Possible locus for bipolar disorder near the dopamine transporter on chromosome 5

Nature and nurture? A review of the literature on childhood maltreatment and genetic factors in the pathogenesis of borderline personality disorder

BACKGROUND

Borderline Personality Disorder (BPD) is a psychiatric disorder associated with significant morbidity and mortality. However, the neurobiological alterations underlying the condition remain poorly understood. As a result, existing treatments remain inadequate. One of the main risk factors for the development of BPD is a history of childhood maltreatment. However, it is considered neither causative nor specific to the condition. Current theory is therefore increasingly moving toward a 'Gene x Environment' (GxE) model of the condition. The purpose of the current work was to conduct a systematic literature review, which comprehensively identifies all published molecular level GxE studies that have explored the role of specific genetic loci, in influencing the risk of BPD following exposure to childhood abuse or neglect.

METHODS

Four electronic databases were used to systematically search for molecular level GxE studies of any design, which focused on the development of BPD following exposure to childhood abuse or neglect, without language or date restrictions. Articles were screened independently by two reviewers and results were synthesized narratively.

RESULTS

A total of 473 articles were screened of which sixteen were selected for inclusion in our review. Implicated genes were categorised according to their influence on; Neurotransmitter Systems, Neurodevelopment and Neuroendocrine Systems.

CONCLUSIONS

The identified studies have produced several relevant and statistically significant results. Of particular note, is the repeated finding that genes involved in HPA axis regulation, may be altered by exposure to childhood maltreatment, influencing subsequent susceptibility to BPD. This is both biologically plausible and of potential clinical significance.

Dopamine transporter mutant animals: a translational perspective

The dopamine transporter (DAT) plays an important homeostatic role in the control of both the extracellular and intraneuronal concentrations of dopamine, thereby providing effective control over activity of dopaminergic transmission. Since brain dopamine is known to be involved in numerous neuropsychiatric disorders, investigations using mice with genetically altered DAT function and thus intensity of dopamine-mediated signaling have provided numerous insights into the pathology of these disorders and novel pathological mechanisms that could be targeted to provide new therapeutic approaches for these disorders. In this brief overview, we discuss recent investigations involving animals with genetically altered DAT function, particularly focusing on translational studies providing new insights into pathology and pharmacology of dopamine-related disorders. Perspective applications of these and newly developed models of DAT dysfunction are also discussed.

Evaluation of VNTR polymorphisms of dopamine transporter gene and the risk of bipolar disorder in Zahedan, southeast Iran

The exact role of dopamine transporter gene (DAT1) in the pathogenesis of bipolar disorder type 1 (BD) is not understood. In the present study, we aimed to evaluate the possible association between 30, 40 and 63 bp variable number tandem repeat (VNTR) polymorphisms of DAT1 gene and the risk of type 1 (BD) in a sample of Iranian population. This case-control study was performed on 152 BD patients and 153 psychiatrically healthy subjects. Genotyping of the variant was done by polymerase chain reaction method. Totally, the findings did not support an association between DAT1 VNTR polymorphisms and the risk of BD in a sample of southeast Iranian population.

Genealogy Study of Three Generations of Patients with Bipolar Mood Disorder Type I

INTRODUCTION

The purpose of this research is genealogy examination of three generation of bipolar mood disorder Type I patients.

METHODS

Patients selected using Poisson sampling method from 100 patients with bipolar mood disorder Type I, referring to a psychiatric center of Amir Kabir Hospital of Arak, Iran. Examine issues such as physical ailments, psychological review of living and deceased family members of each patient, drawn family pedigree using pedigree chart, check the relationship of the different pattern of the autosomal dominant and recessive disease, sex-linked dominant and recessive and linked to Y chromosome have been performed on patients. Different methods used in this study are pedigree chart and young mania rating scale and SPSS and Pearson's correlation test for analyzing the data collected.

RESULTS

Among the studied inheritance patterns, the most common inheritance pattern was autosomal recessive. There was a significant relationship between age, number of generation, and inheritance patterns with physical ailments in families of patients with bipolar mood disorder (P < 0.05), but there was no significant association with mental illness (P > 0.05). Furthermore, there was a significant relation between generation and skin, gastrointestinal, ovarian, lung, coronary heart disease, diabetes mellitus, hypertension, Cerebrovascular accident (CVA), hyperlipidemia, cardiomyopathy, hypothyroidism, and kidney disease in patients with bipolar affective disorder Type I (P < 0.05).

CONCLUSION

The results showed that autosomal recessive was the most pattern of inheritance and there is a significant relationship between generation and some physical disorders in patients with bipolar mood disorder Type I.

Core, social and moral disgust are bounded: A review on behavioral and neural bases of repugnance in clinical disorders

Disgust is a multifaceted experience that might affect several aspects of life. Here, we reviewed research on neurological and psychiatric disorders that are characterized by abnormal disgust processing to test the hypothesis of a shared neurocognitive architecture in the representation of three disgust domains: i) personal experience of 'core disgust'; ii) social disgust, i.e., sensitivity to others' expressions of disgust; iii) moral disgust, i.e., sensitivity to ethical violations. Our review provides some support to the shared neurocognitive hypothesis and suggests that the insula might be the "hub" structure linking the three domains of disgust sensitivity, while other brain regions may subserve specific facets of the multidimensional experience. Our review also suggests a role of serotonin core and moral disgust, supporting "neo-sentimentalist" theories of morality, which posit a causal role of affect in moral judgment.

