Brain-derived neurotrophic factor gene polymorphism (Val66Met) and citalopram response in major depressive disorder

Meta-analysis of BDNF Val66Met polymorphism association with treatment response in patients with major depressive disorder

The aim of our meta-analysis was to assess the association between BDNF Val66Met polymorphism and treatment response in patients with MDD. 8 studies that included data from 1115 subjects were identified. We tested two phenotypes: response rate and remission rate. OR was used as a measure of the effect of the association in a fixed/random effect model. Meta-analysis was performed for genotypes Met/Met versus Val/Val, Val/Met versus Val/Val, Met/Met versus Val/Met, Val/Met+Met/Met versus Val/Val, Met/Met versus Val/Val+Val/Met, and Met allele versus Val allele. When all groups were pooled, a significant association of Val/Met genotype and increased response rate was found in comparison to Val/Val in overall population (OR=1.66, 95%CI=1.07-2.57, P=0.02). In the subgroup analysis, similar result was shown in Asian population (OR=1.83, 95%CI=1.03-3.26, P=0.04), but not in Caucasian population. We didn't observe a significant association of BDNF Val66Met polymorphism with remission rate. This meta-analysis demonstrates the association between BDNF Val66Met polymorphism and treatment response in patients with MDD, and Val66Met heterozygous patients have a better response rate in comparison to Val/Val homozygote patients, especially in Asian population.

Interaction effects between COMT and BDNF polymorphisms on boredom susceptibility of sensation seeking traits

Sensation seeking is a temperament associated with willingness to take risks to obtain arousal. We investigated the relationship between the polymorphisms of the COMT Val158Met and BDNF Val66Met and sensation seeking traits. The Sensation Seeking Scale (SSS) and genotyping were performed in 277 Korean healthy volunteers (165 males, 112 females). Multivariate analysis of covariance was used to test the association between the COMT and BDNF functional polymorphisms and dimensions of sensation seeking, namely, disinhibition, boredom susceptibility, experience seeking and thrill/adventure seeking. No main and interaction effects of the COMT and BDNF on SSS were observed for total subjects. However, in females, a significant gene-gene interaction effect on the boredom susceptibility of SSS was shown. Among females with COMT Met present genotype (Val/Met+Met/Met), subjects with BDNF Met absent genotype (Val/Val) had significantly higher boredom susceptibility than subjects with BDNF Met. The effects of BDNF Val66Met polymorphism on boredom susceptibility of sensation seeking traits could be modulated by COMT Val158Met polymorphism in female.

Serotonergic functioning as measured by the loudness dependence of auditory evoked potentials is related to a haplotype in the brain-derived neurotrophic factor (BDNF) gene

OBJECTIVES

The serotonergic system plays an important pathophysiological role in various psychiatric disorders. Brain-derived neurotrophic factor (BDNF) is involved in the differentiation and survival of serotonergic neurons. A previous study showed that low serum BDNF levels were associated with strong loudness dependence of auditory evoked potentials (LDAEP) as a reflection of low central serotonergic activity. To evaluate the genetic basis of this relationship, we studied whether the LDAEP is correlated with genetic variants within the BDNF gene.

METHODS

Ninety five healthy subjects (41 males, 54 females) received electrophysiological recording of LDAEP and blood drawing for BDNF genotyping. Three BDNF markers (including the single nucleotide polymorphism rs6265(Val66Met)) were analyzed.

RESULTS

Haplotype analysis revealed stronger LDAEP values in carriers of the G(Val)-C-T [rs6265(Val66Met)-rs2030324-rs1491850] haplotype within the BDNF gene in comparison to other haplotype carriers. These findings were demonstrated for the LDAEP of both left and right primary auditory cortices as well as for the vertex electrode (Cz).

CONCLUSION

Subjects with the BDNF haplotype G(Val)-C-T seem to be characterized by low serotonergic activity as well as possibly by low serum BDNF levels. These findings need replication in independent samples.

Review and meta-analysis of antidepressant pharmacogenetic findings in major depressive disorder

This systematic review summarizes pharmacogenetic studies on antidepressant response and side effects. Out of the 17 genes we reviewed, 8 genes were entered into the meta-analysis (SLC6A4, HTR1A, HTR2A, TPH1, gene encoding the beta-3 subunit, brain-derived neurotrophic factor (BDNF), HTR3A and HTR3B). TPH1 218C/C genotype (7 studies, 754 subjects) was significantly associated with a better response (odds ratio, OR=1.62; P=0.005) with no heterogeneity between ethnicities. A better response was also observed in subjects with the Met variant within the BDNF 66Val/Met polymorphism (4 studies, 490 subjects; OR=1.63, P=0.02). Variable number of tandem repeats polymorphism within intron 2 (STin2) 12/12 genotype showed a trend toward a better response in Asians (STin2: 5 studies, 686 subjects; OR=3.89, P=0.03). As for side effects, pooled ORs of serotonin transporter gene promoter polymorphism (5-HTTLPR) l (9 studies, 2642 subjects) and HTR2A -1438G/G (7 studies, 801 subjects) were associated with a significant risk modulation (OR=0.64, P=0.0005) and (OR=1.91, P=0.0006), respectively. Interestingly, this significance became more robust when analyzed with side effect induced by selective serotonin reuptake inhibitors only (5-HTTLPR: P=0.0001, HTR2A: P<0.0001). No significant result could be observed for the other variants. These results were not corrected for multiple testing in each variant, phenotype and subcategory. This would have required a Bonferroni significance level of P<0.0023. Although some heterogeneity was present across studies, our finding suggests that 5-HTTLPR, STin2, HTR1A, HTR2A, TPH1 and BDNF may modulate antidepressant response.

