Genetic research into bipolar disorder: the need for a research framework that integrates sophisticated molecular biology and clinically informed phenotype characterization

Associations of the serotonin transporter promoter polymorphism (5-HTTLPR) with bipolar disorder and treatment response: A systematic review and meta-analysis

BACKGROUND

Associations of the serotonin transporter promoter polymorphism (5-HTTLPR) with bipolar disorder (BPD) and treatment response in bipolar patients were not conclusive. This study not only assessed the association between the 5-HTTLPR and BPD with accumulating relevant studies, but also in the first time evaluated the effect of the 5-HTTLPR on both anti-depressive and anti-manic treatment responses in bipolar patients.

METHODS

PubMed, Embase, PsycINFO, Cochrane Library and Cochrane Control Trials databases were systematically searched before February 2017. This meta-analysis followed the PRISMA guidelines.

RESULTS

A total of 32 population-based studies (5567 cases and 6993 controls) and 9 family-based studies (837 trios) were finally screened out and statistically joined into a single meta-analysis that revealed an association between S allele and an increased risk of BPD (OR = 1.06, p = .038). Pooled analysis of the 32 population-based studies indicated an association of S-carrier genotypes with an increased risk of BPD (OR = 1.10, p = .029). Meanwhile, the association remained significant in Caucasians (OR = 1.15, p = .004), which could provide an enough power (88%) to detect a significant association. Regarding the treatment response studies, 6 studies reporting the relationship of the 5-HTTLPR in anti-depressive remission rate (1034 patients) and 7 studies reporting in response rate (1098 patients) were included for pooled analyses. We observed a significant association of S-carrier genotypes with a reduced anti-depressive remission rate (OR = 0.64, p = .006) but not with anti-depressive response rate. The association between the 5-HTTLPR with anti-manic response rate was not observed in the included 6 studies (676 patients).

CONCLUSIONS

The present study supported the presence of a marginal but detectable effect of the 5-HTTLPR on susceptibility to BPD. Moreover, the detected association in Caucasian was statistically reliable. Besides, the 5-HTTLPR was identified as a useful predictor for anti-depressive remission but not for anti-depressive or anti-manic response.

Sex-specific effects of gain-of-function P2RX7 variation on bipolar disorder

BACKGROUND

Patients with bipolar disorder demonstrate sex differences in clinical presentation, particularly in the sub-phenotypes related to periodicity of mood episodes, such as rapid cycling. Additionally, recent studies have linked P2RX7 gene variants with the risk of rapid cycling in clinical cohorts of patients with bipolar disorder, as well as other mood disorders. However, little is known about potential sex differences in the relationship between variants in P2RX7 and bipolar disorder.

METHODS

We investigated sex-specific genetic associations between variants of P2RX7 (rs1621388 and rs2230912) in 756 patients with bipolar disorder and 787 control patients matched on age, sex, and ancestry. We examined sex-specific genetic associations with bipolar disorder by comparing cases and controls, as well as rapid cycling of mood episodes in cases. Findings were replicated in an independent dataset.

RESULTS

P2RX7 variants implying an increased pore activity were more common in bipolar disorder, in females but not in males. Neither P2RX7 variants associated with rapid cycling among bipolar patients.

LIMITATIONS

Low sample size limited power for tests of SNP by sex interaction, and data about the onset of rapid cycling and the timing of medication use were not available.

CONCLUSION

The effects of P2RX7 variants on bipolar disorder may be sex-specific, with increased P2X7 activity potentially elevating risk for bipolar disorder in females. Future research to examine the effect of P2RX7 on bipolar disorder should consider sex-specific effects.

Bipolar Disorder: Its Etiology and How to Model in Rodents

Characterized by the switch of manic and depressive phases, bipolar disorder was described as early as the fifth century BC. Nevertheless up to date, the underlying neurobiology is still largely unclear, assuming a multifactor genesis with both biological-genetic and psychosocial factors. Significant process has been achieved in recent years in researching the causes of bipolar disorder with modern molecular biological (e.g., genetic and epigenetic studies) and imaging techniques (e.g., positron emission tomography (PET) and functional magnetic resonance imaging (fMRI)). In this chapter we will first summarize our recent knowledge on the etiology of bipolar disorder. We then discuss how several factors observed to contribute to bipolar disorder in human patients can be manipulated to generate rodent models for bipolar disorder. Finally, we will give an overview on behavioral test that can be used to assess bipolar-disorder-like behavior in rodents.

Evaluation of the Role of ABCB1gene Polymorphic Variants on Psychiatric Disorders Predisposition in Macedonian Population

The psychiatric and other CNS disorders are characterized with unregulated neuro-inflammatory processes and chronic microglia cell activation resulting with detrimental effect. ABCB1gene polymorphismsC1236T, G2677T/Aand C3435T are associated with P-glycoprotein expression and function andare linked with predisposition to psychiatric disorders such as schizophrenia and bipolar disorders. The relationship between mood disorders and glucocorticoids has been confirmed and ABCB1 SNPs influence the glucocorticoids access to the brain. The aim of the study is evaluation of the influence of the three most common ABCB1SNPs on predisposition to psychiatric disorders in Macedonian population. In the study 107 unrelated healthy Macedonians of both sexes were enrolled as a control group and patient population of 54 patients (22 to 65 years old) diagnosed with schizophrenia or bipolar disorder. ABCB1 for three polymorphisms were analyzed by Real-Time PCR in both groups. The results have confirmed the role of the ABCB1 gene in predisposition to psychiatric disorders and increased risk of developing bipolar disorder in carriers of the heterozygotes and mutant homozygotes for polymorphic variations in 1236 and 2677 in comparison to the normal genotype carriers. Three-fold higher risk was estimated for psychiatric illness in women that are 1236 and 2677 heterozygous carrier (heterozygous and mutant homozygous) compared to healthy control (men and women) population and four-fold higher risk in comparison only to healthy women population. Mutant allele carriers for 1236 and 2677 polymorphisms that are 35 years and below in patients population have almost three-fold higher risk for development of psychiatric illness.

