Dinucleotide repeat polymorphism at the human gene for the brain-derived neurotrophic factor (BDNF)

Convergent neurobiological predictors of mood and anxiety symptoms and treatment response

Introduction: Mood and anxiety disorders are leading contributors to the global burden of diseases. Comorbid mood and anxiety disorders have a lifetime prevalence of ~20% globally and increases the risk for suicide, a leading cause of death. Areas covered: In this review, authors highlight recent advances in the understanding of multilevel-neurobiological mechanisms for normal/pathological human affective-functioning. The authors then address the complex interplay between environmental-adversity and molecular-genetic mediators of brain correlates of affective-symptoms. The molecular focus is strategically limited to GTF2i, BDNF, and FKBP5 genes that are, respectively, involved in transcriptional-, neurodevelopmental- and neuroendocrine-pathway mediation of affective-functions. The importance of these genes is illustrated with studies of copy-number-variants, genome-wide association (GWAS), and candidate gene-sequence variant associations with disease etiology. Authors concluded by highlighting the predictive values of integrative neurobiological processing of gene-environment interactions for affective disorder symptom management. Expert opinion: Given the transcriptional, neurodevelopmental and neuroimmune relevance of GTF2i, BDNF, and FKBP5 genes, respectively, authors reviewed the putative roles of these genes in neurobiological mediation of adaptive affective-responses. Authors discussed the importance of studying gene-dosage effects in understanding affective disorder risk biology, and how such targeted neurogenetic studies could guide precision identification of novel pharmacotherapeutic targets and aid in prediction of treatment response.

Critical Issues in BDNF Val66Met Genetic Studies of Neuropsychiatric Disorders

Neurotrophins have been implicated in the pathophysiology of many neuropsychiatric diseases. Brain-derived neurotrophic factor (BDNF) is the most abundant and widely distributed neurotrophin in the brain. Its Val66Met polymorphism (refSNP Cluster Report: rs6265) is a common and functional single-nucleotide polymorphism (SNP) affecting the activity-dependent release of BDNF. BDNF Val66Met transgenic mice have been generated, which may provide further insight into the functional impact of this polymorphism in the brain. Considering the important role of BDNF in brain function, more than 1,100 genetic studies have investigated this polymorphism in the past 15 years. Although these studies have reported some encouraging positive findings initially, most of the findings cannot be replicated in following studies. These inconsistencies in BDNF Val66Met genetic studies may be attributed to many factors such as age, sex, environmental factors, ethnicity, genetic model used for analysis, and gene–gene interaction, which are discussed in this review. We also discuss the results of recent studies that have reported the novel functions of this polymorphism. Because many BDNF polymorphisms and non-genetic factors have been implicated in the complex traits of neuropsychiatric diseases, the conventional genetic association-based method is limited to address these complex interactions. Future studies should apply data mining and machine learning techniques to determine the genetic role of BDNF in neuropsychiatric diseases.

Sex Differences in the Impact of BDNF Genotype on the Longitudinal Relationship between Physical Activity and Cognitive Performance

BACKGROUND

Physical activity may preserve cognitive function in older adults, but benefits vary by sex and genetic factors.

OBJECTIVE

We tested the longitudinal association between physical activity and cognitive performance to de termine whether a common genetic polymorphism for brain-derived neurotrophic factor (BDNF Val66Met) moderated this effect.

METHODS

In a 12-year longitudinal population-based sample of older adults (n = 2,218), we used growth curve modeling to investigate whether the benefits of physical activity on cognitive preservation differed by BDNF genotype and sex across multiple cognitive domains including processing speed, attention, working memory, and episodic verbal memory.

RESULTS

The relationship between physical activity and cognitive performance was dependent on BDNF carrier status in males (Δχ2 [Δdf] = 12.94 [4], p = 0.01), but not in females (Δχ2 [Δdf] = 4.38 [4], p = 0.36). Cognition benefited from physical activity in male BDNF met noncarriers, but not met carriers, whereas cognition was not statistically significantly related to physical activity in females regardless of genotype.

CONCLUSION

We observed longitudinal, but not cross-sectional, effects of physical activity on cognitive performance. Our study highlights the importance of longitudinal follow-up and consideration of sex differences in the relationships between physical activity, BDNF genotype, and cognitive decline. The findings contribute to understanding gene-lifestyle interactions in promoting cognitive health.

BDNF Val66Met polymorphism tunes frontolimbic circuitry during affective contextual learning

Adaptive learning impairments are common in cognitive and behavioral disorders, but the neurogenetic mechanisms supporting human affective learning are poorly understood. We designed a higher-order contextual learning task in which healthy participants genotyped for the Val⁶⁶Met polymorphism of the brain derived neurotropic factor gene (BDNF) were required to choose the member of a picture pair most congruent with the emotion in a previously-viewed facial expression video in order to produce an advantageous monetary outcome. Functional magnetic resonance imaging (fMRI) identified frontolimbic blood oxygenation level dependent (BOLD) reactivity that was associated with BDNF Val⁶⁶Met genotype during all three phases of the learning task: aversive and reward-predictive learning, contextually-challenging decision-making, and choice-related monetary loss-avoidance and gain outcomes. Relative to Val homozygotes, Met carriers showed attenuated ventromedial prefrontal response to predictive affective cues, dorsolateral prefrontal signaling that depended on decision difficulty, and enhanced ventromedial prefrontal reactivity that was specific to loss-avoidance. These findings indicate that the BDNF Val⁶⁶Met polymorphism is associated with functional tuning of behaviorally-relevant frontolimbic circuitry, particularly involving the ventromedial prefrontal cortex, during higher-order learning.

The dopamine-related polymorphisms BDNF, COMT, DRD2, DRD3, and DRD4 are not linked with changes in CSF dopamine levels and frequency of HIV infection

We showed previously that higher levels in CSF dopamine in HIV patients are associated with the presence of the dopamine transporter (DAT) 10/10-repeat allele which was also detected more frequently in HIV-infected individuals compared to uninfected subjects. In the current study, we investigated further whether other genetic dopamine (DA)-related polymorphisms may be related with changes in CSF DA levels and frequency of HIV infection in HIV-infected subjects. Specifically, we studied genetic polymorphisms of brain-derived neurotrophic factor, catechol-O-methyltransferase, and dopamine receptors DRD2, DRD3, and DRD4 genetic polymorphisms in uninfected and HIV-infected people in two different ethnical groups, a German cohort (Caucasian, 72 individuals with HIV infection and 22 individuals without HIV infection) and a South African cohort (Xhosan, 54 individuals with HIV infection and 19 individuals without HIV infection). We correlated the polymorphisms with CSF DA levels, HIV dementia score, CD4⁺ T cell counts, and HIV viral load. None of the investigated DA-related polymorphisms was associated with altered CSF DA levels, CD4⁺ T cell count, viral load, and HIV dementia score. The respective allele frequencies were equally distributed between HIV-infected patients and controls. Our findings do not show any influence of the studied genetic polymorphisms on CSF DA levels and HIV infection. This is in contrast to what we found previously for the DAT 3'UTR VNTR and highlights the specific role of the DAT VNTR in HIV infection and disease.