The intersection of pharmacology, imaging, and genetics in the development of personalized medicine

We currently rely on large randomized trials and meta-analyses to make clinical decisions; this places us at a risk of discarding subgroup or individually specific treatment options owing to their failure to prove efficacious across entire populations. There is a new era emerging in personalized medicine that will focus on individual differences that are not evident phenomenologically. Much research is directed towards identifying genes, endophenotypes, and biomarkers of disease that will facilitate diagnosis and predict treatment outcome. We are at the threshold of being able to predict treatment response, primarily through genetics and neuroimaging. In this review we discuss the most promising markers of treatment response and adverse effects emerging from the areas of pharmacogenetics and neuroimaging in depression and schizophrenia.

BDNF Val66Met genotype and 6-month remission rates in late-life depression

Although not observed in younger adult cohorts, in older individuals the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is associated with major depressive disorder (MDD) risk. It is further associated with subjective social support and magnetic resonance imaging (MRI) hyperintense lesions, clinical features independently related to MDD. We examined the relationship between this polymorphism and antidepressant remission rates in an elderly sample with MDD, while also testing for mediation effects of social support and hyperintensities. A total of 229 elderly Caucasian subjects with MDD completed baseline assessments, 1.5 T MRI, and BDNF genotyping. They received antidepressant medication under a structured treatment algorithm and were evaluated for remission at 3 and 6 months. At the 3-month evaluation, BDNF Val66Met genotype was not associated with remission (Wald's χ²=2.51, P=0.1131). When not controlling for multiple comparisons, Met66 allele carriers were more likely to be remitted at 6 months (χ²=4.32, P=0.0377) with an odds ratio of 1.82 (95% CI: 1.04, 3.22). This effect persisted after controlling for lesion volume and social support, neither of which mediated this relationship. Thus in this exploratory analysis, the Met66 allele may be associated with increased odds of remission in older subjects, but also with increased time to remission as there was no 3-month effect.

The promise and reality of pharmacogenetics in psychiatry

Existing psychotropic medications for the treatment of mental illnesses, including antidepressants, mood stabilizers, and antipsychotics, are clinically suboptimal. They are effective in only a subset of patients or produce partial responses, and they are often associated with debilitating side effects that discourage adherence. There is growing enthusiasm in the promise of pharmacogenetics to personalize the use of these treatments to maximize their efficacy and tolerability; however, there is still a long way to go before this promise becomes a reality. This article reviews the progress that has been made in research toward understanding how genetic factors influence psychotropic drug responses and the challenges that lie ahead in translating the research findings into clinical practices that yield tangible benefits for patients with mental illnesses.

Association of BDNF Val66Met polymorphism with both baseline HRQOL scores and improvement in HRQOL scores in Chinese major depressive patients treated with fluoxetine

OBJECTIVE

To explore the association of brain-derived neurotrophic-factor (BDNF) Val66Met polymorphism with both baseline health related quality of life (HRQOL) scores and improvement in HRQOL scores in Chinese major depressive patients treated with fluoxetine.

METHODS

Patients with major depressive disorder (MDD) took fluoxetine (20 mg/day) for 6 weeks. The HRQOL was measured with the Medical Outcomes Study Short Form-36 (SF-36) at baseline and at 6th week. Patients were genotyped for Val66Met polymorphism of BDNF gene.

RESULTS

There was a significant association between social function (SF) and BDNF Val66Met polymorphism, and patients with Met/Met genotype had better SF (compared with Val/Val P = 0.004; compared with Val/Met P = 0.005). A significant association was found between improvement in SF and BDNF Val66Met polymorphism, and patients with Met/Met genotype had poorer improvement in SF (compared with Val/Val P = 0.010; compared with Val/Met P = 0.001). Similar association was found between improvement in mental component summary (MCS) and BDNF Val66Met polymorphism, and patients with Met/Met genotype had poorer improvement in MCS (compared with Val/Val P = 0.066; compared with Val/Met P = 0.006).

CONCLUSIONS

These results indicate that there may be association between BDNF Val66Met polymorphism and both baseline HRQOL (SF) scores and improvement in HRQOL (SF, MCS) scores in Chinese major depressive patients treated with fluoxetine.

Meta-analysis of the BDNF Val66Met polymorphism in major depressive disorder: effects of gender and ethnicity

Brain-derived neurotrophic factor (BDNF) is a nerve growth factor that has antidepressant-like effects in animals and may be implicated in the etiology of mood-related phenotypes. However, genetic association studies of the BDNF Val66Met polymorphism (single nucleotide polymorphism rs6265) in major depressive disorder (MDD) have produced inconsistent results. We conducted a meta-analysis of studies comparing the frequency of the BDNF Val66Met-coding variant in depressed cases (MDD) and nondepressed controls. A total of 14 studies involving 2812 cases with DSM-III or -IV defined MDD and 10 843 nondepressed controls met the inclusion criteria. Analyses were stratified either by gender or ethnicity (Asian and Caucasian) because MDD is more prevalent in women and in Caucasians and because BDNF allele frequencies differ by ethnicity. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were provided for allelic analyses (Met versus Val), as well as for genotypic analyses (Met/Met and Val/Met versus Val/Val). In the total sample, the BDNF Val66Met polymorphism was not significantly associated with depression. However, the gender stratified analyses revealed significant effects in both the allelic and genotypic analyses in men (OR(MET), 95% CI; 1.27 (1.10-1.47); OR(MET/MET), 95% CI; 1.67 (1.19-2.36)). Stratification according to ethnicity did not show significant effects of the Val66Met polymorphism on MDD. Our results suggest that the BDNF Val66Met polymorphism is of greater importance in the development of MDD in men than in women. Future research into gender issues will be of interest.

