Evidence of associations between bipolar disorder and the brain-derived neurotrophic factor (BDNF) gene

Association of BDNF risk variant and dorsolateral cortical thickness with long-term treatment response to valproate in type I bipolar disorder: An exploratory study

Valproate is among the most prescribed drugs for bipolar disorder; however, 87% of patients do not report full long-term treatment response (LTTR) to this medication. One of valproate's suggested mechanisms of action involves the brain-derived neurotrophic factor (BDNF), expressed in the brain areas regulating emotions, such as the prefrontal cortex. Nonetheless, data about the role of BDNF in LTTR and its implications in the structure of the dorsolateral prefrontal cortex (dlPFC) is scarce. We explore the association of BDNF variants and dorsolateral cortical thickness (CT) with LTTR to valproate in bipolar disorder type I (BDI). Twenty-eight BDI patients were genotyped for BDNF polymorphisms rs1519480, rs6265, and rs7124442, and T1-weighted 3D brain scans were acquired. LTTR to valproate was evaluated with Alda's scale. A logistic regression analysis was conducted to evaluate LTTR according to BDNF genotypes and CT. We evaluated CT differences by genotypes with analysis of covariance. LTTR was associated with BDNF rs1519480 and right dlPFC thickness. Insufficient responders with the CC genotype had thicker right dlPFC than TC and TT genotypes. Full responders reported thicker right dlPFC in TC and TT genotypes. In conclusion, different patterns of CT related to BDNF genotypes were identified, suggesting a potential biomarker of LTTR to valproate in our population.

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Genotype-expression interactions for BDNF across human brain regions

Background

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

Results

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

Conclusions

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

Supplementary Information

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

Exposure to mercury among 9-year-old children and neurobehavioural function

Mercury (Hg) is an environmental neurotoxicant whose main route of exposure in humans is the consumption of seafood. The aim of this study was to explore the relationship between Hg exposure at 9 years old and behaviour assessed at 9 and 11 years old. Study subjects were mother-child pairs participating in the INMA (Environment and Childhood) Project in Valencia (Spain). Total Hg (THg) was measured in hair samples from the children at 9 years old. Behaviour and emotions were assessed at 9 (n = 472) years and 11 (n = 385) years of age using the Child Behaviour Checklist test (CBCL) and the Conners Parents Rating Scale-Revised: Short Form (CPRS-R:S). Furthermore, the attention function was assessed by the Attention Network Test at 11 years old. Socio-demographic, lifestyle and dietary information was collected through questionnaires during pregnancy and childhood. Polymorphism in BDNF, APOE and GSTP1 were genotyped in cord blood DNA. Multivariable negative binomial regression models were built in order to study the association between THg concentrations and the scores obtained by the children at 9 and 11 years old. Effect modification by sex and genetic polymorphisms was assessed. The association between Hg levels and CBCL scores was positive (worse neurobehavioural development) for the CBCL internalizing and total problem scales (Incidence Rate Ratio [95% confidence interval] = 1.07 [1.01, 1.13] and 1.05 [0.99, 1.11], respectively). The association between Hg and the externalizing and total problems CBCL scales and the Attention Deficit Hyperactivity Disorder (ADHD) index of the CPRS-R:S was different according to sex, with boys obtaining worse scores with increasing Hg, compared to girls. Statistically significant interactions were also observed for genetic polymorphisms affecting the association between early exposure to Hg and both CBCL and CPRS-R:S scores. In conclusion, postnatal Hg exposure is associated with poorer neurobehavioural development in 9- and 11-year-old children. Sex and the presence of certain genetic polymorphisms modified this association.

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

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

The rs6265 Polymorphism of the BDNF Gene Is Related to Higher-Lethality Suicide Attempts in the Korean Population

OBJECTIVE

Since the risk of suicide cannot be predicted by clinical symptoms alone, and suicide is known to have a genetic component, the discovery of genetic markers that can predict the lethality of suicide attempts is a clinically important topic. There have been many studies aiming to determine whether the rs6265 polymorphism of the BDNF gene is associated with suicidality; however, the results have been mixed, and there have been few studies investigating the relationship between this polymorphism and suicide attempt lethality.

