The norepinephrine transporter gene modulates the relationship between urban/rural residency and major depressive disorder in a Chinese population

The association between polymorphism of norepinephrine transporter G1287A and major depressive disorder, antidepressant response: a meta-analysis

OBJECTIVES

Massive research has examined the cause of major depressive disorder (MDD) and accumulating evidence has revealed that the gene for the norepinephrine transporter (NET) is involved in MDDs etiology as well as the antidepressant response. The G1287A (rs5569, GRCh38, Chromosome 16, 55697923) is located in the exon 9 region of the SLC6A2 gene. It was found to be connected with MDD and antidepressant response in people of different genetic ancestries. However, the results are still inconsistent.

METHODS

A meta-analysis was conducted to evaluate the overall association of rs5569 polymorphisms with MDD and the antidepressant response.

RESULTS

Sixteen articles that studied the connection between the G1287A polymorphism and MDD or antidepressant response were identified, and their outcomes revealed there was a significant connection between the polymorphisms and MDD and antidepressant response. Our study indicated that the GG genotype may be a protection factor against the development of MDD [odds ratio (OR = 0.78, 95% confidence interval (CI) = 0.64-0.96, P = 0.02 for Asian population; OR = 0.79, 95% CI = 0.63-0.98, P = 0.03 for Han Chinese population] while the GG genotype had a worse antidepressant response (OR = 0.49, 95% CI = 0.25-0.94, P = 0.03).

CONCLUSIONS

NET G1287A polymorphisms are involved in the etiology of MDD and antidepressant response.

Association between T-182C, G1287A polymorphism in NET gene and suicidality in major depressive disorder in Chinese patients

Objective: Previous studies have implicated norepinephrine transporter gene (NET) polymorphisms in the etiology of major depressive disorder (MDD). A functional NET T-182C polymorphism (rs2242446) in the promoter region and a synonymous polymorphisms G1287A in the exon 9 (rs5569) were associated with MDD in different populations. However, few studies have focused on the relationship between these polymorphisms and MDD patients with suicidality. The objective of the present study was to examine whether the two polymorphisms are associated with MDD patients with suicidality in the Han Chinese population. Methods: Two hundred and sixty-three suicidal depressed patients and 241 non-suicidal depressed patients who met DSM-IV criteria for MDD were recruited from our hospital. Three hundred and three unrelated, age- and sex-matched healthy control subjects participated in this case-control study. Suicidality was assessed using Mini International Neuropsychiatric Interview (MINI) and the Hamilton rating scale for depression (HAMD). Genotypes of T-182C polymorphism (rs2242446) and G1287A (rs5569) were screened by polymerase chain reaction. Results: No statistical significant differences between patients and controls were found for any of the analysed polymorphisms, either in the genotype or allele distribution. Conclusions: Our results suggest that the investigated polymorphisms are not major susceptibility factors in the etiology of MDD with suicidality. However, the results must be verified in larger samples and different ethnicities.

Meta-analysis on the Association Between Norepinephrine Transporter Gene rs2242446, rs5569 Polymorphisms and Risk of Major Depressive Disorder

BACKGROUND AND AIMS

The association between norepinephrine transporter (NET) gene polymorphisms and the risk of major depressive disorder (MDD) has been investigated extensively, but with contradictory findings.

MATERIALS/METHODS

To clarify such contradiction, a comprehensive meta-analysis was conducted by searching PubMed, EMBASE, Web of Science and China Knowledge Resource Integrated Database. Odd ratios (ORs) and 95% confidence intervals (Cis) were used to evaluate the strength of the association.

RESULTS

Totally 23 case-control studies regarding rs2242446 and rs5569 polymorphisms were included. Overall analysis and subgroup analysis indicated no significant association between NET gene rs2242446 polymorphism and MDD risk. However, recessive and homozygous models revealed a significant association between NET rs5569 polymorphism and increased risk of MDD. The stratified analysis further indicated significant associations in Asians, hospital-based studies and studies with other genotyping methods.

CONCLUSIONS

In conclusion, NET gene rs5569 polymorphism could increase the risk of MDD, especially among Asians.

Relationship between G1287A of the NET Gene Polymorphisms and Brain Volume in Major Depressive Disorder: A Voxel-Based MRI Study

Background

Earlier studies implicated norepinephrine transporter (NET) gene (SLC6A2) polymorphisms in the etiology of major depressive disorder (MDD). Recently, two single nucleotide SLC6A2 polymorphisms, G1287A in exon 9 and T-182C in the promoter region, were found to be associated with MDD in different populations. We investigated the relationship between the brain volume and these two polymorphisms of the SLC6A2 in MDD patients.

Methods

We obtained 3D high-resolution T1-weighted images of 30 first-episode MDD patients and 48 age- and sex-matched healthy subjects (HS). All were divided into 4 groups based on polymorphism of either the G1287A or the T-182C genotype. VBM analysis examined the effects of diagnosis, genotype, and genotype-diagnosis interactions.

Results

Diagnosis effects on the brain morphology were found in the left superior temporal cortex. No significant genotype effects were found in the T-182C and the G1287A. A significant genotype (G1287A)–diagnosis interaction was found in the left dorsolateral prefrontal cortex. No significant genotype (T-182C)–diagnosis interaction effects were observed in any brain region.

Conclusions

In MDD patients there seems to be a relationship between the volume of the dorsolateral prefrontal cortex and polymorphism of the SLC6A2 G1287A gene.

