Does the short variant of the serotonin transporter linked polymorphic region constitute a marker of alcohol dependence?

The role of brain serotonin signaling in excessive alcohol consumption and withdrawal: A call for more research in females

Alcohol Use Disorder (AUD) is a leading cause of death and disability worldwide, but current treatments are insufficient in fully addressing the symptoms that often lead to relapses in alcohol consumption. The brain's serotonin system has been implicated in AUD for decades and is a major regulator of stress-related behaviors associated with increased alcohol consumption. This review will discuss the current literature on the association between neurobiological adaptations in serotonin systems and AUD in humans as well as the effectiveness of serotonin receptor manipulations on alcohol-related behaviors like consumption and withdrawal. We will further discuss how these findings in humans relate to findings in animal models, including a comparison of systemic pharmacological manipulations modulating alcohol consumption. We next provide a detailed overview of brain region-specific roles for serotonin and serotonin receptor signaling in alcohol-related behaviors in preclinical animal models, highlighting the complexity of forming a cohesive model of serotonin function in AUD and providing possible avenues for more effective therapeutic intervention. Throughout the review, we discuss what is known about sex differences in the sequelae of AUD and the role of serotonin in these sequelae. We stress a critical need for additional studies in women and female animals so that we may build a clearer path to elucidating sex-specific serotonergic mechanisms and develop better treatments.

Genetic and epigenetic architecture of Obsessive-Compulsive Disorder: In search of possible diagnostic and prognostic biomarkers

Obsessive-Compulsive Disorder (OCD) is a prevalent and severe clinical condition whose hallmarks are excessive, unwanted thoughts (obsessions) and repetitive behaviors (compulsions). The onset of symptoms generally occurs during pre-adult life and typically affects subjects in different aspects of their life's, compromising social and professional relationships. Although robust evidence suggests a genetic component in the etiopathogenesis of OCD, the causes of the disorder are still not completely understood. It is thus of relevance to take into account how genes interact with environmental risk factors, thought to be mediated by epigenetic mechanisms. We here provide an overview of genetic and epigenetic mechanisms of OCD, focusing on the modulation of key central nervous system genes, in the attempt to suggest possible disease biomarkers.

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.

Childhood adversities and 5-HTTLPR polymorphism as risk factors of substance use disorders: retrospective case-control study in Murcia (Spain)

OBJECTIVE

To explore the separate and joint associations of childhood adversities and 5-HTTLPR polymorphism as risk factors for substance use disorders among adults. : Design : Retrospective case-control study.

SETTING

Cases from the substance unit and controls from a representative sample of the adult general population in the metropolitan area of Murcia (Spain).

PARTICIPANTS

Cases were defined as outpatients 18 years old or older currently in the treatment for alcohol, opioids or cocaine use disorders in the clinical unit. Controls were randomly selected among individuals without substance use disorders who participated in the Psychiatric Enquiry to General Population in Southeast Spain-Murcia (PEGASUS-Murcia) project, a cross-sectional study of a representative sample of the adult general population. In all, 142 cases and 531 controls were interviewed and a subsample of 114 cases (80.3%) and 329 controls (62%) provided a biological sample.

EXPOSURE

A history of 12 childhood adversities, lifetime mental disorders and sociodemographic variables was assessed with the Composite International Diagnostic Interview (CIDI)version 3.0). Buccal swabs were obtained to genotype the 5-HTTLPR polymorphism with the biallelic and the triallelic classification.

MAIN OUTCOME AND MEASURE

Multivariable logistic regression models were performed to estimate adjusted ORs and 95% CI.

RESULTS

Childhood adversities were associated with an elevated risk of substance use disorders (OR=5.77, 95% CI 3.46 to 9.61). Homozygotes for the short allele of the 5-HTTLPR polymorphism also showed the elevated risk of substance use disorders for the biallelic and triallelic classification: (1.97 (1.10 to 3.55) and 2.01 (1.11 to 3.64), respectively). No evidence for gene × environment interactions was found.

CONCLUSIONS

Childhood adversities and the 5-HTTLPR polymorphism are involved in the aetiology of substance use disorders though findings exploring the existence of a gene-environment interaction were inconclusive.

Associations of 5HTTLPR polymorphism with major depressive disorder and alcohol dependence: A systematic review and meta-analysis

OBJECTIVE

The neurotransmitter serotonin is understood to control mood and drug response. Carrying a genetic variant in the serotonin transporter gene (5HTT) may increase the risk of major depressive disorder and alcohol dependence. Previous estimates of the association of the S allele of 5HTTLPR polymorphism with major depressive disorder and alcohol dependence have been inconsistent.

METHODS

For the systematic review, we used PubMed MEDLINE and Discovery of The University of Melbourne to search for all relevant case-control studies investigating the associations of 5HTTLPR polymorphism with major depressive disorder and alcohol dependence. Summary odds ratios (OR) and their 95% confidence intervals (CI) were estimated. To investigate whether year of publication, study population or diagnostic criteria used were potential sources of heterogeneity, we performed meta-regression analyses. Publication bias was assessed using Funnel plots and Egger's statistical tests.

RESULTS

We included 23 studies of major depressive disorder without alcohol dependence containing 3392 cases and 5093 controls, and 11 studies of alcohol dependence without major depressive disorder containing 2079 cases and 2273 controls. The summary OR for homozygote carriers of the S allele of 5HTTLPR polymorphism compared with heterozygote and non-carriers combined (SS vs SL+LL genotype) was 1.33 (95% CI = [1.19, 1.48]) for major depressive disorder and 1.18 (95% CI = [1.01, 1.38]) for alcohol dependence. The summary OR per S allele of 5HTTLPR polymorphism was 1.16 (95% CI = [1.08, 1.23]) for major depressive disorder and 1.12 (95% CI = [1.01, 1.23]) for alcohol dependence. Meta-regression models showed that the associations did not substantially change after adjusting for year of publication, study population and diagnostic criteria used. There was no evidence for publication bias of the studies included in our meta-analysis.

CONCLUSIONS

Our meta-analysis confirms that individuals with the homozygous S allele of 5HTTLPR polymorphism are at increased risks of major depressive disorder as well as alcohol dependence. Further studies are required to investigate the association between 5HTTLPR polymorphism and the comorbidity of major depressive disorder and alcohol dependence as well as gene × environmental interactions.

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.

Genetics of alcoholism

Alcohol use and alcohol use disorders are substantially heritable. Variants in genes coding for alcohol metabolic enzymes have long been known to influence consumption. More recent studies in family-based samples have implicated GABRA2, nicotinic receptor genes such as CHRNB3, and a number of other specific single genes as associated with alcohol use disorders. The growing use of genetic analyses, in particular studies using polygenic risk scores; neurobiologic pathways; and methods for quantifying gene × gene and gene × environment interactions have also contributed to an evolving understanding of the genetic architecture of alcohol use disorders. Additionally, the study of behavioral traits associated with alcohol dependence such as impulsivity and sensation seeking, and the influences of demographic factors (i.e., sex and ethnicity) have significantly enhanced the genetics of alcoholism literature. This article provides a brief overview of the current topically relevant findings in the field to date and includes areas of research still requiring attention.

