The study of BDNF Val66Met polymorphism in Chinese schizophrenic patients

Genetic predisposition of BDNF (rs6265) gene is susceptible to Schizophrenia: A prospective study and updated meta-analysis

INTRODUCTION

Genetic polymorphism in the BDNF gene has been found to cause neuronal alterations and has been identified as a causal factor for many neuropsychiatric disorders. Therefore, various neurological case-control studies and meta-analyses have been conducted to find the possible link between BDNF and susceptibility to schizophrenia.

METHOD

This meta-analysis gathered data from 25 case-control studies including a total of 8384 patients with schizophrenia and 8821 controls in order to identify the relationship between the rs6265 single nucleotide polymorphism and the disease, evaluating the combined odds ratio and 95% confidence intervals under 5 different genetic models. Validation followed the "Leave one out" method, and we used the Egger test and Begg's funnel plot to identify publication bias.

RESULTS

Research into the rs6265 (G/A) polymorphism revealed a non-significant association with schizophrenia in all 5 genetic models; in the subgroup analysis, no association was found between white and Asian populations, with a p value>.05.

CONCLUSIONS

Overall, the updated meta-analysis revealed that rs6265 exonic polymorphisms do not increase susceptibility to this disease. However, to better understand the pathogenesis of the disease, there is a need for further case-control studies into the BDNF polymorphism including larger sample sizes and different ethnic groups.

Association Study of BDNF, SLC6A4, and FTO Genetic Variants with Schizophrenia Spectrum Disorders

Schizophrenia spectrum disorders (patients with a diagnosis of schizophrenia, schizotypal, and delusional disorders: F20-F29 according to International Classification of Diseases 10th revision (ICD-10)) are considered highly heritable heterogeneous psychiatric conditions. Their pathophysiology is multifactorial with involved dysregulated serotonergic neurotransmission and synaptic plasticity. The present study aimed to evaluate the association of SLC6A4 (5-HTTLPR), FTO (rs9939609), and BDNF (rs6265, rs962369) polymorphisms with schizophrenia spectrum disorders in Slovak patients. We analyzed the genotypes of 150 patients with schizophrenia, schizotypal, and delusional disorders and compared them with genotypes from 178 healthy volunteers. We have found a marginally protective effect of LS + SS genotypes of 5-HTTLPR variant of the serotonin transporter SLC6A4 gene against the development of schizophrenia spectrum disorders, but the result failed to remain significant after Bonferroni correction. Similarly, we have not proven any significant association between other selected genetic variants and schizophrenia and related disorders. Studies including a higher number of subjects are warranted to reliably confirm the presence or absence of the studied associations.

BDNF affects the mediating effect of negative symptoms on the relationship between age of onset and cognition in patients with chronic schizophrenia

The age of onset of schizophrenia is related to variability in cognitive function and clinical characters, and negative symptoms and cognitive function share similar features that could be closely connected. Alterations in brain-derived neurotrophic factor (BDNF) expression and the Val66Met (rs6562) polymorphism are involved in the pathogenesis of the disease, but few studies have explored its influence on the associations of age of onset, cognitive function and clinical symptoms in schizophrenia. The clinical symptoms of a total of 573 patients with chronic schizophrenia were assessed by using the Positive and Negative Syndrome Scale (PANSS). Cognitive performance was assessed by the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). The serum BDNF level and Val66Met polymorphism were measured after the assessment. Our results showed the following: (1) patients with an earlier age of onset exhibited more negative symptoms and cognitive deficits, as well as lower levels of serum BDNF; (2) negative symptoms and cognitive function showed negative and positive correlations with age of onset, respectively, and worse cognitive function was associated with a high level of negative symptoms and a low level of serum BDNF; and (3) the moderated mediation analyses indicated that negative symptoms partially mediated the relationship between age of onset and cognitive deficits, which was moderated by serum BDNF. The mediating effect of negative symptoms exhibited a Met allele dose-dependent tendency. These results indicate that age of onset, cognitive function, and clinical symptoms of schizophrenia exhibit different relationships under different serum BDNF levels and BDNF Val66met polymorphisms.

