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

BDNF gene Val66Met polymorphisms as a predictor for clinical presentation in schizophrenia - recent findings

Schizophrenia is a highly heritable, severe psychiatric disorder that involves dysfunctions in thinking, emotions, and behavior, with a profound impact on a person's ability to function normally in their daily life. Research efforts continue to focus on elucidating possible genetic underlying mechanisms of the disorder. Although the genetic loci identified to date to be significantly associated with schizophrenia risk do not represent disease-causing factors, each one of them could be seen as a possible incremental contributor. Considering the importance of finding new and more efficient pharmacological approaches to target the complex symptomatology of this disorder, in this scoping review, we are focusing on the most recent findings in studies aiming to elucidate the contribution of one of the genetic factors involved - the BDNF gene Val66Met polymorphisms. Here we performed a systematic search in Pubmed, Embase, and Web of Science databases with the search terms: (BDNF gene polymorphism) AND (schizophrenia) for articles published in the last 5 years. To be selected for this review, articles had to report on studies where genotyping for the BDNF Val66Met polymorphism was performed in participants diagnosed with schizophrenia (or schizophrenia spectrum disorders or first-episode psychosis). The search provided 35 results from Pubmed, 134 results from Embase, and 118 results from the Web of Science database. Twenty-two articles were selected to be included in this review, all reporting on studies where an implication of the BDNF Val66Met polymorphisms in the disorder's pathophysiology was sought to be elucidated. These studies looked at BDNF gene Val66Met polymorphism variants, their interactions with other genes of interest, and different facets of the illness. The Met/Met genotype was found to be associated with higher PANSS positive scores. Furthermore, Met/Met homozygous individuals appear to present with worse cognitive function and lower levels of serum BDNF. In the Val/Val genotype carriers, increased BDNF levels were found to correlate with weight gain under Risperidone treatment. However, due to heterogeneous results, the diversity in study populations and studies' small sample sizes, generalizations cannot be made. Our findings emphasize the need for further research dedicated to clarifying the role of gene polymorphisms in antipsychotic treatment to enhance specificity and efficacy in the treatment of schizophrenia.

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

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

Neuropsychiatric Symptoms of Alzheimer's Disease: An Anatomic-Genetic Framework for Treatment Development

BACKGROUND

Despite the burden on patients and caregivers, there are no approved therapies for the neuropsychiatric symptoms of Alzheimer's disease (NPS-AD). This is likely due to an incomplete understanding of the underlying mechanisms.

OBJECTIVE

To review the neurobiological mechanisms of NPS-AD, including depression, psychosis, and agitation.

METHODS

Understanding that genetic encoding gives rise to the function of neural circuits specific to behavior, we review the genetics and neuroimaging literature to better understand the biological underpinnings of depression, psychosis, and agitation.

RESULTS

We found that mechanisms involving monoaminergic biosynthesis and function are likely key elements of NPS-AD and while current treatment approaches are in line with this, the lack of effectiveness may be due to contributions from additional mechanisms including neurodegenerative, vascular, inflammatory, and immunologic pathways.

CONCLUSION

Within an anatomic-genetic framework, development of novel effective biological targets may engage targets within these pathways but will require a better understanding of the heterogeneity in NPS-AD.

Objective and Measurable Biomarkers in Chronic Subjective Tinnitus

Tinnitus is associated with increased social costs and reduced quality of life through sleep disorders or psychological distress. The pathophysiology of chronic subjective tinnitus, which accounts for most tinnitus, has not been clearly elucidated. This is because chronic subjective tinnitus is difficult to evaluate objectively, and there are no objective markers that represent the diagnosis or therapeutic effect of tinnitus. Based on the results of studies on patients with chronic subjective tinnitus, objective and measurable biomarkers that help to identify the pathophysiology of tinnitus have been summarized. A total of 271 studies in PubMed, 303 in EMBASE, and 45 in Cochrane Library were found on biomarkers related to chronic subjective tinnitus published until April 2021. Duplicate articles, articles not written in English, review articles, case reports, and articles that did not match our topic were excluded. A total of 49 studies were included. Three specimens, including blood, saliva, and urine, and a total of 58 biomarkers were used as indicators for diagnosis, evaluation, prognosis, and therapeutic effectiveness of tinnitus. Biomarkers were classified into eight categories comprising metabolic, hemostatic, inflammatory, endocrine, immunological, neurologic, and oxidative parameters. Biomarkers can help in the diagnosis, measure the severity, predict prognosis, and treatment outcome of tinnitus.