Serotonin transporter gene promoter polymorphism (5-HTTLPR) and alcohol use in general population: interaction effect with birth cohort

RATIONALE AND OBJECTIVE

Prevalence of alcohol use is markedly influenced by socioeconomic conditions and is therefore subject to cohort effects. The common genetic variation 5-HTTLPR (serotonin transporter gene-linked polymorphic region) has been related to several aspects of alcohol use and addiction but with mixed results, probably due to different environmental interaction effects. We aimed at assessing whether the association between alcohol use and 5-HTTLPR genotype is subject to cohort effects as birth cohorts may be raised in significantly different environments.

METHODS

We used the database of the Estonian Children Personality Behaviour and Health Study (beginning in 1998). Cohorts of initially 9-year-old (recalled at ages 15 and 18) and 15-year-old (recalled at ages 18 and 25) children provided self-reports on their alcohol use in all data collection waves (complete data available n = 1,075).

RESULTS

A significant genotype × gender × cohort interaction effect on the age of consuming the first alcoholic drink was found [F(2, 1,063) = 7.2, p < 0.001]. Females with the s/s genotype in the older cohort were the latest experimenters with alcohol, while the s/s females of younger cohort had tried alcohol earlier than any other group. In males, there was no significant cohort × genotype interaction, but the 5-HTTLPR genotype was associated with alcohol use, the s/s subjects reporting the highest consumption.

CONCLUSION

Expression of genetic vulnerability to alcohol use is influenced by birth cohort effects. The 5-HTTLPR genotype is associated with alcohol consumption in general population, but the effect depends on gender and birth cohort.

Alcoholics have more tryptophan hydroxylase 2 mRNA and protein in the dorsal and median raphe nuclei

BACKGROUND

Chronic alcohol use depletes brain serotonin (5-hydroxytryptamine [5-HT]), yet we previously found more tryptophan hydroxylase 2 (TPH2), the rate-limiting biosynthetic enzyme for 5-HT, in the dorsal raphe nucleus (DRN) of alcoholics. We sought to determine whether the increase in amount of TPH2 enzyme is associated with more TPH2 mRNA gene expression in the DRN of a new cohort of alcoholics and controls.

METHODS

TPH2 mRNA and protein were measured by in situ hybridization and immunoautoradiography, respectively, in the DRN and median raphe nucleus (MRN) of age- and sex-matched pairs (n = 16) of alcoholics and nonpsychiatric controls. Alcohol use disorder diagnosis and medical, psychiatric, and family histories were obtained by psychological autopsy. Age and sex were covariates in the analyses.

RESULTS

TPH2 mRNA in alcoholics was greater in the DRN and MRN compared to controls (DRN: controls: 3.6 ± 1.6, alcoholics: 4.8 ± 1.8 nCi/mg of tissue, F = 4.106, p = 0.02; MRN: controls: 2.6 ± 1.2, alcoholics: 3.5 ± 1.1 nCi/mg of tissue, F = 3.96, p = 0.024). The difference in TPH2 mRNA was present in all DRN subnuclei (dorsal [DRd]: 135%, interfascicular [DRif]: 139%, ventral [DRv]: 135%, ventrolateral [DRvl]: 136% of control p < 0.05) except the caudal subnucleus. Alcoholics also had more TPH2 protein in the DRN and MRN than controls (DRN: controls: 265 ± 47, alcoholics: 318 ± 47 μCi/g, F = 8.72, p = 0.001; MRN: controls: 250 ± 33, alcoholics: 345 ± 39 μCi/g, F = 7.78, p = 0.001). There is a positive correlation between TPH2 protein and mRNA expression in the DRN (r = 0.815, p < 0.001), suggesting that the higher amount of TPH2 protein is due to an increase in TPH2 gene expression.

CONCLUSIONS

These findings suggest that greater TPH2 gene expression is the basis for more TPH2 protein in the DRN and MRN in alcoholics.

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.

Serotonin transporter genotype by environment: Studies on alcohol use and misuse in non-human and human primates

Much evidence indicates that gene-by-environment interactions (GxE) play a role in alcohol misuse. It has been proposed that interactions between serotonin and stress confer vulnerability for alcohol misuse. The present review examined studies of the interaction between the serotonin transporter linked polymorphic region (5-HTTLPR) genotype and stressful life events and alcohol-related phenotypes, in rhesus monkeys and humans. Ten studies were found that had investigated the interaction of 5-HTTLPR and various measures of stress and alcohol use or misuse, two studies of rhesus monkeys, and eight of humans. The results are contradictory. Important differences were reported in study samples, experimental designs, measures used to assess environmental variables, definitions and measurements of alcohol-related phenotypes, and in the statistical analyses. These differences may explain the contradictory results. Guidelines for future studies are suggested. Results are discussed in light of findings from molecular, non-human animal, and clinical studies. The review highlights the need for future studies examining associations of interactions between the serotonin transporter gene and environmental factors and alcohol misuse, especially in samples followed over time.

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 transporter gene polymorphisms: a case-control study

Considerable evidence indicates that serotonergic mechanisms, particularly the serotonin transporter, are involved in alcoholism and tobacco use and are influenced by polymorphism of the promoter region of 5HTT (5-HTTLPR). As alcohol and tobacco consumption have been implicated in the pathogenesis of oral cancer, the purpose of this study was to investigate 5-HTTLPR polymorphism in patients with oral squamous cell carcinoma (OSCC) compared with a control group in a sample of Brazilian patients. One hundred and three patients affected by OSCC and 103 volunteers without OSCC were genotyped for 5-HTTLPR. Both groups were matched for age, sex and tobacco use. The chi-squared test was used for statistical analysis (α=0.05). There was no statistically significant difference in 5-HTTLPR genotypes between case and control group (p= 0.408). In conclusion, the present investigation demonstrated that serotonin transporter polymorphisms are not implicated in the OSSC development.

Association of the 5-HTT gene-linked promoter region (5-HTTLPR) polymorphism with psychiatric disorders: review of psychopathology and pharmacotherapy

Serotonin (5-HT) regulates important biological and psychological processes including mood, and may be associated with the development of several psychiatric disorders. An association between psychopathology and genes that regulate 5-HT neurotransmission is a robust area of research. Identification of the genes responsible for the predisposition, development, and pharmacological response of various psychiatric disorders is crucial to the advancement of our understanding of their underlying neurobiology. This review highlights research investigating 5-HT transporter (5-HTTLPR) polymorphism, because studies investigating the impact of the 5-HTTLPR polymorphism have demonstrated significant associations with many psychiatric disorders. Decreased transcriptional activity of the S allele ("risk allele") may be associated with a heightened amygdala response leading to anxiety-related personality traits, major depressive disorder, suicide attempts, and bipolar disorder. By contrast, increased transcriptional activity of the L allele is considered protective for depression but is also associated with completed suicide, nicotine dependence, and attention deficit hyperactivity disorder. For some disorders, such as post-traumatic stress disorder and major depressive disorder, the research suggests that treatment response may vary by allele (such as an enhanced response to serotonin specific reuptake inhibitors in patients with major depressive disorder and post-traumatic stress disorder with L alleles), and for alcohol dependence, the association and treatment for S or L alleles may vary with alcoholic subtype. While some studies suggest that 5-HTTLPR polymorphism can moderate the response to pharmacotherapy, the association between 5-HTTLPR alleles and therapeutic outcomes is inconsistent. The discovery of triallelic 5-HTTLPR alleles (L(A)/L(G)/S) may help to explain some of the conflicting results of many past association studies, while concurrently providing more meaningful data in the future. Studies assessing 5-HTTLPR as the solitary genetic factor contributing to the etiology of psychiatric disorders continue to face the challenges of statistically small effect sizes and limited replication.

