Accumulating evidence for a role of TCF7L2 variants in bipolar disorder with elevated body mass index

Liraglutide in Obese or Overweight Individuals With Stable Bipolar Disorder

BACKGROUND

Obesity is common among persons with bipolar disorder (BD). Liraglutide 3.0 mg/d subcutaneous injection is indicated for chronic weight management and associated with minimal adverse neuropsychiatric effects. This study evaluated whether liraglutide 3 mg/d reduced body weight, improved metabolic factors and eating psychopathology, and was safe and well tolerated in persons with stable BD who were obese (body mass index [BMI] >30 kg/m 2 ) or overweight (BMI ≥27 kg/m 2 ) with at least one weight-related comorbidity.

METHODS

This was a 40-week, randomized (1:1 ratio), placebo-controlled, double-blind, parallel-group, 2-arm clinical trial of liraglutide targeted to 3.0 mg/d (in combination with a reduced-calorie diet and increased physical activity) in 60 participants with stable BD who were obese or overweight. Primary outcome was percent change in body weight from baseline to study end. Secondary outcomes included percentage of patients who lost ≥5% of baseline body weight, and changes in metabolic variables and measures of eating psychopathology.

RESULTS

There were no significant baseline differences between the 29 liraglutide recipients and the 31 placebo recipients, except that liraglutide recipients had higher levels of binge eating and lower levels of high-density lipoprotein cholesterol. Compared with placebo, liraglutide was associated with significantly greater reductions in percent change in body weight, percentage of participants who lost at least 5% of body weight, and reductions in weight, BMI, hemoglobin A 1c levels, binge eating, and hunger. Liraglutide was well tolerated.

CONCLUSIONS

Liraglutide 3 mg/d may be efficacious and safe for weight loss in individuals with stable BD and obesity or overweight.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT03158805).

Differential Expression of Proteins Associated with Bipolar Disorder as Identified Using the PeptideShaker Software

The prevalence of bipolar disorder (BD) in modern society is growing rapidly, but due to the lack of paraclinical criteria, its differential diagnosis with other mental disorders is somewhat challenging. In this regard, the relevance of proteomic studies is increasing due to the development of methods for processing large data arrays; this contributes to the discovery of protein patterns of pathological processes and the creation of new methods of diagnosis and treatment. It seems promising to search for proteins involved in the pathogenesis of BD in an easily accessible material-blood serum. Sera from BD patients and healthy individuals were purified via affinity chromatography to isolate 14 major proteins and separated using 1D SDS-PAGE. After trypsinolysis, the proteins in the samples were identified via HPLC/mass spectrometry. Mass spectrometric data were processed using the OMSSA and X!Tandem search algorithms using the UniProtKB database, and the results were analyzed using PeptideShaker. Differences in proteomes were assessed via an unlabeled NSAF-based analysis using a two-tailed Bonferroni-adjusted t-test. When comparing the blood serum proteomes of BD patients and healthy individuals, 10 proteins showed significant differences in NSAF values. Of these, four proteins were predominantly present in BD patients with the maximum NSAF value: 14-3-3 protein zeta/delta; ectonucleoside triphosphate diphosphohydrolase 7; transforming growth factor-beta-induced protein ig-h3; and B-cell CLL/lymphoma 9 protein. Further exploration of the role of these proteins in BD is warranted; conducting such studies will help develop new paraclinical criteria and discover new targets for BD drug therapy.

TCF7L2 acts as a molecular switch in midbrain to control mammal vocalization through its DNA binding domain but not transcription activation domain

Vocalization is an essential medium for social signaling in birds and mammals. Periaqueductal gray (PAG) a conserved midbrain structure is believed to be responsible for innate vocalizations, but its molecular regulation remains largely unknown. Here, through a mouse forward genetic screening we identified one of the key Wnt/β-catenin effectors TCF7L2/TCF4 controls ultrasonic vocalization (USV) production and syllable complexity during maternal deprivation and sexual encounter. Early developmental expression of TCF7L2 in PAG excitatory neurons is necessary for the complex trait, while TCF7L2 loss reduces neuronal gene expressions and synaptic transmission in PAG. TCF7L2-mediated vocal control is independent of its β-catenin-binding domain but dependent of its DNA binding ability. Patient mutations associated with developmental disorders, including autism spectrum disorders, disrupt the transcriptional repression effect of TCF7L2, while mice carrying those mutations display severe USV impairments. Therefore, we conclude that TCF7L2 orchestrates gene expression in midbrain to control vocal production through its DNA binding but not transcription activation domain.

The genetics of bipolar disorder with obesity and type 2 diabetes

BACKGROUND

Bipolar disorder (BD) presents with high obesity and type 2 diabetes (T2D) and pathophysiological and phenomenological abnormalities shared with cardiometabolic disorders. Genomic studies may help define if they share genetic liability. This selective review of BD with obesity and T2D will focus on genomic studies, stress their current limitations and guide future steps in developing the field.

METHODS

We searched electronic databases (PubMed, Scopus) until December 2021 to identify genome-wide association studies, polygenic risk score analyses, and functional genomics of BD accounting for body mass index (BMI), obesity, or T2D.

