Independent evidence for the selective influence of GABA(A) receptors on one component of the bipolar disorder phenotype

Cross-disorder GWAS meta-analysis of endocannabinoid DNA variations in major depressive disorder, bipolar disorder, attention deficit hyperactivity disorder, autism spectrum disorder, and schizophrenia

The endocannabinoid system (ECS) is implicated in multiple mental disorders. In this study, we explored DNA variations in the ECS across major depressive disorder (MDD), bipolar disorder, attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and schizophrenia by performing a cross-disorder genome-wide association study (GWAS) meta-analysis. We obtained six datasets from the Psychiatric Genomics Consortium containing GWAS summary statistics from European cohorts (284,023 cases and 508,515 controls). Effective sample size weighted meta-analysis was performed for 2241 single nucleotide polymorphisms (SNPs) pertaining to gene bodies of 33 endocannabinoid genes using METAL, where an overall z-statistic is calculated for each marker based on a weighted sum of individual statistics. Heterogeneity was examined with I2 and X2 tests. MAGMA gene-based analysis was also performed. We identified nine SNPs significantly associated with a change in risk of having a mental disorder. The lead SNP was rs12805732 (Gene: Diacylglycerol Lipase Alpha; DAGLA). Four SNPs had substantial heterogeneity (I2>60 %). DAGLA had the strongest association with disease risk in gene-based analysis. Our findings suggest that the ECS may be a shared pathway in mental disorders. Future studies validating these findings would contribute to the identification of biomarkers of disease risk across multiple mental disorders.

GABRB2, a key player in neuropsychiatric disorders and beyond

The GABA receptors represent the main inhibitory system in the central nervous system that ensure synaptogenesis, neurogenesis, and the regulation of neuronal plasticity and learning. GABAA receptors are pentameric in structure and belong to the Cys-loop superfamily. The GABRB2 gene, located on chromosome 5q34, encodes the β2 subunit that combines with the α and γ subunits to form the major subtype of GABAA receptors, which account for 43% of all GABAA receptors in the mammalian brain. Each subunit probably consists of an extracellular N-terminal domain, four membrane-spanning segments, a large intracellular loop between TM3 and TM4, and an extracellular C-terminal domain. Alternative splicing of the RNA transcript of the GABRB2 gene gives rise at least to four long and short isoforms with dissimilar electrophysiological properties. Furthermore, GABRB2 is imprinted and subjected to epigenetic regulation and positive selection. It has been associated with schizophrenia first in Han Chinese, and subsequently validated in other populations. Gabrb2 knockout mice also exhibited schizophrenia-like behavior and neuroinflammation that were ameliorated by the antipsychotic drug risperidone. GABRB2 was also associated with other neuropsychiatric disorders including bipolar disorder, epilepsy, autism spectrum disorder, Alzheimer's disease, frontotemporal dementia, substance dependence, depression, internet gaming disorder, and premenstrual dysphoric disorder. Recently, it has been postulated that GABRB2 might be a potential marker for different cancer types. As GABRB2 has a pivotal role in the central nervous system and is increasingly recognized to contribute to human diseases, further understanding of its structure and function may expedite the generation of new therapeutic approaches.

Expert and self-assessment of lifetime symptoms and diagnosis of major depressive disorder in large-scale genetic studies in the general population: comparison of a clinical interview and a self-administered checklist

