Variability in the serotonin transporter gene and increased risk for major depression with melancholia

Sex-controlled differences in sertraline and citalopram efficacies in major depressive disorder: a randomized, double-blind trial

To investigate the response to antidepressants while controlling for sex, which has been controversial, 92 outpatient males and females with major depressive disorder were assigned to sertraline (100 mg/day) or citalopram (40 mg/day) in two strata and were assessed using Hamilton depression rating scale (HDRS) scores and brain-derived neurotrophic factor (BDNF), interleukin (IL)-6 and cortisol serum levels in this 8-week, randomized, parallel-group, double-blind clinical trial. Data of 40 sertraline and 40 citalopram recipients with equal representation of males and females assigned to each medication were analyzed, while their baseline characteristics were not statistically different (P > 0.05). There were no significant differences between sertraline and citalopram recipients in outcome changes (P > 0.05), all of which indicated improvement, but a significant time-treatment-sex interaction effect in BDNF levels was observed (P = 0.035). Regarding this, subgroup analyses illustrated a significantly greater increase in male BDNF levels following sertraline treatment (P = 0.020) with a moderate to large effect size (Cohen's d = 0.76 and ). Significant associations were observed between percentage changes in IL-6 levels and BDNF levels in sertraline recipients (P = 0.033) and HDRS scores in citalopram recipients (P < 0.001). Sex was an effect modifier in BDNF alterations following sertraline and citalopram administration. Further large-scale, high-quality, long-term studies are recommended.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Genetic and epigenetic architecture of Obsessive-Compulsive Disorder: In search of possible diagnostic and prognostic biomarkers

Obsessive-Compulsive Disorder (OCD) is a prevalent and severe clinical condition whose hallmarks are excessive, unwanted thoughts (obsessions) and repetitive behaviors (compulsions). The onset of symptoms generally occurs during pre-adult life and typically affects subjects in different aspects of their life's, compromising social and professional relationships. Although robust evidence suggests a genetic component in the etiopathogenesis of OCD, the causes of the disorder are still not completely understood. It is thus of relevance to take into account how genes interact with environmental risk factors, thought to be mediated by epigenetic mechanisms. We here provide an overview of genetic and epigenetic mechanisms of OCD, focusing on the modulation of key central nervous system genes, in the attempt to suggest possible disease biomarkers.

The serotonin transporter gene polymorphism (SLC6A4) and risk for psychiatric morbidity and comorbidity in the Baltimore ECA follow-up study

BACKGROUND

The human serotonin transporter (SERT) gene polymorphism (5HTTLPR) has been associated with multiple psychiatric disorders, including major depression, anxiety disorders, and substance use disorders. This study investigated the association between 5HTTLPR and psychiatric morbidity and comorbidity in a psychiatrist-examined population sample.

METHODS

628 participants, mean age 48.3 years old, were assessed by psychiatrists using the Schedules for Clinical Assessment in Neuropsychiatry. Associations between 5HTTLPR and the prevalence, comorbidity, and time-to-diagnoses for 16 psychiatric conditions were evaluated, using several analytical approaches.

RESULTS

The SERT S allele was significantly associated with an increased lifetime prevalence of panic disorder. There was a "protective" association between SERT gene S allele carrier status and the risk of obsessive-compulsive disorder (OCD) in time-to-event analysis. Carriers of the S allele had a significant increased risk of two specific comorbid disorder pairs: major depressive disorder (MDD) and social phobia, and MDD and agoraphobia. Overall, there was no increased risk of receiving an initial or an additional diagnosis for a mental disorder in the SERT S allele carriers CONCLUSIONS: The findings suggest that the S allele carrier status is associated with an increased prevalence of panic disorder in a community sample. There was an increased risk for comorbidity in a more homogeneous subgroup of cases with MDD and social phobia, as well as or agoraphobia. Our findings suggest a specific effect of the SERT promoter gene polymorphism on a subgroup of individuals identifiable by their comorbidity.

The 5-HTTLPR polymorphism impacts moral permissibility of impersonal harmful behaviors

Inspired by the roles of serotonin in an emotional aversion to harmful actions, we examined to what extent serotonin transporter gene (5-HTT)–linked polymorphic region (5-HTTLPR), a proxy for measuring serotonin function, underpinned the individual differences in moral judgment through cross-sectional analysis and two-wave comparison. The cross-sectional analysis with a larger cohort (N = 1197) showed that the SS carriers of the 5-HTTLPR polymorphism, corresponding to the low ratio of serotonin recycling from the synaptic cleft, rated impersonal harmful actions (e.g. flipping a switch to divert a train to hit one person instead of five people) as more permissible as compared with the L-allele carriers. The two-wave comparison with a subsample from the larger cohort (N = 563) indicated that the association between 5-HTTLPR polymorphism and moral permissibility of impersonal harmful actions was stable from wave 1 to wave 2. Thus, these findings highlight the importance of the 5-HTTLPR polymorphism to harmful moral behaviors.

Plastic change of prefrontal cortex mediates anxiety-like behaviors associated with chronic pain in neuropathic rats

Clinical studies show that anxiety and chronic pain are concomitant. The neural basis for the comorbidity is unclear. The prefrontal cortex (PFC) has been recognized as a critical area for affective disorders and chronic pain modulation. In this study, we examined the role of the PFC in the pathogenesis of anxiety associated with chronic pain in a rat model of neuropathic pain with spare nerve injury (SNI). The SNI rats showed apparent anxiety-like behaviors in both open field (OF) test and elevated-plus maze (EPM) test eight weeks after surgery. Thus, the number of entries to the central area in the OF decreased to 45% (±5%, n = 15) of sham control (n = 17), while the overall motor activity (i.e., total distance) was unaffected. In the EPM, the percentage of entries into the open arms significantly (p < 0.001) decreased in SNI rats (SNI: 12.58 ± 2.7%, n = 15; sham: 30.75 ± 2.82%, n = 17), so did the time spent in the open arms (SNI: 4.35 ± 1.45%, n = 15; Sham: 11.65 ± 2.18%, n = 17). To explore the neural basis for the association between anxiety and chronic pain, local field potentials (LFPs) were recorded from the medial PFC (mPFC) and ventral hippocampus. In SNI rats, there were significantly greater increases in both theta-frequency power in the mPFC and theta-frequency synchronization between the mPFC and ventral hippocampus, when animals were displaying elevated anxiety-like behaviors in avoiding anxiogenic regions in EPM and OF chamber. Western blot analyses showed a significant elevation of serotonin transporter expression in the anxious SNI rats. Inhibition of serotonin transporter effectively alleviated anxiety-like behaviors following sub-chronic (15 days) treatment with systemic citalopram (10 mg/kg/day, intraperitoneally). Moreover, the anxiety-like behaviors in the SNI rats were also suppressed by direct mPFC application of serotonin. Taken together, we conclude that the plasticity of serotonin transmission in the mPFC likely contribute to the promotion of anxiety state associated with neuropathic pain.

