Influence of SERTPR and STin2 in the serotonin transporter gene on the effect of selective serotonin reuptake inhibitors in depression: a systematic review

Understanding the Biological Relationship between Migraine and Depression

Migraine is a highly prevalent neurological disorder. Among the risk factors identified, psychiatric comorbidities, such as depression, seem to play an important role in its onset and clinical course. Patients with migraine are 2.5 times more likely to develop a depressive disorder; this risk becomes even higher in patients suffering from chronic migraine or migraine with aura. This relationship is bidirectional, since depression also predicts an earlier/worse onset of migraine, increasing the risk of migraine chronicity and, consequently, requiring a higher healthcare expenditure compared to migraine alone. All these data suggest that migraine and depression may share overlapping biological mechanisms. Herein, this review explores this topic in further detail: firstly, by introducing the common epidemiological and risk factors for this comorbidity; secondly, by focusing on providing the cumulative evidence of common biological aspects, with a particular emphasis on the serotoninergic system, neuropeptides such as calcitonin-gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), substance P, neuropeptide Y and orexins, sexual hormones, and the immune system; lastly, by remarking on the future challenges required to elucidate the etiopathological mechanisms of migraine and depression and providing updated information regarding new key targets for the pharmacological treatment of these clinical entities.

Role of serotonin transporter and receptor gene polymorphisms in treatment response to selective serotonin reuptake inhibitors in major depressive disorder

OBJECTIVE

Significant challenges in the management of major depressive disorder include the lag period from treatment initiation to an evident response, low response rates and unpredictable disparities in outcome between patients. As a large part of these has been linked to genetic mechanisms, we tried to establish a relationship between genes associated with serotonin neurotransmission and outcome to selective serotonin reuptake inhibitor (SSRI) treatment.

METHODS

One hundred and twenty-five patients with moderate to severe depression [at least 15 on the Hamilton Depression (HAM-D) Rating Scale] being started on SSRI were recruited. Those with a reduction of at least 50% from baseline or an absolute score of 7 or less after 8 weeks of treatment were considered as responders. The serotonin transporter linked polymorphic region 5HTTLPR, serotonin transporter intron 2 (STin2) polymorphism and the 5-HT receptor 1A rs6295 polymorphisms were studied in association with outcome.

RESULTS

The l/l genotype of the 5HTTLPR was associated with greater likelihood of response (OR: 4.65, CI: 1.74-12.38, p = 0.003). Patients with the 12/12 repeat variant of the STin2 VNTR polymorphism showed a greater reduction in HAM-D score, compared to patients with the 10/10 genotype (OR: 0.12, CI: 0.03-0.44, p = 0.001). We found no association of the 5HTR1Ars6295 polymorphism with response.

CONCLUSIONS

The 5HTTLPR polymorphism and the SLC6A4 intron 2 polymorphism were associated with treatment response, with the l/l genotype and 12-copy allele showing a tendency towards better outcomes, respectively.

Sertraline hydrochloride for reducing impulsive behaviour in male, repeat-violent offenders (ReINVEST): protocol for a phase IV, double-blind, placebo-controlled, randomised clinical trial

INTRODUCTION

Considerable evidence supports an association between poor impulse control (impulsivity) and violent crime. Furthermore, impulsivity and aggression has been associated with reduced levels of serotonergic activity in the brain. Selective serotonin reuptake inhibitors (SSRIs) are a class of anti-depressants that aim to regulate brain serotonin concentrations. Several small studies in psychiatric populations have administered SSRIs to impulsive--aggressive individuals, resulting in reduced impulsivity, anger, aggression and depression. However, no clinical trial has been undertaken in a criminal justice population. This protocol describes the design and implementation of the first systematic study of the potential benefits of SSRIs in impulsive---violent offenders who are at high risk of reoffending.

METHODS AND ANALYSIS

A randomised, double-blinded, multicentre trial to test the clinical efficacy of an SSRI, sertraline hydrochloride, compared with placebo on recidivism and behavioural measures (including impulsivity, anger, aggression, depression and self-reported offending) over 12 months. 460 participants with histories of violence and screening positive for impulsivity are recruited at several local courts and correctional service offices in New South Wales, Australia.

ETHICS AND DISSEMINATION

Results will be submitted for publication in a peer-reviewed journal. Possible implications of the effectiveness of this pharmacological intervention include economic benefits of reducing prison costs and societal benefits of improving safety. This study has received ethical approval from the University of New South Wales, Aboriginal Health & Medical Research Council, Corrective Services NSW and the NSW Justice Health and Forensic Mental Health Network.

TRIAL REGISTRATION NUMBER

ACTRN12613000442707.

Treatment-Resistant Depression Revisited: A Glimmer of Hope

Major Depressive Disorder (MDD) is a highly prevalent psychiatric disorder worldwide. It causes individual suffering, loss of productivity, increased health care costs and high suicide risk. Current pharmacologic interventions fail to produce at least partial response to approximately one third of these patients, and remission is obtained in approximately 30% of patients. This is known as Treatment-Resistant Depression (TRD). The burden of TRD exponentially increases the longer it persists, with a higher risk of impaired functional and social functioning, vast losses in quality of life and significant risk of somatic morbidity and suicidality. Different approaches have been suggested and utilized, but the results have not been encouraging. In this review article, we present new approaches to identify and correct potential causes of TRD, thereby reducing its prevalence and with it the overall burden of this disease entity. We will address potential contributory factors to TRD, most of which can be investigated in many laboratories as routine tests. We discuss endocrinological aberrations, notably, hypothalamic-pituitary-adrenal (HPA) axis dysregulation and thyroid and gonadal dysfunction. We address the role of Vitamin D in contributing to depression. Pharmacogenomic testing is being increasingly used to determine Single Nucleotide Polymorphisms in Cytochrome P450, Serotonin Transporter, COMT, folic acid conversion (MTHFR). As the role of immune system dysregulation is being recognized as potentially a major contributory factor to TRD, the measurement of C-reactive protein (CRP) and select immune biomarkers, where testing is available, can guide combination treatments with anti-inflammatory agents (e.g., selective COX-2 inhibitors) reversing treatment resistance. We focus on established and emerging test procedures, potential biomarkers and non-biologic assessments and interventions to apply personalized medicine to effectively manage treatment resistance in general and TRD specifically.

Serotonergic sensitivity alleles moderate relations between attachment security at age three and socioemotional competence at age five

Children with higher socioemotional competence are more likely to build constructive relationships with others and experience more positive adjustment outcomes in later periods. Securely attached children are likely to develop better socioemotional competence, but genetic moderation of associations between attachment and later socioemotional competence has received less attention. Using structural equation modeling, this study analyzed data collected from 1,337 children (51% male) born from 1998 to 2000 in the Fragile Families and Child Wellbeing study. The results demonstrated that relations between attachment security at age 3 years and their social competence at age 5 years differed by two serotonin transporter variants (5-HTTLPR, STin2). Effect sizes of these interactions were larger than effect sizes of main effects and the benefit of having sensitive alleles was consistently supported. This implies that having more secure attachment in the early developmental period is advantageous especially for children with minor alleles who have greater environmental sensitivity.

Pharmacogenetic association of bi- and triallelic polymorphisms of SLC6A4 with antidepressant response in major depressive disorder

BACKGROUND

Antidepressants (ADs) are the main clinical therapy for depression, but approximately half of users do not get adequate response. The biallelic (5-HTTLPR) and triallelic (5-HTTLPR/rs25531) polymorphisms in SLC6A4 have been frequently investigated, but their associations with ADs response are in controversy. Here, we performed a meta-analysis to assess their modulation effect to ADs response in major depressive disorder (MDD).