Validity and power of missing data imputation for extreme sampling and terminal measures designs in mediation analysis

Several authors have acknowledged that testing mediational hypotheses between treatments, genes, physiological measures, and behaviors may substantially advance our understanding of how these associations operate. In psychiatric research, the costs of measuring the putative mediator or the outcome can be prohibitive. Extreme sampling designs have been validated as methods for reducing study costs by increasing power per subject measured on the more expensive variable when assessing bivariate relationships. However, there exist concerns about how missing data can potentially bias the results. Additionally, most mediation analysis techniques presuppose the joint measurement of mediators and outcomes for all subjects. There have been limited methodological developments for techniques that can evaluate putative mediators in studies that have employed extreme sampling, resulting in missing data. We demonstrate that extreme (selective) sampling strategies can be beneficial in the context of mediation analyses. Handling the missing data with maximum likelihood (ML) resulted in minimal power loss and unbiased parameter estimates. We must be cautious, though, in recommending the ML approach for extreme sampling designs because it yielded inflated Type 1 error rates under some null conditions. Yet, the use of extreme sampling designs and methods to handle the resultant missing data presents a viable research strategy.

[Association of polymorphism in the serotonin transporter gene promote with the susceptibility to alcohol dependence in Yunnan Han Population]

To explore the association of polymorphism in the serotonin transporter gene and the susceptibility to alcohol dependence in Yunnan Han population, PCR and DNA sequencing techniques were used to detect 5-HTT-linked promoter region (5-HTTLPR). One hundred and eighteen alcohol dependent patients as case group and 214 normal people as control group were employed in this study. Significant differences in genotype frequencies were present between case group and control group of 5-HTTLPR (P<0.05). The proportion of L/L and L/S genotype was significantly smaller in case group than that was in control group (OR=0.581, P=0.026). No significant association was observed in allelic frequencies, which differed in different ethnic groups. In conclusion, 5-HTTLPR polymorphism may be associated with alcohol dependent patients, and the genotype L/L or L/S may be a genetic factor that is responsible for decreasing susceptibility of alcohol dependence in Yunnan Han population.

Availability of the serotonin transporter in patients with alcohol dependence

OBJECTIVES

Evidence has suggested that the serotonin transporter (SERT) plays a role in the pathogenesis of alcohol dependence, anxiety and depression and that polymorphisms of the serotonin-transporter-linked promoter region (5-HTTLPR) may influence the SERT. This study evaluated the differences in SERT availability between healthy controls and alcoholic patients and the impact of 5-HTTLPR polymorphisms on SERT availability.

METHODS

Eleven healthy controls and 28 alcoholic patients were recruited. SERT availability was measured in vivo with single photon emission computed tomography and (123)I-labelled 2-((2-((dimethyl-amino)methyl)phenyl)thio)-5-iodophenylamine in the midbrain, thalamus and striatum. Each subject was genotyped for the 5-HTTLPR polymorphism.

RESULTS

Compared to healthy controls, there was a significantly lower availability of SERT in the midbrain among patients with pure alcohol dependence (pure ALC). Of patients with anxiety, depression and alcohol dependence (ANX/DEPALC), the carriers of one L(A) allele showed a significantly higher availability of SERT in the striatum compared to non-L(A) carriers. After Bonferroni correction, these significances vanished. There were no significant differences in SERT availability between controls and ANX/DEP ALC.

CONCLUSIONS

The results suggest that pure alcoholics may have lower SERT availability in the midbrain; the 5HTTLPR polymorphism may influence SERT availability in ANX/DEP ALC. These findings may serve as a springboard for future large-scale studies.

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.

An investigation of associations between alcohol use disorder and polymorphisms on ALDH2, BDNF, 5-HTTLPR, and MTHFR genes in older Korean men

BACKGROUND

This study aimed to investigate the association of alcohol use disorder (AUD) with four candidate genes in older Korean men: aldehyde dehydrogenase 2 (ALDH2, 1/2), brain-derived neurotrophic factor (BDNF, val66met), serotonin transporter gene linked polymorphic region (5-HTTLPR, s/l), and methylenetetrahydrofolate reductase (MTHFR, c.677C > T).

METHODS

A community sample of 300 men aged 65 or over were categorized into 68 subjects with AUD and 232 controls according to clinical examinations and DSM-IV criteria. Genotype distributions and allele frequencies were compared.

RESULTS

Men with AUD had significantly higher ALDH2*1 and BDNF met allele frequencies compared to controls (p-values < 0.05). No significant differences in genotype or allele frequencies were found for 5-HTTLPR or MTHFR (p-values > 0.3).

CONCLUSIONS

AUD was associated with ALDH2*1 and BDNF met alleles in older Korean men. The first is consistent with previous research and likely to be explained by a protective effect of unpleasant symptoms following alcohol consumption associated with ALDH2*2. The second finding is novel and might be accounted for by BDNF-mediated serotonin or dopamine pathways. However, given the relatively small sample size, the results should be regarded as preliminary and requiring independent replication.

Search for genetic markers and functional variants involved in the development of opiate and cocaine addiction and treatment

Addiction to opiates and illicit use of psychostimulants is a chronic, relapsing brain disease that, if left untreated, can cause major medical, social, and economic problems. This article reviews recent progress in studies of association of gene variants with vulnerability to develop opiate and cocaine addictions, focusing primarily on genes of the opioid and monoaminergic systems. In addition, we provide the first evidence of a cis-acting polymorphism and a functional haplotype in the PDYN gene, of significantly higher DNA methylation rate of the OPRM1 gene in the lymphocytes of heroin addicts, and significant differences in genotype frequencies of three single-nucleotide polymorphisms of the P-glycoprotein gene (ABCB1) between "higher" and "lower" methadone doses in methadone-maintained patients. In genomewide and multigene association studies, we found association of several new genes and new variants of known genes with heroin addiction. Finally, we describe the development and application of a novel technique: molecular haplotyping for studies in genetics of drug addiction.

The serotonin transporter gene and risk for alcohol dependence: a meta-analytic review

Previous studies have implicated a relationship between particular allelic variations of the serotonin transporter gene (5HTTLPR) and alcohol dependence. To provide a current estimate of the strength of this association, particularly in light of inconsistent results for 5HTTLPR, we conducted a meta-analytic review of the association between 5HTTLPR and a clinical diagnosis of alcohol dependence. Of 145 studies initially identified, 22 (including 8050 participants) met inclusion criteria. Results indicated that there was a significant albeit modest association between alcohol dependence diagnosis and the presence of at least 1 short allele (OR=1.15, 95% CI=1.01, 1.30, p<.05). Slightly more robust results were observed for participants who were homogeneous for the short allele (OR=1.21, 95% CI=1.02, 1.44, p<.05). These results were unrelated to sex and race/ethnicity of participants; however, the effect size was moderated by study sample size and publication year. Additionally, the fail-safe N analysis indicated potential publication bias. Therefore, although our review indicates that there is a significant association between 5HTTLPR and alcohol dependence diagnosis, this result should be interpreted with caution.