Pharmacogenetics of clinical response to risperidone

Despite risperidone's proven safety and efficacy, existing pharmacogenetic knowledge could be applied to improve its clinical use. The present work aims to summarize the information about genetic polymorphisms affecting risperidone adverse reactions and efficacy during routine clinical practice. The most relevant genes involved in the metabolism of the drug (i.e., CYP2D6, CYP3A and ABCB1) appear to have the greatest potential to predict differences in plasma concentrations of the drug and its interactions, but also relate to side effects, such as neuroleptic syndrome, weight gain or polydipsia. Other genes that have been found in association at least twice with any adverse reactions including metabolic changes, extrapyramidal symptoms or prolactine increase are: 5HT2A; 5HT2C; 5HT6; DRD2; DRD3; and BDNF. Some of these genes (5HTR2A, DRD2 and DRD3), along with 5-HTTLPR and COMT, have also been reported to be related with negative clinical outcomes. However, there is not yet enough evidence to support their routine screening during clinical practice.

[Precursors and propeptides of neurotrophic factors as the modulators of biological activity of its mature forms]

Here, we review the problems of neurotrophic factors' folding, the role of its precursors (proneurotrophins) and the contribution of elements deleted during its maturation (propeptides) in biological functioning of these growth factors.

Reprint of: Effects of BDNF polymorphisms on brain function and behavior in health and disease

Brain-derived neurotrophic factor (BDNF), the most abundant neurotrophin in the brain, serves an important role during brain development and in synaptic plasticity. Given its pleiotropic effects in the central nervous system, BDNF has been implicated in cognitive function and personality development as well as the pathogenesis of various psychiatric disorders. Thus, BDNF is considered an attractive candidate gene for the study of healthy and diseased brain function and behaviors. Over the past decade, many studies have tested BDNF genetic association, particularly its functional Val66Met polymorphism, with psychiatric diseases, personality disorders, and cognitive function. Although many reports indicated a possible role for BDNF genetic effects in mental problems or brain function, other reports were unable to replicate the findings. The conflicting results in BDNF genetic studies may result from confounding factors such as age, gender, other environmental factors, sample size, ethnicity and phenotype assessment. Future studies with more homogenous populations, well-controlled confounding factors, and well-defined phenotypes are needed to clarify the BDNF genetic effects on mental diseases and human behaviors.

Effects of BDNF polymorphisms on brain function and behavior in health and disease

Brain-derived neurotrophic factor (BDNF), the most abundant neurotrophin in the brain, serves an important role during brain development and in synaptic plasticity. Given its pleiotropic effects in the central nervous system, BDNF has been implicated in cognitive function and personality development as well as the pathogenesis of various psychiatric disorders. Thus, BDNF is considered an attractive candidate gene for the study of healthy and diseased brain function and behaviors. Over the past decade, many studies have tested BDNF genetic association, particularly its functional Val66Met polymorphism, with psychiatric diseases, personality disorders, and cognitive function. Although many reports indicated a possible role for BDNF genetic effects in mental problems or brain function, other reports were unable to replicate the findings. The conflicting results in BDNF genetic studies may result from confounding factors such as age, gender, other environmental factors, sample size, ethnicity and phenotype assessment. Future studies with more homogenous populations, well-controlled confounding factors, and well-defined phenotypes are needed to clarify the BDNF genetic effects on mental diseases and human behaviors.

Neuroplasticity signaling pathways linked to the pathophysiology of schizophrenia

Schizophrenia is a severe mental illness that afflicts nearly 1% of the world's population. One of the cardinal pathological features of schizophrenia is perturbation in synaptic connectivity. Although the etiology of schizophrenia is unknown, it appears to be a developmental disorder involving the interaction of a potentially large number of risk genes, with no one gene producing a strong effect except rare, highly penetrant copy number variants. The purpose of this review is to detail how putative schizophrenia risk genes (DISC-1, neuregulin/ErbB4, dysbindin, Akt1, BDNF, and the NMDA receptor) are involved in regulating neuroplasticity and how alterations in their expression may contribute to the disconnectivity observed in schizophrenia. Moreover, this review highlights how many of these risk genes converge to regulate common neurotransmitter systems and signaling pathways. Future studies aimed at elucidating the functions of these risk genes will provide new insights into the pathophysiology of schizophrenia and will likely lead to the nomination of novel therapeutic targets for restoring proper synaptic connectivity in the brain in schizophrenia and related disorders.

Brain-derived neurotrophic factor gene polymorphisms and mirtazapine responses in Koreans with major depression

Brain-derived neurotrophic factor (BDNF) is a candidate molecule for influencing the clinical response to antidepressant treatment. The aims of this study were to determine the relationship between the Val66Met polymorphism in the BDNF gene and the response to mirtazapine in 243 Korean subjects with major depressive disorder (MDD). The reduction in the Hamilton Depression score over the 8-week treatment period was not influenced by BDNF V66M genotypes. A marginal effect of genotype on somatic anxiety score was observed at baseline (P = 0.047 in the dominant model). However, genotype-time interaction had no effect on somatic anxiety score after the 8-week a treatment period. Plasma BDNF levels tended to increase during mirtazapine treatment, although without statistical significance (P = 0.055). After 8 weeks of mirtazapine treatment, plasma BDNF levels were higher in Met allele homozygotes (1499.7 ± 370.6 ng/mL) than in Val allele carriers (649.7 ± 158.5 ng/mL, P = 0.049). Our results do not support the hypothesis that the Val66Met promoter polymorphism in the BDNF gene influences the therapeutic response to mirtazapine in Korean MDD patients. However, our data indicate that this polymorphism results in increased plasma BDNF after mirtazapine treatment.

