Association between low-activity serotonin transporter genotype and heroin dependence: behavioral and personality correlates

Aggressiveness in Italian Children with ADHD: MAOA Gene Polymorphism Involvement

ADHD is a neurodevelopmental disorder that children and adults can develop. A complex interplay of genetic and environmental factors may underlie interindividual variability in ADHD and potentially related aggressive behavior. Using high-resolution molecular biology techniques, we investigated the impact of some MAOA and SLC6A4 variations on ADHD and aggressive behavior in a group of 80 Italian children with ADHD and in 80 healthy controls. We found that homozygous genotypes of MAOA rs6323 and rs1137070 were associated with an increased risk of ADHD (p = 0.02 and p = 0.03, respectively), whereas the heterozygous genotypes (GT of rs6323 and CT of rs1137030) (p = 0.0002 and p = 0.0006) were strongly linked to a lower risk of developing this disorder. In patients with aggressive behavior, we highlighted only a weak negative association of both MAOA polymorphisms (heterozygous genotypes) with aggressiveness, suggesting that these genotypes may be protective towards specific changes in behavior (p = 0.05). Interestingly, an increase in the GG genotype of rs6323 (p = 0.01) and a decrease in GT genotype (p = 0.0005) was also found in patients without aggressive behavior compared to controls. Regarding 5HTT gene genotyping, no allele and genotype differences have been detected among patients and controls. Our work shows that defining a genetic profile of ADHD may help in the early detection of patients who are more vulnerable to ADHD and/or antisocial and aggressive behavior and to design precision-targeted therapies.

Forensic Value of Genetic Variants Associated with Anti-Social Behavior

Insanity defense is sometimes invoked in criminal cases, and its demonstration is usually based on a multifactorial contribution of behavioural, clinical, and neurological elements. Neuroradiological evidence of structural alterations in cerebral areas that involve decision-making and moral reasoning is often accepted as a useful tool in these evaluations. On the other hand, the genetic predisposition to anti-social behavior is still controversial. In this paper, we describe two cases of violent crimes committed by young carriers of genetic variants associated with personality disorder; both the defendants claimed to be insane at the time of the crime. We discuss these cases and review the scientific literature regarding the relationship between legal incapacity/predisposition to criminal behavior and genetic mutations. In conclusion, despite some genetic variants being able to influence several cognitive processes (like moral judgement and impulse control), there is currently no evidence that carriers of these mutations are, per se, incapable of intentionally committing crimes.

Association of Serotonergic Pathway Gene Polymorphisms With Behavioral Parameters in Patients With Opioid Dependence

Background and aims Opioid dependence is a chronic, relapsing substance use disorder with a multifactorial etiology, including a genetic component. Serotonin pathway gene polymorphisms have been an important focus of research for psychiatric disorders, including substance use disorders. This study aimed to identify the association of serotonin pathway gene polymorphisms with self-harm, depressive symptoms, impulsiveness, and aggression in patients with opioid dependence. Method The study group comprised 366 subjects with opioid dependence and 200 healthy volunteers. Patients were assessed for a history of self-harm, depressive symptoms, impulsiveness, and aggression using standard tools. Genomic DNA was used for genotyping of four polymorphisms - 5-HTTLPR, STin2 VNTR, TPH1 A218C, and TPH2 G703T. Results The short allele of 5-HTTLPR polymorphism showed a significant difference between cases (59.8%) and controls (40.1%) (p=0.001) and revealed an association with age at opioid dependence (p=0.033). There was a borderline significance of the short allele of 5-HTTLPR with the duration of opioid use (p=0.061) and non-plan impulsivity (p=0.076), suggesting a role of 5-HTTLPR in the susceptibility of opioid dependence. The other markers did not differ between cases and controls. However, the STin2A polymorphism revealed a significant association with anger scores, which may indicate its role in aggressive behavior. Conclusions The present study, the first of its kind, suggests an association of 5-HTTLPR polymorphism with opioid dependence and STin2A polymorphism with aggressive behavior among opioid-dependence patients, signifying the role of these markers in our patient population.

Early parent-child interactions and substance use disorder: An attachment perspective on a biopsychosocial entanglement

This review aims to elucidate environmental and genetic factors, as well as their epigenetic and neuroendocrine moderators, that may underlie the association between early childhood experiences and Substance Use Disorders (SUD), through the lens of parental attachment. Here we review those attachment-related studies that examined the monoaminergic systems, the hypothalamic pituitary adrenal stress response system, the oxytoninergic system, and the endogenous opioid system from a genetic, epigenetic, and neuroendocrine perspective. Overall, the selected studies point to a moderating effect of insecure attachment between genetic vulnerability and SUD, reasonably through epigenetic modifications. Preliminary evidence suggests that vulnerability to SUDs is related with hypo-methylation (e.g. hyper-expression) of high-risk polymorphisms on the monoaminergic and hypothalamic pituitary adrenal system and hyper-methylation (e.g. hypo-expressions) of protective polymorphisms on the opioid and oxytocin system. These epigenetic modifications may induce a cascade of neuroendocrine changes contributing to the subclinical and behavioural manifestations that precede the clinical onset of SUD. Protective and supportive parenting could hence represent a key therapeutic target to prevent addiction and moderate insecure attachment.