METHODS

We performed literature search in PubMed, Web of Science and EMBASE before June 2019. Pooled analysis of genetic associations with response and remission, meta-regression and sensitivity analysis were performed, and publication bias was assessed.

RESULTS

Literature search yielded 49 eligible studies with 46 and 10 studies for biallelic and triallelic polymorphism, respectively. L allele of 5-HTTLPR was associated with both of response and remission rates. In the Caucasians using SSRIs only, carriers of LL/LS or LL genotype were more likely to be responders compared to SS carriers (LL/LS vs. SS: OR=1.55, 95%CI 1.20-2.00, p=0.001; LL vs. SS: OR=1.97, 95%CI 1.45-2.67, p<0.001). Similar associations were also found with remission rate. However, no effects on response or remission were found in the Asians or mixed/other antidepressant subgroups. Additionally, the 5-HTTLPR/rs25531 triallelic polymorphism may not associate with ADs response. Meta-regression showed that percent of female in participants, year of publication and treatment duration modulated the association in Caucasians.

CONCLUSION

5-HTTLPR, instead of 5-HTTLPR/rs25531 triallelic polymorphism, may exert as a marker for the prediction of response to SSRIs in Caucasians with MDD.

Associations of the serotonin transporter promoter polymorphism (5-HTTLPR) with bipolar disorder and treatment response: A systematic review and meta-analysis

BACKGROUND

Associations of the serotonin transporter promoter polymorphism (5-HTTLPR) with bipolar disorder (BPD) and treatment response in bipolar patients were not conclusive. This study not only assessed the association between the 5-HTTLPR and BPD with accumulating relevant studies, but also in the first time evaluated the effect of the 5-HTTLPR on both anti-depressive and anti-manic treatment responses in bipolar patients.

METHODS

PubMed, Embase, PsycINFO, Cochrane Library and Cochrane Control Trials databases were systematically searched before February 2017. This meta-analysis followed the PRISMA guidelines.

RESULTS

A total of 32 population-based studies (5567 cases and 6993 controls) and 9 family-based studies (837 trios) were finally screened out and statistically joined into a single meta-analysis that revealed an association between S allele and an increased risk of BPD (OR = 1.06, p = .038). Pooled analysis of the 32 population-based studies indicated an association of S-carrier genotypes with an increased risk of BPD (OR = 1.10, p = .029). Meanwhile, the association remained significant in Caucasians (OR = 1.15, p = .004), which could provide an enough power (88%) to detect a significant association. Regarding the treatment response studies, 6 studies reporting the relationship of the 5-HTTLPR in anti-depressive remission rate (1034 patients) and 7 studies reporting in response rate (1098 patients) were included for pooled analyses. We observed a significant association of S-carrier genotypes with a reduced anti-depressive remission rate (OR = 0.64, p = .006) but not with anti-depressive response rate. The association between the 5-HTTLPR with anti-manic response rate was not observed in the included 6 studies (676 patients).

CONCLUSIONS

The present study supported the presence of a marginal but detectable effect of the 5-HTTLPR on susceptibility to BPD. Moreover, the detected association in Caucasian was statistically reliable. Besides, the 5-HTTLPR was identified as a useful predictor for anti-depressive remission but not for anti-depressive or anti-manic response.

Effects of Central Nervous System Drugs on Recovery After Stroke: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND AND OBJECTIVE

Pilot trials have suggested that pharmacotherapy may aid stroke recovery. The aim of this study was to systematically review the effects of antidepressants, anti-Alzheimer drugs, anti-Parkinson drugs, central nervous system (CNS) stimulants and piracetam on gross motor function, cognition, disability, dependency and quality of life (QOL) after stroke.

METHODS

PubMed, EMBASE and the Cochrane Central Register of Controlled Trials databases were searched, and 44 randomized controlled trials that compared outcomes of interest between drug treatment and placebo or no treatment were included. For each study, standardized mean difference (SMD) or mean difference (MD) with 95% confidence interval (CI) were calculated. Meta-analyses were conducted to pool results using either the fixed-effects or random-effects model.

RESULTS

Selective serotonin reuptake inhibitors (SSRIs) improved gross motor function (SMD 0.54, 95% CI 0.22-0.85; three studies), disability (SMD 0.49, 95% CI 0.32-0.66; 14 studies) and QOL (MD 6.46, 95% CI 4.71-8.22; two studies), but there was insufficient evidence for their use in enhancing global cognition (SMD 0.23, 95% CI -0.01 to 0.46; five studies) and dependency (risk ratio 0.81, 95% CI 0.68-0.97; one fluoxetine study). In particular, gross motor function was improved by fluoxetine (SMD 0.64, 95% CI 0.31-0.98; two studies), while disability was improved by paroxetine (SMD 1.05, 95% CI 0.63-1.46; two studies), citalopram (SMD 0.51, 95% CI 0.08-0.93; two studies) and fluoxetine (SMD 0.41, 95% CI 0.22-0.60; nine studies). There is insufficient evidence for the use of anti-Alzheimer drugs, anti-Parkinson drugs, CNS stimulants and piracetam to promote stroke recovery.

CONCLUSIONS

Administration of SSRIs may improve gross motor function, reduce disability and enhance QOL for patients recovering from stroke.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Association Study and Meta-Analysis of Polymorphisms, Methylation Profiles, and Peripheral mRNA Expression of the Serotonin Transporter Gene in Patients with Alzheimer's Disease

BACKGROUND/AIM

The aim of this study was to elucidate the relationship between Alzheimer's disease (AD) and the serotonin transporter gene (SLC6A4).

METHODS

AD subjects (n = 43) and controls (n = 47) were recruited and evaluated. In leukocytes, we evaluated two polymorphisms in SLC6A4, the serotonin transporter length polymorphic region (5-HTT-LPR) and rs25531, as well as methylation rates of the SLC6A4 promoter region and the SLC6A4 mRNA expression level. We also performed a meta-analysis to examine the relationship between the frequency of the L allele and the risk of AD.

RESULTS

The distributions of 5-HTT-LPR and rs25531 polymorphisms in AD subjects were not different from those of controls. Although the methylation rates in AD subjects were not significantly different from those of controls, the expression level in AD subjects was significantly higher than in controls. Additionally, the expression level in AD subjects was significantly correlated with apathy. Meta-analysis revealed that the L/L genotype significantly reduced the risk of AD, but only in the Caucasian population.

CONCLUSION

Higher SLC6A4 mRNA expression in leukocytes in AD was associated with apathy regardless of SLC6A4 genotypes and methylation rates of the promoter region. The L/L genotype may reduce the risk of AD in the Caucasian population.

Deep brain stimulation induces antidepressant-like effects in serotonin transporter knockout mice

BACKGROUND

Some of the antidepressant-like effects of ventromedial prefrontal cortex (vmPFC) deep brain stimulation (DBS) in rodents have been attributed to the modulation of prefrontal-raphe pathways. This is largely different from selective serotonin reuptake inhibitors (SSRIs), which increase serotonin (5-HT) levels by inhibiting the serotonin transporter (SERT). SSRIs have limited efficacy when given to SERT knockout (KO) mice, or patients with mutations in the serotonin transporter promoter gene (5-HTTLPR).

HYPOTHESIS

vmPFC DBS will induce antidepressant-like effects and serotonin release in SERT KOs.

RESULTS

DBS-treated wild-type and SERT KO mice had a significant 22-26% decrease in immobility in the forced swim test. DBS delivered to either group was associated with 33-55% increase in 5-HT levels.