Associations of 5HTTLPR polymorphism with major depressive disorder and alcohol dependence: A systematic review and meta-analysis

OBJECTIVE

The neurotransmitter serotonin is understood to control mood and drug response. Carrying a genetic variant in the serotonin transporter gene (5HTT) may increase the risk of major depressive disorder and alcohol dependence. Previous estimates of the association of the S allele of 5HTTLPR polymorphism with major depressive disorder and alcohol dependence have been inconsistent.

METHODS

For the systematic review, we used PubMed MEDLINE and Discovery of The University of Melbourne to search for all relevant case-control studies investigating the associations of 5HTTLPR polymorphism with major depressive disorder and alcohol dependence. Summary odds ratios (OR) and their 95% confidence intervals (CI) were estimated. To investigate whether year of publication, study population or diagnostic criteria used were potential sources of heterogeneity, we performed meta-regression analyses. Publication bias was assessed using Funnel plots and Egger's statistical tests.

RESULTS

We included 23 studies of major depressive disorder without alcohol dependence containing 3392 cases and 5093 controls, and 11 studies of alcohol dependence without major depressive disorder containing 2079 cases and 2273 controls. The summary OR for homozygote carriers of the S allele of 5HTTLPR polymorphism compared with heterozygote and non-carriers combined (SS vs SL+LL genotype) was 1.33 (95% CI = [1.19, 1.48]) for major depressive disorder and 1.18 (95% CI = [1.01, 1.38]) for alcohol dependence. The summary OR per S allele of 5HTTLPR polymorphism was 1.16 (95% CI = [1.08, 1.23]) for major depressive disorder and 1.12 (95% CI = [1.01, 1.23]) for alcohol dependence. Meta-regression models showed that the associations did not substantially change after adjusting for year of publication, study population and diagnostic criteria used. There was no evidence for publication bias of the studies included in our meta-analysis.

CONCLUSIONS

Our meta-analysis confirms that individuals with the homozygous S allele of 5HTTLPR polymorphism are at increased risks of major depressive disorder as well as alcohol dependence. Further studies are required to investigate the association between 5HTTLPR polymorphism and the comorbidity of major depressive disorder and alcohol dependence as well as gene × environmental interactions.

Imaging genetics studies on monoaminergic genes in major depressive disorder

Although depression is the leading cause of disability worldwide, current understanding of the neurobiology of depression has failed to be translated into clinical practice. Major depressive disorder (MDD) pathogenesis is considered to be significantly influenced by multiple risk genes, however genetic effects are not simply expressed at a behavioral level. Therefore the concept of endophenotype has been applied in psychiatric genetics. Imaging genetics applies anatomical or functional imaging technologies as phenotypic assays to evaluate genetic variation and their impact on behavior. This paper attempts to provide a comprehensive review of available imaging genetics studies, including reports on genetic variants that have most frequently been linked to MDD, such as the monoaminergic genes (serotonin transporter gene, monoamine oxidase A gene, tryptophan hydroxylase-2 gene, serotonin receptor 1A gene and catechol-O-methyl transferase gene), with regard to key structures involved in emotion processing, such as the hippocampus, amygdala, anterior cingulate cortex and orbitofrontal cortex.

The risk for major depression conferred by childhood maltreatment is multiplied by BDNF and SERT genetic vulnerability: a replication study

BACKGROUND

There is limited evidence for a moderating role of both serotonin transporter (SERT) and brain-derived neurotrophic factor (BDNF) genes on the risk for major depression (MD) developing after childhood maltreatment. However, research on this topic remains inconclusive, and there is a lack of data from longitudinal studies with large and representative population samples. Our study aimed to clarify whether, in the presence of previous childhood maltreatment, individuals carrying low functional alleles for both SERT 5-HTTLPR and BDNF Val66Met polymorphisms had a higher risk for MD.

METHODS

We explored 2- and 3-way gene (SERT and BDNF) × environment (childhood maltreatment) interactions in a large sample of Spanish adults who were followed up over a 3-year period and assessed in person for both DSM-IV MD and exposure to childhood maltreatment.

RESULTS

Our study included 2679 participants. Those with both the 5-HTTLPR s allele and the BDNF Met allele showed the highest risk of MD if they had previously experienced emotional (z = 2.08, p = 0.037), sexual (z = 2.19, p = 0.029) or any kind of childhood abuse (z = 2.37, p = 0.018). These 3-way interactions remained significant regardless of whether the 5-HTTLPR triallelic or the 5-HTTLPR biallelic polymorphisms were included in the analyses.

LIMITATIONS

Retrospective assessment of childhood maltreatment may have resulted in a moderate degree of recall bias.

CONCLUSION

Our results confirm that the risk of depression conferred by childhood maltreatment is modified by variation at both SERT and BDNF genes.

STin2 VNTR polymorphism is associated with comorbid tobacco use and mood disorders

BACKGROUND

There is a significant comorbidity between mood disorders and tobacco use disorder (TUD), which may be related to both genetic and environmental factors. Gene variants of the 5-HT transporter, such as STin2 VNTR (a variable number of tandem repeats in the functional serotonin transporter intron 2) may be associated with mood disorders and TUD.

AIMS

This study aimed to delineate the association between the STin2 genetic polymorphism and comorbid TUD and mood disorders, including depression or bipolar disorder.

METHODS

We examined the STin2 VNTR polymorphism in never-smokers (n=113); patients with mood disorders without TUD (n=62); patients with TUD without mood disorders (n=90); and patients with both disorders (n=95).