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Major depression disorder (MDD) is a complex neuropsychiatric disorder and an increasing number of genetic risk variants are being identified. Investigation of their influence in the general population requires accurate and efficient assessment of depressive symptoms. Here, clinical interviews conducted by clinicians are the gold standard. We investigated whether valid and reliable clinical phenotypes can be obtained efficiently using self-administered instruments. Lifetime depressive symptoms and lifetime MDD diagnosis were assessed in 464 population-based individuals using a clinical interview and a structured, self-administered checklist. Analyses were carried out of the following: (i) intraclass correlations (ICC) between checklist and interview; (ii) sensitivity/specificity of the checklist; and (iii) the association of interview and checklist with a positive family history of MDD (FH-MDD+). The correspondence of the self-administered checklist with the clinical interview was good for most depressive symptoms (ICC=0.60–0.80) and moderate for MDD diagnosis (ICC=0.45). With the consecutive inclusion of MDD diagnostic criteria, sensitivity decreased from 0.67 to 0.46, whereas specificity remained high (0.95). For checklist and interview, strong associations were found between FH-MDD+ and most depressive symptoms and MDD diagnosis (all odds ratio≥1.83). The self-administered checklist showed high reliability for both the assessment of lifetime depressive symptoms and screening for individuals with no lifetime diagnosis of MDD. However, attention is warranted when the aim is to identify MDD cases. The positive association between depressive symptomatology and FH-MDD+ indicates the usefulness of both instruments to assess patients in genetic studies. Our data suggest that the more time-efficient and cost-efficient self-administered instruments also allow for the assessment of depressive symptoms accurate enough to investigate the influence of MDD genetic risk variants in the general population.

Genome-wide significant locus for Research Diagnostic Criteria Schizoaffective Disorder Bipolar type

Studies have suggested that Research Diagnostic Criteria for Schizoaffective Disorder Bipolar type (RDC-SABP) might identify a more genetically homogenous subgroup of bipolar disorder. Aiming to identify loci associated with RDC-SABP, we have performed a replication study using independent RDC-SABP cases (n = 144) and controls (n = 6,559), focusing on the 10 loci that reached a p-value <10^-5 for RDC-SABP in the Wellcome Trust Case Control Consortium (WTCCC) bipolar disorder sample. Combining the WTCCC and replication datasets by meta-analysis (combined RDC-SABP, n = 423, controls, n = 9,494), we observed genome-wide significant association at one SNP, rs2352974, located within the intron of the gene TRAIP on chromosome 3p21.31 (p-value, 4.37 × 10^-8 ). This locus did not reach genome-wide significance in bipolar disorder or schizophrenia large Psychiatric Genomic Consortium datasets, suggesting that it may represent a relatively specific genetic risk for the bipolar subtype of schizoaffective disorder.

Towards diagnostic markers for the psychoses

Psychotic disorders are currently grouped under broad phenomenological diagnostic rubrics. Researchers hope that progress in identifying aetiological mechanisms will ultimately enable more precise division of heterogeneous diagnoses into specific and valid subgroups. This goal has been an aim of psychiatry since the 19th century, when patients with general paresis were thought to have "insanity" similar to dementia praecox and manic depressive illness. Nowadays, the constructs of organic-induced and substance-induced psychotic disorder show that our diagnostic classification system already reflects, in part, aetiological factors. Most recently, gene copy number variation and autoimmunity have been associated with schizophrenia. We suggest how, on the basis of recent scientific advances, we can progress the identification of further putative subgroups and make the most of currently available interventions. Prompt diagnosis and treatment, and a more routine search for causes, could preserve function and improve outcome, and therefore be more acceptable to patients and carers.

From Prader-Willi syndrome to psychosis: translating parent-of-origin effects into schizophrenia research

Prader-Willi syndrome (PWS) is a relatively rare disorder that originates from paternally inherited deletions and maternal disomy (mUPD) within the 15q11-q13 region or alterations in the PWS imprinting center. Evidence is accumulating that mUPD underlies high prevalence of psychosis among PWS patients. Several genes involved in differentiation and survival of neurons as well as neurotransmission known to act in the development of PWS have been also implicated in schizophrenia. In this article, we provide an overview of genetic and epigenetic underpinnings of psychosis in PWS indicating overlapping points in the molecular background of PWS and schizophrenia. Simultaneously, we highlight the need for studies investigating genetic and epigenetic makeup of the 15q11-q13 in schizophrenia indicating promising candidate genes.

