Meta-analyses of genetic studies on major depressive disorder

Neurogenetics of depression: a focus on reward processing and stress sensitivity

Major depressive disorder (MDD) is etiologically complex and has a heterogeneous presentation. This heterogeneity hinders the ability of molecular genetic research to reliably detect the small effects conferred by common genetic variation. As a result, significant research efforts have been directed at investigating more homogenous intermediate phenotypes believed to be more proximal to gene function and lie between genes and/or environmental effects and disease processes. In the current review we survey and integrate research on two promising intermediate phenotypes linked to depression: reward processing and stress sensitivity. A synthesis of this burgeoning literature indicates that a molecular genetic approach focused on intermediate phenotypes holds significant promise to fundamentally improve our understanding of the pathophysiology and etiology of depression, which will be required for improved diagnostic definitions and the development of novel and more efficacious treatment and prevention strategies. We conclude by highlighting challenges facing intermediate phenotype research and future development that will be required to propel this pivotal research into new directions.

Prediction of susceptibility to major depression by a model of interactions of multiple functional genetic variants and environmental factors

Major depressive disorder (MDD) is the most common psychiatric disorder and the second overall cause of disability. Even though a significant amount of the variance in the MDD phenotype is explained by inheritance, specific genetic variants conferring susceptibility to MDD explain only a minimal proportion of MDD causality. Moreover, genome-wide association studies have only identified two small-sized effect loci that reach genome-wide significance. In this study, a group of Mexican-American patients with MDD and controls recruited for a pharmacogenetic study were genotyped for nonsynonymous single-nucleotide polymorphisms (nsSNPs) and used to explore the interactions of multiple functional genetic variants with risk-classification tree analysis. The risk-classification tree analysis model and linkage disequilibrium blocks were used to replicate exploratory findings in the database of genotypes and phenotypes (dbGaP) for major depression, and pathway analysis was performed to explore potential biological mechanisms using the branching events. In exploratory analyses, we found that risk-classification tree analysis, using 15 nsSNPs that had a nominal association with MDD diagnosis, identified multiple increased-MDD genotype clusters and significant additive interactions in combinations of genotype variants that were significantly associated with MDD. The results in the dbGaP for major depression disclosed a multidimensional dependent phenotype constituted of MDD plus significant modifiers (smoking, marriage status, age, alcohol abuse/dependence and gender), which then was used for the association tree analysis. The reconstructed tree analysis for the dbGaP data showed robust reliability and replicated most of the genes involved in the branching process found in our exploratory analyses. Pathway analysis using all six major events of branching (PSMD9, HSD3B1, BDNF, GHRHR, PDE6C and PDLIM5) was significant for positive regulation of cellular and biological processes that are relevant to growth and organ development. Our findings not only provide important insights into the biological pathways underlying innate susceptibility to MDD but also offer a predictive framework based on interactions of multiple functional genetic variants and environmental factors. These findings identify novel targets for therapeutics and for translation into preventive, clinical and personalized health care.

A fine-mapping study of 7 top scoring genes from a GWAS for major depressive disorder

Major depressive disorder (MDD) is a psychiatric disorder that is characterized--amongst others--by persistent depressed mood, loss of interest and pleasure and psychomotor retardation. Environmental circumstances have proven to influence the aetiology of the disease, but MDD also has an estimated 40% heritability, probably with a polygenic background. In 2009, a genome wide association study (GWAS) was performed on the Dutch GAIN-MDD cohort. A non-synonymous coding single nucleotide polymorphism (SNP) rs2522833 in the PCLO gene became only nominally significant after post-hoc analysis with an Australian cohort which used similar ascertainment. The absence of genome-wide significance may be caused by low SNP coverage of genes. To increase SNP coverage to 100% for common variants (m.a.f.>0.1, r(2)>0.8), we selected seven genes from the GAIN-MDD GWAS: PCLO, GZMK, ANPEP, AFAP1L1, ST3GAL6, FGF14 and PTK2B. We genotyped 349 SNPs and obtained the lowest P-value for rs2715147 in PCLO at P = 6.8E-7. We imputed, filling in missing genotypes, after which rs2715147 and rs2715148 showed the lowest P-value at P = 1.2E-6. When we created a haplotype of these SNPs together with the non-synonymous coding SNP rs2522833, the P-value decreased to P = 9.9E-7 but was not genome wide significant. Although our study did not identify a more strongly associated variant, the results for PCLO suggest that the causal variant is in high LD with rs2715147, rs2715148 and rs2522833.

Association between a genetic variant in the serotonin transporter gene (SLC6A4) and suicidal behavior in patients with schizophrenia

Background

The serotonin (5-hydroxytryptamin; 5-HT) system has a central role in the circuitry of cognition and emotions. Multiple lines of evidence suggest that genetic variation in the serotonin transporter gene (SLC6A4; 5-HTT) is associated with schizophrenia and suicidal behavior. In this study, we wanted to elucidate whether SLC6A4 variations is involved in attempted suicide among patients with schizophrenia in a Scandinavian case–control sample.

Methods

Patients diagnosed with schizophrenia from three Scandinavian samples were assessed for presence or absence of suicide attempts, based on record reviews and interview data. Seven SLC6A4 single nucleotide polymorphisms (SNPs) were genotyped in 837 schizophrenia patients and 1,473 control individuals. Association analyses and statistical evaluations were performed with the program UNPHASED (version 3.0.9).

Results

We observed an allele association between the SNP rs16965628, located in intron one of SLC6A4, and attempted suicide (adjusted p-value 0.01), among patients with schizophrenia. No association was found to a diagnosis of schizophrenia, when patients were compared to healthy control individuals.

Conclusion

The gene SLC6A4 appears to be involved in suicidal ideation among patients with schizophrenia. Independent replication is needed before more firm conclusions can be drawn.

Genetics of smoking and depression

Smoking and depression are significant public health problems with multiple etiological dimensions and outcomes. Although each condition is important by itself, they are important because they often potentiate each other. Consequently, it is also essential to understand the nature their relationship. This representative review focuses on the genetic etiology of the relationship in the context of reviewing first the epidemiology of depression and smoking, and then by exploring behavioral and molecular genetic studies, and other psychiatric and medical comorbidities. At this point, epidemiological evidence for a relationship between depression and smoking/nicotine dependence is compelling. Although behavioral genetic results differ somewhat by gender and in accordance with specific definitions of depression and smoking variables, recent studies show converging evidence for common genetic factors underlying the relationship, often in addition to non-shared environmental factors. The search for underlying genes and genetic mechanisms is at an early stage, but shows promising candidate genes and genetic approaches for future studies.

