No association of two common SNPs at position −1727 A/T, −50 C/T of GSK-3 beta polymorphisms with schizophrenia and bipolar disorder of Korean population

Neurobiology of bipolar disorders: a review of genetic components, signaling pathways, biochemical changes, and neuroimaging findings

Bipolar disorder (BD) is a chronic mental illness characterized by changes in mood that alternate between mania and hypomania or between depression and mixed states, often associated with functional impairment. Although effective pharmacological and non-pharmacological treatments are available, several patients with BD remain symptomatic. The advance in the understanding of the neurobiology underlying BD could help in the identification of new therapeutic targets as well as biomarkers for early detection, prognosis, and response to treatment in BD. In this review, we discuss genetic, epigenetic, molecular, physiological and neuroimaging findings associated with the neurobiology of BD. Despite the advances in the pathophysiological knowledge of BD, the diagnosis and management of the disease are still essentially clinical. Given the complexity of the brain and the close relationship between environmental exposure and brain function, initiatives that incorporate genetic, epigenetic, molecular, physiological, clinical, environmental data, and brain imaging are necessary to produce information that can be translated into prevention and better outcomes for patients with BD.

Circadian rhythm in bipolar disorder: A review of the literature

Sleep disturbances and circadian rhythm dysfunction have been widely demonstrated in patients with bipolar disorder (BD). Irregularity of the sleep-wake rhythm, eveningness chronotype, abnormality of melatonin secretion, vulnerability of clock genes, and the irregularity of social time cues have also been well-documented in BD. Circadian rhythm dysfunction is prominent in BD compared with that in major depressive disorders, implying that circadian rhythm dysfunction is a trait marker of BD. In the clinical course of BD, the circadian rhythm dysfunctions may act as predictors for the first onset of BD and the relapse of mood episodes. Treatments focusing on sleep disturbances and circadian rhythm dysfunction in combination with pharmacological, psychosocial, and chronobiological treatments are believed to be useful for relapse prevention. Further studies are therefore warranted to clarify the relation between circadian rhythm dysfunction and the pathophysiology of BD to develop treatment strategies for achieving recovery in BD patients.

An Association Study Between Genetic Polymorphisms in Functional Regions of Five Genes and the Risk of Schizophrenia

Schizophrenia is a severe mental disorder that is likely to be strongly determined by genetic factors. To identify markers of disks, large homolog 2 (DLG2), FAT atypical cadherin 3 (FAT3), kinectin1 (KTN1), deleted in colorectal carcinoma (DCC), and glycogen synthase kinase-3β (GSK3β) that contribute to the genetic susceptibility to schizophrenia, we systematically screened for polymorphisms in the functional regions of these genes. A total of 22 functional single-nucleotide polymorphisms (SNPs) in 940 Chinese subjects were genotyped using SNaPshot. The results first suggested that the allelic and genotypic frequencies of the DCC polymorphism rs2229080 were nominally associated with schizophrenia. The patients were significantly less likely to be CC homozygous (P = 0.005, odds ratio [OR] = 0.635, 95 % confidence interval [95 % CI] = 0.462-0.873), and the schizophrenia subjects exhibited lower frequency of the C allele (P = 0.024, OR = 0.811, 95 % CI = 0.676-0.972). Regarding GSK3β, there was a significant difference in genotype distribution of rs3755557 between schizophrenia and healthy control subjects (P = 0.009). The patients exhibited a significantly lower frequency of the T allele of rs3755557 (P = 0.002, OR = 0.654, 95 % CI = 0.498-0.860). Our results point to the polymorphisms of DCC and GSK3β as contributors to the genetic basis of individual differences in the susceptibility to schizophrenia.

The GSK3B gene confers risk for both major depressive disorder and schizophrenia in the Han Chinese population

BACKGROUND

Glycogen synthease kinase-3B is a key gene encoding a protein kinase which is abundant in brain, and is involved in signal transduction cascades of neuronal cell development and energy metabolism. Previous researches proposed GSK3B as a potential region for schizophrenia.

METHOD

To validate the susceptibility of GSK3B to major depressive disorder, and to investigate the overlapping risk conferred by GSK3B for mental disorders, we performed a large-scale case-control study, analyzed 6 tag single nucleotide polymorphisms using TaqMan® technology in 1,045 major depressive disorder patients, 1,235 schizophrenia patients and 1,235 normal controls of Han Chinese origin.

RESULTS

We found rs334535 (Pallele=2.79E-03, Pgenotype=5.00E-03, OR=1.429) and rs2199503 (Pallele=0.020, Pgenotype= 0.040, OR=1.157) showed association with major depressive disorder before Bonferroni correction. rs6771023 (adjusted Pallele=1.64E-03, adjusted Pgenotype=6.00E-03, OR=0.701) and rs2199503 (adjusted Pallele=0.001, adjusted Pgenotype=0.002, OR=1.251) showed significant association with schizophrenia after Bonferroni correction. rs2199503 (adjusted Pallele=1.70E-03, adjusted Pgenotype=0.006, OR=1.208) remained to be significant in the combined cases of major depressive disorder and schizophrenia after Bonferroni correction.

LIMITATIONS

Further validations of our findings in samples with larger scale are suggested, and functional genomic study is needed to elucidate the role of GSK3B in signal pathway and psychiatric disorders.

CONCLUSIONS

Our results provide evidence that the GSK3B gene could be a promising region which contains genetic risk for both major depressive disorder and schizophrenia in the Han Chinese population. The study on variants conferring overlapping risk for multiple psychiatric disorders could be tangible pathogenesis support and clinical or diagnostic references.

The bipolarity of light and dark: A review on Bipolar Disorder and circadian cycles

BACKGROUND

Bipolar Disorder is characterized by episodes running the full mood spectrum, from mania to depression. Between mood episodes, residual symptoms remain, as sleep alterations, circadian cycle disturbances, emotional deregulation, cognitive impairment and increased risk for comorbidities. The present review intends to reflect about the most recent and relevant information concerning the biunivocal relation between bipolar disorder and circadian cycles.

METHODS

It was conducted a literature search on PubMed database using the search terms "bipolar", "circadian", "melatonin", "cortisol", "body temperature", "Clock gene", "Bmal1 gene", "Per gene", "Cry gene", "GSK3β", "chronotype", "light therapy", "dark therapy", "sleep deprivation", "lithum" and "agomelatine". Search results were manually reviewed, and pertinent studies were selected for inclusion as appropriate.

