Endophenotypes in bipolar disorder

Relationship between endophenotype and phenotype in ADHD

Background

It has been hypothesized that genetic and environmental factors relate to psychiatric disorders through the effect of intermediating, vulnerability traits called endophenotypes. The study had a threefold aim: to examine the predictive validity of an endophenotypic construct for the ADHD diagnosis, to test whether the magnitude of group differences at the endophenotypic and phenotypic level is comparable, and to investigate whether four factors (gender, age, IQ, rater bias) have an effect (moderation or mediation) on the relation between endophenotype and phenotype.

Methods

Ten neurocognitive tasks were administered to 143 children with ADHD, 68 non-affected siblings, and 120 control children (first-borns) and 132 children with ADHD, 78 non-affected siblings, and 113 controls (second-borns) (5 – 19 years). The task measures have been investigated previously for their endophenotypic viability and were combined to one component which was labeled 'the endophenotypic construct': one measure representative of endophenotypic functioning across several domains of functioning.

Results

The endophenotypic construct classified children with moderate accuracy (about 50% for each of the three groups). Non-affected children differed as much from controls at the endophenotypic as at the phenotypic level, but affected children displayed a more severe phenotype than endophenotype. Although a potentially moderating effect (age) and several mediating effects (gender, age, IQ) were found affecting the relation between endophenotypic construct and phenotype, none of the effects studied could account for the finding that affected children had a more severe phenotype than endophenotype.

Conclusion

Endophenotypic functioning is moderately predictive of the ADHD diagnosis, though findings suggest substantial overlap exists between endophenotypic functioning in the groups of affected children, non-affected siblings, and controls. Results suggest other factors may be crucial and aggravate the ADHD symptoms in affected children.

Neuroplasticity mediated by altered gene expression

Plasticity in the brain is important for learning and memory, and allows us to respond to changes in the environment. Furthermore, long periods of stress can lead to structural and excitatory changes associated with anxiety and depression that can be reversed by pharmacological treatment. Drugs of abuse can also cause long-lasting changes in reward-related circuits, resulting in addiction. Each of these forms of long-term plasticity in the brain requires changes in gene expression. Upon stimulation, second messenger pathways are activated that lead to an enhancement in transcription factor activity at gene promoters. This stimulation results in the expression of new growth factors, ion channels, structural molecules, and other proteins necessary to alter the neuronal circuit. With repeated stimulation, more permanent modifications to transcription factors and chromatin structure are made that result in either sensitization or desensitization of a circuit. Studies are beginning to uncover the molecular mechanisms that lead to these types of long-term changes in the brain. This review summarizes some of the major transcriptional mechanisms that are thought to underlie neuronal and behavioral plasticity.

Cellular plasticity cascades in the pathophysiology and treatment of bipolar disorder

Bipolar disorder (BPD) is characterized by recurrent episodes of disturbed affect including mania and depression as well as changes in psychovegetative function, cognitive performance, and general health. A growing body of data suggests that BPD arises from abnormalities in synaptic and neuronal plasticity cascades, leading to aberrant information processing in critical synapses and circuits. Thus, these illnesses can best be conceptualized as genetically influenced disorders of synapses and circuits rather than simply as deficits or excesses in individual neurotransmitters. In addition, commonly used mood-stabilizing drugs that are effective in treating BPD have been shown to target intracellular signaling pathways that control synaptic plasticity and cellular resilience. In this article we draw on clinical, preclinical, neuroimaging, and post-mortem data to discuss the neurobiology of BPD within a conceptual framework while highlighting the role of neuroplasticity in the pathophysiology and treatment of this disorder.

Setting the stage: from prodrome to treatment resistance in bipolar disorder

Bipolar disorder is common, and both difficult to detect and diagnose. Treatment is contingent on clinical needs, which differ according to phase and stage of the illness. A staging model could allow examination of the longitudinal course of the illness and the temporal impact of interventions and events. It could allow for a structured examination of the illness, which could set the stage for algorithms that are tailored to the individuals needs. A staging model could further provide as structure for assessment, gauging treatment and outcomes. The model incorporates prodromal stages and emphasizes early detection and algorithm appropriate intervention where possible. At the other end of the spectrum, the model attempts to operationalize treatment resistance. The utility of the model will need to be validated by empirical research.

The use of genetic epidemiology to guide classification in child and adult psychopathology

The goal of this paper is to illustrate the application of the tools of genetic epidemiology, particularly the family study method, to inform the classification of psychiatric disorders in adults and children. The first section describes family studies of adults designed to investigate the causes of comorbidity of anxiety and depression. The analysis of familial traits provides stronger evidence for the validity of certain sub-types of anxiety and mood disorders that co-occur within the same individual and within families. The second section presents an example of the use of the family study method to examine the validity of the autism spectrum disorders (ASD). A review of these studies suggests that the most consistently familial traits in ASD are language and communication skills, insistence on sameness and non-verbal IQ. These are also the traits most commonly associated with the differentiation of autism from Asperger disorder and PDDNOS using both cross-sectional and longitudinal studies. From these data, a new classification system of the ASDs is proposed based on these familial traits.

Personality and the predisposition(s) to bipolar disorder: heuristic benefits of a two-dimensional model

OBJECTIVES

The aim of this study was to model normal personality correlates of the predisposition(s) to bipolar disorder (BD), and in so doing explore the proposition that the tendency to bipolar depression [trait depression (T-Depression)] and the tendency to mania [trait mania (T-Mania)] can usefully be viewed as separable but correlated dimensions of BD predisposition.

METHODS

A well student sample (n = 176, modal age 18-25 years, 71% female) completed the NEO Personality Inventory-Revised and the General Behavior Inventory.

RESULTS

A good-fitting model (normed chi2 = 0.60, significance of chi2 = 0.73) was identified in which T-Depression was determined solely by neuroticism, while T-Mania was determined by extraversion and (negative) agreeableness. The pathway from T-Depression to T-Mania was also significant (standardized regression weight = 0.80), with a weaker significant reciprocal path (coefficient = 0.27). A model in which bipolar vulnerability was represented as a single dimension (T-Bipolarity) also provided a good fit to the data, but provided less heuristic power.

CONCLUSIONS

Predisposition to BD can be usefully understood in terms of two reciprocally related dimensions of vulnerability (T-Depression and T-Mania), which can be separated on the basis of their personality correlates.

Is autoimmune thyroiditis part of the genetic vulnerability (or an endophenotype) for bipolar disorder?