Disruption of the circadian timing systems: molecular mechanisms in mood disorders

Depression is one of the leading causes of morbidity worldwide and represents a huge burden to society. As with many other psychiatric disorders, a genetic basis for depression has been identified. Evidence for the role of circadian genes in depression is particularly compelling. Circadian gene mutations are also associated with circadian rhythm disorders such as familial advanced sleep phase syndrome, delayed sleep phase syndrome, and non-24-hour sleep-wake syndrome. Such disorders, plus the other manifestations of a disrupted circadian system such as hormone dysregulation, are often observed among those with depression. This suggests a shared aetiology between circadian disruption and depression, although the exact mechanisms underlying the association are unclear. This paper reviews the molecular mechanisms involved in depression, with an emphasis on circadian genes. Twin studies in depression have reported probandwise concordance rates of 40% and 70% using narrow and broad diagnostic criteria, respectively, and heritability of over 85% for bipolar disorder. In association studies, increased susceptibility to depression has been noted in those with polymorphisms in the following: D-amino-acid-oxidase activator/G30 gene complex, glucocorticoid receptor gene, serotonin transporter gene, tryptophan hydroxylase 2 gene, dopamine transporter gene and G protein-coupled receptor 50 gene. Polymorphisms in these genes have also been linked to a better or worse response to antidepressant therapy, an increased likelihood of responding poorly to adversity and increased suicide ideation. Polymorphisms in the CLOCK, BMAL1, Per3 and TIMELESS genes have been associated with susceptibility to mood disorder, and single nucleotide polymorphisms and haplotypes in several circadian genes have been observed among those displaying certain circadian phenotypes, including worse mood in the evening, insomnia in mania and early, middle or late insomnia in depression. Manipulation of the circadian timing system via sleep deprivation, bright light or pharmacological therapy has also been shown to alleviate depressive symptoms, providing further evidence for the role of circadian dysfunction in depression pathophysiology. The new antidepressant agomelatine is the first melatonergic antidepressant with an innovative mode of action: it is a melatonergic MT(1), MT(2) receptor agonist and 5-HT(2c) antagonist, and is able to restore the internal clock, which is profoundly disturbed in depression, thus being efficacious in major depressive disorders. In conclusion, a wealth of evidence is now available supporting a genetic basis for depression. The apparent importance of mutations in the circadian genes in determining disease susceptibility, disease recurrence and response to treatment suggests that the circadian pathway represents an attractive target for pharmacological manipulation to improve management of this debilitating disorder.

Genetic and non-genetic influences on the development of co-occurring alcohol problem use and internalizing symptomatology in adolescence: a review

AIMS

Alcohol problem use during adolescence has been linked to a variety of adverse consequences, including cigarette and illicit drug use, delinquency, adverse effects on pubertal brain development and increased risk of morbidity and mortality. In addition, heavy alcohol-drinking adolescents are at increased risk of comorbid psychopathology, including internalizing symptomatology (especially depression and anxiety). A range of genetic and non-genetic factors have been implicated in both alcohol problem use as well as internalizing symptomatology. However, to what extent shared risk factors contribute to their comorbidity in adolescence is poorly understood.

DESIGN

We conducted a systematic review on Medline, PsycINFO, Embase and Web of Science to identify epidemiological and molecular genetic studies published between November 1997 and November 2007 that examined risk factors that may be shared in common between alcohol problem use and internalizing symptomatology in adolescence.

FINDINGS

Externalizing disorders, family alcohol problems and stress, as well as the serotonin transporter (5-HTT) S-allele, the monoamine oxidase A (MAOA) low-activity alleles and the dopamine D2 receptor (DDR2) Taq A1 allele have been associated most frequently with both traits. An increasing number of papers are focusing upon the role of gene-gene (epistasis) and gene-environment interactions in the development of comorbid alcohol problem use and internalizing symptomatology.

CONCLUSIONS

Further research in adolescents is warranted; the increasing availability of large longitudinal genetically informative studies will provide the evidence base from which effective prevention and intervention strategies for comorbid alcohol problems and internalizing symptomatology can be developed.

The relationship between serotonin receptor 1B polymorphisms A-161T and alcohol dependence

BACKGROUND

Several studies have suggested that the serotonin receptor 1B gene (5HT1B) may be important in the pathogenesis of alcohol dependence (alcoholism; ALC; AD). We examined whether 5HT1B gene A-161T polymorphisms (rs130058) are a susceptibility factor for total AD and subgroups of AD. We further explored correlation of this 5HT1B gene variant between anxiety-depression alcoholism (ANX/DEP ALC) and antisocial alcoholism (antisocial ALC) subgroups because of the high comorbidity of anxiety-depression, antisocial personality disorder, and AD.

METHODS

We recruited 522 Han Chinese in Taiwan for this study: 322 AD patients and 200 controls. The patient group was recruited primarily from medical teaching hospitals; patients with antisocial alcoholism were recruited from Taiwanese prisons. Individuals with AD were classified into 3 homogeneous clinical subgroups -- pure alcoholism (pure ALC), ANX/DEP ALC, and antisocial ALC -- using DSM-IV diagnosis. The 5HT1B gene A-161T polymorphism was determined using PCR-RFLP.

RESULTS

No significant differences in genotypic and allelic frequencies were found between controls and the total AD group or between controls and the 3 AD subgroups. However, there were significant differences in the 5HT1B gene A-161T polymorphism at both the genotype and allelic levels between the ANX/DEP ALC and antisocial ALC subgroups.

CONCLUSIONS

This study suggests that the 5HT1B gene A-161T polymorphism alone is not a risk factor for increasing susceptibility to either AD or its subtypes. However, 5HT1B gene A-161T polymorphisms might be one of the common genetic factors between the ANX/DEP ALC and antisocial ALC subgroups.

Serotonin transporter (5-HTTLPR) and monoamine oxidase (MAOA) promoter polymorphisms in women with severe alcoholism

The serotonin system is known to play a pivotal role for mood, behaviour and psychic illness as e.g. alcoholism. Alcoholism in both males and females has been associated with polymorphisms in genes encoding for proteins of importance for central serotonergic function. Genotyping of two functional polymorphisms in the promoter region of the serotonin transporter and monoamine oxidase-A, respectively, (5-HTT-LPR and MAOA-VNTR), was performed in a group of women with severe alcohol addiction. A large sample of adolescent females from a normal population was used as controls. A significantly higher frequency of the LL 5-HTT genotype (high activity) was found in female addicts without a known co-morbid psychiatric disorder than in the controls. Genotype of the MAOA-VNTR polymorphism did not differ significantly between addicts and controls. However, within the group of alcoholics, when the patients with known co-morbid psychiatric disorders were excluded, aggressive anti-social behaviour was significantly linked to the presence of the high activity MAOA allele. The pattern of associations between genotypes of 5-HTT-LPR and MAOA-VNTR in women with severe alcoholism differs from most corresponding studies on males.