Depressive symptoms and serum lipid levels in young adult women

Accumulating data suggest that depression is associated with risk factors for cardiovascular disease, but few studies have investigated potential behavioral mediators of such associations, particularly among women. In this study of healthy young adult women (n = 225), we examined associations among depressive symptoms, health behaviors, and serum lipid levels. Depressive symptoms were assessed with the 20-item Center for Epidemiologic Studies-Depression scale, and a fasting blood sample was obtained for serum lipid levels, including total cholesterol, high-density lipoprotein (HDL-C) and low-density lipoprotein (LDL-C). Diet was measured using 24-h recalls, and other health behaviors (physical activity, smoking) were assessed via self-report questionnaire. Results indicated a modest negative association between depressive symptoms and LDL-C levels. Higher levels of depressive symptoms were also associated with lower total and insoluble dietary fiber intake, both of which were associated with HDL-C and LDL-C. Mediational analyses indicated a significant indirect effect of depressive symptoms on LDL-C via total and insoluble dietary fiber in unadjusted analyses, but not in adjusted analyses. The present findings suggest that depressive symptoms are inversely associated with serum LDL-C levels in young adult women, but that these associations are not likely mediated by adverse lifestyle behaviors.

What Stresses University Students: An Interview Investigation of the Demands of Tertiary Studies

Although several previous scales have been developed to measure the presence and effects of the stressful demands encountered by university students, most of these have been validated with samples drawn from US universities, commonly using only undergraduate psychology students. In addition, many of the items used are from scales designed for application within general adult populations, with little focus upon the specific stressors met by students. In order to identify what are the major changes these students encounter that they find stressful, a sample of 32 university students from different degree areas within an Australian university was individually interviewed using a standardised protocol. Results indicated that (unlike US data) these students found dislocation to family, friend and partner relationships most stressful, followed by the time demands of study and financial restrictions. Limitations of the study, future research directions and implications for counsellors are discussed.

Plasma metabonomics as a novel diagnostic approach for major depressive disorder

Major depressive disorder (MDD) is a socially detrimental psychiatric disorder, contributing to increased healthcare expenditures and suicide rates. However, no empirical laboratory-based tests are available to support the diagnosis of MDD. In this study, a NMR-based plasma metabonomic method for the diagnosis of MDD was tested. Proton nuclear magnetic resonance ((1)H NMR) spectra of plasma sampled from first-episode drug-naı̈ve depressed patients (n = 58) and healthy controls (n = 42) were recorded and analyzed by orthogonal partial least-squares discriminant analysis (OPLS-DA). The OPLS-DA score plots of the spectra demonstrated that the depressed patient group was significantly distinguishable from the healthy control group. Moreover, the method accurately diagnosed blinded samples (n = 26) in an independent replication cohort with a sensitivity and specificity of 92.8% and 83.3%, respectively. Taken together, NMR-based plasma metabonomics may offer an accurate empirical laboratory-based method applicable to the diagnosis of MDD.

Interaction of catechol O-methyltransferase and serotonin transporter genes modulates effective connectivity in a facial emotion-processing circuitry

Imaging genetic studies showed exaggerated blood oxygenation level-dependent response in limbic structures in carriers of low activity alleles of serotonin transporter-linked promoter region (5-HTTLPR) as well as catechol O-methyltransferase (COMT) genes. This was suggested to underlie the vulnerability to mood disorders. To better understand the mechanisms of vulnerability, it is important to investigate the genetic modulation of frontal-limbic connectivity that underlies emotional regulation and control. In this study, we have examined the interaction of 5-HTTLPR and COMT genetic markers on effective connectivity within neural circuitry for emotional facial expressions. A total of 91 healthy Caucasian adults underwent functional magnetic resonance imaging experiments with a task presenting dynamic emotional facial expressions of fear, sadness, happiness and anger. The effective connectivity within the facial processing circuitry was assessed with Granger causality method. We have demonstrated that in fear processing condition, an interaction between 5-HTTLPR (S) and COMT (met) low activity alleles was associated with reduced reciprocal connectivity within the circuitry including bilateral fusiform/inferior occipital regions, right superior temporal gyrus/superior temporal sulcus, bilateral inferior/middle prefrontal cortex and right amygdala. We suggest that the epistatic effect of reduced effective connectivity may underlie an inefficient emotion regulation that places these individuals at greater risk for depressive disorders.

Behavioral genetics of affective and anxiety disorders

As shown by clinical genetic studies, affective and anxiety disorders are complex genetic disorders with genetic and environmental factors interactively determining their respective pathomechanism. Advances in molecular genetic techniques including linkage studies, association studies, and genome-wide association studies allow for the detailed dissection of the genetic influence on the development of these disorders. Besides the molecular genetic investigation of categorical entities according to standardized diagnostic criteria, intermediate phenotypes comprising neurobiological or neuropsychological traits (e.g., neuronal correlates of emotional processing) that are linked to the disease of interest and that are heritable, have been proposed to be closer to the underlying genotype than the overall disease phenotype. These intermediate phenotypes are dimensional and more precisely defined than the categorical disease phenotype, and therefore have attracted much interest in the genetic investigation of affective and anxiety disorders. Given the complex genetic nature of affective and anxiety disorders with an interaction of multiple risk genes and environmental influences, the interplay of genetic factors with environmental factors is investigated by means of gene-environment interaction (GxE) studies. Pharmacogenetic studies aid in the dissection of the genetically influenced heterogeneity of psychotropic drug response and may contribute to the development of a more individualized treatment of affective and anxiety disorders. Finally, there is some evidence for genetic factors potentially shared between affective and anxiety disorders pointing to a possible overlapping phenotype between anxiety disorders and depression.