BACKGROUND

Both genetic and environmental factors are involved in the etiology of bipolar disorder; however, biological markers for the transmission of the bipolar genotype ("endophenotypes") have not been found. Autoimmune thyroiditis with raised levels of thyroperoxidase antibodies (TPO-Abs) is related to bipolar disorder and may be such an endophenotype. This study was intended to examine whether autoimmune thyroiditis is related to the disease itself, to the (genetic) vulnerability to develop bipolar disorder, or both.

METHOD

Blood was collected from 22 monozygotic (MZ) and 29 dizygotic (DZ) bipolar twins and 35 healthy matched control twins to determine TPO-Abs.

RESULTS

The TPO-Abs were positive in 27% of the bipolar index twins, 29% of the monozygotic bipolar cotwins, 27% of the monozygotic nonbipolar cotwins, 25% of the dizygotic bipolar cotwins, 17% of the dizygotic nonbipolar cotwins, and in 16% of the control twins. Repeated measures analysis of covariance on log-transformed absolute TPO-Abs values revealed significantly increased mean TPO-Abs levels in discordant twin pairs as compared with healthy twin pairs, whereas no difference was found between bipolar patients and their (discordant) nonbipolar cotwins.

CONCLUSIONS

This study shows that autoimmune thyroiditis is related not only to bipolar disorder itself but also to the genetic vulnerability to develop the disorder. Autoimmune thyroiditis, with TPO-Abs as marker, is a possible endophenotype for bipolar disorder.

Informative phenotypes for genetic studies of psychiatric disorders

Despite its initial promise, there has been both progress and some set backs in genetic studies of the major psychiatric disorders of childhood and adulthood. Finding true susceptibility genes may be delayed because the most genetically informative phenotypes are not being used on a regular basis in linkage analysis and association studies. It is highly likely that using alternative phenotypes instead of DSM diagnostic categories will lead more rapid success in the search for these susceptibility genes. The objective of this paper is to describe the different types of informative phenotypes that can be employed in psychiatric genetic studies, to clarify their uses, to identify several methodologic issues the design and conduct of linkage and association studies that use alternative phenotypes and finally to suggest possible solutions to those difficulties. This is a conceptual review with a focus on methodological issues that may arise in psychiatric genetics and examples are taken from the literature on autism, schizophrenia, bipolar disorder, and alcoholism.

Structure-Based Design Leads to the Identification of Lithium Mimetics That Block Mania-like Effects in Rodents. Possible New GSK-3β Therapies for Bipolar Disorders

More than two million American adults, or approximately one percent of the population 18 years or older, suffer from bipolar disorder. Current treatments include the so-called "mood stabilizers," lithium and valproic acid. Both are relatively dated drugs that are only partially effective and produce various undesirable side effects including weight gain. Based upon continued efforts to understand the molecular target for lithium, it now appears that specific inhibitors of the enzyme glycogen synthase kinase-3beta (GSK-3beta) may mimic the therapeutic action of mood stabilizers and might therefore allow for the design of improved drugs for treating patients with bipolar disorder as well as certain neurodegenerative disorders. Furthermore, the pro-apoptotic properties of the GSK-3 enzyme suggest the possible use of such inhibitors as neuroprotective agents. In fact, neuroprotection may contribute to the treatment of mood disorders. The present chemistry, modeling, and biology efforts have identified 3-benzofuranyl-4-indolylmaleimides as potent and relatively selective GSK-3beta inhibitors. The best ligand in this series (having a Ki value of 4.6 nM against GSK-3beta) was studied in a novel mouse model of mania that has recently been validated with several clinically effective mood stabilizers. This study presents the first demonstration of the efficacy of a GSK-3beta inhibitor in this mouse model of mania. Selective brain penetrable GSK-3 ligands like those described herein become valuable research tools in better defining the role of this multifaceted kinase in both physiological and pathophysiological events.

Mood stabilizers target cellular plasticity and resilience cascades: implications for the development of novel therapeutics

Bipolar disorder is a devastating disease with a lifetime incidence of about 1% in the general population. Suicide is the cause of death in 10 to 15% of patients and in addition to suicide, mood disorders are associated with many other harmful health effects. Mood stabilizers are medications used to treat bipolar disorder. In addition to their therapeutic effects for the treatment of acute manic episodes, mood stabilizers are useful as prophylaxis against future episodes and as adjunctive antidepressant medications. The most established and investigated mood-stabilizing drugs are lithium and valproate but other anticonvulsants (such as carbamazepine and lamotrigine) and antipsychotics are also considered as mood stabilizers. Despite the efficacy of these diverse medications, their mechanisms of action remain, to a great extent, unknown. Lithium's inhibition of some enzymes, such as inositol monophosphatase and glycogen synthase kinase-3, probably results in its mood-stabilizing effects. Valproate may share its anticonvulsant target with its mood-stabilizing target or may act through other mechanisms. It has been shown that lithium, valproate, and/or carbamazepine regulate numerous factors involved in cell survival pathways, including cyclic adenine monophospate response element-binding protein, brain-derived neurotrophic factor, bcl-2, and mitogen-activated protein kinases. These drugs have been suggested to have neurotrophic and neuroprotective properties that ameliorate impairments of cellular plasticity and resilience underlying the pathophysiology of mood disorders. This article also discusses approaches to develop novel treatments specifically for bipolar disorder.

Early identification and high-risk strategies for bipolar disorder

OBJECTIVES

To describe and compare the relative merits of different identification strategies for individuals at risk for bipolar disorder (BPD).

METHODS

Selective review of data that support early identification in BPD, with a particular focus on emerging clinical high-risk strategies.

RESULTS

Early detection of individuals at risk for BPD can utilize genetic, endophenotypic and clinical methods. Most published work focuses on genetic familial endophenotypic risk markers for BPD. However, despite encouraging results, problems with specificity and sensitivity limit the application of these data to early prevention programs. In addition, offspring studies of BPD patients systematically exclude the majority of subjects without a first-degree bipolar relative. On the other hand, emerging work in the clinical-high-risk arena has already produced encouraging results. Although still preliminary, the identification of individuals in subsyndromal or attenuated symptom 'prodromal' stages of BPD seems to be an under-researched area that holds considerable promise deserving increased attention. Required next steps include the development of rating tools for attenuated and subsyndromal manic and depressive symptoms and of prodromal criteria that will allow prodromal symptomatology to be systematically studied in patients with recent-onset bipolar, as well as in prospective population-based phenomenology trials and attenuated symptom-based high-risk studies.