Interface between hypothalamic-pituitary-adrenal axis and brain-derived neurotrophic factor in depression

Although the pathophysiology of depressive disorder remains elusive, two hypothetical frameworks seem to be promising: the involvement of hypothalamic pituitary-adrenal (HPA) axis abnormalities and brain-derived neurotrophic factor (BDNF) in the pathogenesis and in the mechanism of action of antidepressant treatments. In this review, we focused on research based on these two frameworks in relation to depression and related conditions and tried to formulate an integrated theory of the disorder. Hormonal challenge tests, such as the dexamethasone/corticotropin-releasing hormone test, have revealed elevated HPA activity (hypercortisolism) in at least a portion of patients with depression, although growing evidence has suggested that abnormally low HPA axis (hypocortisolism) has also been implicated in a variety of stress-related conditions. Several lines of evidence from postmortem studies, animal studies, blood levels, and genetic studies have suggested that BDNF is involved in the pathogenesis of depression and in the mechanism of action of biological treatments for depression. Considerable evidence has suggested that stress reduces the expression of BDNF and that antidepressant treatments increase it. Moreover, the glucocorticoid receptor interacts with the specific receptor of BDNF, TrkB, and excessive glucocorticoid interferes with BDNF signaling. Altered BDNF function is involved in the structural changes and possibly impaired neurogenesis in the brain of depressed patients. Based on these findings, an integrated schema of the pathological and recovery processes of depression is illustrated.

Population genetic study of the brain-derived neurotrophic factor (BDNF) gene

Genetic variants in the brain-derived neurotrophic factor (BDNF) gene, predominantly the functional Val66Met polymorphism, have been associated with risk of bipolar disorder and other psychiatric disorders. However, not all studies support these findings, and overall the evidence for the association of BDNF with disease risk is weak. As differences in population genetic structure between patient samples could cause discrepant or spurious association results, we investigated this possibility by carrying out population genetic analyses of the BDNF genomic region. Substantial variation was detected in BDNF coding region single-nucleotide polymorphism (SNP) allele and haplotype frequencies between 58 global populations, with the derived Met allele of Val66Met ranging in frequency from 0 to 72% across populations. F(ST) analyses to assess diversity in the HapMap populations determined that the Val66Met F(ST) value was at the 99.8th percentile among all SNPs in the genome. As the BDNF population genetic differences may be due to local selection, we performed the long-range haplotype test for selection using 68 SNPs spanning the BDNF genomic region in 12 European-derived pedigrees. Evidence for positive selection was found for a high-frequency Val-carrying haplotype, with a relative extended haplotype homozygosity value above the 99 th percentile compared with HapMap data (P=4.6 x 10(-4)). In conclusion, we observed considerable BDNF allele and haplotype diversity among global populations and evidence for positive selection at the BDNF locus. These phenomena can have a profound impact on the detection of disease susceptibility genes and must be considered in gene association studies of BDNF.

An investigation of associations between alcohol use disorder and polymorphisms on ALDH2, BDNF, 5-HTTLPR, and MTHFR genes in older Korean men

BACKGROUND

This study aimed to investigate the association of alcohol use disorder (AUD) with four candidate genes in older Korean men: aldehyde dehydrogenase 2 (ALDH2, 1/2), brain-derived neurotrophic factor (BDNF, val66met), serotonin transporter gene linked polymorphic region (5-HTTLPR, s/l), and methylenetetrahydrofolate reductase (MTHFR, c.677C > T).

METHODS

A community sample of 300 men aged 65 or over were categorized into 68 subjects with AUD and 232 controls according to clinical examinations and DSM-IV criteria. Genotype distributions and allele frequencies were compared.

RESULTS

Men with AUD had significantly higher ALDH2*1 and BDNF met allele frequencies compared to controls (p-values < 0.05). No significant differences in genotype or allele frequencies were found for 5-HTTLPR or MTHFR (p-values > 0.3).

CONCLUSIONS

AUD was associated with ALDH2*1 and BDNF met alleles in older Korean men. The first is consistent with previous research and likely to be explained by a protective effect of unpleasant symptoms following alcohol consumption associated with ALDH2*2. The second finding is novel and might be accounted for by BDNF-mediated serotonin or dopamine pathways. However, given the relatively small sample size, the results should be regarded as preliminary and requiring independent replication.

Interest of using genetically manipulated mice as models of depression to evaluate antidepressant drugs activity: a review

Among the multiple possibilities to study human depressive disorders, animal models remain important preclinical tools. They allow the understanding of the mechanisms of action of antidepressant drugs. Primarily developed in rat, animal models of depression have been adapted to the mouse, an easy-to-use mammal with better genetic possibilities than rats. As an example, genetic manipulation of the serotoninergic 5-hydroxytryptamine-HT; (5-HT) system provided important opportunities to investigate the role of this monoamine in mood disorders. The contribution of either constitutive knockout (KO), tissue specific, or inducible KO mice and animal models in the current knowledge of the pathophysiology and treatment of depression is unanimously recognized. The phenotype of genetically manipulated animals is strongly influenced by both the genetic background of the animal as well as environmental factors. For these reasons, it is necessary to underline that KO mice have been generated on various genetic backgrounds, which strongly influence the behavioral and neurochemical responses to the tests. The present review will thus focus on KO mice lacking G protein-coupled monoaminergic receptors (e.g; 5-HT1B, 5-HT1A, and 5-HT4 receptors) and the 5-HT serotonin transporter, which is the main target of antidepressant drugs (or strategies). The importance of KO mice for neurotrophic factors, particularly for brain-derived neurotrophic factor and its main receptor displaying a tyrosine kinase activity, will also be addressed to illustrate the fact that in preclinical studies, combination of genetic manipulations with pharmacological ones should allow further progress in the field of neuropsychopharmacology.

Interspecies comparisons of functional genetic variations and their implications in neuropsychiatry

Animal studies are important for the identification and functional characterization of the biological substrates underlying complex psychiatric disorders. However, novel insights into the relationship between the genome and behavior are needed for the development of fully valid translational models. Based on the notion that in different species, the same genes may independently give rise to alleles with similar functional and phenotypic effects, either under similar selection or through similar genomic mechanisms, we propose the use of genetic validity as a tool for identifying analogous pathology between animals and human neuropsychiatric disorders. Furthermore, the identification of copy number variants which disrupt entire genes, reinforces the notion that transgenic animals, such as knockouts or knock-ins, may provide unexpectedly valid disease models for psychiatric traits. To illustrate interspecies comparison of genetic variations in relation to neurobehavioral traits, examples are provided for the BDNF, COMT, and DISC1 genes in mouse and man. We propose that alignment of individual genetic variations with endophenotypes obtained from mice and across categories of neuropsychiatric disorders will provide an important step in translational research.

