron 2 (a various number tandem repeat in serotonin transporter intron 2 [STin2]). Data from studies with 5-httlpr (6 studies) and STin2 (8 studies) were synthesized by random effects model.

RESULTS

In the analysis, heroin dependence was found to be significantly associated with the S allele of 5-httlpr (odds ratio [OR] =1.22, 95% confidence interval [CI] =1.08-1.41, P=0.002). The association between the S allele of 5-httlpr and heroin dependence was significant in Caucasian subjects (OR =1.37, 95% CI =1.12-1.68, P=0.003), but not in non-Caucasian subjects. On the other hand, no association with STin2 polymorphism was found (OR =1.14, 95% CI =0.91-1.42, P=0.242).

CONCLUSION

The results suggest an ethnic-specific effect of the 5-httlpr polymorphism on the risk for heroin dependence, but the influence of the genetic variance in the patients with comorbidities or intermediate phenotypes of heroin dependence needs to be further examined.

Loudness dependence of auditory evoked potentials (LDAEP) in clinical monitoring of suicidal patients with major depression in comparison with non-suicidal depressed patients and healthy volunteers: A follow-up-study

Differences in central serotonergic function due to affective disorders and due to extraordinary situations like suicidality may be visualized using the loudness dependence of auditory evoked potentials (LDAEP). Twenty patients (mean age 43.25 ± 10.85, age range 20-61, 11 male) suffering from a major depressive episode who had either acutely attempted suicide or who had suicidal plans and behavior, which are reflected by item 3 of Hamilton Depression Rating Scale ≥ 3 (suicidality), were included in the study. Furthermore, we intended to compare their LDAEP to those of non-suicidal depressed patients as well as to healthy volunteers, each matched according to age and gender. LDAEP measurement and psychometric tests took place about 2, 5, 9, 16 and 30 days after acute suicidal action or suicide attempts. In contrast to previous results, significant differences in LDAEP could not have been shown in between the suicidal group, or by comparing results of suicidal patients to non-suicidal depressed patients or to healthy volunteers. However, when the LDAEP of non-suicidal depressed patients were compared to healthy volunteers, there was a trend for a higher LDAEP in the healthy volunteers. Further studies are necessary to detect and describe further influences on serotonergic function and confounding factors like medication, smoking, age, gender, comorbidities and methods of suicidal attempts.

Association and interaction analyses of 5-HT3 receptor and serotonin transporter genes with alcohol, cocaine, and nicotine dependence using the SAGE data

Previous studies have implicated genes encoding the 5-HT3AB receptors (HTR3A and HTR3B) and the serotonin transporter (SLC6A4), both independently and interactively, in alcohol (AD), cocaine (CD), and nicotine dependence (ND). However, whether these genetic effects also exist in subjects with comorbidities remains largely unknown. We used 1,136 African-American (AA) and 2,428 European-American (EA) subjects from the Study of Addiction: Genetics and Environment (SAGE) to determine associations between 88 genotyped or imputed variants within HTR3A, HTR3B, and SLC6A4 and three types of addictions, which were measured by DSM-IV diagnoses of AD, CD, and ND and the Fagerström Test for Nicotine Dependence (FTND), an independent measure of ND commonly used in tobacco research. Individual SNP-based association analysis revealed a significant association of rs2066713 in SLC6A4 with FTND in AA (β = -1.39; P = 1.6E - 04). Haplotype-based association analysis found one major haplotype formed by SNPs rs3891484 and rs3758987 in HTR3B that was significantly associated with AD in the AA sample, and another major haplotype T-T-G, formed by SNPs rs7118530, rs12221649, and rs2085421 in HTR3A, which showed significant association with FTND in the EA sample. Considering the biologic roles of the three genes and their functional relations, we used the GPU-based Generalized Multifactor Dimensionality Reduction (GMDR-GPU) program to test SNP-by-SNP interactions within the three genes and discovered two- to five-variant models that have significant impacts on AD, CD, ND, or FTND. Interestingly, most of the SNPs included in the genetic interaction model(s) for each addictive phenotype are either overlapped or in high linkage disequilibrium for both AA and EA samples, suggesting these detected variants in HTR3A, HTR3B, and SLC6A4 are interactively contributing to etiology of the three addictive phenotypes examined in this study.

