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

Mechanisms of neurodegeneration and axonal dysfunction in multiple sclerosis

Multiple sclerosis (MS) is the most frequent chronic inflammatory disease of the CNS, and imposes major burdens on young lives. Great progress has been made in understanding and moderating the acute inflammatory components of MS, but the pathophysiological mechanisms of the concomitant neurodegeneration--which causes irreversible disability--are still not understood. Chronic inflammatory processes that continuously disturb neuroaxonal homeostasis drive neurodegeneration, so the clinical outcome probably depends on the balance of stressor load (inflammation) and any remaining capacity for neuronal self-protection. Hence, suitable drugs that promote the latter state are sorely needed. With the aim of identifying potential novel therapeutic targets in MS, we review research on the pathological mechanisms of neuroaxonal dysfunction and injury, such as altered ion channel activity, and the endogenous neuroprotective pathways that counteract oxidative stress and mitochondrial dysfunction. We focus on mechanisms inherent to neurons and their axons, which are separable from those acting on inflammatory responses and might, therefore, represent bona fide neuroprotective drug targets with the capability to halt MS progression.

The serotonin transporter linked polymorphic region and brain-derived neurotrophic factor valine to methionine at position 66 polymorphisms and maternal history of depression: associations with cognitive vulnerability to depression in childhood

Preliminary work indicates that cognitive vulnerability to depression may be associated with variants of the serotonin transporter promoter polymorphism (5-HTTLPR) and the valine to methionine at position 66 (val66met) polymorphism of the brain-derived neurotrophic factor (BDNF) gene; however, existing reports come from small samples. The present study sought to replicate and extend this research in a sample of 375 community-dwelling children and their parents. Following a negative mood induction, children completed a self-referent encoding task tapping memory for positive and negative self-descriptive traits. Consistent with previous work, we found that children with at least one short variant of the 5-HTTLPR had enhanced memory for negative self-descriptive traits. The BDNF val66met polymorphism had no main effect but was moderated by maternal depression, such that children with a BDNF methionine allele had a heightened memory for negative self-descriptive traits when mothers had experienced depression during children's lifetimes; in contrast, children with a methionine allele had low recall of negative traits when mothers had no depression history. The findings provide further support for the notion that the 5-HTTLPR is associated with cognitive markers of depression vulnerability and that the BDNF methionine allele moderates children's sensitivity to contextual factors.

BDNF Val66Met polymorphism and antipsychotic-induced tardive dyskinesia occurrence and severity: a meta-analysis

BACKGROUND

Tardive dyskinesia (TD) is a serious long-term consequence of antipsychotic treatment. Since brain-derived neurotrophic factor (BDNF) has potent neurotrophic activity, genetic alterations in the BDNF gene may affect antipsychotic-induced TD.

METHODS

Searching PubMed and Web of Science until 05/31/13, we conducted a systematic review and a meta-analysis of the effects of BDNF Val66Met polymorphism on antipsychotic-induced TD. Pooled odds ratio was calculated to assess the effects of BDNF Val66Met polymorphism on TD occurrence. Additionally, pooled standardized mean differences (Hedges' g) were calculated to assess the effects on Abnormal Involuntary Movement Scale (AIMS) total score.

RESULTS

Out of 699 potentially eligible hits, 6 studies (N=1740, mean age=46.0±10.4years; males=73.1%; Asians=80.5%, Caucasians=19.5%; schizophrenia=96.2%) were included in this meta-analysis. Pooling data from all studies, no significant associations were found between BDNF Val66Met polymorphism and TD (p=0.82) or AIMS total scores (p=0.11). However, in studies including only Caucasians (n=339), Met allele carriers had significantly higher AIMS total scores (Hedges' g=0.253, 95% confidence interval=0.030 to 0.476, p=0.026) and non-significantly higher TD occurrence (p=0.127). Conversely, there was no association between BDNF and AIMS scores (p=0.57) or TD (p=0.65) in Asians.

CONCLUSION

Although there was no significant association between BDNF Val66Met polymorphism and TD or AIMS scores across all patients, our results suggest that BDNF Val66Met polymorphism affects severity and, possibly, TD development in Caucasians. Since the number of studies and patients was still small, additional data are needed to confirm genotype-racial interactions. Furthermore, BDNF enhancing treatments for TD may require further study, especially in Caucasians.

From pharmacogenetics to pharmacogenomics: the way toward the personalization of antidepressant treatment

OBJECTIVE

Major depressive disorder is the most common psychiatric disorder, worldwide, yet response and remission rates are still unsatisfactory. The identification of genetic predictors of antidepressant (AD) response could provide a promising opportunity to improve current AD efficacy through the personalization of treatment. The major steps and findings along this path are reviewed together with their clinical implications and limitations.

METHOD

We systematically reviewed the literature through MEDLINE and Embase database searches, using any word combination of "antidepressant," "gene," "polymorphism," "pharmacogenetics," "genome-wide association study," "GWAS," "response," and "adverse drug reactions." Experimental works and reviews published until March 2012 were collected and compared.

RESULTS

Numerous genes pertaining to several functional systems were associated with AD response. The more robust findings were found for the following genes: solute carrier family 6 (neurotransmitter transporter), member 4; serotonin receptor 1A and 2A; brain-derived neurotrophic factor; and catechol-O-methyltransferase. Genome-wide association studies (GWASs) provided many top markers, even if none of them reached genome-wide significance.

CONCLUSIONS

AD pharmacogenetics have not produced any knowledge applicable to routine clinical practice yet, as results were mainly inconsistent across studies. Despite this, the rising awareness about methodological deficits of past studies could allow for the identication of more suitable strategies, such as the integration of the GWAS approach with the candidate gene approach, and innovative methodologies, such as pathway analysis and study of depressive endophenotypes.

Interaction between stress and the BDNF Val66Met polymorphism in depression: a systematic review and meta-analysis

BACKGROUND

Major depression is a disabling psychiatric illness with complex origins. Life stress (childhood adversity and recent stressful events) is a robust risk factor for depression. The relationship between life stress and Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene has received much attention. The aim of the present work was to review and conduct a meta-analysis on the results from published studies examining this interaction.