CONCLUSIONS

Given the current limitations of each early identification method, combining clinical, endophenotypic and genetic strategies will increase prediction accuracy. Since reliable biological markers for BPD have not been established and since most patients with BPD lack a first-degree relative with this disorder, clinical high-risk approaches have great potential to inform early identification and intervention programs.

Neuroimaging endophenotypes: strategies for finding genes influencing brain structure and function

It is vitally important to identify the genetic determinants of complex brain-related disorders such as autism, dementia, mood disorders, and schizophrenia. However, the search for genes predisposing individuals to these illnesses has been hampered by their genetic and phenotypic complexity and by reliance upon phenomenologically based qualitative diagnostic systems. Neuroimaging endophenotypes are quantitative indicators of brain structure or function that index genetic liability for an illness. These indices will significantly improve gene discovery and help us to understand the functional consequences of specific genes at the level of systems neuroscience. Here, we review the feasibility of using neuroanatomic and neuropsychological measures as endophenotypes for brain-related disorders. Specifically, we examine specific indices of brain structure or function that are genetically influenced and associated with neurological and psychiatric illness. In addition, we review genetic approaches that capitalize on the use of quantitative traits, including those derived from brain images.

Animal models of bipolar disorder and mood stabilizer efficacy: a critical need for improvement

The limited number of suitable animal models of bipolar disorder available for in-depth behavioral, biochemical, histological, and pharmacological analysis is a rate-limiting step in the process of understanding the relevant neurobiology of the disorder, as well as the development of novel medications. In the search for new models, both new and old approaches hold promise for future discoveries. Clinical studies regarding the underlying genetics and pathophysiology of bipolar disorder are providing important clues. In particular, the identification of susceptibility genes for bipolar disorder will help to define specific neurobiological processes, and associated behaviors, that are unquestionably involved in the pathways connecting genes and distal symptoms. These endophenotypes will hold great value in further enhancing the validity of animal models and will strongly complement symptom-based models and models of medication efficacy. Regardless of the path taken by different researchers to develop better models, we believe that this area of work requires additional attention not only from researchers but also from funding agencies.

Mitochondrial dysfunction as the molecular basis of bipolar disorder: therapeutic implications

Multiple lines of evidence, such as impaired energy metabolism in the brain detected by magnetic resonance spectroscopy, a possible role of maternal inheritance, co-morbidity with mitochondrial diseases, the effects of mood stabilisers on mitochondria, increased mitochondrial DNA (mtDNA) deletion in the brain, and association with mtDNA mutations/polymorphisms or nuclear-encoded mitochondrial genes, suggest that mitochondrial dysfunction is an important component of bipolar disorder. Global reduction of mitochondria-related gene expression in the postmortem brains of patients with bipolar disorder may also be an indicator, but such findings are affected by sample pH and thus need to be interpreted with caution. A recently developed animal model carrying mtDNA deletion in neurons suggested that accumulation of mtDNA deletions causes bipolar disorder-like phenotypes. The next step in the study of mitochondrial dysfunction in bipolar disorder should be clarification of how mitochondrial dysfunction, a nonspecific risk factor, can cause specific symptoms of bipolar disorder. Two hypothetical mechanisms are mtDNA neuroplasticity and nonvisual photoreception impairment. Further study of mitochondrial dysfunction in bipolar disorder is expected to be useful for the development of new mood stabilisers.

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.

Glycogen synthase kinase 3, circadian rhythms, and bipolar disorder: a molecular link in the therapeutic action of lithium

Background

Bipolar disorder (BPD) is a widespread condition characterized by recurring states of mania and depression. Lithium, a direct inhibitor of glycogen synthase kinase 3 (GSK3) activity, and a mainstay in BPD therapeutics, has been proposed to target GSK3 as a mechanism of mood stabilization. In addition to mood imbalances, patients with BPD often suffer from circadian disturbances. GSK3, an essential kinase with widespread roles in development, cell survival, and metabolism has been demonstrated to be an essential component of the Drosophila circadian clock. We sought to investigate the role of GSK3 in the mammalian clock mechanism, as a possible mediator of lithium's therapeutic effects.

Methods

GSK3 activity was decreased in mouse embryonic fibroblasts (MEFs) genetically and pharmacologically, and changes in the cyclical expression of core clock genes – mPer2 in particular – were examined.

Results

We demonstrate that genetic depletion of GSK3 in synchronized oscillating MEFs results in a significant delay in the periodicity of the endogenous clock mechanism, particularly in the cycling period of mPer2. Furthermore, we demonstrate that pharmacological inhibition of GSK3 activity by kenpaullone, a known antagonist of GSK3 activity, as well as by lithium, a direct inhibitor of GSK3 and the most common treatment for BPD, induces a phase delay in mPer2 transcription that resembles the effect observed with GSK3 knockdown.

Conclusion

These results confirm GSK3 as a plausible target of lithium action in BPD therapeutics, and suggest the circadian clock mechanism as a significant modulator of lithium's clinical benefits.

Role for the Clock gene in bipolar disorder

Nearly all patients with bipolar disorder have severely disrupted circadian rhythms. Treatment with mood stabilizers can restore these daily rhythms, and this is correlated with patient recovery. However, it is still uncertain whether clock abnormalities are the cause of bipolar disorder or if these rhythm disruptions are secondary to alterations in other circuits. Furthermore, the mechanism by which the circadian clock might influence mood is still unclear. With cloning and characterization of the circadian genes and recent advances in molecular biology, we are starting to understand this strong association between circadian rhythms and bipolar disorder. Recent human genetic and mouse behavioral studies indicate that the Clock gene is particularly relevant in the mood disruptions associated with this disorder. Furthermore, it appears that Clock expression outside of the central pacemaker of the suprachiasmatic nucleus (SCN) is involved in mood regulation. In this chapter, the evidence linking circadian rhythms, the Clock gene, and bipolar disorder is discussed, along with the possible biology that underlies this connection.

Animal models of bipolar disorder

Animal models of human diseases should meet three sets of criteria: construct validity, face validity, and predictive validity. To date, several putative animal models of bipolar disorder have been reported. They are classified into various categories: pharmacological models, nutritional models, environmental models, and genetic models. None of them, however, totally fulfills the three validity criteria, and thus may not be useful for drug development. Mounting evidence suggests that mitochondrial dysfunction has a role in bipolar disorder. To test whether accumulation of mtDNA deletions in the brain can cause bipolar disorder, we generated transgenic mice with neuron-specific expression of mutant Polg (D181A). These mice showed altered diurnal activity rhythm and periodic activity change associated with the estrous cycle. These phenotypes were worsened by administration of a tricyclic antidepressant, but improved after lithium treatment. This mouse model of bipolar disorder potentially fulfills the three validity criteria, and therefore might be used for future drug development studies.