Mutant mouse models and antidepressant drug research: focus on serotonin and brain-derived neurotrophic factor

Several lines of knockout (KO) mice have been evaluated as models of depression-related behavioral and neurobiological changes, and used to investigate molecular and cellular mechanisms underlying the activity of antidepressant drugs. Adult neurogenesis and brain 5-hydroxytryptamine (5-HT)/neurotrophic factor interactions have recently attracted great interest in relation to the mechanism of action of antidepressant drugs. The present review focuses primarily on genetic manipulation of the serotoninergic (5-HT) system. Basal neurochemical and behavioral changes occurring in mice lacking the 5-HT transporter (SERT), which is the main target of antidepressant drugs, as well as in those lacking G protein-coupled serotonin receptors (e.g. 5-HT1B, 5-HT1A, and 5-HT4 receptors) are described and evaluated. The importance of KO mice for neurotrophic factors, particularly for brain-derived neurotrophic factor and its high-affinity receptor (R-TrkB), is also addressed. Constitutive KO, tissue specific, or inducible KO mice targeting both 5-HT and brain-derived neurotrophic factor systems may potentially make an important contribution to knowledge of the pathophysiology and treatment of depression.

BDNF gene is a genetic risk factor for schizophrenia and is related to the chlorpromazine-induced extrapyramidal syndrome in the Chinese population

BACKGROUND

Brain-derived neurotrophic factor (BDNF) belongs to a family of the neurotrophin, which plays important roles in the neurodevelopment of dopaminergic-related systems and interacts with meso-limbic dopaminergic systems involved in the therapeutic response to antipsychotics. Functional experiments have suggested that BDNF may be involved in the etiology of schizophrenia.

METHODS AND RESULTS

In this study, we genotyped two important functional polymorphisms in the BDNF gene using a sample of Han Chinese patients consisting of 340 schizophrenic patients and 343 healthy controls. We found a statistical difference in the 232-bp allele distribution of the BDNF gene (GT)n dinucleotide repeat polymorphism between the schizophrenic patients and controls. In early onset patients, the 234-bp allele had a risk role. For the chlorpromazine-induced extrapyramidal syndrome, the 230-bp allele and the 234-bp allele acted in opposite directions, that is, patients with the 230-bp allele of the (GT)n polymorphism exhibited a lower degree of induced extrapyramidal syndrome. Haplotype-based analysis also revealed a very important risk haplotype (P=0.0000226546).

CONCLUSION

These findings suggest that BDNF plays an important role in the susceptibility to schizophrenia and that the (GT)n repeat polymorphism of the BDNF gene may be an independent contributor to the chlorpromazine treatment-sensitive form of schizophrenia.

A genetic-demographic approach reveals male-specific association between survival and tumor necrosis factor (A/G)-308 polymorphism

The (A/G)-308 polymorphism of the tumor necrosis factor alpha gene (TNF) is associated with age-related diseases, but its influence on longevity is controversial. We genotyped for this polymorphism 747 Italian volunteers (401 women and 346 men, age 19-110 years). By applying a genetic-demographic (GD) approach we found that, in men, the survival function of allele A carriers is lower than that of noncarriers at all the ages (p =.044). After defining (by exploiting again demographic information) three age classes, we found that the frequency of men carrying the A allele decreases with age (p =.019), thus confirming the GD analysis results. The same analyses gave negative results in women. Therefore, allele A has a detrimental effect on life expectancy, and this effect is specific to men. A haplotype analysis carried out in men by screening the TNFa, TNFc, and TNFe microsatellite polymorphisms (spanning about 20 kb) confirmed the association of the TNF region with life expectancy.

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.

Interactions between life stressors and susceptibility genes (5-HTTLPR and BDNF) on depression in Korean elders

BACKGROUND

It has been reported that the functional polymorphism in the serotonin transporter gene linked promoter region (5-HTTLPR) modifies the association between stressful life events (SLEs) and depression in child, adolescent, and adult populations. We sought to replicate this finding in elders and, additionally, to test modifying effects of the brain-derived neurotrophic factor (BDNF) val66met polymorphism.

METHODS

In 732 Korean community residents ages 65+, diagnosis of depression (Geriatric Mental State Schedule), information on SLEs, and genotypes for 5-HTTLPR and BDNF val66met were ascertained. Of those without depression at baseline, 521 (88%) were followed up 2.5 years later. Interactions between SLEs and the two genotypes were investigated for both prevalent depression at baseline and incident depression at follow-up.

RESULTS

Significant interactions of SLEs with both 5-HTTLPR and BDNF genotypes were observed on risk of depression after adjustment for age, gender, education, and disability. A significant three-way interaction between 5-HTTLPR, BDNF, and SLEs was also found. The same findings were observed for predictors of incident depression in the prospective analysis.

CONCLUSIONS

These findings suggest that environmental risk of depression is modified by at least two genes and that gene-environment interactions are found even into old age.

Brain-derived neurotrophic factor and its receptor tropomyosin-related kinase B in the mechanism of action of antidepressant therapies

The focus of this review is to critically examine and review the literature on the role of brain-derived neurotrophic factor (BDNF) and its primary receptor, tropomyosin-related kinase B (TrkB), in the actions of pharmacologically diverse antidepressant treatments for depression. This will include a review of the studies on the regulation of BDNF and TrkB by different types of antidepressant drug treatments and animal in models of depression, as well as altered levels of BDNF and TrkB in the blood and postmortem brain of patients with depression. Results from clinical and basic studies have demonstrated that stress and depression decrease BDNF expression and neurogenesis and antidepressant treatment reverses or blocks these effects, leading to the neurotrophic hypothesis of depression. Clinical studies demonstrate an association between BDNF levels and several disorders, including depression, epilepsy, bipolar disorder, Parkinson's and Alzheimer's diseases. Physical activity and diet exert neurotrophic effects and positively modulate BDNF levels. A common single nucleotide polymorphism (SNP) in the BDNF gene, a methionine substitution for valine, is associated with alterations in brain anatomy and memory, but what role it has in clinical disorders is unclear. Findings suggest that early childhood events and adult stress produce neurodegenerative alterations in the brain that can eventually cause breakdown of information processing in the neuronal networks regulating mood. Antidepressant treatments elevate activity-dependent neuronal plasticity by activating BDNF, thereby gradually restoring network function and ultimately mood.

Brain-derived neurotrophic factor (BDNF) gene not associated with antidepressant-induced mania

BACKGROUND

Brain-derived neurotrophic factor (BDNF) plays an important role in the regulation of synaptic plasticity and neurotransmitter release across multiple neurotransmitter systems. Recent studies have suggested that BDNF plays a role in the pathogenesis of bipolar disorder (BPD). Moreover, increasing BDNF production might be one of the mechanisms involved in the alleviation of depression and aggravation of mania in antidepressant treatment.

