Evidence for association of bipolar disorder to haplotypes in the 22q12.3 region near the genes stargazin, IFT27 and parvalbumin

Study of 45 candidate genes suggests CACNG2 may be associated with lithium response in bipolar disorder

BACKGROUND

Bipolar disorder is a neuropsychiatric disorder that is characterized by fluctuations between manic and depressive phases. Lithium is the original and best mood stabilizing treatment for bipolar disorder. While its mechanism is not well understood, it is believed to have a strong genetic component, as several studies suggest that lithium responsiveness, in bipolar disorder, is heritable. In this study we aimed to identify genetic variants that are associated with lithium responsiveness in bipolar disorder.

METHODS

Here we present two cohorts; a retrospective cohort in which patients were surveyed about their response to lithium, and a prospective cohort, in which patients were placed on a lithium monotherapy and monitored for their response to lithium. In both cohorts, patients were stratified into two categories in terms of lithium response; good responders and poor responders. 45 genes were selected based on previous associations with lithium pathways or bipolar disorder and 684 SNPs within these genes were selected to test for association with lithium response.

RESULTS

While no single SNP was significant after correcting for multiple comparisons, there were several that were nominally significant (p < 0.05). Of these nominally significant SNPs, the most highly significant SNP in both the prospective and retrospective cohorts were found to be in CACNG2, or Stargazin. The second best association with lithium response was several SNPs in NRG1, a gene that has previously been associated with schizophrenia.

CONCLUSIONS

Evidence for the association of lithium response with SNPs in CACNG2 is consistent with previous findings that have identified CACNG2 as associated with both bipolar disorder and lithium responsiveness.

Primary Cilia-An Underexplored Topic in Major Mental Illness

Though much progress has been made in recent years towards understanding the function and physiology of primary cilia, they remain a somewhat elusive organelle. Some studies have explored the role of primary cilia in the developing nervous system, and their dysfunction has been linked with several neurosensory deficits. Yet, very little has been written on their potential role in psychiatric disorders. This article provides an overview of some of the functions of primary cilia in signalling pathways, and demonstrates that they are a worthy candidate in psychiatric research. The links between primary cilia and major mental illness have been demonstrated to exist at several levels, spanning genetics, signalling pathways, and pharmacology as well as cell division and migration. The primary focus of this review is on the sensory role of the primary cilium and the neurodevelopmental hypothesis of psychiatric disease. As such, the primary cilium is demonstrated to be a key link between the cellular environment and cell behaviour, and hence of key importance in the considerations of the nature and nurture debate in psychiatric research.

Intraflagellar transporter protein (IFT27), an IFT25 binding partner, is essential for male fertility and spermiogenesis in mice

Intraflagellar transport (IFT) is an evolutionarily conserved mechanism essential for the assembly and maintenance of most eukaryotic cilia and flagella. In mice, mutations in IFT proteins have been shown to cause several ciliopathies including retinal degeneration, polycystic kidney disease, and hearing loss. However, little is known about its role in the formation of the sperm tail, which has the longest flagella of mammalian cells. IFT27 is a component of IFT-B complex and binds to IFT25 directly. In mice, IFT27 is highly expressed in the testis. To investigate the role of IFT27 in male germ cells, the floxed Ift27 mice were bred with Stra8-iCre mice so that the Ift27 gene was disrupted in spermatocytes/spermatids. The Ift27: Stra8-iCre mutant mice did not show any gross abnormalities, and all of the mutant mice survived to adulthood. There was no difference between testis weight/body weight between controls and mutant mice. All adult homozygous mutant males examined were completely infertile. Histological examination of the testes revealed abnormally developed germ cells during the spermiogenesis phase. The epididymides contained round bodies of cytoplasm. Sperm number was significantly reduced compared to the controls and only about 2% of them remained significantly reduced motility. Examination of epididymal sperm by light microscopy and SEM revealed multiple morphological abnormalities including round heads, short and bent tails, abnormal thickness of sperm tails in some areas, and swollen tail tips in some sperm. TEM examination of epididymal sperm showed that most sperm lost the "9+2″ axoneme structure, and the mitochondria sheath, fibrous sheath, and outer dense fibers were also disorganized. Some sperm flagella also lost cell membrane. Levels of IFT25 and IFT81 were significantly reduced in the testis of the conditional Ift27 knockout mice, and levels of IFT20, IFT74, and IFT140 were not changed. Sperm lipid rafts, which were disrupted in the conditional Ift25 knockout mice, appeared to be normal in the conditional Ift27 knockout mice. Our findings suggest that like IFT25, IFT27, even though not required for ciliogenesis in somatic cells, is essential for sperm flagella formation, sperm function, and male fertility in mice. IFT25 and IFT27 control sperm formation/function through many common mechanisms, but IFT25 has additional roles beyond IFT27.

