Peripheral mitochondrial DNA as a neuroinflammatory biomarker for major depressive disorder

In the pathogenesis of major depressive disorder, chronic stress-related neuroinflammation hinders favorable prognosis and antidepressant response. Mitochondrial DNA may be an inflammatory trigger, after its release from stress-induced dysfunctional central nervous system mitochondria into peripheral circulation. This evidence supports the potential use of peripheral mitochondrial DNA as a neuroinflammatory biomarker for the diagnosis and treatment of major depressive disorder. Herein, we critically review the neuroinflammation theory in major depressive disorder, providing compelling evidence that mitochondrial DNA release acts as a critical biological substrate, and that it constitutes the neuroinflammatory disease pathway. After its release, mitochondrial DNA can be carried in the exosomes and transported to extracellular spaces in the central nervous system and peripheral circulation. Detectable exosomes render encaged mitochondrial DNA relatively stable. This mitochondrial DNA in peripheral circulation can thus be directly detected in clinical practice. These characteristics illustrate the potential for mitochondrial DNA to serve as an innovative clinical biomarker and molecular treatment target for major depressive disorder. This review also highlights the future potential value of clinical applications combining mitochondrial DNA with a panel of other biomarkers, to improve diagnostic precision in major depressive disorder.

Vulnerable brain regions in adolescent major depressive disorder:A resting-state functional magnetic resonance imaging activation likelihood estimation meta-analysis

BACKGROUND Adolescent major depressive disorder(MDD)is a significant mental health concern that often leads to recurrent depression in adulthood.Resting-state functional magnetic resonance imaging(rs-fMRI)offers unique insights into the neural mechanisms underlying this condition.However,despite previous research,the specific vulnerable brain regions affected in adolescent MDD patients have not been fully elucidated.AIM To identify consistent vulnerable brain regions in adolescent MDD patients using rs-fMRI and activation likelihood estimation(ALE)meta-analysis.METHODS We performed a comprehensive literature search through July 12,2023,for studies investigating brain functional changes in adolescent MDD patients.We utilized regional homogeneity(ReHo),amplitude of low-frequency fluctuations(ALFF)and fractional ALFF(fALFF)analyses.We compared the regions of aberrant spontaneous neural activity in adolescents with MDD vs healthy controls(HCs)using ALE.RESULTS Ten studies(369 adolescent MDD patients and 313 HCs)were included.Combining the ReHo and ALFF/fALFF data,the results revealed that the activity in the right cuneus and left precuneus was lower in the adolescent MDD patients than in the HCs(voxel size:648 mm3,P<0.05),and no brain region exhibited increased activity.Based on the ALFF data,we found decreased activity in the right cuneus and left precuneus in adolescent MDD patients(voxel size:736 mm3,P<0.05),with no regions exhibiting increased activity.CONCLUSION Through ALE meta-analysis,we consistently identified the right cuneus and left precuneus as vulnerable brain regions in adolescent MDD patients,increasing our understanding of the neuropathology of affected adolescents.

Meteorological factors, ambient air pollution, and daily hospital admissions for depressive disorder in Harbin: A time-series study

