The 5-HTTLPR s/s genotype at the serotonin transporter gene (SLC6A4) increases the risk for depression in a large cohort of primary care attendees: the PREDICT-gene study

The effect of acute tryptophan depletion on performance and the BOLD response during a Stroop task in healthy first-degree relatives of patients with unipolar depression

Previous research has shown that low central serotonin, induced by acute tryptophan depletion (ATD), results in depressed mood and impairs cognition in healthy volunteers with a predisposition for depression. It remains unknown whether ATD affects emotional processing via mood changes or directly. In the present study we investigated the interaction between vulnerability for depression and the effect of ATD on mood, cognition and the associated brain activation. In a previous functional MRI study, we tested the effect of ATD during a combined cognitive and emotional Stroop task in healthy women without a family history of depression (FH-). In this study, we present the data of an additional group of 12 healthy women with a positive family history of unipolar depression (FH+). The effect of ATD on mood and Stroop performance was different for the FH+ group as compared with the FH- group. Scores on the depression sub-scale of the Profile of Mood States (POMS) did not correlate with performance changes, but did correlate with the anterior cingulate cortex response during Stroop interference. This study showed that a family history of unipolar depression interacts with the effect of ATD.

Effect of the 5-HTTLPR polymorphism in the serotonin transporter gene on major depressive disorder and related comorbid disorders

OBJECTIVES

The serotonin transporter gene (5-HTT) has been proposed as a candidate gene for major depressive disorder (MDD). Association studies, however, have revealed inconsistent results. This could be because of the phenotypic heterogeneity of MDD, as it often presents with comorbid disorders such as generalized anxiety disorder (GAD), alcohol-related disorders, and dysthymia.

METHODS

In this exploratory study, we performed regression analyses with generalized estimating equations in patients with familial MDD (n=233) in order to explore whether a polymorphism in the serotonin transporter gene (5-HTTLPR) is differentially associated with MDD and a comorbid disorder compared with MDD without that particular comorbidity. As in general, GAD is more common in females and alcohol-related disorders are more common in males, the analyses were stratified for sex.

RESULTS

Comorbid dysthymia was less common in s-allele carriers with MDD (P<0.05) than in patients homozygous for the long allele. In the sex-specific analyses, an association between the 5-HTTLPR and comorbid alcohol use disorders was observed in females, with s-carriers reporting significantly less alcohol use disorders. The relationship with comorbid GAD differed by sex with male s-carriers reporting more comorbid GAD than female s-carriers.

CONCLUSION

The effect of the 5-HTTLPR polymorphism on MDD is co-dependent on the presence of comorbid disorders and sex. In this study, the s-allele of the 5-HTTLPR polymorphism was associated with significantly lower rates of particular lifetime comorbid disorders. Therefore, the presence of comorbid psychiatric disorders should be taken into account to clarify the association of the 5-HTTLPR polymorphism with MDD phenotypes.

High-activity variants of the uMAOA polymorphism increase the risk for depression in a large primary care sample

Studies on the association between the functional uMAOA polymorphism and depression have yielded non-conclusive results up till now. One thousand two hundred twenty eight consecutive Spanish primary care attendees, participating in the PREDICT study, agreed to take part in this genetic PREDICT-Gene study. We explored the association between depression and either high-activity uMAOA alleles or genotypes. Depression was diagnosed using the Composite International Diagnostic Interview (CIDI) to establish three different depressive outcomes (ICD-10 Depressive Episode (DE), ICD-10 Severe Depressive Episode (SDE) and DSM-IV Major Depression (MD)). uMAOA genetic variation was determined by PCR amplification and subsequent electrophoresis. Crude and adjusted (gender and/or age) odds ratios, with 95% confidence intervals, were calculated for the associations between allele or genotype frequencies and all three depressive outcomes. We found associations between all three depressive phenotypes and either high-activity alleles or high-activity genotypes in both sexes. The associations were statistically significant for females but not for males. Testing the same associations on the entire sample (males and females) also yielded significant associations between depression and either high-activity alleles or high-activity genotype distribution that were independent of age and/or gender (ICD-10 DE: OR = 1.98; 95% CI: 1.42-1.77; P = 0.00002; ICD-10-SDE: OR = 2.05; 95% CI: 1.38-3.05; P = 0.0002; DSM-IV MD: OR = 1.91; 95% CI: (1.26-2.91); P = 0.0014). Our results provide fairly consistent evidence that high-activity variants of the MAOA promoter polymorphism confer a modestly higher risk for depression.