Apolipoprotein E genotypes and neuropsychiatric symptoms and syndromes in late-onset Alzheimer's disease

Neuropsychiatric symptoms (NPS) in dementia, previously denominated as behavioural and psychological symptoms of dementia, are often more distressing, impairing, and costly than cognitive symptoms, representing a major health burden for older adults. These symptoms are common features of Alzheimer's disease (AD), and are one of the major risk factors for institutionalization. There is a high prevalence of neuropsychiatric disturbances in patients with AD, including depression, anxiety, apathy, psychosis, aggression, and agitation. At present, the role of the apolipoprotein E (APOE) genotypes in the development of NPS or neuropsychiatric syndromes/endophenotypes in AD patients is unclear. In this article, we summarized the findings of the studies of NPS and neuropsychiatric syndromes in AD in relation to APOE genotypes, with special attention to the possible underlying mechanisms. While some studies failed to find a significant association between the APOE polymorphism and NPS in late-onset AD, other studies reported a significant association between the APOE ɛ4 allele and an increase in agitation/aggression, hallucinations, delusions, and late-life depression or anxiety. However, current cumulative evidence coming from the few existing longitudinal studies shows no association of APOE genotypes with NPS as a whole in AD. Some negative studies that focused on the distribution of APOE genotypes between AD patients with or without NPS further emphasized the importance of sub-grouping NPS in distinct neuropsychiatric syndromes. Explanations for the variable findings in the existing studies included differences in patient populations, differences in the assessment of neuropsychiatric symptomatology, possible lack of statistical power to detect associations in the negative studies, and small sample sizes generating false positives that cannot be consistently replicated. Finally, many reviewed studies were cross-sectional, whereas it would be of paramount importance to evaluate the risk for incident NPS in relation to the APOE genotype in prospectively followed cohorts of AD patients. In fact, identifying predisposing genetic risk factors may allow us to understand the pathophysiological features of neuropsychiatric syndromes or symptoms in AD, so optimizing possible therapeutic options.

The genetic basis of depression

Since the publication of the working draft of the human genome just over a decade ago, there have been dramatic advances in our understanding of the role genetics play in both normal human functioning as well as in disease. The identification of genes, which influence an individual's susceptibility to depression, is not only an intriguing scientific endeavour in its own right, but further, if a gene can be confidently implicated in depression, then this could shed light on the aetiological processes involved in the disease. Moreover, a genetic association with depression may identify targets for consideration in the development of novel treatments for the illness. This chapter will summarise the current research into the genetic basis of depression. A number of genes of interest have been highlighted, although a genetic variant, that is unequivocally associated with increased risk for the disease, is yet to be identified. However, technologies and methodologies are evolving rapidly, and genetic approaches have helped shape how we conceptualise depression as an illness.

Genome-wide association study of major depressive disorder: new results, meta-analysis, and lessons learned

Major depressive disorder (MDD) is a common complex disorder with a partly genetic etiology. We conducted a genome-wide association study of the MDD2000+ sample (2431 cases, 3673 screened controls and >1 M imputed single-nucleotide polymorphisms (SNPs)). No SNPs achieved genome-wide significance either in the MDD2000+ study, or in meta-analysis with two other studies totaling 5763 cases and 6901 controls. These results imply that common variants of intermediate or large effect do not have main effects in the genetic architecture of MDD. Suggestive but notable results were (a) gene-based tests suggesting roles for adenylate cyclase 3 (ADCY3, 2p23.3) and galanin (GAL, 11q13.3); published functional evidence relates both of these to MDD and serotonergic signaling; (b) support for the bipolar disorder risk variant SNP rs1006737 in CACNA1C (P=0.020, odds ratio=1.10); and (c) lack of support for rs2251219, a SNP identified in a meta-analysis of affective disorder studies (P=0.51). We estimate that sample sizes 1.8- to 2.4-fold greater are needed for association studies of MDD compared with those for schizophrenia to detect variants that explain the same proportion of total variance in liability. Larger study cohorts characterized for genetic and environmental risk factors accumulated prospectively are likely to be needed to dissect more fully the etiology of MDD.

The GNB3 C825T polymorphism as a pharmacogenetic marker in the treatment of hypertension, obesity, and depression

Heterotrimeric guanine-binding proteins (G proteins) transmit signals from the cell surface to intracellular signal cascades. The β3-subunit encoded by the gene GNB3 is widely expressed and, therefore, involved in various physiological and pathophysiological processes. A C825T polymorphism located in exon 10 of GNB3 was described in 1998 and the T allele was associated with alternative splicing and with increased signal transduction in human cells and tissues. In several disease-association studies, the 825T allele could be linked to hypertension, obesity, and depression. Meta-analysis available for hypertension and depression confirmed association with these phenotypes. On the basis of these findings, subsequent studies investigated whether the C825T polymorphism serves as a pharmacogenetic marker. Most pharmacogenetic investigations have focused on the treatment of hypertension, obesity, and depression. In this study, we will comprehensively describe and discuss these studies.

Research review: gene-environment interaction research in youth depression - a systematic review with recommendations for future research

BACKGROUND

Depression is a major public health problem among youth, currently estimated to affect as many as 9% of US children and adolescents. The recognition that both genes (nature) and environments (nurture) are important for understanding the etiology of depression has led to a rapid growth in research exploring gene-environment interactions (GxE). However, there has been no systematic review of GxE in youth depression to date.

METHODS

The goal of this article was to systematically review evidence on the contribution of GxE to the risk of child and adolescent depression. Through a search of PubMed and PsycINFO databases to 1 April 2010, we identified 20 candidate gene-environment interaction studies focused on depression in youth (up to age 26) and compared each study in terms of the following characteristics: research design and sample studied; measure of depression and environment used; genes explored; and GxE findings in relation to these factors.

RESULTS

In total, 80% of studies (n = 16) found at least one significant GxE association. However, there was wide variation in methods and analyses adopted across studies, especially with respect to environmental measures used and tests conducted to estimate GxE. This heterogeneity made it difficult to compare findings and evaluate the strength of the evidence for GxE.

CONCLUSIONS

The existing body of GxE research on depression in youth contains studies that are conceptually and methodologically quite different, which contributes to mixed findings and makes it difficult to assess the current state of the evidence. To decrease this heterogeneity, we offer 20 recommendations that are focused on: (a) reporting GxE research; (b) testing and reporting GxE effects; (c) conceptualizing, measuring and analyzing depression; (d) conceptualizing, measuring and analyzing environment; (e) increasing power to test for GxE; and (f) improving the quality of genetic data used. Although targeted to GxE research on depression, these recommendations can be adopted by GxE researchers focusing on other mental health outcomes.