Brain-derived neurotrophic factor ( BDNF) gene: no major impact on antidepressant treatment response

The brain-derived neurotrophic factor (BDNF) has been suggested to play a pivotal role in the aetiology of affective disorders. In order to further clarify the impact of BDNF gene variation on major depression as well as antidepressant treatment response, association of three BDNF polymorphisms [rs7103411, Val66Met (rs6265) and rs7124442] with major depression and antidepressant treatment response was investigated in an overall sample of 268 German patients with major depression and 424 healthy controls. False discovery rate (FDR) was applied to control for multiple testing. Additionally, ten markers in BDNF were tested for association with citalopram outcome in the STAR*D sample. While BDNF was not associated with major depression as a categorical diagnosis, the BDNF rs7124442 TT genotype was significantly related to worse treatment outcome over 6 wk in major depression (p = 0.01) particularly in anxious depression (p = 0.003) in the German sample. However, BDNF rs7103411 and rs6265 similarly predicted worse treatment response over 6 wk in clinical subtypes of depression such as melancholic depression only (rs7103411: TT < CC, p = 0.003; rs6265: GG < AA, p = 0.001). All SNPs had main effects on antidepressant treatment response in ANOVA models when the remaining SNPs were considered as covariates. The STAR*D analyses did not yield significant results at any of the ten BDNF markers. Our results do not support an association between genetic variation in BDNF and antidepressant treatment response or remission. Post-hoc analyses provide some preliminary support for a potential minor role of genetic variation in BDNF and antidepressant treatment outcome in the context of melancholic depression.

No association of the Val66Met polymorphism of the brain-derived neurotrophic factor with hippocampal volume in major depression

Recently, an association of the Val66Met polymorphism of the brain-derived neurotrophic factor with hippocampal volume in patients with major depression has been reported. Here, we aimed at replicating this finding in an independent German sample. We included 79 patients with unipolar major depressive episodes and 84 healthy comparison participants. The brain-derived neurotrophic factor Val66Met polymorphism was determined in all participants. The volume of the hippocampus was manually traced on high-resolution magnetic resonance images. The hippocampal volumes of patients were significantly smaller than those of the comparison participants, confirming previous reports. There was, however, no Val66Met effect on hippocampal volume in either group. To conclude, we did not replicate the Val66Met effect on hippocampal volume in neither patients with major depression nor in healthy participants.

Pharmacogenetics studies in STAR*D: strengths, limitations, and results

Several lines of evidence support an important genetic contribution to the wide individual variation in therapeutic response to antidepressant medications. The Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study provided the largest cohort assembled to date of DNA from patients with nonpsychotic major depressive disorder, uniformly treated with citalopram and followed prospectively for up to 12 weeks. This pivotal study changed the face of pharmacogenetics research by increasing the sample size by an order of magnitude as well as by providing detailed prospective information about antidepressant response and tolerability. Several groups have identified markers in genes and tested the replication of previous findings of genes associated with outcome and side effects of antidepressant treatment. Variants in HTR2A, GRIK4, and KCNK2 were associated with citalopram treatment outcome. Replication was achieved in markers in the FKBP5 gene. Other findings in PDE11A and BDNF were not successfully replicated, and reports of potential confounders in previous associations with serotonin transporter variation (SLC6A4) were identified. Polymorphisms in pharmacokinetic genes involved in metabolism and transmembrane transport were also not associated with antidepressant response. Adverse events were also tested. Treatment-emergent suicidal ideation was associated with GRIK2, GRIA3, PAPLN, IL28RA, and CREB1. Sexual dysfunction was linked with variation in GRIN3A, GRIA1 GRIA3, and GRIK2. Reported and future findings of pharmacogenetics studies in STAR*D could help elucidate pathways involved in major depression and those pertinent to antidepressant outcome and side effects. Replication of these findings in independent samples could lead to the development of new treatments and to optimization of available treatments.

The role of pharmacogenetics in the treatment of depression and anxiety disorders

Although effective treatment for mood and anxiety disorders have been available for more than 40 years, 30-50% of depressed patients and 25% of patients with anxiety disorder do not respond sufficiently to first-line treatment with antidepressants. Genetic factors are supposed to play a major role in both variation of treatment response and incidence of adverse effects to medication. So far, candidate genes of pharmacokinetic and pharmacodynamic pathways of antidepressants have been investigated, and associations between several candidate genes and response to antidepressants are reported. Two functional polymorphisms of the serotonin transporter gene, 5-HTTLPR and STin2 have been investigated in a large number of pharmacogenetic studies of depression; other candidate genes include serotonin receptor genes, brain-derived neurotrophic factor, P-glycoprotein (located in the blood-brain barrier), G-proteins, TPH1 and TPH2, MAOA, the noradrenaline transporter gene, FKBP5, or cytochrome P450 (CYP450) genes. CYP450 genes play a major role in the metabolism of a substantial part of psychotropics, including antidepressants, and the first estimates of dosage adjustments for antidepressants have been provided based on metabolizer status. Genome-wide association studies that use large numbers of single-nucleotide polymorphisms to screen the entire genome for alleles that influence a trait are now feasible, and the results of the first genome-wide association studies of antidepressant treatment outcome will soon be available. The current review not only updates pharmacogenetic research in depression but also focuses on antidepressant treatment response in anxiety disorders.

A brain-derived neurotrophic factor haplotype is associated with therapeutic response in obsessive-compulsive disorder

BACKGROUND

Several clinical and genetic studies have focused on the role of brain-derived neurotrophic factor (BDNF) in the pathophysiology of various mental disorders. Recent lines of evidence regarding the network hypothesis of treatment outcome point towards the involvement of BDNF variants in the pharmacologic response in mood disorders (MD). Furthermore, there is strong evidence of a role for the serotonergic system in the pathophysiology and treatment of OCD, and upregulation of BDNF has been observed with various classes of antidepressants, including selective serotonin reuptake inhibitors (SSRI). Thus, we hypothesized that the BDNF gene might also be associated with treatment outcome in OCD.

METHODS

We performed a single-marker and haplotype association study of eight tag single nucleotide polymorphisms in the BDNF genomic region and related this to pharmacologic response in a sample of 131 OCD patients.

RESULTS

We found an association for a haplotype containing two single nucleotide polymorphisms that have previously been reported to be associated with treatment outcome in MD (rs908867 and rs1491850).