The role of CREB and BDNF in neurobiology and treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia worldwide. β-amyloid peptide (Aβ) is currently assumed to be the main cause of synaptic dysfunction and cognitive impairments in AD, but the molecular signaling pathways underlying its neurotoxic consequences have not yet been completely explored. Additional investigations regarding these pathways will contribute to development of new therapeutic targets. In context, developing evidence suggest that Aβ decreases brain-derived neurotrophic factor (BDNF) mostly by lowering phosphorylated cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) protein. In fact, it has been observed that brain or serum levels of BDNF appear to be beneficial markers for cognitive condition. In addition, the participation of transcription mediated by CREB has been widely analyzed in the memory process and AD development. Designing pharmacologic or genetic therapeutic approaches based on the targeting of CREB-BDNF signaling could be a promising treatment potential for AD. In this review, we summarize data demonstrating the role of CREB-BDNF signaling pathway in cognitive status and mediation of Aβ toxicity in AD. Finally, we also focus on the developing intervention methods for improvement of cognitive decline in AD based on targeting of CREB-BDNF pathway.

Function and Mechanisms of Truncated BDNF Receptor TrkB.T1 in Neuropathic Pain

Brain-derived neurotrophic factor (BDNF), a major focus for regenerative therapeutics, has been lauded for its pro-survival characteristics and involvement in both development and recovery of function within the central nervous system (CNS). However, studies of tyrosine receptor kinase B (TrkB), a major receptor for BDNF, indicate that certain effects of the TrkB receptor in response to disease or injury may be maladaptive. More specifically, imbalance among TrkB receptor isoforms appears to contribute to aberrant signaling and hyperpathic pain. A truncated isoform of the receptor, TrkB.T1, lacks the intracellular kinase domain of the full length receptor and is up-regulated in multiple CNS injury models. Such up-regulation is associated with hyperpathic pain, and TrkB.T1 inhibition reduces neuropathic pain in various experimental paradigms. Deletion of TrkB.T1 also limits astrocyte changes in vitro, including proliferation, migration, and activation. Mechanistically, TrkB.T1 is believed to act through release of intracellular calcium in astrocytes, as well as through interactions with neurotrophins, leading to cell cycle activation. Together, these studies support a potential role for astrocytic TrkB.T1 in hyperpathic pain and suggest that targeted strategies directed at this receptor may have therapeutic potential.

Genetic factors associated with the predisposition to late onset Alzheimer's disease

BACKGROUND

Alzheimer's disease is a progressive, irreversible neurodegenerative disorder characterized by loss of memory and cognitive skills. More than 90% of cases are sporadic and have later age of onset. Many studies have shown a genetic predisposition for late onset Alzheimer's disease (LOAD). The most studied genetic predisposition factor is apolipoprotein E gene besides other susceptibility genes involved in vascular pathologies, homocysteine metabolism, and neuronal growth and differentiation such as methylenetetrahydrofolate reductase (MTHFR), angiotensin-converting enzyme (ACE), APOB and brain derived neurotrophic factor (BDNF).

METHODS

In this study Factor V Leiden (G1691A) and H1299R, prothrombin G20210A, Factor XIII V34L, B-fibrinogen -455G>A, PAI-1 5G/4G, HPA1 b/a, MTHFR C677T, MTHFR A1298C, APOE, ACE I/D, BDNF C270T and G196A polymorphisms were evaluated in 100 LOAD patients and 100 age matched healthy controls.

RESULTS

APOE4 allele, MTHFR CC^A1298C and BDNF TT^C270T genotypes were significantly higher in LOAD patients compared to the control group (p < 0.001, p = 0.04, p = 0.03, respectively). There were no significant associations between other genotypes and allele frequencies. Mini-Mental State Examination (MMSE) scores and age at onset of the patients were also evaluated for each and combined genotypes. Age at onset was significantly lowered by about approximately 4 and 5 years in patients carrying BDNF TT^C270T and MTHFR TT^C677T genotypes, respectively.

CONCLUSION

APOE, MTHFR A1298C and BDNF C270T polymorphisms may be associated with LOAD and BDNF and MTHFR alleles may play a role in the age at onset of the LOAD.