BACKGROUND The literature has discussed the relationship between environmental factors and depressive disorders;however,the results are inconsistent in different studies and regions,as are the interaction effects between environmental factors.We hypo-thesized that meteorological factors and ambient air pollution individually affect and interact to affect depressive disorder morbidity.AIM To investigate the effects of meteorological factors and air pollution on depressive disorders,including their lagged effects and interactions.METHODS The samples were obtained from a class 3 hospital in Harbin,China.Daily hos-pital admission data for depressive disorders from January 1,2015 to December 31,2022 were obtained.Meteorological and air pollution data were also collected during the same period.Generalized additive models with quasi-Poisson regre-ssion were used for time-series modeling to measure the non-linear and delayed effects of environmental factors.We further incorporated each pair of environ-mental factors into a bivariate response surface model to examine the interaction effects on hospital admissions for depressive disorders.RESULTS Data for 2922 d were included in the study,with no missing values.The total number of depressive admissions was 83905.Medium to high correlations existed between environmental factors.Air temperature(AT)and wind speed(WS)significantly affected the number of admissions for depression.An extremely low temperature(-29.0℃)at lag 0 caused a 53%[relative risk(RR)=1.53,95%confidence interval(CI):1.23-1.89]increase in daily hospital admissions relative to the median temperature.Extremely low WSs(0.4 m/s)at lag 7 increased the number of admissions by 58%(RR=1.58,95%CI:1.07-2.31).In contrast,atmospheric pressure and relative humidity had smaller effects.Among the six air pollutants considered in the time-series model,nitrogen dioxide(NO_(2))was the only pollutant that showed significant effects over non-cumulative,cumulative,immediate,and lagged conditions.The cumulative effect of NO_(2) at lag 7 was 0.47%(RR=1.0047,95%CI:1.0024-1.0071).Interaction effects were found between AT and the five air pollutants,atmospheric temperature and the four air pollutants,WS and sulfur dioxide.CONCLUSION Meteorological factors and the air pollutant NO_(2) affect daily hospital admissions for depressive disorders,and interactions exist between meteorological factors and ambient air pollution.

Death-associated protein kinase 1 is associated with cognitive dysfunction in major depressive disorder

We previously showed that death-associated protein kinase 1(DAPK1)expression is increased in hippocampal tissue in a mouse model of major depressive disorde and is related to cognitive dysfunction in Alzheimer's disease.In addition,depression is a risk factor for developing Alzheimer's disease,as well as an early clinical manifestation of Alzheimer's disease.Meanwhile,cognitive dysfunction is a distinctive feature of major depressive disorder.Therefore,DAPK1 may be related to cognitive dysfunction in major depressive disorder.In this study,we established a mouse model of major depressive disorder by housing mice individually and exposing them to chronic,mild,unpredictable stressors.We found that DAPK1 and tau protein levels were increased in the hippocampal CA3 area,and tau was hyperphosphorylated at Thr231,Ser262,and Ser396 in these mice.Furthermore,DAPK1 shifted from axonal expression to overexpression on the cell membrane.Exercise and treatment with the antidepressant drug citalopram decreased DAPK1 expression and tau protein phosphorylation in hippocampal tissue and improved both depressive symptoms and cognitive dysfunction.These results indicate that DAPK1 may be a potential reason and therapeutic target of cognitive dysfunction in major depressive disorder.

Major depressive disorder is correlated with the mitochondrial ND1 T3394C mutation in two Han Chinese families:Two case reports

BACKGROUND Major depressive disorder(MDD)is the most frequent reason of disabled people in the world,as reported by the World Health Organization.However,the diagnosis of MDD is mainly based on clinical symptoms.CASE SUMMARY The clinical,genetic,and molecular characteristics of two Chinese families with MDD are described in this study.There were variable ages of onset and severity in depression among the families.Both Chinese families had a very low prevalence of MDD.The mitochondrial genomes of these pedigrees were sequenced and indicated a homoplasmic T3394C(Y30H)mutation,with the polymorphism located at a highly conserved tyrosine at position 30 of ND1.The analysis also revealed unique sets of mitochondrial DNA(mtDNA)polymorphisms originating from haplogroups M9a3 and M9a.CONCLUSION This finding of the T3394C mutation in two unrelated depressed patients provides strong evidence that this mutation may have a part in the etiology of MDD.However,In these two Chinese families having the T3394C mutation,no functional mt DNA mutation was observed.Therefore,T3394C mutations are related with MDD,and the phenotypic manifestation of these mutations may be affected by changes in nuclear genes or environmental factors.