METHODS

We assessed suicide lethality in 258 individuals who had attempted suicide using the relative risk ratio (RRR) scale and by genotyping the rs6265 polymorphism of the BDNF gene.

RESULTS

The RRR score for suicide attempts was higher in subjects with Met/Val and Val/Val genotypes than in that with a Met/Met genotype (p=0.015). The RRR score for suicide attempts was also higher in Val allele carriers (Met/Val+Val/Val) than in Met/Met homozygotes (p=0.006).

CONCLUSION

This study demonstrates the possibility that the rs6265 polymorphism of the BDNF gene could be used as a genetic marker to predict the lethality of suicide attempts, but more replication studies are needed for the application of this result in clinical practice.

Buyang Huanwu Decoction Ameliorates Poststroke Depression via Promoting Neurotrophic Pathway Mediated Neuroprotection and Neurogenesis

Objective. The aim of the present research is to investigate the therapeutic effect of Buyang Huanwu Decoction (BHD) in poststroke depression (PSD) animal model and illustrate its underlying mechanism via promoting neurotrophic pathway mediated neuroprotection and neurogenesis. Methods. To induce PSD rat model, isolation housed rats that received middle cerebral artery occlusion (MCAO) surgery successively suffered from chronic mild stress (CMS) treatment for consecutive twenty-one days. Meanwhile, rats were correspondingly given vehicle, BHD, and fluoxetine. Then, neurologic function was scored and depressive-like behaviors were assessed by sucrose preference test, locomotor activity, novelty-suppressed feeding test, and forced swim test. Thereafter, the neuroprotection and neurogenesis related molecular markers and signaling were detected. Results. We firstly observed a significant neurological function recovery and antidepressants effect of BHD after MCAO together with CMS treatment. Our study also found that treatment with BHD and fluoxetine can significantly rescue neurons from apoptosis and promote neurogenesis in the CA3 and DG regions in the hippocampus. Notably, BHD and fluoxetine treatment can activate BDNF/ERK/CREB signaling. Conclusion. The results suggest that BHD is a promising candidate for treating PSD. Its curative effects can be attributed to neurotrophic pathway mediated neuroprotection and neurogenesis.

Genetic polymorphisms are associated with hair, blood, and urine mercury levels in the American Dental Association (ADA) study participants

BACKGROUND/AIMS

Mercury (Hg) is a potent toxicant of concern to the general public. Recent studies suggest that several genes that mediate Hg metabolism are polymorphic. We hypothesize that single nucleotide polymorphisms (SNPs) in such genes may underline inter-individual differences in exposure biomarker concentrations.

METHODS

Dental professionals were recruited during the American Dental Association (ADA) 2012 Annual Meeting. Samples of hair, blood, and urine were collected for quantifying Hg levels and genotyping (88 SNPs in classes relevant to Hg toxicokinetics including glutathione metabolism, selenoproteins, metallothioneins, and xenobiotic transporters). Questionnaires were administrated to obtain information on demographics and sources of Hg exposure (e.g., fish consumption and use of dental amalgam). Here, we report results for 380 participants with complete genotype and Hg biomarker datasets. ANOVA and linear regressions were used for statistical analysis.

RESULTS

Mean (geometric) Hg levels in hair (hHg), blood (bHg), urine (uHg), and the average estimated Hg intake from fish were 0.62µg/g, 3.75µg/L, 1.32µg/L, and 0.12µg/kg body weight/day, respectively. Out of 88 SNPs successfully genotyped, Hg biomarker levels differed by genotype for 25 SNPs, one of which remained significant following Bonferroni correction in ANOVA. When the associations between sources of Hg exposure and SNPs were analyzed with respect to Hg biomarker concentrations, 38 SNPs had significant main effects and/or gene-Hg exposure source interactions. Twenty-five, 23, and four SNPs showed significant main effects and/or interactions for hHg, bHg, and uHg levels, respectively (p<0.05), and six SNPs (in GCLC, MT1M, MT4, ATP7B, and BDNF) remained significant following Bonferroni correction.

