Association of Brain-Derived Neurotrophic Factor rs6265 G>A polymorphism and Post-traumatic Stress Disorder susceptibility: A systematic review and meta-analysis

Assessing Causality Between Plasma Brain-Derived Neurotrophic Factor With Major Depression Disorder: A Bidirectional Mendelian Randomization Study

PURPOSE

This study employed a two-sample Mendelian randomization (MR) approach to investigate the bidirectional relationship between brain-derived neurotrophic factor (BDNF) and major depressive disorder (MDD), addressing gaps left by prior observational studies.

METHODS

We utilized Genome-Wide Association Study (GWAS) datasets, including MDD information from the Psychiatric Genomics Consortium (PGC) and the UK Biobank (N = 500,199), along with plasma BDNF measurements from the FinnGen Consortium (N = 619). In a subsequent phase, we analyzed MDD data from FinnGen (N = 448,069) with plasma BDNF data from three additional GWAS sources: UK Biobank (N = 33,924), deCODE (N = 35,353), and INTERVAL (N = 3301). Multiple MR methods were applied to ensure a robust analysis.

RESULTS

The inverse variance weighted (IVW) method revealed no significant association between plasma BDNF levels and the risk of developing MDD (IVW odds ratio [OR] = 1.00, 95% confidence interval [CI] = 0.99-1.01, p = 0.769). Similarly, no causal effect of the BDNF gene on MDD was identified (OR = 0.91, CI = 0.23-3.56, p = 0.893). Furthermore, there was no evidence supporting a causal link between MDD and plasma BDNF levels (OR = 0.99, CI = 0.89-1.09, p = 0.783). The second phase of analysis confirmed the absence of bidirectional causal relationships.

CONCLUSION

This bidirectional MR analysis provides no evidence of a causal association between plasma BDNF levels and MDD. These findings prompt a re-evaluation of plasma BDNF as a biomarker for MDD and emphasize the need for further investigation into its functional role within the plasma as well as its levels and activity in the brain and cerebrospinal fluid.

Association of Brain-derived Neurotrophic Factor Polymorphisms With Alcohol Use Disorder: An Updated Meta-Analysis of Genetic Association Studies

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has been proposed to play a role in chronic alcohol consumption. However, studies investigating the association of single nucleotide polymorphisms (SNPs) in the BDNF gene with alcohol use disorder (AUD), including alcohol dependence, have obtained inconsistent results. This meta-analysis aims to examine the role of BDNF SNPs (rs6265, rs16917204, rs7103411, and rs11030104) in the risk of AUD.

MATERIALS AND METHODS

A multidatabase search identified 17 articles (20 studies) for inclusion. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to estimate associations using standard genetic models (homozygous, recessive, dominant, and codominant). Significant associations were defined as those with a p-value ≤ 0.05 after applying the Bonferroni correction (pBC). Subgroup analysis was conducted based on ethnicity (Caucasian and Asian populations). Sources of heterogeneity were investigated through outlier treatment and meta-regression analysis. Only significant outcomes were further subjected to sensitivity analysis and assessment of publication bias.

RESULTS

This meta-analysis generated four significant pooled ORs, representing the core outcomes, all of which indicated reduced risks. Overall, the results indicated a significant association between the BDNF polymorphism and the risk of AUD in homozygous (OR = 0.72, 95% CIs = 0.60-0.85, pBC = 0.0038) and codominant (OR = 0.84, 95% CIs = 0.78-0.91, pBC = 0.0019) model. In subgroup analysis by ethnicity, homozygous (OR = 0.59, 95% CIs = 0.44-0.78, pBC = 0.0057) and recessive (OR = 0.61, 95% CIs = 0.46-0.81, pBC = 0.0133) models of BDNF polymorphisms were significantly associated with a reduced risk of AUD in Caucasians. However, no significant associations were found in Asians. Meta-regression analysis did not identify any covariates that significantly contributed to the observed heterogeneity. The core significant associations were robust and showed no evidence of publication bias.

CONCLUSION

The current meta-analysis suggests that the examined BDNF SNPs have a protective effect in the overall analysis (homozygous and codominant) and in the Caucasians subgroup (homozygous and recessive) while the Asians exhibited no effects of BDNF SNPs on AUD. BDNF polymorphisms might serve as a protective factor against the risk of AUD and could be useful markers in the clinical genetics of AUD.

The BDNF Protein is Associated With Glucose Homeostasis and Food Intake in Carriers of Common BDNF Gene Variants

CONTEXT

Brain-derived neurotrophic factor (BDNF) concentrations may differ between BDNF genotype carriers. These changes occur in individuals with metabolic and mental disorders.

OBJECTIVE

The aim of this study was to assess the associations of glucose homeostasis parameters and the frequency of food consumption with BDNF protein concentrations based on BDNF single nucleotide polymorphisms (SNPs).

METHODS

Among the 439 participants, some common rs10835211 BDNF gene variants were analyzed. We evaluated BDNF concentrations, and measured glucose and insulin after fasting and during oral glucose tolerance tests. Anthropometric measurements, body composition, and body fat distribution were assessed, and a 3-day food intake diary and food frequency questionnaire were completed.