A within-group design of nontreatment seeking 5-HTTLPR genotyped alcohol-dependent subjects receiving ondansetron and sertraline

BACKGROUND

Serotonergic mechanisms are associated with the development of alcohol dependence (AD), however, studies evaluating serotonergic medications have produced conflicting results. One hypothesis suggests that differential response may be due to a functional polymorphism of the 5-HTTLPR promoter region of the serotonin re-uptake transporter (5-HTT). The L/L genotype is postulated to be associated with early onset alcoholism and the S/S or S/L genotypes associated with late onset alcoholism. The aim of this study was to match and mismatch L/L, S/S, or S/L genotypes with administration of ondansetron and sertraline.

METHODS

Fifteen nontreatment seeking alcohol-dependent individuals were randomized to 1 of 2 counterbalanced arms to receive either 200 mg/d of sertraline or ondansetron 0.5 mg/d for 3 weeks followed by an alcohol self-administration experiment (ASAE), then received placebo for 3 weeks followed by a second ASAE. Participants then received the alternate drug for 2 weeks followed by a third ASAE.

RESULTS

At the first ASAE compared to sertraline, ondansetron significantly improved drinking outcomes for the L/L genotype for the ASAE volume consumed (100% reduction based on between-subjects comparison, t = 2.35), and for drinks per drinking day during the 7 days prior to the ASAE (79% reduction and t = 4.34). Compared with ondansetron for S/S or S/L genotypes, outcomes at ASAE 1 for sertraline and S/S or S/L genotypes are opposite than hypothesized. Overall, subjects reduced drinking across their participation in the trial, as there appears to be an order effect.

CONCLUSION

This study suggests that ondansetron may reduce alcohol consumption in alcohol-dependent individuals who have the L/L genotype as measured naturalistically and during the ASAE. By contrast there was no support that sertraline reduces alcohol use in individuals who have S/S or S/L genotypes. Evidence in the literature suggests that AD in some individuals may be influenced by a gene by socio-environmental interaction making pharmacological treatment with serotonergic drugs complex. Research must consider that typologies may predict successful treatment of AD in future trials.

Ordered subsets linkage analysis of antisocial behavior in substance use disorder among participants in the Collaborative Study on the Genetics of Alcoholism

Heterogeneity in complex diseases such as Substance Use Disorder (SUD) reduces the power to detect linkage and makes replication of findings in other populations unlikely. It is therefore critical to refine the phenotype and use methods that account for genetic heterogeneity between families. SUD was operationalized as diagnosis of abuse or dependence to alcohol and/or any one of five illicit substances. Whole-genome linkage analysis of 241 extended pedigree families from the Collaborative Study on the Genetics of Alcoholism was performed in Merlin using an affected sibship design. An Ordered Subsets Analysis (OSA) using FLOSS sought to increase the homogeneity of the sample by ranking families by their density of childhood and adult antisocial behaviors, producing new maximum Nonparametric Lod (NPL) scores on each chromosome for each subset of families. Prior to OSA, modest evidence for linkage was found on chromosomes 8 and 17. Although changes in NPL scores were not statistically significant, OSA revealed possible evidence of linkages on chromosome 7, near markers D7S1795 and D7S821. NPL scores >3.0 were also observed on chromosomes 2, 3, 5, 9, and 14. However, the number of families used in these latter subsets for linkage may be too small to be meaningful. Results provide some evidence for the ability of OSA to reduce genetic heterogeneity, and add further support to chromosome 7 as a possible location to search for genes related to various SUD related processes. Nonetheless, replication of these results in other samples is essential.

Serotonin transporter gene polymorphisms and sertraline response in major depression patients

Major depression (MD) has a complex multifactorial etiology with genetic and environmental factors contributing to the disorder. As with all antidepressant treatments, there is variability in drug response due to heredity, generally focusing on genetic polymorphism of the drug-metabolizing transporter genes. The serotonin transporter (5-HTT) gene is a particularly important candidate for genetic involvement in MD disorders owing to its key role in the regulation of serotonergic transmission and is therefore considered to be an interesting candidate in the mechanism of antidepressant drugs. In this study, we have focused on the associations between genetic polymorphisms in two regions of the 5-HTT gene (5-HTTLPR and VNTR) related to sertraline responses. Our sample consisted of 64 unrelated Turkish subjects who strictly met DSM-IV and CGI scores. There was no significant difference between the frequency of the SS, LS, LL, 9/10, 10/10, 9/12, 10/12, and 12/12 genotypes and responses to sertraline. However, the number of patients can be increased and different drugs can be studied in order to find a specific pharmacogenetic relation.

The association between DRD2/ANKK1, 5-HTTLPR gene, and specific personality trait on antisocial alcoholism among Han Chinese in Taiwan

Cloninger suggested that type II alcoholism was associated with higher novelty seeking and less harm avoidance behaviors, which was similar to antisocial alcoholism. Most previous studies have failed to recruit subjects that have antisocial personality disorder without alcoholism due to the high coexisting likelihood of having antisocial personality disorder with alcoholism in the majority of the examined populations. Thus, recruitment of individuals with antisocial non-alcoholism (antisocial personality disorder) served as an important control group in examining Cloninger's hypothesis. Due to the documented protective effects against alcoholism of ALDH2*1/*2 or *2/*2 genotype among the Han Chinese population, we recruited antisocial non-alcoholics from the Han Chinese population in Taiwan to verify Cloninger's hypotheses. A total of 127 Han Chinese subjects were recruited who met the diagnosis of antisocial alcoholism (n = 43) or antisocial non-alcoholism (n = 84). We found that the antisocial alcoholism group scored higher on the novelty seeking behavior than did the antisocial non-alcoholism group (t = 2.61, P = 0.01), but no difference was observed on the harm avoidance dimension between these two groups (t = 0.15, P = 0.88). In the novelty seeking scores, after stratification of DRD2 TaqI A genotypes, only a significant difference in 5-HTTLPR polymorphisms between antisocial alcoholics and antisocial non-alcoholics was found, indicating an interaction between DRD2 TaqI A1+ (include A1/A1 or A1/A2) and 5-HTTLPR S/S genotype (t = 2.75, P = 0.01) However, no significant difference was found in the harm avoidance personality trait between these two groups of Han Chinese in Taiwan.

TPH2 and TPH1: association of variants and interactions with heroin addiction

The tryptophan hydroxylase 2 gene (TPH2) was resequenced at the 5' upstream, coding, and 3' downstream regions, including all 11 exons in 185 subjects. Twenty-three novel and 14 known variants were identified. In a cohort of 583 consecutively ascertained subjects, including normal volunteers and those with specific addictive diseases, six common TPH2 and one TPH1 variant were genotyped. Allele frequencies of three TPH2 variants and the TPH1 variant varied significantly among the four ethnic groups within the control subjects. Of these subjects, 385 who met heroin addiction or control criteria and were of Caucasian, African-American, or Hispanic ethnicity were examined for potential association with vulnerability to develop heroin addiction. At the two locus genotype level in Hispanics, the TPH1 rs1799913 variant was found to significantly interact with the TPH2 rs7963720 variant and heroin addiction (P=0.022), and with the TPH2 rs4290270 variant and heroin addiction (P=0.011). In the African-American group, a significant association of a specific TPH2 haplotype with heroin addiction also was found (SNPHAP, P=0.004; PHASE P=0.036).

