The impact of catechol-O-methyltransferase SNPs and haplotypes on treatment response phenotypes in major depressive disorder: a case-control association study

Genetic Landscape of Major Depressive Disorder: Assessment of Potential Diagnostic and Antidepressant Response Markers

BACKGROUND

The clinical heterogeneity in major depressive disorder (MDD), variable treatment response, and conflicting findings limit the ability of genomics toward the discovery of evidence-based diagnosis and treatment regimen. This study attempts to curate all genetic association findings to evaluate potential variants for clinical translation.

METHODS

We systematically reviewed all candidates and genome-wide association studies for both MDD susceptibility and antidepressant response, independently, using MEDLINE, particularly to identify replicated findings. These variants were evaluated for functional consequences using different in silico tools and further estimated their diagnostic predictability by calculating positive predictive values.

RESULTS

A total of 217 significantly associated studies comprising 1200 variants across 545 genes and 128 studies including 921 variants across 412 genes were included with MDD susceptibility and antidepressant response, respectively. Although the majority of associations were confirmed by a single study, we identified 31 and 18 replicated variants (in at least 2 studies) for MDD and antidepressant response. Functional annotation of these 31 variants predicted 20% coding variants as deleterious/damaging and 80.6% variants with regulatory effect. Similarly, the response-related 18 variants revealed 25% coding variant as damaging and 88.2% with substantial regulatory potential. Finally, we could calculate the diagnostic predictability of 19 and 5 variants whose positive predictive values ranges from 0.49 to 0.66 for MDD and 0.36 to 0.66 for response.

CONCLUSIONS

The replicated variants presented in our data are promising for disease diagnosis and improved response outcomes. Although these quantitative assessment measures are solely directive of available observational evidence, robust homogenous validation studies are required to strengthen these variants for molecular diagnostic application.

Point-of-Care Testing of Enzyme Polymorphisms for Predicting Hypnotizability and Postoperative Pain

Hypnotizability is a stable trait that moderates the benefit of hypnosis for treating pain, but limited availability of hypnotizability testing deters widespread use of hypnosis. Inexpensive genotyping of four single-nucleotide polymorphisms in the catechol-o-methyltransferase (COMT) gene was performed using giant magnetoresistive biosensors to determine if hypnotizable individuals can be identified for targeted hypnosis referrals. For individuals with the proposed optimal COMT diplotypes, 89.5% score highly on the Hypnotic Induction Profile (odds ratio, 6.12; 95% CI, 1.26-28.75), which identified 40.5% of the treatable population. Mean hypnotizability scores of the optimal group were significantly higher than the total population (P = 0.015; effect size = 0.60), an effect that was present in women (P = 0.0015; effect size = 0.83), but not in men (P = 0.28). In an exploratory cohort, optimal individuals also reported significantly higher postoperative pain scores (P = 0.00030; effect size = 1.93), indicating a greater need for treatment.

Polymorphisms of COMT and CREB1 are associated with treatment-resistant depression in a Chinese Han population

Genetic factors play a crucial role for the pathophysiology of treatment-resistant depression (TRD). It has been established that Catechol-O-methyltransferase (COMT) and cyclic amp-response element-binding protein (CREB) are associated with antidepressant response. The aim of this study was to explore the association between single nucleotide polymorphisms (SNPs) in COMT and CREB1 genes and TRD in a Chinese population. We recruited 181 patients with major depressive disorder (MDD) and 80 healthy controls, including 81 TRD patients. Depressive symptoms were assessed with the Hamilton Depression Rating Scale-17 (HDRS). Genotyping was performed using mass spectrometry. Genetic analyses were conducted by PLINK Software. The distribution of COMT SNP rs4818 allele and genotypes were significantly different between TRD and controls. Statistical differences in allele frequencies were observed between TRD and non-TRD groups, including rs11904814 and rs6740584 in CREB1 gene, rs4680 and rs4818 in COMT gene. There were differences in the distribution of HDRS total scores among different phenotypes of CREB1 rs11904814, CREB1 rs6740584, COMT rs4680 and rs4818. Gene-gene interaction effect of COMT-CREB1 (rs4680 × rs6740584) revealed significant epistasis in TRD. There findings indicate that COMT and CREB1 polymorphisms influence the risk of TRD and affect the severity of depressive symptoms of MDD.

Depression: Biological markers and treatment

Nowadays depression is considered as a systemic illness with different biological mechanisms involved in its etiology, including inflammatory response, hypothalamic-pituitary-adrenal (HPA) axis dysregulation and neurotransmitter and neurotrophic systems imbalance. Novel "omics" approaches, such as metabolomics and glycomics provide information about altered metabolic pathways and metabolites, as well as disturbances in glycosylation processes affected by or causing the development of depression. The clinical diagnosis of depression continues to be established based on the presence of the specific symptoms, but due to its heterogeneous underlying biological background, that differs according to the disease stage, there is an unmet need for treatment response biomarkers which would facilitate the process of appropriate treatment selection. This paper provides an overview of the role of major stress response system, the HPA axis, and its dysregulation in depression, possible involvement of neurotrophins, especially brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor and insulin-like growth factor-1, in the development of depression. Article discusses how activated inflammation processes and increased cytokine levels, as well as disturbed neurotransmitter systems can contribute to different stages of depression and could specific metabolomic and glycomic species be considered as potential biomarkers of depression. The second part of the paper includes the most recent findings about available medical treatment of depression. The described biological factors impose an optimistic conclusion that they could represent easy obtainable biomarkers potentially predicting more personalized treatment and diagnostic options.

Application of antidepressants in depression: A systematic review and meta-analysis

BACKGROUND

The type and quantities of antidepressants are increasing, but the efficacy and safety of first-line and emerging drugs vary between studies. In this article, we estimated the efficacy and safety of first-line and emerging antidepressants (anti-inflammatory drugs and ketamine).

METHOD

ystematic search of EMBASE, ERIC, MEDLINE, psycARTICLES, and psycINFO without language restriction for studies on the depression, depressive symptoms, antidepressants, fluoxetine (Prozac), paroxetine, escitalopram, sertraline, fluvoxamine, venlafaxine, duloxetine, NSAIDs, anti-cytokine drugs or pioglitazone published before May 1st, 2019. Information on study characteristics, depression or depressive symptoms, antidepressants and the descriptive statistics (including efficacy and safety of antidepressants) was extracted independently by 2 investigators. Estimates were pooled using random-effects meta-analysis. Differences by study-level characteristics were estimated using stratified meta-analysis and meta-regression. The response and remission of antidepressants were used as clinical evaluation indicators, and the evaluation criteria were clinical depression scales. OR value of antidepressants as assessed by meta-analysis.