BDNF and nicotine dependence: associations and potential mechanisms

Smoking is the leading preventable cause of death worldwide and tobacco addiction has become a serious public health problem. Nicotine is the main addictive component of tobacco, and the majority of people that smoke regularly develop nicotine dependence. Nicotine addiction is deemed to be a chronic mental disorder. Although it is well known that nicotine binds to the nicotinic acetylcholine receptors (nAChRs) and activates the mesolimbic dopaminergic system (MDS) to generate the pleasant and rewarding effects, the molecular mechanisms of nicotine addiction are not fully understood. Brain-derived neurotrophic factor (BDNF) is the most prevalent growth factor in the brain, which regulates neuron survival, differentiation, and synaptic plasticity, mainly through binding to the high affinity receptor tyrosine kinase receptor B (TrkB). BDNF gene polymorphisms are associated with nicotine dependence and blood BDNF levels are altered in smokers. In this review, we discussed the effects of nicotine on BDNF expression in the brain and summarized the underlying signaling pathways, which further indicated BDNF as a key regulator in nicotine dependence. Further studies that aim to understand the neurobiological mechanism of BDNF in nicotine addcition would provide a valuable reference for quitting smoking and developing the treatment of other addictive substances.

Effects of smoking on cognition and BDNF levels in a male Chinese population: relationship with BDNF Val66Met polymorphism

Recent studies demonstrate that brain-derived neurotrophic factor (BDNF) might be associated with nicotine addiction, and circulating BDNF is a biomarker of memory and general cognitive function. Moreover, studies suggest that a functional polymorphism of the BDNF Val66Met may mediate hippocampal-dependent cognitive functions. We aimed to explore the relationships between smoking, cognitive performance and BDNF in a normal Chinese Han population. We recruited 628 male healthy subjects, inducing 322 smokers and 306 nonsmokers, and genotyped them the BDNF Val66Met polymorphism. Of these, we assessed 114 smokers and 98 nonsmokers on the repeatable battery for the assessment of neuropsychological status (RBANS), and 103 smokers and 89 nonsmokers on serum BDNF levels. Smokers scored lower than the nonsmokers on RBANS total score (p = 0.002), immediate memory (p = 0.003) and delayed memory (p = 0.021). BDNF levels among the smokers who were Val allele carriers were correlated with the degree of cognitive impairments, especially attention, as well as with the carbon monoxide concentrations. Our findings suggest that smoking is associated with cognitive impairment in a male Chinese Han population. The association between higher BDNF levels and cognitive impairment, mainly attention in smokers appears to be dependent on the BDNF Val66Met polymorphism.

Redox dysregulation, immuno-inflammatory alterations and genetic variants of BDNF and MMP-9 in schizophrenia: Pathophysiological and phenotypic implications

BACKGROUND

Although a clear mechanism underlying the pathophysiology of schizophrenia (SZ) remains elusive, oxidative stress, inflammatory syndrome and immune activation have become an attractive hypothesis for explaining the pathophysiology of SZ. Data from prior studies on the role of matrix metalloproteinase 9 (MMP-9) and brain-derived neurotrophic factor (BDNF) single nucleotide polymorphisms (SNPs) in SZ are contradictory. We aimed to investigate whether oxidative stress, inflammatory and immune activation markers as well as MMP-9 levels may be implicated in SZ pathogenesis. The association of MMP-9 and BDNF SNPs with the clinical expression of SZ was examined.

SUBJECTS AND METHODS

Ninety-four subjects were recruited, including 44 SZ patients and 50 healthy controls. Serum levels of thiobarbituric acid reactive substances (TBARS), protein carbonyl content (PCC), nitrite, C-reactive protein (CRP), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), Beta-2 microglobulin (Β2M), complement component 3 (C3), C4 and MMP-9 were measured. The MMP-9 -1562C>T and BDNF196G>A SNPs were genotyped using polymerase chain reaction-restriction fragment length polymorphism assay. Psychopathology was assessed using the positive and negative syndrome scale (PANSS).

RESULTS

SZ patients showed significantly higher TBARS, PCC, nitrite, CRP, IL-6, TNF-α, Β2M, C3 and MMP-9 levels than controls. In distinguishing SZ patients from healthy controls, CRP and MMP-9 yielded similar discriminatory performance, and both perform better than IL-6, Β2M, C3, nitrite, TBARS, PCC, TNF-α and C4. The MMP-9 -1562C>T SNP genotypes distribution didn't differ significantly between controls and SZ patients. As compared to controls, SZ patients harbor a significantly higher frequency of the BDNF196GG genotype and a lower frequency of the BDNF196GA/AA genotype. Patients carrying the MMP-9 -1562CC or BDNF196GG genotype revealed a significantly higher PANSS than those carrying MMP-9 -1562CT/TT or BDNF196GA/AA genotype. Male gender and the MMP-9 -1562CC genotype were identified as independent predictive factors for higher PANSS.