Building a genetic risk model for bipolar disorder from genome-wide association data with random forest algorithm

A genetic risk score could be beneficial in assisting clinical diagnosis for complex diseases with high heritability. With large-scale genome-wide association (GWA) data, the current study constructed a genetic risk model with a machine learning approach for bipolar disorder (BPD). The GWA dataset of BPD from the Genetic Association Information Network was used as the training data for model construction, and the Systematic Treatment Enhancement Program (STEP) GWA data were used as the validation dataset. A random forest algorithm was applied for pre-filtered markers, and variable importance indices were assessed. 289 candidate markers were selected by random forest procedures with good discriminability; the area under the receiver operating characteristic curve was 0.944 (0.935–0.953) in the training set and 0.702 (0.681–0.723) in the STEP dataset. Using a score with the cutoff of 184, the sensitivity and specificity for BPD was 0.777 and 0.854, respectively. Pathway analyses revealed important biological pathways for identified genes. In conclusion, the present study identified informative genetic markers to differentiate BPD from healthy controls with acceptable discriminability in the validation dataset. In the future, diagnosis classification can be further improved by assessing more comprehensive clinical risk factors and jointly analysing them with genetic data in large samples.

Genetic deletion of fibroblast growth factor 14 recapitulates phenotypic alterations underlying cognitive impairment associated with schizophrenia

Cognitive processing is highly dependent on the functional integrity of gamma-amino-butyric acid (GABA) interneurons in the brain. These cells regulate excitability and synaptic plasticity of principal neurons balancing the excitatory/inhibitory tone of cortical networks. Reduced function of parvalbumin (PV) interneurons and disruption of GABAergic synapses in the cortical circuitry result in desynchronized network activity associated with cognitive impairment across many psychiatric disorders, including schizophrenia. However, the mechanisms underlying these complex phenotypes are still poorly understood. Here we show that in animal models, genetic deletion of fibroblast growth factor 14 (Fgf14), a regulator of neuronal excitability and synaptic transmission, leads to loss of PV interneurons in the CA1 hippocampal region, a critical area for cognitive function. Strikingly, this cellular phenotype associates with decreased expression of glutamic acid decarboxylase 67 (GAD67) and vesicular GABA transporter (VGAT) and also coincides with disrupted CA1 inhibitory circuitry, reduced in vivo gamma frequency oscillations and impaired working memory. Bioinformatics analysis of schizophrenia transcriptomics revealed functional co-clustering of FGF14 and genes enriched within the GABAergic pathway along with correlatively decreased expression of FGF14, PVALB, GAD67 and VGAT in the disease context. These results indicate that Fgf14(-/-) mice recapitulate salient molecular, cellular, functional and behavioral features associated with human cognitive impairment, and FGF14 loss of function might be associated with the biology of complex brain disorders such as schizophrenia.

Zebrafish models of major depressive disorders

The zebrafish (Danio rerio) has emerged as a model species for translational research in various neuroscience areas, including depressive disorders. Because of their physiological (neuroanatomical, neuroendocrine, neurochemical) and genetic homology to mammals, robust phenotypes, and value in high-throughput genetic and chemical genetic screens, zebrafish are ideal for developing valid experimental models of major depression and discovering novel therapeutics. Behavioral testing approaches, such as approach-avoidance, cognitive, and social paradigms, are available in zebrafish and have utility in identifying depression-like indices in zebrafish in response to physiological, genetic, environmental, and/or psychopharmacological alterations. In addition, the high sensitivity of zebrafish to commonly prescribed psychotropic drugs supports the use of this model as an invaluable tool for pharmacological research and drug screening. This Review outlines the benefits of using the zebrafish model for depression studies and summarizes the current research in this field.

