Genetic variants in brain-derived neurotrophic factor associated with Alzheimer's disease

Alzheimer's diseases in America, Europe, and Asian regions: a global genetic variation

Background

Alzheimer's disease (AD) is one of the multifaceted neurodegenerative diseases influenced by many genetic and epigenetic factors. Genetic factors are merely not responsible for developing AD in the whole population. The studies of genetic variants can provide significant insights into the molecular basis of Alzheimer's disease. Our research aimed to show how genetic variants interact with environmental influences in different parts of the world.

Methodology

We searched PubMed and Google Scholar for articles exploring the relationship between genetic variations and global regions such as America, Europe, and Asia. We aimed to identify common genetic variations susceptible to AD and have no significant heterogeneity. To achieve this, we analyzed 35 single-nucleotide polymorphisms (SNPs) from 17 genes (ABCA7, APOE, BIN1, CD2AP, CD33, CLU, CR1, EPHA1, TOMM40, MS4A6A, ARID5B, SORL1, APOC1, MTHFD1L, BDNF, TFAM, and PICALM) from different regions based on previous genomic studies of AD. It has been reported that rs3865444, CD33, is the most common polymorphism in the American and European populations. From TOMM40 and APOE rs2075650, rs429358, and rs6656401, CR1 is the common investigational polymorphism in the Asian population.

Conclusion

The results of all the research conducted on AD have consistently shown a correlation between genetic variations and the incidence of AD in the populations of each region. This review is expected to be of immense value in future genetic research and precision medicine on AD, as it provides a comprehensive understanding of the genetic factors contributing to the development of this debilitating disease.

Cognitive Dysfunction and Exercise: From Epigenetic to Genetic Molecular Mechanisms

Maintaining good health is crucial, and exercise plays a vital role in achieving this goal. It offers a range of positive benefits for cognitive function, regardless of age. However, as our population ages and life expectancy increases, cognitive impairment has become a prevalent issue, often coexisting with age-related neurodegenerative conditions. This can result in devastating consequences such as memory loss, difficulty speaking, and confusion, greatly hindering one's ability to lead an ordinary life. In addition, the decrease in mental capacity has a significant effect on an individual's physical and emotional well-being, greatly reducing their overall level of contentment and causing a significant financial burden for communities. While most current approaches aim to slow the decline of cognition, exercise offers a non-pharmacological, safe, and accessible solution. Its effects on cognition are intricate and involve changes in the brain's neural plasticity, mitochondrial stability, and energy metabolism. Moreover, exercise triggers the release of cytokines, playing a significant role in the body-brain connection and its impact on cognition. Additionally, exercise can influence gene expression through epigenetic mechanisms, leading to lasting improvements in brain function and behavior. Herein, we summarized various genetic and epigenetic mechanisms that can be modulated by exercise in cognitive dysfunction.

OPRM1 and BDNF polymorphisms associated with a compensatory neurophysiologic signature in knee osteoarthritis patients

OBJECTIVE

The present study investigated the relationship between three genetic polymorphisms of OPRM1 (rs1799971 - A118G and rs1799972 - C17T) and BDNF (rs6265 - C196T) and EEG-measured brain oscillations in Knee Osteoarthritis (KOA) patients.

MATERIALS AND METHODS

We performed a cross-sectional analysis of a cohort study (DEFINE cohort), KOA arm, with 66 patients, considering demographic (age, sex, and education), clinical (pain intensity and duration), OPRM1 (rs1799971 - A118G and rs1799972 - C17T) and BDNF (rs6265 - C196T) genotypes, and electrophysiological measures. Brain oscillations relative power from Delta, Theta, Alpha, Low Alpha, High Alpha, Beta, Low Beta and High Beta oscillations were measured during resting state EEG. Multivariate regression models were used to explore the main brain oscillation predictors of the three genetic polymorphisms.

RESULTS

Our findings demonstrate that Theta and Low Beta oscillations are associated with the variant allele of OPRM1-rs1799971 (A118G) on left frontal and left central regions, respectively, while Alpha brain oscillation is associated with variant genotypes (CT/TT) of BDNF-rs6265 on frontal (decrease of oscillation power) and left central (increase of oscillation power) regions. No significant model was found for OPRM1-rs1799972 (C17T) in addition to the inclusion of pain intensity as a significant predictor of this last model.

CONCLUSION

One potential interpretation for these findings is that polymorphisms of OPRM1 - that is involved with endogenous pain control - lead to increased compensatory oscillatory mechanisms, characterized by increased theta oscillations. Along the same line, polymorphisms of the BDNF lead to decreased alpha oscillations in the frontal area, likely also reflecting the disruption of resting states to also compensate for the increased injury associated with knee OA. It is possible that these polymorphisms require additional brain adaption to the knee OA related injury.

Comparison and development of machine learning for thalidomide-induced peripheral neuropathy prediction of refractory Crohn’s disease in Chinese population

BACKGROUND

Thalidomide is an effective treatment for refractory Crohn’s disease (CD). However, thalidomide-induced peripheral neuropathy (TiPN), which has a large individual variation, is a major cause of treatment failure. TiPN is rarely predictable and recognized, especially in CD. It is necessary to develop a risk model to predict TiPN occurrence.

AIM

To develop and compare a predictive model of TiPN using machine learning based on comprehensive clinical and genetic variables.

METHODS

A retrospective cohort of 164 CD patients from January 2016 to June 2022 was used to establish the model. The National Cancer Institute Common Toxicity Criteria Sensory Scale (version 4.0) was used to assess TiPN. With 18 clinical features and 150 genetic variables, five predictive models were established and evaluated by the confusion matrix receiver operating characteristic curve (AUROC), area under the precision-recall curve (AUPRC), specificity, sensitivity (recall rate), precision, accuracy, and F1 score.

RESULTS

The top-ranking five risk variables associated with TiPN were interleukin-12 rs1353248 [P = 0.0004, odds ratio (OR): 8.983, 95% confidence interval (CI): 2.497-30.90], dose (mg/d, P = 0.002), brain-derived neurotrophic factor (BDNF) rs2030324 (P = 0.001, OR: 3.164, 95%CI: 1.561-6.434), BDNF rs6265 (P = 0.001, OR: 3.150, 95%CI: 1.546-6.073) and BDNF rs11030104 (P = 0.001, OR: 3.091, 95%CI: 1.525-5.960). In the training set, gradient boosting decision tree (GBDT), extremely random trees (ET), random forest, logistic regression and extreme gradient boosting (XGBoost) obtained AUROC values > 0.90 and AUPRC > 0.87. Among these models, XGBoost and GBDT obtained the first two highest AUROC (0.90 and 1), AUPRC (0.98 and 1), accuracy (0.96 and 0.98), precision (0.90 and 0.95), F1 score (0.95 and 0.98), specificity (0.94 and 0.97), and sensitivity (1). In the validation set, XGBoost algorithm exhibited the best predictive performance with the highest specificity (0.857), accuracy (0.818), AUPRC (0.86) and AUROC (0.89). ET and GBDT obtained the highest sensitivity (1) and F1 score (0.8). Overall, compared with other state-of-the-art classifiers such as ET, GBDT and RF, XGBoost algorithm not only showed a more stable performance, but also yielded higher ROC-AUC and PRC-AUC scores, demonstrating its high accuracy in prediction of TiPN occurrence.

CONCLUSION

The powerful XGBoost algorithm accurately predicts TiPN using 18 clinical features and 14 genetic variables. With the ability to identify high-risk patients using single nucleotide polymorphisms, it offers a feasible option for improving thalidomide efficacy in CD patients.

Effects of radiation exposure on brain health: a state of the art and new challenges

Good brain health refers to a condition in which a person may fully realize their talents and improve their psychological, emotional, cognitive, and behavioral functioning to cope with life's challenges. Various causes of CNS diseases are now being investigated. Radiation is one of the factors that affects the brain and causes a variety of problems. The emission or transmission of energy in the form of waves or particles via space or a material medium is known as radiation. Particle beams and electromagnetic waves are two types of ionizing radiation that have the potential to ionize atoms in a material (separating them into positively charged ions and negatively charged electrons). Radiation to the CNS can induce delayed puberty, which can lead to hyperprolactinemia, and the hypothalamic-pituitary axis can lead to gonadotropin deficit if the hypothalamic-pituitary axis is involved in the radiation field. Ionizing radiation is the most common kind of radiation. Here, we focus on the different effects of radiation on brain health. In this article, we will look at a variety of CNS diseases and how radiation affects each one, as well as how it affects the brain's numerous processes.

