Genetics of bipolar disorder

Altered neuroepithelial morphogenesis and migration defects in iPSC-derived cerebral organoids and 2D neural stem cells in familial bipolar disorder

Bipolar disorder (BD) is a severe mental illness that can result from neurodevelopmental aberrations, particularly in familial BD, which may include causative genetic variants. In the present study, we derived cortical organoids from BD patients and healthy (control) individuals from a clinically dense family in the Indian population. Our data reveal that the patient organoids show neurodevelopmental anomalies, including organisational, proliferation and migration defects. The BD organoids show a reduction in both the number of neuroepithelial buds/cortical rosettes and the ventricular zone size. Additionally, patient organoids show a lower number of SOX2-positive and EdU-positive cycling progenitors, suggesting a progenitor proliferation defect. Further, the patient neurons show abnormal positioning in the ventricular/intermediate zone of the neuroepithelial bud. Transcriptomic analysis of control and patient organoids supports our cellular topology data and reveals dysregulation of genes crucial for progenitor proliferation and neuronal migration. Lastly, time-lapse imaging of neural stem cells in 2D in vitro cultures reveals abnormal cellular migration in BD samples. Overall, our study pinpoints a cellular and molecular deficit in BD patient-derived organoids and neural stem cell cultures.

Progress and Implications from Genetic Studies of Bipolar Disorder

With the advancements in gene sequencing technologies, including genome-wide association studies, polygenetic risk scores, and high-throughput sequencing, there has been a tremendous advantage in mapping a detailed blueprint for the genetic model of bipolar disorder (BD). To date, intriguing genetic clues have been identified to explain the development of BD, as well as the genetic association that might be applied for the development of susceptibility prediction and pharmacogenetic intervention. Risk genes of BD, such as CACNA1C, ANK3, TRANK1, and CLOCK, have been found to be involved in various pathophysiological processes correlated with BD. Although the specific roles of these genes have yet to be determined, genetic research on BD will help improve the prevention, therapeutics, and prognosis in clinical practice. The latest preclinical and clinical studies, and reviews of the genetics of BD, are analyzed in this review, aiming to summarize the progress in this intriguing field and to provide perspectives for individualized, precise, and effective clinical practice.

Multiple psychiatric polygenic risk scores predict associations between childhood adversity and bipolar disorder

BACKGROUND

It remains unclear how adverse childhood experiences (ACE) and increased genetic risk for bipolar disorder (BD) interact to influence BD symptom outcomes. Here we calculated multiple psychiatric polygenic risk scores (PRS) and used the measures of ACE to understand these gene-environment interactions.

METHOD

885 BD subjects were included for analyses. BD, ADHD, MDD and SCZ PRSs were calculated using the PRS-CS-auto method. ACEs were evaluated using the Children Life Event Questionnaire (CLEQ). Participants were divided into groups based on the presence of ACE and the total number of ACEs. The associations between total ACE number, PRSs and their interactions were evaluated using multiple linear and logistic regressions. Secondary analyses were performed to evaluate the influence of ACE and PRS on sub-phenotypes of BD.

RESULTS

The number of ACEs increased with the ADHD PRS. BD participants who had ACEs showed an earlier age of BD onset and higher odds of having rapid cycling. Increased BD PRS was associated with increased odds of developing psychotic symptoms. Higher ADHD PRS was associated with increased odds of having rapid cycling. No prediction effect was observed from MDD and SCZ PRS. And, we found no significant interaction between ACE numbers and any of the PRSs in predicting any selected BD sub-phenotypes.

LIMITATIONS

The study was limited by sample size, ACE definition, and cross-sectional data collection method.

CONCLUSIONS

The findings consolidate the importance of considering multiple psychiatric PRSs in predicting symptom outcomes among BD patients.