RESULTS

The first genome-wide association studies (GWAS) of BD accounting for obesity found a promising genome-wide association in an intronic gene variant of TCF7L2 that was further replicated. Polygenic risk scores of obesity and T2D have also been associated with BD, yet, no genetic correlations have been demonstrated. Finally, human-induced stem cell studies of the intronic variant in TCF7L2 show a potential biological impact of the products of this genetic variant in BD risk.

LIMITATIONS

The narrative nature of this review.

CONCLUSIONS

Findings from BD GWAS accounting for obesity and their functional testing, have prompted potential biological insights. Yet, BD, obesity, and T2D display high phenotypic, genetic, and population-related heterogeneity, limiting our ability to detect genetic associations. Further studies should refine cardiometabolic phenotypes, test gene-environmental interactions and add population diversity.

Dynamic insulin-stimulated mTOR/GSK3 signaling in peripheral immune cells: Preliminary evidence for an association with lithium response in bipolar disorder

INTRODUCTION

A key mechanism of lithium is the inhibition of glycogen synthase kinase-3β (GSK3β) and activation of mammalian target of rapamycin (mTOR), two contributors to insulin signaling. We explored the relationship between these markers and clinical response to lithium in bipolar disorder (BD).

METHODS

Thirty-four subjects with BD who had been taking lithium for ≥2 years and had a maintenance lithium Alda score defined as either high (≥7; n = 20) or low (≤2; n = 14) were included in the study. Baseline protein expression of GSK3β and mTOR (total and phosphorylated (p)) was obtained from a buffy coat. Peripheral blood mononuclear cells (PBMCs) from a subset of each group (n = 11) were stimulated with insulin (10 µg) and change in protein expression was determined using Western blot.

RESULTS

In buffy coat samples, significantly higher levels of pmTOR were present in subjects with an Alda score ≤2 (lithium non-responsive), relative to those with scores ≥7 (lithium-responsive). No differences were observed for pGSK3β. In contrast, functional PBMC responses to 5 min of insulin stimulation demonstrated robust increases in pGSK3β (87.05 ± 43.41%) and pmTOR (105.7 ± 66.48%) in the lithium responsive group only. This contrasted observed decreases in pGSK3β (34.08 ± 16.12%) and pmTOR (37.84 ± 14.39%) 5 mins post-insulin in non-responders.

CONCLUSIONS

Dynamic increases in pmTOR and pGSK3β post-insulin stimulation may reflect an immunometabolic state that facilitates lithium response. Further prospective analyses are needed to replicate and extend these preliminary findings and further investigate the role of insulin signaling in lithium response in BD.

The broad pathogenetic role of TCF7L2 in human diseases beyond type 2 diabetes

The TCF7L2 protein is a key transcriptional effector of the Wnt/β‐catenin signaling pathway, regulating gene expression. It was initially identified in cancer research and embryologic developmental studies. Later, the TCF7L2 gene was linked to type 2 diabetes (T2D), implicating TCF7L2 and Wnt‐signaling in metabolic disorders and homeostasis. In fact, TCF7L2‐T2D variants confer the greatest relative risk for T2D, unquestionably predicting conversion to T2D in individuals with impaired glucose tolerance. We aim to describe the relevance of TCF7L2 in other human disorders. The TCF7L2‐single nucleotide polymorphisms (SNPs) and T2D‐risk association have been replicated in numerous follow‐up studies, and research has now been performed in several other diseases. In this article, we discuss common TCF7L2‐T2D variants within the framework of their association with human diseases. The TCF7L2 functional regions need to be further investigated because the molecular and cellular mechanisms through which TCF7L2 contributes to risk associations with different diseases are still not fully elucidated. In this review, we show the association of common TCF7L2‐T2D variants with many types of diseases. However, the role of rare genetic variations in the TCF7L2 gene in distinct diseases and ethnic groups has not been explored, and understanding their impact on specific phenotypes will be of clinical relevance. This offers an excellent opportunity to gain a clearer picture of the role that the TCF7L2 gene plays in the pathophysiology of human diseases. The potential pleiotropic role of TCF7L2 may underlie a possible pathway for comorbidity in human disorders.

Body mass index and blood pressure in bipolar patients: Target cardiometabolic markers for clinical practice

OBJECTIVE

To evaluate the association between cardiometabolic markers and bipolar disorder (BD), examining the impact of sex and cardiometabolic medication use, from a large case-control biorepository of more than 1300 participants.

PATIENTS AND METHODS

Recruited from July 2009 through September 2017, cardiometabolic markers were harvested from electronic health records (EHR) of participants (n=661) from the Mayo Clinic Individualized Medicine Biobank for Bipolar Disorder and Mayo Clinic Biobank age-sex-matched controls (n=706). Markers were compared between cases and controls using logistic regression, stratified by sex, adjusting for cardiometabolic medications and current smoking status. We studied the effect of psychotropics in case-only analyses.