The relationships between neuroglial and neuronal changes in Alzheimer's disease, and the related controversies II:

Since the original description of Alzheimer´s disease (AD), research into this condition has mainly focused on assessing the alterations to neurons associated with dementia, and those to the circuits in which they are involved. In most of the studies on human brains and in many models of AD, the glial cells accompanying these neurons undergo concomitant alterations that aggravate the course of neurodegeneration. As a result, these changes to neuroglial cells are now included in all the "pathogenic cascades" described in AD. Accordingly, astrogliosis and microgliosis, the main components of neuroinflammation, have been integrated into all the pathogenic theories of this disease, as discussed in this part of the two-part monograph that follows an accompanying article on gliopathogenesis and glioprotection. This initial reflection verified the implication of alterations to the neuroglia in AD, suggesting that these cells may also represent therapeutic targets to prevent neurodegeneration. In this second part of the monograph, we will analyze the possibilities of acting on glial cells to prevent or treat the neurodegeneration that is the hallmark of AD and other pathologies. Evidence of the potential of different pharmacological, non-pharmacological, cell and gene therapies (widely treated) to prevent or treat this disease is now forthcoming, in most cases as adjuncts to other therapies. A comprehensive AD multimodal therapy is proposed in which neuronal and neuroglial pharmacological treatments are jointly considered, as well as the use of new cell and gene therapies and non-pharmacological therapies that tend to slow down the progress of dementia.

New Frontiers in Neurodegeneration and Regeneration Associated with Brain-Derived Neurotrophic Factor and the rs6265 Single Nucleotide Polymorphism

Brain-derived neurotrophic factor is an extensively studied neurotrophin implicated in the pathology of multiple neurodegenerative and psychiatric disorders including, but not limited to, Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, traumatic brain injury, major de-pressive disorder, and schizophrenia. Here we provide a brief summary of current knowledge on the role of BDNF and the common human single nucleotide polymorphism, rs6265, in driving the pathogenesis and rehabilitation in these disorders, as well as the status of BDNF-targeted therapies. A common trend has emerged correlating low BDNF levels, either detected within the central nervous system or peripherally, to disease states, suggesting that BDNF replacement therapies may hold clinical promise. In addition, we introduce evidence for a distinct role of the BDNF pro-peptide as a biologically active ligand and the need for continuing studies on its neurological function outside of that as a molecular chaperone. Finally, we highlight the latest research describing the role of rs6265 expression in mechanisms of neurodegeneration as well as paradoxical advances in the understanding of this genetic variant in neuroregeneration. All of this is discussed in the context of personalized medicine, acknowledging there is no “one size fits all” therapy for neurodegenerative or psychiatric disorders and that continued study of the multiple BDNF isoforms and genetic variants represents an avenue for discovery ripe with therapeutic potential.

Exploring the Key Genes and Identification of Potential Diagnosis Biomarkers in Alzheimer's Disease Using Bioinformatics Analysis

Background

Alzheimer’s disease (AD) is one of the major threats of the twenty-first century and lacks available therapy. Identification of novel molecular markers for diagnosis and treatment of AD is urgently demanded, and genetic biomarkers show potential prospects.

Method

We identify and intersected differentially expressed genes (DEGs) from five microarray datasets to detect consensus DEGs. Based on these DEGs, we conducted Gene Ontology (GO), performed the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, constructed a protein—protein interaction (PPI) network, and utilized Cytoscape to identify hub genes. The least absolute shrinkage and selection operator (LASSO) logistic regression was applied to identify potential diagnostic biomarkers. Gene set enrichment analysis (GSEA) was performed to investigate the biological functions of the key genes.

Result

We identified 608 consensus DEGs, several dysregulated pathways, and 18 hub genes. Sixteen hub genes dysregulated as AD progressed. The diagnostic model of 35 genes was constructed, which has a high area under the curve (AUC) value in both the validation dataset and combined dataset (AUC = 0.992 and AUC = 0.985, respectively). The model can also differentiate mild cognitive impairment and AD patients from controls in two blood datasets. Brain-derived neurotrophic factor (BDNF) and WW domain-containing transcription regulator protein 1 (WWTR1), which are associated with the Braak stage, Aβ 42 levels, and β-secretase activity, were identified as critical genes of AD.

Conclusion

Our study identified 16 hub genes correlated to the neuropathological stage and 35 potential biomarkers for the diagnosis of AD. WWTR1 were identified as candidate genes for future studies. This study deepens our understanding of the transcriptomic and functional features and provides new potential diagnostic biomarkers and therapeutic targets for AD.

Intranasal delivery of BDNF rescues memory deficits in AD11 mice and reduces brain microgliosis

A decrease in brain-derived neurotrophic factor (BDNF), a neurotrophin essential for synaptic function, plasticity and neuronal survival, is evident early in the progression of Alzheimer’s disease (AD), being apparent in subjects with mild cognitive impairment or mild AD, and both proBDNF and mature BDNF levels are positively correlated with cognitive measures. BDNF delivery is, therefore, considered of great interest as a potentially useful therapeutic strategy to contrast AD. Invasive BDNF administration has indeed been recently used in animal models of AD with promising results in rescuing memory deficits, synaptic density and cell loss. Here, we tested whether non-invasive intranasal administration of different BDNF concentrations after the onset of cognitive and anatomical deficits (6 months of age) could rescue neuropathological and memory deficits in AD11 mice, a model of NGF deprivation-induced neurodegeneration. In addition to AD hallmarks, we investigated BDNF effects on microglia presence in the brain of AD11 mice, since alterations in microglia activation have been associated with ageing-related cognitive decline and with the progression of neurodegenerative diseases, including AD. We found that intranasal delivery of 42 pmol BDNF (1 μM), but not PBS, was sufficient to completely rescue performance of AD11 mice both in the object recognition test and in the object context test. No further improvement was obtained with 420 pmol (10 μM) BDNF dose. The strong improvement in memory performance in BDNF-treated mice was not accompanied by an amelioration of AD-like pathology, Aβ burden, tau hyperphosphorylation and cholinergic deficit, but there was a dramatic decrease of CD11b immunoreactive brain microglia. These results reinforce the potential therapeutic uses of BDNF in AD and the non-invasive intranasal route as an effective delivery strategy of BDNF to the brain. They also strengthen the connection between neuroinflammation and neurodegenerative dementia and suggest microglia as a possible mediator of BDNF therapeutic actions in the brain.

Genotype-expression interactions for BDNF across human brain regions

Background

Genetic variations in brain-derived neurotrophic factor (BDNF) are associated with various psychiatric disorders including depression, obsessive-compulsive disorder, substance use disorders, and schizophrenia; altered gene expression triggered by these genetic variants may serve to create these phenotypes. But genotype-expression interactions for this gene have not been well-studied across brain regions relevant for psychiatric disorders.

Results

At false discovery rate (FDR) of 10% (q < 0.1), a total of 61 SNPs were associated with BDNF expression in cerebellum (n = 209), 55 SNPs in cortex (n = 205), 48 SNPs in nucleus accumbens (n = 202), 47 SNPs in caudate (n = 194), and 58 SNPs in cerebellar hemisphere (n = 175). We identified a set of 30 SNPs in 2 haplotype blocks that were associated with alterations in expression for each of these 5 regions. The first haplotype block included variants associated in the literature with panic disorders (rs16917204), addiction (rs11030104), bipolar disorder (rs16917237/rs2049045), and obsessive-compulsive disorder (rs6265). Likewise, variants in the second haplotype block have been previously associated with disorders such as nicotine addiction, major depressive disorder (rs988748), and epilepsy (rs6484320/rs7103411).

Conclusions

This work supports the association of variants within BDNF for expression changes in these key brain regions that may contribute to common behavioral phenotypes for disorders of compulsion, impulsivity, and addiction. These SNPs should be further investigated as possible therapeutic and diagnostic targets to aid in management of these and other psychiatric disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07525-1.

Influence of BDNF Genetic Polymorphisms in the Pathophysiology of Aging-related Diseases

For the first time in history, most of the population has a life expectancy equal or greater than 60 years. By the year 2050, it is expected that the world population in that age range will reach 2000 million, an increase of 900 million with respect to 2015, which poses new challenges for health systems. In this way, it is relevant to analyze the most common diseases associated with the aging process, namely Alzheimer´s disease, Parkinson Disease and Type II Diabetes, some of which may have a common genetic component that can be detected before manifesting, in order to delay their progress. Genetic inheritance and epigenetics are factors that could be linked in the development of these pathologies. Some researchers indicate that the BDNF gene is a common factor of these diseases, and apparently some of its polymorphisms favor the progression of them. In this regard, alterations in the level of BDNF expression and secretion, due to polymorphisms, could be linked to the development and/or progression of neurodegenerative and metabolic disorders. In this review we will deepen on the different polymorphisms in the BDNF gene and their possible association with age-related pathologies, to open the possibilities of potential therapeutic targets.