Deconstructing schizophrenia: an overview of the use of endophenotypes in order to understand a complex disorder

The genetics of schizophrenia has been approached utilizing a variety of methods. One emerging strategy is the use of endophenotypes in order to understand and identify the functional importance of genetically transmitted, brain-based deficits across schizophrenia kindreds. The endophenotype strategy is a topic of this issue of Schizophrenia Bulletin. Endophenotypes are quantitative, heritable, trait-related deficits typically assessed by laboratory-based methods rather than clinical observation. Endophenotypes are seen as closer to genetic variation than are clinical symptoms of schizophrenia, and are therefore closely linked to heritable risk factors. There has been a broad expansion of opportunities available to psychiatric neuroscientists who use the endophenotype strategy to understand the genetic basis of schizophrenia. In this context, genetic variation such as single nucleotide polymorphisms (SNPs) induces abnormalities in endophenotypic domains such as neurocognition, neurodevelopment, metabolism, and neurophysiology. This article discusses the challenges that abound in genetic research of schizophrenia, including issues in ascertainment, epistasis, ethnic diversity, and the potentially normalizing effects of second-generation antipsychotic medications on neurocognitive and neurophysiological measures. Robust strategies for meeting these challenges are discussed in this review and the subsequent articles in this issue. This article summarizes conceptual advances and progress in the measurement and use of endophenotypes in schizophrenia that form the basis of the multisite National Institute of Mental Health Consortium on the Genetics of Schizophrenia. The endophenotype strategy offers powerful and exciting opportunities to understand the genetically conferred neurobiological vulnerabilities and possible new strong inference and molecularly based treatments for schizophrenia.

PhenoChipping of psychotic disorders: a novel approach for deconstructing and quantitating psychiatric phenotypes

Psychiatric phenotypes as currently defined are primarily the result of clinical consensus criteria rather than empirical research. We propose, and present initial proof of principle for, a novel approach to characterizing psychiatric phenotypes. We have termed our approach PhenoChipping, by analogy with, and borrowing paradigms and tools from, gene expression microarray studies (GeneChipping). A massive parallel profiling of cognitive and affective state is done with a PhenoChip composed of a battery of existing and new quantitative psychiatric rating scales, as well as hand neuromotor measures. We present preliminary data from 104 subjects, 72 with psychotic disorders (bipolar disorder-41, schizophrenia-17, schizoaffective disorder-14), and 32 normal controls. Microarray data analysis software and visualization tools were used to investigate: 1. relationships between phenotypic items ("phenes"), including with objective motor measures, and 2. relationships between subjects. Our analyses revealed phenotypic overlap among, as well as phenotypic heterogeneity within, the three major psychotic disorders studied. This approach may be useful in helping us move beyond current diagnostic classifications, and suggests a combinatorial building-block (Lego-like) structure underlies psychiatric syndromes. The adaptation of microarray informatic tools for phenotypic analysis readily facilitates direct integration with gene expression profiling of lymphocytes in the same individuals, a strategy for molecular biomarker identification. Empirically derived clusterings of (endo)phenotypes and of patients will better serve genetic, pharmacological, and imaging research, as well as clinical practice.

Modelling facets of mania--new directions related to the notion of endophenotypes

The lack of appropriate animal models is a major limitation in research of bipolar disorder (BPD): at this time there are very few models for this devastating disease. Whereas limited attempts have been made to develop comprehensive models for BPD, the new notion of endophenotypes encourages us to explore the possibility of developing separate models for separate facets of the disorder. Since more models are available for depression, there is a dire need for models for mania that will be relatively easy and simple to induce and test and will therefore be practical for purposes of screening possible new drugs or mutant mice that are developed based on novel molecular theories. Such models may already be tentatively available as they were developed in the context of other disorders, but there is a need to validate them for mania. The present paper proposes such models for most of the facets of mania including: increased energy, activity or restlessness; extreme irritability; reduced sleep; provocative, intrusive or aggressive behaviour; increased sexual drive; abuse of drugs; distractibility, reduced ability to concentrate; and unrealistic beliefs in one's abilities and powers resulting in poor judgement. Validating these models may demand a major research effort but it may be worthy as validated models for the different facets of mania could then be used efficiently and may be utilized to construct a standard battery of tests that can serve to explore the various components of manic-like behaviour in rodents.

The heritability of melatonin secretion and sensitivity to bright nocturnal light in twins

The super-sensitivity of the neurohormone melatonin to light in patients with bipolar disorder provides evidence of the circadian nature of the disorder. This response has been proposed as an endophenotype for identifying people at risk of the disorder and guiding investigations of molecular genetic targets. However, before this response is used as an endophenotypic marker, the heritable nature of melatonin sensitivity in the normal population must be established. The aim of this study was to investigate the heritability of nocturnal melatonin secretion and sensitivity to light in monozygotic and dizygotic twins with no psychiatric history. This study investigated overall melatonin levels (between 2000 and 2400 h) and suppression by 500 lx of light (between 2400 and 0100 h) in 20 pairs of twins (nine monozygotic, 11 dizygotic). The results indicate that melatonin secretion is highly heritable with secretion in one twin being a significant predictor of secretion in their twin in both monozygotic and dizygotic pairs. In relation to light sensitivity, genetic loading appears to play a significant role with the greatest concordance between monozygotic twins, followed by dizygotic twins and finally low concordance in unrelated individuals. This provides additional support for the usefulness of melatonin sensitivity to light as a potential endophenotypic marker of bipolar affective disorder.