METHODS

A literature search was conducted using PsychINFO and PubMed databases until 22 November 2013. A total of 22 studies with a pooled total of 14,233 participants met the inclusion criteria, the results of which were combined and a meta-analysis performed using the Liptak-Stouffer z-score method.

RESULTS

The results suggest that the Met allele of BDNF Val66Met significantly moderates the relationship between life stress and depression (P = 0.03). When the studies were stratified by type of environmental stressor, the evidence was stronger for an interaction with stressful life events (P = 0.01) and weaker for interaction of BDNF Val66Met with childhood adversity (P = 0.051).

CONCLUSIONS

The interaction between BDNF and life stress in depression is stronger for stressful life events rather than childhood adversity. Methodological limitations of existing studies include poor measurement of life stress.

Effect of the BDNF Val66Met polymorphism on regional gray matter volumes and cognitive function in the Chinese population

The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is common and influences the activity-dependent secretion of BDNF, which is critical for neuronal plasticity and survival. This study investigated the genetic effect of the BDNF Val66Met polymorphism on cognitive function and regional gray matter (GM) volume in a healthy Chinese population (n = 330). Voxel-based morphometry (VBM)-optimized analysis was used. There was no significant difference in the neuropsychological performances among the three BDNF genotypic groups. VBM analyses demonstrated that Met homozygotes had greater GM volumes than Val homozygotes in the left medial frontal gyrus, the left middle temporal gyrus, the left cerebellum, and the right middle temporal gyrus, and had larger GM volumes than Val/Met heterozygotes in the left middle temporal gyrus, the left inferior temporal gyrus, and the right superior frontal gyrus. Our findings suggest that the presence of two Met alleles has a protective effect on regional GM volumes in the Chinese population.

The interacting effect of the BDNF Val66Met polymorphism and stressful life events on adolescent depression is not an artifact of gene-environment correlation: evidence from a longitudinal twin study

BACKGROUND

Confounding introduced by gene-environment correlation (rGE) may prevent one from observing a true gene-environment interaction (G × E) effect on psychopathology. The present study investigated the interacting effect of the BDNF Val66Met polymorphism and stressful life events (SLEs) on adolescent depression while controlling for the rGE by two means: separating pure environmental factors (independent SLEs) from the environmental factors under partial genetic control (dependent SLEs) and adopting a prospective longitudinal design.

METHODS

A total of 780 pairs of Chinese twins, aged 11-17 years (mean = 13.6, SD = 1.8) at intake, were followed up twice. Self-reported depression symptoms at Time 1 and Time 2 were assessed by the Children's Depression Inventory (CDI). SLEs occurring between Time 1 and Time 2 were assessed by a self-reported checklist. SLEs were differentiated into independent and dependent ones and were validated by heritability analyses using twin design. The interacting effects between the BDNF Val66Met polymorphism and numbers of SLEs (total SLEs and independent SLEs) on intraindividual change of depression symptoms were examined.

RESULTS

After controlling for sex, age, age square, and Time 1 depression, both total SLEs × BDNF Val66Met genotype and independent SLEs × BDNF Val66Met genotype significantly predicted Time 2 depression. Val allele carriers (Val/Val and Val/Met) were more susceptible to the detrimental effects of stress.

CONCLUSIONS

There is a true G × E effect underlying the observed interaction between BDNF Val66Met polymorphism and environmental stress on depression.

BDNF Val(66)Met genotype is associated with drug-seeking phenotypes in heroin-dependent individuals: a pilot study

Brain-derived neurotrophic factor (BDNF) Val(66)Met genotype has been associated with neurobehavioral deficits. To examine its relevance for addiction, we examined BDNF genotype differences in drug-seeking behavior. Heroin-dependent volunteers (n = 128) completed an interview that assessed past-month naturalistic drug-seeking/use behaviors. In African Americans (n = 74), the Met allele was uncommon (carrier frequency 6.8%); thus, analyses focused on European Americans (n = 54), in whom the Met allele was common (carrier frequency 37.0%). In their natural setting, Met carriers (n = 20) reported more time- and cost-intensive heroin-seeking and more cigarette use than Val homozygotes (n = 34). BDNF Val(66)Met genotype predicted 18.4% of variance in 'weekly heroin investment' (purchasing time × amount × frequency). These data suggest that the BDNF Met allele may confer a 'preferred drug-invested' phenotype, resistant to moderating effects of higher drug prices and non-drug reinforcement. These preliminary hypothesis-generating findings require replication, but are consistent with pre-clinical data that demonstrate neurotrophic influence in drug reinforcement. Whether this genotype is relevant to other abused substances besides opioids or nicotine, or treatment response, remains to be determined.

Pharmacogenetics of antidepressant drugs: an update after almost 20 years of research

Major depressive disorder (MDD) is an emergent cause of personal and socio-economic burden, both for the high prevalence of the disorder and the unsatisfying response rate of the available antidepressant treatments. No reliable predictor of treatment efficacy and tolerance in the single patient is available, thus drug choice is based on a trial and error principle with poor clinical efficiency. Among modulators of treatment outcome, genetic polymorphisms are thought to explain a significant share of the inter-individual variability. The present review collected the main pharmacogenetic findings primarily about antidepressant response and secondly about antidepressant induced side effects, and discussed the main strengths and limits of both candidate and genome-wide association studies and the most promising methodological opportunities and challenges of the field. Despite clinical applications of antidepressant pharmacogenetics are not available yet, previous findings suggest that genotyping may be applied in the clinical practice. In order to reach this objective, further rigorous pharmacogenetic studies (adequate sample size, study of better defined clinical subtypes of MDD, adequate covering of the genetic variability), their combination with the results obtained through complementary methodologies (e.g., pathway analysis, epigenetics, transcriptomics, and proteomics), and finally cost-effectiveness trials are required.

