Haplotypes of dopamine and serotonin transporter genes are associated with antisocial personality disorder in alcoholics

Genetic association of SLC6A3 (dopamine transporter) gene polymorphisms with personality disorders and substance abuse disorders: a systematic review and meta-analysis

INTRODUCTION

Personality disorders (PD) are characterized by socially dysfunctional behavioral patterns that affect patients and show higher incidence rates within families. Substance abuse disorders (SAD) are exemplified by extensive and prolonged use of substances, including alcohol, nicotine, or illegal drugs. Genetic predisposition for both PD and SAD has been reported to involve gene variants regulating dopaminergic pathways. Yet, discrepancy among reported results necessitates further elucidation of potential hereditary-related risk factors. Because both disorders impose a societal burden, knowledge on the impact of certain genetic backgrounds on these diseases could help develop evidence-based strategies for efficacious treatment approaches.

MATERIALS AND METHODS

In the present study a systematic review was performed, and the association between dopamine transporter gene polymorphism (SLC6A3), particularly rs28363170 entailing a 40-bp variable number tandem repeat, and PD as well as SAD was investigated recruiting meta-analysis approach.

RESULTS

Initial literature search for PD yielded 1577, from which nine fulfilled eligibility criteria to be used in a meta-analysis including 729 cases and 2113 controls. From the 934 studies retrieved for SAD, only 29 articles with 5221 cases and 4822 controls were used for meta-analysis. A statistically significant association was seen between rs28363170 (for the 9-repeat allele) and PD in European populations according to the co-dominant mode of inheritance. For SAD no statistically significant correlation under any mode of inheritance was observed. There was no indication of time-trend phenomena.

CONCLUSION

Our findings demonstrate the association of SLC6A3 gene polymorphism with PD, thus underling the need to understand neurobiological mechanisms inherent to the above disorders to guide treatment strategies under the perspective of personalized medicine.

The effects of 5-HTTLPR/rs25531 serotonin transporter gene polymorphisms on antisocial personality disorder among criminals in a sample of the Turkish population

Antisocial personality disorder (ASPD) is a cluster B personality disorder characterized by a disposition for criminal behaviors. It has been determined by previous studies that ASPD may have a genetic origin and the human serotonin transporter gene (SLC6A4) is one of the two serotonergic genes expected to be associated with this disorder. 5-HTT-linked polymorphic promoter region (5-HTTLPR) is a degenerate repeat polymorphic region in SLC6A4, the gene that codes for the serotonin transporter. Among many polymorphisms in SLC6A4, 5-HTTLPR an insertion/deletion (indel) polymorphism and rs25531 single nucleotide polymorphism (SNP) in the 5-HTTLPR polymorphic region contribute to the regulation of SLC6A4 expression. In this study, we aimed to reveal the relationship between frequencies of 5-HTTLPR variants and ASPD among criminals in the Turkish population. Moreover, it was also attempted to figure out the SLC6A4 gene expression level differences regarding these polymorphisms. The 5-HTTLPR/rs25531 genotypes were determined by PCR and restriction length polymorphism (RFLP) analyses and quantitative real-time-PCR was done for measuring the gene expression levels in the case and control groups. Although no significant difference was observed in the distributions of the 5-HTTLPR/rs25531 polymorphisms between the case and control groups, SLC6A4 expression level in the control group was found significantly higher than the case group (p < 0.0001). There was also no significant difference between genotypes in terms of mRNA expression levels in either the control or the case group. According to our results, ASPD in Turkish society is associated with the SLC6A4 gene expression levels, though the distributions of 5-HTTLPR polymorphisms are not different. This study sheds light on future relevant studies as the first study which is conducted in criminals with ASPD in the Turkish community.

The dopamine transporter role in psychiatric phenotypes

The dopamine transporter (DAT) is one of the most relevant and investigated neurotransmitter transporters. DAT is a plasma membrane protein which plays a homeostatic role, controlling both extracellular and intracellular concentrations of dopamine (DA). Since unbalanced DA levels are known to be involved in numerous mental disorders, a wealth of investigations has provided valuable insights concerning DAT role into normal brain functioning and pathological processes. Briefly, this extensive but non-systematic review discusses what is recently known about the role of SLC6A3 gene which encodes the dopamine transporter in psychiatric phenotypes. DAT protein, SLC6A3 gene, animal models, neuropsychology, and neuroimaging investigations are also concisely discussed. To conclude, current challenges are reviewed in order to provide perspectives for future studies.