Structural brain abnormalities in patients with type I bipolar disorder and suicidal behavior

Some studies have identified brain morphological changes in the frontolimbic network (FLN) in bipolar subjects who attempt suicide (SA). The present study investigated neuroanatomical abnormalities in the FLN to find a possible neural signature for suicidal behavior in patients with bipolar disorder type I (BD-I). We used voxel-based morphometry to compare euthymic patients with BD-I who had attempted suicide (n=20), who had not attempted suicide (n=19) and healthy controls (HCs) (n=20). We also assessed the highest medical lethality of their previous SA. Compared to the participants who had not attempted suicide, the patients with BD-I who had attempted suicide exhibited significantly increased gray matter volume (GMV) in the right rostral anterior cingulate cortex (ACC), which was more pronounced and extended further to the left ACC in the high-lethality subgroup (p<0.05, with family-wise error (FWE) correction for multiple comparisons using small-volume correction). GMV in the insula and orbitofrontal cortex was also related to suicide lethality (p<0.05, FWE-corrected). The current findings suggest that morphological changes in the FLN could be a signature of previous etiopathogenic processes affecting regions related to suicidality and its severity in BD-I patients.

[The German research network for mental disorders]

Mental disorders are among the greatest medical and social challenges facing us. They can occur at all stages of life and are among the most important commonly occurring diseases. In Germany 28 % of the population suffer from a mental disorder every year, while the lifetime risk of suffering from a mental disorder is almost 50 %. Mental disorders cause great suffering for those affected and their social network. Quantitatively speaking, they can be considered to be among those diseases creating the greatest burden for society due to reduced productivity, absence from work and premature retirement. The Federal Ministry of Education and Research is funding a new research network from 2015 to 2019 with up to 35 million euros to investigate mental disorders in order to devise and develop better therapeutic measures and strategies for this population by means of basic and translational clinical research. This is the result of a competitive call for research proposals entitled research network for mental diseases. It is a nationwide network of nine consortia with up to ten psychiatric and clinical psychology partner institutions from largely university-based research facilities for adults and/or children and adolescents. Furthermore, three cross-consortia platform projects will seek to identify shared causes of diseases and new diagnostic modalities for anxiety disorders, attention deficit hyperactivity disorders (ADHS), autism, bipolar disorders, depression, schizophrenia and psychotic disorders as well as substance-related and addictive disorders. The spectrum of therapeutic approaches to be examined ranges from innovative pharmacological and psychotherapeutic treatment to novel brain stimulation procedures. In light of the enormous burden such diseases represent for society as a whole, a sustainable improvement in the financial support for those researching mental disorders seems essential. This network aims to become a nucleus for long overdue and sustained support for a German center for mental disorders.

Update on bipolar disorder biomarker candidates

INTRODUCTION

Bipolar disorder is a chronic and disabling mood disorder with a complex pathophysiological basis. A significant percentage of patients do not receive correct diagnosis which directly influences therapeutic response, rendering recovery troublesome. There is a long-standing need for proper non-clinically based tools for diagnosis, treatment selection and follow-up of such patients. Areas covered: In the past decade, the scientific community has shown a great interest in biomarker development. Here, we highlight the different potential biomarkers and we discuss their feasibility and their possible clinical relevance. Expert commentary: To date, despite the major ongoing trials and consortia with promising future perspectives, no reliable biomarker of bipolar disorder has been fully defined.

Clinical features of bipolar spectrum with binge eating behaviour

OBJECTIVE

To determine whether bipolar spectrum disorder with binge eating behavior (BE) is an important clinical sub-phenotype.

METHODS

Prevalence rates and correlates of different levels of BE were assessed in 1114 bipolar spectrum patients participating in a genetic biobank. BE and eating disorders (EDs) were assessed with the Eating Disorder Diagnostic Scale (EDDS). Psychiatric illness burden was evaluated with measures of suicidality, psychosis, mood instability, anxiety disorder comorbidity, and substance abuse comorbidity. Medical illness burden was evaluated with body mass index (BMI) and the Cumulative Index Rating Scale (CIRS).

RESULTS

Thirty percent of patients had any BE and 27% had BE plus an ED diagnosis. Compared with bipolar spectrum patients without BE, bipolar spectrum patients with BE were younger and more likely to be female; had significantly higher levels of eating psychopathology, suicidality, mood instability, and anxiety disorder comorbidity; had a significantly higher mean BMI and a significantly higher rate of obesity; and had a significantly higher medical illness burden. Bipolar spectrum patients with BE but no ED diagnosis were more similar to bipolar spectrum patients without BE than to those with an ED. Nonetheless, the positive predictive value and specificity of BE predicting an ED was 0.90 and 0.96, respectively.

LIMITATIONS

As only two patients had co-occurring anorexia nervosa, these results may not generalize to bipolar spectrum patients with restricting EDs.

CONCLUSION

Bipolar spectrum disorder with broadly-defined BE may not be as clinically relevant a sub-phenotype as bipolar spectrum disorder with an ED but may be an adequate proxy for the latter when phenotyping large samples of individuals.

Volume, metabolites and neuroinflammation of the hippocampus in bipolar disorder - A combined magnetic resonance imaging and positron emission tomography study

BACKGROUND

The hippocampus is one of the brain regions that is involved in several pathophysiological theories about bipolar disorder (BD), such as the neuroinflammation theory and the corticolimbic metabolic dysregulation theory. We compared hippocampal volume and hippocampal metabolites in bipolar I disorder (BD-I) patients versus healthy controls (HCs) with magnetic resonance imaging (MRI) and spectroscopy (MRS). We post hoc investigated whether hippocampal volume and hippocampal metabolites were associated with microglial activation and explored if potential illness modifying factors affected these hippocampal measurements and whether these were associated with experienced mood and functioning.