RESULTS

Several studies support the relationship between bipolar disorder and circadian cycles, discussing alterations in melatonin, body temperature and cortisol rhythms; disruption of sleep/wake cycle; variations of clock genes; and chronotype. Some therapeutics for bipolar disorder directed to the circadian cycles disturbances are also discussed, including lithium carbonate, agomelatine, light therapy, dark therapy, sleep deprivation and interpersonal and social rhythm therapy.

LIMITATIONS

This review provides a summary of an extensive research for the relevant literature on this theme, not a patient-wise meta-analysis.

CONCLUSIONS

In the future, it is essential to achieve a better understanding of the relation between bipolar disorder and the circadian system. It is required to establish new treatment protocols, combining psychotherapy, therapies targeting the circadian rhythms and the latest drugs, in order to reduce the risk of relapse and improve affective behaviour.

Sleep- and circadian rhythm-associated pathways as therapeutic targets in bipolar disorder

INTRODUCTION

Disruptions in sleep and circadian rhythms are observed in individuals with bipolar disorders (BD), both during acute mood episodes and remission. Such abnormalities may relate to dysfunction of the molecular circadian clock and could offer a target for new drugs.

AREAS COVERED

This review focuses on clinical, actigraphic, biochemical and genetic biomarkers of BDs, as well as animal and cellular models, and highlights that sleep and circadian rhythm disturbances are closely linked to the susceptibility to BDs and vulnerability to mood relapses. As lithium is likely to act as a synchronizer and stabilizer of circadian rhythms, we will review pharmacogenetic studies testing circadian gene polymorphisms and prophylactic response to lithium. Interventions such as sleep deprivation, light therapy and psychological therapies may also target sleep and circadian disruptions in BDs efficiently for treatment and prevention of bipolar depression.

EXPERT OPINION

We suggest that future research should clarify the associations between sleep and circadian rhythm disturbances and alterations of the molecular clock in order to identify critical targets within the circadian pathway. The investigation of such targets using human cellular models or animal models combined with 'omics' approaches are crucial steps for new drug development.

Haplotype analysis of GSK-3β gene polymorphisms in bipolar disorder lithium responders and nonresponders

The GSK-3β gene, GSK3B, codes for an enzyme that is a target for the action of mood stabilizers, lithium and possibly valproic acid.

In this study, the relationship between haplotypes consisting of single nucleotide polymorphisms (SNPs) of GSK3B −50T/C and −1727A/T and the effect of lithium was studied among Japanese bipolar disorder lithium nonresponders and responders.

The distributions of the GSK3B haplotypes (−50T/C and −1727A/T) showed a trend for significant difference between the lithium nonresponders and responders (global P=0.07074). Haplotype 1 (T-A) was associated with a higher lithium response (haplotype-specific P=0.03477), whereas haplotype 2 (C-A) was associated with a lower lithium response (haplotype-specific P=0.03443).

The pairwise D′ and r² values between the 2 SNPs in this study were 1.0 and 0.097, respectively. The 2 SNPs showed weak linkage disequilibrium with each other.

Glycogen synthase kinase-3 as a therapeutic target for cognitive dysfunction in neuropsychiatric disorders

The serine/threonine kinase glycogen synthase kinase-3 (GSK-3) is involved in a broad range of cellular processes including cell proliferation, apoptosis and inflammation. It is now also increasingly acknowledged as having a role to play in cognitive-related processes such as neurogenesis, synaptic plasticity and neural cell survival. Cognitive impairment represents a major debilitating feature of many neurodegenerative and psychiatric disorders, including Alzheimer's disease, mood disorders, schizophrenia and fragile X syndrome, as well as being a result of traumatic brain injury or cranial irradiation. Accordingly, GSK-3 has been identified as an important therapeutic target for cognitive impairment, and recent preclinical studies have yielded important evidence demonstrating that GSK-3 inhibitors may be useful therapeutic interventions for restoring cognitive function in some of these brain disorders. The current review summarises the role of GSK-3 as a regulator of cognitive-dependent functions, examines current preclinical and clinical evidence of the potential of GSK-3 inhibitors as therapeutic agents for cognitive impairments in neuropsychiatric disorders, and offers some insight into the current obstacles that are impeding the clinical use of selective GSK-3 inhibitors in the treatment of cognitive impairment.

The emerging role of dopamine-glutamate interaction and of the postsynaptic density in bipolar disorder pathophysiology: Implications for treatment

Aberrant synaptic plasticity, originating from abnormalities in dopamine and/or glutamate transduction pathways, may contribute to the complex clinical manifestations of bipolar disorder (BD). Dopamine and glutamate systems cross-talk at multiple levels, such as at the postsynaptic density (PSD). The PSD is a structural and functional protein mesh implicated in dopamine and glutamate-mediated synaptic plasticity. Proteins at PSD have been demonstrated to be involved in mood disorders pathophysiology and to be modulated by antipsychotics and mood stabilizers. On the other side, post-receptor effectors such as protein kinase B (Akt), glycogen synthase kinase-3 (GSK-3) and the extracellular signal-regulated kinase (Erk), which are implicated in both molecular abnormalities and treatment of BD, may interact with PSD proteins, and participate in the interplay of the dopamine-glutamate signalling pathway. In this review, we describe emerging evidence on the molecular cross-talk between dopamine and glutamate signalling in BD pathophysiology and pharmacological treatment, mainly focusing on dysfunctions in PSD molecules. We also aim to discuss future therapeutic strategies that could selectively target the PSD-mediated signalling cascade at the crossroads of dopamine-glutamate neurotransmission.

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.

Neurodevelopment in schizophrenia: the role of the wnt pathways

OBJECTIVES

To review the role of Wnt pathways in the neurodevelopment of schizophrenia.

METHODS

SYSTEMATIC PUBMED SEARCH, USING AS KEYWORDS ALL THE TERMS RELATED TO THE WNT PATHWAYS AND CROSSING THEM WITH EACH OF THE FOLLOWING AREAS: normal neurodevelopment and physiology, neurodevelopmental theory of schizophrenia, schizophrenia, and antipsychotic drug action.