RESULTS

We found a significant association between the STin2 genetic polymorphism and the above diagnostic groups whereby the STin2.12 allele shows a positive association with comorbid TUD and mood disorders (Odds ratio=3.07, 95% CI=1.41-6.68), while the STin2.10/10 homozygous genotype shows a negative association (Odds ratio=0.34, 95% CI=0.16-0.74). Adjusting for years of education, age, gender, marital status and ethnicity did not change these results, but showed that TUD was associated with lower education levels and less stable relationships, whereas mood disorders were related to female gender. A family history of TUD was significantly associated with TUD in subjects without mood disorders only.

CONCLUSIONS

The STin2.12 allele is positively and the STin2.10/10 genotype is negatively associated with comorbid TUD and mood disorders, depression or bipolar depression, suggesting that biological endophenotypes, e.g. disorders in serotonin metabolism, may in part underpin this comorbidity.

SLC6A4 polymorphisms and age of onset in late-life depression on treatment outcomes with citalopram: a Sequenced Treatment Alternatives to Relieve Depression (STAR*D) report

OBJECTIVE

Age at onset of first major depressive episode (MDE) does not necessarily translate into different treatment outcomes to antidepressants in late-life depression. The influence of genetic variants may affect this relationship.

DESIGN

Post hoc data set analysis of the association between variants in the promoter region (indel, rs25531) and within intron 2 (Stin2 VNTR) of the SCL6A4 gene and treatment outcomes among older participants in the first treatment arm of the Sequenced Treatment Alternatives to Relieve Depression trial (STAR*D).

SETTING

Participants were enrolled from 23 psychiatric and 18 primary care settings.

PARTICIPANTS

Two hundred twenty-one, white non-Hispanic subjects, aged 60 to 75 years, with 16-item Quick Inventory of Depressive Symptomatology-Clinician Rating (QIDS-CR16) initial score ≥10, and who remained in the study for at least 6 weeks, were genotyped.

INTERVENTION

Citalopram treatment for up to 14 weeks.

MEASUREMENTS

Main outcome was remission rate defined as a score of ≤5 on the QIDS-CR16. Response was a secondary outcome defined as a reduction of ≥50% of baseline QIDS-CR16.

RESULTS

Polymorphism in the indel promoter region was associated with remission among subjects whose first lifetime episode of major depression occurred later than age 55. In this group, subjects with L/L genotype had significantly higher remission (80% versus 43%) compared to those subjects with any other indel promoter genotype. Multivariate analysis demonstrated that the genetic effect of the indel promoter region on remission increases along with age at onset of MDE.

CONCLUSIONS

Variants in the indel promoter region of the SLC6A4 gene have a more robust effect to antidepressant outcome among older subjects who experienced their first MDE at a later age. The mechanism of action of these variants remains to be determined.

The potential role of monocyte chemoattractant protein-1 for major depressive disorder

The immune hypothesis of major depressive disorder (MDD) fits well with the supposed interaction between genetic and environmental factors in disorders with a complicated etiopathogenesis. It has been suggested that infectious diseases are associated with MDD in that cytokines may play a critical role as a key modulator in the transition between infection and the development of MDD. It has been also suggested that antidepressants have immunomodulatory effects on some cytokines and cytokine receptors, although the exact mechanism has not yet been fully elucidated. Among cytokines, monocyte chemoattractant protein-1 (MCP-1) is especially well known and has attracted considerable interest owing to its immunomodulatory functions. MCP-1 is expressed in highly regionalized neuronal areas in the brain, leading to kind of modulation of neuronal activity and neuroendocrine functions commonly seen in patients with MDD. Additionally, it is involved in the control of other cytokines that have been consistently proposed as associated with the development of MDD. It also has a possible role in the neurodegenerative process of a number of central nervous system (CNS) diseases. Hence, this paper draws from the perspective of immunology to offer several suggestions about the role of MPC-1 in the development of MDD.

Behavioural genetics of the serotonin transporter

The serotonin transporter is a key regulator of the bioavailability of serotonin and therefore any modulation in the expression or action of the transporter would be expected to have consequences on behaviour. The transporter has therefore become a target for pharmaceutical intervention in behavioural and mood disorders. The search for polymorphic variants in the transporter that would associate with neurological disorders has been extensive but has become focused on two domains which are both termed variable number tandem repeat (VNTR)polymorphisms. Both of these VNTRs are in non-coding DNA and therefore proposed to be mechanistically involved in a disorder through their ability to modulate transcriptional or post-transcriptional regulation of the transporter. The most extensively studied is in the promoter and is a bi-allelic insertion/deletion found in the 50 promoter region of the gene 1.2 kb upstream of the transcriptional start site. This VNTR, termed, 5-HTTLPR was initially identified as two variants containing either, 14 (short/deletion) or 16 (long/insertion) copies of a 22 bp repeat. A second widely studied VNTR found in the non-coding region of the transporter is located within intron 2 and comprises 9, 10 or 12 copies of a16–17 bp repeat termed, STin2.9, STin2.10 and STin2.12, respectively. These VNTR polymorphisms have been associated with a range of behavioural and psychiatric disorders including depression, OCD, anxiety and schizophrenia, however often the lack of reproducibility in different cohorts has led to debate on the actual association of the polymorphisms with this extensive range of neurological conditions. Here we review these two polymorphic VNTRs in depth and relate that to pharmaceutical response, their ability to regulate differential transporter expression, their core involvement in gene-environment interaction and their genetic association with specific disorders.

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.

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.

Pharmacogenetics of antidepressants

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

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.

Ethnic differences in the serotonin transporter polymorphism (5-HTTLPR) in several European populations

The serotonin transporter (5-HTT) is a protein that has a major role in divergent psychiatric disorders, personality traits and behaviors, by regulating serotonergic synaptic function. Transcriptional activity of the 5-HTT gene (5-HTT or SLC6A4) is modulated by a polymorphic repetitive element (5-HTT gene-linked polymorphic region, 5-HTTLPR), which consists of a 44-base pairs insertion-deletion in the promoter region, creating a short (S) allele and a long (L) allele. Ethnic differences in the allele frequencies of the 5-HTTLPR exist between Caucasian and Asian populations. This study investigated ethnic differences in 5-HTTLPR in 1804 healthy Caucasian subjects from several European populations living in Croatia and the Russian Federation. The genotype and allele frequency of the 5-HTTLPR differed significantly (P<0.001) between male and female Croats, Russians, Tatars and Bashkirs, due to the lower frequency of the S allele (38% and 37%) and S/S genotype (14% and 15%) in Croat men and women compared to other studied groups. When male and female data were collapsed, Russians had marginally different allele and genotype distribution compared to Bashkirs and Tatars. Bashkirs and Tatars had similar allele and genotype frequency. The higher frequency of the S/S genotype was found in Tatars and Bashkirs compared to Croats and Russians. Gender related differences occurred only in the allele distribution within Bashkir population. These ethnic differences might be responsible for the inconsistent findings in the studies of the association between various psychiatric disorders, personality traits, behaviors and 5-HTTLPR across different ethnicities, and should be controlled to enable the generalization of results across various population groups.