Altered white matter architecture in BDNF met carriers

Brain-derived neurotrophic factor (BDNF) modulates the pruning of synaptically silent axonal arbors. The Met allele of the BDNF gene is associated with a reduction in the neurotrophin's activity-dependent release. We used diffusion-weighted imaging to construct structural brain networks for 36 healthy subjects with known BDNF genotypes. Through permutation testing we discovered clear differences in connection strength between subjects carrying the Met allele and those homozygotic for the Val allele. We trained a Gaussian process classifier capable of identifying the subjects' allelic group with 86% accuracy and high predictive value. In Met carriers structural connectivity was greatly increased throughout the forebrain, particularly in connections corresponding to the anterior and superior corona radiata as well as corticothalamic and corticospinal projections from the sensorimotor, premotor, and prefrontal portions of the internal capsule. Interhemispheric connectivity was also increased via the corpus callosum and anterior commissure, and extremely high connectivity values were found between inferior medial frontal polar regions via the anterior forceps. We propose that the decreased availability of BDNF leads to deficits in axonal maintenance in carriers of the Met allele, and that this produces mesoscale changes in white matter architecture.

Decreased serum levels of brain-derived neurotrophic factor in adults with attention-deficit hyperactivity disorder

It has been hypothesized that brain-derived neurotrophic factor (BDNF) is involved in the pathogenesis of attention-deficit hyperactivity disorder (ADHD), although experimental data regarding the contribution of BDNF gene polymorphisms to this psychiatric disorder are controversial. Recently, changes in BDNF serum levels have been reported in children with ADHD, but there are no studies about the possible role of this neurotrophin in adults. A total of 54 Caucasoid ADHD adults, including the predominantly inattentive and combined types (aged 33.43 ± 8.99 yr) and 59 Caucasoid unrelated healthy controls (aged 35.52 ± 9.37 yr) were included in a study to evaluate BDNF levels in serum. Medical, neurological and psychiatric co-morbidities were excluded. Clinical data concerning ADHD diagnosis and blood samples for patients and controls were collected. BDNF serum levels were significantly lower in adults with ADHD compared to healthy controls (p < 0.0001). Although the combined type of ADHD subgroup displayed lower BDNF serum levels than the inattentive type, the differences did not reach statistical significance. No significant correlations were found between serum BDNF levels and scores on the Conners' Adult ADHD Rating Subscales. These results suggest a role for BDNF in ADHD, at least in those patients whose disorder persists throughout life. Low BDNF levels may contribute to the neurodevelopmental deficits of ADHD and to the persistence of the disorder into adulthood. BDNF differences between ADHD subtypes should be further studied.

Possible associations of NTRK2 polymorphisms with antidepressant treatment outcome: findings from an extended tag SNP approach

BACKGROUND

Data from clinical studies and results from animal models suggest an involvement of the neurotrophin system in the pathology of depression and antidepressant treatment response. Genetic variations within the genes coding for the brain-derived neurotrophic factor (BDNF) and its key receptor Trkb (NTRK2) may therefore influence the response to antidepressant treatment.

METHODS

We performed a single and multi-marker association study with antidepressant treatment outcome in 398 depressed Caucasian inpatients participating in the Munich Antidepressant Response Signature (MARS) project. Two Caucasian replication samples (N = 249 and N = 247) were investigated, resulting in a total number of 894 patients. 18 tagging SNPs in the BDNF gene region and 64 tagging SNPs in the NTRK2 gene region were genotyped in the discovery sample; 16 nominally associated SNPs were tested in two replication samples.

RESULTS

In the discovery analysis, 7 BDNF SNPs and 9 NTRK2 SNPs were nominally associated with treatment response. Three NTRK2 SNPs (rs10868223, rs1659412 and rs11140778) also showed associations in at least one replication sample and in the combined sample with the same direction of effects (Pcorr  = .018, Pcorr  = .015 and Pcorr  = .004, respectively). We observed an across-gene BDNF-NTRK2 SNP interaction for rs4923468 and rs1387926. No robust interaction of associated SNPs was found in an analysis of BDNF serum protein levels as a predictor for treatment outcome in a subset of 93 patients.

CONCLUSIONS/LIMITATIONS

Although not all associations in the discovery analysis could be unambiguously replicated, the findings of the present study identified single nucleotide variations in the BDNF and NTRK2 genes that might be involved in antidepressant treatment outcome and that have not been previously reported in this context. These new variants need further validation in future association studies.

BDNF Val66Met homozygosity does not influence plasma BDNF levels in healthy human subjects

A putative pathway by which the BDNF Val66Met polymorphism (rs6265) leads to aberrant phenotypes is its influence on plasma BDNF. Research into the impact of rs6265 on plasma BDNF has given rise to conflicting results. Moreover, most such studies have compared Met-carriers with Val-homozygous subjects. We therefore genotyped subjects from a population-based cohort (the Utrecht Health Project, N=2743) and assessed whether plasma BDNF differs between rs6265 homozygous groups. We maximized the number of Met-homozygous subjects in whom we measured plasma BDNF, resulting in plasma BDNF being available for 19 Met-homozygous and 42 matched Val-homozygous subjects. Mean concentrations (S.D.) were 1963.1 (750.1) and 2133.2 pg/ml (1164.3) for the Val/Val and Met/Met groups, respectively. Using ANOVA, no differences in plasma BDNF between the two groups were detected. In conclusion, these results add to a growing body of evidence indicating that allelic variation at rs6265 does not have medium to large effects on plasma BDNF concentrations.

Selfish brain and neuroprogression in bipolar disorder

Bipolar disorder is associated with increases in mortality rates due to metabolic complications when compared to the general population. The "selfish brain" theory postulates that the CNS modulates energy metabolism in the periphery in order to prioritize its own demand and offers an heurist value framework to understand how and why metabolic abnormalities develop in the course of BD. Mood episodes, especially those of manic polarity are neurotoxic, because of the acute release of the neurotransmitters dopamine and glutamate, oxidative species, inflammatory cytokines and the deprivation of neuroprotective factors, such as neurotrophins. The cell loss and malfunctioning require from the brain an extra effort to repair itself, which will demand energetic supplies. Application of "selfish brain" theory in BD can potentially offer new insights about how to prevent and treat metabolic complications in BD.