CONCLUSIONS

DBS induced a significant antidepressant-like effect in KO mice. This suggests that it may be reasonable to consider DBS in states where SERT is not fully operational.

Association of the serotonin transporter-linked polymorphic region genotype with lower bone mineral density

The serotonin transporter-linked polymorphic region (5-HTTLPR) of the serotonin transporter gene (SLC6A4) S allele is linked to pathogenesis of depression and slower response to selective serotonin reuptake inhibitors (SSRIs); depression and SSRIs are independently associated with bone loss. We aimed to determine whether 5-HTTLPR was associated with bone loss. This cross-sectional study included psychiatric patients with both 5-HTTLPR analysis and bone mineral density (BMD) assessment (hip and spine Z-scores if age <50 years and T-scores if ⩾50 years). BMD association with 5-HTTLPR was evaluated under models with additive allele effects and dominant S allele effects using linear regression models. Patients were stratified by age (<50 and ⩾50 years) and sex. Of 3016 patients with 5-HTTLPR genotyping, 239 had BMD assessments. Among the younger patients, the S allele was associated with lower Z-scores at the hip (P=0.002, dominant S allele effects; P=0.004, additive allele effects) and spine (P=0.0006, dominant S allele effects; P=0.01, additive allele effects). In sex-stratified analyses, the association of the S allele with lower BMD in the younger patients was also significant in the subset of women (P⩽0.003 for both hip and spine BMD under the additive allele effect model). In the small group of men younger than 50 years, the S allele was marginally associated with higher spine BMD (P=0.05). BMD T-scores were not associated with 5-HTTLPR genotypes in patients 50 years or older. The 5-HTTLPR variants may modify serotonin effects on bone with sex-specific effects.

Genetics as a molecular window into recovery, its treatment, and stress responses after stroke

Stroke remains a major source of adult disability in the USA and worldwide. Most patients show some recovery during the weeks to months following a stroke, but this is generally incomplete. An emerging branch of therapeutics targets the processes underlying this behavioral recovery from stroke toward the goal of reducing long-term disability. A key factor hampering these efforts is the very large degree of variability between stroke survivors. Available data suggest that genetic differences could explain an important fraction of the differences between subjects. The current review considers this from several angles, including genetic differences in relation to drugs that promote recovery. Genetic factors related to physiological and psychological stress responses may also be critically important to understanding recovery after stroke and its treatment. The studies reviewed provide insights into recovery and suggest directions for further research to improve clinical decision-making in this setting. Genetic differences between patients might be used to help clinical trials select specific patient subgroups, on a biological basis, in order to sharpen the precision with which new treatments are evaluated. Pharmacogenomic factors might also provide insights into inter-subject differences in treatment side effects for pharmacological prescriptions, and behavioral interventions, and others. These efforts must be conducted with the strictest ethical standards given the highly sensitive nature of genetic data. Understanding the effect of selected genetic measures could improve a clinician's ability to predict the risk and efficacy of a restorative therapy and to make maximally informed decisions, and in so doing, facilitate individual patient care.

Serotonin pathway polymorphisms and the treatment of major depressive disorder and anxiety disorders

While antidepressants are widely used to treat major depressive disorder and anxiety disorders, only half of the patients will respond to antidepressant treatment and only a third of patients will experience a remission of symptoms. Identification of genetic biomarkers that predict antidepressant treatment response could thus greatly improve current clinical practice by providing guidance on which drug to use for which patient. Most antidepressant drugs for the treatment of depression and anxiety disorders have effects on the serotonergic neurotransmitter system; thus, genetic polymorphisms in the genes involved in this pathway represent logical candidates for investigation. This article reviews recent findings on the pharmacogenetics of antidepressant drugs with a focus on serotonergic pathway polymorphisms and discusses future clinical applications.

Serotonin transporter availability may moderate the association between perceiving stress and depressive tendencies - A SPECT with 5-HTTLPR genotyping study

It was found that serotonin transporter (SERT) gene (5-HTTLPR) polymorphism may moderate the association between perceiving stress and depressive tendency. Although SERT availability in the central nervous system could be associated with 5-HTTLPR polymorphism, whether SERT availability moderates the association between stress and depressive tendency is unclear. This study aimed to investigate whether there is a SERT availability×environmental stress interaction effect, as well as a gene-by-environmental (G×E) interaction effect, using single-photon emission computed tomography (SPECT) with a serotonin transporter radiotracer, [(123)I]ADAM. 87 healthy volunteers were enrolled. The SERT availability was approximated using SPECT with [(123)I]ADAM. Stress and depressive tendencies were measured by the Recent Life Change Questionnaire (RLCQ) and the Taiwanese Depression Questionnaire (TDQ), respectively. A significant interaction of sex×RLCQ×thalamic SERT availability on the TDQ was found, and this effect was robust after controlling for the effect of the SS genotype. The interaction of RLCQ×thalamic SERT availability on the TDQ was significant among males. In particular, a significant association between RLCQ and TDQ (Spearman correlation, ρ=0.64, p<0.01) was found among male subjects with a lower level of thalamic SERT availability. SERT availability may play a role in depressive tendency when under perceived stress among healthy individuals, independent of G×E. This finding provides new evidence that confirms the role of the serotonergic system in the association between stress and depression. Males with lower levels of SERT availability may be more vulnerable to the effects of negative life events.

Genetic Variations in the Serotonergic System Mediate a Combined, Weakened Response to SSRI Treatment: A Proposed Model

Individuals with the short (S) allele in the promoter region of the serotonin transporter gene (5-HTTLPR) show a less favorable response to selective serotonin reuptake inhibitor (SSRI) treatment than individuals with the long (L) allele. Similarly, individuals with the C(-1019)G allele for the mutation found in the promoter region of the serotonin 1A receptor gene (5-HTR1A) have shown blunted responses to SSRI treatment when compared with individuals lacking this polymorphism. While these findings have been replicated across multiple studies, only two studies to date have reported data for a gene-gene interaction associated with response to SSRI treatment. Both of these studies reported a combined effect for these genotypes, with individuals homozygous for the L allele and the C allele (5-HTT(L/L)-1A(C/C)) reporting the most favorable response to SSRI treatment, and individuals homozygous for the S allele and the G allele (5-HTT(S/S)-1A(G/G)) reporting the least favorable response to SSRI treatment. Additionally, no neural mechanisms have been proposed to explain why this gene-gene interaction has been observed. To that end, this article provides a review of the relevant literature associated with these polymorphisms and proposes a feasible model that describes a genotype-dependent modulation of postsynaptic serotonin signaling associated with the 5-HTT and 5-HTR1A genes.

Association of Genetic Factors and Gene-Environment Interactions With Risk of Developing Posttraumatic Stress Disorder in a Case-Control Study

BACKGROUND

The dopamine receptor D2 (DRD2) and serotonin transporter (5-HTT) genes are associated with posttraumatic stress disorder (PTSD). However, it remains largely unknown whether these genes interact with environmental factors to affect the development of PTSD.

PURPOSE

The purpose of this study was to examine the associations of gene polymorphisms and gene-environment interactions with the risk of developing PTSD among adolescent earthquake survivors.

METHOD

A total of 183 adolescent survivors from an earthquake-stricken area participated in this study. Measures included a questionnaire about demographic characteristics and earthquake exposure, the PTSD Checklist-Civilian Version and the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, fourth edition disorders. Genotypes were analyzed by using the polymerase chain reaction-based restriction fragment length polymorphism.