Positive Traits in the Bipolar Spectrum: The Space between Madness and Genius

Bipolar disorder is a severe, lifelong mood disorder for which little is currently understood of the genetic mechanisms underlying risk. By examining related dimensional phenotypes, we may further our understanding of the disorder. Creativity has a historical connection with the bipolar spectrum and is particularly enhanced among unaffected first-degree relatives and those with bipolar spectrum traits. This suggests that some aspects of the bipolar spectrum may confer advantages, while more severe expressions of symptoms negatively influence creative accomplishment. Creativity is a complex, multidimensional construct with both cognitive and affective components, many of which appear to reflect a shared genetic vulnerability with bipolar disorder. It is suggested that a subset of bipolar risk variants confer advantages as positive traits according to an inverted-U-shaped curve with clinically unaffected allele carriers benefitting from the positive traits and serving to maintain the risk alleles in the population. The association of risk genes with creativity in healthy individuals (e.g., NRG1), as well as an overall sharing of common genetic variation between bipolar patients and creative individuals, provides support for this model. Current findings are summarized from a multidisciplinary perspective to demonstrate the feasibility of research in this area to reveal the mechanisms underlying illness.

Excited Delirium and Sudden Death: A Syndromal Disorder at the Extreme End of the Neuropsychiatric Continuum

Over the past decade, the excited delirium syndrome (ExDS) has raised continued controversy regarding the cause and manner of death of some highly agitated persons held in police custody, restrained or incapacitated by electrical devices. At autopsy, medical examiners have difficulty in identifying an anatomic cause of death, but frequently cite psychostimulant intoxication as a contributing factor. The characteristic symptoms of ExDS include bizarre and aggressive behavior, shouting, paranoia, panic, violence toward others, unexpected physical strength, and hyperthermia. Throughout the United States and Canada, these cases are most frequently associated with cocaine, methamphetamine, and designer cathinone abuse. Acute exhaustive mania and sudden death presents with behavioral symptoms that are identical to what is described for ExDS in psychostimulant abusers. Bell's mania or acute exhaustive mania was first described in the 1850's by American psychiatrist Luther Bell in institutionalized psychiatric patients. This rare disorder of violent mania, elevated body temperature and autonomic collapse continued to be described by others in the psychiatric literature, but with different names until the first cases of ExDS were seen at the beginning of the cocaine epidemic by medical examiners. The neurochemical pathology examination of brain tissues after death revealed a loss of dopamine transporter regulation together with increases in heat shock protein 70 (hsp70) expression as a biomarker of hyperthermia. The similarity in the behavioral symptoms between extremely agitated psychostimulant abusers and unmedicated psychiatric patients suggests that a genetic disorder that leads to dysregulated central dopamine transporter function could be a precipitating cause of the acute delirium and sudden death. While the precise cause and mechanism of lethality remains controversial, the likely whys and wherefores of sudden death of ExDS victims are seen to be "biological," since excessive dopamine in the brain triggers the manic excitement and delirium, which unabated, culminates in a loss of autonomic function that progresses to cardiorespiratory collapse.

The mood stabilizer valproic acid opposes the effects of dopamine on circadian rhythms

Endogenous circadian (∼24 h) clocks regulate key physiological and cognitive processes via rhythmic expression of clock genes. The main circadian pacemaker is the hypothalamic suprachiasmatic nucleus (SCN). Mood disorders, including bipolar disorder (BD), are commonly associated with disturbed circadian rhythms. Dopamine (DA) contributes to mania in BD and has direct impact on clock gene expression. Therefore, we hypothesized that high levels of DA during episodes of mania contribute to disturbed circadian rhythms in BD. The mood stabilizer valproic acid (VPA) also affects circadian rhythms. Thus, we further hypothesized that VPA normalizes circadian disturbances caused by elevated levels of DA. To test these hypotheses, we examined locomotor rhythms and circadian gene cycling in mice with reduced expression of the dopamine transporter (DAT-KD mice), which results in elevated DA levels and mania-like behavior. We found that elevated DA signaling lengthened the circadian period of behavioral rhythms in DAT-KD mice and clock gene expression rhythms in SCN explants. In contrast, we found that VPA shortened circadian period of behavioral rhythms in DAT-KD mice and clock gene expression rhythms in SCN explants, hippocampal cell lines, and human fibroblasts from BD patients. Thus, DA and VPA have opposing effects on circadian period. To test whether the impact of VPA on circadian rhythms contributes to its behavioral effects, we fed VPA to DAT-deficient Drosophila with and without functioning circadian clocks. Consistent with our hypothesis, we found that VPA had potent activity-suppressing effects in hyperactive DAT-deficient flies with intact circadian clocks. However, these effects were attenuated in DAT-deficient flies in which circadian clocks were disrupted, suggesting that VPA functions partly through the circadian clock to suppress activity. Here, we provide in vivo and in vitro evidence across species that elevated DA signaling lengthens the circadian period, an effect remediated by VPA treatment. Hence, VPA may exert beneficial effects on mood by normalizing lengthened circadian rhythm period in subjects with elevated DA resulting from reduced DAT.