Identification of Dysregulated Genes for Late-Onset Alzheimer's Disease Using Gene Expression Data in Brain

BACKGROUND

Alzheimer's Disease (AD) is a neurodegenerative complex brain disease that represents a public health concern. AD is considered the fifth leading cause of death in Americans who are older than 65 years which prioritizes the importance of understanding the etiology of AD in its early stages before the onset of symptoms. This study attempted to further understand Alzheimer's disease (AD) etiology by investigating the dysregulated genes using gene expression data from multiple brain regions.

METHODS

A linear mixed-effects model for differential gene expression analysis was used in a sample of 15 AD and 30 control subjects, each with data from four different brain regions, in order to deal with the hierarchical multilevel data. Post-hoc Gene Ontology and pathway enrichment analyses provided insights on the biological implications in AD progression. Supervised machine learning algorithms were used to assess the discriminative power of the top 10 candidate genes in distinguishing between the two groups.

RESULTS

Enrichment analyses revealed biological processes and pathways that are related to structural constituents and organization of the axons and synapses. These biological processes and pathways imply dysfunctional axon and synaptic transmission between neuronal cells in AD. Random Forest classification algorithm gave the best accuracy on the test data with F1-score of 0.88.

CONCLUSION

The differentially expressed genes were associated with axon and synaptic transmissions which affect the neuronal connectivity in cognitive systems involved in AD pathophysiology. These genes may open ways to explore new effective treatments and early diagnosis before the onset of clinical symptoms.

Association between BDNF rs6265 polymorphisms and postoperative cognitive dysfunction in Chinese Han Population

INTRODUCTION

Brain-derived neurotrophic factor (BDNF) plays a critical role in the pathogenesis of postoperative cognitive dysfunction (POCD). In present study, we aimed to assess the possible association between POCD and BDNF rs6265 polymorphisms.

METHODS

124 patients aged 60 years or older scheduled for elective surgery under general anesthesia and 25 age- and gender-matched healthy volunteers were recruited. POCD was identified using a neuropsychological test battery administered preoperatively, 7 days, and 3 months after surgery. Genotyping of rs6265 was performed using polymerase chain reaction amplification and restriction fragment length polymorphism analysis.

RESULTS

99 patients and 25 healthy controls were finally enrolled in the analysis. 29(29.3%) and 18(18.2%) of 99 patients had POCD at 7 days and 3 months after surgery, respectively. The patients carrying a G allele at the rs6265 locus showed a lower risk for POCD than an A allele carriers on postoperative 7 days, but not 3 months after surgery (OR = 0.67; 95% CI: 0.47-0.96; p = .017; OR = 0.69; 95% CI: 0.42-1.13; p = .14, respectively). The risk of POCD at 7 days following surgery was significantly lower in additive model (OR = 0.41; 95% CI: 0.2-0.84; p = .015) and dominant model (OR = 0.35; 95% CI: 0.13-0.96; p = .042).

CONCLUSION

We tentatively demonstrate that BDNF rs6265 polymorphisms might be associated with occurrence of POCD at 7 days after surgery and the A > G mutant at the rs6265 locus be likely a protective factor for early POCD in Chinese Han population.

Protective Functions of Reactive Astrocytes Following Central Nervous System Insult

Astrocytes play important roles in numerous central nervous system disorders including autoimmune inflammatory, hypoxic, and degenerative diseases such as Multiple Sclerosis, ischemic stroke, and Alzheimer’s disease. Depending on the spatial and temporal context, activated astrocytes may contribute to the pathogenesis, progression, and recovery of disease. Recent progress in the dissection of transcriptional responses to varying forms of central nervous system insult has shed light on the mechanisms that govern the complexity of reactive astrocyte functions. While a large body of research focuses on the pathogenic effects of reactive astrocytes, little is known about how they limit inflammation and contribute to tissue regeneration. However, these protective astrocyte pathways might be of relevance for the understanding of the underlying pathology in disease and may lead to novel targeted approaches to treat autoimmune inflammatory and degenerative disorders of the central nervous system. In this review article, we have revisited the emerging concept of protective astrocyte functions and discuss their role in the recovery from inflammatory and ischemic disease as well as their role in degenerative disorders. Focusing on soluble astrocyte derived mediators, we aggregate the existing knowledge on astrocyte functions in the maintenance of homeostasis as well as their reparative and tissue-protective function after acute lesions and in neurodegenerative disorders. Finally, we give an outlook of how these mediators may guide future therapeutic strategies to tackle yet untreatable disorders of the central nervous system.

Interaction Between Physical Activity and Genes Related to Neurotrophin Signaling in Late-Life Cognitive Performance: The Cache County Study

Research indicates that lifestyle and genetic factors influence the course of cognitive impairment in aging, but their interactions have not been well-examined. This study examined the relationship between physical activity and genotypes related to brain-derived neurotrophic factor (BDNF) in predicting cognitive performance in a sample of older adults with up to 12 years of follow-up. Physical activity levels (sedentary, light, and moderate/vigorous) were determined for the sample of 3,591 participants (57% female) without dementia. The genotypes examined included BDNF gene single nucleotide polymorphisms (SNPs) (rs6265 and rs56164415) and receptor gene SNPs (NTRK2 rs2289656 and NGFR rs2072446). Cognition was assessed triennially using the Modified Mini-Mental State Exam. Unadjusted linear mixed models indicated that sedentary (β = -5.05) and light (β = -2.41) groups performed worse than moderate-vigorous (p < .001). Addition of interaction effects showed significant differences in rate of decline between activity levels, particularly among males (p = .006). A three-way interaction with sex, NGFR SNP rs2072446, and physical activity suggested that the C/C allele was associated with better cognitive performance among males engaging in light activity only (p = .004). Physical activity and sex, but not BDNF-related SNPs, predicted rate of cognitive decline in older adults, while NGFR rs2072446 may modify main effects.

Polymorphisms of brain-derived neurotrophic factor genes are associated with anxiety and body mass index in fibromyalgia syndrome patients

Objective

Fibromyalgia syndrome has been associated with familial clusters although the specific genetic predisposition is not clear. Accordingly, studies concerning genetic factors associated with this disease are important. Brain-derived neurotrophic factor (BDNF) has been shown to play a role in patients with fibromyalgia syndrome, particularly in mediating manifestations of pain and mood-related symptoms. Research on genetic factors, including genetic variations or single nucleotide polymorphisms, especially related to BDNF in fibromyalgia is very limited. Therefore, this study was aiming at determining the association of polymorphisms of BDNF, particularly rs2049046 (A>T) and rs7124442 (A>G), with body mass index (BMI) and mood-related symptoms in FMS.

Results

In fibromyalgia syndrome cases, BDNF polymorphisms were associated with body mass index and anxiety score, specifically rs7124442 (A>G) (Fisher’s exact test χ²; p < 0.05; odds ratio (OR): 1.02) and rs2049046 (A>T) (Fisher’s exact test χ²; p < 0.05; OR: 0.55), respectively. Additionally, patients with fibromyalgia syndrome who have AA (95% CI (8.71, 11.63)) and AT (95% CI (9.32, 11.74)) alleles of rs2049046 showed higher score of anxiety compared to patients with TT (95% CI (3.98, 8.20) allele (ANOVA test; p < 0.01). These results suggest that BDNF polymorphisms (rs7124442 and rs2049046) are associated with body mass index and anxiety symptoms in patients with fibromyalgia syndrome.

Screening of brain-derived neurotrophic factor (BDNF) single nucleotide polymorphisms and plasma BDNF levels among Malaysian major depressive disorder patients

Background

Brain-derived neurotrophic factor (BDNF) is a neurotrophin found in abundance in brain regions such as the hippocampus, cortex, cerebellum and basal forebrain. It has been associated with the risk of susceptibility to major depressive disorder (MDD). This study aimed to determine the association of three BDNF variants (rs6265, rs1048218 and rs1048220) with Malaysian MDD patients.

Methods

The correlation of these variants to the plasma BDNF level among Malaysian MDD patients was assessed. A total of 300 cases and 300 matched controls recruited from four public hospitals within the Klang Valley of Selangor State, Malaysia and matched for age, sex and ethnicity were screened for BDNF rs6265, rs1048218 and rs1048220 using high resolution melting (HRM).

Findings

BDNF rs1048218 and BDNF rs1048220 were monomorphic and were excluded from further analysis. The distribution of the alleles and genotypes for BDNF rs6265 was in Hardy-Weinberg equilibrium for the controls (p = 0.13) but was in Hardy Weinberg disequilibrium for the cases (p = 0.011). Findings from this study indicated that having BDNF rs6265 in the Malaysian population increase the odds of developing MDD by 2.05 folds (95% CI = 1.48–3.65). Plasma from 206 cases and 206 controls were randomly selected to measure the BDNF level using enzyme-linked immunosorbent assay (ELISA). A significant decrease in the plasma BDNF level of the cases as compared to controls (p<0.0001) was observed. However, there was no evidence of the effect of the rs6265 genotypes on the BDNF level indicating a possible role of other factors in modulating the BDNF level that warrants further investigation.