CONCLUSIONS

Our results support the hypothesis that the BDNF gene is involved in the response to psychopharmacologic treatment even though these preliminary findings await replication in a follow-up sample.

Brain-derived neurotrophic factor: role in depression and suicide

Depression and suicidal behavior have recently been shown to be associated with disturbances in structural and synaptic plasticity. Brain-derived neurotrophic factor (BDNF), one of the major neurotrophic factors, plays an important role in the maintenance and survival of neurons and in synaptic plasticity. Several lines of evidence suggest that BDNF is involved in depression, such that the expression of BDNF is decreased in depressed patients. In addition, antidepressants up-regulate the expression of BDNF. This has led to the proposal of the "neurotrophin hypothesis of depression". Increasing evidence demonstrates that suicidal behavior is also associated with lower expression of BDNF, which may be independent from depression. Recent genetic studies also support a link of BDNF to depression/suicidal behavior. Not only BDNF, but abnormalities in its cognate receptor tropomycin receptor kinase B (TrkB) and its splice variant (TrkB.T1) have also been reported in depressed/suicidal patients. It has been suggested that epigenetic modulation of the Bdnf and Trkb genes may contribute to their altered expression and functioning. More recently, impairment in the functioning of pan75 neurotrophin receptor has been reported in suicide brain specimens. pan75 neurotrophin receptor is a low-affinity neurotrophin receptor that, when expressed in conjunction with low availability of neurotropins/Trks, induces apoptosis. Overall, these studies suggest the possibility that BDNF and its mediated signaling may participate in the pathophysiology of depression and suicidal behavior. This review focuses on the critical evidence demonstrating the involvement of BDNF in depression and suicide.

Pharmacogenomics of antidepressant drugs

While antidepressant pharmacotherapy is an effective treatment of depression, it is still hampered by the slow onset of appreciable clinical improvement and a series of side effects. Moreover, a substantial group of patients does not achieve remission or fails to respond at all. One possible source accounting for these variations in treatment outcome are genetic differences. In recent years a number of pharmacogenetic studies on antidepressant drugs have been published. This manuscript summarizes findings related to the pharmacogenetics of genes involved in the pharmacokinetics as well as pharmacodynamics of antidepressants to date. Illustrated by examples from current candidate gene- and whole genome association studies, this manuscript critically discusses aspects of pharmacogenetic studies in antidepressant response related to study design and clinical relevance.

Development of a new genotyping assay for detection of the BDNF Val66Met polymorphism using melting-curve analysis

Brain-derived neurotrophic factor (BDNF) plays a critical role in the growth, differentiation and survival of neurons in the CNS. Recent research has suggested that BDNF may be implicated in the etiology of mood disorders and schizophrenia, as well as in the therapeutic action of some drugs, such as antidepressants and antipsychotics. This study aimed to develop a simple, fast and accurate new method for detecting the Val66Met polymorphism of the BDNF gene in schizophrenia patients using melting-curve analysis and a DNA-specific dye, SYBR Green I. A group of 30 schizophrenia patients were analyzed to detect the BDNF Val66Met polymorphism (rs6265) using the new genotyping method based on the analysis of fluorescence melting curves of PCR products that were labeled with SYBR Green I. The genotype results were confirmed for all 30 samples using the specific BDNF TaqMan allele discrimination assay. This new method allows the analysis of both alleles in the same reaction tube using SYBR Green I, with no need for additional steps. The addition of a GC clamp makes this method universally applicable, since the melting temperature of one allele can be adjusted as necessary to give the distinctive separation of melting curves. Therefore, this new method is simple, fast and accurate for determining the presence of the BDNF Val66Met polymorphism. It may also be useful for the analysis of other SNPs in pharmacogenetic studies.

Novel sequence variations in the brain-derived neurotrophic factor gene and association with major depression and antidepressant treatment response

CONTEXT

Variations in the brain-derived neurotrophic factor gene (BDNF) have been associated with psychiatric disorders. Deep sequencing of the BDNF gene may identify new variations and bring further insight into psychiatric genetics.

OBJECTIVE

To better characterize sequence variability in the BDNF gene by resequencing a genomic DNA region of 22 kilobases that contained all BDNF exons and their flanking regions.

DESIGN

Case-control study.

SETTING

University of California, Los Angeles, and University of Miami.

PARTICIPANTS

Two hundred sixty-four controls and 272 Mexican Americans with major depressive disorder (MDD) from Los Angeles who were assessed by the same bilingual clinical research team.

MAIN OUTCOME MEASURES

Identification of novel genetic polymorphisms in the BDNF gene and assessment of their frequencies and associations with MDD or antidepressant response.

RESULTS

We identified 83 novel single-nucleotide polymorphisms (SNPs): 30 in untranslated regions, 4 in coding sequences, 37 in introns, and 12 in upstream regions; 3 of 4 rare novel coding SNPs were nonsynonymous. Association analyses of patients with MDD and controls showed that 6 SNPs were associated with MDD (rs12273539, rs11030103, rs6265, rs28722151, rs41282918, and rs11030101) and 2 haplotypes in different blocks (one including Val66, another near exon VIIIh) were significantly associated with MDD. One recently reported 5' untranslated region SNP, rs61888800, was associated with antidepressant response after adjusting for age, sex, medication, and baseline score on the 21-item Hamilton Depression Rating Scale.

CONCLUSIONS

Our data support the concept that extensive resequencing of key candidate genes can lead to the discovery of substantial numbers of new variants. Further studies using larger independent samples are needed to confirm the association of the rs61888800 SNP with antidepressant response.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00265291.