Increased visual gamma power in schizoaffective bipolar disorder

BACKGROUND

Electroencephalography and magnetoencephalography (MEG) studies have identified alterations in gamma-band (30-80 Hz) cortical activity in schizophrenia and mood disorders, consistent with neural models of disturbed glutamate (and GABA) neuron influence over cortical pyramidal cells. Genetic evidence suggests specific deficits in GABA-A receptor function in schizoaffective bipolar disorder (SABP), a clinical syndrome with features of both bipolar disorder and schizophrenia. This study investigated gamma oscillations in this under-researched disorder.

METHOD

MEG was used to measure induced gamma and evoked responses to a visual grating stimulus, known to be a potent inducer of primary visual gamma oscillations, in 15 individuals with remitted SABP, defined using Research Diagnostic Criteria, and 22 age- and sex-matched healthy controls.

RESULTS

Individuals with SABP demonstrated increased sustained visual cortical power in the gamma band (t 35 = -2.56, p = 0.015) compared to controls. There were no group differences in baseline gamma power, transient or sustained gamma frequency, alpha band responses or pattern onset visual-evoked responses.

CONCLUSIONS

Gamma power is increased in remitted SABP, which reflects an abnormality in the cortical inhibitory-excitatory balance. Although an interaction between gamma power and medication can not be ruled out, there were no group differences in evoked responses or baseline measures. Further work is needed in other clinical populations and at-risk relatives. Pharmaco-magnetoencephalography studies will help to elucidate the specific GABA and glutamate pathways affected.

Evaluation of neurotransmitter receptor gene expression identifies GABA receptor changes: a follow-up study in antipsychotic-naïve patients with first-episode psychosis

A study of the gene expression levels in the blood of individuals with schizophrenia in the beginning of the disease, such as first-episode psychosis (FEP), is useful to detect gene expression changes in this disorder in response to treatment. Although a large number of genetic studies on schizophrenia have been conducted, little is known about the effects of antipsychotic treatment on gene expression. The aim of the present study was to examine differences in the gene expression in the blood of antipsychotic-naïve FEP patients before and after risperidone treatment (N = 44) and also to verify the correlation with treatment response. In addition, we determined the correlations between differentially expressed genes and clinical variables. The expression of 40 neurotransmitter and neurodevelopment-associated genes was assessed using the RT2 Profiler PCR Array. The results indicated that the GABRR2 gene was downregulated after risperidone treatment, but no genes were associated with response to treatment and clinical variables after Bonferroni correction. GABRR2 downregulation after treatment can both suggest an effect of risperidone treatment or processes related to disease progression, either not necessarily associated with the improvement of symptoms. Despite this change was observed in blood, this decrease in GABRR2 mRNA levels might be an effect of changes in GABA concentrations or other systems interplay consequently to D2 blockage induced by risperidone, for example. Thus, it is important to consider that antipsychotics or the progression of psychotic disorders might interfere with gene expression.

Genetic relationships between schizophrenia, bipolar disorder, and schizoaffective disorder

There is substantial evidence for partial overlap of genetic influences on schizophrenia and bipolar disorder, with family, twin, and adoption studies showing a genetic correlation between the disorders of around 0.6. Results of genome-wide association studies are consistent with commonly occurring genetic risk variants, contributing to both the shared and nonshared aspects, while studies of large, rare chromosomal structural variants, particularly copy number variants, show a stronger influence on schizophrenia than bipolar disorder to date. Schizoaffective disorder has been less investigated but shows substantial familial overlap with both schizophrenia and bipolar disorder. A twin analysis is consistent with genetic influences on schizoaffective episodes being entirely shared with genetic influences on schizophrenic and manic episodes, while association studies suggest the possibility of some relatively specific genetic influences on broadly defined schizoaffective disorder, bipolar subtype. Further insights into genetic relationships between these disorders are expected as studies continue to increase in sample size and in technical and analytical sophistication, information on phenotypes beyond clinical diagnoses are increasingly incorporated, and approaches such as next-generation sequencing identify additional types of genetic risk variant.