Neurotransmitters in alcoholism: A review of neurobiological and genetic studies

Recent advances in the study of alcoholism have thrown light on the involvement of various neurotransmitters in the phenomenon of alcohol addiction. Various neurotransmitters have been implicated in alcohol addiction due to their imbalance in the brain, which could be either due to their excess activity or inhibition. This review paper aims to consolidate and to summarize some of the recent papers which have been published in this regard. The review paper will give an overview of the neurobiology of alcohol addiction, followed by detailed reviews of some of the recent papers published in the context of the genetics of alcohol addiction. Furthermore, the author hopes that the present text will be found useful to novices and experts alike in the field of neurotransmitters in alcoholism.

The role of serotonin in drug use and addiction

The use of psychoactive drugs is a wide spread behaviour in human societies. The systematic use of a drug requires the establishment of different drug use-associated behaviours which need to be learned and controlled. However, controlled drug use may develop into compulsive drug use and addiction, a major psychiatric disorder with severe consequences for the individual and society. Here we review the role of the serotonergic (5-HT) system in the establishment of drug use-associated behaviours on the one hand and the transition and maintenance of addiction on the other hand for the drugs: cocaine, amphetamine, methamphetamine, MDMA (ecstasy), morphine/heroin, cannabis, alcohol, and nicotine. Results show a crucial, but distinct involvement of the 5-HT system in both processes with considerable overlap between psychostimulant and opioidergic drugs and alcohol. A new functional model suggests specific adaptations in the 5-HT system, which coincide with the establishment of controlled drug use-associated behaviours. These serotonergic adaptations render the nervous system susceptible to the transition to compulsive drug use behaviours and often overlap with genetic risk factors for addiction. Altogether we suggest a new trajectory by which serotonergic neuroadaptations induced by first drug exposure pave the way for the establishment of addiction.

The association of 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR gene polymorphisms and borderline personality disorder in female heroin-dependent Chinese subjects

OBJECTIVE

To explore the association between the 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR polymorphisms with co-morbid borderline personality disorder (BPD) in female heroin-dependent patients.

SUBJECTS AND METHODS

In a case control study, we compared the polymorphic distributions of 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR in 296 female heroin-dependent patients (including 61 patients with BPD and 235 without BPD) and 101 normal females by genotypes, alleles, and interaction between genes.

RESULTS

Female heroin-dependent subjects with BPD have lower frequency of the high activity allele (L: 4 repeats (4R)) of MAOA-LPR than those female heroin-dependent subjects without BPD, and have higher 5-HTTVNTR 10R/10R genotype frequency than normal female controls, with adjusted P-value<0.05 (after adjusted for multiple testing by 1000-fold permutation tests) respectively. By MDR (Multifactor Dimensionality Reduction) analyses, the interactive effects between MAOA-LPR and 5-HTTVNTR, and among MAOA-LPR, 5-HTTVNTR and rs6311 were close to the significance level (P=0.05) in predicting the risk of co-morbidity of BPD and heroin dependence relative to normal female controls, with 1000-fold permutation testing P-value<0.06 however >0.05 respectively.

CONCLUSION

5-HTTVNTR and MAOA-LPR may have independent predictive effects on co-morbid BPD in female heroin-dependent patients; the gene-gene interactions between MAOA-LPR and 5-HTTVNTR, and among MAOA-LPR, 5-HTTVNTR and rs6311 might also be involved in the etiology of this co-morbidity.

Phasic boosting of auditory perception by visual emotion

Emotionally negative stimuli boost perceptual processes. There is little known, however, about the timing of this modulation. The present study aims at elucidating the phasic effects of, emotional processing on auditory processing within subsequent time-windows of visual emotional, processing in humans. We recorded the electroencephalogram (EEG) while participants responded to a, discrimination task of faces with neutral or fearful expressions. A brief complex tone, which subjects, were instructed to ignore, was displayed concomitantly, but with different asynchronies respective to, the image onset. Analyses of the N1 auditory event-related potential (ERP) revealed enhanced brain, responses in presence of fearful faces. Importantly, this effect occurred at picture-tone asynchronies of, 100 and 150ms, but not when these were displayed simultaneously, or at 50ms or 200ms asynchrony. These results confirm the existence of a fast-operating crossmodal effect of visual emotion on auditory, processing, suggesting a phasic variation according to the time-course of emotional processing.