RESULTS

The 5-HTTLPR and 5-HTTVNTR polymorphisms and earthquake exposure had statistically significant positive effects on PTSD. The interaction effects of 5-HTTLPR × Earthquake Exposure and 5-HTTVNTR × Earthquake Exposure were statistically significant.

CONCLUSION

The development of PTSD is the result not only of a genetic effect and environmental factors but also of the interactive effect between gene and environment.

Allelic variation in 5-HTTLPR and the effects of citalopram on the emotional neural network

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs), such as citalopram, which selectively block serotonin transporter (5-HTT) activity, are widely used in the treatment of depression and anxiety disorders. Numerous neuroimaging studies have examined the effects of SSRIs on emotional processes. However, there are considerable inter-individual differences in SSRI effect, and a recent meta-analysis further revealed discrepant effects of acute SSRI administration on neural responses to negative emotions in healthy adults.

AIMS

We examined how a variant of the serotonin-transporter polymorphism (5-HTTLPR), which affects the expression and function of 5-HTT, influenced the acute effects of an SSRI (citalopram) on emotion-related brain activity in healthy adults.

METHOD

Combining genetic neuroimaging, pharmacological technique and a psychological paradigm of emotion recognition, we scanned the short/short (s/s) and long/long (l/l) variants of 5-HTTLPR during perception of fearful, happy and neutral facial expressions after the acute administration of an SSRI (i.e. 30 mg citalopram administered orally) or placebo administration.

RESULTS

We found that 5-HTTLPR modulated the acute effects of citalopram on neural responses to negative emotions. Specifically, relative to placebo, citalopram increased amygdala and insula activity in l/l but not s/s homozygotes during perception of fearful faces. Similar analyses of brain activity in response to happy faces did not show any significant effects.

CONCLUSIONS

Our combined pharmacogenetic and functional imaging results provide a neurogenetic mechanism for discrepant acute effects of SSRIs.

Serotonin transporter gene polymorphisms: Relation with platelet serotonin level in patients with primary Sjogren's syndrome

Significantly lower platelet serotonin level (PSL) in patients with primary Sjogren's syndrome (pSS) than in healthy controls has been reported in our prior studies. In the present report, we demonstrated effect of functional polymorphisms in the serotonin transporter gene (5-HTT) on PSL. We describe a group of 61 pSS patients and 100 healthy individuals subjects, who received PSL measurement in our prior study. All subjects were genotyped for the promoter 5-HTTLPR (L/S), rs25531 (A/G) and intronic 5-HTTVNTRin2 (l/s) polymorphisms. Overall, the presence of 5-HTTVNTRin2 ss genotype was associated with significantly lower PSL in pSS patients, not in healthy controls. Reduced PSL in pSS patients is in line with hypothesis of association between chronic immunoinflammation and 5-HT system dysregulation, identifying additional mechanisms such as altered 5-HT transport as potential genetic factor contributing to PSL depletion.

Pharmacogenomics in practice: a case report of personalized inpatient psychiatric care

Given variable response to psychotropic intervention, this case highlights the potential of pharmacogenomics to inform medical decision-making in a male with atypical psychosis and depression with longer-standing attentional difficulties. Likely because of his specific COMT polymorphism and intermediate metabolizing liver enzymes, when the patient's stimulant medications were titrated to affect for attentional needs, he became psychotic secondary to a hyperdopaminergic state. Past prescriptions of dopaminergic antidepressant agents (e.g., bupropion) likely would have exacerbated further the problem. The patient's serotonin transporter polymorphism also potentially was associated with SSRI inefficacy and increased side effects. Knowledge of the patient's genetically influenced departure from average response allowed for personalization of pharmacology with clinical improvement across measures of functioning.

Pharmacogenetics and analgesic effects of antidepressants in chronic pain management

Antidepressants are widely administered to chronic pain patients, but there is large interindividual variability in their efficacy and adverse effect rates that may be attributed to genetic factors. Studies have attempted to determine the impact of genetic polymorphisms in enzymes and transporters that are involved in antidepressant pharmacokinetics, for example, cytochrome P450 and P-gp. The impacts of genetic polymorphisms in the targets of antidepressants, such as the serotonin receptor or transporter, the noradrenaline transporter and the COMT and monoamine oxydase enzymes, have also been described. This manuscript discusses the current knowledge of the influence of genetic factors on the plasma concentrations, efficacy and adverse effects of the major antidepressants used in pain management.

Serotonin transporter gene alters insula activity to threat in social anxiety disorder

Amygdala and insula hyper-reactivity to threat is implicated in social anxiety disorder (SAD) yet inconsistencies in activation have been reported. One source of variance are individual differences in 5-HTTLPR genotype where the short (S), relative to long (L) allele, corresponds with greater amygdala activation. However, the impact of genotype on insula to threat in SAD is not known. During functional MRI, 34 SAD patients and 28 healthy controls completed a perceptual assessment task comprising angry, fear, and happy faces. Results showed no diagnostic group differences in limbic/paralimbic regions but within SAD, greater insula, but not amygdala, activation to fearful faces was observed in patients with SS genotype compared with LaLa genotype. Findings indicate genotype influenced insula activation to threat in SAD.

Serotonin transporter (5-HTTLPR) and norepinephrine transporter (NET) gene polymorphisms: susceptibility and treatment response of electroconvulsive therapy in treatment resistant depression

Serotonin transporter (5-HTTLPR) and norepinephrine transporter (NET182C) polymorphisms are associated with susceptibility and treatment response in major depressive disorder (MDD). Thus, we examined association between these polymorphisms and susceptibility to treatment resistant depression, and treatment response in severe MDD patients treated with electroconvulsive therapy (ECT). In total, 119 Finnish patients with treatment resistant depression and 395 healthy volunteer blood donors were genotyped. Depression severity was assessed using the Montgomery-Åsberg Depression Scale (MADRS), with MADRS score change during ECT the treatment response indicator. Underrepresentation of the 5-HTTLPR l/l genotype in the NET TT subgroup was observed in patients compared with controls. There were no genotype or allele frequency differences between patients and control groups separately. Patients with combined 5-HTTLPR l/l and NET TT genotypes also had poorer treatment responses than other patients. No differences in ECT response were observed when the polymorphisms were examined separately. Our results suggest that a NET 182C and 5-HTTLPR polymorphism interaction is associated with susceptibility to treatment resistant depression and ECT treatment response in antidepressant resistant depression patients.

Pharmacogenomics in psychiatry: the relevance of receptor and transporter polymorphisms

The treatment of severe mental illness, and of psychiatric disorders in general, is limited in its efficacy and tolerability. There appear to be substantial interindividual differences in response to psychiatric drug treatments that are generally far greater than the differences between individual drugs; likewise, the occurrence of adverse effects also varies profoundly between individuals. These differences are thought to reflect, at least in part, genetic variability. The action of psychiatric drugs primarily involves effects on synaptic neurotransmission; the genes for neurotransmitter receptors and transporters have provided strong candidates in pharmacogenetic research in psychiatry. This paper reviews some aspects of the pharmacogenetics of neurotransmitter receptors and transporters in the treatment of psychiatric disorders. A focus on serotonin, catecholamines and amino acid transmitter systems reflects the direction of research efforts, while relevant results from some genome-wide association studies are also presented. There are many inconsistencies, particularly between candidate gene and genome-wide association studies. However, some consistency is seen in candidate gene studies supporting established pharmacological mechanisms of antipsychotic and antidepressant response with associations of functional genetic polymorphisms in, respectively, the dopamine D2 receptor and serotonin transporter and receptors. More recently identified effects of genes related to amino acid neurotransmission on the outcome of treatment of schizophrenia, bipolar illness or depression reflect the growing understanding of the roles of glutamate and γ-aminobutyric acid dysfunction in severe mental illness. A complete understanding of psychiatric pharmacogenomics will also need to take into account epigenetic factors, such as DNA methylation, that influence individual responses to drugs.