Association of the STin2 polymorphism of the serotonin transporter gene with a neurocognitive endophenotype in major depressive disorder

BACKGROUND

The aim of our study was to investigate the association of STin2 polymorphism and cognitive dysfunction in major depression.

METHODS

71 patients with major depression and 99 controls were genotyped for STin2. All depressive subjects and 30 controls also completed tests measuring neurocognitive performance.

RESULTS

We found a significantly higher frequency of the STin2.10/Stin2.10 homozygous genotype in the depressed group compared to controls. In the depressed group subjects with at least one copy of the 10-repeat allele showed decreased interference threshold in Stroop III compared to patients without the 10-repeat allele. Average performance of the depressed group without the 12-repeat allele was significantly weaker in the Rey Auditory Verbal Learning Test working memory and recall tasks compared to patients having at least one copy of the 12-repeat allele.

CONCLUSION

Our results suggest that the presence of STin2.10 and absence of STin2.12 allele may be related to a possible genetic endophenotype for characteristic cognitive dysfunctions detected in MDD.

Serotonin transporter gene polymorphisms and sertraline response in major depression patients

Major depression (MD) has a complex multifactorial etiology with genetic and environmental factors contributing to the disorder. As with all antidepressant treatments, there is variability in drug response due to heredity, generally focusing on genetic polymorphism of the drug-metabolizing transporter genes. The serotonin transporter (5-HTT) gene is a particularly important candidate for genetic involvement in MD disorders owing to its key role in the regulation of serotonergic transmission and is therefore considered to be an interesting candidate in the mechanism of antidepressant drugs. In this study, we have focused on the associations between genetic polymorphisms in two regions of the 5-HTT gene (5-HTTLPR and VNTR) related to sertraline responses. Our sample consisted of 64 unrelated Turkish subjects who strictly met DSM-IV and CGI scores. There was no significant difference between the frequency of the SS, LS, LL, 9/10, 10/10, 9/12, 10/12, and 12/12 genotypes and responses to sertraline. However, the number of patients can be increased and different drugs can be studied in order to find a specific pharmacogenetic relation.

The serotonin transporter gene and personality: association of the 5-HTTLPR s allele, anxiety, depression and affective temperaments

Az 5-HTTLPR-polimorfizmus kiemelt szerepet játszik a hangulatzavarok és a neuroticismus hátterében. Vizsgálatunk célja az 5-HTTLPR és a neuroticismus komponensei közül a szorongásra és a depresszióra való hajlam és az affektív labilitás összefüggésének vizsgálata volt pszichiátriailag egészséges populációban. A vizsgálat résztvevői a Spielberger-féle vonás- és állapotszorongás kérdőívet (STAI), a Zung-féle önértékelő depresszióskálát (ZSDS), valamint a TEMPS-A kérdőívet töltötték ki. Az 5-HTTLPR genotípust PCR segítségével határoztuk meg. A pontszámokat a különböző csoportokban ANOVA segítségével hasonlítottuk össze. Az s allélt hordozók szignifikánsan magasabb pontszámot kaptak a ZSDS és a STAI állapotszorongás-skálán, valamint a depresszív komponenst hordozó affektívtemperamentum-skálákon is. Eredményeink szerint a neuroticismus komponensei önállóan is összefüggést mutatnak az 5-HTTLPR-polimorfizmussal, ami a vonás egységességét támasztja alá. Eredményeink rámutatnak további kutatások szükségességére az egészséges populációban megfigyelhető vonások genetikai hátterének feltárásával kapcsolatban, mivel ezek a neuropszichiátriai betegségek endofenotípusaiként a jövőbeli kutatások alapvető építőkövei lehetnek.

Serotonin transporter gene polymorphisms: effect on serotonin transporter availability in the brain of suicide attempters

The efficacy of serotonin reuptake inhibitors in depression and anxiety disorders suggests the gene coding for the serotonin transporter (5-HTT), SLC6A4, as a candidate of importance for these conditions. Positive findings regarding associations between polymorphisms in SLC6A4 have been reported, indicating that these polymorphisms may influence anxiety-related personality traits, as well as the risk of developing depression and suicidality. Serotonin 5-HTT availability was assessed with single photon emission computed tomography (SPECT), using (123)I-beta-CIT as ligand, in a population of unmedicated male suicide attempters (n=9) and in matched controls (n=9). Two polymorphisms in SLC6A4 were assessed, including the 5-HTTLPR located in the promoter region and a variable number of tandem repeats (VNTR) polymorphism in intron 2 (STin2). In suicide attempters, but not in controls, low 5-HTT availability was associated with the S allele of 5-HTTLPR and with the 12 repeat allele of STin2. Data suggest that polymorphisms in SLC6A4 may influence the expression of the brain serotonin transporter in suicide attempters.

Common genetic and environmental influences on major depressive disorder and conduct disorder

The evidence for common genetic and environmental influences on conduct disorder (CD) and major depressive disorder (MDD) in adolescents was examined. A sample of 570 monozygotic twin pairs, 592 dizygotic twin pairs, and 426 non-twin siblings, aged 12-18 years, was recruited from the Colorado Twin Registry. For the past year data, there was a significant correlation between the genetic influences on MDD and CD and, for the lifetime data, there was a significant correlation between the genetic influences on MDD and CD, and a significant correlation between the nonshared environmental influences on MDD and CD. Our results suggest that some genetic factors will increase an individual's vulnerability to both MDD and CD in adolescence.

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.