Dosage-sensitivity of imprinted genes expressed in the brain: 15q11-q13 and neuropsychiatric illness

Imprinted genes, those genes subject to parent-of-origin-specific epigenetic marking resulting in monoallelic parent-specific expression, are sensitive to subtle changes in expression dosage. This has been illustrated in a number of experimental models and the fact that both decreased (or complete loss) and increased imprinted gene expression can lead to human diseases. In the present paper, we discuss the consequence of increased dosage of imprinted genes for brain function, focusing on the PWS (Prader-Willi syndrome) locus on human chromosome 15q11-q13 and how predicted increases in dosage of maternally expressed imprinted genes from this interval are associated with a higher risk of developing psychotic illness. The evidence for this comes from individuals with PWS itself and also non-syndromic cases of psychosis in carriers of a maternally derived copy number variant spanning this locus. Of the known imprinted genes in this region, the prime candidate is maternally expressed UBE3A, which encodes E6-AP (E6-associated protein) ubiquitin ligase and has an influence on a number of important neurotransmitter systems. Furthermore, these findings point to the fact that brain function is exquisitely sensitive to both decreases and increases in the expression of imprinted genes.

Neurotransmitter receptor and regulatory gene expression in peripheral blood of Brazilian drug-naïve first-episode psychosis patients before and after antipsychotic treatment

Little is known about how genes expressed in blood relate to schizophrenia or antipsychotic use. We analyzed gene expression in 10 first-episode psychosis patients and nine controls using PCR Arrays. GABRR2 and CHRNA3 were found to be differentially expressed after risperidone treatment. These genes may be regulated by antipsychotic use.

mRNA and protein expression for novel GABAA receptors θ and ρ2 are altered in schizophrenia and mood disorders; relevance to FMRP-mGluR5 signaling pathway

Fragile X mental retardation protein (FMRP) is an RNA-binding protein that targets ∼5% of all mRNAs expressed in the brain. Previous work by our laboratory demonstrated significantly lower protein levels for FMRP in lateral cerebella of subjects with schizophrenia, bipolar disorder and major depression when compared with controls. Absence of FMRP expression in animal models of fragile X syndrome (FXS) has been shown to reduce expression of gamma-aminobutyric acid A (GABAA) receptor mRNAs. Previous work by our laboratory has found reduced expression of FMRP, as well as multiple GABAA and GABAB receptor subunits in subjects with autism. Less is known about levels for GABAA subunit protein expression in brains of subjects with schizophrenia and mood disorders. In the current study, we have expanded our previous studies to examine the protein and mRNA expression of two novel GABAA receptors, theta (GABRθ) and rho 2 (GABRρ2) as well as FMRP, and metabotropic glutamate receptor 5 (mGluR5) in lateral cerebella of subjects with schizophrenia, bipolar disorder, major depression and healthy controls, and in superior frontal cortex (Brodmann Area 9 (BA9)) of subjects with schizophrenia, bipolar disorder and healthy controls. We observed multiple statistically significant mRNA and protein changes in levels of GABRθ, GABRρ2, mGluR5 and FMRP molecules including concordant reductions in mRNA and proteins for GABRθ and mGluR5 in lateral cerebella of subjects with schizophrenia; for increased mRNA and protein for GABRρ2 in lateral cerebella of subjects with bipolar disorder; and for reduced mRNA and protein for mGluR5 in BA9 of subjects with bipolar disorder. There were no significant effects of confounds on any of the results.

Genetics of bipolar disorder

Studies of families and twins show the importance of genetic factors affecting susceptibility to bipolar disorder and suggest substantial genetic and phenotypic complexity. Robust and replicable genome-wide significant associations have recently been reported in genome-wide association studies at several common polymorphisms, including variants within the genes CACNA1C, ODZ4, and NCAN. Strong evidence exists for a polygenic contribution to risk (ie, many risk alleles of small effect). A notable finding is the overlap of susceptibility between bipolar disorder and schizophrenia for several individual risk alleles and for the polygenic risk. By contrast, genomic structural variation seems to play a smaller part in bipolar disorder than it does in schizophrenia. Together, these genetic findings suggest directions for future studies to delineate the aetiology and pathogenesis of bipolar disorder, indicate the need to re-evaluate our diagnostic classifications, and might eventually pave the way for major improvements in clinical management.