Identification of rare high-risk copy number variants affecting the dopamine transporter gene in mental disorders

BACKGROUND

The dopamine transporter, also known as solute carrier 6A3 (SLC6A3), plays an important role in synaptic transmission by regulating the reuptake of dopamine in the synapses. In line with this, variations in the gene encoding this transporter have been linked to both schizophrenia and affective disorders. Recently, copy number variants (CNVs) in SLC6A3 have been identified in healthy subjects but so far, the implication of CNVs affecting this gene in psychiatric diseases has not been addressed.

AIMS

In the present study, we aimed to investigate whether CNVs affecting SLC6A3 represent rare high-risk variants of psychiatric disorders.

METHODS

We performed a systematic screening for CNVs affecting SLC6A3 in 761 healthy controls, 672 schizophrenia patients, and 194 patients with bipolar disorder in addition to 253 family members from six large pedigrees affected by mental disorders using single nucleotide polymorphism arrays and subsequent verification by real-time polymerase chain reaction.

RESULTS

We identified two duplications and one deletion affecting SLC6A3 in the patients, while no such CNVs were identified in any of the controls. The identified CNVs were of different sizes and two affected several genes in addition to SLC6A3.

CONCLUSION

Our findings suggest that rare high-risk CNVs affecting the gene encoding the dopamine transporter contribute to the pathogenesis of schizophrenia and affective disorders.

The catecholaminergic-cholinergic balance hypothesis of bipolar disorder revisited

Bipolar disorder is a unique illness characterized by fluctuations between mood states of depression and mania. Originally, an adrenergic-cholinergic balance hypothesis was postulated to underlie these different affective states. In this review, we update this hypothesis with recent findings from human and animal studies, suggesting that a catecholaminergic-cholinergic hypothesis may be more relevant. Evidence from neuroimaging studies, neuropharmacological interventions, and genetic associations support the notion that increased cholinergic functioning underlies depression, whereas increased activations of the catecholamines (dopamine and norepinephrine) underlie mania. Elevated functional acetylcholine during depression may affect both muscarinic and nicotinic acetylcholine receptors in a compensatory fashion. Increased functional dopamine and norepinephrine during mania on the other hand may affect receptor expression and functioning of dopamine reuptake transporters. Despite increasing evidence supporting this hypothesis, a relationship between these two neurotransmitter systems that could explain cycling between states of depression and mania is missing. Future studies should focus on the influence of environmental stimuli and genetic susceptibilities that may affect the catecholaminergic-cholinergic balance underlying cycling between the affective states. Overall, observations from recent studies add important data to this revised balance theory of bipolar disorder, renewing interest in this field of research.

Heritability and genome-wide SNP linkage analysis of temperament in bipolar disorder

BACKGROUND

The many attempts to identify genes for bipolar disorder (BD) have met with limited success, which has generally been attributed to genetic heterogeneity and small gene effects. However, it is also possible that the categorical phenotypes used in genetic studies of BD are not the most informative or biologically relevant. We have explored aspects of temperament as quantitative phenotypes for BD through the use of the Temperament Evaluation of Memphis, Pisa, Paris, and San Diego Auto-questionnaire (TEMPS-A), which is designed to assess lifelong, milder aspects of bipolar symptomatology and defines five temperaments: hyperthymic, dysthymic, cyclothymic, irritable, and anxious.

METHODS

We compared temperament scores between diagnostic groups and assessed heritability in a sample of 101 families collected for genetic studies of BD. A genome-wide SNP linkage study was then performed in the subset of 51 families for which genetic data was available.

RESULTS

Significant group differences were observed between BD subjects, their first-degree relatives, and independent controls, and all five temperaments were found to be significantly heritable, with heritabilities ranging from 21% for the hyperthymic to 52% for the irritable temperaments. Suggestive evidence for linkage was observed for the hyperthymic (chromosomes 1q44, 2p16, 6q16, and 14q23), dysthymic (chromosomes 3p21 and 13q34), and irritable (chromosome 6q24) temperaments.

LIMITATIONS

The relatively small size of our linkage sample likely limited our ability to reach genome-wide significance in this study.

CONCLUSIONS

While not genome-wide significant, these results suggest that aspects of temperament may prove useful in the identification of genes underlying BD susceptibility.