Effects of lithium on locomotor activity and circadian rhythm of honey bees

Lithium has been considered a potential acaricidal agent against the honey bee (Apis mellifera) parasite Varroa. It is known that lithium suppresses elevated activity and regulates circadian rhythms and light response when administered to humans as a primary therapeutic chemical for bipolar disorder and to other bipolar syndrome model organisms, given the crucial role of timing in the bee's foraging activity and the alternating sunlight vs dark colony environment bees are exposed, we explored the influence of lithium on locomotor activity (LMA) and circadian rhythm of honey bees. We conducted acute and chronic lithium administration experiments, altering light conditions and lithium doses to assess LMA and circadian rhythm changes. We fed bees one time 10 μl sucrose solution with 0, 50, 150, and 450 mM LiCl in the acute application experiment and 0, 1, 5, and 10 mmol/kg LiCl ad libitum in bee candy in the chronic application experiment. Both acute and chronic lithium treatments significantly decreased the induced LMA under constant light. Chronic lithium treatment disrupted circadian rhythmicity in constant darkness. The circadian period was lengthened by lithium treatment under constant light. We discuss the results in the context of Varroa control and lithium's effect on bipolar disorder.

Emotional dysregulation, alexithymia and neuroticism: a systematic review on the genetic basis of a subset of psychological traits

Neuroticism, alexithymia and emotion dysregulation are key traits and known risk factors for several psychiatric conditions. In this systematic review, the aim is to evaluate the genetic contribution to these psychological phenotypes. A systematic review of articles found in PubMed was conducted. Search terms included 'genetic', 'GWAS', 'neuroticism', 'alexithymia' and 'emotion dysregulation'. Risk of bias was assessed utilizing the STREGA checklist. Two hundred two papers were selected from existing literature based on the inclusion and exclusion criteria. Among these, 27 were genome-wide studies and 175 were genetic association studies. Single gene association studies focused on selected groups of genes, mostly involved in neurotransmission, with conflicting results. GWAS studies on neuroticism, on the other hand, found several relevant and replicated intergenic and intronic loci affecting the expression and regulation of crucial and well-known genes (such as DRD2 and CRHR1). Mutations in genes coding for trascriptional factors were also found to be associated with neuroticism (DCC, XKR6, TCF4, RBFOX1), as well as a noncoding regulatory RNA (LINC00461). On the other hand, little GWAS data are available on alexythima and emotional dysregulation.

Expression analysis of NF-ƙB-related long non-coding RNAs in bipolar disorder

Bipolar disorder (BD) is a mental disorder that leads to abnormal swings in mood, energy, activity level, attention, and the capability to accomplish daily tasks. Several long non-coding RNAs (lncRNAs) are dysregulated in BD patients. We have compared expression levels of five NF-κB-associated lncRNAs, namely ANRIL, CEBPA-DT, H19, NKILA and HNF1A-AS1 in blood samples of BD patients compared with controls. While ANRIL, CEBPA-DT and HNF1-AS1 were significantly under-expressed in BD patients compared with controls, NKILA levels were higher in patients versus controls. Among differentially expressed genes, HFN1A-AS1 exhibited the best diagnostic parameters in the separation of patients from controls (AUC ± SD = 0.86 ± 0.03, sensitivity = 0.82, specificity = 0.82, P value < 0.0001). AUC values for NKILA, ANRIL and CEBPA-DT were 0.71, 0.68 and 0.65, respectively. In accordance with the previously reported participation of NF-ƙB in the pathophysiology of BD, the current study provides evidence for dysregulation of NF-κB-associated lncRNAs in BD.

Evaluating cognitive function in unaffected relatives of individuals with bipolar disorders: A meta-analysis

BACKGROUND

Available studies have evaluated cognition in the unaffected relatives of bipolar disorder patients; however, to our knowledge, there has been no quantitative analysis evaluating the foregoing association. Herein, this meta-analysis aims to provide a quantitative synthesis of the extant literature reporting on the association between performance in cognitive domains (i.e., executive function, attention, learning and memory or global cognition) amongst unaffected individuals of probands with bipolar disorders.