RESULTS

The mean age of the sample was 52.5 ± 11.6 years and 55% were female. BD patients had higher rates of smoking, but lower utilization of lipid-lowering medication compared with controls. After adjustment, BD was associated with obesity [Odds ratio (CI) 1.62 (1.22-2.15)], elevated systolic blood pressure (SBP) [2.18 (1.55-3.06)] and elevated triglycerides [1.58 (1.13-2.2)]. When stratified by sex, obesity [1.8 (1.23-2.66)] and systolic blood pressure [2.32 (1.46-3.7)] were associated with BD females compared to female controls; however, only systolic blood pressure [2.04 (1.23-3.42)] was associated with male bipolars compared to male controls. Psychotropics were marginally associated with mean BMI, abnormal triglycerides, and HbA1c.

LIMITATIONS

EHR cross-sectional data CONCLUSION: To our knowledge, this is the largest case controlled study to date to explore the association between cardiometabolic markers and bipolar disorder adjusting for utilization of cardiometabolic medication. Identification of significant, non-laboratory based cardiometabolic markers that are associated with increased risk of major cardiovascular adverse events in patients with bipolar disorder, underscores, both the utility and importance of risk monitoring that can be easily done in community mental health centers.

Symptoms of bipolar disorder are associated with lower bariatric surgery completion rates and higher food addiction

BACKGROUND

Bipolar disorder (BP) is highly comorbid with obesity, however, little is known about how BP might be associated with bariatric surgery outcomes.

METHODS

In this retrospective clinical cohort study, 1034 patients completed a psychological evaluation, and screening positive for possible BP was defined as a score ≥7 and moderate disability on the Mood Disorders Questionnaire. Food addiction (FA), subthreshold binge eating disorder (BED), and illegal drug use were also assessed using standardized questionnaires.

RESULTS

The 54 (5.2%) patients screening positive for BP were less likely to have bariatric surgery compared to 980 (94.8%) patients who screened negative for BP (5 patients or 9.3% vs 273 patients, or 27.9%). Patients with possible BP also had significantly higher prevalence of FA (37% vs 13.2%), subthreshold BED (29.6% vs 8.3%) and illegal drug use (7.4% vs 2.1%).

CONCLUSIONS

In this retrospective clinical cohort study, patients who screened positive for BP had a higher prevalence of food addiction, subthreshold binge eating disorder and recent illegal drug use. They also demonstrated lower completion rates for having bariatric surgery. Clearly, more needs to be learned about how to help patients with symptoms of bipolar disorder manage their obesity and behavioral challenges.

TCF7L2 lncRNA: a link between bipolar disorder and body mass index through glucocorticoid signaling

Bipolar disorder (BD) and obesity are highly comorbid. We previously performed a genome-wide association study (GWAS) for BD risk accounting for the effect of body mass index (BMI), which identified a genome-wide significant single-nucleotide polymorphism (SNP) in the gene encoding the transcription factor 7 like 2 (TCF7L2). However, the molecular function of TCF7L2 in the central nervous system (CNS) and its possible role in the BD and BMI interaction remained unclear. In the present study, we demonstrated by studying human induced pluripotent stem cell (hiPSC)-derived astrocytes, cells that highly express TCF7L2 in the CNS, that the BD-BMI GWAS risk SNP is associated with glucocorticoid-dependent repression of the expression of a previously uncharacterized TCF7L2 transcript variant. That transcript is a long non-coding RNA (lncRNA-TCF7L2) that is highly expressed in the CNS but not in peripheral tissues such as the liver and pancreas that are involved in metabolism. In astrocytes, knockdown of the lncRNA-TCF7L2 resulted in decreased expression of the parent gene, TCF7L2, as well as alterations in the expression of a series of genes involved in insulin signaling and diabetes. We also studied the function of TCF7L2 in hiPSC-derived astrocytes by integrating RNA sequencing data after TCF7L2 knockdown with TCF7L2 chromatin-immunoprecipitation sequencing (ChIP-seq) data. Those studies showed that TCF7L2 directly regulated a series of BD risk genes. In summary, these results support the existence of a CNS-based mechanism underlying BD-BMI genetic risk, a mechanism based on a glucocorticoid-dependent expression quantitative trait locus that regulates the expression of a novel TCF7L2 non-coding transcript.

Shared Genetic Loci Between Body Mass Index and Major Psychiatric Disorders: A Genome-wide Association Study

Importance

People with major psychiatric disorders (MPDs) have a 10- to 20-year shorter life span than the rest of the population, and this difference is mainly due to comorbid cardiovascular diseases. Genome-wide association studies have identified common variants involved in schizophrenia (SCZ), bipolar disorder (BIP), and major depression (MD) and body mass index (BMI), a key cardiometabolic risk factor. However, genetic variants jointly influencing MPD and BMI remain largely unknown.

Objective

To assess the extent of the overlap between the genetic architectures of MPDs and BMI and identify genetic loci shared between them.

Design, Setting, and Participants

Using a conditional false discovery rate statistical framework, independent genome-wide association study data on individuals with SCZ (n = 82 315), BIP (n = 51 710), MD (n = 480 359), and BMI (n = 795 640) were analyzed. The UK Biobank cohort (n = 29 740) was excluded from the MD data set to avoid sample overlap. Data were collected from August 2017 to May 2018, and analysis began July 2018.