Multi-cultural association of the serotonin transporter gene (SLC6A4) with substance use disorder

A number of studies have reported associations between the serotonin transporter gene (SLC6A4) and alcohol, heroin, cocaine, or methamphetamine abuse. Other studies have yielded contrary results. There are a number of reasons for non-replication, including inadequate statistical power, population stratification, and poor phenotype definition. This study was to test the association using a meta-analytic approach across a variety of racial and ethnic populations. Using the genotype data of 55 studies (7999 cases, 8264 controls, and 676 families or parent-offspring trios) published in the past 15 years, we have conducted comprehensive meta-analyses to examine the associations of the 5-HTTLPR and STin2 polymorphisms with substance use disorder. The meta-analyses support the associations of 5-HTTLPR with alcohol, heroin, cocaine, and methamphetamine dependence and abuse (eg, the smallest P-values were 0.0058 with odds ratio (OR)=0.54 (0.35, 0.84); 0.0024 with OR=0.77 (0.66, 0.91); 0.018 with OR=1.38 (1.06, 1.81); and 0.028 with OR=0.46 (0.23, 0.92) for alcohol, heroin, cocaine, and methamphetamine dependence/abuse, respectively). When all the phenotypes are combined, the P-value was 0.0006 with OR=0.86 (0.78, 0.94) in the combined European, Asian, and Mexican populations and P-value was 0.0028 with OR=1.41 (1.13, 1.78) in the African populations. Evidence of significant associations was also identified in other subgroup analyses regarding differently combined substance and populations. The effect sizes of 5-HTTLPR were comparable among the European, Asian, and Mexican populations, however, the risk allele was more frequent in Asians than in Europeans and Mexicans. The opposite directions of risk allele in African population might be driven by the opposite directions of risk allele in cocaine dependence. This meta-analysis supports that the association of the SLC6A4 gene with substance use disorder varies depending on substances with different risk allele frequencies in the multi-cultural populations. Further studies using larger sample size are warranted.

A preliminary examination of how serotonergic polymorphisms influence brain response following an adolescent cannabis intervention

Given the link between depression, anxiety, and cannabis abuse, a serotonin receptor (rs6311) and transporter polymorphism (rs2020936) were examined as moderators of neural response as measured by functional magnetic resonance imaging following a psychosocial treatment for cannabis use disorders (CUDs). While the proposed hypotheses were unsupported, we found that the rs6311 C allele was significantly related to brain activation (medial frontal gyrus, precuneus), indicating the role of this serotonin receptor in adolescent treatment response.

Characterization of serotonin transporter gene (SLC6A4) polymorphisms and its association with drug dependence in a Jordanian Arab population

Drug dependence is a pattern of repeated self-administration of a drug, which can result in tolerance, withdrawal and compulsive drug-taking behaviour. It has been recently suggested that 5-HTTLPR (LL/LS/SS) variants and rs25531 (A/G) polymorphism in the serotonin transporter gene (SLC6A4) may play a role in drug dependence. The current study aimed to (1) identify allelic, haplotypic and genotypic frequencies of the 5-HTTLPR variants and rs25531 polymorphisms of SLC6A4 gene in drug and nondrug-dependent Jordanian Arab population and (2) determine whether there is an association of these variants in a drug-dependent population from the same area. Jordanian drug male addicts of Arab descent (n = 192) meeting the Diagnostic and Statistical Manual of Mental Disorders - Fourth edition criteria for drug dependence and 230 healthy male controls from an ethnically homogenous Jordanian Arab population were examined. Genotyping was performed using the restriction fragment length polymorphism-polymerase chain reaction-based method to genotype the 5-HTTLPR variants and detect the A/G polymorphism at position rs25531. The biallelic analysis revealed that the frequency of 5-HTTLPR (LL/LS/SS) genotypes was statistically significant different between drug-dependent individuals and controls (χ (2) (2, N = 422), p = 0.04). Drug-dependent subjects had a higher frequency of 'L' allele. However, using the triallelic approach, the estimated frequency of haplotypes (SA , SG , LA and LG ) and phased genotypes (LA /LA , LA /SA , LA /LG , SA /SA and SA /SG) did not show significant association with drug dependence (χ (2) (3, N = 422), p = 0.53 and χ (2) (4, N = 422), p = 0.06, respectively). This study suggests a putative role of the 5-HTTLPR for drug dependence in the Jordanian Nationals of Arab ancestry.