Prevalence Rates of Personality Disorder and Its Association With Methamphetamine Dependence in Compulsory Treatment Facilities in China

Methamphetamine use is popular and rapidly increasing in China, and the co-occurrence of personality disorders has an impact on treatment outcomes and may increase vulnerability of developing dependence. The aim of the present study was to investigate the prevalence rates of personality disorders in methamphetamine users and further explore the association between personality disorders and methamphetamine use status. Five hundred and seventy-seven male methamphetamine users were recruited. The self-developed questionnaire was used for demographics, and a Structural Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) (SCID-I/II) was performed covering psychiatric diagnosis. Our study found the prevalence of antisocial personality disorder in male methamphetamine users was 71.4%, followed by borderline (20.2%) and obsessive-compulsive (17.9%) personality disorder. Borderline and antisocial personality disorders were found to be risk factors of methamphetamine dependence (adjusted odds ratio = 2.891, p = 0.007 and adjusted odds ratio = 1.680, p = 0.042). These findings suggested personality disorders were highly prevalent in male methamphetamine users, and the comorbidity of antisocial and borderline personality disorders are especially associated with methamphetamine dependence.

Possible role of a dysregulation of the endogenous opioid system in antisocial personality disorder

Around half the inmates in prison institutions have antisocial personality disorder (ASPD). A recent theory has proposed that a dysfunction of the endogenous opioid system (EOS) underlies the neurobiology of borderline personality disorder (BPD). In the present theoretical paper, based on a comprehensive database and hand search of the relevant literature, this hypothesis is extended to ASPD, which may be the predominant expression of EOS dysfunction in men, while the same pathology underlies BPD in women. According to evidence from human and animal studies, the problematic behaviours of persons with antisocial, callous, or psychopathic traits may be seen as desperate, unconscious attempts to stimulate their deficient EOS, which plays a key role in brain reward circuits. If the needs of this system are not being met, the affected persons experience dysphoric mood, discomfort, or irritability, and strive to increase binding of endogenous opioids to receptors by using the rewarding effects of aggression by exertion of physical or manipulative power on others, by abusing alcohol or substances that have the reward system as target, by creating an "endorphin rush" by self-harm, by increasing the frequency of their sexual contacts, or by impulsive actions and sensation seeking. Symptoms associated with ASPD can be treated with opioid antagonists like naltrexone, naloxone, or nalmefene.

Mesocorticolimbic dopamine functioning in primary psychopathy: A source of within-group heterogeneity

Despite similar emotional deficiencies, primary psychopathic individuals can be situated on a continuum that spans from controlled to disinhibited. The constructs on which primary psychopaths are found to diverge, such as self-control, cognitive flexibility, and executive functioning, are crucially regulated by dopamine (DA). As such, the goal of this review is to examine which specific alterations in the meso-cortico-limbic DA system and corresponding genes (e.g., TH, DAT, COMT, DRD2, DRD4) might bias development towards a more controlled or disinhibited expression of primary psychopathy. Based on empirical data, it is argued that primary psychopathy is generally related to a higher tonic and population activity of striatal DA neurons and lower levels of D2-type DA receptors in meso-cortico-limbic projections, which may boost motivational drive towards incentive-laden goals, dampen punishment sensitivity, and increase future reward-expectancy. However, increasingly higher levels of DA activity in the striatum (moderate versus pathological elevations), lower levels of DA functionality in the prefrontal cortex, and higher D1-to-D2-type receptor ratios in meso-cortico-limbic projections may lead to increasingly disinhibited and impetuous phenotypes of primary psychopathy. Finally, in order to provide a more coherent view on etiological mechanisms, we discuss interactions between DA and serotonin that are relevant for primary psychopathy.