Main Outcomes and Measures

The primary outcomes were a list of genetic loci shared between BMI and MPDs and their functional pathways.

Results

Genome-wide association study data from 1 380 284 participants were analyzed, and the genetic correlation between BMI and MPDs varied (SCZ: r for genetic = -0.11, P = 2.1 × 10-10; BIP: r for genetic = -0.06, P = .0103; MD: r for genetic = 0.12, P = 6.7 × 10-10). Overall, 63, 17, and 32 loci shared between BMI and SCZ, BIP, and MD, respectively, were analyzed at conjunctional false discovery rate less than 0.01. Of the shared loci, 34% (73 of 213) in SCZ, 52% (36 of 69) in BIP, and 57% (56 of 99) in MD had risk alleles associated with higher BMI (conjunctional false discovery rate <0.05), while the rest had opposite directions of associations. Functional analyses indicated that the overlapping loci are involved in several pathways including neurodevelopment, neurotransmitter signaling, and intracellular processes, and the loci with concordant and opposite association directions pointed mostly to different pathways.

Conclusions and Relevance

In this genome-wide association study, extensive polygenic overlap between BMI and SCZ, BIP, and MD were found, and 111 shared genetic loci were identified, implicating novel functional mechanisms. There was mixture of association directions in SCZ and BMI, albeit with a preponderance of discordant ones.

Gene expression in peripheral blood in treatment-free major depression

BACKGROUND

Peripheral gene expression of several molecular pathways has been studied in major depressive disorder (MDD) with promising results. We sought to investigate some of these genes in a treatment-free Latino sample of Mexican descent.

MATERIAL AND METHODS

The sample consisted of 50 MDD treatment-free cases and 50 sex and age-matched controls. Gene expression of candidate genes of neuroplasticity (BDNF, p11, and VGF), inflammation (IL1A, IL1B, IL4, IL6, IL7, IL8, IL10, MIF, and TNFA), the canonical Wnt signaling pathway (TCF7L2, APC, and GSK3B), and mTOR, was compared in cases and controls. RNA was obtained from blood samples. We used bivariate analyses to compare subjects versus control mean mRNA quantification of target genes and lineal regression modelling to test for effects of age and body mass index on gene expression.

RESULTS

Most subjects were female (66%) with a mean age of 26.7 (SD 7.9) years. Only GSK3B was differentially expressed between cases and controls at a statistically significant level (p = 0.048). TCF7L-2 showed the highest number of correlations with MDD-related traits, yet these were modest in size.

DISCUSSION

GSK3B encodes a moderator of the canonical Wnt signaling pathway. It has a role in neuroplasticity, neuroprotection, depression, and other psychiatric phenotypes. We found that adding population diversity has the potential to elicit distinct peripheral gene expression markers in MDD and MDD-related traits. However, our results should only be considered as hypothesis-generating research that merits further replication in larger cohorts of similar ancestry.

Statistical methods for testing X chromosome variant associations: application to sex-specific characteristics of bipolar disorder

BACKGROUND

Bipolar disorder (BD) affects both sexes, but important sex differences exist with respect to its symptoms and comorbidities. For example, rapid cycling (RC) is more prevalent in females, and alcohol use disorder (AUD) is more prevalent in males. We hypothesize that X chromosome variants may be associated with sex-specific characteristics of BD. Few studies have explored the role of the X chromosome in BD, which is complicated by X chromosome inactivation (XCI). This process achieves "dosage compensation" for many X chromosome genes by silencing one of the two copies in females, and most statistical methods either ignore that XCI occurs or falsely assume that one copy is inactivated at all loci. We introduce new statistical methods that do not make these assumptions.

METHODS

We investigated this hypothesis in 1001 BD patients from the Genetic Association Information Network (GAIN) and 957 BD patients from the Mayo Clinic Bipolar Disorder Biobank. We examined the association of over 14,000 X chromosome single nucleotide polymorphisms (SNPs) with sex-associated BD traits using two statistical approaches that account for whether a SNP may be undergoing or escaping XCI. In the "XCI-informed approach," we fit a sex-adjusted logistic regression model assuming additive genetic effects where we coded the SNP either assuming one copy is expressed or two copies are expressed based on prior knowledge about which regions are inactivated. In the "XCI-robust approach," we fit a logistic regression model with sex, SNP, and SNP-sex interaction effects that is flexible to whether the region is inactivated or escaping XCI.

RESULTS

Using the "XCI-informed approach," which considers only the main effect of SNP and does not allow the SNP effect to differ by sex, no significant associations were identified for any of the phenotypes. Using the "XCI-robust approach," intergenic SNP rs5932307 was associated with BD (P = 8.3 × 10-8), with a stronger effect in females (odds ratio in males (ORM) = 1.13, odds ratio in females for a change of two allele copies (ORW2) = 3.86).

CONCLUSION

X chromosome association studies should employ methods which account for its unique biology. Future work is needed to validate the identified associations with BD, to formally assess the performance of both approaches under different true genetic architectures, and to apply these approaches to study sex differences in other conditions.