Psychosis is an extension of mood swings from the perspective of neuronal plasticity impairments

We previously hypothesized that depressive and manic states may be consecutive presentations of the same underlying neuronal plasticity, and that moderate impairments in neuronal plasticity cause depressive states while further impairment to neuronal plasticity causes manic states. Psychopathological or biological relationships between bipolar disorder and schizophrenia have also been revealed. Therefore, in addition to depressive and manic states, psychosis may also be considered a manifestation resulting from additional impairments to neuronal plasticity. In the present manuscript, we hypothesize that moderate and more severe impairments to neuronal plasticity cause depressive and manic states, respectively, and that more serious impairments to neuronal plasticity cause psychosis. Many studies have suggested that impairments in neuronal plasticity contribute to schizophrenia and other mental disorders with psychotic features, and that the impairment of neuronal plasticity in schizophrenia is more severe than that in bipolar disorder. Therefore, we hypothesize more specifically that impairments in neuronal plasticity may be more severe in the order of the cases featuring psychosis, mania, and depression. This progression notably overlaps with the arrangement of schizophrenia, bipolar disorder, and depressive disorder in the DSM-5. Psychotic symptoms are thought to appear further towards the base of the psychopathological hierarchy than are manic or depressive symptoms. If impairments to neuronal plasticity contribute to this psychopathological hierarchy, as we contest that they do, our hypothesis may serve as a bridge between clinical psychopathology, diagnosis, and biological psychiatry.

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.

Sex Differences in Risk for Alzheimer's Disease Related to Neurotrophin Gene Polymorphisms: The Cache County Memory Study

Neurotrophins, including nerve-growth factor and brain-derived neurotrophic factor, have been implicated in Alzheimer's disease (AD). Associations between AD and neurotrophin signaling genes have been inconsistent, with few studies examining sex differences in risk. We examined four single-nucleotide polymorphisms (SNPs) involved in neurotrophin signaling (rs6265, rs56164415, rs2289656, rs2072446) and risk for AD by sex in a population-based sample of older adults. Three thousand four hundred and ninety-nine individuals without dementia at baseline [mean (standard deviation) age = 74.64 (6.84), 58% female] underwent dementia screening and assessment over four triennial waves. Cox regression was used to examine time to AD or right censoring for each SNP. Female carriers of the minor T allele for rs2072446 and rs56164415 had a 60% (hazard ratio [HR] = 1.60, 95% confidence interval [CI] = 1.02-2.51) and 93% (HR = 1.93, 95% CI = 1.30-2.84) higher hazard for AD, respectively, than male noncarriers of the T allele. Furthermore, male carriers of the T allele of rs2072446 had a 61% lower hazard (HR = 0.39, 95% CI = 0.14-1.06) than male noncarriers at trend-level significance (p = .07). The association between certain neurotrophin gene polymorphisms and AD differs by sex and may explain inconsistent findings in the literature.

Evidence of associations between brain-derived neurotrophic factor (BDNF) serum levels and gene polymorphisms with tinnitus

BACKGROUND

Brain-derived neurotrophic factor (BDNF) gene polymorphisms are associated with abnormalities in regulation of BDNF secretion. Studies also linked BDNF polymorphisms with changes in brainstem auditory-evoked response test results. Furthermore, BDNF levels are reduced in tinnitus, psychiatric disorders, depression, dysthymic disorder that may be associated with stress, conversion disorder, and suicide attempts due to crises of life. For this purpose, we investigated whether there is any role of BDNF changes in the pathophysiology of tinnitus.

MATERIALS AND METHODS

In this study, we examined the possible effects of BDNF variants in individuals diagnosed with tinnitus for more than 3 months. Fifty-two tinnitus subjects between the ages of 18 and 55, and 42 years healthy control subjects in the same age group, who were free of any otorhinolaryngology and systemic disease, were selected for examination. The intensity of tinnitus and depression was measured using the tinnitus handicap inventory, and the differential diagnosis of psychiatric diagnoses made using the Structured Clinical Interview for Fourth Edition of Mental Disorders. BDNF gene polymorphism was analyzed in the genomic deoxyribonucleic acid (DNA) samples extracted from the venous blood, and the serum levels of BDNF were measured. One-way analysis of variance and Chi-squared tests were applied.

RESULTS

Serum BDNF level was found lower in the tinnitus patients than controls, and it appeared that there is no correlation between BDNF gene polymorphism and tinnitus.

CONCLUSIONS

This study suggests neurotrophic factors such as BDNF may have a role in tinnitus etiology. Future studies with larger sample size may be required to further confirm our results.