OBJECTIVES

Thus, we hypothesized that a genetic variant within the BDNF gene might influence susceptibility to antidepressant-induced mania, as has been suggested previously.

METHODS

We performed a case-control study to test for allelic frequency and genotype distribution differences across six BDNF polymorphisms between 27 patients with antidepressant-induced mania (IM+) and 29 patients without antidepressant-induced mania (IM-).

RESULTS

We did not observe any significant difference in either allelic or genotype frequencies between the two groups.

CONCLUSIONS

Our results did not support the BDNF link to mania hypothesis proposed previously. However, a larger sample would allow for greater power to determine smaller effects of the BDNF gene in antidepressant-induced mania.

Association analysis of brain-derived neurotrophic factor gene polymorphisms in asthmatic children

Brain-derived neurotrophic factor (BDNF) has been described to modulate airway hyper-responsiveness and inflammation and was involved in late allergic reaction in asthma and higher levels of circulating BDNF were present in allergic asthmatics. In BDNF gene, Val66Met and C-270T polymorphisms were described. There were, however, very few studies analyzing BDNF gene polymorphisms in asthma. The aim of this study was to analyze the possible relationship between these two polymorphisms in the BDNF gene and asthma. Fifty-six pediatric asthmatic patients were analyzed, aged from 6 to 18. The diagnosis of atopic asthma was based on clinical manifestation, lung function test and increased immunoglobulin E level, and/or positive skin prick tests. The control group consisted of 109 healthy subjects. The polymorphisms were genotyped with the use of polymerase chain reaction-restriction fragment length polymorphism method. We did not observe an association of Val/Met polymorphism and the presence of asthma. However, we observed that Val allele is much more frequent in the male group of asthmatic patients (p = 0.06). For -270C/T polymorphism, we found significant differences between asthmatic patients and the control group (p = 0.041 for genotypes and p = 0.005 for alleles). The results may suggest a relationship between the BDNF gene and asthma and male gender of asthmatic children.

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.

Brain-derived neurotrophic factor and risk of schizophrenia: An association study and meta-analysis

Brain-derived neurotrophic factor (BDNF) is the most widely distributed neurotrophin in the central nervous system (CNS), and performs many biological functions such as neural survival, differentiation, and plasticity. Previous studies have suggested that variants in the BDNF gene increase the risk of schizophrenia. In this study, we genotyped one (GT)n dinucleotide repeat and three SNPs (rs6265, rs2030324, and rs2883187) in a Chinese sample (617 cases and 672 controls). In addition, we performed an updated meta-analysis based on 16 population-based case-control studies examining association between rs6265 and schizophrenia. In single-locus analysis, no significant association was found between BDNF polymorphisms and schizophrenia in our subjects. The meta-analysis based on Asian and Caucasian subjects did not give positive result that rs6265 is associated with schizophrenia. However, haplotype analysis found a common four-locus haplotype is protective against schizophrenia (Case 3.1% vs Control 7%, p=0.0011). Our data provides evidence that BDNF is a susceptibility gene for schizophrenia in Chinese subjects.

BDNF genotype potentially modifying the association between incident stroke and depression

OBJECTIVE

To investigate the role of the brain-derived neurotrophic factor (BDNF) gene val66met polymorphism in the association between stroke and depression.

METHOD

Five hundred community residents aged >65 years without stroke or depression at baseline were re-evaluated after 2 years. Disability (World Health Organization Disability Assessment Schedule, WHODAS II), cognitive function (Mini-Mental State Examination, MMSE), and BDNF genotype were also measured at baseline.

RESULTS

The association between incident stroke and depression was strengthened progressively with increasing numbers of met alleles, and was only significant in subjects with the met/met genotype after adjustment for disability and cognitive function.

CONCLUSION

The BDNF val66met polymorphism may modify the association between stroke and depression.

Brain-derived neurotrophic factor in schizophrenia and its relation with dopamine

The brain-derived neurotrophic factor (BDNF) belongs to the neurotrophins family and has a role in proliferation, differentiation of neurons but also as a neurotransmitter. This neurotrophin has received much attention during the last year in regard of the pathophysiology of schizophrenia. Results of genetic studies conducted in schizophrenia support a role for BDNF in schizophrenia and in brain function associated with the disorder. The changes of BDNF observed in the brain and in the plasma of patients with schizophrenia have generated results that can be interpreted either as a hallmark of the disease or a consequence of antipsychotic drugs. Antipsychotic drugs act by blocking the dopamine transmission at the dopamine D2-like receptors. BDNF controls the expression of one of these D2-like receptors, the dopamine D3 receptor. This raises the hypothesis of a link between cortical area, via BDNF, and the dopamine neurotransmission pathway in schizophrenia and its treatment.

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

The brain-derived neurotrophic factor (BDNF) gene is a candidate gene for influencing the clinical response to treatment with antidepressants. The purpose of this study was to determine the relationship between the Val66Met polymorphism in the BNDF gene and the response to citalopram in a Korean population with major depressive disorder (MDD). Citalopram was administered for 8 weeks to the 83 patients who completed this study. We found that the genotype, allele, and allele-carrier distributions for the Val66Met polymorphism differed significantly between responders (Rp) and nonresponders (Non-Rp). The frequency of M-allele carriers (VM+MM) was higher in Rp than in Non-Rp (chi(2)=8.926, p=0.003, OR=4.375, 95%CI=1.609-11.892), as was the M-allele frequency (chi(2)=6.879, p=0.009, OR=2.500, 95%CI=1.249-5.005). There were also significant differences in the core (p=0.012) and activity (p=0.008) scores. Patients carrying the M-allele had a lower score. Also, patients carrying the M-allele tended to have lower psychic anxiety (p=0.072). The percentage change in the total HAM-D score was higher for M-allele carriers (VM+MM allele) than for noncarriers (p=0.034) after 8 weeks of medication. We found that the genotype, allele, and allele-carrier distributions did not differ significantly between MDD patients and normal controls. These results suggest that the Val66Met polymorphism of BDNF is associated with citalopram efficacy, with M-allele carriers responding better to citalopram treatment. Moreover, the Val66Met polymorphism was correlated with improvements in core, activity, and psychic anxiety symptoms.

Brain-derived neurotrophic factor (BDNF) gene and rapid-cycling bipolar disorder: family-based association study

BACKGROUND

We have previously reported the Val66Met and GT(n) repeat polymorphisms of the brain-derived neurotrophic factor (BDNF) gene to be associated with bipolar disorder. However, these findings have not been replicated consistently.