RESULTS

We observed significant differences in BDNF concentration between AA and AG genotype rs10835211 carriers (P = .018). The group of AA genotype holders were older, and positive correlation was found between age and BDNF in the whole study population (P = .012) and in the GG genotype carriers (P = .023). Moreover, BDNF protein correlated with fasting insulin (P = .015), HOMA-IR (P = .031), HOMA-B (P = .010), and the visceral/subcutaneous adipose tissue (VAT/SAT) ratio (P = .026) in the GG genotype individuals. Presence of the GG genotype was negatively correlated with nut and seed (P = .047) and lean pork consumption (P = .015), and the BDNF protein. Moreover, we observed correlations between the frequency of chicken (P = .028), pasta (P = .033), and sweet food intake (P = .040) with BDNF concentration in the general population. Among carriers of the AA genotype, we observed a positive correlation between the consumption of rice (P = .048) and sweet food (P = .028) and the BDNF protein level.

CONCLUSION

Peripheral BDNF may be associated with VAT content and insulin concentrations in GG genotype carriers and may vary with particular food intake, which warrants further investigation.

Biomarkers of Neurodegeneration in Post-Traumatic Stress Disorder: An Integrative Review

Post-Traumatic Stress Disorder (PTSD) is a chronic psychiatric disorder that occurs following exposure to traumatic events. Recent evidence suggests that PTSD may be a risk factor for the development of subsequent neurodegenerative disorders, including Alzheimer's dementia and Parkinson's disease. Identification of biomarkers known to be associated with neurodegeneration in patients with PTSD would shed light on the pathophysiological mechanisms linking these disorders and would also help in the development of preventive strategies for neurodegenerative disorders in PTSD. With this background, the PubMed and Scopus databases were searched for studies designed to identify biomarkers that could be associated with an increased risk of neurodegenerative disorders in patients with PTSD. Out of a total of 342 citations retrieved, 29 studies were identified for inclusion in the review. The results of these studies suggest that biomarkers such as cerebral cortical thinning, disrupted white matter integrity, specific genetic polymorphisms, immune-inflammatory alterations, vitamin D deficiency, metabolic syndrome, and objectively documented parasomnias are significantly associated with PTSD and may predict an increased risk of subsequent neurodegenerative disorders. The biological mechanisms underlying these changes, and the interactions between them, are also explored. Though requiring replication, these findings highlight a number of biological pathways that plausibly link PTSD with neurodegenerative disorders and suggest potentially valuable avenues for prevention and early intervention.

The Molecular Genetics of Dissociative Symptomatology: A Transdiagnostic Literature Review

Dissociative disorders are a common and frequently undiagnosed group of psychiatric disorders, characterized by disruptions in the normal integration of awareness, personality, emotion and behavior. The available evidence suggests that these disorders arise from an interaction between genetic vulnerability and stress, particularly traumatic stress, but the attention paid to the underlying genetic diatheses has been sparse. In this paper, the existing literature on the molecular genetics of dissociative disorders, as well as of clinically significant dissociative symptoms not reaching the threshold of a disorder, is reviewed comprehensively across clinical and non-clinical samples. Association studies suggest a link between dissociative symptoms and genes related to serotonergic, dopaminergic and peptidergic transmission, neural plasticity and cortisol receptor sensitivity, particularly following exposure to childhood trauma. Genome-wide association studies have identified loci of interest related to second messenger signaling and synaptic integration. Though these findings are inconsistent, they suggest biologically plausible mechanisms through which traumatic stress can lead to pathological dissociation. However, methodological concerns related to phenotype definition, study power, and correction for the confounding factors limit the value of these findings, and they require replication and extension in studies with better design.

Association of Brain-Derived Neurotrophic Factor rs6265 G>A polymorphism and Post-traumatic Stress Disorder susceptibility: A systematic review and meta-analysis

BACKGROUND

Previous studies have shown that the brain-derived neurotrophic factor (BDNF) rs6265 G > A polymorphism is closely related post-traumatic stress disorder (PTSD) risk. However, the results were not consistent. We therefore conducted a meta-analysis to explore the underlying relationships between BDNF rs6265 G > A polymorphism and PTSD risk.

MATERIALS AND METHODS

Five online databases were searched, and all related studies were reviewed up to July 1, 2020. Odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were calculated to examine the statistical power of each genetic model. In addition, heterogeneity, sensitivity accumulative analysis, and publication bias were examined to check the statistical power.

RESULT

Overall, 16 publications involving 5,369 subjects were included in this systematic review and 11 case-control studies were analyses in meta-analysis. The pooled results indicated an increasing risk of A allele mutations with PTSD risk. Moreover, the sequential subgroup analysis also demonstrated some similar situations in Asian populations and other groups.

CONCLUSION

Current meta-analysis suggests that the BDNF rs6265 G > A polymorphism might be involved in PTSD susceptibility.