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.

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.

Association between the brain-derived neurotrophic factor Val66Met polymorphism and therapeutic response to olanzapine in schizophrenia patients

RATIONALE

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a major role in neurogenesis and neuroplasticity, and in the modulation of several neurotransmitter systems including the dopaminergic system. There are mixed reports about the association between the BDNF Val66Met polymorphism, schizophrenia, and treatment response to antipsychotic drugs.

OBJECTIVES

The present study evaluated the association of the BDNF Val66Met polymorphism with treatment response to atypical antipsychotic olanzapine in schizophrenia and the possible predictive value of the BDNF Val66Met genotype status in treatment response to antipsychotic medication.

METHODS

The study included 590 ethnically homogenous Caucasian patients with schizophrenia (diagnosed using the SCID), 40.2 ± 12.0 years old, treated with olanzapine monotherapy (10-20 mg/day), or with other antipsychotics such as risperidone (3-6 mg/day), clozapine (100-500 mg/day), haloperidol (3-115 mg/day), fluphenazine (4-25 mg/day), and quetiapine (50-800 mg/day). Patients were subdivided into responders and non-responders according to a 50 % reduction in the Positive and Negative Syndrome Scale (PANSS) total and subscale scores after 8 weeks of treatment.

RESULTS

The results, corrected for possible effects of gender and age, showed a significant association between the BDNF Val66Met polymorphism and treatment response to olanzapine in patients. The Val/Val genotype was observed more frequently in treatment responders to olanzapine, and this genotype was associated with an improvement in clinical symptoms.

CONCLUSIONS

Our results suggest that BDNF Val66Met variants might influence the response to 8 weeks of monotherapy with olanzapine, in a relatively large sample of patients with schizophrenia.

Translational findings on brain-derived neurotrophic factor and anxiety: contributions from basic research to clinical practice

BACKGROUND/AIMS

Anxious responses are evolutionarily adaptive, but excessive fear can become disabling and lead to anxiety disorders. Translational models of anxiety might be useful sources for understanding the neurobiology of fear and anxiety and can contribute to future proposals of therapeutic intervention for the disorders studied. Brain-derived neurotrophic factor (BDNF), which is known for its importance on neuroplasticity and contextual memory, has emerged as a relevant element for emotional memory. Recent studies show that the Val(66)Met BDNF polymorphism correlates with various psychiatric disorders, including anxiety, but there are several differences between experimental and clinical studies.

METHODS

In this work, we review the literature focused on the BDNF Val(66)Met polymorphism and anxiety, and discuss biological findings from animal models to clinical studies.

RESULTS

As occurs with other psychiatric disorders, anxiety correlates with anatomical, behavioral and physiological changes related to the BDNF polymorphism. In animal studies, it has been shown that a significant decrease in regulated secretion from both BDNFVal/Met and BDNFMet/Met neurons represented a significant decrease in available BDNF.

CONCLUSION

These studies suggest that developing pharmacological strategies facilitating the release of BDNF from synapses or prolongation of the half-life of secreted BDNF may improve the therapeutic responses of humans expressing the BDNF polymorphism.

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.

Association of BDNF gene polymorphisms with schizophrenia and clinical symptoms in a Chinese population

The neurodevelopmental hypothesis is well established in schizophrenia. Accumulating evidence has shown that BDNF may be involved in the pathogenesis of schizophrenia. This study aimed to investigate the potential association of BDNF gene polymorphisms with susceptibility to schizophrenia and with the psychopathological symptoms in patients with schizophrenia in a Han Chinese population. Three polymorphisms (rs6265, rs12273539, and rs10835210) of the BDNF gene were analyzed in a case-control study of 709 Han Chinese individuals (375 patients and 334 controls). The patients' psychopathology was assessed using the positive and negative syndrome scale (PANSS). We found no significant differences in the genotype and allele distributions of all three polymorphisms between the patient and control groups; however, we found a trend toward to significant overall difference in the estimated haplotype frequencies, with more frequent haplotype ATC of rs6265-rs12273539-rs10835210 in the schizophrenic patients than in controls (P = 0.027). The quantitative trait analysis by the UNPHASED program showed significant associations between the rs6265 (A)-rs12273539 (C)-rs10835210 (A) haplotype and negative symptom scores from the PANSS (x(2)  = 5.79, P = 0.016). Our findings suggest that the BDNF gene polymorphisms may play a small effect on susceptibility to schizophrenia, but may contribute to the negative symptoms of the disease.