METHODS

Online databases (i.e., PubMed, PsycINFO) and Google Scholar were searched from inception to 20 September 2021. Studies with unaffected, first-degree relatives of individuals with DSM-IV or DSM-5 defined bipolar disorders were included. The risk of bias was assessed using the ROBINS-1 tool, and the quality of the sources was evaluated using GRADE criteria. The results of the studies were quantitatively synthesized using Cohen's d effect sizes via a random-effects meta-analytic approach on JASP.

RESULTS

A total of 15 studies were included in the final review. Overall, results indicate that cognitive performance across all domains is moderately impaired in unaffected relatives of individuals with bipolar disorders (d = 0.488). Sub-analysis suggests there is a higher level of impairment in executive functioning (d = 0.612).

DISCUSSION

The identification of cognitive deficits in unaffected relatives of probands with bipolar disorders indicates that cognitive impairment is endophenotypic and a core disturbance in persons with bipolar disorders; future studies should endeavour to target cognition as a potential pre-emptive and prevention strategy of bipolar disorders.

Zika virus-induced TNF-α signaling dysregulates expression of neurologic genes associated with psychiatric disorders

BACKGROUND

Zika virus (ZIKV) is an emerging flavivirus of global concern. ZIKV infection of the central nervous system has been linked to a variety of clinical syndromes, including microcephaly in fetuses and rare but serious neurologic disease in adults. However, the potential for ZIKV to influence brain physiology and host behavior following apparently mild or subclinical infection is less well understood. Furthermore, though deficits in cognitive function are well-documented after recovery from neuroinvasive viral infection, the potential impact of ZIKV on other host behavioral domains has not been thoroughly explored.

METHODS

We used transcriptomic profiling, including unbiased gene ontology enrichment analysis, to assess the impact of ZIKV infection on gene expression in primary cortical neuron cultures. These studies were extended with molecular biological analysis of gene expression and inflammatory cytokine signaling. In vitro observations were further confirmed using established in vivo models of ZIKV infection in immunocompetent hosts.

RESULTS

Transcriptomic profiling of primary neuron cultures following ZIKV infection revealed altered expression of key genes associated with major psychiatric disorders, such as bipolar disorder and schizophrenia. Gene ontology enrichment analysis also revealed significant changes in gene expression associated with fundamental neurobiological processes, including neuronal development, neurotransmission, and others. These alterations to neurologic gene expression were also observed in the brain in vivo using several immunocompetent mouse models of ZIKV infection. Mechanistic studies identified TNF-α signaling via TNFR1 as a major regulatory mechanism controlling ZIKV-induced changes to neurologic gene expression.

CONCLUSIONS

Our studies reveal that cell-intrinsic innate immune responses to ZIKV infection profoundly shape neuronal transcriptional profiles, highlighting the need to further explore associations between ZIKV infection and disordered host behavioral states.

Association study of BDNF Val66Met gene polymorphism with bipolar disorder and lithium treatment response in Indian population

BACKGROUND

The association of the Val66Met (rs6265) polymorphism in the brain-derived neurotrophic factor (BDNF) gene with bipolar disorder (BD) and response to lithium treatment has been suggested, though inconsistently. The considerable diversity of allele frequency across different populations contributes to this. There is no data from South Asia till date. Hence, we examined the association of this polymorphism in BD cases from India, and its association with lithium treatment response.

METHODS

BD patients (N = 301) were recruited from the clinical services of National Institute of Mental Health and Neurosciences (NIMHANS), India. Lithium treatment response for 190 BD subjects was assessed using Alda scale by NIMH life charts. Patients with total score ⩾7 were defined as lithium responders (N = 115) and patients with score <7 were defined as lithium non-responders (N = 75). Healthy controls (N = 484) with no lifetime history of neuropsychiatric illness or a family history of mental illness were recruited as control set. Genotyping was performed by TaqMan genotyping assay.