CONCLUSIONS

Redox dysregulation and alterations in the immuno-inflammatory pathways are major culprits in the pathogenesis of SZ. MMP-9 and BDNF SNPs are associated with the clinical phenotype of SZ and, thus, may be a useful marker predicting the phenotypic expression and prognosis of SZ patients.

Theranostic Biomarkers for Schizophrenia

Schizophrenia is a highly heritable, chronic, severe, disabling neurodevelopmental brain disorder with a heterogeneous genetic and neurobiological background, which is still poorly understood. To allow better diagnostic procedures and therapeutic strategies in schizophrenia patients, use of easy accessible biomarkers is suggested. The most frequently used biomarkers in schizophrenia are those associated with the neuroimmune and neuroendocrine system, metabolism, different neurotransmitter systems and neurotrophic factors. However, there are still no validated and reliable biomarkers in clinical use for schizophrenia. This review will address potential biomarkers in schizophrenia. It will discuss biomarkers in schizophrenia and propose the use of specific blood-based panels that will include a set of markers associated with immune processes, metabolic disorders, and neuroendocrine/neurotrophin/neurotransmitter alterations. The combination of different markers, or complex multi-marker panels, might help in the discrimination of patients with different underlying pathologies and in the better classification of the more homogenous groups. Therefore, the development of the diagnostic, prognostic and theranostic biomarkers is an urgent and an unmet need in psychiatry, with the aim of improving diagnosis, therapy monitoring, prediction of treatment outcome and focus on the personal medicine approach in order to improve the quality of life in patients with schizophrenia and decrease health costs worldwide.

Association of the BDNF Val66Met polymorphism with BMI in chronic schizophrenic patients and healthy controls

Several lines of evidence suggest that a functional variant of the brain-derived neurotrophic factor gene (BDNF Val66Met) correlates with a number of eating disorders. Studies have also shown that the BDNF Val66Met polymorphism was associated with weight gain in patients with schizophrenia on long-term antipsychotic treatment. This study aimed to determine whether there was a relationship between the BDNF Val66Met polymorphism and BMI values in patients with chronic schizophrenia. We compared 308 Han Chinese patients with schizophrenia on long-term antipsychotic medication with 304 healthy normal controls on BDNF polymorphism. Body weight and BMI were measured before breakfast on the day blood samples were taken. The symptomatology of schizophrenia was assessed using the Positive and Negative Syndrome Scale. The results showed that the BDNF Val66Met polymorphism was associated with the BMI value, with genotype having a strong effect on the mean BMI value in male but not in female patients. Our results suggest that variation in the BDNF gene may be a risk factor for weight gain in male patients with schizophrenia on long-term antipsychotic treatment.

Gender-specific Associations of the Brain-derived Neurotrophic Factor Val66Met Polymorphism with Neurocognitive and Clinical Features in Schizophrenia

Objective

To explore associations of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism with cognitive functioning and psychopathology in patients with schizophrenia.

Methods

We included 133 subjects meeting the DSM-IV criteria for schizophrenia who were in the post-acute stage of the disease. BDNF Val66Met genotypes were identified via polymerase chain reaction. The computerized neurocognitive function battery, Positive and Negative Syndrome Scale (PANSS), Calgary Depression Scale for Schizophrenia (CDSS), Social and Occupational Functioning Scale (SOFAS), and the Subjective Well-being under Neuroleptic Treatment (SWN-K) were administered. Gender-stratified sub-analysis was also conducted to identify gender-specific patterns in the findings.

Results

In male patients, no significant difference in any measure by BDNF genotype was evident. In female patients, scores on the CDSS and total PANSS and all subscales were significantly higher in valine (Val) carriers. In addition, scores on the SOFAS and SWN-K were significantly lower in Val carriers. In terms of neurocognitive measures, female patients with the Val allele had significantly poorer reaction times and fewer correct responses on the Continuous Performance Test (CPT) and the Trail Making Test (Parts A and B). After adjustment of PANSS total scores and log-transformed CDSS scores, CPT outcomes were significantly poorer in female patients with than in those without the Val allele.