MATERIALS AND METHODS

Twenty-two BD-I patients and twenty-four HCs were included in the analyses. All subjects underwent psychiatric interviews as well as an MRI scan, including a T1 scan and PRESS magnetic resonance spectroscopy (MRS). Volumetric analysis was performed with Freesurfer. MRS quantification was performed with LC Model. A subgroup of 14 patients and 11 HCs also underwent a successful [(11)C]-(R)-PK11195 neuroinflammation positron emission tomography scan.

RESULTS

In contrast to our hypothesis, hippocampal volumes were not decreased in patients compared to HC after correcting for individual whole-brain volume variations. We demonstrated decreased N-acetylaspartate (NAA)+N-acetyl-aspartyl-glutamate (NAAG) and creatine (Cr)+phosphocreatine (PCr) concentrations in the left hippocampus. In the explorative analyses in the left hippocampus we identified positive associations between microglial activation and the NAA+NAAG concentration, between alcohol use and NAA+NAAG concentration, between microglial activation and the depression score and a negative relation between Cr+PCr concentration and experienced occupational disability. Duration of illness associated positively with volume bilaterally.

CONCLUSION

Compared to HCs, the decreased NAA+NAAG concentration in the left hippocampus of BD-I patients suggests a decreased neuronal integrity in this region. In addition we found a positive relation between microglial activation and neuronal integrity in vivo, corresponding to a differentiated microglial function where some microglia induce apoptosis while others stimulate neurogenesis.

Gray matter brain volumes in childhood-maltreated patients with bipolar disorder type I: A voxel-based morphometric study

BACKGROUND

Childhood maltreatment (CM) may be related to clinical expression and outcome of bipolar disorder (BD). Several neuroimaging studies have detected brain morphological changes in specific neural networks of adults who suffered maltreatment in their childhood. We investigated alterations in gray matter volume (GMV) to determine a possible neuroanatomical basis of vulnerability in patients with CM having type I BD (BD-I).

METHODS

We assessed 39 euthymic DSM-IV BD-I patients with (n=20) and without (n=19) a history of CM and 20 healthy controls without maltreatment as defined by the Childhood Trauma Questionnaire (CTQ). Voxel-based morphometry (VBM) was used to compare GMV differences between patients and controls and perform linear correlations in overall BD group between GMV and CTQ scores.

RESULTS

BD-I patients had significant negative correlations between CTQ total score and GMV in the right dorsolateral prefrontal cortex (PFC) and the right thalamus; between physical abuse and GMV in the right dorsolateral PFC; between physical neglect and GMV in the thalamus bilaterally; and between emotional neglect and GMV in the right thalamus.

LIMITATIONS

Pharmacological treatment could have altered GMV findings. Results emerged only when using SVC approach. CTQ, a retrospective self-report, has the risk of potential recall bias. The cross-sectional design limits longitudinal and neurodevelopmental inferences.

CONCLUSIONS

The severity of self-reported CM in BD-I patients is associated with morphological changes in GMV of specific neural networks relevant to responses to stress and to modulate emotional behavior.

Serum BDNF levels in unaffected first-degree relatives of patients with bipolar disorder

Objective:

Unaffected relatives of bipolar disorder (BD) patients have been investigated for the identification of endophenotypes in an attempt to further elucidate the pathophysiology of the disease. Brain-derived neurotrophic factor (BDNF) is considered to be implicated in the pathophysiology of BD, but its role as an endophenotype has been poorly studied. We investigated abnormal serum BDNF levels in BD patients, in their unaffected relatives, and in healthy controls.

Methods:

BDNF levels were obtained from 25 DSM-IV bipolar I disorder patients, 23 unaffected relatives, and 27 healthy controls. All BD patients were in remission. The unaffected subjects were first-degree relatives of the proband who had no lifetime DSM-IV diagnosis of axis I disorder. BDNF serum levels were determined by sandwich ELISA using monoclonal BDNF-specific antibodies.

Results:

There were no statistical differences in BDNF levels among BD patients, relatives, and healthy controls.

Conclusion:

Serum BDNF levels may not indicate high genetic risk for BD, possibly acting as state markers rather than trait markers of the disease.

Glutamatergic and HPA-axis pathway genes in bipolar disorder comorbid with alcohol- and substance use disorders

Glutamatergic neurotransmission has been shown to be dysregulated in bipolar disorder (BD), alcohol use disorder (AUD) and substance use disorder (SUD). Similarly, disruption in the hypothalamic-pituitary-adrenal (HPA)-axis has also been observed in these conditions. BD is often comorbid with AUD and SUD. The effects of the glutamatergic and HPA systems have not been extensively examined in individuals with BD-AUD and BD-SUD comorbidity. The aim of this investigation was to determine whether variants in the glutamatergic pathway and HPA-axis are associated with BD-AUD and BD-SUD comorbidity. The research cohort consisted of 498 individuals with BD type I from the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD). A subset of the cohort had comorbid current AUD and current SUD. A total of 1935 SNPs from both the glutamatergic and HPA pathways were selected from the STEP-BD genome-wide dataset. To identify population stratification, IBS clustering was performed using the program Plink 1.07. Single SNP association and gene-based association testing were conducted using logistic regression. A pathway analysis of glutamatergic and HPA genes was performed, after imputation using IMPUTE2. No single SNP was associated with BD-AUD or BD-SUD comorbidity after correction for multiple testing. However, from the gene-based analysis, the gene PRKCI was significantly associated with BD-AUD. The pathway analysis provided overall negative findings, although several genes including GRIN2B showed high percentage of associated SNPs for BD-AUD. Even though the glutamatergic and HPA pathways may not be involved in BD-AUD and BD-SUD comorbidity, PRKCI deserves further investigation in BD-AUD.

Neural correlates of hallucinations in bipolar disorder

Objective:

Approximately one-half of all patients affected by bipolar disorder present with psychotic features on at least one occasion. Several studies have found that alterations in the activity of mesolimbic and prefrontal regions are related to aberrant salience in psychotic patients. The aim of the present study was to investigate the structural correlates of a history of hallucinations in a sample of euthymic patients with bipolar I disorder (BD-I).