Deficit in BDNF does not increase vulnerability to stress but dampens antidepressant-like effects in the unpredictable chronic mild stress

Despite growing evidences of an association between brain-derived neurotrophic factor (BDNF) and antidepressant effects, the neurotrophic hypothesis of depression is challenged by the paucity of direct links between BDNF deficit and depressive-like behaviors. The unpredictable chronic mild stress (UCMS) paradigm might take our understanding a step further by examining whether a decrease in bdnf expression can lead to enhanced vulnerability to stress and prevent antidepressant efficacy in all or specific UCMS-induced alterations. Wild-type bdnf(+/+) and heterozygous bdnf(+/-) mice were exposed to an 8-week UCMS regimen and, from the third week onward, treated with either vehicle or imipramine (20mg/kg/day, ip). Physical, behavioral and biological (plasma corticosterone levels, bdnf expression in the dentate gyrus) measures were further analyzed regarding to the genotype and the treatment. Heterozygous bdnf(+/-) mice displayed hyperactivity and increase of body weight but no enhancement of the sensitivity to stress exposure in all the measures investigated here. In contrast, while imipramine treatment reduced anxiety-like behaviors in the novelty-suppressed feeding test in both genotypes, it decreased aggressiveness in the resident/intruder test and immobility in the tail suspension test in wild-type but not in heterozygous mice. Furthermore, imipramine induced a twofold increase of bdnf expression in the dentate gyrus in both genotypes, while bdnf(+/-) mice displayed roughly half-reduced level for the same treatment. In summary, we demonstrate here that depletion in BDNF dampened the antidepressant effects in several behaviors but failed to increase vulnerability to chronic stress exposure.

Molecular differentiation of schizoaffective disorder from schizophrenia using BDNF haplotypes

BACKGROUND

Allelic variation in the gene encoding brain-derived neurotrophic factor (BDNF) has been associated with affective disorders, but generally not schizophrenia. Brain-derived neurotrophic factor variants may help clarify the status of schizoaffective disorder.

AIMS

To test the hypothesis that BDNF haplotypes are associated with psychiatric illness marked by a prominent affective component.

METHOD

Frequencies of a 5-marker BDNF haplotype were examined in 600 White participants across four diagnostic categories and healthy controls.

RESULTS

Individuals with schizoaffective disorder and other affective disorders were significantly more likely to carry two copies of the most common BDNF haplotype (containing the valine allele of the Val66Met polymorphism) compared with healthy volunteers. Moreover, when compared with people with schizophrenia, individuals with schizoaffective disorder were significantly more likely to carry two copies of the common haplotype.

CONCLUSIONS

To our knowledge, this is the first candidate gene study to demonstrate association with schizoaffective disorder but not schizophrenia. Variation in the BDNF gene may be associated with the clinical phenotype of affective dysregulation across several DSM-IV diagnostic categories.

BDNF gene: functional Val66Met polymorphism in mood disorders and schizophrenia

The brain-derived neurotrophic factor (BDNF) gene has become a candidate gene for molecular-genetic studies of mood disorders and schizophrenia, and also for pharmacogenomics of drugs used in the treatment of these conditions, such as mood-stabilizers in bipolar mood disorder, antidepressants in depression, and antipsychotics in schizophrenia. It has been demonstrated that the functional Val66Met polymorphism of the gene can be associated with a number of clinical and pharmacological phenomena in these illnesses.

Association of glucocorticoid receptor polymorphisms with the susceptibility to major depressive disorder and treatment responses in Korean depressive patients

OBJECTIVE

Major depressive disorder (MDD) is closely related to stress reactions and serotonin probably underpins the pathophysiology of MDD. Alterations of the hypothalamic-pituitary-adrenal axis at the gene level have reciprocal consequences on serotonin neurotransmission. Glucocorticoid receptor (GR) polymorphisms affect glucocorticoid sensitivity, which is associated with cortisol feedback effects. Therefore, we hypothesised that GR polymorphisms are associated with the susceptibility to MDD and predict the treatment response.

METHOD

Ninety-six subjects with a minimum score of 17 on the 21-item Hamilton Depression Scale (HAMD) at baseline were enrolled into the present study. The genotypes of GR (N363S, ER22/23EK, Bcl1, and TthIII1 polymorphisms) were analysed. The HAMD score was again measured after 1, 2, 4 and 8 weeks of antidepressant treatment to detect whether the therapeutic effects differed with the GR genotype.

RESULTS

Our subjects carried no N363S or ER22/23EK genetic polymorphisms and three types of Bcl1 and TthIII1 genetic polymorphisms. The C/C genotype and C allele at Bcl1 polymorphism were more frequent in MDD patients than in normal controls (p < 0.01 and p = 0.01, respectively). The genotype distributions did not differ significantly between responders and non-responders.

CONCLUSION

These results suggest that GR polymorphism cannot predict the therapeutic response after antidepressant administration. However, GR polymorphism (Bcl1) might play a role in the pathophysiology of MDD. Future studies should check this finding in larger populations with different characteristics.

Improving the prediction of treatment response in depression: integration of clinical, cognitive, psychophysiological, neuroimaging, and genetic measures

Antidepressants are important in the treatment of depression, and selective serotonin reuptake inhibitors are first-line pharmacologic options. However, only 50% to 70% of patients respond to first treatment and <40% remit. Since depression is associated with substantial morbidity, mortality, and family burden, it is unfortunate and demanding on health resources that patients must remain on their prescribed medications for at least 4 weeks without knowing whether the particular antidepressant will be effective. Studies have suggested a number of predictors of treatment response, including clinical, psychophysiological, neuroimaging, and genetics, each with varying degrees of success and nearly all with poor prognostic sensitivity and specificity. Studies are yet to be conducted that use multiple measures from these different domains to determine whether sensitivity and specificity can be improved to predict individual treatment response. It is proposed that a focus on standardized testing methodologies across multiple testing modalities and their integration will be crucial for translation of research findings into clinical practice.