Association of Cytomegalovirus and Toxoplasma gondii Antibody Titers With Bipolar Disorder

IMPORTANCE

Infection-associated immune activation and inflammation are increasingly recognized in the pathophysiology of bipolar disorder.

OBJECTIVE

To determine whether antibodies to common infectious agents, including cytomegalovirus (CMV), Toxoplasma gondii, and measles, as well as the inflammatory marker C-reactive protein, in serum samples differ between patients with bipolar disorder and control individuals without bipolar disorder.

DESIGN, SETTING, AND PARTICIPANTS

In this case-control study, antibody titers were measured in serum samples from 1207 patients with bipolar disorder and 745 controls that were obtained from biobanks with participating sites in Rochester and Minneapolis, Minnesota (n = 1537), and Cincinnati, Ohio (n = 415), from January 5, 2009, through May 12, 2014. A subset of case patients and controls from Minnesota were matched by age, sex, and educational level. Bipolar type, age at onset, and history of psychosis were assessed for case patients as well as current drug treatment at the time of blood sample obtainment from the biobank. Data were analyzed from February 5, 2018, to January 4, 2019.

EXPOSURES

The CMV and T gondii antibodies with IgM titers were expressed as z scores and IgG titers dichotomized into seropositive and seronegative based on expected prevalence in the US population and further classified based on the joint CMV-positive/T gondii-negative IgG status, C-reactive protein z score, and drug treatments with antitoxoplasma activity.

MAIN OUTCOMES AND MEASURES

Patients were stratified by bipolar disorder type I or type II, nonearly (>19 years of age) and early (≤19 years of age) onset, and history of psychosis during mania or no psychosis.

RESULTS

Of 1207 patients with bipolar disorder (mean [SD] age, 43.2 [15.1] years; 742 [61.5%] female), the CMV-positive/T gondii-negative IgG status was significantly higher (odds ratio [OR], 1.33; 95% CI, 1.09-1.62; P = .004) compared with that in the 745 controls (mean [SD] age, 44.5 [15.5] years; 444 [59.6%] female). The CMV-positive/T gondii-negative IgG status was associated with bipolar cases type I (OR, 1.41; 95% CI, 1.14-1.75; P = .001), nonearly age at onset (OR, 1.41; 95% CI, 1.16-1.72; P = .001), and history of manic psychosis (OR, 1.46; 95% CI, 1.13-1.88; P = .004). Patients with bipolar disorder who received drug treatment with antitoxoplasma activity (n = 272) had significantly lower T gondii IgM titers (median, 1.59; interquartile range, 1.30-2.07) compared with those (n = 900) who did not receive this treatment (median, 1.69; interquartile range, 1.35-2.25) (P = .03).

CONCLUSIONS AND RELEVANCE

In this sample, increased long-term antibody response to CMV and decreased long-term antibody response to T gondii were associated with bipolar disorder and the subphenotypes of bipolar type I, nonearly disease onset, and manic psychosis. Further work appears to be needed to better understand genetic vs environmental disease risk and infection or immune activation contribution to overall disease pathogenesis with particular reference to disease onset.

Evidence that genes involved in hedgehog signaling are associated with both bipolar disorder and high BMI

Patients with bipolar disorder (BD) show higher frequency of obesity and type 2 diabetes (T2D), but the underlying genetic determinants and molecular pathways are not well studied. Using large publicly available datasets, we (1) conducted a gene-based analysis using MAGMA to identify genes associated with BD and body mass index (BMI) or T2D and investigated their functional enrichment; and (2) performed two meta-analyses between BD and BMI, as well as BD and T2D using Metasoft. Target druggability was assessed using the Drug Gene Interaction Database (DGIdb). We identified 518 and 390 genes significantly associated with BD and BMI or BD and T2D, respectively. A total of 52 and 12 genes, respectively, were significant after multiple testing correction. Pathway analyses conducted on nominally significant targets showed that genes associated with BD and BMI were enriched for the Neuronal cell body Gene Ontology (GO) term (p = 1.0E-04; false discovery rate (FDR) = 0.025) and different pathways, including the Signaling by Hedgehog pathway (p = 4.8E-05, FDR = 0.02), while genes associated with BD and T2D showed no specific enrichment. The meta-analysis between BD and BMI identified 64 relevant single nucleotide polymorphisms (SNPs). While the majority of these were located in intergenic regions or in a locus on chromosome 16 near and in the NPIPL1 and SH2B1 genes (best SNP: rs4788101, p = 2.1E-24), five were located in the ETV5 gene (best SNP: rs1516725, p = 1E-24), which was previously associated with both BD and obesity, and one in the RPGRIP1L gene (rs1477199, p = 5.7E-09), which was also included in the Signaling by Hedgehog pathway. The meta-analysis between BD and T2D identified six significant SNPs, three of which were located in ALAS1 (best SNP: rs352165, p = 3.4E-08). Thirteen SNPs associated with BD and BMI, and one with BD and T2D, were located in genes which are part of the druggable genome. Our results support the hypothesis of shared genetic determinants between BD and BMI and point to genes involved in Hedgehog signaling as promising targets.