Methods:

The sample consisted of 21 euthymic patients with BD-I and no comorbid axis I DSM-IV-TR disorders. Voxel based morphometry (VBM) was used to compare patients with and without a lifetime history of hallucinations. Preprocessing was performed using the Diffeomorphic Anatomical Registration through Exponentiated Lie Algebra (DARTEL) algorithm for VBM in SPM8. Images were processed using optimized VBM.

Results:

The main finding of the present study was a reduction in gray matter volume in the right posterior insular cortex of patients with BD-I and a lifetime history of hallucinations, as compared to subjects with the same diagnosis but no history of hallucinations.

Conclusions:

This finding supports the presence of abnormalities in the salience network in BD patients with a lifetime history of hallucinations. These alterations may be associated with an aberrant assignment of salience to the elements of one’s own experience, which could result in psychotic symptoms.

Genetics of emotional reactivity in bipolar disorders

BACKGROUND

Emotional reactivity has been proposed as a relevant intermediate phenotype of bipolar disorder (BD). Our goal was to identify genetic factors underlying emotional reactivity in a sample of bipolar patients.

METHODS

Affect intensity (a proxy measure of emotional reactivity) was measured in a sample of 281 euthymic patients meeting DSM-IV criteria for BD. We use a validated dimensional tool, the 40-item self-report Affect Intensity Measure scale developed by Larsen and Diener. Patients with BD were genotyped for 475. 740 SNPs (using Illumina HumanHap550 Beadchips or HumanHap610 Quad chip). Association was investigated with a general mixed regression model of the continuous trait against genotypes, including gender as covariate.

RESULTS

Four regions (1p31.3, 3q13.11, 11p15.1 and 11q14.4) with a p-value lower or equal to 5×10(-6) were identified. In these regions, the joint effect of the four variants accounted for 24.5% of the variance of AIM score. Epistasis analysis did not detect interaction between these variants. In the 11p15.1 region, the rs10766743 located in the intron of the NELL1 gene remained significant after correction for multiple testing (p=2×10(-7)).

CONCLUSIONS

These findings illustrate that focusing on quantitative intermediate phenotypes can facilitate the identification of genetic susceptibility variants in BD.

Gray matter volumes in patients with bipolar disorder and their first-degree relatives

Bipolar disorder (BD) is highly heritable. First-degree relatives of BD patient have an increased risk to develop the disease. We investigated abnormalities in gray matter (GM) volumes in healthy first-degree relatives of BD patients to identify possible brain structural endophenotypes for the disorder. 3D T1-weighted magnetic resonance images were obtained from 25 DSM-IV BD type I patients, 23 unaffected relatives, and 27 healthy controls (HC). A voxel-based morphometry protocol was used to compare differences in GM volumes between groups. BD patients presented reduced GM volumes bilaterally in the thalamus compared with HC. Relatives presented no global or regional GM differences compared with HC. Our negative results do not support the role of GM volume abnormalities as endophenotypes for BD. Thalamic volume abnormalities may be associated the pathophysiology of the disease.

Functional outcome in major psychiatric disorders and associated clinical and psychosocial variables: A potential cross-diagnostic phenotype for further genetic investigations?

OBJECTIVES

Functional outcome has recently become of interest for cross-diagnostic subphenotype approaches in psychiatric genetics. Therefore, it is crucial to know about clinical, demographic and psychosocial variables that correlate with long-term functioning. Unfortunately, there is a lack of studies that directly compare the importance of correlates for functional outcome between different disorders.

METHODS

Applying regression models to samples of patients with schizophrenia (SZ, n = 238), bipolar disorder (BD, n = 533) and major depressive disorder (MDD, n = 398), we compared the magnitude of association of potential correlates with functional outcome, measured by the Global Assessment of Functioning (GAF) score.

RESULTS

Shared correlates for worse functional outcome were poor premorbid functioning, insidious illness onset and poor premorbid work or social adjustment in all three disorders, and negative symptomatology in SZ and BD. Disorder-specific correlates for SZ were longer duration of illness, lower functioning during episodes and being life-time single, for BD substance abuse and suicidality, and for MDD premorbid unemployment and having a premorbid personality disorder.

CONCLUSIONS

We found different patterns of correlates for long-term functioning in SZ, BD and MDD. Knowledge of these patterns may improve the quality of genetic investigations focussing on functional outcome.

Feature-expression heat maps--a new visual method to explore complex associations between two variable sets

INTRODUCTION

Existing methods such as correlation plots and cluster heat maps are insufficient in the visual exploration of multiple associations between genetics and phenotype, which is of importance to achieve a better understanding of the pathophysiology of psychiatric and other illnesses. The implementation of a combined presentation of effect size and statistical significance in a graphical method, added to the ordering of the variables based on the effect-ordered data display principle was deemed useful by the authors to facilitate in the process of recognizing meaningful patterns in these associations.

MATERIALS AND METHODS

The requirements, analyses and graphical presentation of the feature-expression heat map are described. The graphs display associations of two sets of ordered variables where a one-way direction is assumed. The associations are depicted as circles representing a combination of effect size (color) and statistical significance (radius).

RESULTS

An example dataset is presented and relation to other methods, limitations, areas of application and possible future enhancements are discussed.

CONCLUSION

The feature-expression heat map is a useful graphical instrument to explore associations in complex biological systems where one-way direction is assumed, such as genotype-phenotype pathophysiological models.

Changing requirements and resulting needs for IT-infrastructure for longitudinal research in the neurosciences

The observation of growing "difficulties" in IT-infrastructures in neuroscience research during the last years led to a search for reasons and an analysis on how this phenomenon is reflected in the scientific literature. With a retrospective analysis of nine examples of multicenter research projects in the neurosciences and a literature review the observation was systematically analyzed. Results show that the rise in complexity mainly stems from two reasons: (1) more and more need for information on quality and context of research data (metadata) and (2) long-term requirements to handle the consent and identity/pseudonyms of study participants and biomaterials in relation to legal requirements. The combination of these two aspects together with very long study times and data evaluation periods are components of the subjectively perceived "difficulties". A direct consequence of this result is that big multicenter trials are becoming part of integrated research data environments and are not standing alone for themselves anymore. This drives up the resource needs regarding the IT-infrastructure in neuroscience research. In contrast to these findings, literature on this development is scarce and the problem probably underestimated.