Association Study of SLC6A4 (5-HTTLPR) Polymorphism and Its Promoter Methylation with Rehabilitation Outcome in Patients with Subacute Stroke

Recently it has been suggested that serotonin transporter (SLC6A4) and its 5HTTLPR polymorphism could be involved in post stroke recovery. Here, we characterized the methylation profile of two different CpG islands within the SLC6A4 promoter region in the whole blood of 50 patients with subacute stroke before and after a six-week rehabilitation treatment. These patients were genotyped for 5HTTLPR polymorphism identifying patients on the basis of short (S) and L (L) alleles: 17 patients LL, 22 patients LS and 11 patients SS. At baseline, all CpG sites for both CpG islands displayed a heterogeneous methylation percentage that were not influenced by the different genotypes. After rehabilitation, we found a significant variation in the methylation levels (increase/decrease) in the specific CpG sites of both CpG islands. The statistical analysis showed a significant relationship between the LL, LS and SS alleles and the outcome of the rehabilitation intervention (χ² (2,50) = 6.395, p = 0.041). Specifically, we found a significant difference between patients with or without a favorable outcome in the LL (11.1% with a favorable outcome) and in the SS (54.4% with a favorable outcome) groups. Our data suggest that 5-HTTLPR polymorphisms and SLC6A4 promoter methylation may be employed as a non-invasive biological marker of recovery in patients with stroke undergoing rehabilitation.

Cerebrospinal fluid levels of monoamines among suicide attempters: A systematic review and random-effects meta-analysis

BACKGROUND

It remains unclear whether the dopaminergic and noradrenergic systems may be implied in suicide attempt risk. In addition, although the serotonergic system has been extensively studied, no formal meta-analysis has been performed to examine its association with suicide attempt.

METHODS

Using PRISMA methodology, we performed a systematic literature review and random-effects meta-analyses of the differences in cerebrospinal fluid (CSF) levels of 5-HIAA, HVA and MHPG between suicide attempters and individuals who never attempted suicide.

RESULTS

We identified 30 studies including 937 suicide attempters and 1128 non-attempters; 29 of them measured CSF levels of 5-HIAA, 22 measured CSF levels of HVA and 14 measured CSF levels of MHPG. CSF levels of 5-HIAA and HVA were significantly lower in suicide attempters than in non-attempters [SMD = -0.43 (95% CI: -0.71 to -0.15; p < 0.01) and SMD = -0.45 (95% CI: -0.72 to -0.19; p < 0.01), respectively]. We did not find a significant association between CSF MHPG levels and suicide attempt.

LIMITATIONS

Our analyses relied on a limited number of studies of good quality and most studies included small sample sizes.

CONCLUSION

Both serotonin and dopamine systems may play a role in suicide attempt risk. Our findings suggest that a silo approach to biomarkers should be phased out in favor of the study of multiple systems in parallel and in the same populations to progress in the identification of the biological components independently associated with suicide risk, with the goal of identifying new treatment targets and improving suicide risk prediction.

Association of Serotonin Transporter (SERT) Polymorphisms with Opioid Dependence and Dimensional Aspects of Cocaine Use in a Caucasian Cohort of Opioid Users

INTRODUCTION

A functional tandem repeat polymorphism in the promoter of the serotonin transporter (SERT) gene (SLC6A4) has been studied for association to neuropsychiatric conditions, including substance use disorders. Short (S) forms of this repeat result in reduced transcription, and presumably greater synaptic levels of serotonin, which are involved in opioid and cocaine-induced reward. Dual exposure to heroin and cocaine is a common pattern of poly-drug use and is associated with considerable morbidity. We hypothesize that SLC6A4 variants are associated with cocaine exposure in subjects with an opioid dependence diagnosis (OD), and also in non-dependent opioid users (NOD). Other single nucleotide polymorphisms (SNPs) of SLC6A4 may also be likewise associated.

MATERIALS AND METHODS

This study determined whether variants of the SLC6A4 promoter repeats and two intronic SNPs, rs16965628 and rs2066713, are associated with categorical diagnoses of opioid dependence (DSM-IV criteria) and with dimensional aspects of cocaine use, in a Caucasian cohort (n=591). Three groups of subjects were examined: (1) 276 subjects with opioid dependence diagnosis (OD); (2) 163 subjects who had used opioids for non-medical reasons but never had an opioid dependence diagnosis (NOD); (3) 152 healthy controls (HC).

RESULTS

Aside from high exposure to heroin in the OD group, relatively high exposure to cocaine was detected in both OD and NOD groups. The SERT repeat genotype (classified as "long-long" [LL] versus "short-long" plus "short-short" [SL+SS]) was not associated with categorical opioid dependence diagnoses. A nominally significant association was identified with the [SL+SS] genotype of SLC6A4 and cocaine KMSK scores ≥"cutpoint" for a cocaine dependence diagnosis (p=0.026). The [SL+SS] genotype was associated with more rapid cocaine escalation than the LL genotype. No significant associations of rs16965628 and rs2066713 SNPs were found overall.

CONCLUSION

The functional SERT promoter tandem repeat genotype may be associated to heavy cocaine exposure and more rapid escalation of cocaine use, in persons with and without opioid dependence diagnosis.

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.

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.

VMAT2 gene (SLC18A2) variants associated with a greater risk for developing opioid dependence

Aim: To determine if selected serotonergic and noradrenergic gene variants are associated with heroin addiction. Subjects & methods: A total of 126 variants in 19 genes in subjects with Dutch European ancestry from The Netherlands. Subjects included 281 opioid-dependent volunteers in methadone maintenance or heroin-assisted treatment, 163 opioid-exposed but not opioid-dependent volunteers who have been using illicit opioids but never became opioid-dependent and 153 healthy controls. Results: Nominal associations were indicated for 20 variants in six genes including an experiment-wise significant association from the combined effect of three SLC18A2 SNPs (rs363332, rs363334 and rs363338) with heroin dependence (p_final = 0.047). Conclusion: Further studies are warranted to confirm and elucidate the role of these variants in the vulnerability to opioid addiction.