Serotonin: a never-ending story

The neurotransmitter serotonin is an evolutionary ancient molecule that has remarkable modulatory effects in almost all central nervous system integrative functions, such as mood, anxiety, stress, aggression, feeding, cognition and sexual behavior. After giving a short outline of the serotonergic system (anatomy, receptors, transporter) the author's contributions over the last 40 years in the role of serotonin in depression, aggression, anxiety, stress and sexual behavior is outlined. Each area delineates the work performed on animal model development, drug discovery and development. Most of the research work described has started from an industrial perspective, aimed at developing animals models for psychiatric diseases and leading to putative new innovative psychotropic drugs, like in the cases of the SSRI fluvoxamine, the serenic eltoprazine and the anxiolytic flesinoxan. Later this research work mainly focused on developing translational animal models for psychiatric diseases and implicating them in the search for mechanisms involved in normal and diseased brains and finding new concepts for appropriate drugs.

Genetic polymorphism in the serotonin transporter gene-linked polymorphic region and response to serotonin reuptake inhibitors in patients with premature ejaculation

OBJECTIVES

Serotonin plays a central role in ejaculation and selective serotonin reuptake inhibitors have been successfully used to treat premature ejaculation. Here, we evaluated the relationship between a polymorphism in the serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the response of patients with premature ejaculation to SSRI medication.

METHODS

Sixty-nine premature ejaculation patients were treated with 20 mg/d paroxetine for three months. The Intravaginal Ejaculatory Latency Time and International Index of Erectile Function scores were compared with baseline values. The patients were scored as having responded to therapy when a 2-fold or greater increase was observed in Intravaginal Ejaculatory Latency Time compared with baseline values after three months. Three genotypes of 5-HTTLPR were studied: LL, LS and SS. The appropriateness of the allele frequencies in 5-HTTLPR were analyzed according to Hardy-Weinberg equilibrium using the χ2-test.

RESULTS

The short (S) allele of 5-HTTLPR was significantly more frequent in responders than in nonresponders (p<0.05). Out of the 69 total PE patients, 41 patients (59%) responded to therapy. There was no significant difference in the International Index of Erectile Function score at the end of therapy between the responder and nonresponder groups. The frequencies of the L allele and S allele were 20% and 39%, respectively, in the responder group (p<0.05).

CONCLUSION

We conclude that premature ejaculation patients with the SS genotype respond well to selective serotonin reuptake inhibitor therapy. Further studies with large patient groups are necessary to confirm this conclusion.

Escitalopram efficacy in depression: a cross-ethnicity examination of the serotonin transporter promoter polymorphism

Current evidence suggests that polymorphism in the serotonin transporter gene (5-HTTLPR) predicts antidepressant efficacy in whites but less so in Asians. However, it is not clear whether this effect can be observed for specific types of antidepressant drugs. White (n = 47) and Korean (n = 118) participants with major depressive disorder were treated with escitalopram and assessed over 8 weeks. Among those with the l/l but not l/s or s/s genotypes, whites had greater depression score reductions, response rates, and remission rates compared with Koreans. Our results suggest that 5-HTTLPR predicts escitalopram efficacy in an ethnicity-dependent manner.

Pharmacogenetics of neural injury recovery

Relatively few pharmacological agents are part of routine care for neural injury, although several are used or under consideration in acute stroke, chronic stroke, traumatic brain injury and secondary stroke prevention. Tissue plasminogen activator is approved for the treatment of acute ischemic stroke, and genetic variants may impact the efficacy and safety of this drug. In the chronic phase of stroke, several drugs such as L-dopa, fluoxetine and donepezil are under investigation for enhancing rehabilitation therapy, with varying levels of evidence. One potential reason for the mixed efficacy displayed by these drugs may be the influence of genetic factors that were not considered in prior studies. An understanding of the genetics impacting the efficacy of dopaminergic, serotonergic and cholinergic drugs may allow clinicians to target these potential therapies to those patients most likely to benefit. In the setting of stroke prevention, which is directly linked to neural injury recovery, the most highly studied pharmacogenomic interactions pertain to clopidogrel and warfarin. Incorporating pharmacogenomics into neural injury recovery has the potential to maximize the benefit of several current and potential pharmacological therapies and to refine the choice of pharmacological agent that may be used to enhance benefits from rehabilitation therapy.

Effects of citalopram and escitalopram on fMRI response to affective stimuli in healthy volunteers selected by serotonin transporter genotype

This study was designed to assess whether functional magnetic resonance imaging (fMRI) following antidepressant administration (pharmaco-fMRI) is sufficiently sensitive to detect differences in patterns of activation between enantiomers of the same compound. Healthy adult males (n=11) participated in a randomized, double-blind, cross-over trial with three medication periods during which they received citalopram (racemic mixture), escitalopram (S-citalopram alone), or placebo for 2 weeks. All participants had high expression serotonin transporter genotypes. An fMRI scan that included passive viewing of overt and covert affective faces and affective words was performed after each medication period. Activation in response to overt faces was greater following escitalopram than following citalopram in the right insula, thalamus, and putamen when the faces were compared with a fixation stimulus. For the rapid covert presentation, a greater response was observed in the left middle temporal gyrus in the happy versus fearful contrast following escitalopram than following citalopram. Thus, the combination of genomics and fMRI was successful in discriminating between two very similar drugs. However, the pattern of activation observed suggests that further studies are indicated to understand how to optimally combine the two techniques.

HTR2A gene-child abuse interaction and association with a history of suicide attempt among Caucasian depressed psychiatric inpatients

BACKGROUND

The serotonin transporter gene polymorphism (5HTTLPR) has been associated with vulnerability for depression after exposure to stressful life event as well as with difference in treatment response to SSRI. Although the A/A genotype of the serotonin receptor SNP (rs7997012) was associated with better citalopram response than the G/G in the STAR⁎D sample, the effects of this SNP in the moderation of child abuse history on the characteristics of mental illnesses are not well understood. We examined if there are similar gene-environment interaction with the SNP.

METHODS

Retrospective chart review of 250 Caucasian depressed psychiatric inpatients, who had genotype for rs7997012. Subjects with each genotype were subcategorized into 2 groups with/without history of child abuse. The history of suicide attempts of each group was compared.

RESULTS

A trend for an interaction was found between the HTR2A genotype and child abuse history influencing the prevalence of suicide attempts. Although each genotype did not show significant difference in the risk of suicide attempt when there was no abuse history, the A carriers (A/A+A/G) showed significantly higher rate of suicide attempt compared to the G/G when there is a history of child abuse (48.4% versus 22.7% respectively, p=0.0050). The likelihood ratio test from the logistic model showed a trend for an interaction between the A/A genotype and abuse history (Odds Ratio 2.10, χ(2)=2.49, p=0.11).

LIMITATIONS

Retrospective study design and small sample size with borderline significance.

CONCLUSIONS

Our findings showed a potential interaction between the HTR2A gene and stressful life events.

Do we need pharmacogenetics to personalize antidepressant therapy?