Conclusion

The study indicated that having the BDNF rs6265 allele (A) increase the risk of developing MDD in the Malaysian population suggesting a possible role of BDNF in the etiology of the disorder.

Sex-dependent effect of the BDNF Val66Met polymorphism on executive functioning and processing speed in older adults: evidence from the health ABC study

Brain-derived neurotrophic factor (BDNF) Val66Met polymorphism may be an important source of heterogeneity seen in cognitive aging, although the specific relationship between this polymorphism and cognition remains controversial and may depend on the sex of participants. We assessed 2668 older black and white adults and fit linear mixed models to digit symbol substitution test (DSST) performance assessed in years 0 (baseline), 4, 7, and 9 to examine the interaction between sex and BDNF genotype on the intercept (i.e., estimated baseline DSST) and change in DSST over 9 years, adjusted for covariates. Sex interacted with BDNF genotype to predict DSST intercept (F[1,1599] = 7.4, p < 0.01) and 9-year change (F[1,1183] = 4.1, p = 0.04) in white participants only. Initially, white male Val/Val carriers had lower DSST scores (37.6, SE = 0.8) in comparison with male Met carriers (difference, -1.7; 95% CI, -3.2 to -0.3) and female Val/Val carriers (difference, -5.6; 95% CI, -6.8 to -4.3). White female Met carriers showed a slower rate of change (annual rate of change = -0.6, SE = 0.1) in comparison with female Val/Val carriers (difference, -0.2; 95% CI, -0.4 to -0.02) and male Met carriers (difference, -0.3; 95% CI, -0.5 to -0.02). Our findings suggest that BDNF Val66Met and sex should be considered in future endeavors aimed at treating or preventing neurodegenerative disorders.

BDNF inhibits neurodegenerative disease-associated asparaginyl endopeptidase activity via phosphorylation by AKT

AEP is an age-dependent lysosomal asparaginyl endopeptidase that cleaves numerous substrates including tau and α-synuclein and mediates their pathological roles in neurodegenerative diseases. However, the molecular mechanism regulating this critical protease remains incompletely understood. Here, we show that Akt phosphorylates AEP on residue T322 upon brain-derived neurotrophic factor (BDNF) treatment and triggers its lysosomal translocation and inactivation. When BDNF levels are reduced in neurodegenerative diseases, AEP T322 phosphorylation is attenuated. Consequently, AEP is activated and translocates into the cytoplasm, where it cleaves both tau and α-synuclein. Remarkably, the unphosphorylated T322A mutant increases tau or α-synuclein cleavage by AEP and augments cell death, whereas phosphorylation mimetic T322E mutant represses these effects. Interestingly, viral injection of T322E into Tau P301S mice antagonizes tau N368 cleavage and tau pathologies, rescuing synaptic dysfunction and cognitive deficits. By contrast, viral administration of T322A into young α-SNCA mice elicits α-synuclein N103 cleavage and promotes dopaminergic neuronal loss, facilitating motor defects. Therefore, our findings support the notion that BDNF contributes to the pathogenesis of neurodegenerative diseases by suppressing AEP via Akt phosphorylation.

Neurotransmitter Pathway Genes in Cognitive Decline During Aging: Evidence for GNG4 and KCNQ2 Genes

BACKGROUND/RATIONALE

Experimental studies support the role of neurotransmitter genes in dementia risk, but human studies utilizing single variants in candidate genes have had limited success.

METHODS

We used the gene-based testing program Versatile Gene-based Association Study to assess whether aggregate variation across 6 neurotransmitter pathways influences risk of cognitive decline in 8159 cognitively normal elderly (≥65 years old) adults from 3 community-based cohorts.

RESULTS

Common genetic variation in GNG4 and KCNQ2 was associated with cognitive decline. In human brain tissue data sets, both GNG4 and KCNQ2 show higher expression in hippocampus relative to other brain regions; GNG4 expression decreases with advancing age. Both GNG4 and KCNQ2 show highest expression in fetal astrocytes.

CONCLUSION

Genetic variation analyses and gene expression data suggest that GNG4 and KCNQ2 may be associated with cognitive decline in normal aging. Gene-based testing of neurotransmitter pathways may confirm and reveal novel risk genes in future studies of healthy cognitive aging.

Val66Met Polymorphism in BDNF Has No Sexual and APOE ε4 Status-Based Dimorphic Effects on Susceptibility to Alzheimer's Disease: Evidence From an Updated Meta-Analysis of Case-Control Studies and High-Throughput Genotyping Cohorts

Some studies showed that Val66Met polymorphism of brain-derived neurotrophic factor (BDNF) conveys susceptibility to Alzheimer's disease (AD) in females only. However, the confounding effects of some risk factors for AD were omitted in these studies. The aim of this meta-analysis comprising 19 604 patients with AD and 26 333 controls was to reexamine the association between Val66Met and AD by conditioning the effects of age, sex, and/or apolipoprotein E ( APOE) ε4 status. In agreement with the previous meta-analysis, Val66Met was associated with AD in females without confounding adjustment (odds ratio [OR], 1.08; 95% confidence interval [CI], 1.03-1.14; P = .003). Nevertheless, after adjusting for age and APOE ε4 status, Val66Met was not associated with AD in females (OR, 1.02; 95% CI, 0.94-1.11; P = .57). This comprehensive meta-analysis with the largest sample size demonstrated no association could be observed between Val66Met and AD in general or by dividing samples based on sex or APOE ε4.

A translational approach to the genetics of anxiety disorders

There have been important advances in our understanding of the genetic architecture of anxiety disorders. At the same time, relatively few genes have reached genome wide significance in anxiety disorders, and there is relatively little work on how exposure to an adverse environment impacts on gene expression in either animal models or human clinical populations. Here we assessed differential expression of genes of the dorsal striatum involved in synaptic transmission in an animal models of early adversity (maternal separation followed by restraint stress), and investigated whether variants in these genes were associated with risk for anxiety disorders, particularly in the presence of environmental stressors. Fifty-two male Sprague Dawley rats underwent maternal separation, and gene expression was studied using array technology. The human homologues of the differentially expressed genes were screened and analysed in a DSM-IV anxiety disorders cohort, and healthy controls (patients, n = 92; controls, n = 194), using blood. Two candidate genes (Mmp9 and Bdnf) were aberrantly expressed in the experimental rodent group relative to controls. Four single nucleotide polymorphisms (SNPs) in the human homologues of these genes were significantly associated with susceptibility for anxiety disorders (MMP9: rs3918242 and BDNF: rs6265, rs10835210 and rs11030107). Three of these (BDNF: rs6265, rs10835210, rs11030107) were found to interact significantly with childhood trauma severity resulting in increased likelihood of an anxiety disorder diagnosis. This study provides insights into the utility of rat models for identifying molecular candidates for anxiety disorders in humans.

Confident gene activity prediction based on single histone modification H2BK5ac in human cell lines

BACKGROUND

The histones in the core of nucleosomes may be subject to covalent post-transcriptional modifications. These modifications are thought to correlate with and possibly affect various genomic functions, including transcription. Each modification may alone or in combination with other modifications influence or be influenced by transcription. We aimed to identify correlations between single modifications or combinations of modifications at specific nucleosome sized gene regions with transcription activity based on global histone modification and transcription data of human CD4+ T cells and three other human cell lines. Transcription activity was defined in a binary fashion as either on or off. The analysis was done using the Classification and Regression Tree (CART) data mining protocol, and the Multifactorial Dimensionality Reduction (MDR) method was performed to confirm the CART results. These powerful methods have not previously been used for analysis of histone modification data.

RESULTS

We showed that analysis of the single histone modification H2BK5ac at only four gene regions correctly predicted transcription activity status of over 75% of genes in CD4+ T-cells. The H2BK5ac modification status also had high power for prediction of gene transcription activity in the three other cell lines studied. The informative gene regions with the H2BK5ac modification were all positioned proximal to transcription initiation sites. The CART and MDR methods were appropriate tools for the analysis performed. In the study, we also developed a non-arbitrary protocol for binary classification of genes as transcriptionally active or inactive.

CONCLUSIONS

The importance of H2BK5ac modification with regards to transcription control has not previously been emphasized. Analysis of this single modification at only four nucleosome sized gene regions, all of which are at or proximal to transcription initiation, has high power for prediction of gene transcription activity.

Female-specific effect of the BDNF gene on Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease influenced by genetic and environmental factors. Brain-derived neurotrophic factor (BDNF) plays an important role in the progression of AD, but the genetic association between BDNF and AD remains controversial. In this study, we aimed to explore the potential association between genetic variants in BDNF and AD in Han Chinese and to investigate whether the association is affected by gender. A 3-stage study was conducted to evaluate the genetic association between BDNF and AD. Data mining of the reported expression data, brain-imaging data, and biomarker data in AD patients was also performed to further validate the results. We found a female-specific genetic association of rs6265 with AD and a gender-related messenger RNA expression of BDNF in brain tissues of AD patients. In addition, we observed a clear female-specific risk trend for the effect of rs6265 on AD endophenotypes. Our results clarified the available controversies regarding the role of rs6265 in AD and indicated that BDNF may be a female-specific risk gene for AD.