Clinical phenotype and genetic risk factors for bipolar disorder with binge eating: an update

Introduction: Clinical and genetic study of psychiatric conditions has underscored the co-occurrence of complex phenotypes and the need to refine them. Bipolar Disorder (BD) and Binge Eating (BE) behavior are common psychiatric conditions that have high heritability and high co-occurrence, such that at least one quarter of BD patients have BE (BD + BE). Genetic studies of BD alone and of BE alone suggest complex polygenic risk models, with many genetic risk loci yet to be identified. Areas covered: We review studies of the epidemiology of BD+BE, its clinical features (cognitive traits, psychiatric comorbidity, and role of obesity), genomic studies (of BD, eating disorders (ED) defined by BE, and BD + BE), and therapeutic implications of BD + BE. Expert opinion: Subphenotyping of complex psychiatric disorders reduces heterogeneity and increases statistical power and effect size; thus, it enhances our capacity to find missing genetic (and other) risk factors. BD + BE has a severe clinical picture and genetic studies suggests a distinct genetic architecture. Differential therapeutic interventions may be needed for patients with BD + BE compared with BD patients without BE. Recognizing the BD + BE subphenotype is an example of moving towards more precise clinical and genetic entities.

Wnt/β-catenin signaling in brain development and mental disorders: keeping TCF7L2 in mind

Canonical Wnt signaling, which is transduced by β-catenin and lymphoid enhancer factor 1/T cell-specific transcription factors (LEF1/TCFs), regulates many aspects of metazoan development and tissue renewal. Although much evidence has associated canonical Wnt/β-catenin signaling with mood disorders, the mechanistic links are still unknown. Many components of the canonical Wnt pathway are involved in cellular processes that are unrelated to classical canonical Wnt signaling, thus further blurring the picture. The present review critically evaluates the involvement of classical Wnt/β-catenin signaling in developmental processes that putatively underlie the pathology of mental illnesses. Particular attention is given to the roles of LEF1/TCFs, which have been discussed surprisingly rarely in this context. Highlighting recent discoveries, we propose that alterations in the activity of LEF1/TCFs, and particularly of transcription factor 7-like 2 (TCF7L2), result in defects previously associated with neuropsychiatric disorders, including imbalances in neurogenesis and oligodendrogenesis, the functional disruption of thalamocortical circuitry and dysfunction of the habenula.

Elevated Familial Cardiovascular Burden Among Adolescents With Familial Bipolar Disorder

Background: Bipolar disorder (BD) is one of the most heritable medical conditions, and certain phenotypic characteristics are especially familial in BD. BD is also strongly associated with elevated and premature cardiovascular disease (CVD) morbidity and mortality. Thus, far, little is known regarding the familiality of cardiovascular risk in BD. We therefore examined the extent of CVD-related conditions among relatives of: adolescents with BD with a family history of BD (familial BD), adolescents with BD without a family history of BD (non-familial BD) and healthy controls (HC). Materials and Methods: The sample included 372 adolescents; 75 with familial BD, 96 with non-familial BD, and 201 HC. Parents of the adolescents completed the CARDIA Family Medical History interview regarding the adolescents' first- and second- degree adult relatives. We computed a "cardiovascular risk score" (CRS) for each relative, based on the sum of the presence of diabetes, hypertension, obesity, dyslipidemia, stroke, angina, and myocardial infarction (range 0-7). Primary analyses examined for group differences in mean overall CRS scores among first and second- degree relatives combined, controlling for age, sex, and race. Secondary analyses examined first- and second-degree relatives separately, controlling for age, sex, and race. Results: There were significant between-group differences in CRS in first- and second- degree relatives combined, following the hypothesized ordering: CRS was highest among adolescents with familial BD (1.14 ± 0.78), intermediate among adolescents with non-familial BD (0.92 ± 0.79) and lowest in HC (0.76 ± 0.79; F = 6.23, df = 2, p = 0.002, ηp 2 = 0.03). There was a significant pairwise difference between adolescents with familial BD and HC (p = 0.002, Cohen's d = 0.49). A similar pattern of between-group differences was identified when first-degree and second-degree relatives were examined separately. Limitations: familial cardiovascular burden was determined based on parent interview, not evaluated directly. Conclusions: Adolescents with BD with a family history of BD have elevated rates of CVD-related conditions among their relatives. This may be related to genetic overlap between BD and CVD-related conditions, shared environmental factors that contribute to both BD and CVD-related conditions, or a combination of these factors. More research is warranted to better understand the interaction between familial risk for BD and CVD, and to address this risk using family-wide preventive approaches.