RESULTS

The literature search retrieved 5529 potentially relevant articles of which 49 studies were finally included. We compared the efficacy of antidepressants (seven first-line antidepressants (fluoxetine, paroxetine, escitalopram, sertraline, fluvoxamine, venlafaxine, duloxetine), there kinds of anti-inflammatory drugs(NASIDs, cytokine-inhibitor, pioglitazone) and ketamine) by comparing the OR values.

CONCLUSION

The three drugs with the highest OR value in response were NASID (OR = 3.62(1.58, 8.32)), venlafaxin (OR = 3.50(1.83, 6.70)) and ketamine (OR = 3.28(1.89, 5.68)), while the highest OR value in remission were NASID (OR = 3.17(1.60, 6.29)), ketamine (OR = 2.99(1.58, 5.67)) and venlafaxin (OR = 2.55(1.72, 3.78)). Through reading the literature, we found 69 SNPs associated with depression. Major depression was a debilitating disorder that could ultimately lead to enormous societal and economical challenge [1]. The number of person which affected by depression was up to 16% of the population worldwide. More than 300 million individuals were estimated to suffer depression these days [1,2]. Therefore, it is apparent that safety and effective treatments for depression are necessary. In the 1930 s, the first drug for schizophrenia was discovered. This finding was a landmark for the emerging of biological psychiatry. In the 1950 s, pharmacologists had stumbled upon the antidepressant effect of imipramine. Since then, every 30 years, the use of antidepressants had made a pulsatile leap. Selective serotonin reuptake inhibitors (SSRIs) are the most widely-prescribed psychiatric drugs for the treatment of depression. However, the efficacy was variable and incomplete: 60%-70% of the patients do not experience remission, while 30%-40% do not show a significant response [3,4]. Nevertheless, SSRIs, SNRIs (selective serotonin-norepinephrine reuptake inhibitors, which can block norepinephrine at the same time) and NaSSAs (norepinephrine and selective serotonin receptor agonist), constituted the first-line clinical drugs. Nearly 30 years after the outbreak of SSRIs, antidepressants have ushered in a new chapter. It has been found that anti-inflammatory drugs could also have the small and moderate antidepressant effect and it's widely discussed [5]. More than 40 anti-inflammatory drugs have been certificated to have antidepressant effects in preclinical and clinical studies [6]. The antidepressant that has been approved for use recently is ketamine. There is no comprehensive comparison of the efficacy of all these drugs. In this review, we tried to estimate the efficacy and safety of first-line antidepressants, anti-inflammatory drugs and ketamine. On the other hand, with the development of GWAS, SNPs related to depression have been reported, and the corresponding mechanisms have been elaborated, respectively. However, patients with these SNPs have not been treated with individualized drugs according to the mechanisms. We hope to push this process forward through the summary of this article.

METHODS

Search Strategy and Study Eligibility.

Catechol-O-methyltransferase rs4680 and rs4818 haplotype association with treatment response to olanzapine in patients with schizophrenia

Antipsychotic drugs target primarily dopaminergic system which makes catechol-O-methyltransferase (COMT) an interesting target in studies searching for treatment response predictors in schizophrenia. The study assessed the association of the COMT rs4680 and rs4818 polymorphisms with therapeutic response to olanzapine, risperidone, clozapine or other antipsychotic medication after 8 weeks of monotherapy in patients with schizophrenia. 521 Caucasian patients with schizophrenia received a monotherapy with olanzapine (10–20 mg/day; N = 190), risperidone (3–6 mg/day; N = 99), or clozapine (100–500 mg/day; N = 102). The fourth group (N = 130) consisted of patients receiving haloperidol (3–15 mg/day), fluphenazine (4–25 mg/day) or quetiapine (50–800 mg/day). Treatment response was defined as a 50% reduction from the baseline positive and negative syndrome scale (PANSS) total and subscale scores, but also as an observed percentage reduction from the initial PANSS_0–6 total and subscale scores. Carriers of the COMT rs4680 A allele and carriers of the COMT rs4680–rs4818 C-A haplotype block had greater reduction in the PANSS total scores following olanzapine treatment, compared to carriers of the COMT rs4680 GG genotype and other COMT rs4680–rs4818 haplotypes. The COMT rs4680 A allele, and COMT rs4680–rs4818 C-A haplotype, were significantly associated with therapeutic response in patients treated with olanzapine, but not in patients treated with other antipsychotics.

Genetic influences on the variability of response to repetitive transcranial magnetic stimulation in human pharyngeal motor cortex

BACKGROUND

Recent studies have reported substantial variability in response to repetitive transcranial magnetic stimulation (rTMS). We hypothesized that an individual's genetic predisposition may contribute to such variability in the pharyngeal motor cortex. This study aimed to investigate the response to 1 and 5 Hz rTMS paradigms on pharyngeal motor cortex in healthy participants and its relationship with genetic predisposition.

METHODS

Forty-one healthy participants (25.4 ± 4.6 years old) received either or both 1 Hz (n = 39) and 5 Hz rTMS (n = 40) over pharyngeal motor cortex. Pharyngeal and thenar motor-evoked potentials were recorded at baseline and for 1 hour post-rTMS. The participants were then classified according to their response. The associations between rTMS response and gender, time of day of the stimulation, and eight prespecified single nucleotide polymorphisms (SNPs) were analyzed.

KEY RESULTS

There was no direction-specific response to either paradigm (1 Hz: F[3.69, 129.21] = 0.78, P = 0.56; 5 Hz: F[4.08, 146.85] = 1.38, P = 0.25). Only 13% of participants showed the expected bidirectional response (inhibition for 1 Hz and excitation for 5 Hz). Significant associations were found between response and COMT (1 Hz: P = 0.03) and DRD2 (1 Hz: P = 0.02; 5 Hz: P = 0.04) polymorphisms. Carriers of minor allele G from SNP rs6269 (COMT) were more likely to show inhibitory or excitatory outcomes after 1 Hz rTMS. By contrast, carriers of minor allele A from SNP rs1800497 (DRD2) were more likely to show no response to 1 Hz rTMS and inhibition after 5 Hz rTMS.

CONCLUSIONS & INFERENCES

Two SNPs from COMT and DRD2 genes may partially explain the response variability to rTMS in the pharyngeal motor system. Further research should focus on stratified approaches for neurostimulatory dysphagia treatment using rTMS.