Toward constructing an endophenotype strategy for bipolar disorders

Research aimed at elucidating the underlying neurobiology and genetics of bipolar disorder, and factors associated with treatment response, have been limited by a heterogeneous clinical phenotype and lack of knowledge about its underlying diathesis. We used a survey of clinical, epidemiological, neurobiological, and genetic studies to select and evaluate candidate endophenotypes for bipolar disorder. Numerous findings regarding brain function, brain structure, and response to pharmacological challenge in bipolar patients and their relatives deserve further investigation. Candidate brain function endophenotypes include attention deficits, deficits in verbal learning and memory, cognitive deficits after tryptophan depletion, circadian rhythm instability, and dysmodulation of motivation and reward. We selected reduced anterior cingulate volume and early-onset white matter abnormalities as candidate brain structure endophenotypes. Symptom provocation endophenotypes might be based on bipolar patients' sensitivity to sleep deprivation, psychostimulants, and cholinergic drugs. Phenotypic heterogeneity is a major impediment to the elucidation of the neurobiology and genetics of bipolar disorder. We present a strategy constructed to improve the phenotypic definition of bipolar disorder by elucidating candidate endophenotypes. Studies to evaluate candidate endophenotypes with respect to specificity, heritability, temporal stability, and prevalence in unaffected relatives are encouraged.

Cellular plasticity cascades: genes-to-behavior pathways in animal models of bipolar disorder

BACKGROUND

Despite extensive research, the molecular/cellular underpinnings of bipolar disorder (BD) remain to be fully elucidated. Recent data has demonstrated that mood stabilizers exert major effects on signaling that regulate cellular plasticity; however, a direct extrapolation to mechanisms of disease demands proof that manipulation of candidate genes, proteins, or pathways result in relevant behavioral changes.

METHODS

We critique and evaluate the behavioral changes induced by manipulation of cellular plasticity cascades implicated in BD.

RESULTS

Not surprisingly, the behavioral data suggest that several important signaling molecules might play important roles in mediating facets of the complex symptomatology of BD. Notably, the protein kinase C and extracellular signal-regulated kinase cascades might play important roles in the antimanic effects of mood stabilizers, whereas glycogen synthase kinase (GSK)-3 might mediate facets of lithium's antimanic/antidepressant actions. Glucocorticoid receptor (GR) modulation also seems to be capable to inducing affective-like changes observed in mood disorders. And Bcl-2, amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors, and inositol homeostasis represent important pharmacological targets for mood stabilizers, but additional behavioral research is needed to more fully delineate their behavioral effects.

CONCLUSIONS

Behavioral data support the notion that regulation of cellular plasticity is involved in affective-like behavioral changes observed in BD. These findings are leading to the development of novel therapeutics for this devastating illness.

Molecular genetics of bipolar disorder

Bipolar disorder (BPD) is an often devastating illness characterized by extreme mood dysregulation. Although family, twin and adoption studies consistently indicate a strong genetic component, specific genes that contribute to the illness remain unclear. This study gives an overview of linkage studies of BPD, concluding that the regions with the best evidence for linkage include areas on chromosomes 2p, 4p, 4q, 6q, 8q, 11p, 12q, 13q, 16p, 16q, 18p, 18q, 21q, 22q and Xq. Association studies are summarized, which support a possible role for numerous candidate genes in BPD including COMT, DAT, HTR4, DRD4, DRD2, HTR2A, 5-HTT, the G72/G30 complex, DISC1, P2RX7, MAOA and BDNF. Animal models related to bipolar illness are also reviewed, with special attention paid to those with clear genetic implications. We conclude with suggestions for strategies that may help clarify the genetic bases of this complex illness.

Serum brain-derived neurotrophic factor is decreased in bipolar disorder during depressive and manic episodes

Genetic and pharmacological studies have suggested that brain-derived neurotrophic factor (BDNF) may be associated with the pathophysiology of bipolar disorder (BD). The present study investigated serum BDNF levels in manic, depressed, euthymic BD patients and in matched healthy controls, using an enzyme-linked immunosorbent assay (sandwich-ELISA). Serum BDNF levels were decreased in manic (p=0.019) and depressed (p=0.027) BD patients, as compared with euthymic patients and controls. Serum BDNF levels were negatively correlated with the severity of manic (r=-0.37, p=0.005) and depressive (r=-0.30, p=0.033) symptoms. These findings further support the hypothesis that the BDNF signaling system may play a role in the pathophysiology of BD.

Casein kinase 2, circadian clocks, and the flight from mutagenic light

Circadian clocks play a fundamental role in biology and disease. Much has been learned about the molecular underpinnings of these biological clocks from genetic studies in model organisms, such as the fruit fly, Drosophila melanogaster. Here we review the literature from our lab and others that establish a role for the protein kinase CK2 in Drosophila clock timing. Among the clock genes described thus far, CK2 is unique in its involvement in plant, fungal, as well as animal circadian clocks. We propose that this reflects an ancient, conserved function for CK2 in circadian clocks. CK2 and other clock genes have been implicated in cellular responses to DNA damage, particularly those induced by ultraviolet (UV) light. The finding of a dual function of CK2 in clocks and in UV responses supports the notion that clocks evolved to assist organisms in avoiding the mutagenic effects of daily sunlight.

Neurocognition as a stable endophenotype in bipolar disorder and schizophrenia

Linkage and association studies have paid increasing attention to neurocognition as a putative endophenotype. However, there exists little documentation of its trait stability in schizophrenia or bipolar disorder. Our aim was to determine the longitudinal stability of neurocognitive performance in bipolar versus schizophrenia probands. We administered a neurocognitive battery at two time points, approximately 5 years apart, in 16 schizophrenia and 16 bipolar disorder age-matched subjects. There were no significant changes over time on variables including education, estimated IQ, depression, psychosis, global functioning, or medication status. Schizophrenia subjects showed significant deterioration in one measure of executive functioning but no significant changes in seven of eight other domains. Bipolar patients showed stability over time in attentional measures but greater variability in other domains. These preliminary findings suggest that neurocognitive domains appear longitudinally stable across broad domains in schizophrenia. In contrast, stable functioning may be more limited to attentional domains in bipolar disorder.

Psychiatric endophenotypes and the development of valid animal models

Endophenotypes are quantifiable components in the genes-to-behaviors pathways, distinct from psychiatric symptoms, which make genetic and biological studies of etiologies for disease categories more manageable. The endophenotype concept has emerged as a strategic tool in neuropsychiatric research. This emergence is due to many factors, including the modest reproducibility of results from studies directed toward etiologies and appreciation for the complex relationships between genes and behavior. Disease heterogeneity is often guaranteed, rather than simplified, through the current diagnostic system; inherent benefits of endophenotypes include more specific disease concepts and process definitions. Endophenotypes can be neurophysiological, biochemical, endocrine, neuroanatomical, cognitive or neuropsychological. Heritability and stability (state independence) represent key components of any useful endophenotype. Importantly, they characterize an approach that reduces the complexity of symptoms and multifaceted behaviors, resulting in units of analysis that are more amenable to being modeled in animals. We discuss the benefits of more direct interpretation of clinical endophenotypes by basic behavioral scientists. With the advent of important findings regarding the genes that predispose to psychiatric illness, we are at an important crossroads where, without anthropomorphizing, animal models may provide homologous components of psychiatric illness, rather than simply equating to similar (loosely analogized) behaviors, validators of the efficacy of current medications or models of symptoms. We conclude that there exists a need for increased collaboration between clinicians and basic scientists, the result of which should be to improve diagnosis, classification and treatment on one end and to increase the construct relevance of model organisms on the other.