RESULTS

Neurodevelopmental, behavioural, genetic, and psychopharmacological data point to the possible involvement of Wnt systems, especially the canonical pathway, in the pathophysiology of schizophrenia and in the mechanism of antipsychotic drug action. The molecules most consistently found to be associated with abnormalities or in antipsychotic drug action are Akt1, glycogen synthase kinase3beta, and beta-catenin. However, the extent to which they contribute to the pathophysiology of schizophrenia or to antipsychotic action remains to be established.

CONCLUSIONS

The study of the involvement of Wnt pathway abnormalities in schizophrenia may help in understanding this multifaceted clinical entity; the development of Wnt-related pharmacological targets must await the collection of more data.

Glycogen synthase kinase 3β gene polymorphisms may be associated with bipolar I disorder and the therapeutic response to lithium

BACKGROUND

Glycogen Synthase Kinase 3β (GSK-3β) is thought to be a key feature in the therapeutic mechanism of mood stabilizers (e.g., lithium). Overexpression of GSK-3β might play a role in the pathogenesis of bipolar I disorder. Within the GSK-3β gene, a promoter single nucleotide polymorphism (SNP) rs334558 was identified associated with transcriptional strength, and an intronic SNP rs6438552 was found to regulate selection of splice acceptor sites. The aim of this study is to test the association between the two polymorphisms and bipolar I disorder.

METHODS

We genotyped the two SNPs in 138 Taiwanese bipolar I disorder patients and 131 controls. Lithium treatment efficacy was evaluated for 83 patients who had been treated with lithium carbonate for at least 24 months.

RESULTS

We found no association between each of the two SNPs and the risk of bipolar I disorder. Following correction for multiple testing, CT genotype at rs6438552 was associated with an older age of onset than other genotypes (P=0.042) in female patients. Patients with genotype TT at rs334558 (P=0.044) had poorer response to lithium treatment. There was a trend that haplotype C-T increased the risk for bipolar I disorder (adjusted OR=4.22, corrected P=0.084), and patients with haplotype T-T had poorer treatment response to lithium than those with haplotype C-C.

LIMITATIONS

Limitations included small sample size, retrospective data collection, and a potential sampling bias.

CONCLUSIONS

Despite the several limitations of the study, our results suggested GSK-3β genetic variants may be associated with the risk of bipolar I disorder, age of disease onset in females, and the therapeutic response to lithium.

Meta-analysis of genetic association studies on bipolar disorder

Numerous candidate gene association studies of bipolar disorder (BP) have been carried out, but the results have been inconsistent. Individual studies are typically underpowered to detect associations with genes of small effect sizes. We conducted a meta-analysis of published candidate gene studies to evaluate the cumulative evidence. We systematically searched for all published candidate gene association studies of BP. We then carried out a random-effects meta-analysis on all polymorphisms that were reported on by three or more case-control studies. The results from meta-analyses of these genes were compared with the findings from a recent mega-analysis of eleven genome-wide association studies (GWAS) in BP performed by the Psychiatric GWAS Consortium (PGC). A total of 487 articles were included in our review. Among these, 33 polymorphisms in 18 genes were reported on by three or more case-control studies and included in the random-effects meta-analysis. Polymorphisms in BDNF, DRD4, DAOA, and TPH1, were found to be nominally significant with a P-value < 0.05. However, none of the findings were significant after correction for multiple testing. Moreover, none of these polymorphisms were nominally significant in the PGC-BP GWAS. A number of plausible candidate genes have been previously associated with BP. However, the lack of robust findings in our review of these candidate genes highlights the need for more atheoretical approaches to study the genetics of BP afforded by GWAS. The results of this meta-analysis and from other on-going genomic experiments in BP are available online at Metamoodics (http://metamoodics.igm.jhmi.edu).

Genetic association and identification of a functional SNP at GSK3β for schizophrenia susceptibility

OBJECTIVE

GSK3β is a key gene in neurodevelopment, and also an important target of antipsychotics. Several lines of evidence including association and gene expression studies have suggested GSK3β as a susceptibility gene for schizophrenia, but the underlying genetic mechanism is still unknown. In this study, we test whether the genetic variants in GSK3β contribute to the risk of schizophrenia in Chinese population.

METHODS

We first conducted an association analysis of 9 representative SNPs spanning the entire genomic region of GSK3β in two independent Han Chinese case-control samples from southwestern China (the Kunming sample and the Yuxi sample, a total of 2550 subjects).Then using EMSA and reporter gene assays, we tested the functional impact of the identified risk SNP on transcriptional factor binding affinity and promoter activity.

RESULTS

We observed weak allelic associations of three GSK3β SNPs (rs3755557, rs7431209 and rs13320980) with schizophrenia in the combined Han Chinese samples. Further analysis using genotypes (under recessive genetic model) supported the association of rs3755557 (p = 0.01, corrected), which is located in the GSK3β promoter region. The functional assays demonstrated that the risk SNP (rs3755557) could influence the transcription factor binding affinities, resulting in a higher promoter activity of the risk allele.

CONCLUSION

Our findings suggest that GSK3β is likely a risk gene for schizophrenia, and its expression alteration caused by the risk SNP in the promoter region may contribute to the etiology of schizophrenia.

Glycogen synthase kinase-3 in the etiology and treatment of mood disorders

The mood disorders major depressive disorder and bipolar disorder are prevalent, are inadequately treated, and little is known about their etiologies. A better understanding of the causes of mood disorders would benefit from improved animal models of mood disorders, which now rely on behavioral measurements. This review considers the limitations in relating measures of rodent behaviors to mood disorders, and the evidence from behavioral assessments indicating that glycogen synthase kinase-3 (GSK3) dysregulation promotes mood disorders and is a potential target for treating mood disorders. The classical mood stabilizer lithium was identified by studying animal behaviors and later was discovered to be an inhibitor of GSK3. Several mood-relevant behavioral effects of lithium in rodents have been identified, and most have now been shown to be due to its inhibition of GSK3. An extensive variety of pharmacological and molecular approaches for manipulating GSK3 are discussed, the results of which strongly support the proposal that inhibition of GSK3 reduces both depression-like and manic-like behaviors. Studies in human postmortem brain and peripheral cells also have identified correlations between alterations in GSK3 and mood disorders. Evidence is reviewed that depression may be associated with impaired inhibitory control of GSK3, and mania by hyper-stimulation of GSK3. Taken together, these studies provide substantial support for the hypothesis that inhibition of GSK3 activity is therapeutic for mood disorders. Future research should identify the causes of dysregulated GSK3 in mood disorders and the actions of GSK3 that contribute to these diseases.