CONCLUSION

The findings suggest that polymorphisms in environmentally-responsive genes can influence Hg biomarker levels. Hence, consideration of such gene-environment factors may improve the ability to assess the health risks of Hg more precisely.

Genetic Analysis of BDNF, GNB3, MTHFR, ACE and APOE Variants in Major and Recurrent Depressive Disorders in Russia

This study was conducted to explore the possibility of association between the single-nucleotide polymorphisms rs6264 of BDNF, rs5443 of GNB3, and rs1801133 of MTHFR; the In/Del polymorphism of ACE; and the ε2 allele of APOE and major depressive disorder (MDD) and recurrent depressive disorder (RDD) in an East Slavic population. Generalized multifactor dimensionality reduction (GMDR) method was applied to detect gene-gene interactions. One hundred fifty patients with RDD (101 females and 49 males) and 208 patients with MDD (115 females and 93 males) were included in the study. The comparison group consisted of 200 unrelated individuals. There was no significant difference in genotype distributions or allele frequencies between the controls and any of the diagnostic groups. Nevertheless, the frequency of the G allele of rs1801133 of MTHFR was higher in the RDD group and the frequency of the C allele of rs6264 of BDNF was higher in the MDD group. The difference between the controls and specific disease groups almost reached statistical significance (P = 0.08). A GMDR did not reveal optimal two- and three-dimensional models with significant prediction accuracies (P ˃ 0.05) for the MDD or RDD groups.

Development of a cost-efficient novel method for rapid, concurrent genotyping of five common single nucleotide polymorphisms of the brain derived neurotrophic factor (BDNF) gene by tetra-primer amplification refractory mutation system

Brain derived neurotrophic factor (BDNF) is a molecular trophic factor that plays a key role in neuronal survival and plasticity. Single nucleotide polymorphisms (SNPs) of the BDNF gene have been associated with specific phenotypic traits in a large number of neuropsychiatric disorders and the response to psychotherapeutic medications in patient populations. Nevertheless, due to study differences and occasionally contrasting findings, substantial further research is required to understand in better detail the association between specific BDNF SNPs and these psychiatric disorders. While considerable progress has been made recently in developing advanced genotyping platforms of SNPs, many high-throughput probe- or array-based detection methods currently available are limited by high costs, slow processing times or access to advanced instrumentation. The polymerase chain reaction (PCR)-based, tetra-primer amplification refractory mutation system (T-ARMS) method is a potential alternative technique for detecting SNP genotypes efficiently, quickly, easily, and cheaply. As a tool in psychopathology research, T-ARMS was shown to be capable of detecting five common SNPs in the BDNF gene (rs6265, rs988748, rs11030104, 11757G/C and rs7103411), which are all SNPs with previously demonstrated clinical relevance to schizophrenia and depression. The present technique therefore represents a suitable protocol for many research laboratories to study the genetic correlates of BDNF in psychiatric disorders. Copyright Copyright © 2015 John Wiley & Sons, Ltd.

The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is associated with increased body mass index and insulin resistance measures in bipolar disorder and schizophrenia

OBJECTIVES

We tested the hypothesis that a common functional variant in brain-derived neurotrophic factor (BDNF), Val66Met, which has been shown to be associated with increased body mass index (BMI) in schizophrenia (SCZ) and schizoaffective disorder (SAD), is also associated with antipsychotic-induced weight gain in bipolar disorder (BPD). Association of Val66Met with other metabolic measures, including high- and low-density cholesterol, triglycerides, total cholesterol, fasting blood glucose, and hemoglobin A1c, was also tested.

METHODS

This was a 12-month, prospective, randomized trial of two atypical antipsychotic drugs (APDs) with moderate (risperidone) or high (olanzapine) risk to cause weight gain. Subjects were diagnosed as having BPD (n = 90) and SCZ or SAD (n = 76).

RESULTS

BMI was significantly greater in all diagnoses for Met66 allele carriers at six months (p = 0.01). Met66 carriers with BPD showed a greater increase in the triglycerides/high-density (HDL) cholesterol ratio (p = 0.01), a key marker for metabolic syndrome related to insulin resistance, and log-triglycerides (p = 0.04), after three or six months of treatment. Met66 carriers had the greatest increase in log-triglycerides (p = 0.03) and triglycerides/HDL cholesterol ratio after three months of treatment with risperidone (p = 0.003), and the highest BMI at six months (p = 0.01).