Shared Genetic Risk Factors for Late-Life Depression and Alzheimer's Disease

BACKGROUND

Considerable evidence has been reported for the comorbidity between late-life depression (LLD) and Alzheimer's disease (AD), both of which are very common in the general elderly population and represent a large burden on the health of the elderly. The pathophysiological mechanisms underlying the link between LLD and AD are poorly understood. Because both LLD and AD can be heritable and are influenced by multiple risk genes, shared genetic risk factors between LLD and AD may exist.

OBJECTIVE

The objective is to review the existing evidence for genetic risk factors that are common to LLD and AD and to outline the biological substrates proposed to mediate this association.

METHODS

A literature review was performed.

RESULTS

Genetic polymorphisms of brain-derived neurotrophic factor, apolipoprotein E, interleukin 1-beta, and methylenetetrahydrofolate reductase have been demonstrated to confer increased risk to both LLD and AD by studies examining either LLD or AD patients. These results contribute to the understanding of pathophysiological mechanisms that are common to both of these disorders, including deficits in nerve growth factors, inflammatory changes, and dysregulation mechanisms involving lipoprotein and folate. Other conflicting results have also been reviewed, and few studies have investigated the effects of the described polymorphisms on both LLD and AD.

CONCLUSION

The findings suggest that common genetic pathways may underlie LLD and AD comorbidity. Studies to evaluate the genetic relationship between LLD and AD may provide insights into the molecular mechanisms that trigger disease progression as the population ages.

PoCos: Population Covering Locus Sets for Risk Assessment in Complex Diseases

Susceptibility loci identified by GWAS generally account for a limited fraction of heritability. Predictive models based on identified loci also have modest success in risk assessment and therefore are of limited practical use. Many methods have been developed to overcome these limitations by incorporating prior biological knowledge. However, most of the information utilized by these methods is at the level of genes, limiting analyses to variants that are in or proximate to coding regions. We propose a new method that integrates protein protein interaction (PPI) as well as expression quantitative trait loci (eQTL) data to identify sets of functionally related loci that are collectively associated with a trait of interest. We call such sets of loci “population covering locus sets” (PoCos). The contributions of the proposed approach are three-fold: 1) We consider all possible genotype models for each locus, thereby enabling identification of combinatorial relationships between multiple loci. 2) We develop a framework for the integration of PPI and eQTL into a heterogenous network model, enabling efficient identification of functionally related variants that are associated with the disease. 3) We develop a novel method to integrate the genotypes of multiple loci in a PoCo into a representative genotype to be used in risk assessment. We test the proposed framework in the context of risk assessment for seven complex diseases, type 1 diabetes (T1D), type 2 diabetes (T2D), psoriasis (PS), bipolar disorder (BD), coronary artery disease (CAD), hypertension (HT), and multiple sclerosis (MS). Our results show that the proposed method significantly outperforms individual variant based risk assessment models as well as the state-of-the-art polygenic score. We also show that incorporation of eQTL data improves the performance of identified POCOs in risk assessment. We also assess the biological relevance of PoCos for three diseases that have similar biological mechanisms and identify novel candidate genes. The resulting software is publicly available at http://compbio.case.edu/pocos/.

Several studies try to predict the individual disease risk using genetic data obtained from genome wide association studies (GWAS). Earlier studies only focus on individual genetic variants. However, studies on disease mechanisms suggest the aggregation of genomic variants may contribute to diseases. For this reason, researchers commonly use prior biological knowledge to identify genetic variants that are functionally related. However, these approaches are often limited to variants that are in the coding regions of genes. However, several risk variants are in the regulatory region. Here, we incorporate known regulatory and functional interactions to find sets of genetic variants which are informative features for risk assessment. Our result on seven complex diseases show that our method outperforms individual variant based risk assessment models, as well as other methods that integrate multiple genetic variants.

Missense Mutation of Brain Derived Neurotrophic Factor (BDNF) Alters Neurocognitive Performance in Patients with Mild Traumatic Brain Injury: A Longitudinal Study

The predictability of neurocognitive outcomes in patients with traumatic brain injury is not straightforward. The extent and nature of recovery in patients with mild traumatic brain injury (mTBI) are usually heterogeneous and not substantially explained by the commonly known demographic and injury-related prognostic factors despite having sustained similar injuries or injury severity. Hence, this study evaluated the effects and association of the Brain Derived Neurotrophic Factor (BDNF) missense mutations in relation to neurocognitive performance among patients with mTBI. 48 patients with mTBI were prospectively recruited and MRI scans of the brain were performed within an average 10.1 (SD 4.2) hours post trauma with assessment of their neuropsychological performance post full Glasgow Coma Scale (GCS) recovery. Neurocognitive assessments were repeated again at 6 months follow-up. The paired t-test, Cohen's d effect size and repeated measure ANOVA were performed to delineate statistically significant differences between the groups [wildtype G allele (Val homozygotes) vs. minor A allele (Met carriers)] and their neuropsychological performance across the time point (T1 = baseline/ admission vs. T2 = 6th month follow-up). Minor A allele carriers in this study generally performed more poorly on neuropsychological testing in comparison wildtype G allele group at both time points. Significant mean differences were observed among the wildtype group in the domains of memory (M = -11.44, SD = 10.0, p = .01, d = 1.22), executive function (M = -11.56, SD = 11.7, p = .02, d = 1.05) and overall performance (M = -6.89 SD = 5.3, p = .00, d = 1.39), while the minor A allele carriers showed significant mean differences in the domains of attention (M = -11.0, SD = 13.1, p = .00, d = .86) and overall cognitive performance (M = -5.25, SD = 8.1, p = .01, d = .66).The minor A allele carriers in comparison to the wildtype G allele group, showed considerably lower scores at admission and remained impaired in most domains across the timepoints, although delayed signs of recovery were noted to be significant in the domains attention and overall cognition. In conclusion, the current study has demonstrated the role of the BDNF rs6265 Val66Met polymorphism in influencing specific neurocognitive outcomes in patients with mTBI. Findings were more detrimentally profound among Met allele carriers.

Genetic polymorphisms and the adequacy of brain stimulation: state of the art

INTRODUCTION

Heterogeneity of therapeutic response to brain stimulation techniques has inspired scientists to uncover the secrets to success or failure of these projects. Genetic polymorphisms are one of the major causes of this heterogeneity.

AREAS COVERED

More than twenty genetic variants within more than ten genes (e.g. BDNF, COMT, DRD2, TRPV1, 5-HT1A, 5-HHT, P2RX7, VEGF, TPH1, TPH2, ACE, APOE, GNB3, NET, NMDA receptors, and RGS4) have been investigated, among which the BDNF gene and its polymorphism, Val66Met, is the best documented variant. We review the genotypic combinations, which are reported to interact with the work of brain stimulation, of which the DRD2 C957T polymorphism is the most prominent type. Finally, implications of transcranial magnetic stimulation in deciphering the interaction between genetic background (e.g. SCN1A and 5-HTT) and drugs (e.g. carbamazepine and citalopram) at the cortical excitability level is explained. Expert commentary: Studies are ongoing to find missing factors responsible for heterogeneity of response to brain stimulation techniques. Further knowledge about genetic factors affecting the therapeutic response to brain stimulation techniques might provide helpful guidelines for choosing ideal candidates for treatment.

Genetic Risk Score Predicts Late-Life Cognitive Impairment

Introduction. A family history of Alzheimer's disease is a significant risk factor for its onset, but the genetic risk associated with possessing multiple risk alleles is still poorly understood. Methods. In a sample of 95 older adults (Mean age = 75.1, 64.2% female), we constructed a genetic risk score based on the accumulation of risk alleles in BDNF, COMT, and APOE. A neuropsychological evaluation and consensus determined cognitive status (44 nonimpaired, 51 impaired). Logistic regression was performed to determine whether the genetic risk score predicted cognitive impairment above and beyond that associated with each gene. Results. An increased genetic risk score was associated with a nearly 4-fold increased risk of cognitive impairment (OR = 3.824, P = .013) when including the individual gene polymorphisms as covariates in the model. Discussion. A risk score combining multiple genetic influences may be more useful in predicting late-life cognitive impairment than individual polymorphisms.