Nuclear receptor Rev-erbalpha is a critical lithium-sensitive component of the circadian clock

Lithium is commonly used to treat bipolar disorder, which is associated with altered circadian rhythm. Lithium is a potent inhibitor of glycogen synthase kinase 3 (GSK3), which regulates circadian rhythm in several organisms. In experiments with cultured cells, we show here that GSK3beta phosphorylates and stabilizes the orphan nuclear receptor Rev-erbalpha, a negative component of the circadian clock. Lithium treatment of cells leads to rapid proteasomal degradation of Rev-erbalpha and activation of clock gene Bmal1. A form of Rev-erbalpha that is insensitive to lithium interferes with the expression of circadian genes. Control of Rev-erbalpha protein stability is thus a critical component of the peripheral clock and a biological target of lithium therapy.

Affective instability as rapid cycling: theoretical and clinical implications for borderline personality and bipolar spectrum disorders

OBJECTIVES

The Diagnostic and Statistical Manual of Mental Disorders guidelines provide only a partial solution to the nosology and treatment of bipolar disorder in that disorders with common symptoms and biological correlates may be categorized separately because of superficial differences related to behavior, life history, and temperament. The relationship is explored between extremely rapid switching forms of bipolar disorder, in which manic and depressive symptoms are either mixed or switch rapidly, and forms of borderline personality disorder in which affective lability is a prominent symptom.

METHODS

A MedLine search was conducted of articles that focused on rapid cycling in bipolar disorder, emphasizing recent publications (2001-2004).

RESULTS

Studies examined here suggest a number of points of phenomenological and biological overlap between the affective lability criterion of borderline personality disorder and the extremely rapid cycling bipolar disorders. We propose a model for the development of 'borderline' behaviors on the basis of unstable mood states that sheds light on how the psychological and somatic interventions may be aimed at 'breaking the cycle' of borderline personality disorder development. A review of pharmacologic studies suggests that anticonvulsants may have similar stabilizing effects in both borderline personality disorder and rapid cycling bipolar disorder.

CONCLUSIONS

The same mechanism may drive both the rapid mood switching in some forms of bipolar disorder and the affective instability of borderline personality disorder and may even be rooted in the same genetic etiology. While continued clinical investigation of the use of anticonvulsants in borderline personality disorder is needed, anticonvulsants may be useful in the treatment of this condition, combined with appropriate psychotherapy.

Bipolar II and the bipolar spectrum

In studies made in the last decade, patients consulting doctors because of depression and anxiety have very often turned out to suffer from bipolar type II and similar conditions with alternating depression and hypomania/mania (the bipolar spectrum disorders - BP). Specifically, about every second patient seeking consultation because of depression has been shown to suffer from BP, mainly bipolar type II. BP is often concealed by other psychiatric conditions, e.g. recurrent depression, psychosis, anxiety, addiction, personality disorder, attention-deficit hyperactivity disorder and eating disorder. BP shows strong heredity. Relatives of patients with BP also have a high frequency of the psychiatric conditions just mentioned. Conversion ("switching") from recurrent unipolar depressions (recurrent UP) to BP is common in very long longitudinal studies (over decades). Mood-stabilizing medicines are recommended to a great extent in the treatment of BP, since anti-depressive medicines are often not effective and involve a substantial risk of inducing mood swings. Particularly in the long-term pharmacological treatment of depression in BP anti-depressive medicines may worsen the condition, e.g. inducing a symptom triad of dysphoria, irritability and insomnia: ACID (antidepressant-associated chronic irritable dysphoria).

The phenotypes of bipolar disorder: relevance for genetic investigations

The search for susceptibility genes for bipolar disorder (BD) depends on appropriate definitions of the phenotype. In this paper, we review data on diagnosis and clinical features of BD that could be used in genetic studies to better characterize patients or to define homogeneous subgroups. Clinical symptoms, long-term course, comorbid conditions, and response to prophylactic treatment may define groups associated with more or less specific loci. One such group is characterized by symptoms of psychosis and linkage to 13q and 22q. A second group includes mainly bipolar II patients with comorbid panic disorder, rapid mood switching, and evidence of chromosome 18 linkage. A third group comprises typical BD with an episodic course and favourable response to lithium prophylaxis. Reproducibility of cognitive deficits across studies raises the possibility of using cognitive profiles as endophenotypes of BD, with deficits in verbal explicit memory and executive function commonly reported. Brain imaging provides a more ambiguous data set consistent with heterogeneity of the illness.

Neurobehavioral aspects of cerebral white matter disorders

The study of higher function in humans requires a consideration of all the neural tissues in the brain. Long neglected as a contributor to the organization of cognitive and emotional operations, the cerebral white matter is now the subject of substantial effort to improve understanding. Among the many approaches that can address this area usefully, the study of individuals with white matter disorders offers a wealth of clinical insights that exploits the time-tested lesion method of behavioral neurology. This process is complemented by sophisticated neuroimaging techniques that increasingly enable detailed visualization of white matter tracts as they participate in the cognitive and emotional operations of distributed neural networks. In practical terms, an appreciation of the neurobehavioral importance of white matter disorders can be of great benefit for patients seen by neurologists and psychiatrists alike, especially because early recognition and treatment often can have an important influence on outcome. In theoretical terms, a focus on the white matter and its disorders promises to expand knowledge of the brain as an extraordinarily complex organ in which the connectivity provided by white matter is central to cognition, emotion, and consciousness itself. As the details of white matter structure and function become clarified, a more complete portrait of the organ of the mind can be anticipated.