Association of dopamine transporter gene variants with childhood ADHD features in bipolar disorder

Bipolar disorder (BD) and attention deficit hyperactivity disorder (ADHD) exhibit remarkably high rates of comorbidity, as well as patterns of familial co-segregation. Epidemiological data suggests that these disorders either share a common genetic architecture or that ADHD features in BD may represent an etiologically distinct subtype. We previously used the Wender Utah Rating Scale (WURS) to assess ADHD features in BD families and identified three heritable factors relating to impulsivity, mood instability, and inattention. Linkage analysis revealed a LOD score of 1.33 for the inattention factor on 5p15.3 near the dopamine transporter gene (DAT1), which has been associated with both BD and ADHD. Pharmacological evidence also suggests a role for DAT in both disorders. We have now evaluated the association of ten DAT1 variants for the WURS total score and factors in an overlapping sample of 87 BD families. Significant associations for three SNPs were observed across the WURS measures, notably for a SNP in intron 8 with the WURS total score (P = 0.007) and for variants in introns 9 and 13 with mood instability (P = 0.009 and 0.004, respectively). Analysis of an independent sample of 52 BD cases and 46 healthy controls further supported association of the intron 8 variant with mood instability (P = 0.005), and a combined analysis confirmed the associations of this SNP with WURS total score. Impulsivity and mood instability (P = 0.002, 0.007, and 8 × 10(-4), respectively). These data suggest that variants within DAT1 may predispose to a subtype of BD characterized by early prodromal features that include attentional deficits.

The relationship between oxidative stress and post-translational modification of the dopamine transporter in bipolar disorder

Bipolar disorder (BD) has been consistently associated with altered levels of oxidative stress markers, although the cause and consequences of these alterations remain to be elucidated. One of the main hypotheses regarding the pathogenesis of mania involves increased dopaminergic transmission. In this review, the authors aim to discuss a potential mechanism by which increased oxidative stress inhibits the uptake of dopamine through the post-translational modification of the dopamine transporter and its implications for BD. Within the next 5 years, the authors believe that the mechanisms of dopamine transporter oxidation and its impact on the pathophysiology of BD will be elucidated, which may open avenues for the development of more specific interventions for the treatment of this debilitating illness.

Molecular linkage studies of bipolar disorder

Linkage studies have defined at least five bipolar (BP) disorder susceptibility loci that meet suggested guidelines for initial identification and subsequent confirmation. These loci, found on 18p11, 18q22, 21q21, 4p16, and Xq26, are targets for BP candidate gene investigations. Molecular dissection of expressed sequences for these regions is likely to yield specific BP susceptibility alleles in most cases, in all probability, these BP susceptibility alleles will be common in the general population, and, individually, will be neither necessary nor sufficient for manifestation syndrome. Additive or multiplicative oligogenic models involving several susceptibility loci appear most reasonable at present, it is hoped thai these BP susceptibility genes will increase understanding of many mysteries surrounding these disorders, including drug response, cycling patterns, age-of-onset, and modes of transmission.

Anticonvulsant drugs in bipolar disorder

Although much progress has been made in successfully treating bipolar disorder, there is increasing awareness of the limitations of traditional treatment regimens such as lithium and neuroleptics. The large family of anticonvulsant drugs, however, appears to be capable of providing new treatment options, not only as medication of second choice in patients refractory to treatment, but often as a treatment standard with high efficacy and low incidence of side effects. Besides established mood stabilizers such as carbamazepine and valproate, new antiepileptic drugs are entering the field with promising initial results in the treatment of bipolar patients. Furthermore, bringing to light the mechanisms of action of anticonvulsants and the similarities between anticonvulsants effective in bipolar disorder may also deepen our understanding of the pathophysiological basis of the disorder.

The influence of five monoamine genes on trajectories of depressive symptoms across adolescence and young adulthood

The influence of five monoamine candidate genes on depressive symptom trajectories in adolescence and young adulthood were examined in the Add Health genetic sample. Results indicated that, for all respondents, carriers of the dopamine receptor D4 5-repeat allele were characterized by distinct depressive symptom trajectories across adolescence and early adulthood. Similarly, for males, individuals with the monoamine oxidase A 3.5-repeat allele exhibited unique depressive symptom trajectories. Specifically, the trajectories of those with the dopamine receptor D4 5-repeat allele were characterized by rising levels in the transition to adulthood, while their peers were experiencing a normative drop in depressive symptom frequency. Conversely, males with the monoamine oxidase A 3.5-repeat allele were shown to experience increased distress in late adolescence. An empirical method for examining a wide array of allelic combinations was employed, and false discovery rate methods were used to control the risk of false positives due to multiple testing. Special attention was given to thoroughly interrogate the robustness of the putative genetic effects. These results demonstrate the value of combining dynamic developmental perspectives with statistical genetic methods to optimize the search for genetic influences on psychopathology across the life course.