The impact of glycogen synthase kinase 3β gene on psychotic mania in bipolar disorder patients

OBJECTIVE

The aim of this study was to examine the relationships between glycogen synthase 3β gene polymorphisms and bipolar I disorder, manic in a Korean sample.

METHODS

Patients with bipolar disorder (n=118) and a control group (n=158) were assessed by genotyping for GSK3β single nucleotide polymorphisms (SNPs) -1727A/T and -50C/T. The patients were divided into two groups according to the presence of psychotic symptoms (psychotic mania, n=92; non-psychotic mania, n=26) and also divided based on gender and age of onset. The severity of symptoms was measured using the Young Mania Rating Scale (YMRS) and the Brief Psychiatric Rating Scale (BPRS).

RESULTS

There were no significant differences in the genotype distributions or allelic frequencies of GSK3β polymorphisms and gender between patients with bipolar disorder and a normal control group. According to haplotype analysis, there was no association between these two groups. However, analysis of the age of onset of bipolar disorder revealed significant differences in genotype and allele distributions among the patients. Patients who were homozygous for the wild-type variant (TT) had an older age of onset than carriers of the mutant allele (A/A: 27.4±9.1; A/T: 30.1±11.8; T/T: 42.3±19.9; p=0.034). We detected differences in allele frequencies of the GSK3β -1727A/T polymorphism between the psychotic mania group and the non-psychotic mania group.

CONCLUSION

This study suggests that GSK3β polymorphisms are not associated with bipolar disorder. However, the GSK3β SNP -1727A/T is associated with age of onset and presence of psychotic symptoms in bipolar disorder.

Signal transduction pathways in the pathophysiology of bipolar disorder

Signal transduction pathways and genes associated with cellular life and death have received much attention in bipolar disorder (BPD) and provide scientists with molecular targets for understanding the biological basis of BPD. In this chapter, we describe the signal transduction pathways involved in the molecular biology of BPD and the indications for the mechanisms of disease and treatment. We discuss the BPD literature with respect to the disease itself and the effects of mood stabilizer treatment on cellular receptors, including G-protein-coupled receptors, glutamate receptors, and tyrosine receptor kinase. We also discuss the intracellular alterations observed in BPD to second messenger systems, such as cyclic adenosine monophosphate (cAMP), protein kinase A, phosphoinositide pathways, glycogen synthase kinase-3, protein kinase B, Wnt, and arachidonic acid. We describe how receptor activation and modulation of second messengers occurs, and how transcription factors are activated and altered in this disease (e.g., the transcription factors ?-catenin, cAMP response element binding protein, heat shock transcription factor-1, and activator protein-1). Abnormalities in intracellular signal transduction pathways could generate a functional discrepancy in numerous neurotransmitter systems, which may explain the varied clinical symptoms observed in BPD. The influence of mood stabilizers on transcription factors may be important in connecting the regulation of gene expression to neuroplasticity and cellular resilience.

The neurobiology of the switch process in bipolar disorder: a review

OBJECTIVE

The singular phenomenon of switching from depression to its opposite state of mania or hypomania, and vice versa, distinguishes bipolar disorder from all other psychiatric disorders. Despite the fact that it is a core aspect of the clinical presentation of bipolar disorder, the neurobiology of the switch process is still poorly understood. In this review, we summarize the clinical evidence regarding somatic interventions associated with switching, with a particular focus on the biologic underpinnings presumably involved in the switch process.

DATA SOURCES

Literature for this review was obtained through a search of the MEDLINE database (1966-2008) using the following keywords and phrases: switch, bipolar disorder, bipolar depression, antidepressant, SSRIs, tricyclic antidepressants, norepinephrine, serotonin, treatment emergent affective switch, mania, hypomania, HPA-axis, glucocorticoids, amphetamine, dopamine, and sleep deprivation.

STUDY SELECTION

All English-language, peer-reviewed, published literature, including randomized controlled studies, naturalistic and open-label studies, and case reports, were eligible for inclusion.

DATA SYNTHESIS

Converging evidence suggests that certain pharmacologic and nonpharmacologic interventions with very different mechanisms of action, such as sleep deprivation, exogenous corticosteroids, and dopaminergic agonists, can trigger mood episode switches in patients with bipolar disorder. The switch-inducing potential of antidepressants is unclear, although tricyclic antidepressants, which confer higher risk of switching than other classes of antidepressants, are a possible exception. Several neurobiological factors appear to be associated with both spontaneous and treatment-emergent mood episode switches; these include abnormalities in catecholamine levels, up-regulation of neurotrophic and neuroplastic factors, hypothalamic-pituitary-adrenal axis hyperactivity, and circadian rhythms.

CONCLUSIONS

There is a clear need to improve our understanding of the neurobiology of the switch process; research in this field would benefit from the systematic and integrated assessment of variables associated with switching.

A haplotype of glycogen synthase kinase 3β is associated with early onset of unipolar major depression

Recent findings suggest that glycogen synthase kinase 3β (GSK3β) may play a role in the pathophysiology and treatment of mood disorders. Various genetic studies have shown the association of GSK3β polymorphisms with different mood disorder phenotypes. We hypothesized that genetic variants in the GSK3β gene could partially underlie the susceptibility to mood disorders. We performed a genetic case-control study of 440 psychiatrically screened control subjects and 445 mood disorder patients [256 unipolar major depressive disorder (MDD) and 189 bipolar disorder (BD)]. We genotyped a set of 11 single nucleotide polymorphisms (SNPs) and determined the relative frequency of a known copy number variant (CNV) overlapping the GSK3β by quantitative real-time polymerase chain reaction (PCR). We found no evidence of association with MDD or BD diagnosis, and we further investigated the age at onset (AAO) of the disorder and severity of depressive index episode. We found that rs334555, located in intron 1 of GSK3β, was nominally associated with an earlier AAO of the disease in MDD (P = 0.001). We also identified a haplotype containing three SNPs (rs334555, rs119258668 and rs11927974) associated with AAO of the disorder (permutated P = 0.0025). We detected variability for the CNV, but we could not detect differences between patients and controls for any of the explored phenotypes. This study presents further evidence of the contribution of GSK3β to mood disorders, implicating a specific SNP and a haplotype with an earlier onset of the disorder in a group of well-characterized patients with unipolar MDD. Further replication studies in patients with the same phenotypic characteristics should confirm the results reported here.