RESULTS

Genotype and allele frequency of BDNF Val66Met SNP was significantly different (χ2 = 7.78, p = 0.02) in cases compared to controls, and the Val(G) allele was more frequent (χ2 = 7.08, p = 0.008) in BD patients. However, no significant difference is noted in genotype or allele frequencies of this polymorphism between the lithium responders and non-responders.

CONCLUSIONS

The Val(G) allele of BDNF Val66Met polymorphism is associated with risk of BD in this sample, but it is not related to response to lithium.

The economic burden of bipolar I disorder in the United States in 2015

BACKGROUND

The current societal costs of bipolar I disorder (BDI) have not been comprehensively characterized in the United States, as previous studies are based on data from two decades ago.

METHODS

The costs of BDI were estimated for 2015 and comprised direct healthcare costs, non-healthcare costs, and indirect costs, calculated based on a BDI prevalence of 1%. The excess costs of BDI were estimated as the difference between the costs incurred by individuals with BDI and those incurred by individuals without BD or individuals from the general population. Direct healthcare costs were assessed using three large US claims databases for insured individuals and the literature for uninsured individuals. Direct non-healthcare and indirect costs were based on the literature and governmental publications.

RESULTS

The total costs of BDI were estimated at $202.1 billion in 2015, corresponding to an average of $81,559 per individual, while the excess costs of BDI were estimated at $119.8 billion, corresponding to an average of $48,333 per individual. The largest contributors to excess costs were caregiving (36%), direct healthcare costs (21%), and unemployment (20%). In sensitivity analyses, excess costs ranged from $101.2 to $124.3 billion.

LIMITATIONS

Direct healthcare costs were calculated based on a BDI diagnosis, thus excluding undiagnosed patients. Direct non-healthcare and indirect costs were based on combined estimates from the literature.

CONCLUSIONS

Besides direct healthcare costs, BDI was associated with substantial direct non-healthcare and indirect costs. More effective treatments and practices are needed to optimize therapeutic strategies and contain direct and indirect costs.

Genetic Variants Involved in Bipolar Disorder, a Rough Road Ahead

BACKGROUND

Bipolar Disorder (BD), along with depression and schizophrenia, is one of the most serious mental illnesses, and one of the top 20 causes of severe impairment in everyday life. Recent molecular studies, using both traditional approaches and new procedures such as Whole-Genome Sequencing (WGS), have suggested that genetic factors could significantly contribute to the development of BD, with heritability estimates of up to 85%. However, it is assumed that BD is a multigenic and multifactorial illness with environmental factors that strongly contribute to disease development/progression, which means that progress in genetic knowledge of BD might be difficult to interpret in clinical practice.

OBJECTIVE

The aim of this study is to provide a synthetic description of the main SNPs variants identified/confirmed by recent extensive WGS analysis as well as by reconstruction in an in vitro mechanism or by amygdala activation protocol in vivo.

METHOD

Bibliographic data, genomic and protein Data Banks were consulted so as to carry out a cross genomic study for mutations, SNPs and chromosomal alterations described in these studies in BD patients.

RESULTS

Fifty-five different mutations have been described in 30 research papers by different genetic analyses including recent WGS analysis. Many of these studies have led to the discovery of the most probable susceptibility genes for BD, including ANK3, CACNA1C, NCAN, ODZ4, SYNE1, and TRANK1. Exploration has started the role of several of these mutations in BD pathophysiology using in vitro and animal models.

CONCLUSION

Although new genomic research technology in BD opens up new possibilities, the current results for common variants are still controversial because of four broad conditions: analytical validity, clinical validity, clinical utility and a reasonable cost for genetic analysis are not yet accessible.

Is there any association between Toxoplasma gondii infection and bipolar disorder? A systematic review and meta-analysis

BACKGROUND

The relationship between Toxoplasma gondii infection and the development of bipolar disorder (BD) has long been investigated, yet to date it is still poorly understood and documented. The aim of this review is to derive a summary estimate of the strength of the association between infection with T. gondii and BD from the available published studies.