Predictive animal models of mania: hits, misses and future directions

Mania has long been recognized as aberrant behaviour indicative of mental illness. Manic states include a variety of complex and multifaceted symptoms that challenge clear clinical distinctions. Symptoms include over-activity, hypersexuality, irritability and reduced need for sleep, with cognitive deficits recently linked to functional outcome. Current treatments have arisen through serendipity or from other disorders. Hence, treatments are not efficacious for all patients, and there is an urgent need to develop targeted therapeutics. Part of the drug discovery process is the assessment of therapeutics in animal models. Here we review pharmacological, environmental and genetic manipulations developed to test the efficacy of therapeutics in animal models of mania. The merits of these models are discussed in terms of the manipulation used and the facet of mania measured. Moreover, the predictive validity of these models is discussed in the context of differentiating drugs that succeed or fail to meet criteria as approved mania treatments. The multifaceted symptomatology of mania has not been reflected in the majority of animal models, where locomotor activity remains the primary measure. This approach has resulted in numerous false positives for putative treatments. Recent work highlights the need to utilize multivariate strategies to enable comprehensive assessment of affective and cognitive dysfunction. Advances in therapeutic treatment may depend on novel models developed with an integrated approach that includes: (i) a comprehensive battery of tests for different aspects of mania, (ii) utilization of genetic information to establish aetiological validity and (iii) objective quantification of patient behaviour with translational cross-species paradigms.

Further evidence for linkage of bipolar disorder to chromosomes 6 and 17 in a new independent pedigree series

OBJECTIVES

We have previously reported the results of a linkage analysis of bipolar disorder in an initial set of 20 pedigrees ascertained through collaboration among three sites. We now report the results of our genome-wide linkage analysis in an independent sample of 34 pedigrees segregating bipolar disorder.

METHODS

Families were ascertained through a bipolar I or II disorder proband for the presence of bipolar I disorder, bipolar II disorder, or recurrent major depression in at least two other family members. A total of 440 markers at an average spacing of 8 cM were genotyped in 229 family members using fluorescent methods.

RESULTS

Initial nonparametric analyses of chromosomes 6 and 17 provided evidence for a modest replication of linkage to these chromosomes previously reported in other studies. Additional analyses using multipoint parametric methods provided further evidence to support the 6q25 region with a heterogeneity logarithm of odds score of 3.28. Evidence from two-point parametric analyses also provides a modest replication of our previous findings of linkage to the 23 cM region of chromosome 22q13 in our original University of California, San Diego sample of 20 families and 57 families from the National Institute of Mental Health bipolar disorder sample.

CONCLUSIONS

Our results suggest replication of some reported linkage peaks, such as 6q25 and 17p12; however, other peaks from our own previous study, such as 5p15, 13q32, and 22q13, were either not replicated or were only modestly replicated in these analyses.

RETRACTED: Dysregulated glutamate and dopamine transporters in postmortem frontal cortex from bipolar and schizophrenic patients

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of The National Institutes of Health has found that the first author, Dr. Jagadeesh S. Rao engaged in research misconduct by falsifying data in “Dysregulated glutamate and dopamine transporters in postmortem frontal cortex from bipolar and schizophrenic patients”. Rao JS, Kellom M, Reese EA, Rapoport SI, Kim HW. J. Affect Disord. 136(1–2):63–71. 2012. Data in Figures 2A, 2B, 3A, 3B and 4A were falsified.

Rodent versions of the iowa gambling task: opportunities and challenges for the understanding of decision-making

Impaired decision-making is a core problem in several psychiatric disorders including attention-deficit/hyperactivity disorder, schizophrenia, obsessive–compulsive disorder, mania, drug addiction, eating disorders, and substance abuse as well as in chronic pain. To ensure progress in the understanding of the neuropathophysiology of these disorders, animal models with good construct and predictive validity are indispensable. Many human studies aimed at measuring decision-making capacities use the Iowa gambling task (IGT), a task designed to model everyday life choices through a conflict between immediate gratification and long-term outcomes. Recently, new rodent models based on the same principle have been developed to investigate the neurobiological mechanisms underlying IGT-like decision-making on behavioral, neural, and pharmacological levels. The comparative strengths, as well as the similarities and differences between these paradigms are discussed. The contribution of these models to elucidate the neurobehavioral factors that lead to poor decision-making and to the development of better treatments for psychiatric illness is considered, along with important future directions and potential limitations.

Increased risk-taking behavior in dopamine transporter knockdown mice: further support for a mouse model of mania

Reduced functioning of the dopamine transporter (DAT) has been linked to bipolar disorder (BD). Mice with reduced DAT functioning (knockdown, KD) exhibit a behavioral profile in the mouse Behavioral Pattern Monitor (BPM) consistent with patients with BD mania in the human BPM. Patients with BD also exhibit increased risk taking, which can be quantified using the Iowa Gambling Task (IGT). We hypothesized that DAT KD mice would exhibit increased risk-taking behavior in a novel mouse version of the IGT. DAT KD and wildtype (WT) littermates were trained in the mouse IGT. In session 1, KD mice initially made riskier choices, but later performed comparably to WT mice. Once trained to stable choice performance, DAT KD mice continued to exhibit a trend to choose the riskier options more than WT mice. Finally, we confirmed that these DAT KD mice also exhibited an exploratory profile in the BPM consistent with patients with BD mania, where risky choice behavior modestly correlated with specific exploration. These data demonstrate that DAT KD mice chose the riskier options more than WT mice, providing further support for the use of DAT KD mice as a model of BD mania.