Kynurenine pathway of tryptophan metabolism in pathophysiology and therapy of major depressive disorder

Serotonin deficiency in major depressive disorder(MDD)has formed the basis of antidepressant drug development and was originally attributed to induction of the major tryptophan(Trp)-degrading enzyme,liver Trp 2,3-dioxygenase(TDO),by cortisol,leading to decreased Trp availability to the brain for serotonin synthesis.Subsequently,the serotonin deficiency was proposed to involve induction of the extrahepatic Trp-degrading enzyme indoleamine 2,3-dioxygenase(IDO)by proinflammatory cytokines,with inflammation being the underlying cause.Recent evidence,however,challenges this latter concept,as not all MDD patients are immune-activated and,when present,inflammation is mild and/or transient.A wide range of antidepressant drugs inhibit the activity of liver TDO and bind specifically to the enzyme,but not to IDO.IDO induction is not a major event in MDD,but,when it occurs,its metabolic consequences may be masked and overridden by upregulation of kynurenine monooxygenase(KMO),the gateway to production of modulators of immune and neuronal functions.KMO appears to be activated in MDD by certain proinflammatory cytokines and antidepressants with anti-inflammatory properties may block this activation.We demonstrate the ability of the antidepressant ketamine to dock(bind)to KMO.The pathophysiology of MDD may be underpinned by both the serotonin deficiency and glutamatergic activation mediated respectively by TDO induction and N-methyl-D-aspartate receptor activation.Inhibition of TDO and KMO should be the focus of MDD pharmacotherapy.

Identification and characterization of noncoding RNAs-associated competing endogenous RNA networks in major depressive disorder

BACKGROUND Major depressive disorder(MDD)is a common and serious mental illness.Many novel genes in MDD have been characterized by high-throughput methods such as microarrays or sequencing.Recently,noncoding RNAs(ncRNAs)were suggested to be involved in the complicated environmental-genetic regulatory network of MDD occurrence;however,the interplay among RNA species,including protein-coding RNAs and ncRNAs,in MDD remains unclear.AIM To investigate the RNA expression datasets downloaded from a public database and construct a network based on differentially expressed long noncoding RNA(lncRNAs),microRNAs(miRNAs),and mRNAs between MDD and controls.METHODS Gene expression data were searched in NCBI Gene Expression Omnibus using the search term“major depressive disorder.”Six array datasets from humans were related to the search term:GSE19738,GSE32280,GSE38206,GSE52790,GSE76826,and GSE81152.These datasets were processed for initial assessment and subjected to quality control and differential expression analysis.Differentially expressed lncRNAs,miRNAs,and mRNAs were determined,Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses were performed,and protein-protein interaction network was generated.The results were analyzed for their association with MDD.RESULTS After analysis,3 miRNAs,12 lncRNAs,and 33 mRNAs were identified in the competing endogenous RNA network.Two of these miRNAs were earlier shown to be involved in psychiatric disorders,and differentially expressed mRNAs were found to be highly enriched in pathways related to neurogenesis and neuroplasticity as per Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses.The expression of hub gene fatty acid 2-hydroxylase was enriched,and the encoded protein was found to be involved in myelin formation,indicating that neurological development and signal transduction are involved in MDD pathogenesis.CONCLUSION The present study presents candidate nc RNAs involved in the neurogenesis and neuroplasticity pathways related to MDD.

Intestinal flora and depressive disorders:exploration and prospect of microbial-gut-brain axis

This paper examines the correlation between depressive disorders and intestinal flora.Depression is a common affective disorder characterized by low mood,loss of interest,anhedonia,high incidence,high recurrence rate,high disability rate,and high medical costs.The incidence and harmfulness of depressive disorder are gradually increasing,and its etiology is complex and diverse,among which the abnormal intestinal flora is considered to be one of the causes of depressive disorder.This article reviews the results of several studies that found intestinal flora imbalance in depressed patients,including changes in the type and quantity of flora and changes in metabolic pathways.In addition,antibiotic and probiotic treatments have also been shown to be effective in alleviating depressive symptoms,further indicating the importance of intestinal flora disturbances in the pathogenesis of depression.We also explored the relationship between intestinal flora and the pathogenesis of depressive disorders.Through neuro-immuno-endo-crine-metabolic pathways,intestinal flora can affect the function of the central nervous system,cause changes in the host’s mental behavior,and lead to or aggravate depressive symptoms.Overall,this study not only found differences in the intestinal flora of patients with depressive disorders but also revealed the potential role of intestinal flora in the pathogenesis.Importantly,this provides a new theoretical basis for further clarifying the pathogenesis of depressive disorders and formulating diagnosis and treatment strategies.