This review examines the role of drug metabolism and drug target polymorphism in determining the clinical response to antidepressants. Even though antidepressants are the most effective available treatment for depressive disorders, there is still substantial need for improvement due to the slow onset of appreciable clinical improvement and the association with side effects. Moreover, a substantial group of patients receiving antidepressant therapy does not achieve remission or fails to respond entirely. Even if the large variation in antidepressant treatment outcome across individuals remains poorly understood, one possible source of this variation in treatment outcome are genetic differences. The review focuses on a few polymorphisms which have been extensively studied, while reporting a more comprehensive reference to the existing literature in table format. It is relatively easy to predict the effect of polymorphisms in drug metabolizing enzymes, such as cytochromes P450 2D6 (CYP2D6) and cytochrome P450 2C19 (CYP2C19), which may be determined in the clinical context in order to explain or prevent serious adverse effects. The role of target polymorphism, however, is much more difficult to establish and may be more relevant for disease susceptibility and presentation rather than for response to therapy.

Association between serotonin transporter-linked polymorphic region and escitalopram antidepressant treatment response in Korean patients with major depressive disorder

OBJECTIVE

Various studies have shown that short (s)/long (l) polymorphisms of the serotonin transporter-linked polymorphic region (5-HTTLPR) might predict treatment outcome to selective serotonin reuptake inhibitors. The purpose of this study was to evaluate the association between 5-HTTLPR and clinical response to escitalopram treatment in Korean subjects with major depressive disorder.

METHODS

One hundred and fifteen Korean patients diagnosed with major depressive disorder were evaluated during 8 weeks of escitalopram treatment at a dose of 5-20 mg/day. Patients were genotyped for 5-HTTLPR using polymerase chain reaction. Clinical symptoms were evaluated by the 21-item Hamilton Depression Rating (HAMD-21) scale during the 8 weeks of treatment.

RESULTS

Therapeutic response to antidepressant escitalopram was better in s allele carriers (ss, sl) than in l allele homozygotes (ll) at 8 weeks of treatment (OR = 6.24, p = 0.026). The proportion of s allele carriers in responders was higher than that in non-responders (96.6 vs. 85.7%). The percentile decline in HAMD-21 in s allele carriers (59.86 ± 3.23%) was larger than that in HAMD-21 in l allele homozygotes (43.13 ± 11.49%; p = 0.029). However, 5-HTTLPR genotypes were not significantly associated with remission (p > 0.05).

CONCLUSIONS

Our results show that treatment response to escitalopram at 8 weeks was moderated by 5-HTTLPR, with better response rates for s allele carriers than for l allele homozygotes. Although the role of 5-HTTLPR as a definite predictor of selective serotonin reuptake inhibitor treatment response cannot be confirmed from current results, they do suggest a trend for better response in s allele carriers.

Influence of the serotonin transporter 5HTTLPR polymorphism on symptom severity in irritable bowel syndrome

5HTTLPR polymorphism of serotonin transporter yields short (S) and long (L) alleles. SS and LS genotypes are associated with reduced expression of serotonin transporter. This cross-sectional study investigated the association of 5HTTLPR with symptom severity of irritable bowel syndrome (IBS). Patients with IBS (Rome III) and healthy controls were included. Genomic DNA was extracted from saliva, and 5HTTLPR alleles were assessed by polymerase chain reaction. IBS symptom severity was evaluated by means of IBS-SSS questionnaire. Two hundreds and four IBS patients (159 females; mean age: 39.6±12.3 years; 106 with constipation: C-IBS; 98 with diarrhea: D-IBS) and 200 healthy controls (154 females; mean age: 40.4±15.8 years) were enrolled. The overall IBS-SSS value was higher in LS/SS than LL patients (319.0±71.5 versus 283.8±62.3; P = 0.0006). LS/SS patients had also higher values of abdominal pain (59.7±21.0 versus 51.0±18.8; P = 0.020) and bowel dissatisfaction (80.1±23.9 versus 70.5±22.8; P = 0.035). The overall IBS-SSS values in C-IBS and D-IBS patients were 317.2±68.3 and 296.1±71.4, respectively (P = 0.192), with significantly higher values for abdominal distension (65.0±24.4 versus 51.4±24.8; P = 0.0006), but not for bowel dissatisfaction (80.5±21.7 versus 72.9±25.7; P = 0.138). Frequencies of 5HTTLPR genotypes did not differ significantly when comparing IBS patients (overall or upon stratification in C-IBS and D-IBS) with healthy controls. In conclusion, the LS and SS genotypes are significantly correlated with IBS symptom severity, although their possible direct causal role remains to be proven. In addition, the present findings do not support an association of 5HTTLPR with IBS or its clinical presentation in terms of bowel habit predominance.

A meta-analysis of the effects of the 5-hydroxytryptamine transporter gene-linked promoter region polymorphism on susceptibility to lifelong premature ejaculation

Objective

Premature ejaculation (PE) has been reported as the most common male sexual dysfunction with global prevalence rates estimated at approximately 30%. The neurobiogenesis of ejaculation is very complex and involves the serotoninergic (5-hydroxytryptamine, 5-HT) system. Recently, genetic polymorphisms located on SLC6A4 gene codifying for 5-HT transporter (5-HTT), the major regulator of serotonic neurotransmission, have been linked with the pathogenesis and risk of PE. Apparently studies of this type of polymorphism in PE have show conflicting results.

Methods

A meta-analysis was performed that are available in relation with 5-HTT gene-linked promoter region (5-HTTLPR) polymorphism and the risk of lifelong PE (LPE) in men to clarify this relationship. We searched Pubmed and Embase (last search updated on Aug 2012) using ‘premature ejaculation’, ‘polymorphism or variant’, ‘genotype’, ‘ejaculatory function’, and ‘rapid ejaculation’ as keywords and reference lists of studies corresponded to the inclusion criteria for meta-analysis. These studies involved the total number of 481 LPE men and 466 health control men subjects. Odds ratio (OR) and 95% confidence intervals (CIs) were used to evaluate this relationship.

Results

In the overall analysis, significant associations between LPE risk and 5-HTTLPR polymorphism were found (L-allele vs. S-allele OR = 0.86, 95% CI = 0.79–0.95, P = 0.002; LL vs. SS: OR = 0.80, 95% CI = 0.68–0.95, P = 0.009; LS vs. SS: OR = 0.85, 95% CI = 0.76–0.97, P = 0.012 and LL+LS vs. SS: OR = 0.88, 95% CI = 0.81–0.95, P = 0.002). Moreover, in subgroup analysis based on ethnicity, similar significant associations were detected. The Egger’s test did not reveal presence of a publication bias.

Conclusions

Our investigations demonstrate that 5-HTTLPR (L>S) polymorphism might protect men against LPE risk. Further studies based on larger sample size and gene-environment interactions should be conducted the role of 5-HTTLPR polymorphism and LPE risk.

Clinical efficacy and safety of fluoxetine in generalized anxiety disorder in Chinese patients

BACKGROUND

Generalized anxiety disorder (GAD) is a prevalent, disabling disease and is highly comorbid with other psychiatric disorders both in Western countries and the People's Republic of China. Fluoxetine, a selective inhibitor of serotonin reuptake (SSRI), is widely utilized in the management of GAD in clinical practice despite the lack of strong evidence. This article reviews fluoxetine trials to investigate fluoxetine's efficacy and tolerability in Chinese patients with GAD.

METHODS

A literature review was conducted using the following databases up to and including April 2013: Chinese BioMedical Literature, China National Knowledge Infrastructure, EMBASE, MEDLINE, and PsycINFO. We selected clinical studies that utilized fluoxetine for GAD in which all participants were Chinese.