BDNF-based synaptic repair as a disease-modifying strategy for neurodegenerative diseases

Increasing evidence suggests that synaptic dysfunction is a key pathophysiological hallmark in neurodegenerative disorders, including Alzheimer's disease. Understanding the role of brain-derived neurotrophic factor (BDNF) in synaptic plasticity and synaptogenesis, the impact of the BDNF Val66Met polymorphism in Alzheimer's disease-relevant endophenotypes - including episodic memory and hippocampal volume - and the technological progress in measuring synaptic changes in humans all pave the way for a 'synaptic repair' therapy for neurodegenerative diseases that targets pathophysiology rather than pathogenesis. This article reviews the key issues in translating BDNF biology into synaptic repair therapies.

The brain-derived neurotrophic factor Val66Met polymorphism moderates early deprivation effects on attention problems

Adverse early care is associated with attention regulatory problems, but not all so exposed develop attention problems. In a sample of 612 youth (girls = 432, M = 11.82 years, SD = 1.5) adopted from institutions (e.g., orphanages) in 25 countries, we examined whether the Val66Met polymorphism of the brain-derived neurotrophic factor gene moderates attention problems associated with the duration of institutional care. Parent-reported attention problem symptoms were collected using the MacArthur Health and Behavior Questionnaire. DNA was genotyped for the brain-derived neurotrophic factor Val66Met (rs6265) single nucleotide polymorphism. Among youth from Southeast (SE) Asia, the predominant genotype was valine/methionine (Val/Met), whereas among youth from Russia/Europe and Caribbean/South America, the predominant genotype was Val/Val. For analysis, youth were grouped as carrying Val/Val or Met/Met alleles. Being female, being from SE Asia, and being younger when adopted were associated with fewer attention regulatory problem symptoms. Youth carrying at least one copy of the Met allele were more sensitive to the duration of deprivation, yielding an interaction that followed a differential susceptibility pattern. Thus, youth with Val/Met or Met/Met genotypes exhibited fewer symptoms than Val/Val genotypes when adoption was very early and more symptoms when adoption occurred later in development. Similar patterns were observed when SE Asian youth and youth from other parts of the world were analyzed separately.

Association between BDNF gene polymorphisms and serotonergic activity using loudness dependence of auditory evoked potentials in healthy subjects

It has been proposed that the loudness dependence of auditory evoked potentials (LDAEP) would be a reliable indicator of central serotonin system activity in humans. Serotonin levels and turnover are also increased by brain-derived neurotrophic factor (BDNF). The aim of the present study was to determine whether there is an association between genetic polymorphisms of BDNF and the LDAEP in healthy Korean young adults. The cohort comprised 211 mentally and physically healthy subjects, all of whom were nonsmokers (111 males, 100 females; age: 20∼32 years). To avoid hormonal effects, the LDAEP was measured during days 2–5 after the beginning of menstruation for female subjects. In addition, BDNF polymorphisms (rs6265, rs2030324, and rs1491850) were genotyped. The strength of the LDAEP differed significantly among the BDNF genotype groups. Furthermore, the distribution of genotypic frequencies differed significantly between subjects with high and low LDAEPs. In particular, subjects with the Val/Met (A/G) genotype for rs6265, the T/T genotype for rs2030324, or the C/C genotype for rs1491850 had a higher LDAEP, indicating lower central serotonergic activity. A low LDAEP was more prevalent than a high LDAEP among those with the C-T haplotype (C genotype for rs2030424 and T genotype for rs1491850). Our results concur with previous findings on BDNF polymorphisms and serotonergic drug responses in psychiatric disorder patients. The present results suggest the possibility that BDNF polymorphisms and LDAEP patterns can predict altered serotonergic activity.

Neurotrophic tyrosine kinase receptor type 2 (NTRK2) gene associated with treatment response to mood stabilizers in patients with bipolar I disorder

There is increasing evidence supporting the relationship between bipolar disorder (BP) and neurotrophin. The present study investigated the relationship between neurotrophic tyrosine kinase receptor type 2 (NTRK2) gene polymorphisms and bipolar I disorder (BP I) susceptibility and treatment response to mood stabilizers (lithium or valproate). Two-hundred eighty-four patients who met the DSM-IV criteria for BP I and 295 matched healthy controls were enrolled into this study. TaqMan® SNP genotyping assays were applied to genotype three NTRK2 gene polymorphisms (rs2769605, rs1565445, rs1387923). Our study showed a significant allelic association between NTRK2 gene polymorphism rs2769605 and treatment response to mood stabilizers in BP I patients (t = -2.53, P = 0.01). However, no significant association between NTRK2 gene polymorphisms and BP I susceptibility was observed after correcting for multiple comparisons. The results suggest that the NTRK2 gene polymorphism likely plays an essential role in treatment response to mood stabilizers in Han Chinese BP I patients.

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 effect between the BDNF Val66Met polymorphism and parental rearing for interpersonal sensitivity in healthy subjects

Interpersonal sensitivity is defined as undue and excessive awareness of, and sensitivity to, the behaviour and feelings of others and is one of the vulnerable factors to depression. In a twin study, it was suggested that this personality trait was characterised by both genetic and environmental factors. In the present study, we examined the effects of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism and parental rearing on interpersonal sensitivity in 725 healthy Japanese subjects. Assessment of interpersonal sensitivity was performed by the Japanese version of the Interpersonal Sensitivity Measure (IPSM). Perceived parental rearing was assessed by the Parental Bonding Instrument (PBI), which consists of the care and protection factors. The BDNF polymorphism was detected by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. There was no main effect of the BDNF genotype on the IPSM score, while the PBI factors except maternal care had significant main effect on the IPSM score. There was significant interaction effect between the BDNF genotype and maternal care of the PBI on the IPSM score. Post-hoc analysis of simple slopes showed that the negative relationship between the IPSM score and maternal care was strongest and significant in the Met/Met genotype group, intermediate in the Val/Met genotype group and weakest in the Val/Val genotype group. The present study suggests that the interaction between the BDNF Val66Met polymorphism and parental rearing, especially maternal care, influences interpersonal sensitivity in healthy subjects.