Results of the European Group for the Study of Resistant Depression (GSRD) - basis for further research and clinical practice

Objectives: The overview outlines two decades of research from the European Group for the Study of Resistant Depression (GSRD) that fundamentally impacted evidence-based algorithms for diagnostics and psychopharmacotherapy of treatment-resistant depression (TRD). Methods: The GSRD staging model characterising response, non-response and resistance to antidepressant (AD) treatment was applied to 2762 patients in eight European countries. Results: In case of non-response, dose escalation and switching between different AD classes did not show superiority over continuation of original AD treatment. Predictors for TRD were symptom severity, duration of the current major depressive episode (MDE), suicidality, psychotic and melancholic features, comorbid anxiety and personality disorders, add-on treatment, non-response to the first AD, adverse effects, high occupational level, recurrent disease course, previous hospitalisations, positive family history of MDD, early age of onset and novel associations of single nucleoid polymorphisms (SNPs) within the PPP3CC, ST8SIA2, CHL1, GAP43 and ITGB3 genes and gene pathways associated with neuroplasticity, intracellular signalling and chromatin silencing. A prediction model reaching accuracy of above 0.7 highlighted symptom severity, suicidality, comorbid anxiety and lifetime MDEs as the most informative predictors for TRD. Applying machine-learning algorithms, a signature of three SNPs of the BDNF, PPP3CC and HTR2A genes and lacking melancholia predicted treatment response. Conclusions: The GSRD findings offer a unique and balanced perspective on TRD representing foundation for further research elaborating on specific clinical and genetic hypotheses and treatment strategies within appropriate study-designs, especially interaction-based models and randomized controlled trials.

Pharmacogenetics of Antidepressants: from Genetic Findings to Predictive Strategies

The constantly growing contribution of depressive disorders to the global disease statistics calls for a growth of treatment effectiveness and optimization. Antidepressants are the most frequently prescribed medicines for depressive disorders. However, development of a standardized pharmacotherapeutic approach is burdened by the genomic heterogeneity, lack of reliable predictive biomarkers and variability of the medicines metabolism aggravated by multiple side effects of antidepressants. According to modern assessments up to 20 % of the genes expressed in our brain are involved in the pathogenesis of depression. Large-scale genetic and genomic research has found a number of potentially prognostic genes. It has also been proven that the effectiveness and tolerability of antidepressants directly depend on the variable activity of the enzymes that metabolize medicines. Almost all modern antidepressants are metabolized by the cytochrome P450 family enzymes. The most promising direction of research today is the GWAS (Genome-Wide Association Study) method that is aimed to link genomic variations with phenotypical manifestations. In this type of research genomes of depressive patients with different phenotypes are compared to the genomes of the control group containing same age, sex and other parameters healthy people. Notably, regardless of the large cohorts of patients analyzed, none of the GWA studies conducted so far can reliably reproduce the results of other analogous studies. The explicit heterogeneity of the genes associated with the depression pathogenesis and their pleiotropic effects are strongly influenced by environmental factors. This may explain the difficulty of obtaining clear and reproducible results. However, despite any negative circumstances, the active multidirectional research conducted today, raises the hope of clinicians and their patients to get a whole number of schedules how to achieve remission faster and with guaranteed results

A gender-specific COMT haplotype contributes to risk modulation rather than disease severity of major depressive disorder in a Chinese population

BACKGROUND

COMT rs4680 Val158 allele is associated with high MB-COMT protein expression and elevated activity compared to the Met158 allele in post-mortem brains. A meta-analysis study suggested the link between COMT SNPs and MDD risk; in addition, MB membrane-bound (MB-COMT) specific genetic variation was reported that influences predisposition to depression amongst females.

METHODS

Four tagSNPs, including rs4680, were genotyped. 268 MDD subjects and 223 controls were enrolled. MDD severity was rated by HDRS. Total-COMT and MB-COMT mRNA were detected by quantitative PCR. COMT protein and activity were assayed by western blot and methyltransferase assay, respectively.

RESULTS

Haplotype TG of rs4633-rs4680, rs4646312 C, and rs4633 T allele might be linked to MDD vulnerability. Haplotype TG may interact with gender and affect MDD risk, since female haplotype TG carriers were estimated for a 9.17-fold higher risk than counterparts. COMT SNPs were not associated with HDRS scores. Haplotype TG female controls had higher MB-COMT protein, whereas non-TG female controls had higher soluble cytoplasmic (S-COMT) protein than other groups. COMT activity was much higher in controls than in MDD subjects.

LIMITATIONS

Restricted numbers of homozygous TG carriers were recruited and analyzed for COMT mRNA, protein and activity. Only peripheral blood samples were used.

CONCLUSIONS

A female-specific haplotype (haplotype TG)-MDD vulnerability association was found. TG female controls had higher MB-COMT protein and S-COMT. Altogether, high COMT protein and activity in female TG controls may be predisposing factors for enhanced MDD risk, though not correlated to MDD severity as rated by HDRS.

Genetic variants in major depressive disorder: From pathophysiology to therapy

In spite of promising preclinical results there is a decreasing number of new registered medications in major depression. The main reason behind this fact is the lack of confirmation in clinical studies for the assumed, and in animals confirmed, therapeutic results. This suggests low predictive value of animal studies for central nervous system disorders. One solution for identifying new possible targets is the application of genetics and genomics, which may pinpoint new targets based on the effect of genetic variants in humans. The present review summarizes such research focusing on depression and its therapy. The inconsistency between most genetic studies in depression suggests, first of all, a significant role of environmental stress. Furthermore, effect of individual genes and polymorphisms is weak, therefore gene x gene interactions or complete biochemical pathways should be analyzed. Even genes encoding target proteins of currently used antidepressants remain non-significant in genome-wide case control investigations suggesting no main effect in depression, but rather an interaction with stress. The few significant genes in GWASs are related to neurogenesis, neuronal synapse, cell contact and DNA transcription and as being nonspecific for depression are difficult to harvest pharmacologically. Most candidate genes in replicable gene x environment interactions, on the other hand, are connected to the regulation of stress and the HPA axis and thus could serve as drug targets for depression subgroups characterized by stress-sensitivity and anxiety while other risk polymorphisms such as those related to prominent cognitive symptoms in depression may help to identify additional subgroups and their distinct treatment. Until these new targets find their way into therapy, the optimization of current medications can be approached by pharmacogenomics, where metabolizing enzyme polymorphisms remain prominent determinants of therapeutic success.