Research progress on the effects of positive stress reduction on positive awareness and psychosocial functioning in patients with depressive disorders

To review the current research status of positive thought stress reduction therapy(PTSRT),psychosocial functioning of patients with depressive disorders,the shortcomings and outlook of the influence of PTSRT on positive thought awareness,and psychosocial functioning of patients with depressive disorders.This review has the objective to provide clinical healthcare personnel with essential information about the use of PTSRT to improve the level of positive thought and psychosocial functioning of patients with depressive disorders.

Mechanism of Zuojin Pill in the treatment of anxiety disorder and Major depressive disorder based on network pharmacology and molecular docking validation

Background:Zuojin Pill(ZJP)is a classic Chinese herbal prescription with good efficacy in the treatment of Anxiety disorder(AD)and Major depressive disorder(MDD).Nevertheless,the potential mechanisms of ZJP remain unclear.Based on network pharmacology and molecular docking methods,this study aims to elucidate the possible mechanism of ZJP in the treatment of AD and MDD.Methods:The components and targets of Rhizoma Coptidis and Fructus Evodiae were collected from TCMSP,ETCM,HERB,SWISSADME and STITCH databases.The disease targets related to MDD and AD were collected from DISGENET,GENECARDS and OMIM databases.Protein-protein interaction network was constructed by STRING database,GO and KEGG enrichment analysis was performed by METASCAPE database,and“drugs-components-targets network”was constructed by Cytoscape software.Molecular docking verification was performed by Sailvina2.0 software.Results:ZJP may act on AKT1,IL6,TNF and other targets through caffeine,isorhamnetin,berberine and other components,regulating the Inflammatory mediator regulation of TRP channels,Serotonergic synapse,Dopaminergic synapse,PI3K/AKT signaling pathway,and other pathways.The results of molecular docking showed that berberine had the best binding activity with the core target.Conclusion:ZJP can exert anti-anxiety and anti-depression effects through multiple components,multiple targets and multiple pathways.

Abnormal activation of the occipital lobes during emotion picture processing in major depressive disorder patients

A large number of studies have demonstrated that depression patients have cognitive dysfunction. With recently developed brain functional imaging, studies have focused on changes in brain function to investigate cognitive changes. However, there is still controversy regarding abnormalities in brain functions or correlation between cognitive impairment and brain function changes. Thus, it is important to design an emotion-related task for research into brain function changes. We selected positive, neutral, and negative pictures from the International Affective Picture System. Patients with major depressive disorder were asked to judge emotion pictures. In addition, functional MRI was performed to synchronously record behavior data and imaging data. Results showed that the total correct rate for recognizing pictures was lower in patients compared with normal controls. Moreover, the consistency for recognizing pictures for depressed patients was worse than normal controls, and they frequently recognized positive pictures as negative pictures. The consistency for recognizing pictures was negatively correlated with the Hamilton Depression Rating Scale. Functional MRI suggested that the activation of some areas in the frontal lobe, temporal lobe, parietal lobe, limbic lobe, and cerebellum was enhanced, but that the activation of some areas in the frontal lobe, parietal lobe and occipital lobe was weakened while the patients were watching positive and neutral pictures compared with normal controls. The activation of some areas in the frontal lobe temporal lobe, parietal lobe, and limbic lobe was enhanced, but the activation of some areas in the occipital lobe were weakened while the patients were watching the negative pictures compared with normal controls. These findings indicate that patients with major depressive disorder have negative cognitive disorder and extensive brain dysfunction. Thus, reduced activation of the occipital lobe may be an initiating factor for cognitive disorder in depressed patients.