Association of BDNF and BCHE with Alzheimer's disease: Meta-analysis based on 56 genetic case-control studies of 12,563 cases and 12,622 controls

Alzheimer's disease (AD) is a common neurodegenerative disorder that can destroy the memory of sufferers and lead to distress for the individual and society. Brain-derived neurotrophic factor (BDNF) and butyrylcholinesterase (BCHE) are two genes associated with β-amyloid plaques and neurofibrillary tangles that are two key factors in the pathophysiology of AD. The aim of the current meta-analysis was to evaluate the association between BDNF Val66Met (rs6265), BDNF C270T (rs2030324) and BCHE-K (rs1803274) polymorphisms and AD. A comprehensive meta-analysis was performed using the online database PubMed without a time limitation. A total of 56 articles evaluating 12,563 cases and 12,622 controls were selected for the current meta-analysis. The results showed a moderate association of the BDNF C270T polymorphism with the risk of AD in Asians under a dominant model (P=0.03; odds ratio, 1.88; 95% confidence interval, 1.08-3.27). No other significant association was found during the meta-analysis for the other two polymorphisms (P>0.05). The current meta-analysis suggests that BDNF C270T is a risk factor for AD in Asians. This meta-analysis has been, to the best of our knowledge, the most comprehensive meta-analysis of BDNF Val66Met, BDNF C270T and BCHE-K to date.

Genetic variation at the BDNF locus: evidence for association with long-term outcome after ischemic stroke

Background and Purpose

Rates and extent of recovery after stroke vary considerably between individuals and genetic factors are thought to contribute to post-stroke outcome. Brain-derived neurotrophic factor (BDNF) plays important roles in brain plasticity and repair and has been shown to be involved in stroke severity, recovery, and outcome in animal models. Few clinical studies on BDNF genotypes in relation to ischemic stroke have been performed. The aims of the present study are therefore to investigate whether genetic variation at the BDNF locus is associated with initial stroke severity, recovery and/or short-term and long-term functional outcome after ischemic stroke.

Methods

Four BDNF tagSNPs were analyzed in the Sahlgrenska Academy Study on Ischemic Stroke (SAHLSIS; 600 patients and 600 controls, all aged 18–70 years). Stroke severity was assessed using the NIH Stroke Scale (NIHSS). Stroke recovery was defined as the change in NIHSS over a 3-month period. Short- and long-term functional outcome post-stroke was assessed using the modified Rankin Scale at 3 months and at 2 and 7 years after stroke, respectively.

Results

No SNP was associated with stroke severity or recovery at 3 months and no SNP had an impact on short-term outcome. However, rs11030119 was independently associated with poor functional outcome 7-years after stroke (OR 0.66, 95% CI 0.46–0.92; P =  0.006).

Conclusions

BDNF gene variants were not major contributors to ischemic stroke severity, recovery, or short-term functional outcome. However, this study suggests that variants in the BDNF gene may contribute to poor long-term functional outcome after ischemic stroke.

Brain-Derived Neurotrophic Factor in Alzheimer's Disease: Risk, Mechanisms, and Therapy

Brain-derived neurotrophic factor (BDNF) has a neurotrophic support on neuron of central nervous system (CNS) and is a key molecule in the maintenance of synaptic plasticity and memory storage in hippocampus. However, changes of BDNF level and expression have been reported in the CNS as well as blood of Alzheimer's disease (AD) patients in the last decade, which indicates a potential role of BDNF in the pathogenesis of AD. Therefore, this review aims to summarize the latest progress in the field of BDNF and its biological roles in AD pathogenesis. We will discuss the interaction between BDNF and amyloid beta (Aβ) peptide, the effect of BDNF on synaptic repair in AD, and the association between BDNF polymorphism and AD risk. The most important is, enlightening the detailed biological ability and complicated mechanisms of action of BDNF in the context of AD would provide a future BDNF-related remedy for AD, such as increment in the production or release of endogenous BDNF by some drugs or BDNF mimics.

Association of rs6265 and rs2030324 polymorphisms in brain-derived neurotrophic factor gene with Alzheimer's disease: a meta-analysis

Background

The association between polymorphisms rs6265 and rs2030324 in brain-derived neurotrophic factor (BDNF) and Alzheimer’s disease (AD) has been widely reported, but the results remain controversial.

Methods

A comprehensive search of Pubmed, Web of Science, China National Knowledge Infrastructure (CNKI), Wanfang Med Online and China Biology Medical literature database (CBM) was performed. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using fixed or random-effects models. We excluded the studies with OR>3.0 or OR<0.3 for sensitive analysis. Subgroup analysis by ethnicity, form of AD and gender was carried out. Meta-regression was conducted to explore the potential sources of between-study heterogeneity.

Results

29 articles with 7548 cases and 7334 controls concerning rs6265 and 22 articles with 5796 cases and 5706 controls concerning rs2030324 were included in this meta-analysis. The combined evidence suggested rs6265 contributing significantly to the increased risk of AD in females (codominant: fixed-effects model (FEM): OR = 1.13, 95% CI = 1.04–1.23; dominant: FEM: OR = 1.17, 95% CI = 1.05–1.31), especially for Caucasian females (codominant: FEM: OR = 1.18, 95% CI = 1.03–1.34; dominant: FEM: OR = 1.18, 95% CI = 1.01–1.37) and female late-onset Alzheimer’s disease (LOAD) patients (codominant: FEM: OR = 1.22, 95% CI = 1.05–1.41; dominant: FEM: OR = 1.23, 95% CI = 1.03–1.46). No evidence indicated an association between rs2030324 with AD in codominant (random-effects model (REM): OR = 1.06, 95% CI = 0.89–1.26) and dominant (REM: OR = 1.05, 95% CI = 0.86–1.27) models.

Conclusion

This meta-analysis suggested A allele of rs6265 might increase the risk of AD in Caucasian females and female LOAD patients. In addition, no evidence indicated an association between rs2030324 with AD. Further studies are needed to confirm these results.

Gender-related association of brain-derived neurotrophic factor gene 196A/G polymorphism with Alzheimer's disease--a meta-analysis including 6854 cases and 6868 controls

Epidemiological studies have evaluated the associations between brain-derived neurotrophic factor (BDNF) 196A/G gene polymorphism and Alzheimer's disease (AD) risk. However, the results remain inconclusive. Sexually dimorphic effect of the polymorphism of BDNF 196A/G in AD patients had been proposed previously, specifically in female group. As more cases were reported, therefore, we performed a meta-analysis of published case-control studies to better understand these results. We systematically searched online databases of Embase, PubMed and Web of Science, as well as hand searching of the references of identified articles and meeting abstracts. Review Manager (Version 5.2.4) and Stata software (Version 12.0) were used for statistical analyses. The pooled odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated. A total of 23 publications including 25 studies were identified and entered the analysis. No significant association was observed in overall population, as well as subgroups stratified by ethnicity (Caucasian and Asian). However, when stratified by gender, significant association was observed just in female subgroup (A allele vs. G allele: OR = 1.15, 95% CI = 1.06-1.25; A/A vs. G/G: OR = 1.29, 95% CI = 1.06-1.57; A/A + A/G vs. G/G: OR = 1.30, 95% CI = 1.11-1.53). This meta-analysis confirmed the gender-related association between BDNF 196A/G polymorphism and AD risk, which may indicate a certain effect of female hormone on progression of the disease. Larger sample size and more studies with homogeneous AD patients and well-matched controls are needed in future.

Plasma BDNF levels are correlated with aggressiveness in patients with amnestic mild cognitive impairment or Alzheimer disease

In the present study, we examined whether neuropsychiatric symptoms were correlated with plasma brain-derived neurotrophic factor (BDNF) levels as a state marker or were associated with the BDNF polymorphism Val66Met in patients with amnestic mild cognitive impairment (A-MCI) or Alzheimer disease (AD). One hundred and seventy-six outpatients with AD (n = 129) or A-MCI (n = 47) were selected and their plasma BDNF concentrations measured. Next, we investigated the correlation between the plasma BDNF level and the Behavioral Pathology in Alzheimer Disease (Behave-AD) subscale scores, which reflect neuropsychiatric symptoms. We also compared the plasma BDNF level and the Behave-AD subscale scores among the BDNF Val66Met genotypic groups. Among the seven Behave-AD subscale scores, aggressiveness was positively correlated with the plasma BDNF level (ρ = 0.237, P < 0.005), but did not differ significantly among the three BDNF Val66Met genotypic groups. The Behave-AD total and other subscale scores did not differ significantly among the BDNF Val66Met genotypic groups and were not associated with the plasma BDNF level. Moreover, the plasma BDNF level did not differ significantly among the three BDNF Val66Met genotypic groups or between patients with A-MCI and those with AD. The plasma BDNF level was robustly correlated with aggressiveness, implying that the plasma BDNF level might be useful as a behavioral state marker in patients with AD or A-MCI.