Conclusion

Gender-specific associations of the Val allele with poor neurocognitive function and more severe psychopathology were evident. Further studies are required to explore the mechanisms of these differences and the potential utility of the BDNF genotype as a predictor of outcome in patients with schizophrenia.

A Genome-Wide Association Study in isolated populations reveals new genes associated to common food likings

Food preferences are the first factor driving food choice and thus nutrition. They involve numerous different senses such as taste and olfaction as well as various other factors such as personal experiences and hedonistic aspects. Although it is clear that several of these have a genetic basis, up to now studies have focused mostly on the effects of polymorphisms of taste receptor genes. Therefore, we have carried out one of the first large scale (4611 individuals) GWAS on food likings assessed for 20 specific food likings belonging to 4 different categories (vegetables, fatty, dairy and bitter). A two-step meta-analysis using three different isolated populations from Italy for the discovery step and two populations from The Netherlands and Central Asia for replication, revealed 15 independent genome-wide significant loci (p < 5 × 10(-8)) for 12 different foods. None of the identified genes coded for either taste or olfactory receptors suggesting that genetics impacts in determining food likings in a much broader way than simple differences in taste perception. These results represent a further step in uncovering the genes that underlie liking of common foods that in the end will greatly help understanding the genetics of human nutrition in general.

BDNF polymorphisms are associated with schizophrenia onset and positive symptoms

Numerous studies have showed that brain-derived neurotrophic factor (BDNF) may be involved in the pathogenesis and pathophysiology of schizophrenia. The purposes of this study were to investigate the potential association of BDNF gene polymorphisms with susceptibility to schizophrenia and the psychopathological symptoms in patients with schizophrenia in a Han Chinese population. Four polymorphisms (rs6265, rs12273539, rs10835210 and rs2030324) of the BDNF gene were analyzed in a case-control study of 1887 Han Chinese individuals (844 patients and 1043 controls). We assessed 825 patients for psychopathology using the Positive and Negative Syndrome Scale. In single marker analyses the BDNF rs10835210 mutant A allele was significantly associated with schizophrenia. Haplotype analyses revealed higher frequencies of haplotypes containing the mutant A allele of the rs10835210 in schizophrenia than controls. We also found that this polymorphism rs10835210 was associated with positive symptoms, and the patients carrying the mutational allele A showed more positive symptoms. These findings suggest the role of these BDNF gene variants in both susceptibility to schizophrenia and in clinical symptom severity.

The BDNF gene Val66Met polymorphism as a modifier of psychiatric disorder susceptibility: progress and controversy

Brain-derived neurotrophic factor (BDNF) has a primary role in neuronal development, differentiation and plasticity in both the developing and adult brain. A single-nucleotide polymorphism in the proregion of BDNF, termed the Val66Met polymorphism, results in deficient subcellular translocation and activity-dependent secretion of BDNF, and has been associated with impaired neurocognitive function in healthy adults and in the incidence and clinical features of several psychiatric disorders. Research investigating the Val66Met polymorphism has increased markedly in the past decade, and a gap in integration exists between and within academic subfields interested in the effects of this variant. Here we comprehensively review the role and relevance of the Val66Met polymorphism in psychiatric disorders, with emphasis on suicidal behavior and anxiety, eating, mood and psychotic disorders. The cognitive and molecular neuroscience of the Val66Met polymorphism is also concisely reviewed to illustrate the effects of this genetic variant in healthy controls, and is complemented by a commentary on the behavioral neuroscience of BDNF and the Val66Met polymorphism where relevant to specific disorders. Lastly, a number of controversies and unresolved issues, including small effect sizes, sampling of allele inheritance but not genotype and putative ethnicity-specific effects of the Val66Met polymorphism, are also discussed to direct future research.

Influence of NRGN rs12807809 polymorphism on symptom severity in individuals with schizophrenia in the Han population but not the Zhuang population of south China

BACKGROUND

NRGN is one of the most promising candidate genes for schizophrenia based on function and position. Therefore, this study aimed to examine the genetic association of this polymorphism with schizophrenia in the Zhuang and Han populations of south China. Subjects and methods A total of 282 patients (188 Han and 94 Zhuang) and 282 healthy subjects (188 Han and 94 Zhuang) were recruited. Of these, 246 schizophrenia patients underwent an assessment of psychotic symptoms using the Positive and Negative Syndrome Scale (PANSS). A TaqMan genotyping assay method was used to determine the genotypes.