CONCLUSIONS

The positive association of BNDF Val66Met with high BMI values replicates previous findings in patients with SCZ and indicates the BDNF Val66Met genotype as a potential risk factor for obesity and insulin resistance measures in patients with BPD receiving antipsychotics as well.

BDNF promoter I methylation correlates between post-mortem human peripheral and brain tissues

Several psychiatric disorders have been associated with CpG methylation changes in CG rich promoters of the brain-derived neurotrophic factor (BDNF) mainly by extracting DNA from peripheral blood cells. Whether changes in peripheral DNA methylation can be used as a proxy for brain-specific alterations remains an open question. In this study we aimed to compare DNA methylation levels in BDNF promoter regions in human blood cells, muscle and brain regions using bisulfite-pyrosequencing. We found a significant correlation between the levels of BDNF promoter I methylation measured in quadriceps and vPFC tissues extracted from the same individuals (n = 98, Pearson, r = 0.48, p = 4.5 × 10(-7)). In the hippocampus, BDNF promoter I and IV methylation levels were strongly correlated (Pearson, n = 37, r = 0.74, p = 1.4 × 10(-7)). We found evidence for sex-dependent effect on BDNF promoter methylation levels in the various tissues and blood samples. Taken together, these data indicate a strong intra-individual correlation between peripheral and brain tissue. They also suggest that sex determines methylation patterns in BDNF promoter region across different types of tissue, including muscle, brain, and blood.

Serum Brain-derived neurotrophic factor levels in post-stroke depression

BACKGROUND

Depression is a frequent mood disorder that affects around a third of stroke patients and has been associated with poorer outcome. Our aim was to determine whether there is a relationship between serum Brain-derived neurotrophic factor (BDNF) levels and post-stroke depression (PSD).

METHODS

Two hundred and sixteen ischemic stroke patients admitted to the hospital within the first 24h after stroke onset were consecutively recruited and followed up for 3 months. Based on the symptoms, diagnoses of depression were made in accordance with DSM-IV criteria for post-stroke depression at day 90. Enzyme-linked immunosorbent assay (ELISA) was used to measure serum levels of BDNF at admission. Multivariate analyses were performed using logistic regression models.

RESULTS

In our study, 59 patients (27.3%) were diagnosed as having major depression at 3 months. Patients with major depression showed lower levels of serum BDNF [8.1 (5.6-9.4) vs. 13.7 (10.4-16.5)ng/ml, P<0.0001] at admission. In multivariate analyses, serum BDNF was an independent predictor of PSD at 3 months [odds ratio (OR): 0.79(0.72-0.87), P=0.003]. Serum levels of BDNF≤10.2ng/ml were independently associated with post-stroke (OR, 11.5; 95% CI, 5.6-23.4, P<0.0001), after adjustment for possible variables.

CONCLUSION

The present study demonstrates a strong relationship between serum BDNF levels at admission and the development of PSD within 3 months. Further studies are necessary to confirm this association, which may open the way to the proposal of new therapeutic options.

The neurobiology of bipolar disorder: identifying targets for specific agents and synergies for combination treatment

Bipolar disorder (BD) is a chronic psychiatric illness described by severe changes in mood. Extensive research has been carried out to understand the aetiology and pathophysiology of BD. Several hypotheses have been postulated, including alteration in genetic factors, protein expression, calcium signalling, neuropathological alteration, mitochondrial dysfunction and oxidative stress in BD. In the following paper, we will attempt to integrate these data in a manner which is to understand targets of treatment and how they may be, in particular, relevant to combination treatment. In summary, the data suggested that BD might be associated with neuronal and glial cellular impairment in specific brain areas, including the prefrontal cortex. From molecular and genetics: (1) alterations in dopaminergic system, through catechol-O-aminotransferase; (2) decreased expression and polymorphism on brain-derived neurotrophic factor; (3) alterations cyclic-AMP responsive element binding; (4) dysregulation of calcium signalling, including genome-wide finding for voltage-dependent calcium channel α-1 subunit are relevant findings in BD. Future studies are now necessary to understand how these molecular pathways interact and their connection to the complex clinical manifestations observed in BD.