A Shared Molecular and Genetic Basis for Food and Drug Addiction: Overcoming Hypodopaminergic Trait/State by Incorporating Dopamine Agonistic Therapy in Psychiatry

This article focuses on the shared molecular and neurogenetics of food and drug addiction tied to the understanding of reward deficiency syndrome. Reward deficiency syndrome describes a hypodopaminergic trait/state that provides a rationale for commonality in approaches for treating long-term reduced dopamine function across the reward brain regions. The identification of the role of DNA polymorphic associations with reward circuitry has resulted in new understanding of all addictive behaviors.

Variation in the Serotonin Transporter Gene and Alcoholism: Risk and Response to Pharmacotherapy

SLC6A4, the gene encoding the serotonin transporter protein (5-HTT), has been extensively examined as a risk factor for alcohol dependence (AD). More recently, variability in the transporter gene was identified to be a potential moderator of treatment response to serotonergic medications such as ondansetron and sertraline. There is an insertion-deletion polymorphism in the promoter region (5-HTTLPR) of the SLC6A4, with the most common alleles being a 14-repeat short (S) allele and a 16-repeat long (L) allele. The S allele has often been associated with AD. By contrast, the L allele has been associated with pharmacological responsiveness in some individuals with AD. Differences in clinical phenotype may determine the utility of the 5-HTTLPR polymorphism as a moderator of pharmacological interventions for AD. We review the AD typology and disease onset in the context of pharmacogenetic and genomic studies that examine the utility of 5-HTTLPR in improving treatment outcomes.

Molecular genetics and antisocial behavior: where do we stand?

Over the last two decades, it has become increasingly evident that control of aggressive behavior is modulated by the individual genetic profile as well. Several candidate genes have been proposed to play a role in the risk to develop antisocial behavior, and distinct brain imaging studies have shown that specific cortical areas may be functionally and/or structurally impaired in impulsive violent subjects on the basis of their genotypes. In this paper, we review the findings regarding four polymorphisms-MAOA (Monoamine oxidase A) uVNTR, SLC6A4 (solute carrier family 6 (neurotransmitter transporter), member 4) 5HTTLPR, COMT (Catechol-O-methyltransferase) Val158Met and DRD4 (dopamine D4 receptor) VNTR 1-11-that all have been found to be associated with an increased vulnerability for antisocial and impulsive behavior in response to aversive environmental conditions. These results, however, have not been replicated by other studies, likely because of crucial methodological discrepancies, including variability in the criteria used to define antisocial behavior and assessment of environmental factors. Finally, it has been recently proposed that these genetic variants may actually increase the individual susceptibility not merely to the negative environmental factors, but to the positive ones as well. In this view, such alleles would play a wider modulatory role, by acting as "plasticity" rather than "vulnerability" genes. Overall, these findings have potential important implications that span well outside of neuroscience and psychiatry, to embrace ethics, philosophy, and the law itself, as they pose new challenges to the very notion of Free Will. Novel properly controlled studies that examine multi-allelic genetic profiles, rather than focusing on distinct single variants, will make it possible to achieve a clearer understanding of the molecular underpinnings of the nature by nurture interaction.

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.

Dopamine Genetics and Function in Food and Substance Abuse

Having entered the genomics era with confidence in the future of medicine, including psychiatry, identifying the role of DNA and polymorphic associations with brain reward circuitry has led to a new understanding of all addictive behaviors. It is noteworthy that this strategy may provide treatment for the millions who are the victims of "Reward Deficiency Syndrome" (RDS) a genetic disorder of brain reward circuitry. This article will focus on drugs and food being mutuality addictive, and the role of dopamine genetics and function in addictions, including the interaction of the dopamine transporter, and sodium food. We will briefly review our concept that concerns the genetic antecedents of multiple-addictions (RDS). Studies have also shown that evaluating a panel of established reward genes and polymorphisms enables the stratification of genetic risk to RDS. The panel is called the "Genetic Addiction Risk Score (GARS)", and is a tool for the diagnosis of a genetic predisposition for RDS. The use of this test, as pointed out by others, would benefit the medical community by identifying at risk individuals at a very early age. We encourage, in depth work in both animal and human models of addiction. We encourage further exploration of the neurogenetic correlates of the commonalities between food and drug addiction and endorse forward thinking hypotheses like "The Salted Food Addiction Hypothesis".