Peripheral biomarkers of major depression and antidepressant treatment response: Current knowledge and future outlooks

BACKGROUND

In recent years, we have accomplished a deeper understanding about the pathophysiology of major depressive disorder (MDD). Nevertheless, this improved comprehension has not translated to improved treatment outcome, as identification of specific biologic markers of disease may still be crucial to facilitate a more rapid, successful treatment. Ongoing research explores the importance of screening biomarkers using neuroimaging, neurophysiology, genomics, proteomics, and metabolomics measures.

RESULTS

In the present review, we highlight the biomarkers that are differentially expressed in MDD and treatment response and place a particular emphasis on the most recent progress in advancing technology which will continue the search for blood-based biomarkers.

LIMITATIONS

Due to space constraints, we are unable to detail all biomarker platforms, such as neurophysiological and neuroimaging markers, although their contributions are certainly applicable to a biomarker review and valuable to the field.

CONCLUSIONS

Although the search for reliable biomarkers of depression and/or treatment outcome is ongoing, the rapidly-expanding field of research along with promising new technologies may provide the foundation for identifying key factors which will ultimately help direct patients toward a quicker and more effective treatment for MDD.

Pharmacogenetics and Imaging-Pharmacogenetics of Antidepressant Response: Towards Translational Strategies

Genetic variation underlies both the response to antidepressant treatment and the occurrence of side effects. Over the past two decades, a number of pharmacogenetic variants, among these the SCL6A4, BDNF, FKBP5, GNB3, GRIK4, and ABCB1 genes, have come to the forefront in this regard. However, small effects sizes, mixed results in independent samples, and conflicting meta-analyses results led to inherent difficulties in the field of pharmacogenetics translating these findings into clinical practice. Nearly all antidepressant pharmacogenetic variants have potentially pleiotropic effects in which they are associated with major depressive disorder, intermediate phenotypes involved in emotional processes, and brain areas affected by antidepressant treatment. The purpose of this article is to provide a comprehensive review of the advances made in the field of pharmacogenetics of antidepressant efficacy and side effects, imaging findings of antidepressant response, and the latest results in the expanding field of imaging-pharmacogenetics studies. We suggest there is mounting evidence that genetic factors exert their impact on treatment response by influencing brain structural and functional changes during antidepressant treatment, and combining neuroimaging and genetic methods may be a more powerful way to detect biological mechanisms of response than either method alone. The most promising imaging-pharmacogenetics findings exist for the SCL6A4 gene, with converging associations with antidepressant response, frontolimbic predictors of affective symptoms, and normalization of frontolimbic activity following antidepressant treatment. More research is required before imaging-pharmacogenetics informed personalized medicine can be applied to antidepressant treatment; nevertheless, inroads have been made towards assessing genetic and neuroanatomical liability and potential clinical application.

Meta-analysis of the COMT Val158Met polymorphism in major depressive disorder: the role of gender

OBJECTIVES

Many studies have reported an association of the COMT Val158Met polymorphism and major depressive disorder (MDD), although with conflicting results. The role of gender is a possible modulator. To overcome the problem of poor sample size detecting genes of small effect, we perform a meta-analysis of the current literature, investigating the influence of the COMT Val158Met polymorphism on the pathogenesis of MDD, with a major focus on the effect of gender.

METHODS

Out of 977 retrieved articles, 21 included case-control studies allowed the analysis of 9005 patients with MDD and 12,095 controls. Allelic and genotypic pooled odds ratios (OR) were calculated for the total sample and gender-subgroups.

RESULTS

In the absence of publication bias, allelic and genotypic analyses showed no significant association in the total sample, as well as in gender-specific subgroups. Sensitivity analysis did not alter the ORs.

CONCLUSIONS

The results imply a complex nature of the genotype × phenotype interaction. Further studies of the COMT gene or the locus remain to be justified given the important positional and functional relevance and the plethora of gender-specific findings. A possible way to further dissect this topic is shifting the focus to gene-based or genome-wide analyses of intermediate phenotypes.

Does refining the phenotype improve replication rates? A review and replication of candidate gene studies on Major Depressive Disorder and Chronic Major Depressive Disorder

Replication has been poor for previously reported candidate genes involved in Major Depressive Disorder (MDD). One possible reason is phenotypic and genetic heterogeneity. The present study replicated genetic associations with MDD as defined in DSM-IV and with a more narrowly defined MDD subtype with a chronic and severe course. We first conducted a systematic review of genetic association studies on MDD published between September 2007 and June 2012 to identify all reported candidate genes. Genetic associations were then tested for all identified single nucleotide polymorphisms (SNPs) and the entire genes using data from the GAIN genome-wide association study (MDD: n = 1,352; chronic MDD subsample: n = 225; controls: n =  1,649). The 1,000 Genomes database was used as reference for imputation. From 157 studies identified inthe literature, 81 studies reported significant associations with MDD, involving 245 polymorphisms in 97 candidate genes, from which we were able to investigate 185 SNPs in 89 genes. We replicated nine candidate SNPs in eight genes for MDD and six in five genes for chronic MDD. However, these were not more than expected by chance. At gene level, we replicated 18 genes for MDD and 17 genes for chronic MDD, both significantly more than expected by chance. We showed that replication rates were improved for MDD compared to a previous, highly similar, replication study based on studies published before 2007. Effect sizes of the SNPs and replication rates of the candidate genes were improved in the chronic subsample compared to the full sample. Nonetheless, replication rates were still poor.

Evaluation of psychiatric and genetic risk factors among primary relatives of suicide completers in Delhi NCR region, India

Suicide as a public health problem is studied worldwide and association of psychiatric and genetic risk factors for suicidal behavior are the point of discussion in studies across different ethnic groups. The present study is aimed at evaluating psychiatric and genetic traits among primary relatives of suicide completer families in an urban Indian population. Bi-variate analysis shows significant increase in major depression (PHQ and Hamilton), stress, panic disorder, somatoform disorder and suicide attemptamong primary compared to other relatives. Sib pair correlations also reveal significant results for major depression (Hamilton), stress, suicide attempt, intensity of suicide ideation and other anxiety syndrome. 5-HTTLPR, 5-HTT (Stin2) and COMT risk alleles are higher among primary relatives, though statistically insignificant. Backward conditional logistic regression analysis show only independent variable, Depression (Hamilton) made a unique statistically significant contribution to the model in primary relatives.