Serotonin transporter polymorphism (5-HTTLPR) association with melancholic depression: a female specific effect?

Earlier studies yielded inconsistent results on the association between variation in the serotonin transporter (5-HTT) gene and depression, with evidence for a differential effect of the 5-HTTLPR on melancholic versus atypical depression. To further delineate the impact of 5-HTT gene variation on psychopathology in depression, in this analysis the influence of the 5-HTTLPR and the functionally closely related 5-HTT rs25531 was investigated in 340 Caucasian patients with a major depressive episode (DSM-IV) with particular attention to the subtype of depression (melancholic depression versus atypical depression) applying logistic regression models adjusted for age and gender. The homozygous, more active 5-HTTLPR LL genotype was significantly associated with melancholic depression (odds ratio, OR, 1.7; 95% confidence interval, CI, 1.1-2.6; P=0.04), with the effect originating in the female subgroup of patients (OR 1.9; 95%CI 1.0-3.4; P=0.05). Also, the more active 5-HTTLPR/5-HTT rs25531 haplotype L(A)L(A) conveyed a significant risk for melancholic depression (OR 2.0; 95%CI 1.3-3.1; P=0.001), again only in the female subsample of patients (OR 2.1; 95%CI 1.1-4.1; P=0.02). The present results provide further support for an association of genetic variation increasing serotonin transporter activity with the melancholic subtype of depression as well as evidence for a potential female-specific mechanism underlying this effect.

Molecular epidemiology of major depressive disorder

Major depressive disorder causes significant morbidity, affecting people's ability to work, function in relationships, and engage in social activities. Moreover, major depressive disorder increases the risk of suicidal ideation, attempted suicide and death by completed suicide. There is evidence that chronic stress can cause major depressive disorder. As for genetic factors, only minor susceptibility genes have been reliably identified. The serotonin system provides a logical source of susceptibility genes for depression, because this system is the target of selective serotonin reuptake-inhibitor drugs that are effective in treating depression. The 5-hydroxytryptamine (serotonin) transporter (5-HTT) has received particular attention because it is involved in the reuptake of serotonin at brain synapses. One common polymorphic variant of the 5-HTT-linked polymorphic region (5-HTTLPR), which affects the promoter of the 5-HTT gene, causes reduced uptake of the neurotransmitter serotonin into the presynaptic cells in the brain. The authors discussed the relationship between genetic polymorphisms and major depressive disorder, with special emphasis on the 5-HTTTLPR polymorphism. As the 5-HTTLPR polymorphism was significantly associated with an increased risk of major depressive disorder, the 5-HTT gene may be a candidate for a major depressive disorder susceptibility gene. As major depressive disorder is a multifactorial disease, an improved understanding of the interplay of environmental and genetic polymorphisms at multiple loci may help identify individuals who are at increased risk for major depressive disorder. Hopefully, in the future we will be able to screen for major depressive disorder susceptibility by using specific biomarkers.

Polymorphisms in Genes Encoding the Serotonin and Dopamine Pathways in Two Sisters with Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is a metabolic disease that has recently been investigated as a model for the study of psychosis. We report on two sisters with adult-type MLD who developed psychiatric symptomatology, but differed in their expression of psychotic and depressive symptoms. Association studies have indicated that polymorphisms in genes encoding the serotonin and dopamine transporters and receptors are related to the symptomatology of schizophrenia and/or depression; hence both sisters were genotyped for some of these candidate genes. The sisters shared dopamine receptor D2 (DRD2) c.1047GG (p.311Ser/Ser) and c.–141 Cins/ins polymorphisms, which are significantly associated with schizophrenia, but differed in the serotonin transporter gene-linked polymorphic region and serotonin receptor 1A (5-HT1A) c.–1019C to G polymorphisms, which may have increased the elder sister's susceptibility to depressive symptoms. Much bigger samples would be needed to gain enough statistical power to develop any hypotheses. This is the first report on genotyping MLD patients for candidate genes for psychiatric disorders, although MLD has been proposed as a model for schizophrenia.

New evidence for the association of the serotonin transporter gene (SLC6A4) haplotypes, threatening life events, and depressive phenotype

BACKGROUND

Since the first report of the significant gene-environment interaction (G x E) in depression published by Caspi et al., the literature is considerably contradictory in this field. To clarify this question, we analyzed the interaction between the serotonin transporter gene (SLC6A4) and threatening life events (TLE) on Zung Self-Rating Depression Score (ZSDS).