The influence of the serotonin transporter gene 5-HTTLPR polymorphism on suicidal behaviors: a meta-analysis

Suicidal Behavior (SB) is the second leading cause of death among youths worldwide and the tenth among all age groups. Inherited genetic differences have a role in suicidality with heritability ranging from 30 to 55%. The SLC6A4 5-HTTLPR gene variant has been largely investigated for association with SB, with controversial results. In this work, we sought to determine whether the results of previous meta-analyses were confirmed or modified subsequent to the inclusion of more recent literature data. An electronic literature search was performed to identify relevant studies published until July 2018. Data were analysed through RevMan v5.3. Subgroup and sensitivity meta-analyses were performed considering different SB sub-phenotypes, ethnicity, gender and psychiatric diagnostic categories. Our literature search yielded 1186 articles; among these, we identified 45 pertinent case-control studies (15,341 subjects). No association was found between low-expressing alleles or genotypes (S + L_G alleles or S' carrier genotypes) and SB in the primary analyses. However, low-expressing alleles (S + L_G) were associated with an increased risk of Violent Suicide Attempt (OR = 1.44, C.I. 1.17-1.78, p = .0007). An effect of the same alleles on SB was found in a subpopulation of substance abusers, but this result was not confirmed after the exclusion of healthy subjects from the control group. The other sensitivity meta-analyses did not show any significant effect. Our findings contribute to clarify the conflicting previous evidence by suggesting an association between the 5-HTTLPR and Violent SB. Nonetheless, many other modulators, including environmental factors and epigenetic mechanisms may act to further increase the level of complexity.

Polymorphism of serotonin transporter gene in male subjects with antisocial behavior and MMA fighters

In our study, the frequencies of serotonin transporter gene (5-HTT) polymorphisms and their combinations are compared in the healthy male subjects with antisocial behavior, in general, and in those with its particular forms, as well as in the reference group of MMA fighters. Subjects convicted of unlawful actions were classified into those convicted of violent crimes or non-violent ones. The group of subjects convicted of violent crimes was further subdivided into those convicted of murder, or robbery, or of inflicting grave body injuries. The group of MMA fighters was selected from the subjects without a prior history of antisocial behavior or criminal record in the subjects or their relatives. The frequency of D allele in the groups of convicted subjects and MMA fighters was higher, than in the population sample. Furthermore, the frequencies of D/D and 12/12 genotype combinations were shown to be higher in the group of convicted subjects, especially, in habitual criminals and those convicted of grave crimes or murder. The predisposition of MMA fighters to violent behavior and physical aggressive suppression of an opponent is successfully implemented in their professional career; however, this behavioral pattern appears to represent the controlled aggression.

Median and Dorsal Raphe Serotonergic Neurons Control Moderate Versus Compulsive Cocaine Intake

BACKGROUND

Reduced expression of the serotonin transporter (SERT) promotes anxiety and cocaine intake in both humans and rats. We tested the hypothesis that median raphe nucleus (MRN) and dorsal raphe nucleus (DRN) serotonergic projections differentially mediate these phenotypes.

METHODS

We used virally mediated RNA interference to locally downregulate SERT expression and compared the results with those of constitutive SERT knockout. Rats were allowed either short access (ShA) (1 hour) or long access (LgA) (6 hours) to cocaine self-administration to model moderate versus compulsive-like cocaine taking.

RESULTS

SERT knockdown in the MRN increased cocaine intake selectively under ShA conditions and, like ShA cocaine self-administration, reduced corticotropin-releasing factor (CRF) immunodensity in the paraventricular nucleus of the hypothalamus. In contrast, SERT knockdown in the DRN increased cocaine intake selectively under LgA conditions and, like LgA cocaine self-administration, reduced CRF immunodensity in the central nucleus of the amygdala. SERT knockdown in the MRN or DRN produced anxiety-like behavior, as did withdrawal from ShA or LgA cocaine self-administration. The phenotype of SERT knockout rats was a summation of the phenotypes generated by MRN- and DRN-specific SERT knockdown.

CONCLUSIONS

Our results highlight a differential role of serotonergic projections arising from the MRN and DRN in the regulation of cocaine intake. We propose that a cocaine-induced shift from MRN-driven serotonergic control of CRF levels in the hypothalamus to DRN-driven serotonergic control of CRF levels in the amygdala may contribute to the transition from moderate to compulsive intake of cocaine.

Association of Polymorphisms of Serotonin Transporter (5HTTLPR) and 5-HT2C Receptor Genes with Criminal Behavior in Russian Criminal Offenders

BACKGROUND

Human aggression is a heterogeneous behavior with biological, psychological, and social backgrounds. As the biological mechanisms that regulate aggression are components of both reward-seeking and adversity-fleeing behavior, these phenomena are difficult to disentangle into separate neurochemical processes. Nevertheless, evidence exists linking some forms of aggression to aberrant serotonergic neurotransmission. We determined possible associations between 6 serotonergic neurotransmission-related gene variants and severe criminal offenses.