METHODS

A systematic review was performed using PubMed, LILACS, PsycINFO, and Embase databases. Studies which included a proportion of seropositive BD patients and controls were further examined in a meta-analysis.

RESULTS

One hundred eighteen citations were initially retrieved. Thirteen studies were included in our systematic review. Eight out of these thirteen studies were included in our meta-analysis. Statistical analyses showed that T. gondii infection is associated with with BD (OR=1.26).

LIMITATIONS

Small sample size was the major limitation among the studies that carried out serological analyses. In addition, the available studies did not have enough information on disease status/severity or type of bipolar disorder. Also, it was not possible to analyze pregnancy status or perinatal infection. Future studies addressing the aforementioned topics are clearly needed.

CONCLUSIONS

Despite heterogeneous results, patients with BD are more likely to be infected by T. gondii than controls. Early T. gondii infection might predispose the development of BD. T.gondii infection is becoming clinically relevant in psychiatric disorders and future mechanistic studies are required to elucidate the underlying pathophysiological mechanisms.

Exploring Genetic Variability at PI, GSK3, HPA, and Glutamatergic Pathways in Lithium Response: Association With IMPA2, INPP1, and GSK3B Genes

Lithium is considered the first-line treatment in bipolar disorder, although response could range from an excellent response to a complete lack of response. Response to lithium is a complex phenotype in which different factors, part of them genetics, are involved. In this sense, the aim of this study was to investigate the potential association of genetic variability at genes related to phosphoinositide, glycogen synthetase kinase-3 (GSK3), hypothalamic-pituitary-adrenal, and glutamatergic pathways with lithium response. A sample of 131 bipolar patients (99 type I, 32 type II) were grouped and compared according to their level of response: excellent responders (ER), partial responders (PR), and nonresponders (NR). Genotype and allele distributions of the rs669838 (IMPA2), rs909270 (INNP1), rs11921360 (GSK3B), and rs28522620 (GRIK2) polymorphisms significantly differed between ER, PR, and NR. When we compared the ER versus PR+NR, the logistic regression showed significant association for rs669838-C (IMPA2; P = 0.021), rs909270-G (INPP1; P = 0.009), and rs11921360-A (GSK3B; P = 0.004) with lithium nonresponse. Haplotype analysis showed significant association for the haplotypes rs3791809-rs4853694-rs909270 (INPP1) and rs1732170-rs11921360-rs334558 (GSK3B) and lithium response. Our study is in line with previous studies reporting association between genetic variability at these genes and lithium response, pointing to an effect of IMPA2, INPP1, and GSK3B genes to lithium response in bipolar disorder patients. Further studies with larger samples are warranted to assess the strength of the reported associations.

Childhood-compared to adolescent-onset bipolar disorder has more statistically significant clinical correlates

BACKGROUND

The strengths and limitations of considering childhood-and adolescent-onset bipolar disorder (BD) separately versus together remain to be established. We assessed this issue.

METHODS

BD patients referred to the Stanford Bipolar Disorder Clinic during 2000-2011 were assessed with the Systematic Treatment Enhancement Program for BD Affective Disorders Evaluation. Patients with childhood- and adolescent-onset were compared to those with adult-onset for 7 unfavorable bipolar illness characteristics with replicated associations with early-onset patients.

RESULTS

Among 502 BD outpatients, those with childhood- (<13 years, N=110) and adolescent- (13-18 years, N=218) onset had significantly higher rates for 4/7 unfavorable illness characteristics, including lifetime comorbid anxiety disorder, at least ten lifetime mood episodes, lifetime alcohol use disorder, and prior suicide attempt, than those with adult-onset (>18 years, N=174). Childhood- but not adolescent-onset BD patients also had significantly higher rates of first-degree relative with mood disorder, lifetime substance use disorder, and rapid cycling in the prior year. Patients with pooled childhood/adolescent - compared to adult-onset had significantly higher rates for 5/7 of these unfavorable illness characteristics, while patients with childhood- compared to adolescent-onset had significantly higher rates for 4/7 of these unfavorable illness characteristics.