Serotonin system gene polymorphisms are associated with impulsivity in a context dependent manner

Impulsivity is a risk factor for adverse outcomes and characterizes several psychiatric disorders and risk for suicide. There is strong evidence that genetic variation influences individual differences in impulsivity, but the details are not yet understood. There is growing interest in better understanding the context dependency of genetic effects that is reflected in studies examining gender specificity, gene×environment interaction and epistasis (gene-gene interaction). In a cross-sectional study we examined whether polymorphisms in six serotonin system candidate genes and the experience of early life trauma (age 0-12) were associated with individual differences in impulsivity in a non-clinical sample of Caucasian university students (N=424). We specifically tested potential gender specific, gene-gene, and gene×environment (early life trauma) effects. In our main analyses with Barratt Impulsiveness Scale (BIS-11) total score, there were significant (i.e. p<.01 and False Discovery Rate <.10) interactions between (1) gender and TPH2 (rs1386483) genotype; (2) gender and HTR2A (rs6313) genotype; and epistatic interactions among (3) 5-HTTLPR and MAOA uVNTR; (4) 5-HTTLPR and rs6313 and (5) HTR1B (rs6296) and rs6313 genotypes. Our results strongly support the explicit investigation of context dependent genetic effects on impulsivity and may help to resolve some of the conflicting reports in the literature.

Polymorphisms of the serotonin transporter and receptor genes: susceptibility to substance abuse

Serotonin (5-hydroxytryptamine [5-HT]) is an important neurotransmitter implicated in regulating substance-use disorder (SUD) acquisition, maintenance, and recovery. During the past several years, an abundance of research has begun discovering and describing specific 5-HT genetic polymorphisms associated with SUDs. Genetic variations in the 5-HT system, such as SLC6A4, HTR1B, HTR2A, HTR2C, HTR3 (HTR3A, HTR3B, HTR3C, HTR3D, and HTR3E), likely play a role contributing to SUD patient heterogeneity. The 5-HT transporter-linked polymorphic region S allele, located in SLC6A4, has now been modestly associated with alcohol dependence in two large meta-analyses. Additional 5-HT genes may also play a role but have not been extensively investigated. A limited number of SUD treatment studies have included 5-HT gene variation as moderating treatment outcomes, but the results have been equivocal. Future research on 5-HT addiction genetics should adopt whole-genome sequencing technology, utilize large study samples, and collect data from multiple ethnic groups. Together, these methods will build on the work already conducted with the aim of utilizing 5-HT genetics in SUD treatment settings.

Functional genetic variants that increase synaptic serotonin and 5-HT3 receptor sensitivity predict alcohol and drug dependence

The 5-HT3 receptor is rapidly potentiated by ethanol and mediates fast excitatory serotonin (5-HT) transmission that modulates dopamine release in the reward circuitry. The 5-HT transporter regulates synaptic 5-HT availability. Functional polymorphisms in genes encoding the transporter and receptor may therefore influence addiction vulnerability. In this study, 360 treatment-seeking African American male patients with single and comorbid DSM-IV lifetime diagnoses of alcohol, cocaine and heroin dependence and 187 African American male controls were genotyped for the triallelic 5-HTTLPR functional polymorphism in the 5-HT transporter gene (SLC6A4) and 16 haplotype-tagging single-nucleotide polymorphisms (SNPs) across HTR3B (including the functional rs1176744 Tyr129Ser) and HTR3A, genes encoding 5-HT3 receptors. The HTR3B rs1176744 gain-of-function Ser129 allele predicted alcohol dependence (P=0.002) and low 5-HTTLPR activity predicted cocaine/heroin dependence (P=0.01). Both the HTR3B Ser129 allele (P=0.014, odds ratio (OR)=1.7 (1.1-2.6)) and low 5-HTTLPR activity (P=0.011, OR=2.5 (1.3-4.6)) were more common in men with alcohol+drug dependence compared with controls. Moreover, the HTR3B Ser129 allele and low 5-HTTLPR activity had an additive (but not an interactive) effect on alcohol+drug dependence (OR=6.0 (2.1-16.6)) that accounted for 13% of the variance. One possible explanation of our findings is that increased synaptic 5-HT coupled with increased 5-HT3 receptor responsiveness may result in enhanced dopamine transmission in the reward pathway, a predictor of increased risk for addiction. Our results may have pharmacogenetic implications for 5-HT3 therapeutic antagonists such as ondansetron.