METHODS

Male Russian prisoners who were convicted for murder (n = 117) or theft (n = 77) were genotyped for variants of the serotonin transporter (5HTTLPR), tryptophan hydroxylase, tryptophan-2,3-dioxygenase, or type 2C (5-HT2C) receptor genes and compared with general-population male controls (n = 161). Prisoners were psychologically phenotyped using the Buss-Durkee Hostility Inventory and the Beck Depression Inventory.

RESULTS

No differences were found between murderers and thieves either concerning genotypes or concerning psychological measures. Comparison of polymorphism distribution between groups of prisoners and controls revealed highly significant associations of 5HTTLPR and 5-HTR2C (rs6318) gene polymorphisms with being convicted for criminal behavior.

CONCLUSIONS

The lack of biological differences between the 2 groups of prisoners indicates that the studied 5HT-related genes do not differentiate between the types of crimes committed.

The association of measures of the serotonin system, personality, alcohol use, and smoking with risk-taking traffic behavior in adolescents in a longitudinal study

Studies on the neurobiological basis of risk-taking behavior have most often focused on the serotonin system. The promoter region of the gene encoding the serotonin transporter contains a polymorphic site (5-HTTLPR) that is important for the transcriptional activity, and studies have demonstrated its association with brain activity and behavior. Another molecular mechanism that reflects the capacity of the central serotonin system is the activity of the enzyme monoamine oxidase (MAO) as measured in platelets. The purpose of the present study was to examine how measures of the serotonin system (platelet MAO activity and the 5-HTTLPR polymorphism), personality variables, alcohol use and smoking are associated with risk-taking traffic behavior in schoolchildren through late adolescence. The younger cohort of the longitudinal Estonian Children Personality Behaviour and Health Study (originally n = 583) filled in questionnaires about personality traits, smoking status, alcohol use and traffic behavior at age 15 and 18 years. From venous blood samples, platelet MAO activity was measured radioenzymatically and 5-HTTLPR was genotyped. During late adolescence, subjects with lower platelet MAO activity were more likely to belong to the high-risk traffic behavior group. Male 5-HTTLPRs'-allele carriers were more likely to belong to the high-risk traffic behavior group compared to the l'/l' homozygotes. Other variables predicting risk group were alcohol use, smoking and Maladaptive impulsivity.The results suggest that lower capacity of the serotoninergic system is associated with more risky traffic behavior during late adolescence, but possibly by different mechanisms in boys and girls.

Biochemical Diagnosis in Substance and Non-substance Addiction

An optimal biochemical marker for addiction would be some easily traced molecules in body specimens, which indicates indulgent addictive behaviors, or susceptibility to certain addictive stimuli. In this chapter, we discussed existing literature about possible biomarkers, and classified them into three categories: origin forms and metabolites of substances, markers from biochemical responses to certain addiction, and genetic and epigenetic biomarkers suggesting susceptibility to addiction. In every category, we examined studies concerning certain type of addiction one by one, with focuses mainly on opiates, psychostimulants, and pathological gambling. Several promising molecules were highlighted, including those of neurotrophic factors, inflammatory factors, and indicators of vascular injury, and genetic and epigenetic biomarkers such as serum miRNAs. DNA methylation signatures and signal nucleotide polymorphism of candidate gene underlying the addiction.

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.

Susceptibility loci for heroin and cocaine addiction in the serotonergic and adrenergic pathways in populations of different ancestry

BACKGROUND

Drug addiction is influenced by genetic factors.

AIM

To determine if genetic variants in the serotonergic and adrenergic pathways are associated with heroin and/or cocaine addiction.

SUBJECTS & METHODS

The study examined 140 polymorphisms in 19 genes in 1855 subjects with predominantly European or African ancestries.

RESULTS

A total of 38 polymorphisms (13 genes) showed nominal associations, including novel associations in S100A10 (p11) and SLC18A2 (VMAT2). The association of HTR3B SNP rs11606194 with heroin addiction in the European ancestry subgroup remained significant after correction for multiple testing (p(corrected) = 0.04).

CONCLUSION

The study strengthens our previous findings of association of polymorphisms in HTR3A, HTR3B and ADRA1A. The study suggests partial overlap in genetic susceptibility between populations of different ancestry and between heroin and cocaine addiction.

The association between heroin expenditure and dopamine transporter availability--a single-photon emission computed tomography study

One of the consequences of heroin dependency is a huge expenditure on drugs. This underlying economic expense may be a grave burden for heroin users and may lead to criminal behavior, which is a huge cost to society. The neuropsychological mechanism related to heroin purchase remains unclear. Based on recent findings and the established dopamine hypothesis of addiction, we speculated that expenditure on heroin and central dopamine activity may be associated. A total of 21 heroin users were enrolled in this study. The annual expenditure on heroin was assessed, and the availability of the dopamine transporter (DAT) was assessed by single-photon emission computed tomography (SPECT) using [(99m)TC]TRODAT-1. Parametric and nonparametric correlation analyses indicated that annual expenditure on heroin was significantly and negatively correlated with the availability of striatal DAT. After adjustment for potential confounders, the predictive power of DAT availability was significant. Striatal dopamine function may be associated with opioid purchasing behavior among heroin users, and the cycle of spiraling dysfunction in the dopamine reward system could play a role in this association.