Saffron (Crocus sativus L.) and major depressive disorder:a meta-analysis of randomized clinical trials

Due to safety concerns and side effects of many antidepressant medications, herbal psychopharmacology research has increased, and herbal remedies are becoming increasingly popular as alternatives to prescribed medications for the treatment of major depressive disorder （MDD）. Of these, accumulating trials reveal positive effects of the spice saffron （Crocus sativus L.） for the treatment of depression. A comprehensive and statistical review of the clinical trials examining the effects of saffron for treatment of MDD is warranted. OBJECTIVE： The purpose of this study was to conduct a meta-analysis of published randomized controlled trials examining the effects of saffron supplementation on symptoms of depression among participants with MDD. SEARCH STRATEGY： We conducted electronic and non-electronic searches to identify all relevant randomized, double-blind controlled trials. Reference lists of all retrieved articles were searched for relevant studies. INCLUSION CRITERIA： The criteria for study selection included the following： （1） adults （aged 18 and older） with symptoms of depression, （2） randomized controlled trial, （3） effects of saffron supplementation on depressive symptoms examined, and （4） study had either a placebo control or antidepressant comparison group. DATA EXTRACTION AND ANALYSIS： Using random effects modeling procedures, we calculated weighted mean effect sizes separately for the saffron supplementation vs placebo control groups, and for the saffron supplementation vs antidepressant groups. The methodological quality of all studies was assessed using the Jadad score. The computer software Comprehensive Meta- analysis 2 was used to analyze the data. RESULTS： Based on our pre-specified criteria, five randomized controlled trials （n = 2 placebo controlled trials, n = 3 antidepressant controlled trials） were included in our review. A large effect size was found for saffron supplementation vs placebo control in treating depressive symptoms （M ES = 1.62, P 〈 0.001）, revealing that saffron supplementation significantly reduced depression symptoms compared to the placebo control. A null effect size was evidenced between saffron supplementation and the antidepressant groups （M ES = -0.15） indicating that both treatments were similarly effective in reducing depression symptoms. The mean Jadad score was 5 indicating high quality of trials. CONCLUSION： Findings from clinical trials conducted to date indicate that saffron supplementation can improve symptoms of depression in adults with MDD. Larger clinical trials, conducted by research teams outside of Iran, with long-term follow-ups are needed before firm conclusions can be made regarding saffron＇s efficacy and safety for treating depressive symptoms.

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 Hart 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 Hart Chinese population.

Brain functional changes in facial expression recognition in patients with major depressive disorder before and after antidepressant treatment A functional magnetic resonance imaging study

Functional magnetic resonance imaging was used during emotion recognition to identify changes in functional brain activation in 21 first-episode, treatment-naive major depressive disorder patients before and after antidepressant treatment. Following escitalopram oxalate treatment, patients exhibited decreased activation in bilateral precentral gyrus, bilateral middle frontal gyrus, left middle temporal gyrus, bilateral postcentral gyrus, left cingulate and right parahippocampal gyrus, and increased activation in right superior frontal gyrus, bilateral superior parietal Iobule and left occipital gyrus during sad facial expression recognition. After antidepressant treatment, patients also exhibited decreased activation in the bilateral middle frontal gyrus, bilateral cingulate and right parahippocampal gyrus, and increased activation in the right inferior frontal gyrus, left fusiform gyrus and right precuneus during happy facial expression recognition. Our experimental findings indicate that the limbic-cortical network might be a key target region for antidepressant treatment in major depressive disorder.