Neuroinflammation in bipolar disorder - A [(11)C]-(R)-PK11195 positron emission tomography study

BACKGROUND

The "monocyte-T-cell theory of mood disorders" regards neuroinflammation, i.e. marked activation of microglia, as a driving force in bipolar disorder. Microglia activation can be visualized in vivo using [(11)C]-(R)-PK11195 PET. Indirect evidence suggests the hippocampus as a potential focus of neuroinflammation in bipolar disorder. We aim to determine if there is increased [(11)C]-(R)-PK11195 binding to activated microglia in the hippocampus of patients with bipolar I disorder when compared to healthy controls.

MATERIAL AND METHODS

Fourteen patients with bipolar I disorder and eleven healthy controls were included in the analyses. Dynamic 60-min PET scans were acquired after the injection of [(11)C]-(R)-PK11195. All subjects underwent psychiatric interviews as well as an MRI scan, which was used for anatomic co-registration in the data analysis. The data from the PET scans was analyzed with a two-tissue-compartment model to calculate the binding potential, using the metabolite-corrected plasma and blood curve as input.

RESULTS

A significantly increased [(11)C]-(R)-PK11195 binding potential, which is indicative of neuroinflammation, was found in the right hippocampus of the patients when compared to the healthy controls (1.66 (CI 1.45-1.91) versus 1.33 (CI 1.16-1.53); p=0.033, respectively). Although the same trend was observed in the left hippocampus, this difference was not statistically significant.

CONCLUSION

This study is the first to demonstrate the presence of focal neuroinflammation in the right hippocampus in bipolar I disorder.

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.

Molecular genetic overlap in bipolar disorder, schizophrenia, and major depressive disorder

OBJECTIVES

Genome-wide association studies (GWAS) in complex phenotypes, including psychiatric disorders, have yielded many replicated findings, yet individual markers account for only a small fraction of the inherited differences in risk. We tested the performance of polygenic models in discriminating between cases and healthy controls and among cases with distinct psychiatric diagnoses.

METHODS

GWAS results in bipolar disorder (BD), major depressive disorder (MDD), schizophrenia (SZ), and Parkinson's disease (PD) were used to assign weights to individual alleles, based on odds ratios. These weights were used to calculate allele scores for individual cases and controls in independent samples, summing across many single nucleotide polymorphisms (SNPs). How well allele scores discriminated between cases and controls and between cases with different disorders was tested by logistic regression.

RESULTS

Large sets of SNPs were needed to achieve even modest discrimination between cases and controls. The most informative SNPs were overlapping in BD, SZ, and MDD, with correlated effect sizes. Little or no overlap was seen between allele scores for psychiatric disorders and those for PD.

CONCLUSIONS

BD, SZ, and MDD all share a similar polygenic component, but the polygenic models tested lack discriminative accuracy and are unlikely to be useful for clinical diagnosis.

Relationship between clinical features and inflammation-related monocyte gene expression in bipolar disorder - towards a better understanding of psychoimmunological interactions

OBJECTIVES

Existing and previously published datasets were examined for associations between illness and treatment characteristics and monocyte pro-inflammatory gene expression in patients with bipolar disorder (BD). We hypothesized a priori that increased monocyte pro-inflammatory gene expression would be found more frequently in patients with a lifetime history of psychotic symptoms.

METHODS

Monocyte quantitative polymerase chain reaction and symptom data from 64 patients with BD were collected from three Dutch studies. Regression analyses were performed to analyze the various associations between pro-inflammatory gene expression and clinical features, from which feature-expression heat maps were drawn.

RESULTS

No associations were found between pro-inflammatory gene expression and lifetime psychotic symptoms, whereas a positive association was identified between subcluster 2 genes and manic symptoms. For several subcluster 1a genes, a negative association was found with age at onset. For most subcluster 2 genes, a positive association was found with the duration of illness. Current use of antidepressants and of anti-epileptic agents was associated with subcluster 2 gene expression, and current use of lithium and antipsychotic agents with subcluster 1a gene expression.

CONCLUSIONS

Our hypothesis that lifetime psychotic features would be associated with pro-inflammatory monocyte gene expression was not confirmed. In an explorative analysis we found: (i) a possible relationship between pro-inflammatory gene expression and manic symptomatology; (ii) a differential immune activation related to age at onset and duration of illness; and (iii) support for the concept of an immune suppressive action of some of the mood-regulating medications.

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.

Gender-specific association of the SLC6A4 and DRD2 gene variants in bipolar disorder

Findings on the association between the risk for developing bipolar disorder and the functions of the serotonin transporter-linked polymorphic region gene (5-HTTLPR) and dopamine D2 receptor gene (DRD2) variants are contradictory. One explanation for this is that a gender difference may exist for genetic contributions. We compared the gender-related main effects and the gene-to-gene interaction between serotonin transporter gene (SLC6A4) and DRD2 in adult male and female patients with bipolar I (BP-I) and bipolar II (BP-II) disorder. Patients with BP-I (n = 400) and BP-II (n = 493), and healthy controls (n = 442) were recruited from Taiwan's Han Chinese population. The genotypes of the 5-HTTLPR and DRD2 Taq-IA polymorphisms were determined using polymerase chain reaction-restriction fragment length polymorphism analysis. Logistic regression analysis showed a significant gender-specific association of the DRD2 A1/A1 and the 5-HTTLPR S/S, S/LG , and LG/LG (S+) (p = 0.01) genotypes in men with BP-I (p = 0.002 and 0.01, respectively) and BP-II (p = 0.001 and 0.007, respectively), but not in women. A significant interaction for the DRD2 A1/A1 and 5-HTTLPR S+ polymorphisms was also found only in men with BP-I and BP-II (p = 0.003 and 0.001, respectively). We provide preliminary evidence for a gender-specific effect of the SLC6A4 and DRD2 gene variants for the risk of BP-I and of BP-II. We also found gender-specific interaction between 5-HTTLPR and DRD2 Taq-IA polymorphisms in patients with bipolar disorder.