Definition of phenotype

Definition of the phenotype is crucial in designing any genetic study, especially an association study, intended to detect the disease predisposing genes. In this chapter, we review the different types of phenotypes such as discrete or continuous and discuss the issues impacting on the phenotype definition related to study design, specifically, the impact of diagnostic error (misclassification) in case-control studies and measurement error in continuous traits. We show that the power of a study depends heavily on the phenotype measured and that misclassification or measurement error can dramatically reduce the power. We also suggest some possible responses to these challenges.

Serotonin transporter gene polymorphism and treatment response to serotonin reuptake inhibitor (escitalopram) in depression: An open pilot study

BACKGROUND

Blocking of the serotonin transporter is the main mechanism of action of SSRIs; therefore, the gene encoding this protein is a strong candidate for a possible genetic influence on the treatment response.

AIM

To evaluate relationship between serotonin transporter gene promoter region polymorphism and the efficacy of SSRI (escitalopram) treatment in depression.

MATERIALS AND METHODS

Fifty-seven consecutive patients with unipolar depressive episode (DSM IV criteria) were genotyped for the SERT gene polymorphism and treated with escitalopram 20 mg/day. Weekly assessment (HAM-D-21) was made for treatment response up to 6 weeks.

RESULTS

Significant (P > 0.0001) difference between groups (ll vs. ss or ls) in response to treatment by escitalopram was revealed by our study. However, no difference with respect to age, gender, or onset of illness was observed between genotype subgroups.

CONCLUSION

The study suggests that serotonin transporter gene polymorphism may have an influence on the effectiveness of SSRI treatment in depressive disorders, irrespective of clinical variables. Further controlled studies are required to validate these results.

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)).

The functional impact of SLC6 transporter genetic variation

Solute carrier 6 (SLC6) is a gene family of ion-coupled plasma membrane cotransporters, including transporters of neurotransmitters, amino acids, and osmolytes that mediate the movement of their substrates into cells to facilitate or regulate synaptic transmission, neurotransmitter recycling, metabolic function, and fluid homeostasis. Polymorphisms in transporter genes may influence expression and activity of transporters and contribute to behavior, traits, and disease. Determining the relationship between the monoamine transporters and complex psychiatric disorders has been a particular challenge that is being met by evolving approaches. Elucidating the functional consequences of and interactions among polymorphic sites is advancing our understanding of this relationship. Examining the influence of environmental influences, especially early-life events, has helped bridge the gap between genotype and phenotype. Refining phenotypes, through assessment of endophenotypes, specific behavioral tasks, medication response, and brain network properties has also improved detection of the impact of genetic variation on complex behavior and disease.

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

Previous reports and meta-analyses have yielded inconclusive results as to whether the s/s genotype at the 5-HTTLPR serotonin transporter polymorphism confers increased risk for depression. We tested the association between s/s genotype and depression in a large cohort (n = 737) of Spanish primary care consecutive attendees participating in a European study on predictors for depression in primary care (PREDICT study). Participants were administered the Composite International Diagnostic Interview (CIDI) depression subscale allowing diagnoses using ICD-10 criteria for depressive episodes. Participants were genotyped to establish 5HTTLPR genotype. Both univariable and multivariable associations between the s/s genotype and depression were tested twice using two different depressive outcomes (ICD-10 depressive episode and ICD-10 severe depressive episode). We found an association between the s/s genotype and both depressive outcomes that was independent of age, sex, family history of psychological problems among first degree relatives and presence of comorbid generalized anxiety disorder. When comparing s/s homozygous versus the rest, the adjusted odds ratio for any ICD-10 depressive episode and for severe ICD-10 depressive episode were 1.50 (95% CI: 1.0-2.2; P = 0.045) and 1.79 (95% CI: 1.1-2.8; P = 0.016), respectively. The association was significantly stronger with increasing severity of depression (chi2 for linear association=6.1; P = 0.013) suggesting a dose-dependent relationship. Our results are consistent with previous reports suggesting a small but independent effect by the s/s 5-HTTLPR genotype increasing the risk for depression.

Male Reproductive Timing in Rhesus Macaques Is Influenced by the 5HTTLPR Promoter Polymorphism of the Serotonin Transporter Gene1

The 5HTTLPR polymorphism in the promoter region of the human serotonin transporter (SLC6A4) gene is known to be associated with various stress-related psychological and psychiatric phenomena. We observed that a similar diallelic polymorphism in the orthologous gene of rhesus macaques (Macaca mulatta) was related to the reproductive life history of 580 males residing in the free-ranging colony of Cayo Santiago, Puerto Rico, between 1985 and 1998. At first glance, the polymorphism appeared to be selectively neutral because no difference in total reproductive output was noted between males of different 5HTTLPR genotypes. However, whereas heterozygotes were significantly more reproductive than homozygotes at intermediate age (10-13 yr), the opposite held true before and after this period (n = 682 offspring; randomization P = 0.014). This association, which explains approximately 7% of the observed variation in sire age, most likely reflects different natal dispersal patterns and represents the first reported instance of a genetic influence on reproductive timing in mammals.

Early-Life Blockade of the 5-HT Transporter Alters Emotional Behavior in Adult Mice

Reduced serotonin transporter (5-HTT) expression is associated with abnormal affective and anxiety-like symptoms in humans and rodents, but the mechanism of this effect is unknown. Transient inhibition of 5-HTT during early development with fluoxetine, a commonly used serotonin selective reuptake inhibitor, produced abnormal emotional behaviors in adult mice. This effect mimicked the behavioral phenotype of mice genetically deficient in 5-HTT expression. These findings indicate a critical role of serotonin in the maturation of brain systems that modulate emotional function in the adult and suggest a developmental mechanism to explain how low-expressing 5-HTT promoter alleles increase vulnerability to psychiatric disorders.

A case-control and family-based association study of the 5-HTTLPR in pediatric-onset depressive disorders

BACKGROUND

Pediatric depression can be particularly informative for clarification of the causes of mood disorders. The aim of this work was to explore the possible association between childhood- and early-adolescent-onset DSM-IV depressive disorders (DD; including major depression and dysthymia) and the serotonin transporter-linked promoter polymorphism (5-HTTLPR) locus.

METHODS

The case-control sample consisted of 68 unrelated patients with DD, and 68 unrelated age- and gender-matched healthy control subjects. The same patients were included in the family-based study, which consisted of 41 triads and 11 dyads.