Genetic Association between Neurotrophin-3 Polymorphisms and Alzheimer's Disease in Japanese Patients

BACKGROUND

Some polymorphisms of the neurotrophin family have previously been investigated as candidate genes for Alzheimer's disease (AD). In the present study, we examined whether neurotrophin-3 (NTF-3) polymorphisms are genetic risk factors in patients with AD.

METHODS

From a sample of 507 subjects, we recruited 248 age-matched subjects divided into 2 groups: AD patients (n = 143) and normal controls (NCs) (n = 105). We identified 3 representative NTF-3 single nucleotide polymorphisms (SNPs): rs6332, rs6489630, and rs4930767. Next, we statistically compared the allele frequencies of each SNP between the AD and NC groups in the early-onset (<65 years) cases under a more limited age-matched condition.

RESULTS

We found a significant association between rs6332 and the total group of AD patients (p = 0.013) and significant associations between both rs6332 (p = 0.033) and rs6489630 (p = 0.035) and early-onset AD patients.

CONCLUSION

These results suggest that NTF-3 SNPs may not only be associated with AD itself, but also with early-onset AD in Japanese patients, assuming that the NTF-3 gene may have age-related effects on neurodegenerative diseases.

Characterizing the role of brain derived neurotrophic factor genetic variation in Alzheimer's disease neurodegeneration

There is accumulating evidence that neurotrophins, like brain-derived neurotrophic factor (BDNF), may impact aging and Alzheimer's Disease. However, traditional genetic association studies have not found a clear relationship between BDNF and AD. Our goal was to test whether BDNF single nucleotide polymorphisms (SNPs) impact Alzheimer's Disease-related brain imaging and cognitive markers of disease. We completed an imaging genetics study on 645 Alzheimer's Disease Neuroimaging Initiative participants (ND=175, MCI=316, AD=154) who had cognitive, brain imaging, and genetics data at baseline and a subset of those with brain imaging data at two years. Samples were genotyped using the Illumina Human610-Quad BeadChip. 13 SNPs in BDNF were identified in the dataset following quality control measures (rs6265(Val66Met), rs12273363, rs11030094, rs925946, rs1050187, rs2203877, rs11030104, rs11030108, rs10835211, rs7934165, rs908867, rs1491850, rs1157459). We analyzed a subgroup of 8 SNPs that were in low linkage disequilibrium with each other. Automated brain morphometric measures were available through ADNI investigators, and we analyzed baseline cognitive scores, hippocampal and whole brain volumes, and rates of hippocampal and whole brain atrophy and rates of change in the ADAS-Cog over one and two years. Three out of eight BDNF SNPs analyzed were significantly associated with measures of cognitive decline (rs1157659, rs11030094, rs11030108). No SNPs were significantly associated with baseline brain volume measures, however six SNPs were significantly associated with hippocampal and/or whole brain atrophy over two years (rs908867, rs11030094, rs6265, rs10501087, rs1157659, rs1491850). We also found an interaction between the BDNF Val66Met SNP and age with whole brain volume. Our imaging-genetics analysis in a large dataset suggests that while BDNF genetic variation is not specifically associated with a diagnosis of AD, it appears to play a role in AD-related brain neurodegeneration.

Brain-derived neurotrophic factor G196A polymorphism predicts 90-day outcome of ischemic stroke in Chinese: a novel finding

BACKGROUND AND PURPOSE

Recovery after stroke varies considerably between individuals. An abundance of evidence suggests that genetic factors contribute to stroke recovery. The aim of this study was to determine whether or not the BDNF G196A polymorphism independently influences the occurrence, severity, and 90-day functional outcome in Chinese patients with ischemic stroke (IS).

METHODS

BDNF G196A genetic variants were investigated in 494 IS and 346 controls. Severity was assessed by the National Institutes of Health Stroke Scale at the time of admission. Three hundred and eight patients were assessed 90 days post-stroke using the Modified Rankin Scale to determine stroke outcome.

RESULTS

We showed that a significant association existed between the BDNF G196A AA genotype and the occurrence of IS (P=0.021), even after adjustment for covariates (P=0.028). The AA genotype of the BDNF G196A was associated with a poor outcome of recovery 3 months after stroke onset (P=0.008) was a novel finding, independent of other known predictors of poor outcome (P=0.012).

CONCLUSIONS

The BDNF G196A polymorphism was significantly associated with the occurrence and long-term outcomes of IS, thus BDNF G196A may be used as a prognostic biomarker and therapeutic target in IS.

Sociodemographic characteristics, clinical factors, and genetic polymorphisms associated with Alzheimer's disease

OBJECTIVE

Alzheimer's disease (AD) has a multifactorial etiology involving an interaction of genetic and environmental factors. The Apolipoprotein E ε4 (ApoE ε4) is the single most important genetic risk factor for sporadic AD. Our aim was to study the association between sociodemographic, clinical data and gene polymorphisms in patients with sporadic AD in a heterogeneous genomic Brazilian population with low educational levels.

METHODS

We selected 169 sporadic AD patients and 97 controls older than 65 years and compared co-variables between them: age, years of education, vascular risk factors, genomic ancestry, and functional polymorphisms of ApoE, BDNF, COMT, and 5-HTTLPR. We also determined the genomic ancestry of all individuals.

RESULTS

The average years of education was significantly smaller in the patient's group (p = 0.003), and they had a history of depression when compared with controls (p < 0.001). The carriers of ApoE ε4 have an earlier onset of the disease (76.9 years) (p = 0.001) than ApoE ε3 (79.5 years) (p = 0.024). Patients with Met allele of Val66Met have a tendency to later onset of disease (p = 0.056). There were no differences in the genomic ancestry between groups.

CONCLUSION

Low level of education and history of depression were associated with AD. Public policies and intensive observation of old-age patients with lifetime history of depression, especially APOE ε4 carriers, could improve the well-being of our population.

Polymorphism of brain derived neurotrophic factor influences β amyloid load in cognitively intact apolipoprotein E ε4 carriers

Aside from apolipoprotein E (APOE), genetic risk factors for β amyloid deposition in cognitively intact individuals remain to be identified. Brain derived neurotrophic factor (BDNF) modulates neural plasticity, which has been implicated in Alzheimer's disease. We examined in cognitively normal older adults whether the BDNF codon 66 polymorphism affects β amyloid burden and the relationship between β amyloid burden and cognitive scores, and how this relates to the effect of APOE. Amyloid load was measured by means of ¹⁸F-flutemetamol PET in 64 community-recruited cognitively intact individuals (mean age 66, S.D. 5.1). Recruitment was stratified according to a factorial design with APOE (ε4 allele present vs absent) and BDNF (met allele at codon 66 present vs absent) as factors. Individuals in the four resulting cells were matched by the number of cases, age, and gender. Among the APOE ε4 carriers, BDNF met positive subjects had a significantly higher amyloid load than BDNF met negative subjects, while BDNF met carrier status did not have an effect in APOE ε4 noncarriers. This interaction effect was localized to precuneus, orbitofrontal cortex, gyrus rectus, and lateral prefrontal cortex. In the APOE ε4/BDNF met carriers, a significant inverse relationship existed between episodic memory scores and amyloid burden but not in any of the other groups. This hypothesis-generating experiment highlights a potential role of BDNF polymorphisms in the preclinical phase of β amyloid deposition and also suggests that BDNF codon 66 polymorphisms may influence resilience against β amyloid-related effects on cognition.

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Codon 66 BDNF polymorphisms have been associated with various cerebral effects.

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Community-recruited cognitively intact older adults underwent amyloid PET.

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Recruitment was stratified factorially with APOE and BDNF as factors.

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Aβ load in BDNF met carriers was higher but only in the presence of APOE ε4.

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Aβ load was associated with worse episodic memory but only in BDNF met/APOE ε4.

Association between BDNF polymorphism (Val66Met) and executive function in patients with amnestic mild cognitive impairment or mild Alzheimer disease

BACKGROUND

In the present study, we examined whether brain-derived neurotrophic factor (BDNF) polymorphism (Val66Met) influenced the changeable executive dysfunction of patients with two separate disease stages: amnestic mild cognitive impairment (A-MCI) or mild Alzheimer disease (AD), which are comparatively similar demented conditions.

METHODS

Among 200 outpatients with dementia and MCI, 146 outpatients with mild AD or A-MCI were recruited and divided into two genotypic groups, valine homozygosity (Val/Val) and methionine (Met) carriers, based on the representative BDNF functional polymorphism Val66Met. Next, we compared the Frontal Assessment Battery (FAB) total and subtest scores between the two genotypic groups according to each of two different disease stages: A-MCI (n = 42) and mild AD (n = 104).

RESULTS

Among patients with only a mild stage of AD, the FAB total and go/no-go scores were significantly lower (p < 0.05) among the subjects with the Val/Val genotype than among the Met carriers. However, no significant differences in any other demographic variables were observed between the genotypes according to each of different disease stages. A significant interaction between Val66Met and age was not observed for the FAB scores.