Hippocampal α7 nicotinic acetylcholine receptor levels in patients with schizophrenia, bipolar disorder, or major depressive disorder

BACKGROUND

The α7 nicotinic acetylcholine receptor (nAChR) is involved in cognitive function and synaptic plasticity. Consequently, changes in α7 nAChR function have been implicated in a variety of mental disorders, especially schizophrenia. However, there is little knowledge regarding the levels of the α7 nAChR in patients with bipolar disorder.

METHODS

We performed [(125)I]-bungarotoxin autoradiography to selectively visualize and measure α7 nAChRs on postmortem sections of the temporal lobe from patients with schizophrenia, bipolar disorder, or major depressive disorder, as well as control subjects. Radioligand binding was determined in the dentate gyrus, CA3, and CA1 subfields of the hippocampus and the perirhinal cortex.

RESULTS

Bungarotoxin binding was significantly increased in the CA1 and perirhinal cortex of patients with bipolar disorder compared to control subjects, whereas in patients with schizophrenia or major depressive disorder the level of binding did not significantly differ from control subjects in any region measured.

CONCLUSIONS

These data are consistent with the reported genetic associations linking the α7 nAChR to the pathology of bipolar disorder, and may suggest a dysfunction of α7 nAChR-dependent signalling in bipolar disorder. We could not reproduce the previously reported decrease in hippocampal bungarotoxin binding in schizophrenia.

Transmission and prevention of mood disorders among children of affectively ill parents: a review

OBJECTIVE

To provide a conceptual review of the literature on children of depressed parents over the past 12 years.

METHOD

This selective review focused on published studies that delineate the diagnosis of depression in parents, have large samples, describe children 6 to 17 years old, and are methodologically rigorous. The review emphasized conceptual advances and major progress since 1998. Recent efforts in prevention research were discussed, gaps in the existing literature were noted, and directions for targeted research on children of depressed parents were highlighted.

RESULTS

Over the past 12 years there has been considerable progress in delineating the gene-by-environment interplay in determining the range of outcomes in children. In addition, progress has been made in identifying risk mechanisms and moderators that underlie the transmission of disorder and in developing effective prevention programs.

CONCLUSIONS

This review highlights directions for further research, including different areas affected by parental depression in parents and children, and in understanding the underlying mechanisms involved in the intergenerational transmission of depression, so that preventive and treatment efforts can be tailored effectively.

Meta-analysis and genome-wide interpretation of genetic susceptibility to drug addiction

Background

Classical genetic studies provide strong evidence for heritable contributions to susceptibility to developing dependence on addictive substances. Candidate gene and genome-wide association studies (GWAS) have sought genes, chromosomal regions and allelic variants likely to contribute to susceptibility to drug addiction.

Results

Here, we performed a meta-analysis of addiction candidate gene association studies and GWAS to investigate possible functional mechanisms associated with addiction susceptibility. From meta-data retrieved from 212 publications on candidate gene association studies and 5 GWAS reports, we linked a total of 843 haplotypes to addiction susceptibility. We mapped the SNPs in these haplotypes to functional and regulatory elements in the genome and estimated the magnitude of the contributions of different molecular mechanisms to their effects on addiction susceptibility. In addition to SNPs in coding regions, these data suggest that haplotypes in gene regulatory regions may also contribute to addiction susceptibility. When we compared the lists of genes identified by association studies and those identified by molecular biological studies of drug-regulated genes, we observed significantly higher participation in the same gene interaction networks than expected by chance, despite little overlap between the two gene lists.

Conclusions

These results appear to offer new insights into the genetic factors underlying drug addiction.

The genetic blueprint of major depressive disorder: contributions of imaging genetics studies

OBJECTIVES

To review neuroimaging intermediate phenotypes of MDD and their relation to genetic risk variants.

METHODS

A systematic literature search of peer-reviewed English language articels using PubMed ( www.pubmed.org ) was performed.

RESULTS

Comprehensive evidence on the influence of serotonergic genes (SLC6A4, HTR1A, MAOA, TPH2) and BDNF on the following neural intermediate phenotypes is displayed: amygdala reactivity, coupling of amygdala-anterior cingulate cortex (ACC) activity, ACC volume, hippocampal volume and serotonin receptor 1A (5-HT1A) binding potential (BP).

CONCLUSIONS

Intermediate phenotypes may bridge the gap between genotype and phenotype by reducing the impreciseness of psychiatric phenotypes and yield more insights into the underlying biology.

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.

Increasing depressive symptoms in children of Alzheimer parents

Children of persons with Alzheimer disease (AD) are at increased risk of developing AD themselves, but specific factors that predict AD in this population have yet to be elucidated. Various studies indicate depressive symptoms may predate clinical AD and represent a risk factor and/or prodrome of incipient dementia, but their relevance for AD offspring remains uncertain. As part of a longitudinal family study of AD, we assessed depressive symptomatology in 30 middle aged AD offspring (mean age at baseline: 41.2). Their mean total scores on the Hamilton Depression Rating scale increased from 1.8 to 5.3 (P < .001) across a 20-year interval. Neurocognitive performance remained stable in a subset of this cohort (N = 25) over the same interval. Findings from this small convenience sample suggest emerging depressive symptoms may be among the earliest signs of subsequent dementia in this high-risk population but require confirmation through further longitudinal follow-up and replication in larger populations.

The kynurenine pathway in major depression: haplotype analysis of three related functional candidate genes

A consistent finding in major depressive disorder (MDD) research is dysfunction of the immune system. One of the relevant metabolic pathways in this regard is the kynurenine pathway. In patients with major depression, an imbalance between neuroprotective and neurotoxic arms of the pathway with lower plasma kynurenic acid concentration was demonstrated. Therefore, we investigated Single Nucleotide Polymorphism (SNP) and haplotype association of three candidate genes of the three enzymes involved in this metabolism. The three genes, namely, tryptophan hydroxylase 2 (TPH2), kynurenine 3 monooxygenase (KMO) and kynurenine amino transferase 3 (KAT III) SNPs and haplotype association analysis was performed in 338 (266 major depression and 72 bipolar depression) unrelated Caucasian patients with major depressive episodes and 310 age, gender and ethnicity matched controls. In sliding window analyses using PLINK of the haplotypes of KAT III, all windows which include the first SNP (rs12729558), the overall haplotype distribution (OMNIBUS) was significantly different between patients with a major depressive episode and control for all windows, with p-values ranging between 1.75 × 10=5 and 0.006. This is due to the haplotype CGCTCT (referring to 6 SNP window analysis), which is found in about 5.7% of patients and 1.9% of healthy controls. It was due to CGCTCT haplotype and the frequencies of this haplotype in both bipolar patients and patients with major depression showed significantly higher than the control population (p<0.001). This haplotype of KAT III gene CGCTCT may have effect on the function of this enzyme in formation of kynurenic acid in some patients with major depressive episodes.