RESULTS

An excess of the SS-genotype (p =.025) and of the S-allele (p =.021) was found among DD children (odds ratio = 1.81; 95% confidence interval = 1.12-2.94). The family-based results suggested that the S-allele was preferentially transmitted to depressed children (haplotype-based haplotype relative risk: chi(2) = 7.231 df = 1, p =.007; transmission disequilibrium test: chi(2) = 5.233, df = 1, p =.022).

CONCLUSIONS

A role for the 5-HTTLPR locus that needs replication in larger samples is suggested in childhood DD.

Alleles of a functional serotonin transporter promoter polymorphism are associated with major depression in alcoholics

BACKGROUND

Serotonergic neurotransmission has been implicated in the pathogenesis of both alcohol dependence and mood disorders and may therefore be important in understanding the pathophysiology of comorbid alcohol dependence and major depression. Studies of the association of these disorders with a functional polymorphism in the promoter region of the gene encoding the serotonin transporter protein (locus SLC6A4) have yielded inconsistent results. Because the convergence of these disorders may provide a refined phenotype, we examined the association of serotonin (5-HT) transporter linked polymorphic region (5-HTTLPR) alleles to comorbid alcohol dependence and major depression.

METHODS

A sample of 296 European American and 16 African American patients with comorbid alcohol dependence and major depression was recruited from treatment studies. The control group included 260 European Americans and 43 African Americans; all were screened to exclude the presence of a mood or substance use disorder. DNA isolated from whole blood was polymerase chain reaction-amplified, and genotypes were assigned on the basis of agarose gel size fractionation.

RESULTS

The frequency of the short allele in the patient group was in the range of those previously reported for samples with unipolar depression but was significantly more common than among controls (short allele frequency of cases, 45.8%; controls, 39.8%; chi(2)(1) = 4.02; p = 0.045).

CONCLUSIONS

With respect to the frequency of the short allele at the SLC6A4 locus (5-HTTLPR), major depression in alcoholics is similar to major depression in nonalcoholics. Further efforts to characterize depressed alcoholics and to examine genetic predictors of response to antidepressant treatment seem warranted.

Serotonin transporter polymorphism and depressive-related symptoms in schizophrenia

A role for the serotonin transporter (5-HTT) gene polymorphism in mental illnesses and anxiety-traits has been implicated. The contribution of genetic factors in personality traits and the manifestation of specific symptoms in psychiatric illnesses have yet to be elucidated. Anxious-depressive symptoms are a significant component in a pattern of schizophrenic symptoms. This study focused on the relation between 5-HTT polymorphism and clinical presentations of schizophrenia, specifically those related to the affective spectrum. Using clinical and psychological analyses, we tested the genetic association between the 5-HTTLPR polymorphism (5-HTT gene-linked polymorphic region) and anxiety- and depressive-related symptoms emerged in schizophrenia. In 260 patients with an ICD-10 diagnosis of schizophrenia (broad definition), we studied the 5-HTTLPR genotype (insertion-deletion polymorphism), the Positive and Negative Syndrome Scale (PANSS), and self-rated inventories (EPI, MMPI, STAI) scores. Patients with the "ss" genotype (deletion variant) scored significantly higher on "Guilt feelings" and "Depression" items, as compared with those of the "ll" genotype (insertion variant) (P = 0.016, 0.039, respectively). The frequency of the "ss" genotype was reduced in patients with no depression or guilt feelings, or in those patients exhibiting questionable symptoms. In contrast, the "ss" genotype carriers prevailed among the patients with mild, moderate, or severe ratings of the symptoms. The scores on all anxiety- and depression-related traits, self-rated by the patients, did not significantly differ by genotype. Our finding may contribute to understanding of molecular genetic features underlying an appearance of psychopathological symptoms emerged in schizophrenia.

An overview of the genetics of psychotic mood disorders

This article presents a conceptual review of the genetic underpinnings of psychotic mood disorders. Both unipolar and bipolar forms of mood disorder sometimes feature psychotic symptoms. Some evidence from epidemiological research suggests that psychotic forms of mood disorder specifically might be heritable. Linkage studies of mood disorders in general have also provided some support for that notion, as have associated studies involving serotonin and dopamine genes and psychotic mood disorder. Some research suggests there might be a genetic connection between schizophrenia and bipolar disorder, undermining the Kraepelinian dichotomous classification of the psychoses. Future research should continue to examine psychotic forms of mood disorder using both epidemiological and molecular approaches.

Polymorphisms within the promoter and the intron 2 of the serotonin transporter gene in a population of bulimic patients

The serotonin transporter (5-HTT) gene is a firm candidate to explain eating disorders. In this association study, two different polymorphisms were analysed: a variable number of tandem repeat (VNTR) polymorphism in intron 2 and a deletion/insertion polymorphism (5-HTTLPR) in the promoter region. The hypothesis that these gene polymorphisms may be a susceptibility factor in bulimia nervosa (BN) was explored in a female population of 102 purgative bulimics. BN patients who have suffered preceding anorexia nervosa (AN) episodes formed the so-called previous AN bulimic patient group. In our sample of normal-eater controls and purging type bulimics, regardless of whether or not the BN patients had suffered prior AN episodes, no differences were found considering the frequencies of genotypes, alleles or haplotypes of both polymorphic regions of the 5-HTT gene.

Altered depression-related behaviors and functional changes in the dorsal raphe nucleus of serotonin transporter-deficient mice

BACKGROUND

As a key regulator of serotonergic activity and target of many antidepressant treatments, the serotonin transporter (SERT) represents a potential mediator of anxiety- and depression-related behaviors. Using mice lacking the SERT (SERT KO), we examined the role of SERT function in anxiety- and depression-related behaviors and serotonergic neuron function.

METHODS

Serotonin transporter knockout mice were evaluated in paradigms designed to assess anxiety-, depression-, and stress-related behaviors. Dorsal raphe nucleus (DRN) function was assessed by quantitative serotonergic cell counting and extracellular electrical recording of neuronal firing properties.

RESULTS

Serotonin transporter knockout mice showed an increase in latency to feed in a novel situation, more immobility in a forced swim, increased escape latency in a shock escape paradigm, and decreased immobility in tail suspension. No differences in anxiety-related behaviors were seen in the open field and the elevated plus maze. Serotonin transporter knockout mice exhibit a 50% reduction in serotonergic cell number and a fourfold decrease in firing rate in the DRN.