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.

The Beijing Twin Study (BeTwiSt): a longitudinal study of child and adolescent development

Rates of emotional and behavioral problems among children and adolescents in China are increasing and represent a major public health concern. To investigate the etiology of such problems, including the effects and interplay of genes and environment, the Beijing Twin Study (BeTwiSt) was established. A representative sample of adolescent twins in Beijing (N = 1,387 pairs of adolescent twins, mostly between the ages of 10 and 18 years) was recruited and assessed longitudinally. Data collection included the following: emotional and behavioral problems (e.g., depressive symptoms, anxiety, delinquency, drinking, and smoking); family, peer, and school environments; stress; social and academic competence; cognitive traits (e.g., emotion suppression, rumination, and effortful control); and saliva samples for DNA genotyping and sequencing. The combination of quantitative and molecular genetic approaches and the timeliness of the project, with the sample residing in a region with a rapidly changing economic and cultural climate, are particular strengths of this study. Findings from this study are expected to help understanding of the etiological mechanisms underlying child and adolescent normal and abnormal development in regions undergoing substantial social, cultural, and economic changes.

The role of brain-derived neurotrophic factor (BDNF) gene variants in antipsychotic response and antipsychotic-induced weight gain

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has extensive effects on the nervous system including cell survival, differentiation, neuronal growth and maintenance, as well as cell death. Moreover, it promotes synaptic plasticity and interacts with dopaminergic and serotonergic neurons, suggesting an important role on the alteration of brain function with antipsychotic medications and induced weight gain in schizophrenia patients. The differential effects of BDNF gene variants could lead to changes in brain circuitry that would in turn cause variable response to antipsychotic medication. Therefore, we hypothesized that genetic variation in this candidate gene helps in explaining the inter-individual variation observed in antipsychotic drug treatment with respect to response and induced weight gain.

METHOD

We examined four single-nucleotide polymorphisms across the BDNF gene, including Val66Met (rs6265). Prospective BPRS change scores and weight change after six weeks were obtained from a total of 257 schizophrenia patients of European ancestry.

RESULTS

The markers rs11030104 and Val66Met were associated with antipsychotic response (P=0.04; 0.007, respectively). On the other hand, marker rs1519480 was associated with weight gain (P=0.04). Moreover, a two-marker haplotype across rs6265 and rs1519480 was associated with weight change (P=0.001). Results with Val66Met in response, and results with rs6265-rs1519480 haplotypes remained significant at the modified Bonferroni corrected alpha of 0.017.

CONCLUSION

BDNF genetic variants might play an important role in predicting antipsychotic response and antipsychotic-induced weight gain. However, replication in larger and independent samples is required.

Interacting effect of BDNF Val66Met polymorphism and stressful life events on adolescent depression

There is a strong etiological link between brain-derived neurotrophic factor and depression, but the neurocellular mechanisms and gene-environment interactions remain obscure. This study investigated whether one functional polymorphism in the brain-derived neurotrophic factor gene (BDNF Val66Met) modulates the influence of stressful life events on adolescent depressive symptoms. A total of 780 pairs of ethnic Han Chinese adolescent twins, 11-17 years of age, were randomly assigned to one of two subgroups (twin1 and twin2). All subjects were genotyped as Val/Val, Val/Met or Met/Met, and assessed for depressive symptoms using the Children's Depression Inventory. The level of environmental stress was estimated by the frequency of stressful life events using the Life Events Checklist. The frequency of stressful life events was significantly correlated with depressive symptoms (twin1: β = 0.21, P = 0.01; twin2: β = 0.27, P < 0.01), but there was no significant main effect of the BDNF Val66Met genotype on depressive symptoms. In both subgroups, however, the interaction between the BDNF Val66Met genotype and stressful life event frequency was significant (twin1: β = 0.19, P = 0.01; twin2: β = 0.15, P = 0.04); individuals with one or two Val alleles demonstrated a greater susceptibility to both the detrimental effects of higher stress and the beneficial effects of lower stress compared to the Met/Met genotype. These findings support the 'differential-susceptibility' hypothesis, whereby the BDNF Val allele modulates the influence of environmental stress on depression by enhancing the neuroplastic response to all life events.

Variant brain-derived neurotrophic factor (Valine66Methionine) polymorphism contributes to developmental and estrous stage-specific expression of anxiety-like behavior in female mice

BACKGROUND

Most anxiety and depressive disorders are twice as common in women compared with men, and the sex difference in prevalence typically emerges during adolescence. Hormonal changes across the menstrual cycle and during the postpartum and perimenopausal periods are associated with increased risk for anxiety and depression symptoms. In humans and animals, reduced brain-derived neurotrophic factor (BDNF) has been associated with increased expression of affective pathology. Recently, a single nucleotide polymorphism (SNP) in the BDNF gene (BDNF Valine66Methionine [Val66Met]), which reduces BDNF bioavailability, has been identified in humans and associated with a variety of neuropsychiatric disorders. Although BDNF expression can be directly influenced by estrogen and progesterone, the potential impact of the BDNF Val66Met SNP on sensitivity to reproductive hormone changes remains an open question.

METHODS

As a predictive model, we used female mice in which the human SNP (BDNF Val66Met) was inserted into the mouse BDNF gene. Using standard behavioral paradigms, we tested the impact of this SNP on age and estrous-cycle-specific expression of anxiety-like behaviors.

RESULTS

Mice homozygous for the BDNF Val66Met SNP begin to exhibit increased anxiety-like behaviors over prepubertal and early adult development, show significant fluctuations in anxiety-like behaviors over the estrous cycle, and, as adults, differ from wild-type mice by showing significant fluctuations in anxiety-like behaviors over the estrous cycle-specifically, more anxiety-like behaviors during the estrus phase.

CONCLUSIONS

These findings have implications regarding the potential role of this SNP in contributing to developmental and reproductive hormone-dependent changes in affective disorders in humans.

A systematic review and meta-analysis on the association between BDNF val(66)met and hippocampal volume--a genuine effect or a winners curse?