Genetics of opiate addiction

Addiction to MOP-r agonists such as heroin (and also addiction to prescription opioids) has reemerged as an epidemic in the twenty first century, causing massive morbidity. Understanding the genetics contributing to susceptibility to this disease is crucial for the identification of novel therapeutic targets, and also for discovery of genetic markers which would indicate relative protection or vulnerability from addiction, and relative responsiveness to pharmacotherapy. This information could thus eventually inform clinical practice. In this review, we focus primarily on association studies of heroin and opiate addiction, and further describe the studies which have been replicated in this field, and are thus more likely to be useful for translational efforts.

Role of psychosocial factors and serotonin transporter genotype in male adolescent criminal activity

INTRODUCTION

Violent behavior is influenced by various environmental factors and the serotonergic circuitry alike. Nevertheless, studies on relations among genes, personality, social environment, and juvenile violent behavior are limited, and there is no such study in China.

METHODS

In the current study, we aimed to investigate the contribution of serotonin transporter (5-HTT) polymorphisms to the development of violence and to explore the relations among genes, personality, social environment, and juvenile violent behavior in China. We recruited 213 male adolescents with violent crime history and 145 male adolescents without violent crime history. The association between each risk factor and violent behavior for all the participants was examined, and the interrelation of the domains (personality, family, social support, coping style, impulsivity, and aggression) and the adolescents' violent behavior was analyzed. Chi-square test was used to examine the association between genotypes and violent behavior.

RESULTS

Adolescents with a violent crime history had lower education levels, higher neuroticism and psychoticism, but lower dissimulate. Social support and coping style were significantly associated with their criminal behaviors.

DISCUSSION

The 5-HTTLPR genotype distributions differed significantly between the violent and nonviolent groups.

The role of 5-HTTLPR polymorphism in alcohol craving experience

The way in which genetic risk mediates the development of craving in alcohol dependence is still relatively unknown. The authors sought to clarify the extent to which alcohol craving could be predicted by a relevant polymorphism in the promoter region of the gene encoding the 5-HT transporter (5-HTTLPR). A sample of 101 alcohol-dependent patients admitted for alcohol treatment was recruited for the study. At admission, blood samples were taken for DNA extraction and alcohol craving information was collected with a composite measure. The 5-HTT polymorphism was genotyped. Alcohol dependent patients who were homozygous for the long allele (LL) self-reported higher scores of craving when compared to patients that were homozygous for the short allele (SS). However, the results were not statistically significant. Also, no significant associations were observed between the 5-HTTLPR genotype and other drinking variables. No 5-HTTLPR genotype effects were observed on alcohol craving experience in a sample of alcohol-dependent outpatients.

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.

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 long arm of adolescence: school health behavioral environments, tobacco and alcohol co-use, and the 5HTTLPR gene

Although sociologists, demographers, and others have thoroughly studied contextual and life course influences on tobacco and alcohol use in adolescence and young adulthood, far less attention has been paid to the determinants of tobacco and alcohol co-use. This is important to remedy because co-use has a nonadditive effect on long-term health. In this article, we use nationally representative, longitudinal data from adolescents and young adults to examine patterns of joint tobacco and alcohol use behaviors across the life course. Importantly, we describe how these trajectories are linked to respondents' high school's joint profile of tobacco and alcohol use, measured two ways: as the proportion of tobacco and alcohol co-users, and as the "excess proportion" above that expected based on the marginal probabilities of smoking and drinking in that school. Joint tobacco and alcohol use is associated with both measures, emphasizing the "long arm" of adolescent contexts. Furthermore, we extend previous research to assess whether there is a gene-environment interaction between this school-level measure, 5HTTLPR, and tobacco and alcohol co-use, as suggested by recent work analyzing drinking and smoking separately. We find evidence of such a pattern but conclude that it is likely to be due to population stratification or other forms of confounding.

Serotonin Transporter Genotype Linked to Adolescent Substance Use Treatment Outcome through Externalizing Behavior

Meta-analyses suggest that the serotonin transporter linked polymorphic region (5-HTTLPR) short (S) allele, relative to the long (L) allele, is associated with risk for alcohol dependence, particularly among individuals with early onset antisocial alcoholism. Youth in substance use treatment tend to show antisocial or externalizing behaviors, such as conduct problems, which predict worse treatment outcome. This study examined a pathway in which 5-HTTLPR genotype is associated with externalizing behavior, and the intermediate phenotype of externalizing behavior serves as a link between 5-HTTLPR genotype and substance use treatment outcome in youth. Adolescents (n = 142) who were recruited from addictions treatment were genotyped for 5-HTTLPR polymorphisms (S and LG carriers vs. LALA), assessed for externalizing and internalizing behaviors shortly after starting treatment, and followed over 6-months. 5-HTTLPR genotype was not associated with internalizing behaviors, and was not directly associated with 6-month substance use outcomes. However, 5-HTTLPR genotype was associated with externalizing behaviors (S and LG > LALA), and externalizing behaviors predicted alcohol and marijuana problem severity at 6-month follow-up. Results indicated an indirect (p < 0.05) and non-specific (i.e., both alcohol and marijuana severity) effect of 5-HTTLPR genotype on youth substance use treatment outcomes, with externalizing behaviors as an important linking factor. Adolescents in substance use treatment with low expressing (S and LG) 5-HTTLPR alleles and externalizing behavior might benefit from intervention that addresses serotonergic functioning, externalizing behaviors, and substance use to improve outcomes.

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.