Correlates of first-episode polarity in a French cohort of 1089 bipolar I disorder patients: role of temperaments and triggering events

OBJECTIVES

As only a few studies so far systematically reported on bipolar patients subtyped according to first-episode polarity, we took the opportunity of having at disposal a large sample of bipolar I patients to specify the characteristics of patients included in these subtypes, with a special focus on temperament and triggering events.

METHODS

A total of 1089 consecutive DSM-IV bipolar I manic inpatients were subtyped in manic onset (MO), depressive onset (DO) and mixed onset (MXO), and assessed for demographic, illness course, clinical, psychometric, comorbidity and temperament characteristics.

RESULTS

The main characteristics of MO patients were a hyperthymic temperamental predisposition, a first episode triggered by substance abuse and an illness course with pure, severe and psychotic mania. In comparison, DO patients had more depressive temperaments, a first episode triggered by stress and alcohol, an illness course with more episodes, cyclicity, suicide attempts, anxious comorbidity and residual symptoms. Although sharing characteristics with either MO or DO, MXO patients had more mixed episodes and cyclothymic temperament.

LIMITATIONS

The following are the limitations of this study: retrospective design, bias toward preferential enrolment of MO patients, and lack of information on the number and polarity of lifetime episodes.

CONCLUSIONS

Findings from this study tend to confirm most of the differences previously evidenced among patients subtyped according to first-episode polarity. Differences found in temperamental predisposition and illness onset triggering events are worth noting and may help target early preventive interventions as well as orientate the search for specific genetic risk factors.

Striatal structure and function in mood disorders: a comprehensive review

OBJECTIVES

  A large and diverse literature has implicated abnormalities of striatal structure and function in both unipolar and bipolar disorder. Recent functional imaging studies have greatly expanded this body of research. The aim of this review is to provide a comprehensive and critical appraisal of the relevant literature.

METHODS

  A total of 331 relevant articles were reviewed to develop an integrated overview of striatal function in mood disorders.

RESULTS

  There is compelling evidence from multiple studies that functional abnormalities of the striatum and greater corticostriatal circuitry exist in at least some forms of affective illness. The literature does not yet provide data to determine whether these aberrations represent primary pathology or they contribute directly to symptom expression. Finally, there is considerable evidence that bipolar disorder may be associated with striatal hyperactivity and some suggestion that unipolar illness may be associated with hypoactivation.

CONCLUSIONS

  Additional research investigating striatal function in affective disorders will be critical to the development of comprehensive models of the neurobiology of these conditions.

Decreased Serum Hepatocyte Growth Factor (HGF) in Individuals with Bipolar Disorder Normalizes after Zinc and Anti-oxidant Therapy

Aim:

To assess serum HGF concentration in individuals with bipolar disorder and investigate the efficacy of zinc therapy on these levels.

Subjects and methods:

Serum from 35 individuals diagnosed with bipolar disorder and 19 age and gender similar controls were tested for HGF concentration using ELISAs, and copper and zinc plasma levels using inductively-coupled plasma-mass spectrometry.

Results:

HGF serum levels of individuals with bipolar disorder were significantly lower than age and gender similar controls (P = 0.0021). HGF serum concentration was significantly lower in Bipolar patients pre-therapy (P = 0.0009) and HGF levels normalized post-therapy. Zinc levels in these same individuals also normalized (P = 0.0046) and patient’s perceived severity of Bipolar symptoms significantly decreased after therapy (P = 0.0003). We also found a significant direct correlation between Zinc and HGF serum concentration in the bipolar patients (P = 0.04).

Discussion:

These results suggest an association between low HGF levels and bipolar disorder and also demonstrate that zinc therapy may be associated with the normalization of HGF levels and decrease in severity of disease.

The mania-like exploratory profile in genetic dopamine transporter mouse models is diminished in a familiar environment and reinstated by subthreshold psychostimulant administration

Bipolar Disorder (BD) is a neuropsychiatric disorder characterized by symptoms ranging from a hyperactive manic state to depression, with periods of relative stability, known as euthymia, in between. Although prognosis for BD sufferers remains poor, treatment development has been restricted due to a paucity of validated animal models. Moreover, most models focus on the manic state of BD with little done to characterize the longitudinal behavior of these models. We recently presented two dopamine transporter (DAT) mouse models of BD mania: genetic (DAT knockdown; KD, mice) and pharmacological (the selective DAT inhibitor GBR 12909). These models exhibit an exploratory profile consistent with the quantified exploratory profile of manic BD patients observed in the cross-species translational test, the Behavioral Pattern Monitor (BPM). To further explore the suitability of these models, we examined the effects of reduced DAT function on the behavior of mice tested after familiarization to the BPM environment. Testing with 16mg/kg GBR 12909 in familiarized mice resulted in a consistent mania-like profile. In contrast, the mania-like profile of DAT KD mice disappears in a familiar environment, with partial reinstatement elicited by the introduction of novelty. In addition, we found that a subthreshold dose of GBR 12909 (9mg/kg) reinstated the mania-like profile in DAT KD mice without affecting wildtype behavior. Thus, the mania-like exploratory profile of DAT KD mice is reduced in a familiar environment, partially reinstated with novelty, but is fully restored when administered a stimulant that is ineffective in wildtype mice. These mice may provide a model of BD from mania to euthymia and back again with stimulant treatment. Acute blockade of the DAT by GBR 12909 however, may provide a consistent model for BD mania.