Inconsistenties have been reported with regard to an association between val(66)met, a polymorphism on the BDNF gene, and hippocampal volume. We performed a systematic review and a meta-analysis to determine the magnitude and direction of this putative association and estimated the potential influence of demographic, clinical, and methodological characteristics of studies. Tests of publication bias and time-related trends were performed and statistical power of the included studies was calculated. The literature search for MRI studies on differences in total hippocampal volume as a function of BDNF val(66)met returned 25 records that fulfilled our criteria (total N = 3,620). Meta-analysis showed that carriers of a met allele had lower hippocampal volumes relative to val/val homozygotes (d = 0.13, P = 0.02). Between-study heterogeneity in effect size estimates was substantial (Q = 54.47, P < .001) and this could not be explained by demographic, clinical, and methodological differences across studies. Funnel plot inspection and trim-and-fill estimations suggested evidence for publication bias and effect sizes decreased substantially over the years (Pearson's r = -0.54, P < .01). All included studies were underpowered. This meta-analysis shows that carriers of a met allele have lower total hippocampal volumes relative to val/val homozygotes. However, effect sizes converged closer to null with virtually each attempt at replication and were based on underpowered studies. Altogether, this may call into question whether the observed effect is a genuine biological effect of the met allele or whether it is subject to a winners curse, with large effect sizes found in a few early studies and increasingly smaller effect sizes in later studies.

Influence of brain-derived neurotrophic factor genetic polymorphisms on the ages of onset for heroin dependence in a Chinese population

AIM

The study aims at evaluating the association between brain-derived neurotrophic factor (BDNF) gene polymorphisms and heroin-dependent patients in the Chinese population. Three polymorphisms of the BDNF-gene (rs10835210, rs16917234, and rs6265) in 486 heroin-dependent patients and in 226 healthy controls were genotyped for analyzing the association of these polymorphisms with age of onset of heroin dependence. We defined the healthy cases as "unknown phenotype" and used the endophenotype (behavior traits) to stratify the heroin dependents group on the basis of self-reporting traits for examining the association between BDNF polymorphisms (rs10835210, rs16917234, and rs6265) and heroin dependence.

RESULTS

Allelic distributions of BDNF gene polymorphisms did not differ significantly between heroin-dependent patients and controls. However, we found that the AA carriers of BDNF rs6265 had an earlier onset of heroin dependence and a clearer tendency of family history of heroin-dependent than GG carriers after controlling behavior characteristics across rs6265 genotypes.

CONCLUSIONS

Our findings suggested that the BDNF genetic polymorphism (rs6265) may have effects on the age of onset of heroin dependence among the Chinese population. The BDNF gene could contribute to vulnerabilities to heroin dependence.

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

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

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

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

Variants in SNAP25 are targets of natural selection and influence verbal performances in women

Descriptions of genes that are adaptively evolving in humans and that carry polymorphisms with an effect on cognitive performances have been virtually absent. SNAP25 encodes a presynaptic protein with a role in regulation of neurotransmitter release. We analysed the intra-specific diversity along SNAP25 and identified a region in intron 1 that shows signatures of balancing selection in humans. The estimated TMRCA (time to the most recent common ancestor) of the SNAP25 haplotype phylogeny amounted to 2.08 million years. The balancing selection signature is not secondary to demographic events or to biased gene conversion, and encompasses rs363039. This SNP has previously been associated to cognitive performances with contrasting results in different populations. We analysed this variant in two Italian cohorts in different age ranges and observed a significant genotype effect for rs363039 on verbal performances in females alone. Post hoc analysis revealed that the effect is driven by differences between heterozygotes and both homozygous genotypes. Thus, heterozygote females for rs363039 display higher verbal performances compared to both homozygotes. This finding was replicated in a cohort of Italian subjects suffering from neuromuscular diseases that do not affect cognition. Heterozygote advantage is one of the possible reasons underlying the maintenance of genetic diversity in natural populations. The observation that heterozygotes for rs363039 display higher verbal abilities compared to homozygotes perfectly fits the underlying balancing selection model. Although caution should be used in inferring selective pressures from observed signatures, SNAP25 might represent the first description of an adaptively evolving gene with a role in cognition.

Polymorphisms in the brain-derived neurotrophic factor gene influence memory and processing speed one month after brain injury

Brain-derived neurotrophic factor (BDNF) plays a role in cognition, as well as neural survival and plasticity. There are several common polymorphisms in the BDNF gene, one of which (rs6265) is an extensively studied non-synonymous coding polymorphism (Val66Met) which has been linked to cognitive performance in healthy controls and some clinical populations. We hypothesized that the Met allele of rs6265 would be associated with poorer cognitive performance in individuals with mild-to-moderate traumatic brain injury, and that other polymorphisms in the BDNF gene would also affect cognition. Genotype at 9 single-nucleotide polymorphisms (SNPs) in the BDNF gene, and measures of speed of information processing, learning, and memory were assessed in 75 patients with mTBI and 38 healthy subjects. Consistent with previous reports, the Met allele of rs6265 was associated with cognition (slower processing speed) in the entire group. Two other SNPs were associated with processing speed in the mTBI group, but both are in linkage disequilibrium with rs6265, and neither remained significant after adjustment for rs6265 status. Within the mTBI group, but not the controls, 4 SNPs, but not rs6265, were associated with memory measures. These associations were not affected by adjustment for rs6265 status. Polymorphisms in BDNF influence cognitive performance shortly after mTBI. The results raise the possibility that a functional polymorphism other than rs6265 may contribute to memory function after mTBI.

Reversible cerebral vasoconstriction syndrome: current and future perspectives

Reversible cerebral vasoconstriction syndromes (RCVS) are characterized by recurrent acute severe headaches, namely thunderclap headaches, and multifocal segmental vasoconstrictions. Interest has arisen in the definitions, clinical presentations, differential diagnoses, risk factors and complications of RCVS. This article will comprehensively review the milestone monographs and the latest research work addressing these issues. Studies that have focused on the relationship between RCVS and thunderclap headache will be detailed. We will also discuss research on the enigmatic pathophysiology and potential therapeutic approaches. Up-to-date information and challenges, undergoing studies and future research directions will be deeply probed.