The combined effect of genetic polymorphisms and clinical parameters on treatment outcome in treatment-resistant depression

For over a decade, the European Group for the Study of Resistant Depression (GSRD) has examined single nucleotide polymorphisms (SNP) and clinical parameters in regard to treatment outcome. However, an interaction based model combining these factors has not been established yet. Regarding the low effect of individual SNPs, a model investigating the interactive role of SNPs and clinical variables in treatment-resistant depression (TRD) seems auspicious. Thus 225 patients featured in previous work of the GSRD were enrolled in this investigation. According to data availability and previous positive results, 12 SNPs in HTR2A, COMT, ST8SIA2, PPP3CC and BDNF as well as 8 clinical variables featured in other GSRD studies were chosen for this investigation. Random forests algorithm were used for variable shrinkage and k-means clustering for surfacing variable characteristics determining treatment outcome. Using these machine learning and clustering algorithms, we detected a set of 3 SNPs and a clinical variable that was significantly associated with treatment response. About 62% of patients exhibiting the allelic combination of GG-GG-TT for rs6265, rs7430 and rs6313 of the BDNF, PPP3CC and HTR2A genes, respectively, and without melancholia showed a HAM-D decline under 17 compared to about 34% of the whole study sample. Our random forests prediction model for treatment outcome showed that combining clinical and genetic variables gradually increased the prediction performance recognizing correctly 25% of responders using all 4 factors. Thus, we could confirm our previous findings and furthermore show the strength of an interaction-based model combining statistical algorithms in identifying and operating treatment predictors.

Association of COMT and TPH-2 genes with DSM-5 based PTSD symptoms

BACKGROUND

Dopaminergic and serotonergic systems have been implicated in PTSD. The present study evaluated the association of four catechol-O-methyltransferase (COMT) gene loci, and the joint effect of COMT and tryptophan hydroxylase 2 (TPH2) genes on PTSD symptoms.

METHODS

Subjects included 200 Caucasian Armenian adults exposed to the 1988 Spitak earthquake from 12 multigenerational (3-5 generations) families. Instruments used included the UCLA PTSD Reaction Index based on DSM-5 criteria, and the Beck Depression Inventory.

RESULTS

The adjusted heritabilitiy of vulnerability to DSM-5 based PTSD symptoms was 0.60 (p<10(-4)). There was a significant association of the COMT allele rs4633C with total PTSD (p<0.03), and D category (p<0.04) (negative alterations in cognitions and mood) severity scores, but not with C category (avoidance) scores. There was no genetic correlation between C and D category severity scores. COMT allele rs4633C and the TPH-2 allele rs11178997T together accounted for 7% of the variance in PTSD severity scores (p<0.001). None of the COMT alleles were associated with depression.

LIMITATIONS

The ratings of earthquake exposure and prior trauma may have been subject to recall bias. The findings may not be generalizable to other ethnic/racial populations.

CONCLUSION

COMT allele rs4633C may be causally related and/or is in linkage disequilibrium with gene(s) that are causally related to PTSD symptoms. Carriers of these COMT and the TPH-2 alleles may be at increased risk for PTSD. The findings provide biological support for dividing DSM-IV category C symptoms into DSM-5 categories C and D.

Advances in biomarkers of major depressive disorder

Major depressive disorder (MDD) is characterized by mood, vegetative, cognitive, and even psychotic symptoms and signs that can cause substantial impairments in quality of life and functioning. Biomarkers are measurable indicators that could help diagnosing MDD or predicting treatment response. In this chapter, lipid profiles, immune/inflammation, and neurotrophic factor pathways that have long been implicated in the pathogenesis of MDD are discussed. Then, pharmacogenetics and epigenetics of serotonin transport and its metabolism pathway, brain-derived neurotrophic factor, and abnormality of hypothalamo-pituitary-adrenocortical axis also revealed new biomarkers. Lastly, new techniques, such as proteomics and metabolomics, which allow researchers to approach the studying of MDD with new directions and make new discoveries are addressed. In the future, more data are needed regarding pathophysiology of MDD, including protein levels, single nucleotide polymorphism, epigenetic regulation, and clinical data in order to better identify reliable and consistent biomarkers for diagnosis, treatment choice, and outcome prediction.

Association of TMEM132D, COMT, and GABRA6 genotypes with cingulate, frontal cortex and hippocampal emotional processing in panic and major depressive disorder

OBJECTIVE

The aim of the study was to evaluate the association of transmembrane protein 132D (TMEM132D), catechol-O-methyltransferase (COMT), and gamma-aminobutyric acid (GABA) receptor alpha 6 subunit (GABRA6) genotypes with cingulate, frontal cortex and hippocampal emotional processing in panic disorder (PD) and major depressive disorder (MDD).

METHOD

The single nucleotide polymorphisms (SNPs) in TMEM132D, COMT, and GABRA6 were examined in patients with MDD, PD, and healthy controls. Functional magnetic resonance imaging (fMRI) was performed in patients with MDD, PD, and healthy controls.

RESULTS

rs4680 in COMT and rs3219151 in GABRA6 showed positive associations with PD and MDD. A dynamic fearful face was shown to the participants during fMRI scanning. In PD patients, responses in the bilateral anterior cingulate were stronger in carriers of the AA genotype of SNP rs11060369 in TMEM132D compared with carriers of the AC + CC genotype, and stronger in CT + TT genotype carriers of SNP rs3219151 in GABRA6 compared with carriers of the CC genotype. The response in the medial orbital frontal cortex was stronger in carriers of the CT + TT genotypes of SNP rs3219151 in PD. In MDD patients, the response in the right parahippocampus of carriers of the GG genotype of rs4680 in COMT was stronger than that of carriers of the AA + AG genotype.

CONCLUSION

These results suggest that TMEM132D, GABRA6, and COMT variants may increase vulnerability to panic.

Promoter variation in the catechol-O-methyltransferase gene is associated with remission of symptoms during fluvoxamine treatment for major depression

We investigated the association between remission of depressive symptoms in fluvoxamine treatment and catechol-O-methyltransferase (COMT) gene. Sixteen SNPs in the COMT gene were investigated in 123 outpatients with major depression. Three single nucleotide polymorphisms located in the 5' region were associated with remission in fluvoxamine-treated outpatients with moderate to severe depression.