Brain-derived neurotrophic factor (Val66Met) polymorphism and olfactory ability in young adults

Background

Brain- derived neurotrophic factor (BDNF) is linked to neurodegenerative diseases (e.g. Alzheimer disease and Parkinson disease) which are often characterized by olfactory impairment. A specific single nucleotide polymorphism of the BDNF gene, the Val66Met, modulates intracellular trafficking and activity-dependent secretion of BDNF protein. The aim of this study was to investigate a possible association between brain- derived neurotrophic factor Val66Met polymorphism and olfactory function, a well-known biomarker for neurodegeneration, in healthy young adults. A total of 101 subjects (45 males, age 38.7 ± 9.4 years) were assessed using the Sniffin’ Sticks Extended Test, a highly reliable commercial olfactory test composed of three sub-parts, calculating olfactory threshold (sensitivity), odor discrimination and odor identification. The Val66Met polymorphism was determined by polymerase chain reaction -restriction fragment length polymorphism (PCR-RFLP) analysis.

Results

An impaired function in Met carriers was found, especially when compared to subjects with Val/Val genotype, in the threshold (5.5 ± 2.0 vs 6.5 ± 1.8, p = 0.009), discrimination (10.3± 2.5 vs 11.9 ± 2.2, p = 0.002), and identification task (13.3 ± 1.6 vs 14.1 ± 1.3, p = 0.007), as well as in the overall TDI Score (29.1 ± 4.5 vs 32.6 ± 3.9, p < 0.001).

Conclusions

These findings appear to have implications for the evaluation of olfactory function and the relation of its impairment to cognitive decline and neurodegenerative disease.

Lack of association between brain-derived neurotrophic factor Val66Met polymorphism and body mass index change over time in healthy adults

Obesity is becoming the epidemic health problem worldwide with a very complex etiology. The interaction between diverse genetic and environmental factors contributes to development of obesity. Among myriad of functions in central and peripheral tissues, brain-derived neurotrophic factor (BDNF) also regulates energy homeostasis, food intake and feeding behavior, and has a role in obesity and increased body mass index (BMI). BDNF Val66Met (rs6265) polymorphism is associated with BMI gain, but both positive associations and non-replications are reported. Since BMI changes over time and since genetic influences on BMI vary with age, the aim of the study was to evaluate association between BDNF Val66Met polymorphism and BMI gain in healthy subjects with middle or old age. The study included a cohort of 339 adult healthy Caucasians of Croatian origin, free of eating and metabolic disorders, evaluated in three time periods in the year 1972, 1982 and 2006, when the subjects were around 40, 50 and 70 years old, respectively. The results revealed a significant effect of smoking on BMI, but a lack of significant association between BDNF Val66Met polymorphism and overweight or obesity, and no significant association between BDNF Val66Met and BMI changes over time. These results did not confirm the major role of BDNF Val66Met in the regulation of BMI changes in adult and old healthy subjects.

Brain-derived neurotrophic factor Val66Met polymorphism and alcohol-related phenotypes

Alcoholism is a chronic psychiatric disorder affecting neural pathways that regulate motivation, stress, reward and arousal. Brain-derived neurotrophic factor (BDNF) regulates mood, response to stress and interacts with neurotransmitters and stress systems involved in reward pathways and addiction. Aim of the study was to evaluate the association between a single nucleotide polymorphism (BDNF Val66Met or rs6265) and alcohol related phenotypes in Caucasian patients. In ethnically homogenous Caucasian subjects of the Croatian origin, the BDNF Val66Met genotype distribution was determined in 549 male and 126 female patients with alcohol dependence and in 655 male and 259 female healthy non-alcoholic control subjects. Based on the structured clinical interview, additional detailed clinical interview, the Brown-Goodwin Scale, the Hamilton Rating Scale for Depression and the Clinical Global Impression scores, alcoholic patients were subdivided into those with or without comorbid depression, aggression, delirium tremens, withdrawal syndrome, early/late onset of alcohol abuse, prior suicidal attempt during lifetime, current suicidal behavior, and severity of alcohol dependence. The results showed no significant association between BDNF Val66Met variants and alcohol dependence and/or any of the alcohol related phenotypes in either Caucasian women, or men, with alcohol dependence. There are few limitations of the study. The overall study sample size was large (N=1589) but not well-powered to detect differences in BDNF Val66Met genotype distribution between studied groups. Healthy control women were older than female alcoholic patients. Only one BDNF polymorphism (rs6265) was studied. In conclusion, these data do not support the view that BDNF Val66Met polymorphism correlates with the specific alcohol related phenotypes in ethnically homogenous medication-free Caucasian subjects with alcohol dependence.