Association study of a brain-derived neurotrophic-factor polymorphism and short-term antidepressant response in major depressive disorders

Major depressive disorder (MDD) is one of the most common mental disorders worldwide. Single nucleotide polymorphisms (SNPs) can be used in clinical association studies to determine the contribution of genes to drug efficacy. A common SNP in the brain-derived neurotrophic factor (BDNF) gene, a methionine (Met) substitution for valine (Val) at codon 66 (Val66Met), is a candidate SNP for influencing antidepressant treatment outcome. In this study, our goal was to determine the relationship between the Val66Met polymorphism in the BDNF gene and the rapid antidepressant response to venlafaxine in a Taiwanese population with MDD. Overall, the BDNF Val66Met polymorphism was found not to be associated with short-term venlafaxine treatment outcome. However, the BDNF Val66Met polymorphism showed a trend to be associated with rapid venlafaxine treatment response in female patients. Future research with independent replication in large sample sizes is needed to confirm the role of the BDNF Val66Met polymorphism identified in this study.

Neuropeptides in depression: role of VGF

The monoamine hypothesis of depression is increasingly called into question by newer theories that revolve around changes in neuronal plasticity, primarily in the hippocampus, at both the structural and the functional levels. Chronic stress negatively regulates hippocampal function while antidepressants ameliorate the effects of stress on neuronal morphology and activity. Both stress and antidepressants have been shown to affect levels of brain-derived neurotrophic factor (BDNF) whose transcription is dependent on cAMP response element binding protein (CREB). BDNF itself has antidepressant-like actions and can induce transcription of a number of molecules. One class of genes regulated by both BDNF and serotonin (5-HT) are neuropeptides including VGF (non-acryonimic) which has a novel role in depression. Neuropeptides are important modulators of neuronal function but their role in affective disorders is just emerging. Recent studies demonstrate that VGF, which is also a CREB-dependent gene, is upregulated by antidepressant drugs and voluntary exercise and is reduced in animal models of depression. VGF enhances hippocampal synaptic plasticity as well as neurogenesis in the dentate gyrus but the mechanisms of antidepressant-like actions of VGF in behavioral paradigms are not known. We summarize experimental data describing the roles of BDNF, VGF and other neuropeptides in depression and how they may be acting through the generation of new neurons and altered synaptic activity. Understanding the molecular and cellular changes that underlie the actions of neuropeptides and how these adaptations result in antidepressant-like effects will aid in developing drugs that target novel pathways for major depressive disorders.

TrkB regulates hippocampal neurogenesis and governs sensitivity to antidepressive treatment

Adult hippocampal neurogenesis is stimulated by chronic administration of antidepressants (ADs) and by voluntary exercise. Neural progenitor cells (NPCs) in the dentate gyrus (DG) that are capable of continuous proliferation and neuronal differentiation are the source of such structural plasticity. Here we report that mice lacking the receptor tyrosine kinase TrkB in hippocampal NPCs have impaired proliferation and neurogenesis. When exposed to chronic ADs or wheel-running, no increase in proliferation or neurogenesis is observed. Ablation of TrkB also renders these mice behaviorally insensitive to antidepressive treatment in depression- and anxiety-like paradigms. In contrast, mice lacking TrkB only in differentiated DG neurons display typical neurogenesis and respond normally to chronic ADs. Thus, our data establish an essential cell-autonomous role for TrkB in regulating hippocampal neurogenesis and behavioral sensitivity to antidepressive treatments, and support the notion that impairment of the neurogenic niche is an etiological factor for refractory responses to an antidepressive regimen.

Genetic association study of BDNF in depression: finding from two cohort studies and a meta-analysis

Depression is common and a major cause of morbidity and mortality and is also known to have serious effects on quality of life. Both clinical and pharmacologic studies have implicated the role of brain-derived neurotrophic factor (BDNF) as a susceptibility locus for the development of mental illness, including depression, bipolar disorder, and schizophrenia. Population-based genetic studies have examined the association between BDNF and a variety of depression outcomes, but the results have not clearly established the role of BDNF in the development of this complex disorder. The aim of this study was to test for associations between two genetic variants in BDNF, Val66Met (rs6265) and -270 C > T, and depression measured in two independent samples. In this analysis we included 3,548 participants from British Women's Heart and Health Study (BWHHS) and 6,836 mothers from Avon Longitudinal Study of Parents and Children (ALSPAC) who had complete data on genotype and depression outcomes. We did not detect any strong evidence of associations between any of the two polymorphisms and indicators of depression in either BWHHS or ALSPAC samples. Further, we carried out a systematic review and meta-analysis of all association studies of these two BDNF polymorphisms and depression. The meta-analysis of Val66Met in depression obtained an overall summary OR of 1.06 (95% CI: 0.89-1.26, P = 0.537) comparing MM with VV genotypes and an OR of 0.97 (95% CI: 0.89-1.05, P = 0.403) comparing MV with VV genotypes. Our findings suggest that BDNF genotype does not exert a major influence on the development of depression.

Brain-derived neurotrophic factor and antidepressant action: another piece of evidence from pharmacogenetics

Evaluation of: Gratacòs M, Soria V, Urretavizcaya M et al.: A brain-derived neurotrophic factor (BDNF) haplotype is associated with antidepressant treatment outcome in mood disorders. Pharmacogenomics J. 8, 101–112 (2008). The neurotrophin hypothesis of depression and antidepressant drug action postulates that reduced activity of neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF), plays an important role in the pathogenesis of major depression, and that its restoration may represent a critical mechanism underlying antidepressant therapeutic effect. This hypothesis is supported by numerous animal studies; however, evidence from clinical studies is lacking. This study is the first to use both single-marker as well as haplotype analysis to test the effect of genetic variants of BDNF on the therapeutic effects of antidepressant treatment in mood disorder. Among eight BDNF TagSNPs tested, one allele (rs908867) is associated with antidepressant response, with heterozygote carriers showing a better response than homozygous analog. The authors also identified a haplotype associated with the therapeutic response. This study provides clinical evidence to support the role of BDNF in antidepressant therapeutic mechanisms. However, further work is needed to confirm the findings, for several reasons. First, the study included not only major depression but also bipolar disorder patients; second, various antidepressants were used in this study, which could affect patients’ responses; third, the frequency of the haplotype associated with treatment response is rare; and fourth, previous studies of the effects of single BDNF polymorphisms on antidepressant action have reported conflicting findings. Several suggestions for further work are discussed below.