Interactions among catechol-O-methyltransferase genotype, parenting, and sex predict children's internalizing symptoms and inhibitory control: Evidence for differential susceptibility

We used sex, observed parenting quality at 18 months, and three variants of the catechol-O-methyltransferase gene (Val158Met [rs4680], intron1 [rs737865], and 3'-untranslated region [rs165599]) to predict mothers' reports of inhibitory and attentional control (assessed at 42, 54, 72, and 84 months) and internalizing symptoms (assessed at 24, 30, 42, 48, and 54 months) in a sample of 146 children (79 male). Although the pattern for all three variants was very similar, Val158Met explained more variance in both outcomes than did intron1, the 3'-untranslated region, or a haplotype that combined all three catechol-O-methyltransferase variants. In separate models, there were significant three-way interactions among each of the variants, parenting, and sex, predicting the intercepts of inhibitory control and internalizing symptoms. Results suggested that Val158Met indexes plasticity, although this effect was moderated by sex. Parenting was positively associated with inhibitory control for methionine-methionine boys and for valine-valine/valine-methionine girls, and was negatively associated with internalizing symptoms for methionine-methionine boys. Using the "regions of significance" technique, genetic differences in inhibitory control were found for children exposed to high-quality parenting, whereas genetic differences in internalizing were found for children exposed to low-quality parenting. These findings provide evidence in support of testing for differential susceptibility across multiple outcomes.

The influence of COMT Val¹⁵⁸Met genotype on the character dimension cooperativeness in healthy females

OBJECTIVES

Although the Val(158)Met catechol-O-methyltransferase (COMT) gene has been linked with the temperament dimension Novelty Seeking (NS), new insights in this polymorphism might point to a major role for character features as well. Given that individual life experiences may influence Val(158) and Met(158) allele carriers differently it has been suggested that the character trait cooperativeness could be implicated.

CASE REPORT

A homogeneous group of eighty right-handed Caucasian healthy female university students were assessed with the TCI and genotyped for the COMT Val(158)Met polymorphism (rs4680). Gene determination showed that eighteen were Val(158) homozygotes, forty-four Val/Met(158) heterozygotes, and eighteen were Met(158) homozygotes. All were within the same age range and never documented to have suffered from any neuropsychiatric illness. Bonferroni corrected non-parametric analyses showed that only for the character scale cooperativeness Val(158) homozygotes displayed significant higher scores when compared to Met(158) homozygotes. No significant differences on cooperativeness scores were found between Val(158) and Val/Met(158) carriers or between Met(158) and Val/Met(158) carriers. No differences were observed for the COMT Val(158)Met polymorphism and the other temperament and character scales.

CONCLUSIONS

Our findings support the assumption that the Val(158)Met single nucleotide polymorphism (SNP) influences character traits and not only temperament. Our results add to the notion that Val(158) homozygotes are considered to be helpful and empathic and it suggest that these cooperativeness character traits are related to the dopaminergic system.

COMT Val(158)Met genotypes differentially influence subgenual cingulate functional connectivity in healthy females

Brain imaging studies have consistently shown subgenual Anterior Cingulate Cortical (sgACC) involvement in emotion processing. catechol-O-methyltransferase (COMT) Val(158) and Met(158) polymorphisms may influence such emotional brain processes in specific ways. Given that resting-state fMRI (rsfMRI) may increase our understanding on brain functioning, we integrated genetic and rsfMRI data and focused on sgACC functional connections. No studies have yet investigated the influence of the COMT Val(158)Met polymorphism (rs4680) on sgACC resting-state functional connectivity (rsFC) in healthy individuals. A homogeneous group of 61 Caucasian right-handed healthy female university students, all within the same age range, underwent rsfMRI. Compared to Met(158) homozygotes, Val(158) allele carriers displayed significantly stronger rsFC between the sgACC and the left parahippocampal gyrus, ventromedial parts of the inferior frontal gyrus (IFG), and the nucleus accumbens (NAc). On the other hand, compared to Val(158) homozygotes, we found in Met(158) allele carriers stronger sgACC rsFC with the medial frontal gyrus (MFG), more in particular the anterior parts of the medial orbitofrontal cortex. Although we did not use emotional or cognitive tasks, our sgACC rsFC results point to possible distinct differences in emotional and cognitive processes between Val(158) and Met(158) allele carriers. However, the exact nature of these directions remains to be determined.

Lack of influence of rs4680 (COMT) and rs6276 (DRD2) on diagnosis and clinical outcomes in patients with major depression

OBJECTIVE

The gene coding for the catechol-O-methyltransferase (COMT) and the one coding for the dopamine receptor 2 (DRD2) have been linked with major depression (MD) and with the response to antidepressants in several studies. However, contrasting findings have been reported as well. The aim of the present study is, therefore, to investigate possible influences of rs4680 within COMT and rs6276 within DRD2, analyzed both individually and in combination, on the diagnosis and clinical outcomes in a sample of Korean MD patients treated with antidepressants.

METHODS

Totally, 184 Korean in-patients suffering from MD treated with either paroxetine or venlafaxine and 220 healthy control subjects were included in the present study. Depression severity was assessed by means of the Hamilton Rating Scale for Depression.

RESULTS

We were not able to find any association between the two variants under investigation and diagnosis of MD, as well as with antidepressant response.

CONCLUSIONS

Although limited by several factors, including the small sample size and the impossibility to extend our findings to patients treated with different antidepressants, the results of our study provide support to the notion that these variants might not play a major role in the etiology and clinical outcomes of MD.

PPP3CC gene: a putative modulator of antidepressant response through the B-cell receptor signaling pathway

Antidepressant pharmacogenetics represents a stimulating, but often discouraging field. The present study proposes a combination of several methodologies across three independent samples. Genes belonging to monoamine, neuroplasticity, circadian rhythm and transcription factor pathways were investigated in two samples (n=369 and 88) with diagnosis of major depression who were treated with antidepressants. Phenotypes were response, remission and treatment-resistant depression. Logistic regression including appropriate covariates was performed. Genes associated with outcomes were investigated in the STAR*D (Sequenced Treatment Alternatives to Relieve Depression) genome-wide study (n=1861). Top genes were further studied through a pathway analysis. In both original samples, markers associated with outcomes were concentrated in the PPP3CC gene. Other interesting findings were particularly in the HTR2A gene in one original sample and the STAR*D. The B-cell receptor signaling pathway proved to be the putative mediator of PPP3CC's effect on antidepressant response (P=0.03). Among innovative candidates, PPP3CC, involved in the regulation of immune system and synaptic plasticity, seems promising for further investigation.

Are there meaningful biomarkers of treatment response for depression?