Bipolar disorder with binge eating behavior: a genome-wide association study implicates PRR5-ARHGAP8

Bipolar disorder (BD) is associated with binge eating behavior (BE), and both conditions are heritable. Previously, using data from the Genetic Association Information Network (GAIN) study of BD, we performed genome-wide association (GWA) analyses of BD with BE comorbidity. Here, utilizing data from the Mayo Clinic BD Biobank (969 BD cases, 777 controls), we performed a GWA analysis of a BD subtype defined by BE, and case-only analysis comparing BD subjects with and without BE. We then performed a meta-analysis of the Mayo and GAIN results. The meta-analysis provided genome-wide significant evidence of association between single nucleotide polymorphisms (SNPs) in PRR5-ARHGAP8 and BE in BD cases (rs726170 OR = 1.91, P = 3.05E-08). In the meta-analysis comparing cases with BD with comorbid BE vs. non-BD controls, a genome-wide significant association was observed at SNP rs111940429 in an intergenic region near PPP1R2P5 (p = 1.21E-08). PRR5-ARHGAP8 is a read-through transcript resulting in a fusion protein of PRR5 and ARHGAP8. PRR5 encodes a subunit of mTORC2, a serine/threonine kinase that participates in food intake regulation, while ARHGAP8 encodes a member of the RhoGAP family of proteins that mediate cross-talk between Rho GTPases and other signaling pathways. Without BE information in controls, it is not possible to determine whether the observed association reflects a risk factor for BE in general, risk for BE in individuals with BD, or risk of a subtype of BD with BE. The effect of PRR5-ARHGAP8 on BE risk thus warrants further investigation.

Obesity and frontal-striatal brain structures in offspring of individuals with bipolar disorder: Results from the global mood and brain science initiative

OBJECTIVES

To compare frontal-striatal brain volumes between offspring of individuals with bipolar disorder (BD) and healthy controls; to investigate the associations of body mass index (BMI) and age with brain volumes; and to assess the moderating effects of BMI and age on the relationship between risk status and structural brain differences.

METHODS

We cross-sectionally assessed structural regional and global brain volumes using magnetic resonance imaging and BMI among 53 BD offspring subjects, stratified by risk status, and 23 non-BD offspring controls (aged 8-28 years). Analyses of variance and covariance and linear regression analyses were conducted to investigate the associations between BMI and measures of brain volume, as well as the interaction effects between age, BMI, and risk status on brain volumes.

RESULTS

After adjusting for age, sex, and intracranial volume, higher BD risk status was associated with lower bilateral cerebellar cortical and right pars orbitalis volumes. Higher BMI was significantly associated with greater brain volumes in frontal and subcortical structures. A significant interaction effect between BMI and risk status was observed in right middle frontal volume. The moderating effect of BMI on brain volume was most robustly observed among subjects aged 14-19 years and less robustly observed among those aged 20-28 years; BMI and brain volumes were negatively correlated among subjects aged 8-13 years.

CONCLUSIONS

Alterations in brain structures in individuals at risk for BD may be moderated by BMI. Obesity among individuals with a family history of BD may confer additional risk, particularly in mid-adolescence.

Genetic Risk Score Analysis in Early-Onset Bipolar Disorder

OBJECTIVE

In this study, we performed a candidate genetic risk score (GRS) analysis of early-onset bipolar disorder (BD).

METHODS

Treatment of Early Age Mania (TEAM) study enrollment and sample collection took place from 2003 to 2008. Mayo Clinic Bipolar Biobank samples were collected from 2009 to 2013. Genotyping and analyses for the present study took place from 2013 to 2014. The diagnosis of BD was based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria. Eight single-nucleotide polymorphisms (SNPs), previously reported in genome-wide association studies to be associated with BD, were chosen for GRS analysis in early-onset bipolar disease. These SNPs map to 3 genes: CACNA1C (calcium channel, voltage-dependent, L type, alpha 1C subunit), ANK3 (ankyrin-3, node of Ranvier [ankyrin G]), and ODZ4 (teneurin transmembrane protein 4 [formerly "odz, odd Oz/10-m homolog 4 {Drosophila}, ODZ4"]). The 8 candidate SNPs were genotyped in patients from the TEAM study (n = 69); adult patients with BD (n = 732), including a subset with early-onset illness (n = 192); and healthy controls (n = 776). GRS analyses were performed to compare early-onset cases with controls. In addition, associations of early-onset BD with individual SNPs and haplotypes were explored.

RESULTS

GRS analysis revealed associations of the risk score with early-onset BD (P = .01). Gene-level haplotype analysis comparing TEAM patients with controls suggested association of early-onset BD with a CACNA1C haplotype (global test, P = .01). At the level of individual SNPs, comparison of TEAM cases with healthy controls provided nominally significant evidence for association of SNP rs10848632 in CACNA1C with early-onset BD (P = .017), which did not remain significant after correction for multiple comparisons.

CONCLUSIONS

These preliminary analyses suggest that previously identified BD risk loci, especially CACNA1C, have a role in early-onset BD, possibly with stronger effects than for late-onset BD.