AIMS

To dissect the association of the BDNF gene with bipolar disorder by examining additional markers at the DNA level and by testing the illness categories of bipolar disorder I and II and rapid cycling.

METHOD

We performed a family-based association study and haplotype analyses with 312 nuclear families using four single nucleotide polymorphisms (SNPs) and the Val66Met and GT(n) repeat polymorphisms.

RESULTS

The SNPs hCV11592756 and rs2049045, the Val66Met and GT(n) were significantly associated with bipolar disorder using transmission disequilibrium analyses (P=0.02, 0.009, 0.001 and 0.008 respectively). The effect atthese markers was mainly driven by the rapid-cycling patients.

CONCLUSIONS

Within bipolar disorder, variation in the BDNF gene appears to predict risk for developing rapid cycling according to DSM-IV. Incorporating this clinical sub-phenotyping into other studies of the BDNF gene may help to resolve some of the inconsistencies reported thus far concerning BDNF and bipolar disorder.

Transmission distortion of BDNF variants to bipolar disorder type I patients from a South American population isolate

Recent reports have implicated polymorphisms in the brain derived neurotrophic factor (BDNF) gene region in the etiology of several psychiatric phenotypes, including bipolar disorder. Significant disease association has been reported for the G allele at SNP rs6265, which encodes for Valine at position 66 of BDNF (Val66Met), an apparently functional variant of this key BDNF. Here we examined a sample of 224 bipolar type I patients and available parents (comprising a total of 212 nuclear families) ascertained in a South American population isolate (Antioquia, Colombia). We tested for transmission distortion to bipolar patients of alleles at the rs6265 polymorphism and at a microsatellite marker 1.3 kb away from this SNP. Significant excess transmission of the rs6265 G allele to cases was observed (chi(2) = 10.77, d.f. = 1, P = 0.001). Two-locus haplotype analysis showed a significant global transmission distortion (chi(2) = 16.059, d.f. = 7, P = 0.025) with an excess transmission of a haplotype comprising the rs6265 G allele and microsatellite allele 227. These results are consistent with previous studies pointing to a role for BDNF in susceptibility to mood disorders.

A complex polymorphic region in the brain-derived neurotrophic factor (BDNF) gene confers susceptibility to bipolar disorder and affects transcriptional activity

Previous studies have suggested that genetic variations in the brain-derived neurotrophic factor (BDNF) gene may be associated with several neuropsychiatric diseases including bipolar disorder. The present study examined a microsatellite polymorphism located approximately 1.0 kb upstream of the translation initiation site of the BDNF gene for novel sequence variations, association with bipolar disorder, and effects on transcriptional activity. Detailed sequencing analysis revealed that this polymorphism is not a simple dinucleotide repeat, but it is highly polymorphic with a complex structure containing three types of dinucleotide repeats, insertion/deletion, and nucleotide substitutions that gives rise to a total of 23 novel allelic variants. We obtained evidence supporting the association between this polymorphic region (designated as BDNF-linked complex polymorphic region (BDNF-LCPR)) and bipolar disorder. One of the major alleles ('A1' allele) was significantly more common in patients than in controls (odds ratio 2.8, 95% confidential interval 1.5-5.3, P=0.001). Furthermore, a luciferase reporter gene assay in rat primary cultured neurons suggests that this risk allele (A1) has a lower-transcription activity, compared to the other alleles. Our results suggest that the BDNF-LCPR is a functional variation that confers susceptibility to bipolar disorder and affects transcriptional activity of the BDNF gene.

Association between the brain-derived neurotrophic factor (BDNF) gene and Schizophrenia in the Chinese population

Brain-derived neurotrophic factor (BDNF) belongs to a family of the neurotrophin which plays important roles in the development of the brain. BDNF has been suggested as a factor that increases the risk of schizophrenia. In this study, we genotyped three single nucleotide polymorphisms (SNPs) in the BDNF gene using a set sample of Han Chinese subjects consisting of 560 schizophrenes and 576 controls. No significant differences were found for either the genotype or allele distribution of analyzed polymorphisms, nor was any gender-specific association found. Thus, our data suggest that the BDNF gene may not be an important factor in susceptibility to schizophrenia.

Brain-derived neurotrophic factor variants are associated with childhood-onset mood disorder: confirmation in a Hungarian sample

Brain-derived neurotrophic factor (BDNF) is a nerve growth factor that has been implicated in the neurobiology of depression. Our group has previously reported an association between a BDNF variant and childhood-onset mood disorder (COMD) in an adult sample from Pittsburgh. We hypothesize that variants at the BDNF locus are associated with COMD. Six BDNF polymorphisms were genotyped in 258 trios having juvenile probands with childhood-onset DSM-IV major depressive or dysthymic disorder. BDNF markers included the (GT)n microsatellite, Val66Met and four other single-nucleotide polymorphisms (SNPs) distributed across the BDNF gene. Family-based association and evolutionary haplotype analysis methods were used. Analysis of linkage disequilibrium (LD) revealed substantial LD among all six polymorphisms. Analyses of the Val66Met polymorphism demonstrated significant overtransmission of the val allele (chi2=7.12, d.f.=1, P=0.0076). Consistent with the pattern of LD, all other SNPs showed significant biased transmission. The (GT)n microsatellite alleles also indicated a trend towards biased transmission (170 bp: Z=2.095, P=0.036). Significant haplotypes involved Val66Met and BDNF2 (P=0.0029). In this Hungarian sample, we found all five BDNF SNPs tested and a haplotype containing the BDNF Val66Met Val allele to be associated with COMD. These results provide evidence that BDNF variants affect liability to juvenile-onset mood disorders, supported by data from two independent samples.

Evidence for a relationship between genetic variants at the brain-derived neurotrophic factor (BDNF) locus and major depression

BACKGROUND

Previous genetic studies investigating a possible involvement of variations at the brain derived neurotrophic factor (BDNF) gene locus in major depressive disorder (MDD), bipolar affective disorder (BPAD), and schizophrenia have provided inconsistent results.

METHODS

We performed single-marker and haplotype analyses using three BDNF polymorphisms in 2,376 individuals (465 MDD, 281 BPAD, 533 schizophrenia, and 1,097 control subjects).

RESULTS

Single-marker analysis did not provide strong evidence for association. Haplotype analysis of marker combination rs988748-(GT)n-rs6265 produced nominally significant associations for all investigated phenotypes (global p values: MDD p = .00006, BPAD p = .0057, schizophrenia p = .016). Association with MDD was the most robust finding and could be replicated in a second German sample of MDD patients and control subjects (p = .0092, uncorrected). Stratification of our schizophrenia sample according to the presence or absence of a lifetime history of depressive symptoms showed that our finding in schizophrenia might be attributable mainly to the presence of depressive symptoms.