During the past decades, the prevalence of affective disorders has been on the rise globally, with only one out of three patients achieving remission in acute treatment with antidepressants. The identification of physiological markers that predict treatment course proves useful in increasing therapeutic success. On the basis of well-documented, recent findings in depression research, we highlight and discuss the most promising biomarkers for antidepressant therapy response. These include genetic variants and gene expression profiles, proteomic and metabolomic markers, neuroendocrine function tests, electrophysiology and imaging techniques. Ultimately, this review proposes an integrative use of biomarkers for antidepressant treatment outcome.

Association of the catechol-o-methyltransferase gene polymorphisms with Korean autism spectrum disorders

This study evaluated the family-based genetic association between autism spectrum disorders (ASDs) and 5 single-nucleotide polymorphisms (SNPs) in the catechol-o-methyltransferase gene (COMT), which was found among 151 Korean ASDs family trios (dominant model Z = 2.598, P = 0.009, P FDR = 0.045). We found a statistically significant allele transmission or association in terms of the rs6269 SNP in the ASDs trios. Moreover, in the haplotype analysis, the haplotypes with rs6269 demonstrated significant evidence of an association with ASDs (additive model rs6269-rs4818-rs4680-rs769224 haplotype P = 0.004, P FDR = 0.040). Thus, an association may exist between the variants of the COMT gene and the occurrence of ASDs in Koreans.

Pharmacogenetics of antidepressant drugs: an update after almost 20 years of research

Major depressive disorder (MDD) is an emergent cause of personal and socio-economic burden, both for the high prevalence of the disorder and the unsatisfying response rate of the available antidepressant treatments. No reliable predictor of treatment efficacy and tolerance in the single patient is available, thus drug choice is based on a trial and error principle with poor clinical efficiency. Among modulators of treatment outcome, genetic polymorphisms are thought to explain a significant share of the inter-individual variability. The present review collected the main pharmacogenetic findings primarily about antidepressant response and secondly about antidepressant induced side effects, and discussed the main strengths and limits of both candidate and genome-wide association studies and the most promising methodological opportunities and challenges of the field. Despite clinical applications of antidepressant pharmacogenetics are not available yet, previous findings suggest that genotyping may be applied in the clinical practice. In order to reach this objective, further rigorous pharmacogenetic studies (adequate sample size, study of better defined clinical subtypes of MDD, adequate covering of the genetic variability), their combination with the results obtained through complementary methodologies (e.g., pathway analysis, epigenetics, transcriptomics, and proteomics), and finally cost-effectiveness trials are required.

Pharmacogenetics in major depression: a comprehensive meta-analysis

A number of candidate gene studies focused on major depression (MD) and antidepressant (AD) efficacy have been carried out, but results mainly remain inconclusive. We performed a comprehensive meta-analysis of published candidate gene studies focused on AD efficacy in MD to evaluate the cumulative evidence. A random-effect model was applied to study the polymorphisms with genotypic counts available from at least three independent studies. On the base of previous evidence, the analysis was stratified by ethnicity (Caucasian, Asian, and other/mixed), and AD class (SSRIs and mixed/other ADs). Genotypic data were available for 16 polymorphisms in 11 genes. After the exclusion of 5-HTTLPR in SLC6A4 included in another recent meta-analysis, 15 polymorphisms in 11 genes were included in the present meta-analysis (BDNF rs6265, SLC6A4 STin2, HTR1A rs6295, HTR2A rs6311, rs6313 and rs7997012, HTR6 rs1805054, TPH1 rs1800532, SLC6A2 rs5569, COMT rs4680, GNB3 rs5443, FKBP5 rs1360780 and rs3800373, and ABCB1 rs1045642 and rs2032582). Our results suggested that BDNF rs6265 (Val66Met) heterozygous genotype was associated with better SSRIs response compared to the homozygous genotypes, particularly in Asians (OR=1.53, 95%CI 1.12-2.07, p=0.007). SLC6A4 STin2, HTR2A rs6311 and rs7997012, GNB3 rs5443, FKBP5 rs1360780 and rs3800373, and ABCB1 rs2032582 showed associations with AD efficacy, but these results were highly dependent on one or two single studies. In conclusion, our findings suggested the BDNF Val66Met as the best single candidate involved in AD response, with a selective effect on SSRI treatment. Our overall results supported no major effect of any single gene variant on AD efficacy.

European Group for the Study of Resistant Depression (GSRD)--where have we gone so far: review of clinical and genetic findings

The primary objective of this review is to give an overview of the main findings of the European multicenter project "Patterns of Treatment Resistance and Switching Strategies in Affective Disorder", performed by the Group for the Study of Resistant Depression (GSRD). The aim was to study methodological issues, operational criteria, clinical characteristics, and genetic variables associated with treatment resistant depression (TRD), that is failure to reach response after at least two consecutive adequate antidepressant trials. The primary findings of clinical variables associated with treatment resistance include comorbid anxiety disorders as well as non-response to the first antidepressant received lifetime. Although there is a plethora of hints in textbooks that switching the mechanism of action should be obtained in case of nonresponse to one medication, the results of the GSRD challenge this notion by demonstrating in retrospective and prospective evaluations that staying on the same antidepressant mechanism of action for a longer time is more beneficial than switching, however, when switching is an option there is no benefit to switch across class. The GSRD candidate gene studies found that metabolism status according to cytochrome P450 gene polymorphisms may not be helpful to predict response and remission rates to antidepressants. Significant associations with MDD and antidepressant treatment response were found for COMT SNPs. Investigating the impact of COMT on suicidal behaviour, we found a significant association with suicide risk in MDD patients not responding to antidepressant treatment, but not in responders. Further significant associations with treatment response phenotypes were found with BDNF, 5HTR2A and CREB1. Additional investigated candidate genes were DTNBP1, 5HT1A, PTGS2, GRIK4 and GNB3.

Variation in the catechol-O-methyltransferase (COMT) gene and treatment response to venlafaxine XR in generalized anxiety disorder

Antidepressant drugs are the preferred choice for the treatment of generalized anxiety disorder (GAD). However, the choice of pharmacotherapy is determined on a trial-and-error basis, as the underlying mechanisms of treatment response are unknown. We examined whether the COMT gene, which has been known to play a role in antidepressant treatment response in major depressive disorder (MDD), has a pharmacogenetic effect in antidepressant treatment response in GAD. In our study, 156 patients diagnosed with GAD received venlafaxine XR treatment as part of an 18-month relapse prevention study. Genotypes were obtained for the COMT functional variant rs4680 (Val158Met) for all patients; however, pharmacogenetic analysis was only conducted for the European American population (n=112). We found no significant association between our primary Hamilton Anxiety Scale outcome measure and rs4680. However, we did find a nominally significant allelic association between this variant and a secondary treatment outcome measure (CGI-I) in our European American population (n=112). Furthermore, we show a slight dominant effect of the A-allele with the CGI-I measure in the European American population indicating a possible pharmacogenetic role of rs4680 in antidepressant treatment outcome in GAD. Further studies in a larger population are needed to confirm this effect.