Interaction between serotonin 5-HT2A receptor gene and dopamine transporter (DAT1) gene polymorphisms influences personality trait of persistence in Austrian Caucasians

We examined 89 normal volunteers using Cloninger's Temperament and Character Inventory (TCI). Genotyping the 102T/C polymorphism of the serotonin 5HT2A receptor gene and the ser9gly polymorphism in exon 1 of the dopamine D3 receptor (DRD3) gene was performed using PCR-RFLP, whereas the dopamine transporter (DAT1) gene variable number of tandem repeats (VNTR) polymorphism was investigated using PCR amplification followed by electrophoresis in an 8% acrylamide gel with a set of size markers. We found a nominally significant association between gender and harm avoidance (P=0.017; women showing higher scores). There was no association of either DAT1, DRD3 or 5HT2A alleles or genotypes with any dimension of the TCI applying Kruskal-Wallis rank-sum tests. Comparing homozygote and heterozygote DAT1 genotypes, we found higher novelty seeking scores in homozygotes (P=0.054). We further found a nominally significant interaction between DAT1 and 5HT2A homo-/heterozygous gene variants (P=0.0071; DAT1 and 5HT2A genotypes P value of 0.05), performing multivariate analysis of variance (MANOVA). Examining the temperamental TCI subscales, this interaction was associated with persistence (genotypes: P=0.004; homo-/heterozygous gene variants: P=0.0004). We conclude that an interaction between DAT1 and 5HT2A genes might influence the temperamental personality trait persistence.

GBR 12909 administration as a mouse model of bipolar disorder mania: mimicking quantitative assessment of manic behavior

RATIONALE

Mania is a core feature of bipolar disorder (BD) that traditionally is assessed using rating scales. Studies using a new human behavioral pattern monitor (BPM) recently demonstrated that manic BD patients exhibit a specific profile of behavior that differs from schizophrenia and is characterized by increased motor activity, increased specific exploration, and perseverative locomotor patterns as assessed by spatial d.

OBJECTIVES

It was hypothesized that disrupting dopaminergic homeostasis by inhibiting dopamine transporter (DAT) function would produce a BD mania-like phenotype in mice as assessed by the mouse BPM.

METHODS

We compared the spontaneous locomotor and exploratory behavior of C57BL/6J mice treated with the catecholamine transporter inhibitor amphetamine or the selective DAT inhibitor GBR 12909 in the mouse BPM. We also assessed the duration of the effect of GBR 12909 by testing mice in the BPM for 3 h and its potential strain dependency by testing 129/SvJ mice.

RESULTS

Amphetamine produced hyperactivity and increased perseverative patterns of locomotion as reflected in reduced spatial d values but reduced exploratory activity in contrast to the increased exploration observed in BD patients. GBR 12909 increased activity and reduced spatial d in combination with increased exploratory behavior, irrespective of inbred strain. These effects persisted for at least 3 h.

CONCLUSIONS

Thus, selectively inhibiting the DAT produced a long-lasting cross-strain behavioral profile in mice that was consistent with that observed in manic BD patients. These findings support the use of selective DAT inhibition in animal models of the impaired dopaminergic homeostasis putatively involved in the pathophysiology of BD mania.

A reverse-translational study of dysfunctional exploration in psychiatric disorders: from mice to men

CONTEXT

Bipolar mania and schizophrenia are recognized as separate disorders but share many commonalities, which raises the question of whether they are the same disorder on different ends of a continuum. The lack of distinct endophenotypes of bipolar mania and schizophrenia has complicated the development of animal models that are specific to these disorders. Exploration is fundamental to survival and is dysregulated in these 2 disorders. Although exploratory behavior in rodents has been widely studied, surprisingly little work has examined this critical function in humans.

OBJECTIVES

To quantify the exploratory behavior of individuals with bipolar mania and schizophrenia and to identify distinctive phenotypes of these illnesses.

DESIGN

Static group comparison by the use of a novel human open field paradigm, the human Behavioral Pattern Monitor (BPM).

SETTING

Psychiatric hospital.

PARTICIPANTS

Fifteen patients with bipolar mania and 16 patients with schizophrenia were compared with 26 healthy volunteers in the human BPM. The effects of amphetamine sulfate, the selective dopamine transporter inhibitor GBR12909, and the genetic knockdown of the dopamine transporter were compared with controls in the mouse BPM.

MAIN OUTCOME MEASURES

The amount of motor activity, spatial patterns of activity, and exploration of novel stimuli were quantified in both the human and mouse BPMs.

RESULTS

Patients with bipolar mania demonstrated a unique exploratory pattern, characterized by high motor activity and increased object exploration. Patients with schizophrenia did not show the expected habituation of motor activity. Selective genetic or pharmacologic inhibition of the dopamine transporter matched the mania phenotype better than the effects of amphetamine, which has been the criterion standard for animal models of mania.