CONCLUSIONS

Developmental loss of SERT produces altered behaviors in models of depression that are generally opposite to those produced by antidepressant treatment. The reduced serotonergic cell number and firing rate in the DRN of adult SERT KO mice suggest a mechanism for these altered behaviors.

Association of the serotonin transporter gene with sudden infant death syndrome: a haplotype analysis

Serotonergic receptor binding in the arcuate nucleus, n. raphé obscurus, and other medullary regions is decreased in sudden infant death syndrome (SIDS) cases. Further, an insertion/deletion polymorphism in the promoter region of the serotonin transporter protein (5-HTT) gene has recently been associated with risk of SIDS. This polymorphism differentially regulates 5-HTT expression, with the long allele (L), the SIDS-associated allele, being a more effective promoter than the short allele (S). To further elucidate the role of the 5-HTT gene in SIDS, we investigated the 5-HTT intron 2 polymorphism, which also differentially regulates 5-HTT expression with the 12 repeat allele being the more effective promoter. In a cohort of 90 SIDS cases (44 African-American and 46 Caucasian) and gender/ethnicity-matched controls, significant positive associations were found between SIDS and the intron 2 genotype distribution (P-value = 0.041) among African-American SIDS vs. African-American controls, specifically with the 12/12 genotype (P-value = 0.03), and with the 12 repeat allele (P-value=0.018). The frequency of the 12/12 genotype and 12-repeat allele was significantly different (P < 0.001) between the African-American and Caucasian SIDS cases. Furthermore, the promoter and intron 2 loci were in significant linkage disequilibrium, and the L-12 haplotype was significantly associated with SIDS in the African-American (P = 0.002) but not Caucasian (P = 0.117) subgroups. These results indicate a relationship between SIDS and the 12-repeat allele of the intron 2 variable number tandem repeat of the 5-HTT gene in African-Americans, and a significant role of the haplotype containing the 12-repeat allele and the promoter L-allele in defining SIDS risk in African-Americans. These data, if confirmed in larger studies, may begin to explain the differences in SIDS incidence by ethnicity, suggest a role for levels of 5-HTT expression in generation of SIDS susceptibility, and provide an important tool for identifying at-risk individuals and estimating the risk of recurrence.

Sibling-based association analyses of the serotonin transporter polymorphism and internalizing behavior problems in children

BACKGROUND

Childhood internalizing problems are often precursors in the development of more serious psychiatric syndromes including anxiety and depressive disorders. Twin studies of the etiology of these disorders suggest that the genetic risk factors underlying anxiety and depression are highly correlated. However, the specific genetic mechanisms responsible for this risk have not yet been identified.

METHODS

We examined the association between childhood internalizing problems and a functional polymorphism in the serotonin transporter gene (5-HTTLPR) in 711 children participating in a longitudinal twin study of behavioral and emotional development. Internalizing problems were measured at ages 4, 7, 9, 10, 11 and 12 years using the Child Behavior Checklist (CBCL) parent report form. We applied a sibling-based methodology for estimating allelic association with quantitative traits, while controlling for population stratification.

RESULTS

No associations were found for CBCL Internalizing problems at any age, including the subscales for Somatic Complaints, Withdrawn and Anxiety/Depression.

CONCLUSIONS

Thus, although our results did not support the hypothesis that the 5-HTTLPR contributes to a dimensional expression of internalizing behavior problems, this does not rule out the possibility that it is an interesting polymorphism to pursue in the search for genetic risk factors related to major depressive and/or anxiety disorders.

Serotonin transporter gene functional polymorphism: a plausible candidate gene for increased vascular risk in depression

The evidence of increased vascular morbidity and mortality associated with depression has generated research interest in studying the mechanisms or causal pathways underlying this association. Recent advances in molecular genetics have demonstrated that serotonin transporter gene functional polymorphism may confer susceptibility for affective disorder as well as for some cardiovascular risk factors. Taking into account these genetic findings, this article proposes a hypothesis that serotonin transporter gene functional polymorphism may be a plausible candidate gene to study the genetic mechanisms of depression-related increased vascular morbidity and mortality. Future research projects to test this hypothesis is warranted.

Le test de déplétion en tryptophane : aspects méthodologiques et pratiques

INTRODUCTION

This paper focuses on the methodology and behavioural results of the tryptophan depletion challenge.

METHODS

A Medline search (1985-2002) using the keywords 'tryptophan depletion' and 'mood' has been performed.

RESULTS

Rapid depletion is obtained by morning intake under fasting condition of a tryptophan-free amino-acid mixture. Subjects with a family history of mood disorders and depressed patients receiving serotoninergic drugs demonstrate a mood-lowering effect. However, these effects are limited or absent in normal volunteers and naive depressed patients.

CONCLUSION

The tryptophan depletion challenge has largely contributed to the understanding of the physiopathology of depression. However, the mood response to acute tryptophan depletion challenge in healthy volunteers is not as sensitive as a 'depression model'.

A systematic review of association studies investigating genes coding for serotonin receptors and the serotonin transporter: I. Affective disorders

The different 5-HT (serotonin) receptors including the serotonin transporter (5-HTT) are candidate genes for affective disorders such as major depressive disorder (MDD) and bipolar disorder (BD). They have been investigated in a number of allelic association studies where the individual results have been inconsistent, and therefore, definite conclusions are difficult to make. Systematic reviews using meta-analytical techniques are a reliable method for objectively and reproducibly assessing individual studies and generating combined result. This study aimed at reviewing published studies investigating the association between affective disorders (MDD and BD) and variation at genes coding for serotonin receptors and the serotonin transporter. We performed National Library of Medicine database searches to identify potential studies. More than 430 articles were reviewed and 86 studies met the inclusion criteria for participation in our review. Of these, 41 studies investigated 45 different 5-HT receptor variants and 45 studies investigated at least one of two commonly studied 5-HTT polymorphisms in MDD. Many studies investigated the association between MDD and BD with the 5-HT2A 102 T/C, the 5-HTT promoter 44 bp insertion/deletion and the intron 2 VNTR polymorphisms, and thus, these could be pooled using meta-analytic techniques. The overall odds ratio (OR) for the combined individual results was significant for BD and the two 5-HTT polymorphisms: Mantel-Haenszel weighted OR=1.14, CI: 1.03-1.26, P=0.015 for the promoter locus (N=3467) and Mantel-Haenszel Weighted odds ratio OR=1.18, CI: 1.05-1.32, P=0.004 for the VNTR locus (N=3620). However, sensitivity analysis indicated that, in each case, the overall positive association could be mostly attributed to the large effect of one individual study. Therefore, these results suggest that, although promising, further studies are required to assess appropriately the evidence suggesting an association between BD and 5-HTT.