CONCLUSIONS

Association studies of genetic variants of the BDNF gene with various psychiatric disorders have been published with reports of associations and nonreplications. Our findings suggest that BDNF may be a susceptibility gene for MDD and schizophrenia-in particular, in a subgroup of patients with schizophrenia with a lifetime history of depressive symptoms.

No association of the brain-derived neurotrophic factor (BDNF) gene C-270T polymorphism with schizophrenia

Brain-derived neurotrophic factor (BDNF) regulates a variety of neuromodulatory processes during development, as well as in adulthood. It has been proposed as a risk factor for schizophrenia. We have investigated a possible association between schizophrenia and the C-270T polymorphism in the brain-derived neurotrophic factor (BDNF) gene in 397 schizophrenic patients and 380 control subjects. The diagnosis of schizophrenia was made for each patient by at least two psychiatrists, using DSM-IV and ICD-10 criteria in structured clinical interviews for DSM-IV Axis I disorders (SCID). No association was found between schizophrenia and the analyzed polymorphism, for either genotype or allele distribution (for genotype: p=0.513, for alleles: p=0.812). Differences were not statistically significant when analyzed separately by sex. For males, the differences for genotype distribution and allele frequency were p=0.078 and p=0.162 respectively and for females: p=0.441 and p=0.315. Thus, our data indicate that variations in the BDNF gene are unlikely to be an important factor in susceptibility to schizophrenia.

Association analysis of brain-derived neurotrophic factor (BDNF) gene Val66Met polymorphism in schizophrenia and bipolar affective disorder

Brain-derived neurotrophic factor (BDNF) has been implicated in the pathogenesis of schizophrenia and bipolar disorder. A functional polymorphism Val66Met of BDNF gene was studied in patients with schizophrenia (n=336), bipolar affective disorder (n=352) and healthy controls (n=375). Consensus diagnosis by at least two psychiatrists, according to DSM-IV and ICD-10 criteria, was made for each patient using a structured clinical interview for DSM-IV Axis I disorders (SCID). No association was found between the studied polymorphism and schizophrenia or bipolar affective disorder either for genotype or allele distribution (for genotype: p=0.210 in schizophrenia, p=0.400 in bipolar disorder; for alleles: p=0.260 in schizophrenia, p=0.406 in bipolar disorder). Results were also not significant when analysed by gender. For males genotype distribution and allele frequency were (respectively): p=0.480 and p=0.312 in schizophrenia, p=0.819 and p=0.673 in bipolar affective disorder. Genotype distribution and allele frequency observed in the female group were: p=0.258 for genotypes, p=0.482 for alleles in schizophrenia; p=0.432 for genotypes, p=0.464 for alleles in bipolar affective disorder. A subgroup of schizophrenic (n=62) and bipolar affective patients (n=28) with early age at onset (18 years or younger) was analysed (p=0.328 for genotypes, p=0.253 for alleles in schizophrenia; p=0.032 for genotypes, p=0.858 for alleles in bipolar affective disorder).

BDNF gene is a risk factor for schizophrenia in a Scottish population

Schizophrenia is a severe psychiatric disease with a strong genetic component. Brain-derived neurotrophic factor (BDNF) has been implicated in the pathogenesis of schizophrenia and bipolar (BP) disorders. The present study has examined two polymorphisms in linkage disequilibrium in the BDNF gene, which have been variously reported as associated with schizophrenia and BP. In our study, 321 probands with a primary diagnosis of schizophrenia or schizoaffective disorder, and 263 with a diagnosis of bipolar affective disorder, were examined together with 350 controls drawn from the same geographical region of Scotland. The val66met single-nucleotide polymorphism (SNP) showed significant (P = 0.005) association for valine (allele G) with schizophrenia but not bipolar disorder. Haplotype analysis of val/met SNP and a dinucleotide repeat polymorphism in the putative promoter region revealed highly significant (P < 1 x 10(-8)) under-representation of the methionine or met-1 haplotype in the schizophrenic but not the BP population. We conclude that, although the val66met polymorphism has been reported to alter gene function, the risk may depend upon the haplotypic background on which the val/met variant is carried.

Neurotrophic factors and the pathophysiology of schizophrenic psychoses

The aim of this review is to summarize the present state of findings on altered neurotrophic factor levels in schizophrenic psychoses, on variations in genes coding for neurotrophic factors, and on the effect of antipsychotic drugs on the expression level of neurotrophic factors. This is a conceptual paper that aims to establish the link between the neuromaldevelopment theory of schizophrenia and neurotrophic factors. An extensive literature review has been done using the Pub Med database, a service of the National Library of Medicine, which includes over 14 million citations for biomedical articles back to the 1950s. The majority of studies discussed in this review support the notion of alterations of neurotrophic factors at the protein and gene level, respectively, and support the hypothesis that these alterations could, at least partially, explain some of the morphological, cytoarchitectural and neurobiochemical abnormalities found in the brain of schizophrenic patients. However, the results are not always conclusive and the clinical significance of these alterations is not fully understood. It is, thus, important to further neurotrophic factor research in order to better understand the etiopathogenesis of schizophrenic psychoses and, thus, potentially develop new treatment strategies urgently needed for patients suffering from these devastating disorders.

Association study of brain-derived neurotrophic factor in adults with a history of childhood onset mood disorder

Brain-derived neurotrophic factor (BDNF) is a nerve growth factor that has antidepressant-like effects in animals. BDNF gene polymorphisms have been associated with bipolar disorder. We tested two genetic polymorphisms of BDNF for their association with childhood-onset mood disorders (COMD) within the context of a case-control design. Two BDNF polymorphisms, a dinucleotide repeat (GT)(n), and a single nucleotide polymorphism (SNP) in the coding region, val66met, were genotyped in 99 adults with a history of COMD and matched psychiatrically healthy controls. A genomic control (GC) method was used to evaluate population substructure. Alleles at (GT)(n) were highly associated with COMD in this sample (chi(2) = 17.8; d.f. = 5; P = 0.0032). The odds of carrying the 168 bp allele were 3.94 times greater for cases than controls (CI = 1.72-9.04). Alleles of val66met were not significantly associated with COMD. GC analysis suggested population substructure was not a confounder of association. Analysis of haplotypes, in which (GT)(n) was treated as a binary variable (long vs. short alleles), provided significant evidence that the haplotype val/short contributes to liability to COMD. The BDNF (GT)(n) marker and the val/short haplotype are associated with COMD in this sample, in accordance with the previously described neurotrophic hypothesis of depression and some previous studies of association for bipolar disorder and neuroticism.