Association of COL25A1 with comorbid antisocial personality disorder and substance dependence

BACKGROUND

Antisocial personality disorder (ASPD) is a psychiatric disorder characterized by a long-term pattern of manipulating, exploiting, or violating the rights of others.

METHODS

Subjects ascertained for genetic studies of substance dependence (SD) and diagnosed with ASPD and comorbid SD were included in a two-stage genetic association study. In the discovery stage, 627 single nucleotide polymorphisms (SNPs) located in 179 candidate genes for addiction were analyzed in a case-control cohort and family-based cohort. The significant findings were replicated in an independent case-control cohort.

RESULTS

One SNP, rs13134663, in the collagen XXV alpha 1 gene (COL25A1) was significantly associated with ASPD in both African Americans and European Americans (smallest p values were .0002 and .0004, respectively). There was also evidence of association with the same SNP in independent samples of African American and European American cases and control subjects (p = .035 and .033, respectively). Analysis of the combined set of case-control subjects yielded an allelic p value of 9 × 10(-6) with odds ratio (95% confidence interval) of 1.3 (1.16, 1.47) (smallest p = 1 × 10(-7); Bonferroni threshold p = .00012).

CONCLUSIONS

The COL25A1 gene, located at chromosome 4q25, encodes the collagen-like Alzheimer amyloid plaque component precursor, a type II transmembrane protein specifically expressed in neurons; it co-localizes with amyloid β in senile plaques in Alzheimer disease brains. This SNP maps to the transcription factor binding site and is conserved in 17 vertebrates, including mice and rats. Our findings suggest that COL25A1 may be associated with ASPD, especially in the context of SD.

Early-onset alcohol dependence increases the acoustic startle reflex

BACKGROUND

Hyperreactivity and impaired sensory gating of the acoustic startle response in alcohol dependence has been suggested to reflect a residual effect of previous detoxifications, increasing the severity of subsequent withdrawal episodes. Previous studies on the acoustic startle only included early-onset alcohol-dependent patients. The observed abnormalities may therefore also be specific for this subtype of alcohol dependence. We investigated the acoustic startle response in alcohol-dependent patients and healthy controls and hypothesized that (i) early-onset alcohol-dependent patients show increased acoustic startle responses compared with late-onset alcohol-dependent patients and healthy controls, and (ii) the duration of alcohol dependence or the number of prior detoxifications would not explain the differences in the acoustic startle between early- and late-onset alcohol dependence.

METHODS

The acoustic startle reflex was assessed in detoxified, male alcohol-dependent patients (N = 83) and age-matched healthy male controls (N = 86). Reflex eye blink responses to an auditory startle stimulus were measured by means of electromyographic recordings over the right orbicularis oculi muscle. Reflex amplitudes and levels of prepulse inhibition (PPI) were analyzed.

RESULTS

There was no association between number of previous withdrawals and the startle response or PPI. Early-onset alcohol-dependent patients showed higher acoustic startle amplitudes compared with late-onset alcohol-dependent patients and healthy controls [75/105 dB: F(2, 166) = 9.2, p < 0.001; 85/105 dB: F(2, 166) = 12.1, p < 0.001; 95 dB: F(2, 166) = 8.2, p < 0.001; 105 dB: F(2, 166) = 9.7, p < 0.001], and there were no differences in PPI.

CONCLUSIONS

Increased acoustic startle response in detoxified early-onset alcohol-dependent patients may reflect a trait marker specifically involved in early-onset alcohol dependence. The findings of the current study do not support the hypothesis that the increased startle response is a residual state marker.