Response to lithium in bipolar disorder: clinical and genetic findings

The use of lithium is a cornerstone for preventing recurrences in bipolar disorder (BD). The response of patients with bipolar disorder to lithium has different levels of magnitude. About one-third of lithium-treated patients are excellent lithium responders (ELR), showing total prevention of the episodes. A number of clinical characteristics were delineated in patients with favorable response to lithium as regards to clinical course, family history of mood disorders, and psychiatric comorbidity. We have also demonstrated that temperamental features of hypomania (a hyperthymic temperament) and a lack of cognitive disorganization predict the best results of lithium prophylaxis. A degree of prevention against manic and depressive episodes has been regarded as an endophenotype for pharmacogenetic studies. The majority of data have been gathered from so-called "candidate" gene studies. The candidates were selected on the basis of neurobiology of bipolar disorder and mechanisms of lithium action including, among others, neurotransmission, intracellular signaling, neuroprotection or circadian rhythms. We demonstrated that response to lithium has been connected with the genotype of BDNF gene and serum BDNF levels and have shown that ELR have normal cognitive functions and serum BDNF levels, even after long-term duration of the illness. A number of genome-wide association studies (GWAS) of BD have been also performed in recent years, some of which also focused on lithium response. The Consortium on Lithium Genetics (ConLiGen) has established the large sample for performing the genome-wide association study (GWAS) of lithium response in BD, and the first results have already been published.

Towards the clinical implementation of pharmacogenetics in bipolar disorder

BACKGROUND

Bipolar disorder (BD) is a psychiatric illness defined by pathological alterations between the mood states of mania and depression, causing disability, imposing healthcare costs and elevating the risk of suicide. Although effective treatments for BD exist, variability in outcomes leads to a large number of treatment failures, typically followed by a trial and error process of medication switches that can take years. Pharmacogenetic testing (PGT), by tailoring drug choice to an individual, may personalize and expedite treatment so as to identify more rapidly medications well suited to individual BD patients.

DISCUSSION

A number of associations have been made in BD between medication response phenotypes and specific genetic markers. However, to date clinical adoption of PGT has been limited, often citing questions that must be answered before it can be widely utilized. These include: What are the requirements of supporting evidence? How large is a clinically relevant effect? What degree of specificity and sensitivity are required? Does a given marker influence decision making and have clinical utility? In many cases, the answers to these questions remain unknown, and ultimately, the question of whether PGT is valid and useful must be determined empirically. Towards this aim, we have reviewed the literature and selected drug-genotype associations with the strongest evidence for utility in BD.

SUMMARY

Based upon these findings, we propose a preliminary panel for use in PGT, and a method by which the results of a PGT panel can be integrated for clinical interpretation. Finally, we argue that based on the sufficiency of accumulated evidence, PGT implementation studies are now warranted. We propose and discuss the design for a randomized clinical trial to test the use of PGT in the treatment of BD.

White matter alterations in bipolar disorder: potential for drug discovery and development

OBJECTIVES

Brain white matter (WM) alterations have recently emerged as potentially relevant in bipolar disorder. New techniques such as diffusion tensor imaging allow precise exploration of these WM microstructural alterations in bipolar disorder. Our objective was to critically review WM alterations in bipolar disorder, using neuroimaging and neuropathological studies, in the context of neural models and the potential for drug discovery and development.

METHODS

We conducted a systematic PubMed and Google Scholar search of the WM and bipolar disorder literature up to and including January 2013.

RESULTS

Findings relating to WM alterations are consistent in neuroimaging and neuropathology studies of bipolar disorder, especially in regions involved in emotional processing such as the anterior frontal lobe, corpus callosum, cingulate cortex, and in fronto-limbic connections. Some of the structural alterations are related to genetic risk factors for bipolar disorder and may underlie the dysfunctional emotional processing described in recent neurobiological models of bipolar disorder. Medication effects in bipolar disorder, from lithium and other mood stabilizers, might impact myelinating processes, particularly by inhibition of glycogen synthase kinase-3 beta.