Social cognitive role of schizophrenia candidate gene GABRB2

The occurrence of positive selection in schizophrenia-associated GABRB2 suggests a broader impact of the gene product on population fitness. The present study considered the possibility of cognition-related GABRB2 involvement by examining the association of GABRB2 with psychosis and altruism, respectively representing psychiatric and psychological facets of social cognition. Four single nucleotide polymorphisms (SNPs) were genotyped for quantitative trait analyses and population-based association studies. Psychosis was measured by either the Positive and Negative Syndrome Scale (PANSS) or antipsychotics dosage, and altruism was based on a self-report altruism scale. The minor alleles of SNPs rs6556547, rs1816071 and rs187269 in GABRB2 were correlated with high PANSS score for positive symptoms in a Han Chinese schizophrenic cohort, whereas those of rs1816071 and rs1816072 were associated with high antipsychotics dosage in a US Caucasian schizophrenic cohort. Moreover, strongly significant GABRB2-disease associations were found among schizophrenics with severe psychosis based on high PANSS positive score, but no significant association was observed for schizophrenics with only mild psychosis. Interestingly, in addition to association with psychosis in schizophrenics, rs187269 was also associated with altruism in healthy Han Chinese. Furthermore, parallel to correlation with severe psychosis, its minor allele was correlated with high altruism scores. These findings revealed that GABRB2 is associated with psychosis, the core symptom and an endophenotype of schizophrenia. Importantly, the association was found across the breadth of the psychiatric (psychosis) to psychological (altruism) spectrum of social cognition suggesting GABRB2 involvement in human cognition.

The genetics of alcohol dependence

Alcohol consumption dates back to the Neolithic period, and alcohol dependence contributes substantially to the current global burden of disease. Despite this, optimal therapies and preventive strategies are lacking. Formal genetic studies of alcohol dependence have shown that genetic factors play as large a role in disease etiology as environmental factors. Molecular genetic studies may identify causal factors and facilitate the development of novel preventive and therapeutic approaches. Whereas earlier studies involved the use of linkage- and candidate-gene approaches, recent years have witnessed the introduction of genome-wide association studies (GWAS). The present review provides a brief overview of the findings of formal genetic studies, summarizes the results of earlier molecular-genetic investigations, and presents a detailed overview of all published GWAS in the field of alcohol dependence research. To date, few genome-wide significant findings have been reported. However, through the polygenic approach, GWAS have both confirmed the existence of a multitude of novel risk genes and indicated interesting new candidates.

A larval zebrafish model of bipolar disorder as a screening platform for neuro-therapeutics

Modelling neurological diseases has proven extraordinarily difficult due to the phenotypic complexity of each disorder. The zebrafish has become a useful model system with which to study abnormal neurological and behavioural activity and holds promise as a model of human disease. While most of the disease modelling using zebrafish has made use of adults, larvae hold tremendous promise for the high-throughput screening of potential therapeutics. The further development of larval disease models will strengthen their ability to contribute to the drug screening process. Here we have used zebrafish larvae to model the symptoms of bipolar disorder by treating larvae with sub-convulsive concentrations of the GABA antagonist pentylenetetrazol (PTZ). A number of therapeutics that act on different targets, in addition to those that have been used to treat bipolar disorder, were tested against this model to assess its predictive value. Carbamazepine, valproic acid, baclofen and honokiol, were found to oppose various aspects of the PTZ-induced changes in activity. Lidocaine and haloperidol exacerbated the PTZ-induced activity changes and sulpiride had no effect. By comparing the degree of phenotypic rescue with the mechanism of action of each therapeutic we have shown that the low-concentration PTZ model can produce a number of intermediate phenotypes that model symptoms of bipolar disorder, may be useful in modelling other disease states, and will help predict the efficacy of novel therapeutics.