The norepinephrine transporter gene is associated with the retardation symptoms of major depressive disorder in the Han Chinese population

The norepinephrine transporter plays an important role in the pathophysiology and pharmacological treatment of major depressive disorder. Consequently, the norepinephrine transporter gene is an attractive candidate in major depressive disorder research. In the present study, we evaluated the depression symptoms of subjects with major depressive disorder, who were all from the North of China and of Han Chinese origin, using the Hamilton Depression Scale. We examined the relationship between two single nucleotide polymorphisms in the norepinephrine transporter, rs2242446 and rs5569, and the retardation symptoms of major depressive disorder using quantitative trait testing with the UNPHASED program. rs5569 was associated with depressed mood, and the GG genotype may be a risk factor for this; rs2242446 was associated with work and interest, and the TT genotype may be a risk factor for loss of interest. Our findings suggest that rs2242446 and rs5569 in the norepinephrine transporter gene are associated with the retardation symptoms of depression in the Han Chinese population.

Gene × environment interaction studies have not properly controlled for potential confounders: the problem and the (simple) solution

Candidate gene × environment (G × E) interaction research tests the hypothesis that the effects of some environmental variable (e.g., childhood maltreatment) on some outcome measure (e.g., depression) depend on a particular genetic polymorphism. Because this research is inherently nonexperimental, investigators have been rightly concerned that detected interactions could be driven by confounders (e.g., ethnicity, gender, age, socioeconomic status) rather than by the specified genetic or environmental variables per se. In an attempt to eliminate such alternative explanations for detected G × E interactions, investigators routinely enter the potential confounders as covariates in general linear models. However, this practice does not control for the effects these variables might have on the G × E interaction. Rather, to properly control for confounders, researchers need to enter the covariate × environment and the covariate × gene interaction terms in the same model that tests the G × E term. In this manuscript, I demonstrate this point analytically and show that the practice of improperly controlling for covariates is the norm in the G × E interaction literature to date. Thus, many alternative explanations for G × E findings that investigators had thought were eliminated have not been.

Association between major depressive disorder and the norepinephrine transporter polymorphisms T-182C and G1287A: a meta-analysis

BACKGROUND

Previous studies have implicated norepinephrine transporter (NET) gene polymorphisms in the etiology of major depressive disorder (MDD). Recently, two single nucleotide NET polymorphisms, T-182C (rs2242446) in the promoter region and G1287A (rs5569) in exon 9, were found to be associated with MDD in different populations. However, inconsistent and inconclusive results have also been obtained.

METHODS

In this study, we examined whether rs2242446 and rs5569 genetic variants are related to the etiology of MDD using a meta-analysis. Relevant case-control studies were retrieved by database searching and selected according to established inclusion criteria.

RESULTS

Eight articles were identified that tested the relationship between the NET T-182C and/or G1287A polymorphism and MDD. Statistical analyses revealed no significant association between these polymorphisms and MDD (OR=1.23, 95% CI=0.77-1.97, P=0.38 for T-182C; OR=1.00, 95% CI=0.78-1.29, P=0.99 for G1287A).

LIMITATIONS

The results must be treated with caution because of the small sample sizes of several included studies.

CONCLUSIONS

Our findings suggest that the NET T-182C and G1287A polymorphisms are not susceptibility factors for MDD.

Gene environment interaction studies in depression and suicidal behavior: An update

Increasing evidence supports the involvement of both heritable and environmental risk factors in major depression (MD) and suicidal behavior (SB). Studies investigating gene-environment interaction (G × E) may be useful for elucidating the role of biological mechanisms in the risk for mental disorders. In the present paper, we review the literature regarding the interaction between genes modulating brain functions and stressful life events in the etiology of MD and SB and discuss their potential added benefit compared to genetic studies only. Within the context of G × E investigation, thus far, only a few reliable results have been obtained, although some genes have consistently shown interactive effects with environmental risk in MD and, to a lesser extent, in SB. Further investigation is required to disentangle the direct and mediated effects that are common or specific to MD and SB. Since traditional G × E studies overall suffer from important methodological limitations, further effort is required to develop novel methodological strategies with an interdisciplinary approach.

Association of galanin and major depressive disorder in the Chinese Han population

Objective

This study aimed to investigate the association of galanin (GAL) gene and the development of depression in the Chinese Han population.

Methods

A total of 700 patients with depression who met the diagnostic criteria of Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) and 673 healthy controls were used in this study. Ligase detection reactions were performed on 10 selected single nucleotide polymorphism (SNP) sites in the GAL gene. A series of statistical methods were carried out to investigate the correlation between the GAL gene SNP and the patient susceptibility to depression.

Results

The SNPs of rs694066 in the GAL gene showed a positive correlation with MDD. Compared with the healthy controls, lower frequency of G/G genotype and higher frequency of A/G genotype were observed in rs694066 in MDD patients, a lower frequency of G-allele and higher frequency of A-allele were observed in rs694066. These correlations were more pronounced in the 376 female patients and 360 female control subjects than in the 324 male patients and 313 healthy male subjects.

Conclusions

This study investigated the relationship between the GAL gene SNP and the susceptibility to depression in the Chinese Han population. The findings clearly indicate that the GAL gene polymorphism is closely correlated to the incidence of depression in the Chinese Han female patients.

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.

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.