Interaction of sex steroid hormones and brain-derived neurotrophic factor-tyrosine kinase B signalling: relevance to schizophrenia and depression

Sex steroid hormones and neurotrophic factors are involved in pruning and shaping the developing brain and have been implicated in the pathogenesis of neurodevelopmental disorders. Sex steroid hormones are also involved in the regulation of brain-derived neurotrophic factor expression. A review of the literature is provided on the relationship between brain-derived neurotrophic factor and sex steroid hormones, as well as the mechanisms behind this interaction, in the context of how this relationship may be involved in the development of neurodevelopmental psychiatric illnesses, such as schizophrenia and depression.

A Review of Brain-derived Neurotrophic Factor as a Candidate Biomarker in Schizophrenia

Brain-derived neurotrophic factor (BDNF), a neurotrophin known to be responsible for development, regeneration, survival and maintenance of neurons has been implicated in the pathophysiology of schizophrenia. This review seeks to complement previous reviews on biological roles of BDNF and summarizes evidence on the involvement of BDNF in the pathophysiology of schizophrenia with an emphasis on clinical relevance. The expressions of BDNF were altered in patients with schizophrenia and were found to be correlated with psychotic symptomatology. Antipsychotics appeared to have differential effects on expression of BDNF but did not restore BDNF expression of patients with schizophrenia to normal levels. In addition, evidence suggests that BDNF is involved in the major neurotransmitter systems and is associated with disruptions in brain structure, neurodevelopmental process, cognitive function, metabolic and immune systems commonly associated with schizophrenia. Besides that, BDNF has been demonstrated to be tightly regulated with estrogen which has also been previously implicated in schizophrenia. Evidence gathered in this review confirms the relevance of BDNF in the pathophysiology of schizophrenia and the potential utility of BDNF as a suitable biomarker for diagnostic and prognostic purposes for disease outcome and other co-morbidities. However, further investigations are warranted to examine the specificity of BDNF in schizophrenia compared to other neurodegenerative disorders and other neuropsychiatric illness. Longitudinal prospective studies will also be of added advantage for evaluation of prognostic utility of BDNF in schizophrenia.

The association between brain-derived neurotrophic factor Val66Met variants and psychotic symptoms in posttraumatic stress disorder

OBJECTIVES

Psychotic symptoms frequently occur in veterans with combat-related posttraumatic stress disorder (PTSD). Brain-derived neurotrophic factor (BDNF) plays a major role in neurodevelopment, neuro-regeneration, neurotransmission, learning, regulation of mood and stress responses. The Met allele of the functional polymorphism, BDNF Val66Met, is associated with psychotic disorders. This study intended to assess whether the Met allele is overrepresented in unrelated Caucasian male veterans with psychotic PTSD compared to veteran controls.

METHODS

The BDNF Val66Met variants were genotyped in 576 veterans: 206 veterans without PTSD and 370 veterans with PTSD subdivided into groups with or without psychotic features.

RESULTS

Veterans with psychotic PTSD were more frequently carriers of one or two Met alleles of the BDNF Val66Met polymorphism than veterans with PTSD without psychotic features and veterans without PTSD.

CONCLUSIONS

The study shows that veterans with psychotic PTSD carried more Met alleles of the BDNF Val66Met than non-psychotic veterans with PTSD or veterans without PTSD. The results might add further support to the hypothesis that psychotic PTSD is a more severe subtype of PTSD.

Truncated TrkB: beyond a dominant negative receptor

BDNF activates trkB receptors to regulate neuronal survival, differentiation, and proliferation. Mutations in the BDNF gene, altered BDNF expression, and altered trkB expression are associated with degenerative and psychiatric disorders. The full-length trkB receptor (trkB.tk(+)) undergoes autophosphorylation to activate intracellular signaling pathways. The truncated trkB receptor (trkB.t1) is abundantly expressed in the brain but lacks the catalytic tyrosine kinase domain. TrkB.t1 is a dominant-negative receptor that inhibits trkB.tk(+) signaling. While this is an important function of trkB.t1, it is only one of its many functions. TrkB.t1 sequesters and translocate BDNF, induces filopodia and neurite outgrowth, stimulates intracellular signaling cascades, regulates Rho GTPase signaling, and modifies cytoskeletal structures. TrkB.t1 is an active signaling molecule with regulatory effects on neurons and astrocytes.