Casein kinase 1-epsilon deletion increases mu opioid receptor-dependent behaviors and binge eating1

Genetic and pharmacological studies indicate that casein kinase 1 epsilon (Csnk1e) contributes to psychostimulant, opioid, and ethanol motivated behaviors. We previously used pharmacological inhibition to demonstrate that Csnk1e negatively regulates the locomotor stimulant properties of opioids and psychostimulants. Here, we tested the hypothesis that Csnk1e negatively regulates opioid and psychostimulant reward using genetic inhibition and the conditioned place preference assay in Csnk1e knockout mice. Similar to pharmacological inhibition, Csnk1e knockout mice showed enhanced opioid-induced locomotor activity with the mu opioid receptor agonist fentanyl (0.2 mg/kg i.p.) as well as enhanced sensitivity to low-dose fentanyl reward (0.05 mg/kg). Interestingly, female knockout mice also showed a markedly greater escalation in consumption of sweetened palatable food - a behavioral pattern consistent with binge eating that also depends on mu opioid receptor activation. No difference was observed in fentanyl analgesia in the 52.5°C hot plate assay (0-0.4 mg/kg), naloxone conditioned place aversion (4 mg/kg), or methamphetamine conditioned place preference (0-4 mg/kg). To identify molecular adaptations associated with increased drug and food behaviors in knockout mice, we completed transcriptome analysis via mRNA sequencing of the striatum. Enrichment analysis identified terms associated with myelination and axon guidance and pathway analysis identified a differentially expressed gene set predicted to be regulated by the Wnt signaling transcription factor, Tcf7l2. To summarize, Csnk1e deletion increased mu opioid receptor-dependent behaviors, supporting previous studies indicating an endogenous negative regulatory role of Csnk1e in opioid behavior.

Cytoplasmic FMR1-Interacting Protein 2 Is a Major Genetic Factor Underlying Binge Eating

BACKGROUND

Eating disorders are lethal and heritable; however, the underlying genetic factors are unknown. Binge eating is a highly heritable trait associated with eating disorders that is comorbid with mood and substance use disorders. Therefore, understanding its genetic basis will inform therapeutic development that could improve several comorbid neuropsychiatric conditions.

METHODS

We assessed binge eating in closely related C57BL/6 mouse substrains and in an F₂ cross to identify quantitative trait loci associated with binge eating. We used gene targeting to validate candidate genetic factors. Finally, we used transcriptome analysis of the striatum via messenger RNA sequencing to identify the premorbid transcriptome and the binge-induced transcriptome to inform molecular mechanisms mediating binge eating susceptibility and establishment.

RESULTS

C57BL/6NJ but not C57BL/6J mice showed rapid and robust escalation in palatable food consumption. We mapped a single genome-wide significant quantitative trait locus on chromosome 11 (logarithm of the odds = 7.4) to a missense mutation in cytoplasmic FMR1-interacting protein 2 (Cyfip2). We validated Cyfip2 as a major genetic factor underlying binge eating in heterozygous knockout mice on a C57BL/6N background that showed reduced binge eating toward a wild-type C57BL/6J-like level. Transcriptome analysis of premorbid genetic risk identified the enrichment terms morphine addiction and retrograde endocannabinoid signaling, whereas binge eating resulted in the downregulation of a gene set enriched for decreased myelination, oligodendrocyte differentiation, and expression.

CONCLUSIONS

We identified Cyfip2 as a major significant genetic factor underlying binge eating and provide a behavioral paradigm for future genome-wide association studies in populations with increased genetic complexity.

Neurodevelopmental Perspectives on Wnt Signaling in Psychiatry

Mounting evidence indicates that Wnt signaling is relevant to pathophysiology of diverse mental illnesses including schizophrenia, bipolar disorder, and autism spectrum disorder. In the 35 years since Wnt ligands were first described, animal studies have richly explored how downstream Wnt signaling pathways affect an array of neurodevelopmental processes and how their disruption can lead to both neurological and behavioral phenotypes. Recently, human induced pluripotent stem cell (hiPSC) models have begun to contribute to this literature while pushing it in increasingly translational directions. Simultaneously, large-scale human genomic studies are providing evidence that sequence variation in Wnt signal pathway genes contributes to pathogenesis in several psychiatric disorders. This article reviews neurodevelopmental and postneurodevelopmental functions of Wnt signaling, highlighting mechanisms, whereby its disruption might contribute to psychiatric illness, and then reviews the most reliable recent genetic evidence supporting that mutations in Wnt pathway genes contribute to psychiatric illness. We are proponents of the notion that studies in animal and hiPSC models informed by the human genetic data combined with the deep knowledge base and tool kits generated over the last several decades of basic neurodevelopmental research will yield near-term tangible advances in neuropsychiatry.

Metabolic pathways in the periphery and brain: Contribution to mental disorders?

The association between mental disorders and diabetes has a long history. Recent large-scale, well-controlled epidemiological studies confirmed a link between diabetes and psychiatric illnesses. The scope of this review is to summarize our current understanding of this relationship from a molecular perspective. We first discuss the potential contribution of diabetes-associated metabolic impairments to the etiology of mental conditions. Then, we focus on possible shared molecular risk factors and mechanisms. Simple comorbidity, shared susceptibility loci, and common pathophysiological processes in diabetes and mental illnesses have changed our traditional way of thinking about mental illness. We conclude that schizophrenia and affective disorders are not limited to an imbalance in dopaminergic and serotoninergic neurotransmission in the brain. They are also systemic disorders that can be considered, to some extent, as metabolic disorders.