Monoamine transporter gene structure and polymorphisms in relation to psychiatric and other complex disorders

The norepinephrine, dopamine and serotonin transporters (NET, DAT and SERT, respectively), limit cellular signaling by recapturing released neurotransmitter, and serve as targets for antidepressants and drugs of abuse, emphasizing the integral role these molecules play in neurotransmission and pathology. This has compelled researchers to search for polymorphisms in monoamine (MA) transporter genes. Studies support linkage and association of MA transporter genetic variation in psychiatric and other complex disorders. Understanding the contribution of MA transporter polymorphisms to human behavior, disease susceptibility and response to pharmacotherapies will involve further progress in linkage and association that will be aided by both definition of highly selective phenotypes and utilization of a large number of polymorphic markers. The relationship of polymorphisms to alterations in transport capacity, likely a complex interaction, involving genetic background, disease state, and medication, will elucidate the means by which MA transporter genetic variability contributes to our individuality.

The serotonin transporter intronic VNTR enhancer correlated with a predisposition to affective disorders has distinct regulatory elements within the domain based on the primary DNA sequence of the repeat unit

We have demonstrated that a variable number tandem repeat domain (VNTR) within intron 2 of the serotonin transporter gene is a transcriptional regulatory domain which is potentially correlated with a predisposition to affective disorders and other behavioural conditions. This correlation based on copy number of the VNTR alone (nine, 10 or 12 copies of 16/17 base-pair element) has been controversial and not reproduced in all studies. We demonstrate that individual repeat elements within the VNTR domain differ in their enhancer activity in an embryonic stem cell model. This has implications for both the mechanism by which these VNTRs are correlated with the progression of the disease and suggests that clinical analysis should now be extended to correlate sequence variation within the VNTR with the disorder. The latter may resolve some of the conflicting data published to date.

Serotonin transporter gene polymorphism in irritable bowel syndrome

OBJECTIVES

Serotonin is a key mediator of intestinal peristalsis, and after it is secreted, it is effectively cleansed from the neuronal gap by means of a high affinity substance called serotonin transporter (SERT), which depends on the Na+ and Cl- ions localized in the presynaptic neuronal membranes. The aim of this study was to investigate SERT polymorphism in patients with irritable bowel syndrome (IBS).

METHODS

SERT gene polymorphism was assessed by polymerase chain reaction on DNA chains obtained from leukocytes in serum samples from 54 patients diagnosed with IBS and 91 healthy subjects. The polymorphism of two regions (variable number tandem repeats and the SERT gene-linked polymorphic region [5-HTTLPR]) of SERT was assessed.

RESULTS

SERT polymorphisms were found to be similar in healthy subjects and IBS patients (p > 0.05). IBS patients were divided into three groups: diarrhea predominant (n = 18), constipation predominant (n = 26), and alternating diarrhea and constipation (n = 10). These groups were compared with respect to gene polymorphism, and it was found that the 5-HTTLPR allele S/S genotype occurred with greater frequency in the constipation predominant group than in the other two subgroups (p < 0.05), and L/S genotype frequency in the diarrhea predominant group was higher than those in the constipation and control groups.

CONCLUSIONS

No relationship was found between IBS and SERT gene polymorphism. It is conceivable that the presence of the S/S genotype in IBS patients carries an increased risk of the constipation predominant type of IBS, whereas the presence of the 5-HTTLPR allele L/S genotype carries an increased risk of the diarrhea predominant type.

Possible association of temporomandibular joint pain and dysfunction with a polymorphism in the serotonin transporter gene

The purpose of this study was to evaluate the relationship between temporomandibular joint pain and dysfunction and serotonin transporter (5-HTT) gene polymorphism. Forty-eight patients with temporomandibular joint pain and 111 healthy control subjects were examined. The results for the patients and control subjects were not significantly different (P >.05). The analysis of genotype distribution (homozygous for STin 2.10 genotypes of the variable-number tandem-repeat polymorphism) showed significant differences between the patients and control subjects (P =.003). ST 2.10 allele was more frequent in the patients with temporomandibular joint pain and dysfunction. In the control group, however, STin 2.12/12 genotype was significantly higher (P =.017). In the patients who were homozygous or heterozygous for variable-number tandem-repeat variants of 5-HTT STin 2.12 copies, the average scores of somatization and anger were significantly higher than those who were homozygous for STin 2.10 variant (P <.05). The patients who were homozygous for STin 2.10 genotype were also homozygous for "L" genotype (P =.019). However, this was not the condition in the control subjects. This study does not provide evidence to support the involvement of 5-HTT gene-linked polymorphic region in temporomandibular joint pain and dysfunction. Our findings indicated that only the presence of the homozygous STin 2.10 genotype of variable-number tandem-repeat is likely to play a substantial role in the genetic predisposition to temporomandibular joint pain and dysfunction and that the STin 2.12/12 genotype may have a protective role against temporomandibular joint pain and dysfunction.

Rearrangements of minisatellites in the human telomerase reverse transcriptase gene are not correlated with its expression in colon carcinomas

Telomerase activation is crucial in human carcinogenesis. The limiting component of telomerase, the catalytic subunit (hTERT), is undetectable in normal somatic cells but present in most tumor cells, including the earliest stages of colon carcinoma. The mechanisms involved in the differential expression in normal and tumor cells are not understood. In normal cells hTERT expression is shut down by a repressor, and upregulation could be a consequence of cis-acting changes in the hTERT gene, making it resistant to repression. We have identified a polymorphic and a monomorphic minisatellite in the second intron of the hTERT gene, and polymorphic one in intron 6. The polymorphic minisatellite in intron 2 contains binding sites for c-Myc, which has been shown to upregulate hTERT transcription. Screening colon carcinoma DNAs for rearrangements of hTERT minisatellites we detected no changes in 33 samples from tumors, most of which express hTERT. This indicates that size rearrangements of the hTERT minisatellites are not required for telomerase expression in colon carcinomas. Minor changes and one LOH were seen in five tumors.