How do genes exert their role? Period 3 gene variants and possible influences on mood disorder phenotypes

The action of multiple liability genes is responsible for complex phenotypes at the same time, a single gene, could control several phenotypic features. This is the case of human period 3 gene (hper3), mainly involved in the setting of the biologic clock. Some variants of this gene, besides being associated with the Delayed Sleep Phase Syndrome, showed a key role in determining evening preference rather than morning one. According to this rationale, we hypothesized that this gene could influence circadian mood fluctuations, in mood disorders. Our study demonstrated that rare genetic variants of hper3 are significantly associated to a number of mood disorders features, such as age of onset, response to SSRIs treatment, circadian mood oscillations and characteristics of temperament. These preliminary results could shed further light on the involvement of circadian genes in various aspects of physiological and psychopathological mechanisms of the brain.

Serotonin transporter gene polymorphism and the phenotypic heterogeneity of adult ADHD

The present study investigates possible associations between the 5-HTT control region polymorphism (5-HTTLPR) with adult ADHD, including subtypes, severity, temperament profile and comorbidities. The polymorphic site was genotyped in 312 adult patients with ADHD and 236 controls, all of them Brazilians of European descent. The interviews followed the DSM-IV criteria, using the K-SADS-E for ADHD and oppositional defiant disorder, SCID-I and MINI for comorbidities and the TCI for temperament dimensions. The 5-HTTLPR polymorphism was not associated with ADHD. Carriers of the S allele presented slightly higher inattention and novelty seeking scores, and a higher frequency of drug dependence. These differences do not persist after correction for multiple comparisons. These results suggest that the 5-HTTLPR polymorphism does not have a direct role in the predisposition to adult ADHD. There is suggestive evidence for a small effect in some behavioral phenotypes related to ADHD.

Association analyses of the serotonin transporter gene with lifetime depression and alcohol dependence in the Collaborative Study on the Genetics of Alcoholism (COGA) sample

The objective of this study was to analyze association of the serotonin transporter gene 5-HTTLPR polymorphism on lifetime depression and alcohol dependence in the Collaborative Study on the Genetics of Alcoholism sample. We conducted family-based association analyses in 1913 Caucasians genotyped for the 5-HTTLPR polymorphism. We found evidence for association of the short allele with depression, but no evidence of association with alcohol dependence. On the basis of the evidence that the effect of this polymorphism may be moderated by stressful life events, we classified individuals for the presence and/or absence of stress, as defined by unemployment, relationship problems, or poor health. The evidence for the association with lifetime depression was limited to the group of individuals who had experienced stress, paralleling the direction of effects originally reported by Caspi and colleagues. No evidence was found for the association with alcohol dependence in either the stress or the no-stress groups.

The functional impact of SLC6 transporter genetic variation

Solute carrier 6 (SLC6) is a gene family of ion-coupled plasma membrane cotransporters, including transporters of neurotransmitters, amino acids, and osmolytes that mediate the movement of their substrates into cells to facilitate or regulate synaptic transmission, neurotransmitter recycling, metabolic function, and fluid homeostasis. Polymorphisms in transporter genes may influence expression and activity of transporters and contribute to behavior, traits, and disease. Determining the relationship between the monoamine transporters and complex psychiatric disorders has been a particular challenge that is being met by evolving approaches. Elucidating the functional consequences of and interactions among polymorphic sites is advancing our understanding of this relationship. Examining the influence of environmental influences, especially early-life events, has helped bridge the gap between genotype and phenotype. Refining phenotypes, through assessment of endophenotypes, specific behavioral tasks, medication response, and brain network properties has also improved detection of the impact of genetic variation on complex behavior and disease.

Interactive effects of the serotonin transporter 5-HTTLPR polymorphism and stressful life events on college student drinking and drug use

BACKGROUND

A common functional polymorphism, 5-HTTLPR, in the serotonin transporter gene has been associated with heavy drinking in college students. We examined this polymorphism as it interacted with negative life events to predict drinking and drug use in college students.

METHODS

Daily reports of drinking and drug use obtained using a daily web-based survey were combined with self-reports of past-year negative life events and 5-HTTLPR genotypes in a regression analysis of alcohol and nonprescribed drug use in a sample of 295 college students.

RESULTS

Genotype and negative life events significantly interacted in relation to drinking and drug use outcomes. Individuals homozygous for the short (s) allele who experienced multiple negative life events in the prior year reported more frequent drinking and heavy drinking, stronger intentions to drink, and greater nonprescribed drug use. In individuals homozygous for the long (l) allele, drinking and drug use were unaffected by past-year negative life events. Heterozygous subjects showed drinking outcomes that were intermediate to the two homozygous groups.

CONCLUSIONS

The 5-HTTLPR s-allele is associated with increased drinking and drug use among college students who have experienced multiple negative life events. The s-allele carriers may be at risk for a variety of adverse behavioral outcomes in response to stress.

Interleukin-1 alpha and beta, TNF-alpha and HTTLPR gene variants study on alcohol toxicity and detoxification outcome

Genetic factors may influence the liability to treatment outcome and medical complications in alcoholism. In the present study we investigated the IL-1A rs1800587, IL-1B rs3087258, TNF-alpha rs1799724 and the HTTLPR variants in a sample of 64 alcohol dependents and 47 relatives versus a set of clinical parameters and outcome measures. Alcohol dependents had a less favorable clinical profile compared to relatives (higher cholesterol, triglycerides, glucose, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, gamma-glutamyltransferase). After detoxification, all clinical indexes improved and hepatic enzyme levels were similar in alcohol dependents and relatives, except for the GGT that remained significantly higher in alcohol dependents. Alcoholic depressive and anxiety scores were significantly reduced after detoxification. IL-1A, IL-1B, TNF-alpha and HTTLPR variants were not associated with any baseline clinical index or change after detoxification. In our sample IL-1A, IL-1B, TNF-alpha and HTTLPR do not appear as liability factors for alcohol toxicity or detoxification outcome, however the small sample size may influence the observed results.

Influence of the serotonin transporter gene on comorbid disorders among alcohol-dependent individuals

OBJECTIVE

The role of the human serotonin transporter protein (5-HTT) gene in psychiatric disorders suggests that its variation may influence the comorbidity pattern and the heterogeneity of alcoholism. The aim of the present study is to verify possible associations between the 5-HTTLPR control region polymorphism with alcoholism and comorbid disorders.

METHODS

The polymorphic site was genotyped in 114 patients with alcohol dependence and 218 controls, all of them Brazilians of European descent. A comprehensive diagnostic interview identified the comorbid disorders.