Oestrogen receptor polymorphisms and late-life depression

BACKGROUND

Evidence suggests a role for oestrogen in depression but the involvement of oestrogen receptor polymorphisms remains unknown.

AIMS

To determine the association between oestrogen receptor polymorphisms and late-life depression and the modifying effect of hormone treatment.

METHOD

Depression was assessed using the Mini-International Neuropsychiatric Interview, according to DSM-IV criteria and the Centre for Epidemiologic Studies - Depression Scale. The association between oestrogen receptor α and β (ER-α and ER-β) polymorphisms with severe depression was examined in 6017 community-dwelling elderly people using multivariate logistic regression.

RESULTS

In women, the ER-α rs2234693 and rs9340799 polymorphisms were significantly associated with the risk of late-life depression. The A allele of ER-β rs1256049 increased the risk of depression, but only for non-current users of hormone treatment. In men, only the ER-β rs4986938 polymorphism showed a weak association with depression risk.

CONCLUSIONS

Oestrogen receptor polymorphisms are associated with severe late-life depression risk in women only.

Genetic risk profiles for depression and anxiety in adult and elderly cohorts

The first generation of genome-wide association studies (GWA studies) for psychiatric disorders has led to new insights regarding the genetic architecture of these disorders. We now start to realize that a larger number of genes, each with a small contribution, are likely to explain the heritability of psychiatric diseases. The contribution of a large number of genes to complex traits can be analyzed with genome-wide profiling. In a discovery sample, a genetic risk profile for depression was defined based on a GWA study of 1738 adult cases and 1802 controls. The genetic risk scores were tested in two population-based samples of elderly participants. The genetic risk profiles were evaluated for depression and anxiety in the Rotterdam Study cohort and the Erasmus Rucphen Family (ERF) study. The genetic risk scores were significantly associated with different measures of depression and explained up to ∼0.7% of the variance in depression in Rotterdam Study and up to ∼1% in ERF study. The genetic score for depression was also significantly associated with anxiety explaining up to 2.1% in Rotterdam study. These findings suggest the presence of many genetic loci of small effect that influence both depression and anxiety. Remarkably, the predictive value of these profiles was as large in the sample of elderly participants as in the middle-aged samples.

Dopamine polymorphisms and depressive symptoms predict foods intake. Results from a nationally representative sample

Depression and variation in dopamine related genes have both independently been associated with food consumption. Depressive symptoms could synergistically interact with genetic variation to influence food intake. We examined the interaction between high depressive symptoms and functional polymorphisms of dopamine transporter (SLC6A3), monoamine oxidase A (MAOA), dopamine receptor D2 (DRD2) and dopamine receptor D4 (DRD4) on intake of high-calorie sweet, high-calorie non-sweet, and low-calorie foods in the National Longitudinal Study of Adolescent Health (Add Health). Multivariate linear regression analyses were used to examine main effects of gene and depression symptoms and their interaction (genotype-by-high depression symptoms) on food categories. Applying a false discovery rate criterion for multiple comparisons indicated a statistically significant interaction for females with high depressive symptoms and the SLC6A3 gene, such that those with the SLC6A3 10/10 allele reported greater intake of high-calorie sweet foods than their counterparts high in depressive symptoms with the SLC6A3 any 9 allele (LS mean 10/10 allele=2.5, SE=.13; LS mean any 9 allele=1.8, SE=.13, p<.05). These findings highlight that the relationship between depression and food intake may vary as a function of genetic polymorphism. Further research is needed to confirm these findings.

Gene-environment interactions in geriatric depression

In older adults, several environmental challenges can potentially trigger the onset of an episode of major depression. Vulnerability to these challenges can be influenced by genetics. There is accumulating evidence for an interaction between stress and a serotonin transporter polymorphism, though there is also heterogeneity among studies. Other relevant genes include those encoding for the neuroendocrine stress axis, growth factors, and other monoaminergic systems. Each of these may interact with either predisposing traumas in early childhood or precipitating events later in life.

P2RX7 gene is associated consistently with mood disorders and predicts clinical outcome in three clinical cohorts

We investigated the effect of nine candidate genes on risk for mood disorders, hypothesizing that predisposing gene variants not only elevate the risk for mood disorders but also result in clinically significant differences in the clinical course of mood disorders. We genotyped 178 DSM-IV bipolar I and II and 272 major depressive disorder patients from three independent clinical cohorts carefully diagnosed with semistructured interviews and prospectively followed up with life charts for a median of 60 (range 6-83) months. Healthy control subjects (n = 1322) were obtained from the population-based national Health 2000 Study. We analyzed 62 genotyped variants within the selected genes (BDNF, NTRK2, SLC6A4, TPH2, P2RX7, DAOA, COMT, DISC1, and MAOA) against the presence of mood disorder, and in post-hoc analyses, specifically against bipolar disorder or major depressive disorder. Estimates for time ill were based on life charts. The P2RX7 gene variants rs208294 and rs2230912 significantly elevated the risk for a familial mood disorder (OR = 1.35, P = 0.0013, permuted P = 0.06, and OR = 1.44, P = 0.0031, permuted P = 0.17, respectively). The results were consistent in all three cohorts. The same risk alleles predicted more time ill in all cohorts (OR 1.3, 95% CI 1.1-1.6, P = 0.0069 and OR 1.7, 95% CI 1.3-2.3, P = 0.0002 with rs208294 and rs2230912, respectively), so that homozygous carriers spent 12 and 24% more time ill. P2RX7 and its risk alleles predisposed to mood disorders consistently in three independent clinical cohorts. The same risk alleles resulted in clinically significant differences in outcome of patients with major depressive and bipolar disorder.