NCK2 is significantly associated with opiates addiction in African-origin men

Substance dependence is a complex environmental and genetic disorder with significant social and medical concerns. Understanding the etiology of substance dependence is imperative to the development of effective treatment and prevention strategies. To this end, substantial effort has been made to identify genes underlying substance dependence, and in recent years, genome-wide association studies (GWASs) have led to discoveries of numerous genetic variants for complex diseases including substance dependence. Most of the GWAS discoveries were only based on single nucleotide polymorphisms (SNPs) and a single dichotomized outcome. By employing both SNP- and gene-based methods of analysis, we identified a strong (odds ratio = 13.87) and significant (P value = 1.33E - 11) association of an SNP in the NCK2 gene on chromosome 2 with opiates addiction in African-origin men. Codependence analysis also identified a genome-wide significant association between NCK2 and comorbidity of substance dependence (P value = 3.65E - 08) in African-origin men. Furthermore, we observed that the association between the NCK2 gene (P value = 3.12E - 10) and opiates addiction reached the gene-based genome-wide significant level. In summary, our findings provided the first evidence for the involvement of NCK2 in the susceptibility to opiates addiction and further revealed the racial and gender specificities of its impact.

The role of the serotonergic system at the interface of aggression and suicide

Alterations in serotonin (5-HT) neurochemistry have been implicated in the aetiology of all major neuropsychiatric disorders, ranging from schizophrenia to mood and anxiety-spectrum disorders. This review will focus on the multifaceted implications of 5-HT-ergic dysfunctions in the pathophysiology of aggressive and suicidal behaviours. After a brief overview of the anatomical distribution of the 5-HT-ergic system in the key brain areas that govern aggression and suicidal behaviours, the implication of 5-HT markers (5-HT receptors, transporter as well as synthetic and metabolic enzymes) in these conditions is discussed. In this regard, particular emphasis is placed on the integration of pharmacological and genetic evidence from animal studies with the findings of human experimental and genetic association studies. Traditional views postulated an inverse relationship between 5-HT and aggression and suicidal behaviours; however, ample evidence has shown that this perspective may be overly simplistic, and that such pathological manifestations may reflect alterations in 5-HT homoeostasis due to the interaction of genetic, environmental and gender-related factors, particularly during early critical developmental stages. The development of animal models that may capture the complexity of such interactions promises to afford a powerful tool to elucidate the pathophysiology of impulsive aggression and suicidability, and identify new effective therapies for these conditions.

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.

The association between availability of serotonin transporters and time to relapse in heroin users: a two-isotope SPECT small sample pilot study

Neuroimaging evidence supporting an association between either dopamine or serotonin and time to relapse of heroin users is limited. In this two-isotope SPECT small sample (N=9) pilot study, the relationship between the availability of serotonin transporter (SERT) and dopamine transporter (DAT) and the relapse of heroin users was investigated. A significant negative association between SERT availability and time to relapse among those who relapsed (N=7) was found.

Clinical implications of genetic variation in the serotonin transporter promoter region: a review

OBJECTIVE

To determine the state of the art in understanding the role of genetic variation in the serotonin transporter (5-HTT) promoter region (5-HTTLPR) in the development of a depressive episode and in its response to treatment.

DATA SOURCES

PubMed and Ovid were used to search for articles published prior to December 2007 utilizing the key words serotonin transporter, 5-HTT, 5-HTTLPR, serotonin transporter gene, and SLC6A4.

STUDY SELECTION

All studies were reviewed, but case reports and small case series were excluded.

DATA EXTRACTION

All relevant articles were read by at least 2 of the coauthors and notes regarding study design, measures, data analysis, and findings were later used to construct the review.

DATA SYNTHESIS

A common genetic variant, the short allele, in which 44 base pairs are missing from the promoter of SLC6A4, is associated with a greater risk for developing a major depressive disorder in patients following exposure to adversity. This association appears to be most important in the early stages of the depressive disorder. Additionally, the likelihood of a positive response to antidepressant treatment may be reduced in these patients in terms of delayed response, greater adverse event load, or, in bipolar patients, mania induction and rapid cycling.

CONCLUSIONS

Selected genetic testing of patients with a recent history of significant adversity may be a reasonable tool that can enlighten treatment options and the course of illness. Ongoing work with the short allele of 5-HTT may also inform clinical guidelines of long-term treatment with antidepressants.

Interaction of serotonin transporter linked polymorphic region and childhood neglect on criminal behavior and substance use for males and females

Childhood neglect has been cited as a risk factor for later substance abuse and criminal behavior. However, a large body of literature shows that a substantial percentage of neglected and abused individuals do not go on to abuse substances or engage in criminal behavior. The current study investigates whether a genetic variant (serotonin transporter linked polymorphic region [5-HTTLPR]) in the 5-hydroxytryptamine (5-HTT) gene moderates the effect of childhood neglect on alcohol use problems, marijuana use, and criminal behavior. Data from the National Longitudinal Study of Adolescent Health shows that 5-HTTLPR conditions the effect of neglect on marijuana use for females, but not for males. Findings also reveal a significant gene-environment correlation between 5-HTTLPR and neglect for females only. These results suggest that 5-HTTLPR is associated with an increased risk of neglect for females, and it also increases neglected females' risk of abusing marijuana.

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.

Common and specific liability to addiction: approaches to association studies of opioid addiction

BACKGROUND

Opioid addiction, whether to opiates such as heroin and morphine, and/or to non-medical use of opioids, is a major problem worldwide. Although drug-induced and environmental factors are essential for the liability to develop opioid addiction, the genetic background of an individual is now known also to play a substantial role.