Association between glycogen synthase kinase-3beta gene polymorphisms and major depression and suicidal behavior in a Korean population

BACKGROUND

Glycogen synthase kinase (GSK)-3beta plays a key role in the phosphorylation and regulation of metabolic enzymes and many transcription factors. Several lines of evidence implicate GSK-3beta in the pathophysiology of mood disorders and susceptibility to suicidal behavior. In this study, we aimed to investigate the GSK-3beta gene's association with major depressive disorder (MDD) and suicidal behavior.

METHODS

One hundred seventy suicidal depressed patients and 147 non-suicidal depressed patients who met DSM-IV criteria for MDD were recruited. One hundred sixty-four healthy volunteers recruited by local advertisement served as controls. Patients and normal controls were genotyped for GSK-3beta -1727A/T and -50C/T. Haplotype trend regression (HTR) analysis was used for the evaluation of haplotype association.

RESULTS

The genotype distributions of -1727A/T and -50C/T were in agreement with Hardy-Weinberg equilibrium. The results showed that the alleles, genotypes, and haplotypes of the two SNPs do not differ between suicidal MDD subjects, non-suicidal MDD subjects, and normal controls. There was no difference in the haplotype frequency combination between the three groups.

CONCLUSION

Our study suggests that two promoter polymorphisms of the GSK-3beta gene may not be related to the pathogenesis of MDD and the risk of suicidal behavior in Korean depressive patients. Further studies with larger sample sizes and different populations are needed.

Disruption of the circadian timing systems: molecular mechanisms in mood disorders

Depression is one of the leading causes of morbidity worldwide and represents a huge burden to society. As with many other psychiatric disorders, a genetic basis for depression has been identified. Evidence for the role of circadian genes in depression is particularly compelling. Circadian gene mutations are also associated with circadian rhythm disorders such as familial advanced sleep phase syndrome, delayed sleep phase syndrome, and non-24-hour sleep-wake syndrome. Such disorders, plus the other manifestations of a disrupted circadian system such as hormone dysregulation, are often observed among those with depression. This suggests a shared aetiology between circadian disruption and depression, although the exact mechanisms underlying the association are unclear. This paper reviews the molecular mechanisms involved in depression, with an emphasis on circadian genes. Twin studies in depression have reported probandwise concordance rates of 40% and 70% using narrow and broad diagnostic criteria, respectively, and heritability of over 85% for bipolar disorder. In association studies, increased susceptibility to depression has been noted in those with polymorphisms in the following: D-amino-acid-oxidase activator/G30 gene complex, glucocorticoid receptor gene, serotonin transporter gene, tryptophan hydroxylase 2 gene, dopamine transporter gene and G protein-coupled receptor 50 gene. Polymorphisms in these genes have also been linked to a better or worse response to antidepressant therapy, an increased likelihood of responding poorly to adversity and increased suicide ideation. Polymorphisms in the CLOCK, BMAL1, Per3 and TIMELESS genes have been associated with susceptibility to mood disorder, and single nucleotide polymorphisms and haplotypes in several circadian genes have been observed among those displaying certain circadian phenotypes, including worse mood in the evening, insomnia in mania and early, middle or late insomnia in depression. Manipulation of the circadian timing system via sleep deprivation, bright light or pharmacological therapy has also been shown to alleviate depressive symptoms, providing further evidence for the role of circadian dysfunction in depression pathophysiology. The new antidepressant agomelatine is the first melatonergic antidepressant with an innovative mode of action: it is a melatonergic MT(1), MT(2) receptor agonist and 5-HT(2c) antagonist, and is able to restore the internal clock, which is profoundly disturbed in depression, thus being efficacious in major depressive disorders. In conclusion, a wealth of evidence is now available supporting a genetic basis for depression. The apparent importance of mutations in the circadian genes in determining disease susceptibility, disease recurrence and response to treatment suggests that the circadian pathway represents an attractive target for pharmacological manipulation to improve management of this debilitating disorder.

Association study of 21 circadian genes with bipolar I disorder, schizoaffective disorder, and schizophrenia

OBJECTIVE

Published studies suggest associations between circadian gene polymorphisms and bipolar I disorder (BPI), as well as schizoaffective disorder (SZA) and schizophrenia (SZ). The results are plausible, based on prior studies of circadian abnormalities. As replications have not been attempted uniformly, we evaluated representative, common polymorphisms in all three disorders.

METHODS

We assayed 276 publicly available 'tag' single nucleotide polymorphisms (SNPs) at 21 circadian genes among 523 patients with BPI, 527 patients with SZ/SZA, and 477 screened adult controls. Detected associations were evaluated in relation to two published genome-wide association studies (GWAS).

RESULTS

Using gene-based tests, suggestive associations were noted between EGR3 and BPI (p = 0.017), and between NPAS2 and SZ/SZA (p = 0.034). Three SNPs were associated with both sets of disorders (NPAS2: rs13025524 and rs11123857; RORB: rs10491929; p < 0.05). None of the associations remained significant following corrections for multiple comparisons. Approximately 15% of the analyzed SNPs overlapped with an independent study that conducted GWAS for BPI; suggestive overlap between the GWAS analyses and ours was noted at ARNTL.

CONCLUSIONS

Several suggestive, novel associations were detected with circadian genes and BPI and SZ/SZA, but the present analyses do not support associations with common polymorphisms that confer risk with odds ratios greater than 1.5. Additional analyses using adequately powered samples are warranted to further evaluate these results.