LIMITATIONS

Caucasian, insured, suburban, low substance abuse, American specialty clinic-referred sample limits generalizability. Onset age is based on retrospective recall.

CONCLUSIONS

Childhood- compared to adolescent-onset BD was more robustly related to unfavorable bipolar illness characteristics, so pooling these groups attenuated such relationships. Further study is warranted to determine the extent to which adolescent-onset BD represents an intermediate phenotype between childhood- and adult-onset BD.

An observational study of inflammation in the central nervous system in patients with bipolar disorder

OBJECTIVES

The potential influence of infections and immunological changes on the aetiology and pathogenesis of bipolar disorder (BD) has been discussed. Our aim was to detect intrathecal specific antibody synthesis against the neurotropic infectious agents that have previously been linked to BD.

METHODS

Paired cerebrospinal fluid (CSF) and serum samples from 40 patients with BD were analysed using the enzyme-linked immunosorbent assay to detect the concentration of antibodies against the following neurotropic infectious pathogens: Toxoplasma gondii (T. gondii), herpes simplex virus (HSV) types 1 and 2, cytomegalovirus (CMV), and Epstein-Barr virus (EBV). The specific antibody index (AI) was calculated, and an AI > 1.4 was considered to be evidence of intrathecal specific antibody synthesis. Twenty-six patients with pseudotumour cerebri served as controls.

RESULTS

Eight out of 40 patients with BD displayed specific intrathecal antibody synthesis against at least one of the tested neurotropic agents compared to only one patient in the control group (p = 0.061, not significant). Of these eight patients with BD, no significant prevalence of any particular neurotropic pathogen was evident. Five out of 40 patients with BD showed oligoclonal bands in the CSF, suggestive of a chronic immune reaction in the central nervous system (CNS).

CONCLUSIONS

We found evidence for increased production of antibody in the CSF of individuals with BD. However, the trend for polyspecific intrathecal antibody synthesis, as well as the presence of oligoclonal bands, might indicate activation of the intrathecal humoral immune system in a subgroup of patients with BD, as it is known to be associated with autoimmune disorders of the CNS.

Prevalence of child sexual abuse among adults and youths with bipolar disorder: a systematic review

To estimate the prevalence and social and demographic correlates of child sexual abuse among people with bipolar disorder, the findings of all the pertinent studies were qualitatively and semi-quantitatively analyzed. Five databases were searched. Blind assessments of study eligibility and quality were conducted by two independent researchers. Twenty studies, meeting minimum quality standards and including 3407 adults and youths with bipolar disorder across 10 countries and 3 continents, were examined. The prevalence of child sexual abuse was 24% (23% without outliers); however, such prevalence rate might be underestimated, because many studies restricted definitions to the most severe forms of abuse. Child sexual abuse was a common experience for both males and females, while it was more frequent for adults than for youths. Compared to healthy individuals, patients with bipolar disorder reported higher rates of child sexual abuse; compared to populations with other mental disorders, participants with bipolar disorder reported similar or lower rates of such abuse. Individuals with bipolar disorder are at risk of having a history of child sexual abuse, although such risk seems to be neither more specific to nor stronger for these individuals, compared to people with other psychiatric disorders.

Are obstetrical, perinatal, and infantile difficulties associated with pediatric bipolar disorder?

OBJECTIVES

Despite increasing acknowledgement of bipolar disorder (BD) in childhood, there is a paucity of literature that has investigated obstetrical, perinatal, and infantile difficulties and their potential link with BD. To this end, we examined difficulties during delivery, immediate post-birth, and infancy and the association with BD in childhood.