METHODS

Five markers tagging the whole SLC6A4 gene (5-HTTLPR and 4 single nucleotide polymorphisms: rs2020942, rs140700, rs3798908, rs1042173) were genotyped in 567 nonclinical individuals. Generalized linear models were used to analyze single marker associations, and likelihood ratio tests and score tests were used for haplotype analysis.

RESULTS

Haplotype analysis revealed a significant global effect of haplotypes on ZSDS score in high TLE subgroup (p = .008). Besides the 5-HTTLPR, rs140700 tagging the middle region of the gene had significant effects. Subjects carrying the A allele of rs140700 scored lower on ZSDS independently of 5-HTTLPR carrier status. Explained variances for depressive phenotype were 1%, 4%, and 6% when 5-HTTLPR, 5-HTTLPR x TLE and 5-HTTLPR x rs140700 x TLE were included in the model, respectively.

CONCLUSIONS

Our results demonstrate heterogeneity of individuals carrying S alleles of 5-HTTLPR in association with high TLE providing possible explanation for the inconsistency of previous studies. In addition to the promoter, the middle region of the SLC6A4 gene carries the G x G x E interaction for mood, and this new model provided a higher explained variance. We report the first evidence for the significant effects of haplotypes of the SLC6A4 gene and threatening life events on depressive phenotype.

The comparative distributions of the monoamine transporters in the rodent, monkey, and human amygdala

The monoamines in the amygdala modulate multiple aspects of emotional processing in the mammalian brain, and organic or pharmacological dysregulation of these systems can result in affective pathologies. Knowledge of the normal distribution of these neurotransmitters, therefore, is central to our understanding of both the normal processes regulated by the amygdala and the pathological conditions associated with monoaminergic dysregulation. The monoaminergic transporters have proven to be accurate and reliable markers of the distributions of their substrates. The purpose of this review was twofold: First, to briefly recount the functional relevance of dopamine, serotonin, and norepinephrine transmission in the amygdala, and second, to describe and compare the distributions of the monoamine transporters in the rodent, monkey, and human brain. The transporters were found to be heterogeneously distributed in the amygdala. The dopamine transporter (DAT) is consistently found to be extremely sparsely distributed, however the various accounts of its subregional topography are inconsistent, making any cross-species comparisons difficult. The serotonin transporter (SERT) had the greatest overall degree of labeling of the three markers, and was characterized by substantial inter-species variability in its relative distribution. The norepinephrine transporter (NET) was shown to possess an intermediate level of labeling, and like the SERT, its distribution is not consistent across the three species. The results of these comparisons indicate that caution should be exercised when using animal models to investigate the complex processes modulated by the monoamines in the amygdala, as their relative contributions to these functions may differ across species.

Meta-analyses of genetic studies on major depressive disorder

The genetic basis of major depressive disorder (MDD) has been investigated extensively, but the identification of MDD genes has been hampered by conflicting results from underpowered studies. We review all MDD case-control genetic association studies published before June 2007 and perform meta-analyses for polymorphisms that had been investigated in at least three studies. The study selection and data extraction were performed in duplicate by two independent investigators. The 183 papers that met our criteria studied 393 polymorphisms in 102 genes. Twenty-two polymorphisms (6%) were investigated in at least three studies. Seven polymorphisms had been evaluated in previous meta-analyses, 5 of these had new data available. Hence, we performed meta-analyses for 20 polymorphisms in 18 genes. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Statistically significant associations were found for the APOE varepsilon2 (OR, 0.51), GNB3 825T (OR, 1.38), MTHFR 677T (OR, 1.20), SLC6A4 44 bp Ins/Del S (OR, 1.11) alleles and the SLC6A3 40 bpVNTR 9/10 genotype (OR, 2.06). To date, there is statistically significant evidence for six MDD susceptibility genes (APOE, DRD4, GNB3, MTHFR, SLC6A3 and SLC6A4).

Predicting the onset and persistence of episodes of depression in primary health care. The predictD-Spain study: methodology

Background

The effects of putative risk factors on the onset and/or persistence of depression remain unclear. We aim to develop comprehensive models to predict the onset and persistence of episodes of depression in primary care. Here we explain the general methodology of the predictD-Spain study and evaluate the reliability of the questionnaires used.

Methods

This is a prospective cohort study. A systematic random sample of general practice attendees aged 18 to 75 has been recruited in seven Spanish provinces. Depression is being measured with the CIDI at baseline, and at 6, 12, 24 and 36 months. A set of individual, environmental, genetic, professional and organizational risk factors are to be assessed at each follow-up point. In a separate reliability study, a proportional random sample of 401 participants completed the test-retest (251 researcher-administered and 150 self-administered) between October 2005 and February 2006. We have also checked 118,398 items for data entry from a random sample of 480 patients stratified by province.