SNPs in genes encoding G proteins in pharmacogenetics

Heterotrimeric guanine-binding proteins (G proteins) transmit signals from the cell surface to intracellular signal cascades and are involved in various physiological and pathophysiological processes. Polymorphisms in the genes GNB3 (encoding the Gβ3 subunit), GNAS (encoding the Gαs subunit) and GNAQ (encoding the Gαq subunit) have been the primary focus of investigation. Polymorphisms in these genes could be associated with different complex phenotypes underlining that alterations in G-protein signaling can cause multiple disorders. G proteins present a point of convergence or ‘bottleneck’ between various receptors and effectors, thus making them a sensible tool for pharmacogenetic studies. The pharmacogenetic studies performed to date mostly demonstrate an association between G-protein polymorphisms and response to therapy or occurrence of adverse drug effects. Therefore, polymorphisms in genes encoding G-protein subunits may help to individualize drug treatment in various diseases with regard to both efficacy and safety.

Poor replication of candidate genes for major depressive disorder using genome-wide association data

Data from the Genetic Association Information Network (GAIN) genome-wide association study (GWAS) in major depressive disorder (MDD) were used to explore previously reported candidate gene and single-nucleotide polymorphism (SNP) associations in MDD. A systematic literature search of candidate genes associated with MDD in case-control studies was performed before the results of the GAIN MDD study became available. Measured and imputed candidate SNPs and genes were tested in the GAIN MDD study encompassing 1738 cases and 1802 controls. Imputation was used to increase the number of SNPs from the GWAS and to improve coverage of SNPs in the candidate genes selected. Tests were carried out for individual SNPs and the entire gene using different statistical approaches, with permutation analysis as the final arbiter. In all, 78 papers reporting on 57 genes were identified, from which 92 SNPs could be mapped. In the GAIN MDD study, two SNPs were associated with MDD: C5orf20 (rs12520799; P=0.038; odds ratio (OR) AT=1.10, 95% CI 0.95-1.29; OR TT=1.21, 95% confidence interval (CI) 1.01-1.47) and NPY (rs16139; P=0.034; OR C allele=0.73, 95% CI 0.55-0.97), constituting a direct replication of previously identified SNPs. At the gene level, TNF (rs76917; OR T=1.35, 95% CI 1.13-1.63; P=0.0034) was identified as the only gene for which the association with MDD remained significant after correction for multiple testing. For SLC6A2 (norepinephrine transporter (NET)) significantly more SNPs (19 out of 100; P=0.039) than expected were associated while accounting for the linkage disequilibrium (LD) structure. Thus, we found support for involvement in MDD for only four genes. However, given the number of candidate SNPs and genes that were tested, even these significant may well be false positives. The poor replication may point to publication bias and false-positive findings in previous candidate gene studies, and may also be related to heterogeneity of the MDD phenotype as well as contextual genetic or environmental factors.

Neuropsychiatric Symptoms, Endophenotypes, and Syndromes in Late-Onset Alzheimer's Disease: Focus on APOE Gene

Neuropsychiatric symptoms, previously denominated as behavioural and psychological symptoms of dementia, are common features of Alzheimer's disease (AD) and are one of the major risk factors for institutionalization. At present, the role of the apolipoprotein E (APOE) gene in the development of neuropsychiatric symptoms in AD patients is unclear. In this paper, we summarized the findings of the studies of neuropsychiatric symptoms and neuropsychiatric syndromes/endophenotypes in AD in relation to APOE genotypes, with special attention to the possible underlying mechanisms. While some studies failed to find a significant association between APOE and neuropsychiatric symptoms in late-onset AD, other studies reported a significant association between the APOE ε4 allele and an increase in agitation/aggression, hallucinations, delusions, and late-life depression or anxiety. Furthermore, some negative studies that focused on the distribution of APOE genotypes between AD patients with or without neuropsychiatric symptoms further emphasized the importance of subgrouping neuropsychiatric symptoms in distinct neuropsychiatric syndromes. Explanations for the variable findings in the existing studies included differences in patient populations, differences in the assessment of neuropsychiatric symptomatology, and possible lack of statistical power to detect associations in the negative studies.

Prioritization and evaluation of depression candidate genes by combining multidimensional data resources

Background

Large scale and individual genetic studies have suggested numerous susceptible genes for depression in the past decade without conclusive results. There is a strong need to review and integrate multi-dimensional data for follow up validation. The present study aimed to apply prioritization procedures to build-up an evidence-based candidate genes dataset for depression.

Methods

Depression candidate genes were collected in human and animal studies across various data resources. Each gene was scored according to its magnitude of evidence related to depression and was multiplied by a source-specific weight to form a combined score measure. All genes were evaluated through a prioritization system to obtain an optimal weight matrix to rank their relative importance with depression using the combined scores. The resulting candidate gene list for depression (DEPgenes) was further evaluated by a genome-wide association (GWA) dataset and microarray gene expression in human tissues.

Results

A total of 5,055 candidate genes (4,850 genes from human and 387 genes from animal studies with 182 being overlapped) were included from seven data sources. Through the prioritization procedures, we identified 169 DEPgenes, which exhibited high chance to be associated with depression in GWA dataset (Wilcoxon rank-sum test, p = 0.00005). Additionally, the DEPgenes had a higher percentage to express in human brain or nerve related tissues than non-DEPgenes, supporting the neurotransmitter and neuroplasticity theories in depression.

Conclusions

With comprehensive data collection and curation and an application of integrative approach, we successfully generated DEPgenes through an effective gene prioritization system. The prioritized DEPgenes are promising for future biological experiments or replication efforts to discoverthe underlying molecular mechanisms for depression.

Droplets of black bile? Development of vulnerability and resilience to depression in young age

Major depressive disorder is predicted by enduring anxiety-related personality traits, in particular by neuroticism, which have genetic foundations. Neuroticism in turn is strongly related with the genetic risk for depression. Search for gene variants associated with neuroticism and depression has led to some good candidates, but the consistency of findings is very far from ideal. Adverse life events are causal to development of mood disorders, and often the vulnerability genes can be detected only when environmental impact has been objectively assessed. Yet the continuity of depression diagnosis from early childhood to adulthood is limited, while childhood depression increases odds of other affect-related disorders such as substance abuse and personality disorders. Whether specific genes have an impact seems to depend on the period of life both because of biological maturation and differences in major environmental factors, but also active engagement--or the failure to do so--of the vulnerable subjects with their environment. It is proposed that subjects with genetically determined neurotic tendencies are likely to attempt to select coping strategies that reduce events perceived as harmful and can by this means develop resilience towards affective disorders.