Altered growth factor signaling pathways as the basis of aberrant stem cell maturation in schizophrenia

In recent years evidence has accumulated that the activity of the signaling cascades of Neuregulin-1, Wnt, TGF-beta, BDNF-p75 and DISC1 is different between control subjects and patients with schizophrenia. These pathways are involved in embryonic and adult neurogenesis and neuronal maturation. A review of the clinical data indicates that in schizophrenia the Wnt pathway is most likely hypoactive, whereas the Nrg1-ErbB4, the TGF-beta- and the BDNF-p75-pathways are hyperactive. Haplo-insuffiency of the DISC1 gene is currently the best established schizophrenia risk factor. Preclinical experiments indicate that suppression of DISC1 signaling leads to accelerated dendrite development in neuronal stem cells, accelerated migration and aberrant integration into the neuronal network. Other preclinical experiments show that increasing NRG1-, BDNF- and TGF-beta signaling and decreasing Wnt signaling, also promotes adult neuronal differentiation and migration. Thus deviations in these pathways detected in schizophrenia could contribute to premature neuronal differentiation, accelerated migration and inappropriate insertion into the neuronal network. Initial clinical findings are confirmatory: neuronal stem cells isolated from nasal biopsies from schizophrenia patients display signs of accelerated development, whilst increased erosion of telomeres and bone age provide further support for accelerated cell maturation in schizophrenia.

Clock genes may influence bipolar disorder susceptibility and dysfunctional circadian rhythm

Several previous studies suggest that dysfunction of circadian rhythms may increase susceptibility to bipolar disorder (BP). We conducted an association study of five circadian genes (CRY2, PER1-3, and TIMELESS) in a family collection of 36 trios and 79 quads (Sample I), and 10 circadian genes (ARNTL, ARNTL2, BHLHB2, BHLHB3, CLOCK, CRY1, CSNK1D, CSNK1E, DBP, and NR1D1) in an extended family collection of 70 trios and 237 quads (Sample II), which includes the same 114 families but not necessarily the same individuals as Sample I. In Sample II, the Sibling-Transmission Disequilibrium Test (sib-tdt) analysis showed nominally significant association of BP with three SNPs within or near the CLOCK gene (rs534654, P = 0.0097; rs6850524, P = 0.012; rs4340844, P = 0.015). In addition, SNPs in the ARNTL2, CLOCK, DBP, and TIMELESS genes and haplotypes in the ARNTL, CLOCK, CSNK1E, and TIMELESS genes showed suggestive evidence of association with several circadian phenotypes identified in BP patients. However, none of these associations reached gene-wide or experiment-wide significance after correction for multiple-testing. A multi-locus interaction between rs6442925 in the 5' upstream of BHLHB2, rs1534891 in CSNK1E, and rs534654 near the 3' end of the CLOCK gene, however, is significantly associated with BP (P = 0.00000172). It remains significant after correcting for multiple testing using the False Discovery Rate method. Our results indicate an interaction between three circadian genes in susceptibility to bipolar disorder.

Association study of GSK3 gene polymorphisms with schizophrenia and clozapine response

RATIONALE

A number of human and animal studies implicate GSK3 in the pathophysiology and genetics of schizophrenia. In general, the data suggest that phosphorylation levels of GSK3beta are reduced in schizophrenia, resulting in increased GSK3beta activity. Since GSK3beta regulation is altered in schizophrenia, polymorphic variation in this gene may affect susceptibility to schizophrenia or treatment response.

OBJECTIVE

To analyze GSK3beta genetic variants for association with schizophrenia and clozapine response.

MATERIALS AND METHODS

We examined GSK3beta markers in 185 matched case-control subjects, 85 small nuclear families, and 150 schizophrenia patients treated with clozapine for 6 months.

RESULTS

Three markers (rs7624540, rs4072520, and rs6779828) showed genotypic association with schizophrenia in the case-control sample. We did not observe any family and clozapine response association with a specific allele, genotype, or haplotype.

CONCLUSIONS

Our results suggest that GSK3beta polymorphisms might be involved in schizophrenia risk but do not appear to play a significant role in clozapine response.

Antipsychotic drug mechanisms: links between therapeutic effects, metabolic side effects and the insulin signaling pathway

The exact therapeutic mechanism of action of antipsychotic drugs remains unclear. Recent evidence has shown that second-generation antipsychotic drugs (SGAs) are differentially associated with metabolic side effects compared to first-generation antipsychotic drugs (FGAs). Their proclivity to cause metabolic disturbances correlates, to some degree, with their comparative efficacy. This is particularly the case for clozapine and olanzapine. In addition, the insulin signaling pathway is vital for normal brain development and function. Abnormalities of this pathway have been found in persons with schizophrenia and antipsychotic drugs may ameliorate some of these alterations. This prompted us to hypothesize that the therapeutic antipsychotic and adverse metabolic effects of antipsychotic drugs might be related to a common pharmacologic mechanism. This article reviews insulin metabolism in the brain and related abnormalities associated with schizophrenia with the goals of gaining insight into antipsychotic drug effects and possibly also into the pathophysiology of schizophrenia. Finally, we speculate about one potential mechanism of action (that is, functional selectivity) that would be consistent with the data reviewed herein and make suggestions for the future investigation that is required before a therapeutic agent based on these data can be realized.

The genetics of bipolar disorder: genome 'hot regions,' genes, new potential candidates and future directions

Bipolar disorder (BP) is a complex disorder caused by a number of liability genes interacting with the environment. In recent years, a large number of linkage and association studies have been conducted producing an extremely large number of findings often not replicated or partially replicated. Further, results from linkage and association studies are not always easily comparable. Unfortunately, at present a comprehensive coverage of available evidence is still lacking. In the present paper, we summarized results obtained from both linkage and association studies in BP. Further, we indicated new potential interesting genes, located in genome 'hot regions' for BP and being expressed in the brain. We reviewed published studies on the subject till December 2007. We precisely localized regions where positive linkage has been found, by the NCBI Map viewer (http://www.ncbi.nlm.nih.gov/mapview/); further, we identified genes located in interesting areas and expressed in the brain, by the Entrez gene, Unigene databases (http://www.ncbi.nlm.nih.gov/entrez/) and Human Protein Reference Database (http://www.hprd.org); these genes could be of interest in future investigations. The review of association studies gave interesting results, as a number of genes seem to be definitively involved in BP, such as SLC6A4, TPH2, DRD4, SLC6A3, DAOA, DTNBP1, NRG1, DISC1 and BDNF. A number of promising genes, which received independent confirmations, and genes that have to be further investigated in BP, have been also systematically listed. In conclusion, the combination of linkage and association approaches provided a number of liability genes. Nevertheless, other approaches are required to disentangle conflicting findings, such as gene interaction analyses, interaction with psychosocial and environmental factors and, finally, endophenotype investigations.