RESULTS

Study participants with alcohol dependence and controls did not differ in the genotype and allele frequencies (genotypes: chi(2) = 2.52, P = 0.28; alleles: chi(2) = 0.37; P = 0.54). Patients with comorbid major depressive disorder (chi(2) = 6.14, P = 0.01), drug abuse (chi(2) = 6.82, P = 0.01) and nicotine dependence (chi(2) = 4.10, P = 0.04), however, presented a higher frequency of the S allele than patients without these comorbidities. Patients with comorbid depression and drug abuse also presented a higher frequency of the S allele than controls.

CONCLUSIONS

The present results are consistent with the importance of the 5-HTT gene in psychiatry. They suggest a role of the 5-HTTLPR polymorphism in a group of comorbid disorders among alcohol-dependent individuals, supporting a genetic influence in alcoholism heterogeneity.

Clinical and genetic characteristics of Korean male alcoholics with and without attention deficit hyperactivity disorder

AIMS

To examine the clinical and genetic characteristics of Korean male alcoholics with and without attention deficit hyperactivity disorder (ADHD).

METHODS

The present study included 85 male alcoholics who were diagnosed as having DSM-IV alcohol dependence. A total of 28 (32.9%) alcoholics were diagnosed as having DSM-IV ADHD with ongoing symptoms in adulthood. For the evaluation of their psychiatric conditions, the alcohol dependence scale (ADS), Beck depression inventory (BDI), Beck anxiety inventory (BAI), Barratt impulsiveness scale (BIS), brief anger-aggression questionnaire (BAQ), overt aggression scale (OAS), codependence test, and obsessive compulsive drinking scale (OCDS) were administered. The genotype frequencies of the dopamine type 2 receptor gene (DRD2), aldehyde dehydrogenase type 2 gene (ALDH2), functional polymorphism in the regulatory region of the serotonin transporter gene (5-HTTLPR), and catechol-O-methyltransferase gene (COMT) polymorphisms were examined.

RESULTS

Compared with alcoholics without ADHD, the mean ages for the onset of pathological drinking and alcohol withdrawal hallucinations were significantly earlier in alcoholics with ADHD. There was also a significant difference in the history of antisocial behaviour between the two groups. Compared with alcoholics without ADHD, the mean scores of the ADS, BDI, BAI, OAS, and OCDS were significantly higher in alcoholics with ADHD. With regard to the codependence test results, the mean scores of the interpersonal problem, low self-esteem and anxiety/fear subscales, and the mean total score of the codependence test were significantly higher in alcoholics with ADHD when compared with those without ADHD. There were no significant differences in the genotype frequencies of the DRD2, ALDH2, 5-HTTLPR, and COMT polymorphisms between alcoholics with and without ADHD.

CONCLUSIONS

The results of this study suggest that the comorbidity of alcohol dependence and ADHD in this Korean sample forms a distinct clinical phenotype that shows an increased severity of alcohol-related symptoms and behavioural/emotional problems and that ADHD is associated with an increased risk for the early onset of alcohol dependence in Korean male alcoholics.

Candidate gene studies in the 21st century: meta-analysis, mediation, moderation

The results of a large body of candidate gene studies of behavioural and psychiatric phenotypes have been largely inconclusive, with most findings failing to replicate reliably. A variety of approaches that augment the 'traditional' candidate gene approach are discussed, including the use of meta-analysis to combine findings from existing published reports, the investigation of mediating variables (including the use of intermediate phenotypes or endophenotypes) and the awareness of possible moderating influences (such as sex or ethnicity) and gene-environment interactions on genetic associations, possibly via epigenetic mechanisms. Advances in genotyping technology will also allow the routine use of haplotype analysis and linkage disequilibrium mapping. Examples of how these approaches may improve our understanding of how genetic associations with behavioural and psychiatric phenotypes obtain are given.

Genetic polymorphisms of alcohol and aldehyde dehydrogenase, dopamine and serotonin transporters in familial and non-familial alcoholism

One hundred and eleven male patients with alcohol dependence and 123 nonalcoholic healthy men were tested for the genetic polymorphisms of alcohol dehydrogenase 2 (ADH2), aldehyde dehydrogenase 2 (ALDH2), serotonin transporter (5-HTT) and dopamine transporter (DAT1). There were significant differences in genotype frequencies of ADH2 C992G and A13543G SNPs between alcoholic patients with family history of alcohol dependence (familial) and alcoholic patients without family history (non-familial). Genotype and allele frequencies of ALDH2 G1951A SNP in familial or non-familial alcoholic patients differ from normal controls. Neither 5-HTTLPR L/S nor DAT1 G2319A SNP genotypes nor alleles discriminated alcoholic patients from normal controls. These findings suggest that the genetic characteristics of alcohol metabolism in non-familial alcoholics fall between non-alcoholism and familial alcoholics.

Gender difference in association between polymorphism of serotonin transporter gene regulatory region and anxiety

OBJECTIVE

The objective of this study was to verify the hypothesis that variation of the serotonin transporter gene promoter region (5-HTTLPR) is associated with sensitivity to stress.

METHODS

Genotyping of 5-HTTLPR and evaluation of emotional states were performed on 194 participants. Participants' emotional states were evaluated using the Perceived-Stress Scale (PSS), the State-Trait Anxiety Inventory (STAI), and the Self-rating Depression Scale (SDS).

RESULTS

There was significant GenderxGenotype interaction in STAI (state, P<.05; trait, P<.05). Females with the l/s genotype showed higher anxiety than those with the s/s genotype in both state and trait anxiety. Oppositely, males with the s/s genotype showed higher anxiety than those with the l/s genotype.

CONCLUSION

On all emotional scales, females with the l/s genotype showed high scores, contrary to males with the same genotype. Therefore, our results suggest that 5-HTTLPR l allele may be one pathway that activates negative emotion in females but acts contrary in males.

Alcoholism: the dissection for endophenotypes

Alcohol dependence (alcoholism) is a complex disorder attributed to the interaction of genetic and environmental factors that form a collage of "disease" predisposition, which is not identical for every alcohol-dependent individual. There is considerable evidence to demonstrate that genetic predisposition accounts for roughly half the risk in the development of alcohol dependence. Both family and population studies have identified a number of genomic regions with suggestive links to alcoholism, yet there have been relatively few definitive findings with regard to genetic determinants of alcoholism. This ambiguity can be attributed to a multitude of complications of studying complex mental disorders, such as clinical heterogeneity, polygenic determinants, reduced penetrance, and epistatic effects. Complex mental disorders are clinical manifestations described by combinations of various signs and symptoms. One approach to overcoming the ambiguity in studying the association between genetic risk factors and disease is to dissect the complex, heterogeneous disorder by using intermediate phenotypes--or endophenotypes--to generate more homogeneous diagnostic groupings than an all-encompassing definition, such as the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV)-derived term "alcohol dependence" or the commonly used term "alcoholism." The advantage of using endophenotypes is that the number of influential factors that contribute to these characteristics should be fewer and more easily identified than the number of factors affecting the heterogeneous entity of alcohol dependence (alcoholism). A variety of alcohol-related characteristics have been investigated in epidemiological, clinical, and basic research as potential endophenotypes of alcohol dependence. These include phenotypes related to alcohol metabolism, physiological and endocrine measures, neural imaging, electrophysiology, personality, drinking behavior, and responses to alcohol and alcohol-derived cues. This review summarizes the current literature, focused on human data, of promising endophenotypes for dissecting alcoholism.