CONCLUSIONS

Pathways leading to WM alterations in bipolar disorder represent potential targets for the development and discovery of new drugs. Myelin damage in bipolar disorder suggests that the effects of existing pro-myelinating drugs should also be evaluated to improve our understanding and treatment of this disease.

Molecular actions and clinical pharmacogenetics of lithium therapy

Mood disorders, including bipolar disorder and depression, are relatively common human diseases for which pharmacological treatment options are often not optimal. Among existing pharmacological agents and mood stabilizers used for the treatment of mood disorders, lithium has a unique clinical profile. Lithium has efficacy in the treatment of bipolar disorder generally, and in particular mania, while also being useful in the adjunct treatment of refractory depression. In addition to antimanic and adjunct antidepressant efficacy, lithium is also proven effective in the reduction of suicide and suicidal behaviors. However, only a subset of patients manifests beneficial responses to lithium therapy and the underlying genetic factors of response are not exactly known. Here we discuss preclinical research suggesting mechanisms likely to underlie lithium's therapeutic actions including direct targets inositol monophosphatase and glycogen synthase kinase-3 (GSK-3) among others, as well as indirect actions including modulation of neurotrophic and neurotransmitter systems and circadian function. We follow with a discussion of current knowledge related to the pharmacogenetic underpinnings of effective lithium therapy in patients within this context. Progress in elucidation of genetic factors that may be involved in human response to lithium pharmacology has been slow, and there is still limited conclusive evidence for the role of a particular genetic factor. However, the development of new approaches such as genome-wide association studies (GWAS), and increased use of genetic testing and improved identification of mood disorder patients sub-groups will lead to improved elucidation of relevant genetic factors in the future.

Association study between BDNF gene variants and Mexican patients with obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a psychiatric disorder whose etiology is not yet known. We investigate the role of three variants of the BDNF gene (rs6265, rs1519480 and rs7124442) by single SNP and haplotype analysis in OCD Mexican patients using a case-control and family-based association design. BDNF gene variants were genotyped in 283 control subjects, 232 OCD patients and first degree relatives of 111 OCD subjects. Single SNP analysis in case-control study showed an association between rs6265 and OCD with a high frequency of Val/Val genotype and Val allele (p=0.0001 and p=0.0001, respectively). Also, genotype and allele analysis of rs1519480 showed significant differences (p=0.0001, p=0.0001; respectively) between OCD and control groups. Haplotype analysis showed a high frequency of A-T (rs6265-rs1519480) in OCD patients compared with the control group (OR=2.06 [1.18-3.59], p=0.0093) and a low frequency of haplotype A-C in the OCD patients (OR=0.04 [0.01-0.16], p=0.000002). The family-based association study showed no significant differences in the transmission of any variant. Our study replicated the association between BDNF Val66Met gene polymorphism and OCD. Also, we found a significant association of rs1519480 in OCD patients compared with a control group, region that has never been analyzed in OCD. In conclusion, our findings suggest that BDNF gene could be related to the development of OCD.

Investigating the role of BDNF and CCK system genes in suicidality in a familial bipolar cohort

BACKGROUND

Suicidal behaviour is a phenotype widely associated with psychiatric disorders such as major depressive disorder and bipolar disorder. However, recent evidence indicates that part of the heritability of suicidal behaviour is independent of the heritability of individual psychiatric disorders. This allows investigation into genetic risk factors for suicidal behaviour within a disorder using a candidate gene association approach.

METHODS

We used family-based association testing in a cohort of 130 multiplex bipolar pedigrees, comprising 795 individuals, to look for associations between suicidal behaviour and 32 single nucleotide polymorphisms (SNPs) from across the genes brain-derived neurotrophic factor (BDNF), cholecystokinin (CCK) and the cholecystokinin beta-receptor (CCKBR).

RESULTS

We found associations (p≤0.05) between suicide attempt and 12 SNPs of CCKBR and five SNPs of BDNF. After correction for multiple testing, seven SNPs of CCKBR remained significantly associated. No association was found between CCK and suicidal behaviour.