Transcript-specific associations of SLC12A5 (KCC2) in human prefrontal cortex with development, schizophrenia, and affective disorders

The neuron-specific K(+)-Cl(-) cotransporter SLC12A5, also known as KCC2, helps mediate the electrophysiological effects of GABA. The pattern of KCC2 expression during early brain development suggests that its upregulation drives the postsynaptic switch of GABA from excitation to inhibition. We previously found decreased expression of full-length KCC2 in the postmortem hippocampus of patients with schizophrenia, but not in the dorsolateral prefrontal cortex (DLPFC). Using PCR and rapid amplification of cDNA ends, we discovered several previously unrecognized alternative KCC2 transcripts in both human adult and fetal brain in addition to the previously identified full-length (NM_020708.3) and truncated (AK098371) transcripts. We measured the expression levels of four relatively abundant truncated splice variants, including three novel transcripts (ΔEXON6, EXON2B, and EXON6B) and one previously described transcript (AK098371), in a large human cohort of nonpsychiatric controls across the lifespan, and in patients with schizophrenia and affective disorders. In SH-SY5Y cell lines, these transcripts were translated into proteins and expressed at their predicted sizes. Expression of the EXON6B transcript is increased in the DLPFC of patients with schizophrenia (p = 0.03) but decreased in patients with major depression (p = 0.04). The expression of AK098371 is associated with a GAD1 single nucleotide polymorphism (rs3749034) that previously has been associated with GAD67 expression and risk for schizophrenia. Our data confirm the developmental regulation of KCC2 expression, and provide evidence that KCC2 transcripts are differentially expressed in schizophrenia and affective disorders. Alternate transcripts from KCC2 may participate in the abnormal GABA signaling in the DLPFC associated with schizophrenia.

A twin study of schizoaffective-mania, schizoaffective-depression, and other psychotic syndromes

The nosological status of schizoaffective disorders remains controversial. Twin studies are potentially valuable for investigating relationships between schizoaffective-mania, schizoaffective-depression, and other psychotic syndromes, but no such study has yet been reported. We ascertained 224 probandwise twin pairs [106 monozygotic (MZ), 118 same-sex dizygotic (DZ)], where probands had psychotic or manic symptoms, from the Maudsley Twin Register in London (1948-1993). We investigated Research Diagnostic Criteria schizoaffective-mania, schizoaffective-depression, schizophrenia, mania and depressive psychosis primarily using a non-hierarchical classification, and additionally using hierarchical and data-derived classifications, and a classification featuring broad schizophrenic and manic syndromes without separate schizoaffective syndromes. We investigated inter-rater reliability and co-occurrence of syndromes within twin probands and twin pairs. The schizoaffective syndromes showed only moderate inter-rater reliability. There was general significant co-occurrence between syndromes within twin probands and MZ pairs, and a trend for schizoaffective-mania and mania to have the greatest co-occurrence. Schizoaffective syndromes in MZ probands were associated with relatively high risk of a psychotic syndrome occurring in their co-twins. The classification of broad schizophrenic and manic syndromes without separate schizoaffective syndromes showed improved inter-rater reliability, but high genetic and environmental correlations between the two broad syndromes. The results are consistent with regarding schizoaffective-mania as due to co-occurring elevated liability to schizophrenia, mania, and depression; and schizoaffective-depression as due to co-occurring elevated liability to schizophrenia and depression, but with less elevation of liability to mania. If in due course schizoaffective syndromes show satisfactory inter-rater reliability and some specific etiological factors they could alternatively be regarded as partly independent disorders.