The impact of COMT gene polymorphisms on suicidality in treatment resistant major depressive disorder--a European multicenter study

Many association studies have reported associations between the catechol-O-methyltransferase (COMT) gene and psychiatric disorders including major depression (MDD). The COMT gene has further been associated with suicidal behaviour, as well as with treatment response, although with conflicting results. In the present study, we further elucidate the impact of COMT in treatment response in MDD patients with suicide risk and/or a personal history of suicide attempts. Two hundred fifty MDD patients were collected in the context of a European multicentre resistant depression study and treated with antidepressants at adequate doses for at least 4 weeks. Suicidality was assessed using Mini International Neuropsychiatric Interview (MINI) and the Hamilton Rating Scale for Depression (HAM-D). Treatment response was defined as HAM-D ≤ 17 and remission as HAM-D ≤ 7 after 4 weeks of treatment with antidepressants at adequate dose. Genotyping was performed for seven SNPs (rs4680, rs2075507, rs737865, rs6269, rs4633, rs4818 and rs165599) within the COMT gene. With regard to suicide risk and personal history of suicide attempts, neither single marker nor haplotypic association was found with any SNP after multiple testing correction. In non-responders, we found significant single marker and haplotypic association with suicide risk, but not in responders. The same holds true for both remitters and non-remitters, and when testing for association with a personal history of suicide attempts and treatment response phenotypes. In conclusion, we found significant association of COMT SNPs with suicide risk in MDD patients not responding to antidepressant treatment. Larger well-defined cohorts will be required to dissect this further.

No association between COMT val158met polymorphism and suicidal behavior: meta-analysis and new data

BACKGROUND

The polymorphism COMTval158met has been associated with suicidal behavior in case-control and meta-analysis studies, but results and conclusions remain controversial. The objective of this study was to examine the association between COMT val158met with suicidal behavior in a case-control study and to assess the combined evidence -this case-control study and available data from other related studies- we carried out a meta-analysis.

METHODS

We conducted a case-control study with 105 patients with suicide attempts and 236 controls. Subsequently, we performed a meta-analysis of published genetic association studies by searching through Medline, PubMed and Web of Science databases.

RESULTS

No significant differences were found in the distribution of alleles (χ2 = 0.33, 1 df, p = 0.56) or genotypes (χ2 = 2.36, 2 df, p = 0.26). The meta-analysis comprising 12 association studies (including the present one) showed that the risk COMTmet allele of COMTval158/met is not associated with suicidal behavior (OR: 1.09, 95% CI: 0.97-1.23), even in the absence of heterogeneity (OR: 1.09, 95% CI: 0.97-1.23).

CONCLUSION

Our results showed no association between COMTval158/met and suicidal behavior. However, more studies are necessary to determine conclusively an association between COMT and suicidal behavior.

Influence and interaction of genetic polymorphisms in catecholamine neurotransmitter systems and early life stress on antidepressant drug response

BACKGROUND

Catecholamine neurotransmission plays an important role in major depression. Variation in genes implicated in the synthesis and signal transduction of catecholamines (norepinephrine and dopamine) may interact with environmental factors to affect the outcome of antidepressant treatment. We aimed to determine how a range of polymorphisms in noradrenergic and dopaminergic genes influence this response to treatment and how they interact with childhood trauma and recent life stress in a Chinese sample.

METHODS

In a sample of 308 Chinese Han patients with major depressive disorder, 13 single nucleotide polymorphisms (SNPs) in coding regions of six genes (MAOA, SLC6A2, TH, COMT, DRD2, DRD3) with minor allele frequencies >5% were successfully genotyped from an initial series of 35 SNPs in 11 candidate genes associated with catecholamine neurotransmission. The responses to 6 weeks' treatment with antidepressant drugs was determined by changes in the 17-item Hamilton Depression Rating Scale (HAMD-17) score, and previous stressful events were evaluated by the Life Events Scale (LES) and Childhood Trauma Questionnaire-Short Form (CTQ-SF). Single SNP and haplotype associations with treatment response were analysed by UNPHASED 3.0.13, gene-gene interactions were analysed by generalized multifactor dimensionality reduction (GMDR) and gene-environment interactions by logistic regression.

RESULTS

A haplotype in MAOA (rs1137070 and rs6323) was significantly associated with antidepressant response in the total group, the nonSSRI subgroup and the female subgroup. Two haplotypes in COMT (involving rs4633, rs4818 and rs769224) were significantly associated with antidepressant response in the nonSSRI subgroup. The SLC6A2 SNPs interacted with childhood trauma to influence antidepressant response.

CONCLUSIONS

A haplotype in MAOA and two haplotypes in COMT are found to be associated with antidepressant treatment response in this sample. Stressors in early life may interact with polymorphisms in SLC6A2 to influence response to antidepressant treatment.

Pharmacogenetics of antidepressants

Up to 60% of depressed patients do not respond completely to antidepressants (ADs) and up to 30% do not respond at all. Genetic factors contribute for about 50% of the AD response. During the recent years the possible influence of a set of candidate genes as genetic predictors of AD response efficacy was investigated by us and others. They include the cytochrome P450 superfamily, the P-glycoprotein (ABCB1), the tryptophan hydroxylase, the catechol-O-methyltransferase, the monoamine oxidase A, the serotonin transporter (5-HTTLPR), the norepinephrine transporter, the dopamine transporter, variants in the 5-hydroxytryptamine receptors (5-HT1A, 5-HT2A, 5-HT3A, 5-HT3B, and 5-HT6), adrenoreceptor beta-1 and alpha-2, the dopamine receptors (D2), the G protein beta 3 subunit, the corticotropin releasing hormone receptors (CRHR1 and CRHR2), the glucocorticoid receptors, the c-AMP response-element binding, and the brain-derived neurotrophic factor. Marginal associations were reported for angiotensin I converting enzyme, circadian locomotor output cycles kaput protein, glutamatergic system, nitric oxide synthase, and interleukin 1-beta gene. In conclusion, gene variants seem to influence human behavior, liability to disorders and treatment response. Nonetheless, gene × environment interactions have been hypothesized to modulate several of these effects.