Alcohol dependence and gene x environment interaction in emotion regulation: Is serotonin the link?

Alcohol dependence is characterized by frequent, compulsive and uncontrolled consumption of alcohol associated with behavior of maladaption and destruction. It is an etiologically and clinically heterogeneous syndrome, moderately to highly heritable, and caused by interaction of genes and environment. Alcohol dependence is related to other psychiatric diseases by common neurobiological pathways, including those that modulate reward, behavioral control as well as anxiety and stress response. Alcohol induces adaptive changes in brain function providing the basis for tolerance, craving, withdrawal, and emotional disturbance. The differentiation of psychobiological traits of addictive behavior reflecting neurobiological processes is therefore of particular importance for the dissection of the complex genetic susceptibility to alcohol dependence. A central serotonin (5-HT) deficit is thought to be involved in the pathogenesis of alcohol dependence by modulating motivational behavior, neuroadaptive processes, and resulting emotional disturbance. 5-HT-related impulsive, aggressive, and suicidal behavior has been linked to a primordial personality that is susceptible to alcohol dependence. Although variations in many of the genes that encode receptors, enzymes, and transporters of the 5-HT system have been tested as risk factors for alcohol dependence, genetic analyses of 5-HT signaling in alcohol dependence have mainly been focused on the 5-HT transporter (5-HTT) gene. Due to its central role in the fine-tuning serotonergic neurotransmission, a regulatory variant of the 5-HTT, which is associated with anxiety related traits, is not only a key player in the neurobiological mechanism of gene x environment interaction in the etiology of depression, but also contributes to the risk to develop alcohol dependence with antisocial behavior and suicidality. Evidence for a modulatory effect of allelic variation of 5-HTT function on limbic circuit responses to emotional stimuli suggests that genotype-endophenotype correlations may be accessible to molecular functional imaging of the brain. These new developments have broad implications for our understanding how genetic vulnerability to alcohol dependence is manifested in the brain's response to emotional stimuli.

Role of the serotonin transporter gene and family function in adolescent alcohol consumption

BACKGROUND

That the extent to which a particular individual will engage in problematic behaviors such as delinquency, violence, or drug abuse is determined by the way psychosocial, situational, and hereditary factors interact is widely accepted. However, only recently have researchers begun to investigate the interactions between specific genotypes and psychosocial factors in relation to behavior. The purpose of the present study was to investigate possible interactions between a polymorphism in the promoter region of the serotonin transporter (5-HTT) gene and family relations on adolescent alcohol consumption.

METHODS

A cross-sectional study with a randomized sample from a total population of 16- and 19-year-old adolescents from a Swedish county was conducted. Eighty-one male and 119 female adolescents, who volunteered to participate after having answered a questionnaire, were randomly selected from quartiles of volunteers representing various degrees of psychosocial risk behavior.

RESULTS

5-HTT genotype (p=0.029) and family relations (p=0.022) predicted alcohol consumption independently as well as through an interaction with one another (p=0.05). The model explained 11% of the variance in alcohol consumption. In a binary logistic model, we found that adolescents with the LS variant of the 5-HTT gene and with family relations being "neutral" or "bad" had a 12- to 14-fold increased risk for high intoxication frequency.

CONCLUSIONS

In sum, our results show that a functional polymorphism of the 5-HTT genotype, family relations, and interactions between these variables predict adolescent alcohol consumption in a randomized sample of adolescents.

Association of the serotonin transporter gene polymorphism with Korean male alcoholics

This study investigated the association between the serotonin transporter polymorphism (5-HTTLPR) and alcoholism in the Korean population. In addition, in order to reduce the clinical heterogeneity, sub-analysis was carried out according to some clinical variables such as a family history of alcoholism, aggressive/violent behavior and the age of onset of alcoholism. One hundred and forty-five patients meeting the DSM-VI criteria for alcohol dependence and 201 healthy controls were examined. Genotyping was performed using a polymerase chain reaction (PCR)-based method. The frequency of the L-allele of 5-HTTLPR was significantly higher in the alcohol dependent patients than in the normal controls (chi(2)=19.11, df=1, p<0.001). Furthermore, there was a significant difference in the allelic distribution between the subgroups defined by a family history of alcoholism (chi(2)=4.005, df=1, p=0.045). This study suggests a putative role of the 5-HTTLPR for alcoholism in the Korean population. However, a replication study with larger different ethnic samples and a refinement of the subtype of alcoholism is needed.

Association between the serotonin transporter gene and alcohol consumption in social drinkers

Relatively few studies have investigated the role of the 5HTT gene in intermediate phenotypes such as alcohol consumption in non-alcohol dependent populations. A recent study reported an association with alcohol consumption in a student population. We attempted to replicate these findings and extend on this work in a representative, ethnically homogenous, non-alcohol dependent sample of social drinkers in the United Kingdom. The short allele of the 5HTT gene was significantly associated with increased alcohol consumption (P = 0.03). There was suggestive evidence of a genotype-sex interaction (P = 0.04). Post-hoc tests indicated higher alcohol consumption in men with one or more copies of the short allele, while in women consumption was highest among heterozygotes compared to both homozygote groups. Age at time of data collection and cigarette consumption were entered as covariates. These results replicate recent previous findings and suggest a possibility that this association may differ in men and women.

Molecular genetics of personality

Although initial reports of genetic contributions to personality dimensions were promising, continued empirical support remains controversial. The focus has largely revolved around polymorphisms of the serotonin transporter gene-linked polymorphic region and the D4 dopamine receptor subtype. Equivocal findings likely stem from numerous sources including ethnic diversity of subject samples, phenotypic characterization of personality traits, and insufficient sample sizes. Research has begun to shy away from single gene causation in support of more complex polygenic models of personality traits. This search has identified numerous other candidate genes including dopamine D2 and D3 receptor subtypes, serotonin receptors, and catecholaminergic enzymes, to name a few. This article endeavors to review and evaluate the most recent literature within the context of this burgeoning field. Some considerations for future research are presented in summary.

Meta-analysis of the association of a functional serotonin transporter promoter polymorphism with alcohol dependence

The neurotransmitter serotonin (5-HT) has been shown to regulate alcohol consumption in both animals and humans. Since activity of the 5-HT transporter protein (5-HTT) regulates 5-HT levels, the gene encoding this protein may contribute to the risk of alcohol dependence (AD). Studies of the association to AD of a functional insertion-deletion polymorphism in the 5-HTT-linked promoter region (5-HTTLPR) have yielded inconsistent results. We conducted a meta-analysis of data from 17 published studies (including 3,489 alcoholics and 2,325 controls) investigating the association between 5-HTTLPR alleles and AD. The frequency of the short (S) allele at 5-HTTLPR was significantly associated with AD [odds ratio (OR) = 1.18, 95% CI = 1.03-1.33). Moreover, a greater association with the S allele was seen among individuals with AD complicated by either a co-morbid psychiatric condition or an early-onset or more severe AD subtype [OR = 1.34 (95% CI = 1.11-1.63)]. Allelic variation at 5-HTTLPR contributes to risk for AD, with the greatest effect observed among individuals with a co-occurring clinical feature.