Association between brain-derived neurotrophic factor Val66Met and obesity in children and adolescents

Obesity in children and adolescents is a worldwide health problem, characterized by various somatic, psychosocial and psychiatric complications, and is often associated with adult obesity and related complications. Brain-derived neurotrophic factor (BDNF) is a neurotrophin with important roles in feeding behavior, food intake regulation, energy metabolism and weight control. A common polymorphism of the BDNF genotype (Val66Met) has been associated with various forms of eating disorders, alterations in body mass index (BMI) values and obesity in adult populations. The aim of this study was to determine the association between the gene variants of the BDNF Val66Met polymorphism and obesity in 300 healthy Caucasian children and adolescents of the same ethnic background of Croatian origin, subdivided according to the BMI percentile, but without any form of eating disorders. The frequency of the Met/Met, Met/Val and Val/Val genotypes, Met and Val alleles, and Met carriers (the combined Met/Met and Met/Val genotypes versus the homozygous Val/Val genotype) differed significantly between underweight, normal weight, overweight and obese children, and the presence of one or two Met alleles contributed to this significant effect. These results showed for the first time the significant association between the presence of one or two Met alleles and obesity in ethnically homogenous groups of healthy Caucasian children and adolescents. These data confirmed the major role of BDNF in energy metabolism, food regulation and BMI.

Characterizing brain cortical plasticity and network dynamics across the age-span in health and disease with TMS-EEG and TMS-fMRI

Brain plasticity can be conceptualized as nature's invention to overcome limitations of the genome and adapt to a rapidly changing environment. As such, plasticity is an intrinsic property of the brain across the lifespan. However, mechanisms of plasticity may vary with age. The combination of transcranial magnetic stimulation (TMS) with electroencephalography (EEG) or functional magnetic resonance imaging (fMRI) enables clinicians and researchers to directly study local and network cortical plasticity, in humans in vivo, and characterize their changes across the age-span. Parallel, translational studies in animals can provide mechanistic insights. Here, we argue that, for each individual, the efficiency of neuronal plasticity declines throughout the age-span and may do so more or less prominently depending on variable 'starting-points' and different 'slopes of change' defined by genetic, biological, and environmental factors. Furthermore, aberrant, excessive, insufficient, or mistimed plasticity may represent the proximal pathogenic cause of neurodevelopmental and neurodegenerative disorders such as autism spectrum disorders or Alzheimer's disease.

Noninvasive brain stimulation in Alzheimer's disease: systematic review and perspectives for the future

BACKGROUND

A number of studies have applied transcranial magnetic stimulation (TMS) to physiologically characterize Alzheimer's disease (AD) and to monitor effects of pharmacological agents, while others have begun to therapeutically use TMS and transcranial direct current stimulation (tDCS) to improve cognitive function in AD. These applications are still very early in development, but offer the opportunity of learning from them for future development.

METHODS

We performed a systematic search of all studies using noninvasive stimulation in AD and reviewed all 29 identified articles. Twenty-four focused on measures of motor cortical reactivity and (local) plasticity and functional connectivity, with eight of these studies assessing also effects of pharmacological agents. Five studies focused on the enhancement of cognitive function in AD.

RESULTS

Short-latency afferent inhibition (SAI) and resting motor threshold are significantly reduced in AD patients as compared to healthy elders. Results on other measures of cortical reactivity, e.g. intracortical inhibition (ICI), are more divergent. Acetylcholine-esterase inhibitors and dopaminergic drugs may increase SAI and ICI in AD. Motor cortical plasticity and connectivity are impaired in AD. TMS/tDCS can induce acute and short-duration beneficial effects on cognitive function, but the therapeutic clinical significance in AD is unclear. Safety of TMS/tDCS is supported by studies to date.

CONCLUSIONS

TMS/tDCS appears safe in AD, but longer-term risks have been insufficiently considered. TMS holds promise as a physiologic biomarker in AD to identify therapeutic targets and monitor pharmacologic effects. In addition, TMS/tDCS may have therapeutic utility in AD, though the evidence is still very preliminary and cautious interpretation is warranted.