Variants in Ion Channel Genes Link Phenotypic Features of Bipolar Illness to Specific Neurobiological Process Domains

Recent advances in genome-wide association studies are pointing towards a major role for voltage-gated ion channels in neuropsychiatric disorders and, in particular, bipolar disorder (BD). The phenotype of BD is complex, with symptoms during mood episodes and deficits persisting between episodes. We have tried to elucidate the common neurobiological mechanisms associated with ion channel signaling in order to provide a new perspective on the clinical symptoms and possible endophenotypes seen in BD patients. We propose a model in which the multiple variants in genes coding for ion channel proteins would perturb motivational circuits, synaptic plasticity, myelination, hypothalamic-pituitary-adrenal axis function, circadian neuronal rhythms, and energy regulation. These changes in neurobiological mechanisms would manifest in endophenotypes of aberrant reward processing, white matter hyperintensities, deficits in executive function, altered frontolimbic connectivity, increased amygdala activity, increased melatonin suppression, decreased REM latency, and aberrant myo-inositol/ATP shuttling. The endophenotypes result in behaviors of poor impulse control, motivational changes, cognitive deficits, abnormal stress response, sleep disturbances, and energy changes involving different neurobiological process domains. The hypothesis is that these disturbances start with altered neural circuitry during development, following which multiple environmental triggers may disrupt the neuronal excitability balance through an activity-dependent molecular process, resulting in clinical mood episodes.

Molecular actions and clinical pharmacogenetics of lithium therapy

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

Vascular mortality in participants of a bipolar genomics study

BACKGROUND

In prior work, we identified a relationship between symptom burden and vascular outcomes in bipolar disorder.

OBJECTIVE

We sought to replicate these findings using a readily accessible measure of mood disorder chronicity and vascular mortality.

METHODS

We conducted a mortality assessment using the National Death Index for 1716 participants with bipolar I disorder from the National Institute of Mental Health Genetics Initiative Bipolar Disorder Consortium. We assessed the relationship between the duration of the most severe depressive and manic episodes and time to vascular mortality (cardiovascular or cerebrovascular) using Cox proportional hazards models, adjusting for potentially confounding variables.

RESULTS

Mortality was assessed a mean for 7 years following study intake, at which time 58 participants died, 18 of vascular causes. These participants had depression for much longer than their counterparts did (Wilcoxon rank sum Z = 2.30, p = 0.02) and the duration of the longest depressive episode in years was significantly associated with time to vascular mortality in models (hazard ratio = 1.16, 95% confidence interval: 1.02-1.33, p = 0.02), which controlled for age, gender, vascular disease equivalents, and vascular disease risk factors. The duration of longest mania was not related to vascular mortality.

CONCLUSION

The duration of the most severe depression is independently predictive of vascular mortality, lending further support to the idea that mood disorders hasten vascular mortality in a dose-dependent fashion. Further study of the relevant mechanisms by which mood disorders may hasten vascular disease and of integrated treatments for mood and cardiovascular risk factors is warranted.

Chronic unpredictable stress (CUS)-induced anxiety and related mood disorders in a zebrafish model: altered brain proteome profile implicates mitochondrial dysfunction

Anxiety and depression are major chronic mood disorders, and the etiopathology for each appears to be repeated exposure to diverse unpredictable stress factors. Most of the studies on anxiety and related mood disorders are performed in rodents, and a good model is chronic unpredictable stress (CUS). In this study, we have attempted to understand the molecular basis of the neuroglial and behavioral changes underlying CUS-induced mood disorders in the simplest vertebrate model, the zebrafish, Danio rerio. Zebrafish were subjected to a CUS paradigm in which two different stressors were used daily for 15 days, and thorough behavioral analyses were performed to assess anxiety and related mood disorder phenotypes using the novel tank test, shoal cohesion and scototaxis. Fifteen days of exposure to chronic stressors appears to induce an anxiety and related mood disorder phenotype. Decreased neurogenesis, another hallmark of anxiety and related disorders in rodents, was also observed in this zebrafish model. The common molecular markers of rodent anxiety and related disorders, corticotropin-releasing factor (CRF), calcineurin (ppp3r1a) and phospho cyclic AMP response element binding protein (pCREB), were also replicated in the fish model. Finally, using 2DE FTMS/ITMSMS proteomics analyses, 18 proteins were found to be deregulated in zebrafish anxiety and related disorders. The most affected process was mitochondrial function, 4 of the 18 differentially regulated proteins were mitochondrial proteins: PHB2, SLC25A5, VDAC3 and IDH2, as reported in rodent and clinical samples. Thus, the zebrafish CUS model and proteomics can facilitate not only uncovering new molecular targets of anxiety and related mood disorders but also the routine screening of compounds for drug development.