CONCLUSION

These results suggested that the BDNF gene may significantly influence executive dysfunction, including inhibition tasks, among patients with mild-stage AD.

Brain-derived neurotrophic factor gene polymorphisms, neurotransmitter levels, and depressive symptoms in an elderly population

A large number of studies have examined associations between brain-derived neurotrophic factor (BDNF) gene polymorphisms and depressive symptoms. However, results still remain controversial. Recent studies suggested a significant age and gender effect on the heritability of depression. The potential neurobiological pathways that could possibly mediate this relationship have not been examined so far. Since BDNF is involved in the regulation of neurotransmitter production, a mediating role of neurotransmitters seems plausible. The present study aims to examine the association between three common BDNF single-nucleotid polymorphisms (SNPs; rs7103411, rs7124442, and rs6265) and depressive symptoms in a community-based elderly population taking into account the serum levels of four neurotransmitters, serotonin, dopamine, adrenalin, and noradrenalin, as potential mediating factors. We also examined whether age and gender had a modifying effect on this association. We collected and analyzed the genetic and laboratory data as well as Center for Epidemiologic Studies-Depression scores of 350 community-dwelling elderly individuals (aged 65+ years). We found that the BDNF rs6265 polymorphism was related to the severity of depressive symptoms, and that this association was independent of neurotransmitter levels. Stratified analyses showed that this association was restricted to older individuals (≥74 years) and men. The associations of SNPs rs7103411 or rs7124442 SNP with depressive symptoms were not statistically significant. This study importantly adds to the existing literature by affirming previous assumptions on an age and gender difference in the relation between BDNF genotype and depression. We moreover first-time report a missing mediating role of neurotransmitters in this association.

GDNF and BDNF gene interplay in chronic tinnitus

BACKGROUND

Glial cell-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) play key roles in the early development of the central auditory pathway and the inner ear. Both have been successfully employed to treat experimental forms of hearing loss and are likely to operate in a broad spectrum of auditory phenotypes, including phantom perceptions of sound. We conducted a genetic association study addressing five biallelic candidate variants in 240 Caucasian subjects who had been diagnosed with tinnitus for more than 6 months.

FINDINGS

Allele frequencies were determined for three GDNF and two BDNF markers, including a functional missense substitution (V66M). When data were compared to previously examined control populations, no significant allelic associations were noted after corrections for multiple testing. However, using a multiple regression approach and scores from a validated self-report questionnaire, GDNF and BDNF genotypes jointly predicted tinnitus severity in women (N=69, uncorrected p=0.04) but not in men (N=171, n.s.).

CONCLUSIONS

The present findings serve as an incentive for further explorations of neurotrophic factors' role in predicting clinical features of tinnitus. Possible implications of sexually dimorphic at-risk genotypes are discussed with regard to hearing and neural plasticity.

Genetic knockdown of brain-derived neurotrophic factor in 3xTg-AD mice does not alter Aβ or tau pathology

Brain-derived neurotrophic factor (BDNF) is a neurotrophin critically involved in cell survival, synaptic plasticity, and memory. BDNF has recently garnered significant attention as a potential therapeutic target for neurodegenerative diseases such as Alzheimer disease (AD), but emerging evidence suggests that BDNF may also be mechanistically involved in the pathogenesis of AD. AD patients have substantially reduced BDNF levels, which may be a result of Aβ and tau pathology. Recent evidence, however, indicates reduced BDNF levels may also serve to drive pathology in neuronal cultures, although this has not yet been established in vivo. To further investigate the mechanistic role of BDNF in AD, we generated 3xTg-AD mice with a heterozygous BDNF knockout (BDNF^+/−) and analyzed Aβ and tau pathology. Aged 3xTg-AD/BDNF^+/− mice have significantly reduced levels of brain BDNF, but have comparable levels of Aβ and tau pathology to 3xTg-AD/BDNF^+/+ mice. These findings indicate that chronic reduction of BDNF does not exacerbate the development of Aβ and tau pathology, and instead suggests the reduced BDNF levels found in AD patients are a consequence of these pathologies.

Brain-derived neurotrophic factor (BDNF) gene: a gender-specific role in cognitive function during normal cognitive aging of the MEMO-Study?

Cognitive aging processes are underpinned by multiple processes including genetic factors. The brain-derived neurotrophic factor (BDNF) has been suggested to be involved in age-related cognitive decline in otherwise healthy individuals. The gender-specific role of the BDNF gene in cognitive aging remains unclear. The identification of genetic biomarkers might be a useful approach to identify individuals at risk of cognitive decline during healthy aging processes. The aim of this study was to investigate the associations between three single-nucleotide polymorphisms (SNPs) in the BDNF gene and domains of cognitive functioning in normal cognitive aging. The sample, comprising 369 participants (M = 72.7 years, SD = 4.45 years), completed an extensive neuropsychological test battery measuring memory, motor function, and perceptual speed. The relationships between the SNPs rs6265, rs7103411, and rs7124442 and cognitive domains were examined. While significant main effects of BDNF SNPs on cognitive function were found for the association between rs7103411 and memory performance, gender-specific analyses revealed for females significant main effects of rs7103411 for memory and of rs6265 for perceptual speed independent of the APOE*E4 status and education. The finding for the association between rs6265 and perceptual speed in females remained significant after Bonferroni correction for multiple comparisons. None of the analyses showed significant results for males. This study is the first to implicate that the SNPs rs6265 and rs7103411 affect cognitive function in the elderly in a gender-specific way.

BDNF polymorphism predicts general intelligence after penetrating traumatic brain injury

Neuronal plasticity is a fundamental factor in cognitive outcome following traumatic brain injury. Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays an important role in this process. While there are many ways to measure cognitive outcome, general cognitive intelligence is a strong predictor of everyday decision-making, occupational attainment, social mobility and job performance. Thus it is an excellent measure of cognitive outcome following traumatic brain injury (TBI). Although the importance of the single-nucleotide polymorphisms polymorphism on cognitive function has been previously addressed, its role in recovery of general intelligence following TBI is unknown. We genotyped male Caucasian Vietnam combat veterans with focal penetrating TBI (pTBI) (n = 109) and non-head injured controls (n = 38) for 7 BDNF single-nucleotide polymorphisms. Subjects were administrated the Armed Forces Qualification Test (AFQT) at three different time periods: pre-injury on induction into the military, Phase II (10-15 years post-injury, and Phase III (30-35 years post-injury). Two single-nucleotide polymorphisms, rs7124442 and rs1519480, were significantly associated with post-injury recovery of general cognitive intelligence with the most pronounced effect at the Phase II time point, indicating lesion-induced plasticity. The genotypes accounted for 5% of the variance of the AFQT scores, independently of other significant predictors such as pre-injury intelligence and percentage of brain volume loss. These data indicate that genetic variations in BDNF play a significant role in lesion-induced recovery following pTBI. Identifying the underlying mechanism of this brain-derived neurotrophic factor effect could provide insight into an important aspect of post-traumatic cognitive recovery.

Association between brain-derived neurotrophic factor (BDNF) gene polymorphisms and executive function in Japanese patients with Alzheimer's disease

BACKGROUND

To address the functional roles of genetic polymorphisms of brain-derived neurotrophic factor (BDNF) in Alzheimer's disease (AD) from a neuropsychological aspect, we used a cross-sectional study design to investigate the association between novel single nucleotide polymorphisms (SNPs) of the BDNF gene (Val66Met (G196A) and C270T) and the Frontal Assessment Battery (FAB) score, which reflects executive function as a non-memory cognitive impairment.

METHODS

One hundred and sixty-nine outpatients with AD or amnestic mild cognitive impairment (A-MCI) were recruited to the study and divided into three genotypic groups for each representative BDNF functional polymorphism as follows: (i) Val66Met (G196A): G/G (n = 45), G/A (n = 104), and A/A (n = 20); and (ii) C270T: C/C (n = 160), C/T (n = 9), and T/T (n = 0). Then, age, sex ratio, duration of illness (months), education years, Mini-Mental State Examination (MMSE) score, behavioral pathology in Alzheimer disease (Behave-AD) score, Clinical Dementia Rating (CDR) ratio, and total and subtest FAB scores were compared between the genotypic groups for each SNP.

RESULTS

Significant differences were found in the total (P < 0.01) and subtest (conflicting instructions and prehension behavior; P < 0.01) FAB scores between the C270T polymorphism groups (C/C and C/T), but not among the G196A polymorphism groups. However, no significant differences in age, sex ratio, duration of illness (months), education years, Behave-AD score, CDR ratio, or MMSE score (reflecting attention and memory function) were found between the individual polymorphism genotypes (G196A and C270T).

CONCLUSION

Of the known BDNF polymorphisms, the C270T SNP may influence executive dysfunction as a non-memory cognitive impairment in Japanese patients with AD.