No association between the brain-derived neurotrophic factor gene Val66Met polymorphism and tardive dyskinesia in schizophrenic patients

OBJECTIVE

This study investigated whether the brain-derived neurotrophic factor (BDNF) gene Val66Met single-nucleotide polymorphism (SNP) is associated with antipsychotic-induced tardive dyskinesia (TD) in schizophrenia.

METHODS

Genotyping was performed for the BDNF gene Val66Met SNP in Korean schizophrenic patients with (n=83) and without TD (n=126) who were matched for antipsychotic drug exposure and other relevant variables.

RESULTS

The frequencies of genotypes (chi2=2.37, p=0.306) and alleles (chi2=0.03, p=0.867) did not differ significantly between these two groups.

CONCLUSION

These findings suggest that the BDNF polymorphism does not play a major role in the susceptibility to TD in schizophrenic patients.

Pharmacogenomics with antidepressants in the STAR*D study

Major depressive disorder is one of the most common psychiatric disorders worldwide. No single antidepressant has been shown to be more effective than any other in lifting depression, and the effectiveness of any particular antidepressant in an individual is difficult to predict; therefore, doctors must prescribe antidepressants based on educated guesses. SNPs can be used in clinical association studies to determine the contribution of genes to drug efficacy. Evidence is accumulating to suggest that the efficacy of antidepressants results from the combined effects of a number of genetic variants, such as SNPs. Although there are not enough data currently available to prove this hypothesis, an increasing number of genetic variants associated with antidepressant response are being discovered. In this article, we review the pharmacogenomics of the drug efficacy of antidepressants in major depressive disorder. First, we survey the SNPs and genes identified as genetic markers that are correlated and associated with the drug efficacy of antidepressants in the Sequenced Treatment Alternatives for Depression (STAR*D) study. Second, we investigate candidate genes that have been suggested as contributing to treatment-emergent suicidal ideation during the course of antidepressant treatment in the STAR*D study. Third, we briefly describe the pharmacokinetic genes examined in the STAR*D study, and finally, we summarize the limitations with respect to the pharmacogenomics studies in the STAR*D study. Future research with independent replication in large sample sizes is needed to confirm the role of the candidate genes identified in the STAR*D study in antidepressant treatment response.

Ethanol-BDNF interactions: still more questions than answers

Brain-derived neurotrophic factor (BDNF) has emerged as a regulator of development, plasticity and, recently, addiction. Decreased neurotrophic activity may be involved in ethanol-induced neurodegeneration in the adult brain and in the etiology of alcohol-related neurodevelopmental disorders. This can occur through decreased expression of BDNF or through inability of the receptor to transduce signals in the presence of ethanol. In contrast, recent studies implicate region-specific up-regulation of BDNF and associated signaling pathways in anxiety, addiction and homeostasis after ethanol exposure. Anxiety and depression are precipitating factors for substance abuse and these disorders also involve region-specific changes in BDNF in both pathogenesis and response to pharmacotherapy. Polymorphisms in the genes coding for BDNF and its receptor TrkB are linked to affective, substance abuse and appetitive disorders and therefore may play a role in the development of alcoholism. This review summarizes historical and pre-clinical data on BDNF and TrkB as it relates to ethanol toxicity and addiction. Many unresolved questions about region-specific changes in BDNF expression and the precise role of BDNF in neuropsychiatric disorders and addiction remain to be elucidated. Resolution of these questions will require significant integration of the literature on addiction and comorbid psychiatric disorders that contribute to the development of alcoholism.

Role of BDNF Val66Met functional polymorphism in Alzheimer's disease-related depression

BACKGROUND

The gene encoding brain-derived neurotrophic factor (BDNF) has been suggested as a candidate for major depression, and for depression susceptibility in different neurological and psychiatric diseases. No study has investigated the role of BDNF genetic variation and depressive symptoms in Alzheimer's disease (AD).

OBJECTIVE

The aim of this study was to assess the genetic contribution of BDNF Val66Met functional polymorphism to AD-related depression.

METHODS

Two-hundred and sixty-four AD patients underwent clinical and neuropsychological examination as well as an evaluation of behavioral and psychiatric disturbances. They were subsequently divided into two subgroups according to the presence (AD-D) or the absence (AD-nD), based on DSM-IV criteria for depression in AD. In each subject, BDNF Val66Met functional polymorphism and apolipoprotein E (APOE) genotype were evaluated.

RESULTS

In our sample, 35.2% of patients (n=93) reported AD-related depressive symptoms. Compared to patients bearing no polymorphisms (BDNF G/G), BDNF G/A carriers showed more than twofold-time risk (OR=2.38; 95%CI=1.38-4.13), and BDNF A/A carriers had a threefold-time risk (OR=3.04; 95%CI=1.15-8.00) for depression in AD. Accordingly, considering the allele frequencies, BDNF A allele was significantly over-represented in AD-D (32.8%) compared to AD-nD (19.0%) (OR=2.08; 95%CI=1.38-3.13). An association between the number of carried A allele and the severity of depressive symptoms was observed (P<0.002). No effect of APOE genotype on risk for depression was found.

CONCLUSIONS

The present findings provide evidence of BDNF genetic variation role in the susceptibility to AD-related depression. This study puts emphasis on the usefulness of considering genetic background for better defining individualized risk profiles in AD.

Molecular adaptations underlying susceptibility and resistance to social defeat in brain reward regions

While stressful life events are an important cause of psychopathology, most individuals exposed to adversity maintain normal psychological functioning. The molecular mechanisms underlying such resilience are poorly understood. Here, we demonstrate that an inbred population of mice subjected to social defeat can be separated into susceptible and unsusceptible subpopulations that differ along several behavioral and physiological domains. By a combination of molecular and electrophysiological techniques, we identify signature adaptations within the mesolimbic dopamine circuit that are uniquely associated with vulnerability or insusceptibility. We show that molecular recapitulations of three prototypical adaptations associated with the unsusceptible phenotype are each sufficient to promote resistant behavior. Our results validate a multidisciplinary approach to examine the neurobiological mechanisms of variations in stress resistance, and illustrate the importance of plasticity within the brain's reward circuits in actively maintaining an emotional homeostasis.