Results

All items and questionnaires had good test-retest reliability for both methods of administration, except for the use of recreational drugs over the previous six months. Cronbach's alphas were good and their factorial analyses coherent for the three scales evaluated (social support from family and friends, dissatisfaction with paid work, and dissatisfaction with unpaid work). There were 191 (0.16%) data entry errors.

Conclusion

The items and questionnaires were reliable and data quality control was excellent. When we eventually obtain our risk index for the onset and persistence of depression, we will be able to determine the individual risk of each patient evaluated in primary health care.

Polymorphism C in the serotonin transporter gene (SLC6A4) in questionable dementia and Alzheimer's disease

The promoter region of the serotonin transporter gene (SLC6A4) shows a 22-bp tandem repeat polymorphism, indicated as polymorphism C, that has been associated to depression, obsessive-compulsive disorder, memory impairment, and anxiety. Less clear are data regarding its association with Alzheimer's disease (AD). No data were reported regarding its association with questionable dementia (QD). In this study we investigate for polymorphism C in the SLC6A4 gene 302 elderly subjects with a clinical diagnosis of AD (n=105), QD (n=88) and no cognitive impairment (n=114) attending a geriatric ward. A community-dwelling sample of 390 healthy subjects was also included in the analysis. A significant higher prevalence of the C16/C16 genotype in AD than in QD was observed (37.14% vs. 3%; p=0.041, OR 2.001, 95%CI 1.018-4.024), while no differences in the C16/C14 and C14/C14 genotypes as well as in the estimated allele frequencies were found. No further differences among the three groups of subjects were found, also when they were compared with the community-dwelling sample. These findings suggest that SLC6A4 gene variation may have only a minor role, if any, in AD or QD.

Molecular genetics of monoamine transporters: relevance to brain disorders

We have demonstrated in both the human serotonin transporter gene (5HTT) and the dopamine transporter gene (DAT1) that specific polymorphic variants termed Variable Number Tandem Repeats (VNTRs), which correlate with predisposition to a number of neurological and psychiatric disorders, act as transcriptional regulatory domains. We have demonstrated that these domains can act as both tissue-specific and stimulus-inducible regulators of gene expression. As such they can act to be mechanistically associated with the progression or initiation of a behavioural disorder by altering the level of transporter mRNA, which in turn regulates the concentration of transporter in specific cells or in response to a challenge; chemical, environmental or physiological. The synergistic actions of such transcriptional domains will modulate gene expression. Our hypothesis is that these VNTR variants are one mechanism by which nurture can modify concentrations of neurotransmitters in a differential manner.

The risk for depression conferred by stressful life events is modified by variation at the serotonin transporter 5HTTLPR genotype: evidence from the Spanish PREDICT-Gene cohort

We report results from the PREDICT-Gene case-control study nested in a prospective cohort designed to identify predictors of the onset of depression among adult primary-care attendees. We tested the potential gene-by-environment interaction between 5HTTLPR genotype at the serotonin transporter gene and previous exposure to threatening life events (TLEs) in depression. A total of 737 consecutively recruited participants were genotyped. Additional information was gathered on exposure to TLEs over a 6-month period, socio-demographic data and family history of psychological problems among first-degree relatives. Diagnoses of depression were ascertained using the Composite International Diagnostic Interview (CIDI) by trained interviewers. Two different depressive outcomes were used (ICD-10 depressive episode and ICD-10 severe depressive episode). Both the s/s genotype and exposure to increasing number of TLEs were significantly associated with depression. Moreover, the 5HTTLPR s/s genotype significantly modified the risk conferred by TLEs for both depressive outcomes. Thus, s/s homozygous participants required minimal exposure to TLE (1 TLE) to acquire a level of risk for depression that was only found among l/s or l/l individuals after significantly higher exposure to TLEs (two or more TLEs). The interaction was more apparent when applied to the diagnosis of ICD-10 severe depressive episode and after adjusting for gender, age and family history of psychological problems. Likelihood ratios tests for the interaction were statistically significant for both depressive outcomes (ICD-10 depressive episode: LR X(2)=4.7, P=0.09 (crude), LR-X(2)=6.4, P=0.04 (adjusted); ICD-10 severe depressive episode: LR X(2)=6.9, P=0.032 (crude), LR-X(2)=8.1, P=0.017 (adjusted)).