The ecology of bipolar disorder: the importance of sleep

Although much of the emphasis in treating Bipolar Disorder patients is on pharmacotherapy, sleep loss is an important trigger for mania and plays an important role in the condition. The purpose of this paper is to fully explore the chronobiological, environmental, social, and genetic factors that contribute to the sleep disruption that is characteristic of mania and bipolar disorder. This review is important because sleep, chronobiology, and genetics are under-emphasized content areas in nursing education. As a result, many practicing nurses are unaware of the importance of sleep for mental health or what to teach patients to improve both the quality of their sleep and the management of their condition.

Investigating responders to lithium prophylaxis as a strategy for mapping susceptibility genes for bipolar disorder

Attempts to map susceptibility genes for bipolar disorder have been complicated by genetic complexity of the illness and, above all by heterogeneity. This paper reviews the genetic research of bipolar disorder aiming to reduce the heterogeneity by focusing on definite responders to long-term lithium treatment. The available evidence strongly suggests that lithium-responsive bipolar disorder is the core bipolar phenotype, characterized by a more prominent role of genetic factors. Responders to lithium have typically a family history of bipolar disorder (often responsive to lithium). They differ from responders to other mood stabilizing drugs in their family histories as well as in other clinical characteristics. The molecular genetic investigations of bipolar disorder responsive to lithium indicate possibly several loci linked to and/or associated with the illness. A combination of research strategies employing multiple methods such as linkage, association, and gene-expression studies will be needed to clarify which of these represent true susceptibility loci.

The emergence of a new paradigm of pharmacogenomics

A series of qualitatively new properties of the complex polygenic systems are transforming the dominant, genome-centric approach of pharmacogenomics towards a more integrative, holistic paradigm. The recent concepts of interposition of regulatory networks between genotype and phenotype, and the emergence of epigenotype as the locus of integration of genetic background with nutritional and lifestyle influences, render problematic any prediction of the consequences of individual gene alterations. In addition, the redefinition of the traditional boundaries of clinical phenotypes, with the promotion of the endophenotypes as methodological strategy, and the initiative of the phenome elucidation, reshape both the research, as well as the application, of pharmacogenomics. These concepts and developments can explain some of the complexity, and the multifactorial nature, of most drug responses and imply another understanding of education in the field, which aims at stimulating a critical reflection on these major shifts prior to a practical training on the immediate application of pharmacogenomics.

Glycogen synthase kinase-3: a putative molecular target for lithium mimetic drugs

Despite many decades of clinical use, the therapeutic target of lithium remains uncertain. It is recognized that therapeutic concentrations of lithium, through competition with the similarly sized magnesium cation, inhibit the activity of select enzymes. Among these is glycogen synthase kinase-3 (GSK-3). Recent preclinical evidence, including biochemical, pharmacological, genetic, and rodent behavioral models, supports the hypothesis that inhibition of GSK-3 may represent a target for lithium's mood-stabilizing properties. Specifically, it has been demonstrated that lithium administration regulates multiple GSK-3 targets in vivo and that multiple additional classes of mood-stabilizing and antidepressant drugs regulate GSK-3 signaling. Pharmacological or genetic inhibition of GSK-3 results in mood stabilizer-like behavior in rodent models, and genetic association studies implicate GSK-3 as a possible modulator of particular aspects of bipolar disorder including response to lithium. Furthermore, numerous recent studies have provided a more complete understanding of GSK-3's role in diverse neurological processes strengthening the hypothesis that GSK-3 may represent a therapeutically relevant target of lithium. For example, GSK-3 is a primary regulator of neuronal survival, and cellular responses to glucocorticoids and estrogen may involve GSK-3-regulated pathways. While the preclinical evidence discussed in this review is encouraging, ultimate validation of GSK-3 as a therapeutically relevant target will require clinical trials of selective novel inhibitors. In this regard, as is discussed, there is a major effort underway to develop novel, specific, GSK-3 inhibitors.

Biochemical characterization of the recombinant human Drosophila homologues Timekeeper and Andante involved in the Drosophila circadian oscillator

The Drosophila clock proteins timekeeper (CK2a(Tik)) and andante (CK2beta(And)) are mutated CK2alpha and CK2beta subunits, respectively. In order to revisit the hypothesis concerning a perturbation of the beta/beta and/or alpha/beta subunit association, involving the andante mutant we have cloned, expressed and purified the recombinant andante mutant CK2beta(And) and a CK2 holoenzyme composed of CK2beta(And) and the wildtype CK2alpha subunit. Biochemical analyses using gel filtration analysis, inhibitor and heat treatment, as well as urea denaturation studies did not yield significant differences between the wildtype holoenzyme (alpha2beta2) and a holoenzyme containing wildtype CK2alpha and andante CK2beta(And). The timekeeper mutant, CK2alpha(Tik) has been reported to show a significant reduction in enzyme activity. In order to closely investigate the reason for this reduction in activity, we have also cloned and expressed the human homologue of Drosophila timekeeper. Using a CK2 holoenzyme containing the human timekeeper mutant and the wildtype CK2beta subunit we could confirm a strongly reduced activity towards CK2 substrates, but also a significant reduction in the autophosphorylation of the CK2beta in the absence of any substrate. Based on a structure-based model we postulate that the mutation M161K in Drosophila (i.e. M163K in human) is responsible for the drastic loss of activity, where the lysine residue may cause improper binding of the tri-nucleotide.

Human development: biological and genetic processes

Adaptation is a central organizing principle throughout biology, whether we are studying species, populations, or individuals. Adaptation in biological systems occurs in response to molar and molecular environments. Thus, we would predict that genetic systems and nervous systems would be dynamic (cybernetic) in contrast to previous conceptualizations with genes and brains fixed in form and function. Questions of nature versus nurture are meaningless, and we must turn to epigenetics--the way in which biology and experience work together to enhance adaptation throughout thick and thin. Defining endophenotypes--road markers that bring us closer to the biological origins of the developmental journey--facilitates our understanding of adaptive or maladaptive processes. For human behavioral disorders such as schizophrenia and autism, the inherent plasticity of the nervous system requires a systems approach to incorporate all of the myriad epigenetic factors that can influence such outcomes.

Bipolar disorder and diabetes mellitus: epidemiology, etiology, and treatment implications

INTRODUCTION

Bipolar disorder (BD) is a highly prevalent and disabling condition with significant mortality risk from suicide and other unnatural causes. This ignominious description is alongside recent observations that the majority of excess deaths in BD are secondary to medical comorbidity. The medical burden in BD is associated with a clustering of risk factors (e.g., obesity, smoking, unhealthy dietary habits) and inadequate utilization of preventative and primary healthcare. Diabetes mellitus (DM) is also a prevalent multifactorial disease which imparts substantial illness burden. Preliminary investigations indicate that patients who suffer from BD with comorbid DM have a more severe course and outcome, lower quality of life, higher prevalence of medical comorbidity and higher cost of illness.