Hippocampal volume and the brain-derived neurotrophic factor Val66Met polymorphism in first episode psychosis

INTRODUCTION

Small hippocampi and impaired memory are common in patients with psychosis and brain-derived neurotrophic factor (BDNF) plays a critical role in hippocampal neuroplasticity and memory. A common BDNF allele (Val66Met) has been the focus of numerous studies but results from the few BDNF-imaging studies are complex and contradictory. The objective of this study was to determine the association between Val66Met and hippocampal volume in patients with first episode psychosis. Secondary analyses explored age-related associations and the relationship between Val66Met and memory.

METHOD

Hippocampal volume and BDNF genotyping were obtained for 58 patients with first-episode psychosis and 39 healthy volunteers. Patients were recruited from an early psychosis program serving a catchment-area population.

RESULTS

Hippocampal volume was significantly smaller in patients than controls (F(1,92)=4.03, p<0.05) and there was a significant group-by-allele interaction (F(1,92)=3.99, p<0.05). Hippocampal volume was significantly smaller in patients than controls who were Val-homozygotes but no group differences were found for Met carriers. Findings were not affected by diagnosis, antipsychotic medication, or age, and there was no change in hippocampal volume during a one-year follow-up. Val-homozygous patients had worse immediate and delayed memory than their Met counterparts.

CONCLUSIONS

Results suggest the effects of the BDNF Val66Met allele may be different in patients with psychosis than in healthy adults. Hippocampal volume in patient and control Met allele carriers was very similar suggesting that illness-related factors have minimal influence in this group. In contrast, Val homozygosity was related to smaller hippocampi and poorer memory functioning only in patients with psychosis.

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.

Two selected models of missense mutations in mice for the study of learning behaviour

A large number of genome-wide association studies have linked missense mutations, mutations altering the amino acid sequence of proteins, with cognitive impairment in humans. However, these studies are correlative. As there may be multiple mutations for one particular patient, it is essential to address the functional impact of a missense mutation in a model system. The most suitable model system is the generation of knock-in mice with the homologous missense mutation followed by behavioural phenotyping. Here, we review selected mutants demonstrating an impact of single mutations on learning and memory in mice and discuss the relevance of such studies for understanding the role of these polymorphisms in human behaviour. We conclude that using these animal models has been instrumental in decoding the mechanisms underlying behaviour, and assists the design of therapeutic strategies for humans.

Variation in the BDNF Val66Met polymorphism and response to cognitive-behavior therapy in obsessive-compulsive disorder

BACKGROUND

Recent research suggests that the brain-derived neurotrophic factor (BDNF) may play a role in extinction learning. The goal of this study was to test whether variation in the BDNF Val66Met polymorphism is related to treatment response to exposure-based cognitive-behavior therapy (CBT), a form of extinction learning, in obsessive-compulsive disorder (OCD).

METHODS

One hundred and six OCD patients from a specialized clinic, who underwent a standardized CBT treatment after partial or non-response to a 12-week pharmacological trial, were genotyped for the BDNF Val66Met and the relationship between genotype and treatment response was analyzed.

RESULTS

Among 98 CBT completers, 36% of those carrying the BDNF Met allele were rated as CBT responders compared to 60% of nonMet allele carriers (P=0.027). When analyzing the different obsessive-compulsive symptom dimensions, in patients with contamination/cleaning symptoms, the Met allele was associated with a significantly worse CBT response (P<0.0001) and a lower obsessions severity decrease from pre- to posttreatment (P=0.046).

CONCLUSION

Genetic variation in BDNF may be associated with treatment response in exposure-based CBT in OCD, especially in those patients exhibiting contamination/cleaning symptoms.

BDNF Val66Met and cognition: all, none, or some? A meta-analysis of the genetic association

The Val66Met, G196A (rs6265) polymorphism in the brain-derived neurotrophic factor gene, BDNF, located at 11p13, has been associated with a wide range of cognitive functions. Yet, the pattern of results is complex and conflicting. In this study, we conducted a meta-analysis that included 23 publications containing 31 independent samples comprised of 7095 individuals. The phenotypes that were examined in this analysis covered a wide variety of cognitive functions and included indicators of general cognitive ability, memory, executive function, visual processing skills and cognitive fluency. The meta-analysis did not establish significant genetic associations between the Val66Met polymorphism and any of the phenotypes that were included.

Genetics of Obesity: What have we Learned?

Candidate gene and genome-wide association studies have led to the discovery of nine loci involved in Mendelian forms of obesity and 58 loci contributing to polygenic obesity. These loci explain a small fraction of the heritability for obesity and many genes remain to be discovered. However, efforts in obesity gene identification greatly modified our understanding of this disorder. In this review, we propose an overlook of major lessons learned from 15 years of research in the field of genetics and obesity. We comment on the existence of the genetic continuum between monogenic and polygenic forms of obesity that pinpoints the role of genes involved in the central regulation of food intake and genetic predisposition to obesity. We explain how the identification of novel obesity predisposing genes has clarified unsuspected biological pathways involved in the control of energy balance that have helped to understand past human history and to explore causality in epidemiology. We provide evidence that obesity predisposing genes interact with the environment and influence the response to treatment relevant to disease prediction.

Association of BDNF and COMT genotypes with cognitive processing of anti-smoking PSAs

Anti-smoking public service announcements (PSAs) often use persuasive arguments to attempt to influence attitudes about smoking. The persuasiveness of a PSA has previously been associated with factors that influence the cognitive processing of its message. Genetic factors that influence cognitive processing might thus affect individuals' responses to the persuasive arguments presented in PSAs. In the present study, we examined polymorphisms in the genes encoding brain-derived neurotrophic factor (BDNF Val66Met) and catechol-O-methyltransferase (COMT Val158Met), which affect cognitive processing in the prefrontal cortex, to identify genetic factors associated with self-reported outcomes of message processing, perceived effectiveness and quitting intentions among smokers viewing PSAs. A total of 120 smokers viewed sets of four PSAs that varied with respect to features of argument strength (AS) and message sensation value. We observed significant associations of BDNF genotype with central processing, narrative processing, perceived effectiveness of the anti-smoking PSAs and participant quitting intentions; the BDNF Met allele was associated with lower scores on all these measures. Central processing acted as a mediator of the association of genotype with quitting intentions and perceived effectiveness. There was a significant interaction of COMT genotype by AS in the model of narrative processing, such that individuals homozygous for the COMT Val allele reported higher narrative processing in the high-AS condition but not in the low-AS condition. To our knowledge, this is the first study to identify genetic factors associated with cognitive processing of anti-smoking PSAs.