LIMITATIONS

The study relied on retrospective self-reporting by individuals to determine phenotype, and the sample size was relatively small.

CONCLUSIONS

The results of the study support the hypothesis that some CCKBR polymorphisms may contribute to an underlying predisposition towards suicidal behaviour in bipolar disorder.

Genetic influences on response to mood stabilizers in bipolar disorder: current status of knowledge

Mood stabilizers form a cornerstone in the long-term treatment of bipolar disorder. The first representative of their family was lithium, still considered a prototype drug for the prevention of manic and depressive recurrences in bipolar disorder. Along with carbamazepine and valproates, lithium belongs to the first generation of mood stabilizers, which appeared in psychiatric treatment in the 1960s. Atypical antipsychotics with mood-stabilizing properties and lamotrigine, which were introduced in the mid-1990 s, form the second generation of such drugs. The response of patients with bipolar disorder to mood stabilizers has different levels of magnitude. About one-third of lithium-treated patients are excellent responders, showing total prevention of the episodes, and these patients are clinically characterized by an episodic clinical course, complete remission, a bipolar family history, low psychiatric co-morbidity and a hyperthymic temperament. It has been suggested that responders to carbamazepine or lamotrigine may differ clinically from responders to lithium. The main phenotype of the response to mood stabilizers is a degree of prevention against recurrences of manic and depressive episodes during long-term treatment. The most specific scale in this respect is the so-called Alda scale, where retrospective assessment of lithium response is scored on a 0-10 scale. The vast majority of data on genetic influences on the response to mood stabilizers has been gathered in relation to lithium. The studies on the mechanisms of action of lithium and on the neurobiology of bipolar disorder have led to the identification of a number of candidate genes. The genes studied for their association with lithium response have been those connected with neurotransmitters (serotonin, dopamine and glutamate), second messengers (phosphatidyl inositol [PI], cyclic adenosine-monophosphate [cAMP] and protein kinase C [PKC] pathways), substances involved in neuroprotection (brain-derived neurotrophic factor [BDNF] and glycogen synthase kinase 3-β [GSK-3β]) and a number of other miscellaneous genes. There are no published pharmacogenomic studies of mood stabilizers other than lithium, except for one study of the X-box binding protein 1 (XBP1) gene in relation to the efficacy of valproate. In recent years, a number of genome-wide association studies (GWAS) in bipolar disorders have been performed and some of those have also focused on lithium response. They suggest roles for the glutamatergic receptor AMPA (GRIA2) gene and the amiloride-sensitive cation channel 1 neuronal (ACCN1) gene in long-term lithium response. A promise for better elucidating the genetics of lithium response has been created by the formation of the Consortium on Lithium Genetics (ConLiGen) to establish the largest sample, to date, for the GWAS of lithium response in bipolar disorder. The sample currently comprises more than 1,200 patients, characterized by their response to lithium treatment according to the Alda scale. Preliminary results from this international study suggest a possible involvement of the sodium bicarbonate transporter (SLC4A10) gene in lithium response. It is concluded that the pharmacogenetics of response to mood stabilizers has recently become a growing field of research, especially so far as the pharmacogenetics of the response to lithium is concerned. Clearly, the ConLiGen project is a highly significant step in this research. Although the results of pharmacogenetic studies are of significant scientific value, their possible practical implications are yet to be seen.

Evidence for single nucleotide polymorphisms and their association with bipolar disorder