RESULTS

We did not find a significant association of rs12807809 polymorphism with schizophrenia in the total pooled samples, or in the separate ethnic groups. However, in Han schizophrenia patients, quantitative data analyses showed that the CC genotype of the rs12807809 polymorphism was associated with PANSS aggression subscale score and activation subscale score. Furthermore, carriers of the C allele of rs12807809 polymorphism among Han schizophrenia patients had higher scores of general, activation, depression, aggression, and global symptoms than the T allele carriers.

CONCLUSION

In conclusion rs12807809 polymorphism may not contribute to the risk of schizophrenia but influence the clinical symptoms of schizophrenia in the Han population.

Brain-Derived Neurotrophic Factor Gene Val66Met Polymorphism and Risk of Schizophrenia: A Meta-analysis of Case-Control Studies

According to evidences from previous family and association studies, it has been claimed that genetic factors are involved in the neuropathogenesis of Schizophrenia disorder. Whether the Val66Met variant of brain-derived neurotrophic factor (BDNF) gene plays any roles in the pathogenesis of this syndrome or could be a potential biomarker for prognosis of this disorder has been a long-standing controversial issue. We performed a meta-analysis restricted to case-control studies and searched Pubmed, PsychInfo, and Google scholar using keywords including 'association,' 'Val66Met,' 'BDNF,' and 'schizophrenia' published up to May 1, 2015. A total of 39 studies for schizophrenia were combined by fixed- and random-effects models. The pooled results from the schizophrenia sample indicated no significant evidence for the association of Val/Val and Val/Met genotypes of BDNF gene with schizophrenia, but it was observed that there is an association between Met/Met polymorphism and schizophrenia in Asian, European, and Chinese populations, this means that the risk of schizophrenia in Asian, European, and Chinese populations with Met/Met genotype is, respectively, 9, 26, and 9%. There was a significant association between BDNF Val66Met polymorphism and schizophrenia in our meta-analysis study. We cannot rule out the possibility that other polymorphisms in the BDNF gene are involved in the pathophysiology of schizophrenia. In addition, more studies should be conducted on the polymorphisms in other genes to elucidate their possible roles in schizophrenia.

Smoking and BDNF Val66Met polymorphism in male schizophrenia: a case-control study

Some recent studies show an association between a functional polymorphism of BDNF gene (Val66Met) and the susceptibility to nicotine dependence and we hypothesized that this polymorphism was associated with smoking in both schizophrenia patients and healthy controls. The BDNF Val66Met gene polymorphism was genotyped in 690 chronic male schizophrenia patients (smoker/nonsmoker = 522/169) and 628 male controls (smoker/nonsmoker = 322/306) using a case-control design. Nicotine dependence (ND) was assessed by the cigarettes smoked per day (CPD), the Heaviness of Smoking Index (HSI), and the Fagerstrom Test for ND (FTND). Patients also were rated on the Positive and Negative Syndrome Scale (PANSS). The results showed no significant differences in BDNF Val66Met genotype and allele distributions between the patients and healthy controls or between smokers and nonsmokers in either patients or healthy controls alone. In patient groups, however, the smokers with the Met allele had significantly higher HSI scores (Met/Met: 2.8 ± 1.7 vs. Met/Val: 2.2 ± 1.7 vs. Val/Val: 2.0 ± 1.6, p < 0.01) and a trend toward a significantly higher FTND score (p = 0.09) than those with the Val/Val genotype. In addition, the smokers showed significantly lower PANSS negative symptom and total scores, longer duration of illness and more hospitalizations (all p < 0.05). In the control group, the smokers with the Met allele started smoking significantly earlier than those with the Val/Val genotype (both p < 0.05). These results suggest that the BDNF Val66Met polymorphism may affect a smoker's response to nicotine in both schizophrenia and healthy controls from a Chinese Han population, but with differential effects in different aspects of smoking behaviors.