Polymorphism G861C of 5-HT receptor subtype 1B is associated with heroin dependence in Han Chinese

The serotoninergic (5-HT) system regulates neuronal activity in broad brain regions, and appears to be particularly important for modulating behavioral and physiological functions such as mood, emotion, sleep and appetite. Central 5-HT deregulation may be involved in many neuropsychological disorders, which include substance abuse and addiction. Previous studies suggest that genetic polymorphisms in some 5-HT receptor genes may relate to heroin dependency. Here we examined potential association between heroin dependence and four single nucleotide polymorphisms (SNPs) of 5-HT receptors (A-1438G and T102C of HTR(2A), and G861C and A1180G of HTR(1B)) in a cohort of Han Chinese. Participants included 303 heroin-dependent subjects who were recruited into the Methadone Maintenance Treatment (MMT) Program in the Xi'an Mental Health Center, and 300 healthy controls. The resulting data yielded a significantly higher frequency of the HTR(1B) G allele with G861C among the heroin-dependent subjects relative to controls (p=0.001 after Bonferroni correction). Further genotype and clinical phenotype correlation study of the G861C carriers showed that the amount of heroin self-injection was higher in patients with the GG genotype relative to CC and CG genotypes (p<0.01). These findings point to a role for HTR(1B) polymorphism in heroin dependence among Han Chinese, and may be informative for future genetic or neurobiological studies on heroin dependence.

Role of the serotonergic system in alcohol dependence: from animal models to clinics

Alcohol dependence remains among the most common substance abuse problems worldwide, and compulsive alcohol consumption is a significant public health concern. Alcohol is an addictive drug that alters brain function through interactions with multiple neurotransmitter systems. These neurotransmitter systems mediate the reinforcing effects of alcohol. Specifically, the serotonergic system is important in mediating alcohol reward, preference, dependence, and craving. In this review chapter, we first discuss the serotonin system as it relates to alcoholism, and then outline interactions between this system and other neurotransmitter systems. We emphasize the serotonin transporter and its possible role in alcoholism, then present several serotonergic receptors and discuss their contribution to alcoholism, and finally assess the serotonin system as a target for pharmacotherapy, with an emphasis on current and potential treatments.

Association of VNTR polymorphisms in the MAOA promoter and DRD4 exon 3 with heroin dependence in male Chinese addicts

OBJECTIVE

To explore the involvement of variable number tandem repeat (VNTR) polymorphisms in the monoamine oxidase A (MAOA) promoter and exon 3 of the dopamine D4 receptor (DRD4) gene in heroin addiction modulate the vulnerability of individuals to heroin addiction.

METHODS

Eight hundred and ninety-four male heroin addicts without other psychiatric disorders, were recruited as subjects. Another community 180 males were selected randomly as controls.

RESULTS

The geno-distribution of the DRD4 exon 3 VNTR polymorphism in controls was in Hardy-Weinberg equilibrium (HWEchi(2)=0.925), but the distribution in heroin addicts was not (HWEchi(2)=28.35). The long-repeat alleles of the DRD4 exon 3 VNTR polymorphism were found more frequently in the heroin addicts (P=0.019). However, the long-repeat alleles of the MAOA promoter VNTR polymorphism were not (P=0.828). No interaction between these two VNTR polymorphisms was found by using multiple logistic regression analysis (P=0.261).

CONCLUSION

The long-repeat allelic variants (>4-repeats) and 2-repeat allele of the DRD4 exon 3 VNTR polymorphism might be risk alleles for individual vulnerability to heroin addiction in Chinese men, but the MAOA promoter VNTR polymorphism does not mean that the partial dominant inherited mode might involved in the genetics of heroin dependence.