No significant association between the genetic polymorphisms in the GSK-3 beta gene and schizophrenia in the Chinese population

The GSK-3 beta gene encodes a protein kinase which is abundant in the brain, and its product is involved in signal transduction cascades of neuronal cell development, energy metabolism and body pattern formation. Previous studies have suggested that GSK-3 beta might act as a potential candidate locus for schizophrenia susceptibility. We genotyped six SNPs within the gene and conducted a case-control study involving 329 schizophrenic patients and 288 healthy subjects in the Chinese population. We examined allele and genotype frequencies and haplotype distributions in the subtype of paranoid schizophrenic patients as well as schizophrenic subjects in general. Our results fail to replicate the association of the GSK-3 beta gene with susceptibility to schizophrenia in the Chinese population.

Association between GSK-3beta -50T/C polymorphism and personality and psychotic symptoms in mood disorders

The exact role of the enzyme glycogen synthase kinase 3beta (GSK-3beta) in mood disorders is still unknown. GSK-3beta has been mapped to chromosome 3q13.3, a potential susceptibility locus for bipolar disorder. The -50T/C polymorphism, falling within the promoter region of the gene coding for GSK-3beta, was previously reported to be associated with age at onset, therapeutic response to lithium salts and total sleep deprivation in bipolar patients. In the present study we investigated the association between the -50T/C polymorphism and both symptomatic and personality features in mood disorders. The sample comprised 365 inpatients affected by major depressive disorder and bipolar disorder, genotyped for the GSK-3beta-50 polymorphism and assessed with the Operational Criteria Checklist for Psychotic Illness (OPCRIT). Ninety-five subjects were also evaluated with the Temperament and Character Inventory (TCI). The GSK-3beta-50 polymorphism showed a positive association with delusional symptomatology and with the personality features linked to Self-Transcendence. Finally, GSK-3beta-50 and personality showed an interactive effect on delusional scores. In conclusion, our findings support the role of GSK-3beta-50 in both normal and psychopathological aspects of human cognition and further suggest a possible interaction between genes and personality in the liability to psychotic disorders.

Response to lithium augmentation in depression is associated with the glycogen synthase kinase 3-beta -50T/C single nucleotide polymorphism

BACKGROUND

Glycogen synthase kinase 3-beta (GSK3B) is a serine/threonine kinase which is directly inhibited by lithium. A -50T/C single nucleotide polymorphism (SNP) localized within the promoter region of the GSK3B gene has previously been shown to be associated with response to lithium prophylaxis in bipolar disorder. This study investigates the association of the GSK3B -50T/C SNP and response to lithium augmentation in acutely depressed antidepressant nonresponders.

METHODS

Eighty-one patients who had not responded to at least one adequate trial of antidepressant monotherapy underwent a standardized trial of lithium augmentation for up to 8 weeks. We genotyped for the GSK3B -50T/C SNP using polymerase chain reaction and restriction fragment length polymorphism methods and investigated the association with remission.

RESULTS

The allele frequencies in our sample were CC 14.8%, CT 48.2% and TT 37% (no deviation from the Hardy-Weinberg equilibrium). Carriers of the C-allele of the -50T/C SNP showed a significantly better response to lithium augmentation (hazard ratio: 2.70, p = .007), with a mean remission rate of 56.25% after 4 weeks compared to 31% in patients with the TT-genotype (chi(2) = 4.1; p = .04).

CONCLUSIONS

Our results support the finding of recent studies demonstrating a superior response of C-allele carriers with bipolar disorder to lithium prophylaxis.

No association of the MCP-1 promoter A-2518G polymorphism with bipolar disorder in the Korean population

It has been suggested that bipolar disorder is associated with altered immune function. Monocyte chemoattractant protein-1 (MCP-1) is a chemokine that influences both neural and immune functions. We thus hypothesized that MCP-1 may be related to the development or pathophysiology of bipolar disorder. In this case-control study, we investigated the association between the A-2518G single nucleotide polymorphism (SNP) of the MCP-1 promoter and bipolar disorder. Patients with bipolar disorder (n=183; bipolar I=145, bipolar II=38) and healthy controls (350) were recruited for the study. No significant allelic or genotypic association was detected between the A-2518G polymorphism and any sample of bipolar disorder patients. When we pooled the healthy controls and the cases of bipolar I disorder from previous Korean studies and this study, we again found no significant association. No significant difference in either allele frequency or genotype distribution was observed between bipolar I and bipolar II disorders. There was no difference in the age at onset of bipolar disorder among the three genotype groups. Our data suggest that the A-2518G polymorphism of MCP-1 is not a major susceptibility factor for bipolar disorder in the Korean population. However, the physiological role of MCP-1 is highly suggestive of its being associated with bipolar disorder, and further analyses of other SNPs of MCP-1 remain to be performed.

Increase in GSK3beta gene copy number variation in bipolar disorder

The analysis of submicroscopic copy number variations (CNVs), also known as copy number polymorphisms (CNPs), is emerging as a new tool for understanding the genetic basis of cancer, developmental disorders, and complex traits. One area where this may be particularly useful is in the identification of genetic variants underlying schizophrenia (SZ) and bipolar disorder (BD). Linkage analysis and pharmacological studies carried out over the past decade have implicated a number of positional and physiological candidate genes. Yet, despite extensive analysis, the underlying allelic variants responsible for disease susceptibility have remained, largely, elusive. Although the borders of most CNV have not been precisely mapped, it appears that a considerable number of SZ and BD candidate genes have their coding elements disrupted by polymorphic CNVs, suggesting that these would be good variants to consider for underlying disease susceptibility. One such gene is GSK3beta, which codes for glycogen synthase kinase, a key component of the Wnt signaling pathway and a target of lithium salts. A CNV in the GSK3beta locus at chromosome 3q13.3 appears to disrupt the gene's 3'-coding elements. The CNV also affects two other annotated genes. We now report that patients with BD have an increased frequency of this CNV-primarily the duplication variant-compared with controls (P = 0.002). The finding suggests that GSK3beta may be involved in BD susceptibility in some individuals and that CNVs in this and other candidate genes for psychiatric disorders should be analyzed as causative functional genetic variants.