RESULTS

Fifteen open-label, non-placebo trials were identified and analyzed; eleven anxiolytics were compared with fluoxetine separately. Short-term efficacy of fluoxetine had been established in these open-label, head-to-head controlled trials. Fluoxetine had rapid onset of action (approximately 1-2 weeks) and seemed to be effective in maintenance treatment. Fluoxetine was generally well-tolerated with the most common side effect of dry month and nausea. Compared to other anxiolytic agents, fluoxetine was equivalent with all of the comparative anxiolytics in terms of efficacy except mirtazapine which showed conflicting results with fluoxetine in two studies. In terms of side effects, fluoxetine was better tolerated than diazepam, doxepine, and amitriptyline, less tolerated than escitalopram, and had similar tolerability with duloxetine as well as alprazolam.

CONCLUSION

Given the high risk of bias of the included studies, the overall small sample size of the studies, the lack of placebo control groups as well as the lack of certain clinically meaningful outcomes, it is not possible to recommend fluoxetine as a reliable first-line treatment in Chinese patients with GAD. Furthermore, no definitive implications for clinical practice in choosing anxiolytics can be drawn from this review. Trials with larger sample sizes, better quality, longer duration, and more clinically meaningful outcomes are needed in future research.

Fluoxetine pharmacogenetics in child and adult populations

Although fluoxetine is useful in the treatment of major depression, 30-40 % of the patients do not respond to therapy. The response seems to be influenced by certain genes which are involved in the drug's pharmacodynamics and pharmacokinetics. The present study reviews the literature on genetic contributions to fluoxetine response in children and adults, and concludes that the different polymorphisms of CYP2D6 and CYP2C9 may influence the blood concentrations of fluoxetine. If the childhood dose is adjusted for weight, differences between children and adults are unlikely. As regards the genes that influence the drug's pharmacodynamics, polymorphisms of SLC6A4, HTR1A and MAO-A seem to be involved in the response to fluoxetine, while the genes COMT, CRHR1, PDEA1, PDEA11 GSK3B and serpin-1 also seem to play a role. Comparison of different studies reveals that the results are not always consistent, probably due to methodological differences. Other factors such as gender or ethnicity may also influence treatment response.

Imaging genetics: implications for research on variable antidepressant drug response

Genetic variation of SLC6A4, HTR1A, MAOA, COMT and BDNF has been associated with depression, variable antidepressant drug responses as well as impacts on brain regions of emotion processing that are modulated by antidepressants. Pharmacogenetic studies are using psychometric outcome measures of drug response and are hampered by small effect sizes that might be overcome by the use of intermediate endophenotypes of drug response, which are suggested by imaging studies. Such an approach will not only tighten the relationship between genes and drug response, but also yield new insights into the neurobiology of depression and individual drug responses. This article provides a comprehensive overview of pharmacogenetic, imaging genetics and drug response studies, utilizing imaging techniques within the context of antidepressive drug therapy.

The genetics of selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are among the most widely prescribed drugs in psychiatry. Based on the fact that SSRIs increase extracellular monoamine levels in the brain, the monoamine hypothesis of depression was introduced, postulating that depression is associated with too low serotonin, dopamine and noradrenaline levels. However, several lines of evidence indicate that this hypothesis is too simplistic and that depression and the efficacy of SSRIs are dependent on neuroplastic changes mediated by changes in gene expression. Because a coherent view on global gene expression is lacking, we aim to provide an overview of the effects of SSRI treatment on the final targets of 5-HT receptor signal transduction pathways, namely the transcriptional regulation of genes. We address gene polymorphisms in humans that affect SSRI efficacy, as well as in vitro studies employing human-derived cells. We also discuss the molecular targets affected by SSRIs in animal models, both in vivo and in vitro. We conclude that serotonin transporter gene variation in humans affects the efficacy and side-effects of SSRIs, whereas SSRIs generally do not affect serotonin transporter gene expression in animals. Instead, SSRIs alter mRNA levels of genes encoding serotonin receptors, components of non-serotonergic neurotransmitter systems, neurotrophic factors, hypothalamic hormones and inflammatory factors. So far little is known about the epigenetic and age-dependent molecular effects of SSRIs, which might give more insights in the working mechanism(s) of SSRIs.

Sex determines which section of the SLC6A4 gene is linked to obsessive-compulsive symptoms in normal Chinese college students

Previous case-control and family-based association studies have implicated the SLC6A4 gene in obsessive-compulsive disorder (OCD). Little research, however, has examined this gene's role in obsessive-compulsive symptoms (OCS) in community samples. The present study genotyped seven tag SNPs and two common functional tandem repeat polymorphisms (5-HTTLPR and STin2), which together cover the whole SLC6A4 gene, and investigated their associations with OCS in normal Chinese college students (N = 572). The results revealed a significant gender main effect and gender-specific genetic effects of the SLC6A4 gene on OCS. Males scored significantly higher on total OCS and its three dimensions than did females (ps < .01). The 5-HTTLPR in the promoter region showed a female-specific genetic effect, with the l/l and l/s genotypes linked to higher OCS scores than the s/s genotype (ps < .05). In contrast, a conserved haplotype polymorphism (rs1042173| rs4325622| rs3794808| rs140701| rs4583306| rs2020942) covering from intron 3 to the 3' UTR of the SLC6A4 gene showed male-specific genetic effects, with the CGAAGG/CGAAGG genotype associated with lower OCS scores than the other genotypes (ps < .05). These effects remained significant after controlling for OCS-related factors including participants' depressive and anxiety symptoms as well as stressful life events, and correction for multiple tests. These results are discussed in terms of their implications for our understanding of the sex-specific role of the different sections of the SLC6A4 gene in OCD.

Surrogate markers of treatment outcome in major depressive disorder

Major depressive disorder (MDD) is a common medical illness affecting millions worldwide. Despite their widespread use since the 1950s and 1960s, the 'downstream' mechanism by which antidepressants ultimately exert their therapeutic effects remains elusive. In addition, except for a few exceptions such as episode severity and the presence of comorbid Axis-I or Axis-III disorders, biological or clinical characteristics which can accurately quantify the risk of poor treatment outcome are lacking, as are factors which could help patients and clinicians select treatment options that would result in superior outcome. The identification of such markers, termed 'surrogate' markers, could help shed further insights into what constitutes illness and recovery, help identify molecular targets for the development of future antidepressants, and lead the way to the design and refinement of a personalized medicine treatment model for MDD. In the following text, several major areas ('leads') where evidence exists regarding the presence of surrogate markers of efficacy outcome in MDD will be briefly reviewed. Leads include evidence from the role of demographic and clinical factors as surrogate markers, to the role of various biological markers including genotype, brain functional imaging, electroencephalography, dichotic listening, and molecular biology and immunology. The purpose of this work is to focus selectively on areas where there have been findings, as opposed to conducting an exhaustive literature review of studies which have failed to yield any significant breakthrough in our knowledge.