Quantitative leukocyte BDNF promoter methylation analysis in bipolar disorder

Background

Bipolar disorder (BD) is a complex psychiatric phenotype with a high heritability and a multifactorial etiology. Multisite collaborative efforts using genome-wide association studies (GWAS) have identified only a portion of DNA sequence-based risk factors in BD. In addition to predisposing DNA sequence variants, epigenetic misregulation may play an etiological role in BD and account for monozygotic twin discordance, parental origin effects, and fluctuating course of BD. In this study, we investigated DNA methylation of the brain-derived neurotrophic factor (BDNF) gene in BD.

Methods

Fifty participants with BD were compared to the same number of age- and sex-matched controls for DNA methylation differences at BDNF promoters 3 and 5. DNA methylation reads were obtained using a mass spectrophotometer for 64 cytosine-guanine (CpG) sites in 36 CpG ‘units’ across three amplicons of BDNF promoters 3 and 5.

Results and Discussion

Methylation fractions differed between BD participants and controls for 11 of 36 CpG units. Five CpG units, mostly in promoter 5, remained significant after false discovery rate correction (FDR) (p values ≤ 0.004) with medium to large effect sizes (Cohen's d ≥ 0.61). Several of the significant CpGs overlapped with or were immediately adjacent to transcription factor binding sites (TFBSs) - including two of the FDR-significant CpG units in promoter 5. For the CpGs in promoter 3, there was a positive and significant correlation between age at sample collection and DNA methylation fraction (rho = 0.56, p = 2.8 ×10⁻⁵) in BD cases, but not in controls. Statistically significant differences in mean methylation fraction at 5/36 CpG units (after FDR), some at or immediately adjacent to TFBSs, suggest possible relevance for the current findings to BD etiopathogenesis. The positive correlation between age and methylation seen in promoter 3 is consistent with age-related decline in BDNF expression previously reported. Future studies should provide more exhaustive epigenetic study of the BDNF locus to better characterize the relationship between BDNF methylation differences and BD.

Electronic supplementary material

The online version of this article (doi:10.1186/2194-7511-1-28) contains supplementary material, which is available to authorized users.

Gray matter abnormalities as brain structural vulnerability factors for bipolar disorder: A review of neuroimaging studies of individuals at high genetic risk for bipolar disorder

OBJECTIVE

Cortical and subcortical gray matter abnormalities have been reported in individuals at high genetic risk for bipolar disorder, but the findings are inconsistent. The aim of this study was to review the available literature to identify common findings that could represent brain structural vulnerability factors for bipolar disorder and to discuss challenges for the advancement of the field.

METHOD

A systematic search was conducted using the PubMed database to identify all original articles investigating cortical or subcortical gray matter abnormalities in first-degree relatives of bipolar disorder patients.

RESULTS

Very few findings were replicated, with the exception of larger insular cortex volumes in adult first-degree relatives and larger right inferior frontal gyrus in offspring of probands with bipolar disorder, both when compared with healthy controls. Isolated findings included decreased gray matter density in the left thalamus, decreased gray matter volumes in the left hippocampus and parahippocampal gyrus, and thicker right hippocampus in unaffected first-degree relatives. Genetic liability for bipolar disorder was associated with gray matter volumes in regions of the anterior cingulate cortex, ventral striatum, medial frontal gyrus, right precentral gyrus, right insular cortex, and medial orbital gyrus. Some studies found no evidence for gray matter abnormalities in first-degree relatives of bipolar disorder patients.

CONCLUSIONS

Possible reasons for the discrepancies of findings across studies include small samples sizes, small effect size of susceptibility genes, the phenotypic heterogeneity of bipolar disorder, and the possible confounding effect of other Axis I psychopathologies among the relatives of patients. Future multisite, prospective, large studies with more homogeneous samples would be a key strategy to advance the field. The ultimate benefit would be an understanding of how to use brain imaging tools to identify individuals at increased risk for bipolar disorder and develop preventive strategies for that population.

Comparison of gene expression profiles in the blood, hippocampus and prefrontal cortex of rats

Background

The comparability of gene expression between blood and brain tissues is a central issue in neuropsychiatric research where the analysis of molecular mechanisms in the brain is of high importance for the understanding of the diseases and the discovery of biomarkers. However, the accessibility of brain tissue is limited. Therefore, knowledge about how easily accessible peripheral tissue, e. g. blood, is comparable to and reflects gene expression of brain regions will help to advance neuropsychiatric research.

Description

Gene expression in the blood, hippocampus (HC) and prefrontal cortex (PFC) of genetically identical rats was compared using a genome-wide Affymetrix gene expression microarray covering 29,215 expressed genes. A total of 56.8% of 15,717 expressed genes were co-expressed in blood and at least one brain tissue, while 55.3% of all genes were co-expressed in all three tissues simultaneously. The overlapping genes included a set of genes of relevance to neuropsychiatric diseases, in particular bipolar disorder, schizophrenia and alcohol addiction. These genes included CLOCK, COMT, FAAH, NPY, NR3C1, NRGN, PBRM1, TCF4, and SYNE.

Conclusions

This study provides baseline data on absolute gene expression and differences between gene expression in the blood, HC and PFC brain tissue of genetically identical rats. The present data represents a valuable resource for future studies as it might be used for first information on gene expression levels of genes of interest in blood and brain under baseline conditions. Limitations of our study comprise possible contamination of brain tissue with blood and the non-detection of genes with very low expression levels. Genes that are more highly expressed in the brain than in the blood are of particular interest since changes in their expression, e.g. due to disease status, or treatment, are likely to be detected in an experiment. In contrast, genes with higher expression in the blood than in the brain are less informative since their higher baseline levels could superimpose variation in brain.