GSK-3 is a viable potential target for therapeutic intervention in bipolar disorder

Bipolar disorder is a serious psychiatric condition that has been treated for over 50 years with lithium. Lithium is a well established glycogen synthase kinase-3 (GSK-3) inhibitor, suggesting that manipulating GSK-3 may have therapeutic value in treating bipolar disorder. GSK-3 is regulated by a wide variety of mechanisms including phosphorylation, binding with protein complexes, phosphorylation state of its substrates, cellular localization and autoregulation, thus providing a wide number of potential therapeutic mechanisms. Mounting evidence suggests that GSK-3 regulation can be used to manage bipolar disorder symptoms. Although GSK-3 mutations have not been detected amongst the general bipolar population, they have been correlated with females with bipolar II and most of the drugs used for successful bipolar disorder treatment regulate GSK-3. These drugs produce a weak anti-depressant-like and a strong anti-mania-like effect in a wide range of animal models tested, mirroring their utility in treating bipolar disorder symptoms. Taken together, the evidence suggests that targeting GSK-3 may be a means to control the symptoms of bipolar disorder.

Circadian genes, rhythms and the biology of mood disorders

For many years, researchers have suggested that abnormalities in circadian rhythms may underlie the development of mood disorders such as bipolar disorder (BPD), major depression and seasonal affective disorder (SAD). Furthermore, some of the treatments that are currently employed to treat mood disorders are thought to act by shifting or "resetting" the circadian clock, including total sleep deprivation (TSD) and bright light therapy. There is also reason to suspect that many of the mood stabilizers and antidepressants used to treat these disorders may derive at least some of their therapeutic efficacy by affecting the circadian clock. Recent genetic, molecular and behavioral studies implicate individual genes that make up the clock in mood regulation. As well, important functions of these genes in brain regions and neurotransmitter systems associated with mood regulation are becoming apparent. In this review, the evidence linking circadian rhythms and mood disorders, and what is known about the underlying biology of this association, is presented.

Molecular genetics of bipolar disorder and depression

In this review, all papers relevant to the molecular genetics of bipolar disorder published from 2004 to the present (mid 2006) are reviewed, and major results on depression are summarized. Several candidate genes for schizophrenia may also be associated with bipolar disorder: G72, DISC1, NRG1, RGS4, NCAM1, DAO, GRM3, GRM4, GRIN2B, MLC1, SYNGR1, and SLC12A6. Of these, association with G72 may be most robust. However, G72 haplotypes and polymorphisms associated with bipolar disorder are not consistent with each other. The positional candidate approach showed an association between bipolar disorder and TRPM2 (21q22.3), GPR50 (Xq28), Citron (12q24), CHMP1.5 (18p11.2), GCHI (14q22-24), MLC1 (22q13), GABRA5 (15q11-q13), BCR (22q11), CUX2, FLJ32356 (12q23-q24), and NAPG (18p11). Studies that focused on mood disorder comorbid with somatic symptoms, suggested roles for the mitochondrial DNA (mtDNA) 3644 mutation and the POLG mutation. From gene expression analysis, PDLIM5, somatostatin, and the mtDNA 3243 mutation were found to be related to bipolar disorder. Whereas most previous positive findings were not supported by subsequent studies, DRD1 and IMPA2 have been implicated in follow-up studies. Several candidate genes in the circadian rhythm pathway, BmaL1, TIMELESS, and PERIOD3, are reported to be associated with bipolar disorder. Linkage studies show many new linkage loci. In depression, the previously reported positive finding of a gene-environmental interaction between HTTLPR (insertion/deletion polymorphism in the promoter of a serotonin transporter) and stress was not replicated. Although the role of the TPH2 mutation in depression had drawn attention previously, this has not been replicated either. Pharmacogenetic studies show a relationship between antidepressant response and HTR2A or FKBP5. New technologies for comprehensive genomic analysis have already been applied. HTTLPR and BDNF promoter polymorphisms are now found to be more complex than previously thought, and previous papers on these polymorphisms should be treated with caution. Finally, this report addresses some possible causes for the lack of replication in this field.

Partial evidence of an association between epidermal growth factor A61G polymorphism and age at onset in male schizophrenia

Epidermal growth factor (EGF) is a well-known neurotrophic factor regulating the development of various neuronal cells, including dopaminergic neurons, and dysfunction of EGF signals has been demonstrated as a risk factor for schizophrenia. Recently, several researchers have investigated associations including age at onset (AAO) with EGF A61G functional polymorphism, but the results of these studies have been controversial. Thus, we investigated whether A61G plays a role in predisposition to schizophrenia and its effects on AAO. Our subjects included 190 patients with schizophrenia and 347 controls. We assessed three different points of AAO: age at first occurrence of positive psychotic symptoms, medication, and hospitalization as a patient with schizophrenia. We found no differences in allele and genotype frequencies between patients and controls or associations between A61G and AAOs across stratified points in the entire sample and in each gender. However, we found significant gender differences in patients with the AA genotype in all stratified points of AAOs. Subset analyses of G allele distribution between clinical subsets with an AAO cutoff of 20 years revealed that male patients with early onset schizophrenia were more likely to exhibit the common AA homozygote than male patients with adulthood onset schizophrenia. In conclusion, although we were unable to support an association between EGF A61G and schizophrenia, the AA genotype might play a disease-modifying role differentially according to gender.

Targeting glycogen synthase kinase-3 as an approach to develop novel mood-stabilising medications

Historically, success in the pharmacological treatment of bipolar disorder has arisen either from serendipitous findings or from studies with drugs (antipsychotics and anticonvulsants) developed for other indications (schizophrenia and epilepsy, respectively). Lithium has been in widespread clinical use in the treatment of bipolar disorder for > 30 years. Development of lithium-mimetic compounds has the potential to result in a more specific medication, with fewer side effects and a less narrow dose range. However, novel medications based upon a known mechanism of action of this drug are yet to be developed. Increasing evidence suggests that a next-generation lithium compound may derive from knowledge of a direct target of lithium, glycogen synthase kinase-3 (GSK-3). GSK-3 is an intracellular enzyme implicated as a critical component in many neuronal signalling pathways. However, despite the large body of preclinical data discussed in this review, definitive validation of GSK-3 as therapeutically relevant target of lithium will require clinical trials with novel GSK-3 inhibitors. A number of recent reports suggest that it is possible to develop selective, small-molecule GSK-3 inhibitors.