Behavioural genetics of the serotonin transporter

The serotonin transporter is a key regulator of the bioavailability of serotonin and therefore any modulation in the expression or action of the transporter would be expected to have consequences on behaviour. The transporter has therefore become a target for pharmaceutical intervention in behavioural and mood disorders. The search for polymorphic variants in the transporter that would associate with neurological disorders has been extensive but has become focused on two domains which are both termed variable number tandem repeat (VNTR)polymorphisms. Both of these VNTRs are in non-coding DNA and therefore proposed to be mechanistically involved in a disorder through their ability to modulate transcriptional or post-transcriptional regulation of the transporter. The most extensively studied is in the promoter and is a bi-allelic insertion/deletion found in the 50 promoter region of the gene 1.2 kb upstream of the transcriptional start site. This VNTR, termed, 5-HTTLPR was initially identified as two variants containing either, 14 (short/deletion) or 16 (long/insertion) copies of a 22 bp repeat. A second widely studied VNTR found in the non-coding region of the transporter is located within intron 2 and comprises 9, 10 or 12 copies of a16–17 bp repeat termed, STin2.9, STin2.10 and STin2.12, respectively. These VNTR polymorphisms have been associated with a range of behavioural and psychiatric disorders including depression, OCD, anxiety and schizophrenia, however often the lack of reproducibility in different cohorts has led to debate on the actual association of the polymorphisms with this extensive range of neurological conditions. Here we review these two polymorphic VNTRs in depth and relate that to pharmaceutical response, their ability to regulate differential transporter expression, their core involvement in gene-environment interaction and their genetic association with specific disorders.

Association between a serotonin transporter promoter polymorphism (5HTTLPR) and personality disorder traits in a community sample

BACKGROUND

The serotonin transporter (SERT) polymorphism (5HTTLPR) has been reported to be associated with several psychiatric conditions. Specific personality disorders could be intermediate factors in the known relationship between 5HTTLPR and psychiatric disorders. This is the first study to test the association between this polymorphism and dimensions of all DSM-IV personality disorders in a community sample.

METHODS

374 white participants were assessed by clinical psychologists using the International Personality Disorder Examination (IPDE). Associations between dimensions of each DSM-IV personality disorder and the long (l) and short (s) alleles of the 5HTTLPR were evaluated using non-parametric tests and regression models.

RESULTS

The s allele of the 5HTTLPR polymorphism was significantly associated with higher avoidant personality trait scores in the whole sample. Males with the s allele had a significantly lower likelihood of higher obsessive-compulsive personality disorder (OCPD) trait scores, whereas females with the s allele were likely to have higher OCPD personality trait scores.

CONCLUSION

This paper provides preliminary data on the relationship between personality disorders and the 5HTTLPR polymorphism. The relationship of the s allele and avoidant PD is consistent with findings of a nonspecific relationship of this polymorphism to anxiety and depressive disorders. Concerning the unusual sexual dimorphic result with OCPD, several hypotheses are presented. These findings need further replication, including a more detailed study of additional variants in SERT.

Dopamine transporter gene variant affecting expression in human brain is associated with bipolar disorder

The gene encoding the dopamine transporter (DAT) has been implicated in CNS disorders, but the responsible polymorphisms remain uncertain. To search for regulatory polymorphisms, we measured allelic DAT mRNA expression in substantia nigra of human autopsy brain tissues, using two marker SNPs (rs6347 in exon 9 and rs27072 in the 3'-UTR). Allelic mRNA expression imbalance (AEI), an indicator of cis-acting regulatory polymorphisms, was observed in all tissues heterozygous for either of the two marker SNPs. SNP scanning of the DAT locus with AEI ratios as the phenotype, followed by in vitro molecular genetics studies, demonstrated that rs27072 C>T affects mRNA expression and translation. Expression of the minor T allele was dynamically regulated in transfected cell cultures, possibly involving microRNA interactions. Both rs6347 and rs3836790 (intron8 5/6 VNTR) also seemed to affect DAT expression, but not the commonly tested 9/10 VNTR in the 3'UTR (rs28363170). All four polymorphisms (rs6347, intron8 5/6 VNTR, rs27072 and 3'UTR 9/10 VNTR) were genotyped in clinical cohorts, representing schizophrenia, bipolar disorder, depression, and controls. Only rs27072 was significantly associated with bipolar disorder (OR = 2.1, p = 0.03). This result was replicated in a second bipolar/control population (OR = 1.65, p = 0.01), supporting a critical role for DAT regulation in bipolar disorder.