BDNF polymorphism predicts the rate of decline in skilled task performance and hippocampal volume in healthy individuals

Numerous studies have indicated a link between the presence of polymorphism in brain-derived neurotrophic factor (BDNF) and cognitive and affective disorders. However, only a few have studied these effects longitudinally along with structural changes in the brain. This study was carried out to investigate whether valine-to-methionine substitution at position 66 (val66met) of pro-BDNF could be linked to alterations in the rate of decline in skilled task performance and structural changes in hippocampal volume. Participants consisted of 144 healthy Caucasian pilots (aged 40-69 years) who completed a minimum of 3 consecutive annual visits. Standardized flight simulator score (SFSS) was measured as a reliable and quantifiable indicator for skilled task performance. In addition, a subset of these individuals was assessed for hippocampal volume alterations using magnetic resonance imaging. We found that val66met substitution in BDNF correlated longitudinally with the rate of decline in SFSS. Structurally, age-dependent hippocampal volume changes were also significantly altered by this substitution. Our study suggests that val66met polymorphism in BDNF can be linked to the rate of decline in skilled task performance. Furthermore, this polymorphism could be used as a predictor of the effects of age on the structure of the hippocampus in healthy individuals. Such results have implications for understanding possible disabilities in older adults performing skilled tasks who are at a higher risk for cognitive and affective disorders.Translational Psychiatry (2011) 1, e51; doi:10.1038/tp.2011.47; published online 25 October 2011.

Association study of brain-derived neurotrophic factor gene polymorphisms and body weight change in schizophrenic patients under long-term atypical antipsychotic treatment

Schizophrenic patients treated with atypical antipsychotics (AAPs) often develop excessive body weight gain, which may lead to further morbidity and poor treatment compliance. This study examined whether genetic variants in the brain-derived neurotrophic factor (BDNF) gene may be associated with body weight change after AAP treatment. The study included 481 schizophrenic patients treated with clozapine (n = 266), olanzapine (n = 79), or risperidone (n = 136) for an average of 49.2 ± 28.2 months. Three common single-nucleotide polymorphisms (SNPs) of the BDNF gene were chosen as tagging SNPs. In single-marker-based analysis, the BDNF rs11030101-T homozygous genotype was found to be associated with significantly increased body weight gain (P = 0.037). The BDNF Val66Met (rs6265) polymorphism was not found to be associated with body weight gain. Haplotype analysis further showed that the rs11030101-T-allele-related haplotype is also associated with increased body weight gain (P = 0.047). Our findings suggest that there is a nominal association with rs11030101 but did not replicate the previously found relationship between the BDNF Val66Met polymorphism and body weight gain during long-term AAP treatment.

Brain-derived neurotrophic factor, food intake regulation, and obesity

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a fundamental role in development and plasticity of the central nervous system (CNS). It is currently recognized as a major participant in the regulation of food intake. Multiple studies have shown that different regulators of appetite such as leptin, insulin and pancreatic polypeptide (PP) potentially exert anorexigenic effects through BDNF. Low circulating levels of BDNF are associated with a higher risk of eating disorders such as anorexia nervosa (AN) and bulimia nervosa (BN). Strict food restriction reduces BDNF and may trigger binge-eating episodes and weight gain. The existence of mutations that cause haploinsufficiency of BDNF as well as some genetic variants, notably the BDNF p.Val66Met polymorphism, are also associated with the development of obese phenotypes and hyperphagia. However, association of the Met allele with AN and BN, which have different phenotypic characteristics, shows clearly the existence of other relevant factors that regulate eating behavior. This may, in part, be explained by the epigenetic regulation of BDNF through mechanisms like DNA methylation and histone acetylation. Environmental factors, primarily during early development, are crucial to the establishment of these stable but reversible changes that alter the transcriptional expression and are transgenerationally heritable, with potential concomitant effects on the development of eating disorders and body weight control.

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

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

Association 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.

Genetic variation in BDNF is associated with allergic asthma and allergic rhinitis in an ethnic Chinese population in Singapore

Allergic diseases affect more than 25% of the world population and result from a complex interplay between genetic and environmental factors. Recent evidence has shown that BDNF (Brain Derived Neurotrophic Factor) could serve as an important marker of allergic disease. Increased levels of BDNF in blood, bronchoalveolar lavage fluid and nasal lavage fluid positively correlate with disease activity and severity in patients with allergic rhinitis (AR), asthma and atopic eczema. However, reports on the association between genetic variation in BDNF and allergic disease have been controversial. This study therefore aims to clarify the relationship between single nucleotide polymorphisms (SNPs) in BDNF and a genetic predisposition to AR and asthma in an ethnic Chinese population of Singapore. Volunteers with a self-reported history of asthma (718 subjects) or a history of AR as determined by a researcher-administered questionnaire (795 subjects) were used in this study, alongside controls with no personal or family history of allergy (717 subjects). The association results identified a significant association for the tagSNP rs10767664 with a significant PDominant=0.0007 and OR=1.3 for AR and PDominant=0.0005 and OR=1.3 for asthma (using a dominant model of association). The haplotype based analysis also identified a significant association further confirming the single SNP association. The SNP rs10767664 is strongly linked (r2=0.95) to the functional polymorphism rs6265 (Val66Met), which has previously been reported to be associated to allergic phenotypes and also shown to affect BDNF expression. BDNF is a therefore a key molecular player in allergy. Further studies on polymorphisms within BDNF may shed light on its role in the pathogenesis of allergic diseases and potentially serve as biomarkers for allergic disease.