Genome-wide association study on bipolar disorder in the Bulgarian population

Bipolar disorder is a severe psychiatric disorder influenced by environmental and genetic factors. Genetic studies have implicated many variants in the disease's etiology but only few have been successfully replicated. We conducted a genome-wide association study (GWAS) on bipolar disorder in the Bulgarian population followed by a replication study of the top 100 single nucleotide polymorphisms (SNPs) showing the smallest P values. The GWAS was performed on 188 bipolar disorder patients and 376 control subjects genotyped on the Illumina 550 platform. The replication study was conducted on 122 patients and 328 controls. Although our study did not show any association P value that achieved genome-wide significance, and none of the top 100 SNPs reached the Bonferroni-corrected P value in the replication study, the plausible involvement of some variants cannot be entirely discarded. Three polymorphisms, rs8099939 [P = 2.12 × 10(-6), odds ratio (OR) = 1.95, 95% confidence interval (CI) = 1.43-2.67] in GRIK5, rs6122972 (P = 3.11 × 10(-6), OR = 2.02, 95% CI = 1.46-2.80) in PARD6B and rs2289700 (P = 9.14 × 10(-6), OR = 2.13, 95% CI = 1.53-2.95) in CTSH remained associated at a similar level after Mantel-Haenszel test for combining the results from the genome-wide and replication studies. A modest association was also detected for SNP rs1012053 (GWAS P = 4.50 × 10(-2)) in DGKH, which has already been reported as the most significant variant in a previous genome-wide scan on bipolar disorder. However, further studies using larger datasets are needed to identify variants with smaller effects that contribute to the risk of bipolar disorder.

Convergent functional genomic studies of ω-3 fatty acids in stress reactivity, bipolar disorder and alcoholism

Omega-3 fatty acids have been proposed as an adjuvant treatment option in psychiatric disorders. Given their other health benefits and their relative lack of toxicity, teratogenicity and side effects, they may be particularly useful in children and in females of child-bearing age, especially during pregnancy and postpartum. A comprehensive mechanistic understanding of their effects is needed. Here we report translational studies demonstrating the phenotypic normalization and gene expression effects of dietary omega-3 fatty acids, specifically docosahexaenoic acid (DHA), in a stress-reactive knockout mouse model of bipolar disorder and co-morbid alcoholism, using a bioinformatic convergent functional genomics approach integrating animal model and human data to prioritize disease-relevant genes. Additionally, to validate at a behavioral level the novel observed effects on decreasing alcohol consumption, we also tested the effects of DHA in an independent animal model, alcohol-preferring (P) rats, a well-established animal model of alcoholism. Our studies uncover sex differences, brain region-specific effects and blood biomarkers that may underpin the effects of DHA. Of note, DHA modulates some of the same genes targeted by current psychotropic medications, as well as increases myelin-related gene expression. Myelin-related gene expression decrease is a common, if nonspecific, denominator of neuropsychiatric disorders. In conclusion, our work supports the potential utility of omega-3 fatty acids, specifically DHA, for a spectrum of psychiatric disorders such as stress disorders, bipolar disorder, alcoholism and beyond.

Polygenic dissection of the bipolar phenotype

BACKGROUND

Recent data provide strong support for a substantial common polygenic contribution (i.e. many alleles each of small effect) to genetic susceptibility for schizophrenia and overlapping susceptibility for bipolar disorder.

AIMS

To test hypotheses about the relationship between schizophrenia and psychotic types of bipolar disorder.

METHOD

Using a polygenic score analysis to test whether schizophrenia polygenic risk alleles, en masse, significantly discriminate between individuals with bipolar disorder with and without psychotic features. The primary sample included 1829 participants with bipolar disorder and the replication sample comprised 506 people with bipolar disorder.

RESULTS

The subset of participants with Research Diagnostic Criteria schizoaffective bipolar disorder (n = 277) were significantly discriminated from the remaining participants with bipolar disorder (n = 1552) in both the primary (P = 0.00059) and the replication data-sets (P = 0.0070). In contrast, those with psychotic bipolar disorder as a whole were not significantly different from those with non-psychotic bipolar disorder in either data-set.

CONCLUSIONS

Genetic susceptibility influences at least two major domains of psychopathological variation in the schizophrenia-bipolar disorder clinical spectrum: one that relates to expression of a 'bipolar disorder-like' phenotype and one that is associated with expression of 'schizophrenia-like' psychotic symptoms.