METHODS

We conducted a MedLine search of all English-language articles 1966-2004 using the key words: bipolar disorder, major depressive disorder, diabetes mellitus, glucose metabolism, mortality, overweight, obesity, body mass index. The search was supplemented with manual review of relevant references. Priority was given to randomized controlled data, when unavailable; studies of sufficient sample size are presented.

RESULTS

Subpopulations of BD patients should be considered at high risk for DM. The prevalence of DM in BD may be three times greater than in the general population.

CONCLUSIONS

Bipolar disorder populations may be an at-risk group for glucose metabolic abnormalities. Opportunistic screening and vigilance for clinical presentations suggestive of DM is encouraged.

Regulation of gene expression by lithium and depletion of inositol in slices of adult rat cortex

Lithium inhibits inositol monophosphatase at therapeutically effective concentrations, and it has been hypothesized that depletion of brain inositol levels is an important chemical alteration for lithium's therapeutic efficacy in bipolar disorder. We have employed adult rat cortical slices as a model to investigate the gene regulatory consequences of inositol depletion effected by lithium using cytidine diphosphoryl-diacylglycerol as a functionally relevant biochemical marker to define treatment conditions. Genes coding for the neuropeptide hormone pituitary adenylate cyclase activating polypeptide (PACAP) and the enzyme that processes PACAP's precursor to the mature form, peptidylglycine alpha-amidating monooxygenase, were upregulated by inositol depletion. Previous work has shown that PACAP can increase tyrosine hydroxylase (TH) activity and dopamine release, and we found that the gene for GTP cyclohydrolase, which effectively regulates TH through synthesis of tetrahydrobiopterin, was also upregulated by inositol depletion. We propose that modulation of brain PACAP signaling might represent a new opportunity in the treatment of bipolar disorder.

Glycogen synthase kinase-3beta haploinsufficiency mimics the behavioral and molecular effects of lithium

Lithium is widely used to treat bipolar disorder, but its mechanism of action in this disorder is unknown. Several molecular targets of lithium have been identified, but these putative targets have not been shown to be responsible for the behavioral effects of lithium in vivo. A robust model for the effects of chronic lithium on behavior in mice would greatly facilitate the characterization of lithium action. We describe behaviors in mice that are robustly affected by chronic lithium. Remarkably, these lithium-sensitive behaviors are also observed in mice lacking one copy of the gene encoding glycogen synthase kinase-3beta (Gsk-3beta), a well established direct target of lithium. In addition, chronic lithium induces molecular changes consistent with inhibition of GSK-3 within regions of the brain that are paralleled in Gsk-3beta+/- heterozygous mice. We also show that lithium therapy activates Wnt signaling in vivo, as measured by increased Wnt-dependent gene expression in the amygdala, hippocampus, and hypothalamus. These observations support a central role for GSK-3beta in mediating behavioral responses to lithium.

[Changes in brain structure in bipolar affective disorders]

The neurobiological basis of bipolar affective disorders is unknown. However, neuroanatomic circuits of mood regulation have been hypothesized. Neuroimaging revealed volumetric changes of specific brain structures in these circuits. The most prominent abnormality is enlargement of the amygdala. In addition there might be structural changes in the frontal lobe, cerebellum, and pituitary. The findings in bipolar disorder differ from those in unipolar depression and schizophrenia. For further identification of the neurobiological basis of bipolar disorders, structural neuroimaging combined with functional neuroimaging such as magnetic resonance spectroscopy, neuroendocrinological studies, and genetical analyses are required to subgroup patients with bipolar disorder by diagnostic, prognostic, and therapeutic criteria.

Long-term response to lithium salts in bipolar illness is influenced by the glycogen synthase kinase 3-beta -50 T/C SNP

The molecular mechanisms driving the biological clock in the suprachiasmatic nucleus of the hypothalamus may play a role in mood disorders. A single nucleotide polymorphism (SNP) (-50 T/C) falling into the effective promoter region (nt -171 to +29) of the gene coding for glycogen synthase kinase 3-beta (GSK3-beta) has been linked with different age at onset of bipolar illness and with different antidepressant effects of total sleep deprivation. GSK3-beta codes for an enzyme which is a target for the action of lithium and possibly of valproic acid. We studied the effect of this polymorphism on the therapeutic response to lithium salts of 88 bipolar type I patients. Data about recurrence rate of mood episodes were collected for at least 2 years before lithium and 2 years on lithium. Results showed that homozygotes for the wild variant did not change their recurrence index while carriers of the mutant allele improved, thus supporting the hypothesis that GSK is a target for the therapeutic action of lithium. Results warrant interest for the variants of genes pertaining to the molecular clock as possible endophenotypes of bipolar disorder, but caution ought to be taken in interpreting these preliminary results and future replication studies must be awaited because of the low frequency of the GSK3-beta*C/C genotype in the studied populations.

Neural network analysis in pharmacogenetics of mood disorders

Background

The increasing number of available genotypes for genetic studies in humans requires more advanced techniques of analysis. We previously reported significant univariate associations between gene polymorphisms and antidepressant response in mood disorders. However the combined analysis of multiple gene polymorphisms and clinical variables requires the use of non linear methods.

Methods

In the present study we tested a neural network strategy for a combined analysis of two gene polymorphisms. A Multi Layer Perceptron model showed the best performance and was therefore selected over the other networks. One hundred and twenty one depressed inpatients treated with fluvoxamine in the context of previously reported pharmacogenetic studies were included. The polymorphism in the transcriptional control region upstream of the 5HTT coding sequence (SERTPR) and in the Tryptophan Hydroxylase (TPH) gene were analysed simultaneously.

Results

A multi layer perceptron network composed by 1 hidden layer with 7 nodes was chosen. 77.5 % of responders and 51.2% of non responders were correctly classified (ROC area = 0.731 – empirical p value = 0.0082). Finally, we performed a comparison with traditional techniques. A discriminant function analysis correctly classified 34.1 % of responders and 68.1 % of non responders (F = 8.16 p = 0.0005).

Conclusions

Overall, our findings suggest that neural networks may be a valid technique for the analysis of gene polymorphisms in pharmacogenetic studies. The complex interactions modelled through NN may be eventually applied at the clinical level for the individualized therapy.