A translational research framework for enhanced validity of mouse models of psychopathological states in depression

Depression presents as a disorder of feelings and thoughts that debilitate daily functioning and can be life threatening. Increased understanding of these specific emotional-cognitive pathological states and their underlying pathophysiologies and neuropathologies is fundamental to an increased understanding of the disorder and, therefore, to development of much-needed improved therapies. Despite this, there is a current lack of emphasis on development and application of translational (i.e. valid) neuropsychological measures in depression research. The appropriate strategy is neuropsychological research translated, bi-directionally, between epidemiological and clinical human research and in vivo - ex vivo preclinical research conducted, primarily, with mice. This paper presents a translational framework to stimulate and inform such research, in four inter-dependent sections. (1) A depression systems-model describes the pathway between human environment-gene (E-G) epidemiology, pathophysiology, psycho- and neuropathology, symptoms, and diagnosis. This model indicates that G→emotional-cognitive endophenotypes and E-G/endophenotype→emotional-cognitive state markers are central to experimental and translational depression research. (2) Human neuropsychological tests with (potential) translational value for the quantitative study of these endophenotypes and state markers are presented. (3) The analogous rodent behavioural tests are presented and their translational validity in terms of providing analogue emotional-cognitive endophenotypes and state markers are discussed. (4) The need for aetiological validity of mouse models in terms of G→endophenotypes and E-G→state markers is presented. We conclude that the informed application of the proposed neuropsychological translational framework will yield mouse models of high face, construct and aetiological validity with respect to emotional-cognitive dysfunction in depression. These models, together with the available technological tools, can then be studied to increase understanding of depression pathophysiology and neuropathology, leading to identification and validation of novel therapeutic targets and the development of effective, personalized antidepressant treatments.

Glycosides, depression and suicidal behaviour: the role of glycoside-linked proteins

Nowadays depression and suicide are two of the most important worldwide public health problems. Although their specific molecular mechanisms are still largely unknown, glycosides can play a fundamental role in their pathogenesis. These molecules act presumably through the up-regulation of plasticity-related proteins: probably they can have a presynaptic facilitatory effect, through the activation of several intracellular signaling pathways that include molecules like protein kinase A, Rap-1, cAMP, cADPR and G proteins. These proteins take part in a myriad of brain functions such as cell survival and synaptic plasticity. In depressed suicide victims, it has been found that their activity is strongly decreased, primarily in hippocampus and prefrontal cortex. These studies suggest that glycosides can regulate neuroprotection through Rap-1 and other molecules, and may play a crucial role in the pathophysiology of depression and suicide.

Effects of two dopamine-modulating genes (DAT1 9/10 and COMT Val/Met) on n-back working memory performance in healthy volunteers

BACKGROUND

Impairments in working memory are present in many psychiatric illnesses such as attention-deficit hyperactivity disorder (ADHD) and schizophrenia. The dopamine transporter and catechol-O-methyltransferase (COMT) are proteins involved in dopamine clearance and the dopamine system is implicated in the modulation of working memory (WM) processes and neurochemical models of psychiatric diseases. The effects of functional polymorphisms of the dopamine transporter gene (DAT1) and the COMT gene were investigated using a visuospatial and numerical n-back working memory paradigm. Our n-back task was designed to reflect WM alone, and made no demands on higher executive functioning.

METHOD

A total of 291 healthy volunteers (aged 18-45 years) were genotyped and matched for age, sex, and Barratt Impulsivity Scale (BIS) and National Adult Reading Test (NART) scores. To assess individual gene effects on WM, factorial mixed model analysis of variances (ANOVAs) were conducted with the between-subjects factor as genotype and difficulty level (0-, 1-, 2- and 3-back) entered as the within-subjects factor.

RESULTS

The analysis revealed that the DAT1 or COMT genotype alone or in combination did not predict performance on the n-back task in our sample of healthy volunteers.

CONCLUSIONS

Behavioral effects of DAT1 and COMT polymorphisms on WM in healthy volunteers may be non-existent, or too subtle to identify without exceedingly large sample sizes. It is proposed that neuroimaging may provide more powerful means of elucidating the modulatory influences of these polymorphisms.

Genetics in psychiatry: are the promises met?

OBJECTIVES

Psychiatric disorders are among the most heritable common disorders, and for more than 20 years researchers have tried to unravel genetic susceptibility genes. This review briefly outlines the pros and cons of genetic approaches, important advances and possible future directions for readers not familiar with genetic studies.

METHODS

In this article the results of 20 years molecular genetics in psychiatry are shortly and critically summarized on the basis of important reviews and meta-analyses of the last decade, without describing and enumerating the different findings (see special reviews).

RESULTS

Conventional linkage and candidate association studies revealed numerous, but also inconsistent and sometimes contradictory results. The reasons are assumed to include the complexity of the disorder with interaction of several genes of small effects, lack of a valid phenotype, and invalid statistical and methodological issues. Recent systematic genome-wide association studies (GWAS) have reported association of some common variants for schizophrenia and bipolar disorder. However, the risk conferred by these variants is small and genome-wide significance is rare. Also structural variations might be important, and interesting data are arising from copy-number-variations (CNVs).

CONCLUSIONS

Although the new data from GWAS are promising, they still do not meet our initial expectations, identifying a "susceptibility gene". However, they opened new aspects concerning aetiology of psychoses, and the incorporation of new approaches, as epigenetics, or gene-environment interaction, is needed in future study designs.

Four potential criteria for deciding when to use antidepressants or psychotherapy for unipolar depression: a literature review

OBJECTIVE

To evaluate the literature supporting four potential criteria for deciding whether to use psychotherapy or pharmacology when treating depression.

METHOD

Literature review of the evidence from the last 10 years on presenting patient's demographics, aetiology, comorbidity, and genetic factors, as predictors of treatment outcome efficacy.