Neurocognitive features in subgroups of bipolar disorder

OBJECTIVE

To examine which subgroups of DSM-IV bipolar disorder (BD) [BD type I (BD-I) or BD type II (BD-II), and subgroups based on history of psychosis, presenting polarity, and age at onset] differentiate best regarding neurocognitive measures.

METHODS

A total of 199 patients with BD were characterized by clinical and neurocognitive features. The distribution of subgroups in this sample was: BD-I, 64% and BD-II, 36%; 60% had a history of psychosis; 57% had depression as the presenting polarity; 61% had an early onset of BD, 25% had a mid onset, and 14% had a late onset. We used multivariate regression analyses to assess relationships between neurocognitive variables and clinical subgroups.

RESULTS

Both BD-I diagnosis and elevated presenting polarity were related to impairments in verbal memory, with elevated presenting polarity explaining more of the variance in this cognitive domain (22.5%). History of psychosis and BD-I diagnosis were both related to impairment in semantic fluency, with history of psychosis explaining more of the variance (11.6%).

CONCLUSION

Poor performance in verbal memory appears to be associated with an elevated presenting polarity, and poor performance in semantic fluency appears to be associated with a lifetime history of psychosis.

Polymorphisms in seizure 6-like gene are associated with bipolar disorder I: evidence of gene × gender interaction

BACKGROUND

Previous reports have suggested that there may be gene × gender interaction for bipolar disorder (BD)-associated genes/loci at 22q11-13. This study aimed to investigate the associations of SEZ6L genetic variants with bipolar disorder I (BD-I) and to examine gender-specific genetic associations.

METHODS

605 BD-I Caucasian cases and 1034 controls were selected from the publicly available data of the Whole Genome Association Study of BD. To increase power, an additional 362 Caucasian controls were added to this study from the Genome-Wide Association Study of Schizophrenia. In total, 605 BD-I cases and 1396 controls (934 males and 1067 females) were available for genetic association analysis of 118 SNPs within the SEZ6L gene using PLINK software.

RESULTS

16 SNPs showed significant gene x gender interactions influencing BD-I (P<0.01). In addition, significant differences in the distribution of the alleles for these 16 SNPs were observed between the female BD-I patients and healthy controls (P<0.015) but no significant associations were found for the male sample (P>0.05). The SNP rs4822691 showed the strongest association with BD-I in the female sample (P=2.18 × 10(-4)) and the strongest gene × gender interaction in influencing BD-I (P=9.16 × 10(-5)).

LIMITATIONS

The findings of this study need to be replicated in independent samples.

CONCLUSIONS

This is the first demonstration that genetic variants in the SEZ6L gene are associated with BD-I in female patients and provides additional compelling evidence for genetic variation at 22q11-13 that influences BD-I risk. The present findings highlight the gene x gender interactions modifying BD-I susceptibility.

Maternal perspectives on the return of genetic results: context matters

The objectives of this study were to study maternal preferences for the return of their child's genetic results and to describe the experiences, perceptions, attitudes, and values that are brought to bear when individuals from different racial and cultural backgrounds consider participating in genetic research. We recruited women with diverse sociodemographic profiles to participate in seven focus groups. Twenty-eight percent of participants self-identified as Hispanic; 49% as White, non-Hispanic; and 21% as Asian or Asian American. Focus groups were conducted in English or Spanish and were audio-recorded and transcribed verbatim. Transcripts were analyzed using qualitative thematic methods. Results indicated that preferences and decisions regarding the return of results may depend on both research and individual contextual factors. Participants understood the return of results as a complex issue, where individual and cultural differences in preferences are certain to arise. Another key finding was that participants desired an interpersonal, dynamic, flexible process that accommodated individual preferences and contextual differences for returning results. Our findings indicate a need to have well-developed systems for allowing participants to make and change over time their choices regarding the return of their child's genetic results.

Managing sensitive phenotypic data and biomaterial in large-scale collaborative psychiatric genetic research projects: practical considerations

Large-scale collaborative research will be a hallmark of future psychiatric genetic research. Ideally, both academic and non-academic institutions should be able to participate in such collaborations to allow for the establishment of very large samples in a straightforward manner. Any such endeavor requires an easy-to-implement information technology (IT) framework. Here we present the requirements for a centralized framework and describe how they can be met through a modular IT toolbox.

Developmental regulation of expression of schizophrenia susceptibility genes in the primate hippocampal formation

The hippocampal formation is essential for normal memory function and is implicated in many neurodevelopmental, neurodegenerative and neuropsychiatric disorders. In particular, abnormalities in hippocampal structure and function have been identified in schizophrenic subjects. Schizophrenia has a strong polygenic component, but the role of numerous susceptibility genes in normal brain development and function has yet to be investigated. Here we described the expression of schizophrenia susceptibility genes in distinct regions of the monkey hippocampal formation during early postnatal development. We found that, as compared with other genes, schizophrenia susceptibility genes exhibit a differential regulation of expression in the dentate gyrus, CA3 and CA1, over the course of postnatal development. A number of these genes involved in synaptic transmission and dendritic morphology exhibit a developmental decrease of expression in CA3. Abnormal CA3 synaptic organization observed in schizophrenics might be related to some specific symptoms, such as loosening of association. Interestingly, changes in gene expression in CA3 might occur at a time possibly corresponding to the late appearance of the first clinical symptoms. We also found earlier changes in expression of schizophrenia susceptibility genes in CA1, which might be linked to prodromal psychotic symptoms. A number of schizophrenia susceptibility genes including APOE, BDNF, MTHFR and SLC6A4 are involved in other disorders, and thus likely contribute to nonspecific changes in hippocampal structure and function that must be combined with the dysregulation of other genes in order to lead to schizophrenia pathogenesis.