Bipolar disorder (BD) is a complex disorder with a number of susceptibility genes and environmental risk factors involved in its pathogenesis. In recent years, huge progress has been made in molecular techniques for genetic studies, which have enabled identification of numerous genomic regions and genetic variants implicated in BD across populations. Despite the abundance of genetic findings, the results have often been inconsistent and not replicated for many candidate genes/single nucleotide polymorphisms (SNPs). Therefore, the aim of the review presented here is to summarize the most important data reported so far in candidate gene and genome-wide association studies. Taking into account the abundance of association data, this review focuses on the most extensively studied genes and polymorphisms reported so far for BD to present the most promising genomic regions/SNPs involved in BD. The review of association data reveals evidence for several genes (SLC6A4/5-HTT [serotonin transporter gene], BDNF [brain-derived neurotrophic factor], DAOA [D-amino acid oxidase activator], DTNBP1 [dysbindin], NRG1 [neuregulin 1], DISC1 [disrupted in schizophrenia 1]) to be crucial candidates in BD, whereas numerous genome-wide association studies conducted in BD indicate polymorphisms in two genes (CACNA1C [calcium channel, voltage-dependent, L type, alpha 1C subunit], ANK3 [ankyrin 3]) replicated for association with BD in most of these studies. Nevertheless, further studies focusing on interactions between multiple candidate genes/SNPs, as well as systems biology and pathway analyses are necessary to integrate and improve the way we analyze the currently available association data.

A theoretical framework informing research about the role of stress in the pathophysiology of bipolar disorder

BACKGROUND

The staggering illness burden associated with Bipolar Disorder (BD) invites the need for primary prevention strategies. Before preventative strategies can be considered in individuals during a pre-symptomatic period (i.e., at risk), unraveling the mechanistic steps wherein external stress is transduced and interacts with genetic vulnerability in the early stages of BD will be a critical conceptual necessity.

METHODS

Herein we comprehensively review extant studies reporting on stress and bipolar disorder. The overarching aim is to propose a conceptual framework to inform research about the role of stress in the pathophysiology of BD. Computerized databases i.e. PubMed, PsychInfo, Cochrane Library and Scielo were searched using the following terms: "bipolar disorder" cross-referenced with "stress", "general reaction to stress", "resilience", "resistance", "recovery" "stress-diathesis", "allostasis", and "hormesis".

RESULTS

Data from literature indicate the existence of some theoretical models to understand the influence of stress in the pathophysiology of BD, including classical stress-diathesis model and new models such as allostasis and hormesis. In addition, molecular mechanisms involved in stress adaptation (resistance, resilience and recovery) can also be translated in research strategies to investigate the impact of stress in the pathophysiology of BD.

LIMITATIONS

Most studies are retrospective and/or cross sectional, do not consider the period of development, assess brain function with only one or few methodologies, and use animal models which are not always similar to human phenotypes.

CONCLUSION

The interaction between stress and brain development is dynamic and complex. In this article we proposed a theoretical model for investigation about the role of stress in the pathophysiology of BD, based on the different kinds of stress adaptation response and their putative neurobiological underpinnings.

No associations found between the genes situated at 6p22.1, HIST1H2BJ, PRSS16, and PGBD1 in Japanese patients diagnosed with schizophrenia

Recent GWAS demonstrated an association between candidate genes located at region 6p22.1 and schizophrenia. This region has been reported to house certain candidate SNPs, which may be associated with schizophrenia at HIST1H2BJ, PRSS16, and PGBD1. These genes may presumably be associated with pathophysiology in schizophrenia, namely epigenetics and psychoneuroimmunology. A three-step study was undertaken to focus on these genes with the following aims: (1) whether these genes may be associated in Japanese patients with schizophrenia by performing a 1st stage case-control study (514 cases and 706 controls) using Japanese tagging SNPs; (2) if the genetic regions of interest for the disease from the 1st stage of analyses were found, re-sequencing was performed to search for new mutations; (3) finally, a replication study was undertaken to confirm positive findings from the 1st stage were reconfirmed using a larger number of subjects (2,583 cases and 2,903 controls) during a 2nd stage multicenter replication study in Japan. Genotyping was performed using TaqMan PCR method for the selected nine tagging SNPs. Although three SNPs situated at the 3' side of PGBD1; rs3800324, rs3800327, and rs2142730, and two-window haplotypes between rs3800327 and rs2142730 showed positive associations with schizophrenia, these associations did not have enough power to sustain significance during the 2nd stage replication study. In addition, re-sequencing for exons 5 and 6 situated at this region did not express any new mutations for schizophrenia. Taken together these results indicate that the genes HIST1H2BJ, PRSS16, and PGBD1 were not associated with Japanese patients with schizophrenia.