Is it time to reassess the BDNF hypothesis of depression?

The brain-derived neurotrophic factor (BDNF) hypothesis of depression postulates that a loss of BDNF is directly involved in the pathophysiology of depression, and that its restoration may underlie the therapeutic efficacy of antidepressant treatment. While this theory has received considerable experimental support, an increasing number of studies have generated evidence which is not only inconsistent, but also directly contradicts the hypothesis. This article provides a critical review of the clinical and preclinical studies which have been responsible for this controversy, outlining pharmacological, behavioural and genetic evidence which demonstrates the contrasting role of BDNF in regulating mood and antidepressant effects throughout the brain. I will also review key studies, both human and animal, which have investigated the association of a BDNF single-nucleotide polymorphism (Val66Met) with depression pathogenesis, and detail the number of inconsistencies which also afflict this novel area of BDNF research. The article will conclude by discussing why now is a critical time to reassess the original BDNF hypothesis of depression, and look towards the formation of new models that can provide a more valid account of the complex relationships between growth factors, mood disorders and their treatment.

Decreased plasma brain-derived neurotrophic factor levels in patients with alcohol dependence

BACKGROUND

Many reports have suggested possible relationships between brain-derived neurotrophic factor (BDNF) and alcohol dependence. A protective effect of BDNF against ethanol-induced cell damage has been suggested, and this effect may contribute to the development or maintenance of alcohol dependence. This study was carried out in order to verify the significance of BDNF in alcohol dependence.

METHODS

Peripheral BDNF levels were measured in alcohol-dependent patients and control subjects using an enzyme-linked immunosorbent assay. A physician's interview and standardized questionnaire were used to obtain information regarding each patient's history of alcohol consumption.

RESULTS

The mean BDNF level was lower in the alcohol dependence group (389.5 +/- 501.7 pg/ml) than in the normal controls (822.5 +/- 420.7 pg/ml) by analysis of covariance (ANCOVA) (F = 25.79, p < 0.01). The mean BDNF level was lower in the alcohol-dependent patients with a positive family history of alcohol dependence (247.6 +/- 289.2 pg/ml) than in those with a negative family history of alcohol dependence (583.9 +/- 652.8 pg/ml) by ANCOVA (F = 6.51, p = 0.01). The BDNF levels did not correlate significantly with any of the variables analyzed in this study, including Beck depression inventory, state and trait anxiety inventory (STAI-S and T), and various drinking behaviors.

CONCLUSIONS

Changes in the levels of BDNF might play a role in the pathophysiology and inheritance of alcohol dependence.

A brain-derived neurotrophic factor (BDNF) haplotype is associated with antidepressant treatment outcome in mood disorders

Brain-derived neurotrophic factor (BDNF) has been studied extensively in relation to the susceptibility to mood disorders (MD), although it remains to be clarified whether BDNF is a susceptibility locus for MD phenotypes, including therapeutic response to antidepressants. We have performed a single-marker and haplotype association study of eight TagSNPs polymorphisms in the genomic region containing the BDNF gene in 342 control subjects and 374 patients with MD, and have tested the association with antidepressant treatment outcome. None of the eight single nucleotide polymorphisms (TagSNPs) was significantly associated with MD phenotype after Bonferroni correction. In the single-marker analysis, a SNP was found to be associated with the patient's state of 'remitter' after adequate trial with a single antidepressant phenotype (odds ratio (OR)=2.95; P=0.0025). We also identified a haplotype associated with this phenotype. This study supports the implication of BDNF in antidepressant treatment outcome in MD, with specific association with 5' upstream region of BDNF gene.

Pharmacogenetic treatment of depressive disorders

Whilst the efficacy of antidepressant-based treatments of major depressive disorder continues to improve, responses remain poor in 30–50% of patients, with many patients discontinuing the medication due to distressing side effects. Drug responses can be influenced by genetic factors and several physiological and environmental factors, including age, renal and liver function, nutritional status, smoking and alcohol consumption. Antidepressants have a multifactorial mechanism of action and their phenotypic expression can be affected by several different genes. Most pharmacogenetic investigations into antidepressants have been conducted on candidate genes from the monoaminergic pathway. Antidepressants are thought to regulate monoaminergic transmission, and this review highlights pharmacogenetic studies into the effects of genes related to the monoaminergic pathway, such as the serotonin transporter, serotonin receptors of the norepinephrine transporter, tryptophan hydroxylase, the β3 subunit of G protein and brain-derived neurotrophic factor, on the action of antidepressants.

Integrating genomics and neuromarkers for the era of brain-related personalized medicine

The harsh reality is that many medical treatments do not work as expected in a significant percentage of patients, and occasionally there are serious side effects. A new paradigm of personalized medicine is emerging, which proactively tailors treatment to each individual’s biological and psychological profile. The first proof-of-concept phase of personalized medicine has now been achieved. However, it has thus far focused on the use of genomic markers and on disorders of the body. The complexity of the brain is likely to require a shift from a single genetic marker focus to a more integrated approach in which additional brain-related information (neuromarkers) is taken into account. Codevelopment of genomic neuromarkers with new compounds in a personalized medicine approach will lead to increased drug R&D and treatment benefits. The emerging genomic neuromarker potential has begun to be incorporated into the template for the next version of the Diagnostic and Statistical Manual (DSM-V). The statistical power of large subject numbers in databases in general (and standardized databases in particular) provides an ideal source for elucidating the best genomic–neuromarker profiles (explaining most of the main-effects variance), which will empower a brain-related personalized medicine into mainstream clinical practice.