Research in China on the molecular genetics of schizophrenia

Schizophrenia is a complex disease caused by genetic and environmental factors with a global heritability of more than 80%. By the end of the 1970s, Chinese scientists reported a heritability of schizophrenia of 82.9% in the Chinese Han population. Continuous improvements in research techniques and the recruitment of larger samples have made it possible for Chinese scientists to identify a number of candidate susceptibility genes for schizophrenia. This article reviews the results in genetic research of schizophrenia by Chinese scientists over the last five decades

BDNF Val66Met variants and brain volume changes in non-affective psychosis patients and healthy controls: a 3 year follow-up study

INTRODUCTION

Functional gene polymorphisms modulating neuroplasticity might mediate brain longitudinal structural changes in schizophrenia. The present study aimed to explore possible effects of BDNF Val66Met polymorphism variations on progressive structural brain changes after 3 years from the first episode of psychosis.

METHOD

Patients were part of a large epidemiological and longitudinal intervention program of first-episode psychosis, carried out at the University Hospital Marqués de Valdecilla, Cantabria, Spain. Eighty first-episode patients and 54 healthy controls were included in the final analyses. Brain magnetic resonance imaging (baseline and 3-year follow-up) and BDNF genotype, and clinical and functional outcome were investigated.

RESULTS

We did not detect significant association between brain changes and BDNF Val66Met polymorphism variations in patients and controls (all p>0.060). At baseline, there were no significant associations between brain anomalies and BDNF genotype. Functional deficits were similar in Met-carrier and Val homozygote patients after 3-year follow-up (X(2) = 0.66; p = 0.564); there was no relationship between significant volume change across time and functional outcome. Otherwise, Met-carrier controls had significant high rates of alcohol-consumption (p = 0.019) compared to Val homozygote controls.

CONCLUSION

Our findings do not support the notion that BDNF genotype variations may mediate brain macroscopic morphological changes across time.

BDNF deficiency and young-adult methamphetamine induce sex-specific effects on prepulse inhibition regulation

Brain-derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of schizophrenia, yet its role in the development of specific symptoms is unclear. Methamphetamine (METH) users have an increased risk of psychosis and schizophrenia, and METH-treated animals have been used extensively as a model to study the positive symptoms of schizophrenia. We investigated whether METH treatment in BDNF heterozygous (HET) mutant mice has cumulative effects on sensorimotor gating, including the disruptive effects of psychotropic drugs. BDNF HETs and wildtype (WT) littermates were treated during young adulthood with METH and, following a 2-week break, prepulse inhibition (PPI) was examined. At baseline, BDNF HETs showed reduced PPI compared to WT mice irrespective of METH pre-treatment. An acute challenge with amphetamine (AMPH) disrupted PPI but male BDNF HETs were more sensitive to this effect, irrespective of METH pre-treatment. In contrast, female mice treated with METH were less sensitive to the disruptive effects of AMPH, and there were no effects of BDNF genotype. Similar changes were not observed in the response to an acute apomorphine (APO) or MK-801 challenge. These results show that genetically-induced reduction of BDNF caused changes in a behavioral endophenotype relevant to the positive symptoms of schizophrenia. However, major sex differences were observed in the effects of a psychotropic drug challenge on this behavior. These findings suggest sex differences in the effects of BDNF depletion and METH treatment on the monoamine signaling pathways that regulate PPI. Given that these same pathways are thought to contribute to the expression of positive symptoms in schizophrenia, this work suggests that there may be significant sex differences in the pathophysiology underlying these symptoms. Elucidating these sex differences may be important for our understanding of the neurobiology of schizophrenia and developing better treatments strategies for the disorder.

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.

Cognitive and serum BDNF correlates of BDNF Val66Met gene polymorphism in patients with schizophrenia and normal controls

Studies suggest that a functional polymorphism of the brain-derived neurotrophic factor gene (BDNF Val66Met) may mediate hippocampal-dependent cognitive functions. A few studies have reported its role in cognitive deficits in schizophrenia including its association with peripheral BDNF levels as a mediator of these cognitive deficits. We assessed 657 schizophrenic inpatients and 445 healthy controls on the repeatable battery for the assessment of neuropsychological status (RBANS), the presence of the BDNF Val66Met polymorphism and serum BDNF levels. We assessed patient psychopathology using the Positive and Negative Syndrome Scale. We showed that visuospatial/constructional abilities significantly differed by genotype but not genotype × diagnosis, and the Val allele was associated with better visuospatial/constructional performance in both schizophrenic patients and healthy controls. Attention performance showed a significant genotype by diagnosis effect. Met allele-associated attention impairment was specific to schizophrenic patients and not shown in healthy controls. In the patient group, partial correlation analysis showed a significant positive correlation between serum BDNF and the RBANS total score. Furthermore, the RBANS total score showed a statistically significant BDNF level × genotype interaction. We demonstrated an association between the BDNF Met variant and poor visuospatial/constructional performance. Furthermore, the BDNF Met variant may be specific to attentional decrements in schizophrenic patients. The association between decreased BDNF serum levels and cognitive impairment in schizophrenia is dependent on the BDNF Val66Met polymorphism.