Nurse-led group cognitive behavioral therapy for major depressive disorder among adults in Japan: A preliminary single-group study

Objectives:The prevalence and burden of disease of depression necessitates effective and accessible treatment options worldwide.Since April 2016,Japanese national health insurance has covered nurseadministered cognitive behavioral therapy(CBT)for mood disorders.However,empirical support for nurse-led CBT for depression in Asian countries,especially in Japan,is still lacking.This preliminary study aimed to examine the feasibility and acceptability of nurse-led group CBT for Japanese patients with depression.Methods:In this single-arm study,we evaluated the effects of a 6-week group CBT,led by trained nurses,on patients with major depression.The primary outcome was the Beck Depression Inventory-Ⅱ(BDI-Ⅱ).Assessments were conducted at the beginning and end of the intervention.Results:Of 25 participants screened,23 were eligible for the study(of these,three dropped out during the trial but were included in the analysis).Nurse-led group CBT led to significant improvements in the severity of depression(BDI-Ⅱ,P<0.001).The mean total BDI-Ⅱscore improved from 23.1(SD=7.56)to 12.4(SD=8.57),and the pre-to post-effect size was large(Cohen's d=1.33).After CBT,45%of the participants were judged to be treatment responders,and 34%met the remission criteria.Conclusions:Our preliminary findings indicate that 6 weeks of nurse-led group CBT produced a favorable treatment outcome for individuals with major depression in a Japanese clinical setting.The results of this study might encourage more Asian nurses to provide CBT as a part of their nursing practice.Further controlled trials that address the limitations of this study are required.

Predicting South Korea adolescents vulnerable to depressive disorder using Bayesian nomogram:A community-based crosssectional study

BACKGROUND Although South Korea has developed and carried out evidence-based interventions and prevention programs to prevent depressive disorder in adolescents,the number of adolescents with depressive disorder has increased every year for the past 10 years.AIM To develop a nomogram based on a naïve Bayesian algorithm by using epidemiological data on adolescents in South Korea and present baseline data for screening depressive disorder in adolescents.METHODS Epidemiological data from 2438 subjects who completed a brief symptom inventory questionnaire were used to develop a model based on a Bayesian nomogram for predicting depressive disorder in adolescents.RESULTS Physical symptoms,aggression,social withdrawal,attention,satisfaction with school life,mean sleeping hours,and conversation time with parents were influential factors on depressive disorder in adolescents.Among them,physical symptoms were the most influential.CONCLUSION Active intervention by periodically checking the emotional state of adolescents and offering individual counseling and in-depth psychological examinations when necessary are required to mitigate depressive disorder in adolescents.

No association between a polymorphism of the adenylate cyclase type IX gene and major depressive disorder in the Chinese Han population

Previous studies have demonstrated that a missense single-nucleotide polymorphism variant （2316A〉G;rs2230739）of the adenylate cyclase type IX gene was associated with bipolar disorder and affective disorder.We determined genotype and allele frequencies using a ligase detection reaction method in 315 patients with major depressive disorder and 278 unrelated, sex-matched healthy control subjects.We did not detect any statistically significant differences in genotype and allele frequencies between patients and healthy control subjects.Furthermore,we found no significant difference between genders in major depressive disorder,nor between patients and controls in the same gender.These results suggest that 2316A〉G（rs2230739）may not be a risk factor for increasing susceptibility to major depressive disorder in the Chinese Han population.

Neuronal degeneration in the hippocampus and dorsolateral prefrontal cortex in depressive disorder Correlation between ~1H-MRS and Minnesota Multiphasic Personality Inventory