Genetic heterogeneity according to age at onset in bipolar disorder: a combined positional cloning and candidate gene approach

This study is the first that formally tests for genetic heterogeneity of bipolar disorder (BD) according to age at onset (AAO) sub-groups by combining positional cloning and candidate gene approaches. Our previous genome-wide linkage-scan identified five genomic regions linked to early-onset form of BD. The present study uses association analysis to test genetic heterogeneity of candidate genes located in these five regions in a sample of 443 unrelated bipolar patients and 1,731 controls. The study involved the following steps: (1) test of heterogeneity by comparing early-onset BD patients versus later-onset BD patients; and (2) for significant results in step 1, comparison of early-onset BD patients and later-onset BD patients separately to controls. Two types of analyses were used: the single SNP test and the gene-based association test. We provide evidence for genetic heterogeneity within the ADRB2 (beta-2adrenoreceptor) gene region that is specifically associated with the early onset form of BD with an OR of 1.8. Unfortunately, the genotyping coverage of ADRB2 in the Wellcome Trust Case Control Consortium sample meant undermined our efforts to undertake a replication. However, as the ADRB2 gene product directly interacts with the CACNA1C gene product, and is known to be implicated in BD susceptibility, we conclude that further exploration of the relationships between ADRB2 and BD needs to be undertaken.

Neuroticism mediates the effect of P2RX7 on outcomes of mood disorders

BACKGROUND

We previously reported an association between P2RX7 variant rs208294, diagnosis, and the longitudinal course of mood disorders. Here, we test whether the personality trait neuroticism mediates the effect of P2RX7 on the course of mood disorders.

METHODS

Patients with DSM-IV mood disorder (256 with major depressive disorder and 168 with bipolar disorder [BD]) were diagnosed with semistructured interviews, genotyped, and followed up for a median of 60 (range 6-83) months. The primary outcome was the prospectively assessed proportion of time spent in any DSM-IV mood episode (time ill). Three types of genetic effect were tested in structural equations models: Model 1: genes directly affect outcome independent of neuroticism, Model 2: neuroticism mediates the effect of genes on outcome, and Model 3: neuroticism and the genetic variant interact in their effect on outcome.

RESULTS

Neuroticism mediated the P2RX7 genetic effect on outcome. The T allele of rs208294 was associated with higher neuroticism, which in turn predicted a higher proportion of time spent in mood episodes (the bootstrap-based test of indirect effect, P = .02). There was no significant interaction between neuroticism and the genotype.

CONCLUSION

Neuroticism is likely to lie on the causal pathway between the rs208294 T variant and the adverse long-term course of major depressive and BDs.

Cognitive dysfunction is worse among pediatric patients with bipolar disorder Type I than Type II

BACKGROUND

  Impaired profiles of neurocognitive function have been consistently demonstrated among pediatric patients with bipolar disorder (BD), and may aid in the identification of endophenotypes across subtypes of the disorder. This study aims to determine phenotypic cognitive profiles of patients with BD Type I and II.

METHODS

  Subjects (N = 79) consisted of BD I (n = 27) and BD II (n = 19) patients and demographic and intellectually matched healthy controls (HC; n = 33) that completed a battery of neurocognitive tasks.

RESULTS

  Bipolar disorder Type I patients performed significantly more poorly compared to HC on all domains of cognitive function including attention, executive function, working memory, visual memory, and verbal learning and memory. BD I patients also performed more poorly compared to BD II patients on all domains of cognitive functioning with the exception of working memory, whereas BD II patients did poorly relative to HC only on verbal learning and memory.

CONCLUSIONS

  Findings from the current study indicate that BD I patients are characterized by more severe cognitive impairment relative to BD II patients who show an intermediate pattern of performance between BD I patients and HC. Verbal learning and memory may effectively differentiate pediatric BD patients and controls, regardless of the subtype of BD, and may serve as a cognitive endophenotype for the disorder. Additionally, these findings move us closer to developing effective cognitive interventions tailored to specific subtypes of pediatric BD patients.

Global mental health: Global strengths and strategies Task-shifting in a shifting health economy

Global mental health challenges sit at the frontiers of health care worldwide. The frequency of mental health disorders is increasing, and represents a large portion of the global burden of human disease (DALYs). There are many impeding forces in delivering mental health care globally. The knowledge of what mental health and its diseased states are limits the ability to seek appropriate care. Limited training and experience among primary providers dilutes the capacity of systems for adequate care, support, and intervention. There are limited numbers of medical personnel worldwide to attend to individuals afflicted by mental health disorders. The challenges of global mental health are the capacity of the global systems to enhance knowledge and literacy surrounding mental health disorders, enhance and expand ways of identifying and treating mental health disorders effectively at an early stage in its course. Much has been written about the epidemiology of mental health disorders globally followed by discussions of the need for improvements in programs that will improve the lot of the mentally ill. Task shifting involves the engaging of human resources, generally nonprofessional, in the care of mental health disorders. Engaging traditional healers and community health workers in the identification and management of mental health disorders is a very strong potential opportunity for task shifting care in mental health. In doing so it will be necessary to study the concept of mental health literacy of traditional healers and health workers in a process of mutual alignment of purpose founded on evidence based research.

Response to treatment in bipolar disorder

PURPOSE OF REVIEW

Bipolar disorder is a complex psychiatric condition that has been shown to carry a great degree of genetic loading. This review addresses current research in the genetics of treatment response in bipolar disorder, with a focus on findings that have shaped our understanding of the changing direction of this field in light of recent technological advancements.

RECENT FINDINGS

The recent publications in bipolar disorder treatment response have helped consolidate or improve upon knowledge of susceptibility loci and genes in the field. There seems to be an increasing trend toward functionally assessing the role played by putative candidate genes and molecular factors modulating expression in bipolar disorder, as well as a movement toward more global, pathway and genome-wide-oriented research.

SUMMARY

Genetic and molecular research to date in bipolar disorder treatment response has not completely answered all the lingering questions in the field, but has contributed to the development of a more patient-based understanding of treatment. In order to apply these findings at a clinical level, more comprehensive treatment response studies are imperative, combining recent advances in high-throughput genomics with functional molecular research.