METHODS

The overall goal of this article is to address the common and specific liabilities to addiction in the context of approaches to studies of one addiction, opioid addiction. Literature on identifying genetic variants that may play a role in the development of opioid addiction was reviewed.

RESULTS

A substantial number of genetic variants have been reported to be associated with opioid addiction. No single variant has been found in any of the reported GWAS studies with a substantial effect size on the liability to develop heroin addiction. It appears that there is a complex interaction of a large number of variants, some rare, some common, which interact with the environment and in response to specific drugs of abuse to increase the liability of developing opioid addiction.

CONCLUSIONS

In spite of the inherent difficulties in obtaining large well-phenotyped cohorts for genetic studies, new findings have been reported that are being used to develop testable hypotheses into the biological basis of opioid addiction.

5-HTTLPR as a potential moderator of the effects of adverse childhood experiences on risk of antisocial personality disorder

INTRODUCTION

Antisocial personality disorder (ASPD) frequently co-occurs with substance dependence (SD). A functional polymorphism (5-HTTLPR) in the serotonin transporter gene has been widely studied as a risk factor for a variety of psychopathologic conditions including aggressive/violent behavior. Childhood abuse is an important predictor of ASPD. We examined 5-HTTLPR genotype and adverse childhood events (ACEs) as risk factors for ASPD in a SD sample.

MATERIALS AND METHODS

Study participants [602 European-Americans (EAs) and 779 African-Americans (AAs)] were interviewed to obtain lifetime diagnoses of ASPD and SD and information on ACEs. Triallelic genotypes for 5-HTTLPR were obtained using standard methods. We used logistic generalized estimating equations regression to examine ACEs and 5-HTTLPR genotype and their interaction as predictors of ASPD, separately by population group.

RESULTS

There were 203 (14.7%) participants diagnosed with ASPD. The frequency of the low-activity 5-HTTLPR S' allele did not differ by ASPD diagnosis, and there was no overall 5-HTTLPR×ACE interaction. However, among European-Americans, male sex (odds ratio=3.36; P<0.001) and ACE history (odds ratio=1.47; P=0.002) were significant predictors of ASPD. Among AAs, there was a significant interaction of sex×5-HTTLPR genotype×ACEs (χ=13.92, P<0.001). Among AA men, each additional ACE significantly increased the odds of ASPD irrespective of genotype, whereas among AA women, the effect of ACEs on ASPD was significant only among S' homozygotes. However, these results are limited by the small sample size in each subgroup, (particularly AA women with S'S' genotype; N=7) and require replication.

CONCLUSIONS

Childhood maltreatment contributes to the risk of ASPD, an effect for which there is preliminary evidence of moderation by 5-HTTLPR genotype in AA women.

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.

Using trajectory analyses to refine phenotype for genetic association: conduct problems and the serotonin transporter (5HTTLPR)

BACKGROUND

Conduct disorder is a serious, relatively common disorder of childhood and adolescence. Findings from genetic association studies searching for genetic determinants of the liability toward such behaviors have been inconsistent. One possible explanation for differential results is that most studies define phenotype from a single assessment; for many adolescents conduct problems decrease in severity over time, whereas for others such behaviors persist. Therefore, longitudinal datasets offer the opportunity to refine phenotype.

METHODS

We used Caucasians that were first assessed during adolescence from the National Youth Survey Family Study. Nine waves of data were used to create latent growth trajectories and test for associations between trajectory class and 5HTTLPR genotype.

RESULTS

For the full sample, 5HTTLPR was not associated with conduct problem phenotypes. However, the short (s) allele was associated with chronic conduct problems in females; a nominally significant sex by 5HTTLPR genotype interaction was noted.

CONCLUSION

Longitudinal studies provide unique opportunities for phenotypic refinement and such techniques, with large samples, may be useful for phenotypic definition with other study designs, such as whole genome association studies.

Adverse childhood experiences (ACEs), genetic polymorphisms and neurochemical correlates in experimentation with psychotropic drugs among adolescents

Epidemiological and clinical data show frequent associations between adverse childhood experiences (ACEs) and substance abuse susceptibility particularly in adolescents. A large body of evidences suggests that the possible dysregulation of neuroendocrine responses as well as neurotransmitters function induced by childhood traumatic experiences and emotional neglect could constitute one of the essential biological changes implementing substance abuse vulnerability. Moreover, genotype variables and its environment interactions have been associated with an increased risk for early onset substance abuse. In this paper we present several data that support the hypothesis of the involvement of hypothalamus-pituitary-adrenal (HPA) axis in mediating the combined effect of early adverse experiences and gene variants affecting neurotransmission. The presented data also confirm the relationship between basal plasma levels of cortisol and ACTH, on the one hand, and retrospective measures of neglect during childhood on the other hand: the higher the mother and father neglect (CECA-Q) scores are, the higher the plasma levels of the two HPA hormones are. Furthermore, such positive relationship has been proved to be particularly effective and important when associated with the "S" promoter polymorphism of the gene encoding the 5-HTT transporter, both in homozygote and heterozygote individuals.

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.

Pharmacogenetics of drug dependence: role of gene variations in susceptibility and treatment

Drug dependency is a highly prevalent mental health disorder that imposes a significant burden on those directly affected, health care systems, and society in general. There is substantial heritability in the susceptibility to drug addiction, which indicates that there are genetic risk factors. Variation in the human genome is abundant and can directly affect drug dependency phenotypes, for example, by altering the function of a gene product or by altering gene expression. Pharmacogenetic studies can assess the effects of genetic variation on the risk for a particular phenotype (e.g., being an alcoholic). In addition, pharmacogenetic variability in treatment efficacy and adverse reactions can be investigated to identify particular genetic variants associated with altered responses. This review highlights examples of genetic variations that are important in the development and maintenance of specific drug dependencies as well as those that affect the response to treatment.