Previous studies using magnetic resonance imaging（MRI）and functional MRI to study depression have primarily focused on proton magnetic resonance spectroscopy（1H-MRS）appearance in various areas of the brain and volume measurements in the limbic system.However,results have not been consistent.To the best of our knowledge,very little is known about the relationship between 1H-MRS appearance and depression inventory.In the present study,the relationship between 1H-MRS appearance in depressive patients and Minnesota Multiphasic Personality Inventory-2 scale was analyzed.MRI and 1H-MRS exhibited widened sulci and cisterns,as well as an absence of abnormal signals in depressive patients.In addition,N-acetyl aspartate/total creatine ratios in bilateral hippocampi and dorsolateral prefrontal cortex were significantly less in depressive patients than in control subjects（P 〈 0.01）.In contrast,choline-containing compounds/total creatine ratios in the dorsolateral prefrontal cortex were significantly greater in depressive patients than in control subjects（P 〈 0.01）.These ratios significantly and positively correlated with patient total depression scores as assessed using the Minnesota Multiphasic Personality Inventory-2 scale（r=0.934 7,0.878 7,P 〈 0.01）.These results suggested that 1H-MRS could be used to reveal a reduced number of neurons in the hippocampus and dorsolateral prefrontal cortex,as well as altered membrane phospholipid metabolism in the dorsolateral prefrontal cortex,in patients with depressive disorder.Abnormal mechanisms partially reflected severity of depressive disorder.

Association of serotonin transporter gene polymorphisms and major depressive disorder in Chinese Han population

BACKGROUND： Serotonin transporter （5-HTT） polymorphisms comprise 5-HTT gene-linked polymorphism region （5-HTTLPR） and variable number of tandem repeats （VNTR）. Studies have revealed an association between 5-HTT polymorphism and major depressive disorder, which suggests that the ＂S＂ allele of 5-HTTLPR and Stin2.9 of 5-HTTVNTR are associated with major depressive disorder. However, there are a number of studies that do not support the 5-HTT polymorphism effect in major depressive disorder. OBJECTIVE： To study the relationship between 5-HTT gene polymorphism and major depressive disorder in Chinese Han population. DESIGN, TIME AND SETTING： Case-controlled study of 5-HTT gene polymorphism. The experiment was performed at the Central Laboratory, Third Affiliated Hospital of Sun Yat-sen University, China from March 2005 to January 2006. PARTICIPANTS： A total of 99 depressive patients of Chinese Han nationality were recruited for this study. All patients met DSM-IV diagnostic criteria for major depressive disorder and had a total score of Hamilton Depression Scale （24 items） ≥21 points. In addition, 101 healthy subjects, matched for age and gender, served as the control group. METHODS： Venous blood was collected from all subjects. 5-HTT genotypes and alleles were determined by polymerase chain reaction. Consistent with the Hardy-Weinberg equilibrium, the association between 5-HTT gene polymorphism and major depressive disorder were analyzed by Chi-square test. MAIN OUTCOME MEASURES： 5-HTTLPR and 5-HTTVNTR genotypes and allele frequencies were measured. RESULTS： No significant differences in 5-HTTLPR genotypes and allele frequencies were determined between patients and controls （P 〉 0.05）. However, significant differences in 5-HTTVNTR genotypes and allele frequencies were detected （P 〈 0.01 ）. The Stin2.10 allele and 10/10 genotype associated with major depressive disorder （OR = 2.61,7.7, P 〈 0.05; analysis of dose-response relationships Х^2 = 12.35, P 〈 0.01）. CONCLUSION： Results from the present study revealed no association between 5-HTTLPR and major depressive disorder. However, a significant association between 5-HTTVNTR and major depressive disorder existed in a population of Chinese Han. The presence of Stin2.10 and 10/10 genotypes increased the risk for major depressive disorder in a dose-dependent manner.

Gene×environment interaction in major depressive disorder

Major depressive disorder(MDD)is a multifactorial disorder,where multiple susceptibility genes interact with environmental factors,predisposing individuals to the development of the illness.In this article,we reviewed different gene×environment interaction(G×E)studies shifting from a candidate gene to a genome-wide approach.Among environmental factors,childhood adversities and stressful life events have been suggested to exert crucial impacts on MDD.Importantly,the diathesis-stress conceptualization of G×E has been challenged by the differential susceptibility theory.Finally,we summarized several limitations of G×E studies and suggested how future G×E studies might reveal complex interactions between genes and environments in MDD.