Clinical features of psychotic disorders and polymorphisms in HT2A, DRD2, DRD4, SLC6A3 (DAT1), and BDNF: a family based association study

Schizophrenia is clinically heterogeneous and multidimensional, but it is not known whether this is due to etiological heterogeneity. Previous studies have not consistently reported association between any specific polymorphisms and clinical features of schizophrenia, and have primarily used case-control designs. We tested for the presence of association between clinical features and polymorphisms in the genes for the serotonin 2A receptor (HT2A), dopamine receptor types 2 and 4, dopamine transporter (SLC6A3), and brain-derived neurotrophic factor (BDNF). Two hundred seventy pedigrees were ascertained on the basis of having two or more members with schizophrenia or poor outcome schizoaffective disorder. Diagnoses were made using a structured interview based on the SCID. All patients were rated on the major symptoms of schizophrenia scale (MSSS), integrating clinical and course features throughout the course of illness. Factor analysis revealed positive, negative, and affective symptom factors. The program QTDT was used to implement a family-based test of association for quantitative traits, controlling for age and sex. We found suggestive evidence of association between the His452Tyr polymorphism in HT2A and affective symptoms (P = 0.02), the 172-bp allele of BDNF and negative symptoms (P = 0.04), and the 480-bp allele in SLC6A3 (= DAT1) and negative symptoms (P = 0.04). As total of 19 alleles were tested, we cannot rule out false positives. However, given prior evidence of involvement of the proteins encoded by these genes in psychopathology, our results suggest that more attention should be focused on the impact of these alleles on clinical features of schizophrenia.

Polymorphism of the brain-derived neurotrophic factor gene and performance on a cognitive prefrontal test in bipolar patients

OBJECTIVES

The aim of the study was to test a possible association between the Val66Met polymorphism of the brain-derived neurotrophic factor (BDNF) gene and performance on a neurocognitive test, the Wisconsin Card Sorting Test (WCST), in bipolar patients.

METHODS

Fifty-four bipolar patients were studied, 18 male and 36 female, aged 18-72 (mean 46 years). The number of perseverative errors (WCST-P), non-perseverative errors (WCST-NP), completed corrected categories (WCST-CC), conceptual level responses (WCST-%CONC) and set to the first category (WCST-1st CAT) were measured in relation to the Val66Met genotypes of BDNF.

RESULTS

The percentages of subjects with Val/Val, Val/Met and Met/Met genotypes were respectively 81.5, 16.7 and 1.8%. Subjects with Val/Val and Val/Met genotypes did not differ on clinical factors except for the age of onset of the illness, which was earlier in Val/Val than Val/Met genotype (27 years versus 38 years). The performance in all domains of WCST was significantly better in subjects with Val/Val BDNF genotype compared with Val/Met genotype.

CONCLUSIONS

The results suggest a role of BDNF in prefrontal cognitive function in bipolar illness. The tests of prefrontal cognition may be considered as endophenotypic markers in bipolar illness.

The brain-derived neurotrophic factor gene confers susceptibility to bipolar disorder: evidence from a family-based association study

Bipolar disorder (BP) is a severe psychiatric disease, with a strong genetic component, that affects 1% of the population worldwide and is characterized by recurrent episodes of mania and depression. Brain-derived neurotrophic factor (BDNF) has been implicated in the pathogenesis of mood disorders, and the aim of the present study was to test for the presence of linkage disequilibrium between two polymorphisms in the BDNF gene and BP in 283 nuclear families. Family-based association test (FBAT) results for the dinucleotide repeat (GT)(N) polymorphism at position -1040 bp showed that allele A3 was preferentially transmitted to the affected individuals (Z=2.035 and P=.042). FBAT results for the val66met SNP showed a significant association for allele G (Z=3.415 and P=.00064). Transmission/disequilibrium test (TDT) haplotype analysis showed a significant result for the 3-G allele combination (P=.000394), suggesting that a DNA variant in the vicinity of the BDNF locus confers susceptibility to BP. Given that there is no direct evidence that either of the polymorphisms we examined alters function, it is unlikely that the actual risk-conferring allele is from these two sites. Rather, the causative site is likely nearby and in linkage disequilibrium with the 3-G haplotype that we have identified.

A novel WT1 gene mutation associated with wilms' tumor and congenital male genitourinary malformation

WT1 is located on the short arm of human chromosome 11 and consists of 10 coding exons. Mutations of this gene have been reported to be the cause of Wilms' tumor, congenital male genitourinary malformations, and/or renal disorders. We describe here a novel WT1 gene mutation, i.e. a point mutation at intron 7 (+2) in both the tumor and the germline cells of a patient with Wilms' tumor and congenital male genitourinary malformation, but without renal disorder. The position of the mutation is at a splice donor site of intron 7, which causes the splicing out of exon 7 and generates a truncated protein. This type of mutation in the WT1 zinc finger domain has not been reported before. The mutation is of paternal origin and is heterozygous in the germline cells. In the tumor cells, however, the maternal allele is largely lost, from 11p12 to 11p15, which results in maternal loss of heterozygosity. These results, together with the data from previous reports, suggest that WT1 may function in gonadogenesis, nephrogenesis, and Wilms' tumor tumorigenesis.

Brain derived neurotrophic factor (BDNF) gene variants association with age at onset and therapeutic response in schizophrenia

Schizophrenia is a heterogeneous disease involving genetic and environmental factors. The frequency of structural brain abnormalities or physical anomalies supports a neurodevelopmental etiology, especially in early onset schizophrenia. Brain-Derived-Neurotrophic-Factor (BDNF) is involved in the neurodevelopment of dopaminergic (DA)-related systems and interacts with the meso-limbic DA systems, involved in the therapeutic response to antipsychotic drugs and substance abuse. In addition, BDNF promotes and maintains dopamine D3 receptor (DRD3) expression. In a French Caucasian population, we found no statistical difference in allele or genotype distribution of the BDNF gene dinucleotide repeat polymorphism (166-174 bp) between the whole group of schizophrenic patients and controls. By contrast, an excess of the 172-176 bp alleles was found in patients with late onset, in neuroleptic-responding patients and in non-substance-abusing patients. BDNF gene variants thus appear to be associated with developmental features of schizophrenia. In addition, this association with good treatment responding was independent from the association found with the DRD3 Ball gene polymorphism in the same population. These results suggest an independent contribution of each gene to a treatment-sensitive form of schizophrenia.