Behavioral genetics in antisocial spectrum disorders and psychopathy: a review of the recent literature

Behavioral geneticists are increasingly using the tools of molecular genetics to extend upon discoveries from twin, family, and adoption studies concerning the heritability of antisocial spectrum disorders and psychopathy. While there is a substantial body of research concerning antisocial spectrum disorders in the behavioral genetics literature, only a few studies could be located using the phenotype of psychopathy. In this report we summarize some of the recent molecular genetics work concerning antisocial spectrum disorders and psychopathy, with a focus on genes involved in the serotonergic and dopaminergic pathways, while also mentioning some of the novel genetic factors being considered. Monoamine oxidase (MAOA) and the serotonin transporter (5HTT) are reviewed at length, as these genes have received significant scientific attention in recent years and are sites of high biological plausibility in antisocial spectrum disorders and psychopathy.

Association of verbal and figural creative achievement with polymorphism in the human serotonin transporter gene

The purpose of this study was to examine the potential association between the S (short) and L (long) alleles of the 5-HTTLPR polymorphism of the serotonin transporter (5-HTT) gene and verbal and figural creative ability. Sixty-two unrelated Caucasian university students (29 men and 33 women) participated in the experiment. The results showed a significant association between verbal and figural creativity scores and the 5-HTTLPR polymorphism. The subjects with S/S and L/S genotypes demonstrated higher verbal creativity scores in comparison with the L/L genotype carriers. The carriers of S/S genotype demonstrated also higher figural creativity scores in comparison with the carries of L/S and L/L genotypes. Thus, it is the first report on a significant association between the 5-HTTLPR polymorphism and creative achievements. As the 5-HTTLPR polymorphism is associated with genetically defined alteration in the brain serotonergic neurotransmission our result provides an evidence of the involvement of the central serotonin system in creativity regulation.

Genetic variation in the serotonin transporter gene (5-HTTLPR, rs25531) influences the analgesic response to the short acting opioid Remifentanil in humans

Background

There is evidence from animal studies that serotonin (5-HT) can influence the antinociceptive effects of opioids at the spinal cord level. Therefore, there could be an influence of genetic polymorphisms in the serotonin system on individual variability in response to opioid treatment of pain. The serotonin transporter (5-HTT) is a key regulator of serotonin metabolism and availability and its gene harbors several known polymorphisms that are known to affect 5-HTT expression (e.g. 5-HTTLPR, rs25531). The aim of this study was to investigate if the triallelic 5-HTTLPR influences pain sensitivity or the analgesic effect of opioids in humans. 43 healthy volunteers (12 men, 31 women, mean age 26 years) underwent heat pain stimulations before and after intravenous injection of Remifentanil; a rapid and potent opioid drug acting on μ-type receptors. Subjects rated their perceived pain on a visual analogue scale (VAS). All participants were genotyped for the 5-HTTLPR and the rs25531 polymorphism. We recruited by advertising, with no history of drug abuse, chronic pain or psychiatric disorders.

Results

At baseline, there was no difference in pain ratings for the different triallelic 5-HTTLPR genotype groups. However, the opiod drug had a differential analgesic effect depending on the triallelic 5-HTTLPR genotype. Remifentanil had a significantly better analgesic effect in individuals with a genotype coding for low 5-HTT expression (S_A/S_A and S_A/L_G) as compared to those with high expression(L_A/L_A), p < 0.02. The analgesic effect for the three different genotype groups was linear to degree of 5-HTT expression.

Conclusion

This is the first report showing an influence of the triallelic 5-HTTLPR on pain sensitivity or the analgesic effect of opioids in humans. Previously the 5-HTTLPR s-allele has been associated with higher risk of developing chronic pain conditions but in this study we show that the genotype coding for low 5-HTT expression is associated with a better analgesic effect of an opioid. The s-allele has been associated with downregulation of 5-HT1 receptors and we suggest that individuals with a desensitization of 5-HT1 receptors have an increased analgesic response to opioids during acute pain stimuli, but may still be at increased risk of developing chronic pain conditions.

The relation of ADHD and violent aggression: What can we learn from epidemiological and genetic studies?

Disruptive behavior includes psychopathological and behavioral constructs like aggression, impulsivity, violence, antisociality and psychopathy and is often closely related with diagnostic categories like conduct disorder (CD), attention deficit disorder (ADHD) and antisocial personality disorder (ASP). There is now clear evidence that neurobiological and environmental factors contribute to these phenotypes. A mounting body of evidence also suggests interactive effects of genetic and environmental risks. In this selective review we give an overview over epidemiological aspects of the relation between ADHD and antisocial behavior, including violent aggression and psychopathy. Moreover, we summarize recent findings from molecular genetic studies and particularly discuss pleiotropic effects of a functional polymorphism of the serotonin transporter promoter gene (5HTTLPR) and childhood adversity on ADHD and violent behavior. The reported gene-environment interactions are not only informative for understanding the neurobiological underpinnings of disruptive behavior, but also throw some light on the relation between ADHD and violent behavior from a genetic perspective. The impact of genetic research on forensic psychiatry and future directions of neurobiological research are discussed.