Meta-analysis of serotonin transporter gene promoter polymorphism (5-HTTLPR) association with antidepressant efficacy

In the last decade the serotonin transporter gene promoter polymorphism (5-HTTLPR) was likely the most studied genetic variant as predictor of antidepressant response. Nevertheless results are not consistent across studies and previous meta-analysis, since various factors seem to modulate its effect on antidepressant response. With the aim of clarifying this issue, we systematically reviewed literature, selecting 33 studies for an exploratory analysis without any a priori hypothesis. Then we analyzed separately 19 studies performed on Caucasians and 11 on Asians. We tested two phenotypes--remission and response rates--and three genotype comparisons--ll versus ls/ss, ss versus ll/ls and ll versus ss - using the Cochrane review manager. Evaluations were performed separately for SSRIs and mixed/other drugs. Possible clinical modulators were investigated. In the exploratory analysis, we found an association between l allele and l/l genotype and remission. When the analysis was split for ethnic group, in Caucasians we found an association between l allele and both response (OR = 1.58, C.I. 1.16-2.16, p = 0.004), and remission (OR = 1.53, C.I. 1.14-2.04, p = 0.004) in the SSRI group. Only a marginal association between l allele and remission (OR = 1.41, C.I. 1.02-1.95, p = 0.04) survived pooling together mixed antidepressant treatments. In Asians, a small effect of 5-HTTLPR on remission for mixed antidepressants was detected (OR = 2.10, C.I. 1.15-3.84, p = 0.02). Gender, age and age at onset modulated the association in Caucasians. Gender, age and depression severity at baseline modulated the association in Asians. In conclusion, in Caucasians 5-HTTLPR may be a predictor of antidepressant response and remission, while in Asians it does not appear to play a major role.

Pharmacogenetics of antidepressant drugs: current clinical practice and future directions

While antidepressants are widely used to treat mood and anxiety disorders, only half of the patients will respond to antidepressant treatment and only one-third of patients experience a full remission of symptoms. The identification of genetic biomarkers that predict antidepressant-treatment response can improve current clinical practice. This is an emerging field known as pharmacogenetics, which comprises of genetic studies on both the pharmacokinetics and pharmacodynamics of treatment response. Recent studies on antidepressant-treatment response have focused on both aspects of pharmacogenetics research, identifying new candidate genes that may predict better treatment response for patients. This paper reviews recent findings on the pharmacogenetics of antidepressant drugs and future clinical applications. Ultimately, these studies should lead to the use of genetic testing to guide the use of antidepressants in clinical practice.

AVPR1A and SLC6A4 polymorphisms in choral singers and non-musicians: a gene association study

Amateur choral singing is a common pastime and worthy of study, possibly conferring benefits to health and social behaviour. Participants might be expected to possess musical ability and share some behavioural characteristics. Polymorphisms in genes concerned with serotonergic neurotransmission are associated with both behaviour and musical aptitude. Those investigated previously include the variable number tandem repeats RS1, RS3 and AVR in the AVPR1A (arginine vasopressin receptor 1a) gene and STin2 in the SLC6A4 (solute carrier family 6 [neurotransmitter transporter, serotonin], member 4) gene, as well as the SLC6A4 promoter region polymorphism, 5-HTTLPR. We conducted a genetic association study on 523 participants to establish whether alleles at these polymorphisms occur more commonly in choral singers than in those not regularly participating in organised musical activity (non-musicians). We also analysed tagging single nucleotide polymorphisms (SNPs) for AVPR1A and SLC6A4 to determine whether other variants in these genes were associated with singer/non-musician status. At the STin2 polymorphism, overall association with singer/non-musician status was evident at P = 0.006. The 9-repeat (P = 0.04) and 12-repeat (P = 0.04) alleles were more common in singers and the 10-repeat allele less so (P = 0.009). Odds ratios were 0.73 (95% CI 0.57–0.94) for the 10-repeat allele and 2.47 (95% CI 0.88–6.94) for the rarer 9-repeat allele. No overall association was detected at P<0.05 between any other polymorphism and singer/non-musician status. Our null findings with respect to RS3, RS1 and AVR, polymorphisms associated with musical ability by other authors, suggest that choir membership may depend partly on factors other than musical ability. In a related musical project involving one participating choir, a new 40-part unaccompanied choral work, “Allele”, was composed and broadcast on national radio. In the piece, each singer's part incorporated their personal RS3 genotype.

5-HT(2B) receptors are required for serotonin-selective antidepressant actions

The therapeutic effects induced by serotonin-selective reuptake inhibitor (SSRI) antidepressants are initially triggered by blocking the serotonin transporter and rely on long-term adaptations of pre- and post-synaptic receptors. We show here that long-term behavioral and neurogenic SSRI effects are abolished after either genetic or pharmacological inactivation of 5-HT(2B) receptors. Conversely, direct agonist stimulation of 5-HT(2B) receptors induces an SSRI-like response in behavioral and neurogenic assays. Moreover, the observation that (i) this receptor is expressed by raphe serotonergic neurons, (ii) the SSRI-induced increase in hippocampal extracellular serotonin concentration is strongly reduced in the absence of functional 5-HT(2B) receptors and (iii) a selective 5-HT(2B) agonist mimics SSRI responses, supports a positive regulation of serotonergic neurons by 5-HT(2B) receptors. The 5-HT(2B) receptor appears, therefore, to positively modulate serotonergic activity and to be required for the therapeutic actions of SSRIs. Consequently, the 5-HT(2B) receptor should be considered as a new tractable target in the combat against depression.

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.

Genetic variants in the serotonin transporter influence the efficacy of bupropion and nortriptyline in smoking cessation

AIMS

We investigated whether variants in the serotonin transporter gene (SLC6A4) influence smoking cessation rates using antidepressant therapy (i.e. bupropion and nortriptyline).

DESIGN

Pharmacogenetic (secondary) analysis of a randomized, placebo-controlled efficacy trial of bupropion and nortriptyline for smoking cessation.

SETTING

Single-centre study, Maastricht University, the Netherlands.

PARTICIPANTS

A total of 214 of 255 (84%) current daily smokers participating in a randomized controlled efficacy trial.

MEASUREMENTS

Subjects were genotyped for three functional variants in SLC6A4 (5-HTTLPR, STin2, rs25531). Primary outcome measures were prolonged abstinence from weeks 4-12, 4-26 and 4-52. Secondary outcome measures included 7-day point prevalence abstinence at weeks 4, 12, 26 and 52.

FINDINGS

Carriers of the 5-HTTLPR high-activity L-variant had higher prolonged cessation rates with bupropion than placebo [odds ratio (OR) = 1.44, 95% confidence interval (CI) = 1.01-2.05, P = 0.04]. Combining the three variants resulted in increased prolonged cessation rates for both bupropion and nortriptyline among carriers of four to five high-activity variants (bupropion: OR = 2.00, 95% CI =1.21-3.29, P = 0.01; nortriptyline: OR = 1.91, 95% CI = 1.02-3.56, P = 0.04). Similar results were found for point prevalence abstinence.

CONCLUSIONS

Bupropion and nortriptyline seem to be more effective in smoking cessation among SLC6A4 high-activity variant carriers, probably by blocking the increased serotonin transporter activity, thereby increasing serotonin levels. Prospective studies have to assess if this can improve cessation rates when treatment is targeted at individuals based on their genotypes.

Serotonin transporter gene polymorphism and psychiatric disorders: is there a link?

Though still in infancy, the field of psychiatric genetics holds great potential to contribute to the development of new diagnostic and therapeutic options to treat these disorders. Among a large number of existing neurotransmitter systems, the serotonin system dysfunction has been implicated in many psychiatric disorders and therapeutic efficacy of many drugs is also thought to be based on modulation of serotonin. Serotonin transporter gene polymorphism is one of the most extensively studied polymorphisms in psychiatric behavioral genetics. In this article, we review the status of evidence for association between the serotonin gene polymorphism and some common mental disorders like affective disorders, post-traumatic stress disorder, obsessive-compulsive disorder, suicide, autism, and other anxiety and personality disorders. Going beyond traditional association studies, gene-environment interaction, currently gaining momentum, is also discussed in the review. While the existing information of psychiatric genetics is inadequate for putting into practice genetic testing in the diagnostic work-up of the psychiatric patient, if consistent in future research attempts, such results can be of great help to improve the clinical care of a vast majority of patients suffering from such disorders.