METHODS

From two similarly designed, ongoing, longitudinal, case-control family studies of pediatric BD (N = 327 families), we analyzed 338 children and adolescents [mean (± standard deviation) age: 12.00 ± 3.37 years]. We stratified them into three groups: healthy controls (N = 98), BD probands (N = 120), and their non-affected siblings (N = 120). All families were comprehensively assessed with a structured psychiatric diagnostic interview for psychopathology and substance use. Mothers were directly questioned regarding the pregnancy, delivery, and infancy difficulties that occurred with each child using a module from the Diagnostic Interview for Children and Adolescents-Parent Version (DICA-P).

RESULTS

Mothers of BD subjects were more likely to report difficulties during infancy than mothers of controls [odds ratio (95% confidence interval) = 6.6 (3.0, 14.6)]. Specifically, children with BD were more likely to have been reported as a stiffened infant [7.2 (1.1, 47.1)] and more likely to have experienced 'other' infantile difficulties [including acting colicky; 4.9 (1.3, 18.8)] compared to controls. We found no significant differences between groups in regards to obstetrical or perinatal difficulties (all p values > 0.05).

CONCLUSIONS

While our results add to previous literature on obstetrical and perinatal difficulties and BD, they also highlight characteristics in infancy that may be prognostic indicators for pediatric BD.

A genetic network model of cellular responses to lithium treatment and cocaine abuse in bipolar disorder

Background

Lithium is an effective treatment for Bipolar Disorder (BD) and significantly reduces suicide risk, though the molecular basis of lithium's effectiveness is not well understood. We seek to improve our understanding of this effectiveness by posing hypotheses based on new experimental data as well as published data, testing these hypotheses in silico, and posing new hypotheses for validation in future studies. We initially hypothesized a gene-by-environment interaction where lithium, acting as an environmental influence, impacts signal transduction pathways leading to differential expression of genes important in the etiology of BD mania.

Results

Using microarray and rt-QPCR assays, we identified candidate genes that are differentially expressed with lithium treatment. We used a systems biology approach to identify interactions among these candidate genes and develop a network of genes that interact with the differentially expressed candidates. Notably, we also identified cocaine as having a potential influence on the network, consistent with the observed high rate of comorbidity for BD and cocaine abuse. The resulting network represents a novel hypothesis on how multiple genetic influences on bipolar disorder are impacted by both lithium treatment and cocaine use. Testing this network for association with BD and related phenotypes, we find that it is significantly over-represented for genes that participate in signal transduction, consistent with our hypothesized-gene-by environment interaction. In addition, it models related pharmacogenomic, psychiatric, and chemical dependence phenotypes.

Conclusions

We offer a network model of gene-by-environment interaction associated with lithium's effectiveness in treating BD mania, as well as the observed high rate of comorbidity of BD and cocaine abuse. We identified drug targets within this network that represent immediate candidates for therapeutic drug testing. Posing novel hypotheses for validation in future work, we prioritized SNPs near genes in the network based on functional annotation. We also developed a "concept signature" for the genes in the network and identified additional candidate genes that may influence the system because they are significantly associated with the signature.

Investigation of an epistastic effect between a set of TAAR6 and HSP-70 genes variations and major mood disorders

Epistasis, the interaction between genes, is a topic of current interest in molecular and quantitative genetics. We have further studied a previously investigated sample of 187 major depressive disorder (MDD) patients, 171 bipolar disorder (BD) patients, and 288 controls, and tried to analyze the interaction between a set of variations of independent genes: the trace amine receptor 6 (rs4305745, rs8192625, rs7452939, rs6903874, and rs6937506) and the heat shock protein 70 (rs562047, rs1061581, rs2227956). The multifactor dimensionality reduction (MDR) method was applied and the covariates associated with diagnosis were also controlled. A significant predictive value of specific interactions between genotypes located in the investigated genes was found. We then report preliminary evidence that the epistasis between trace amine receptor 6 and heat shock protein 70 variations may compose a risk profile for major mood disorders. The level of statistical significance (P < 0.001) and the testing balancing accuracy over 0.62 suggest a cautious optimism toward this result, although the possibility of false positivity warrants further analyses in independent samples.