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.

Association study between BDNF C-281A polymorphism and paranoid schizophrenia in Polish population

Brain-derived neurotrophic factor (BDNF) is one of the candidate genes for schizophrenia. Polymorphism C-281A (rs28383487) in BDNF gene leads to the reduction of promoter activity in the hippocampal neurons in vitro. To our knowledge, this is the first study to examine the influence of alleles and genotypes of BDNF C-281A polymorphism on development, as well as the clinical course (age of onset, suicidal behaviour and psychopathology) of paranoid schizophrenia. The psychopathology was assessed using the Positive and Negative Syndrome Scale (PANSS) as subscale scores and also single-item scores. We have also performed the haplotype analysis with val66met BDNF polymorphism, which is known to be involved in the pathogenesis of schizophrenia. We have not found significant differences in the distribution of genotypes and alleles between schizophrenic patients and controls in both the overall analysis, as well as sex stratified. Also, we have not shown statistically significant differences between genotype groups and PANSS scale. However, an association between C-281A polymorphism and time of the first episode of paranoid schizophrenia was revealed. Genotype C/A had been connected with later age of onset of paranoid schizophrenia in men but not in women (p < 0.01). The C-281A and val66met polymorphisms have been in a strong linkage disequilibrium (D' = 0.9875; p < 0.05). The haplotype analysis has shown a tendency to a significantly lower frequency of the Met-C haplotype in the schizophrenia group compared to the controls.

Brain derived neurotrophic factor Val66Met polymorphism and psychotic symptoms in Alzheimer's disease

OBJECTIVE

Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative disorder with a high prevalence. Since behavioral disturbances, such as psychotic symptoms, represent a key feature of AD, genes related to dopamine, serotonin and brain derived neurotrophic factor (BDNF), are considered as candidate genes for AD. BDNF is a neurotrophin that regulates neurodevelopment, neuroplasticity, and neuronal functions. BDNF is involved in the etiopathogenesis of psychiatric and neurodegenerative disorders. A single base pair polymorphism (BDNF Val66Met) was reported to be associated with AD and/or schizophrenia, as well as other psychoses, although some studies failed to replicate these findings. The aim of the study was to evaluate the association between BDNF Val66Met variants and AD, as well as onset of AD or presence of psychotic symptoms in AD.

METHOD

BDNF Val66Met was analyzed in 211 patients with AD and in 402 aged healthy control subjects. All subjects were ethnically homogenous Caucasians from Croatia, and were subdivided according to the gender, onset of AD, and presence of psychotic symptoms. A χ(2) test, with Bonferroni correction and standardized residuals were used to evaluate the data.

RESULTS

Distribution of the BDNF Val66Met genotypes differed significantly between male and female AD patients with or without psychotic symptoms. This difference was due to the significant contribution of the Met/Val genotype and the combined Met/Met and Met/Val genotypes between psychotic and non-psychotic symptoms in male, but not in female patients with AD. The frequency of the gene variants of the BDNF Val66Met did not differ significantly among male and female patients with AD and control subjects, or between male and female patients with early or late onset AD. There were significant sex related differences in age, duration of illness and scores of dementia between patients with AD.

CONCLUSION

Our male patients were younger, had shorter duration of illness, and had less severe dementia and higher cognitive performance than female AD patients. The gene variants of the BDNF Val66Met polymorphism were significantly associated with the presence of psychotic symptoms in male, but not in female patients with AD. The results had adequate statistical power to suggest that BDNF Val66Met was not related to susceptibility to AD or the onset of AD, but that presence of one or two Met alleles of BDNF Val66Met polymorphism might present a risk factor for psychosis in AD.