RESULTS

Demographic information has little support as a potential criteria for decision-making; aetiology (melancholic vs. non-melancholic) has significant support; presence of personality disorder comorbidity is unproven as a criterion but may have some value; genetic predisposition has the strongest evidence supporting it as a criteria for treatment decision-making.

CONCLUSION

Although some presenting cases will be easier to classify than others, there are substantial data supporting the screening of patients according to three of these criteria.

Monoamine transporters: vulnerable and vital doorkeepers

Transporters of dopamine, serotonin, and norepinephrine have been empirically used as medication targets for several mental illnesses in the last decades. These protein-targeted medications are effective only for subpopulations of patients with transporter-related brain disorders. Since the cDNA clonings in early 1990s, molecular studies of these transporters have revealed a wealth of information about the transporters' structure-activity relationship (SAR), neuropharmacology, cell biology, biochemistry, pharmacogenetics, and the diseases related to the human genes encoding these transporters among related regulators. Such new information creates a unique opportunity to develop transporter-specific medications based on SAR, mRNA, DNA, and perhaps transporter trafficking regulation for a number of highly relevant diseases including substance abuse, depression, schizophrenia, and Parkinson's disease.

Joining the dots: neurobiological links in a functional analysis of depression

Depression is one of the major contributors to the Total Disease Burden and afflicts about one-sixth of Western populations. One of the most effective treatments for depression focuses upon analysis of causal chains in overt behaviour, but does not include brain-related phenomena as steps along these causal pathways. Recent research findings regarding the neurobiological concomitants of depressive behaviour suggest a sequence of structural and functional alterations to the brain which may also produce a beneficial outcome for the depressed individual--that of adaptive withdrawal from uncontrollable aversive stressors. Linking these brain-based explanations to models of observable contingencies for depressive behaviour can provide a comprehensive explanation of how depressive behaviour occurs and why it persists in many patients.

Which patient will feel down, which will be happy? The need to study the genetic disposition of emotional states

PURPOSE

In quality-of-life (QL) research, the genetic susceptibility of negative and positive emotions is frequently ignored, taken for granted, or treated as noise. The objectives are to describe: (1) the major findings of studies addressing the heritable and environmental causes of variation in negative and positive emotional states and (2) the major biological pathways of and genetic variants involved in these emotional states.

METHODS

Literature overview.

RESULTS

The heritability estimates for anxiety and depression are 30-40%. Related traits as neuroticism and loneliness are also highly heritable. The hypothalamo-pituitary-adrenal axis is the 'final common pathway' for most depressive symptoms. The many findings of investigated genes are promising but not definitive. Heritability estimates of positive emotional states range between 40 and 50%. Life satisfaction and mental health share common genetic factors with optimism and self-esteem. The prefrontal cortex is a candidate brain area for positive emotional states. Biological and genetic research into positive emotional states is scarce.

CONCLUSION

Genetically informative studies may provide insights into a wide variety of complex questions that traditional QL studies cannot deliver. This insight in turn will help us to design more effective supportive programs that could moderate the outcomes of genetically based predispositions.

Overview of the genetics of major depressive disorder

Major depressive disorder (MDD) is a common psychiatric illness with high levels of morbidity and mortality. Despite intensive research during the past several decades, the neurobiological basis and pathophysiology of depressive disorders remain unknown. Genetic factors play important roles in the development of MDD, as indicated by family, twin, and adoption studies, and may reveal important information about disease mechanisms. This article describes recent developments in the field of psychiatric genetics, with a focus on MDD. Early twin studies, linkage studies, and association studies are discussed. Recent findings from genome-wide association studies are reviewed and future directions discussed. Despite all efforts, thus far, no single genetic variation has been identified to increase the risk of depression substantially. Genetic variants are expected to have only small effects on overall disease risk, and multiple genetic factors in conjunction with environmental factors are likely necessary for the development of MDD. Future large-scale studies are needed to dissect this complex phenotype and to identify pathways involved in the etiology of MDD.

Association of the 5- HTTLPR genotype and unipolar depression: a meta-analysis

BACKGROUND

We sought to ascertain the strength of evidence for association between the 5-HTTLPR polymorphism and unipolar depression.

METHOD

We applied meta-analytic techniques to data from relevant published studies, and obtained an estimate of the likely magnitude of effect of any association. We also tested for possible publication bias, and explored the impact of various study design characteristics on the magnitude of the observed effect size.

RESULTS

Meta-analysis indicated evidence of a small but statistically significant association between the 5-HTTLPR polymorphism and unipolar depression [odds ratio (OR) 1.08, 95% confidence interval (CI) 1.03-1.12]. This remained significant when data from samples of European and East Asian ancestry were analyzed separately. In all cases there was evidence of significant between-study heterogeneity, although the observed associations were robust to the application of a random-effects framework.

CONCLUSIONS

Our results support the presence of a small effect of a polymorphism in the serotonin transporter promoter on susceptibility to depression. However, we caution that it is possible that the effect has an artifactual basis, rather than a biological origin.

Antidepressant response and the serotonin transporter gene-linked polymorphic region

BACKGROUND

The serotonin transporter gene-linked polymorphic region (5-HTTLPR) has been proposed as a predictor of antidepressant response. Insertion or deletion of a 44-base pair-long region gives rise to short "S" and long "L" forms of the promoter region, the "S" form being associated with reduced serotonin transporter expression.

METHODS

A systematic review and meta-analysis was performed to clarify the effect of 5-HTTLPR on antidepressant response and remission rates. Data were obtained from 28 studies with 5408 participants. Three genotype comparisons were tested-SS versus (SL or LL), (SS or SL) versus LL, and SS versus LL.

RESULTS

There was no statistically significant effect on antidepressant response. Compared with L carriers, there was an apparent effect of the SS genotype on remission rate (relative risk: .88; 95% confidence interval: .79-.98; p = .02). However, after trim and fill correction for missing data, the effect disappeared (relative risk: .92; 95% confidence interval: .81-1.05; p = .23), indicating that the initial significant effect was likely the result of publication bias. No significant effect on remission rate was seen for SS versus LL and SS/SL versus LL. Substantial unexplained heterogeneity of effect sizes was observed between studies, pointing to additional interacting factors contributing to an association in some cases.

CONCLUSIONS

The 5-HTTLPR biallelic short/long polymorphism by itself does not seem to usefully predict antidepressant response.