CONCLUSIONS

These findings validate the human open field paradigm and identify defining characteristics of bipolar mania that are distinct from those of schizophrenia. This cross-species study of exploration calls into question an accepted animal model of mania and should help to develop more accurate human and animal models, which are essential to the identification of the neurobiological underpinnings of neuropsychiatric disorders.

Atypical antipsychotics clozapine and quetiapine attenuate prepulse inhibition deficits in dopamine transporter knockout mice

Sensorimotor gating disruptions are seen in various psychiatric illnesses with putatively different pathologies, including schizophrenia and bipolar disorder. Interestingly, mice lacking the dopamine (DA) transporter (DAT) gene display markedly increased levels of DA, deficits in sensorimotor gating, and hyperactivity relative to wild-type mice. Atypical antipsychotics are effective treatments of schizophrenia and manic symptoms, presumably in part by antagonizing DA receptors. Here we report that treatment with clozapine (3 mg/kg) or quetiapine (2.5 mg/kg) attenuated prepulse inhibition deficits in male DAT knockout mice. Thus male DAT knockout mice may provide a useful animal model for predicting the efficacy of novel drugs in treating psychiatric illnesses characterized by a dysregulated DA system.

Family based association study of pediatric bipolar disorder and the dopamine transporter gene (SLC6A3)

The dopamine transporter gene (SLC6A3) is a compelling candidate for pediatric bipolar disorder because (a) it has been associated with ADHD, (b) bipolar comorbidity with ADHD has been hypothesized to be an etiologically distinct familial subtype (c) blockade of the dopamine transporter with psychostimulants can induce mania in susceptible individuals and (d) previous studies have implicated the gene in bipolar disorder in adults. We conducted a family-based association study of SLC6A3 in 170 affected offspring trios defined by a child (12.9 +/- 5.3 years of age)with DSM-IV Bipolar-I disorder. Twenty-eight tag SNPs were chosen from the CEU (European) population of the International HapMap project (www.hapmap.org). Results indicated nominally positive association for 4 SNPs (rs40184, rs11133767, rs3776512, and rs464049), but only rs40184 survived correction for multiple statistical comparisons (P = 0.038). This is the first examination of the association with SLC6A3 and bipolar disorder in children and, like previous findings in adults with bipolar disorder, we found evidence of association with SNPs in the 3' region of the gene. These data provide suggestive evidence supporting a role for SLC6A3 in the etiology of pediatric bipolar disorder.

Personality endophenotypes for bipolar affective disorder: a family-based genetic association analysis

Genetic analyses of complex conditions such as bipolar disorder (BD) may be facilitated by the use of intermediate phenotypes. Various personality traits are overrepresented in people with BD and their unaffected relatives, and may constitute genetically transmitted risk factors or endophenotypes of the illness. In this study, we administered a battery of seven different personality questionnaires comprising 19 subscales to 31 Caucasian BD families (n = 241). Ten of these personality traits showed significant evidence of heritability and were therefore selected as candidate endophenotypes. In addition, a principal components analysis produced two heritable components (negative affect and appetitive drive), which accounted for a considerable proportion of the variance (29% + 12%) and were also used in the analysis. A family-based quantitative association study was carried out using the orthogonal model from the quantitative transmission disequilibrium tests (QTDT) program. Monte Carlo permutations (M = 500), which allow for non-normal data and provide a global P value, corrected for multiple testing, were used to calculate empirical P values for the within-family component of association. The 3' untranslated region repeat polymorphism of the dopamine transporter gene (SLC6A3) was associated with self-directedness (P < 0.0001) and negative affect (P = 0.010). The short allele of the serotonin transporter gene (SLC6A4) promoter polymorphism showed a trend toward association with higher harm avoidance (P = 0.016) and negative affect (P = 0.028). The catechol-o-methyltransferase val158met polymorphism was weakly associated with the personality traits, 'Spirituality' (P = 0.040) and irritable temperament (P = 0.022). Furthermore, the met allele of the brain-derived neurotrophic factor val66met polymorphism was associated with higher hyperthymic temperament scores. We raise the possibility that the 10R allele of the SLC6A3 repeat polymorphism and the short allele of the SLC6A4 promoter variant constitute risk factors for irritable-aggressive and anxious-dysthymic subtypes of BD, respectively.

Frontiers between attention deficit hyperactivity disorder and bipolar disorder

The co-occurrence of attention deficit hyperactivity disorder (ADHD) and bipolar disorder has received much recent attention in the literature. The authors review the literature examining associations between ADHD and bipolar disorder in children, and data concerning severe irritability in youth with ADHD. This article focuses on (1) population-based studies examining ADHD and bipolar disorder or ADHD and co-occurring irritability, (2) the co-occurrence and prospective relationships of ADHD and bipolar disorder in clinical samples, (3) phenomenology and assessment of bipolar disorder and ADHD, (4) treatment of comorbid ADHD and bipolar disorder, (5) family and genetic studies of ADHD and bipolar disorder, and (6) pathophysiologic comparisons between children with ADHD and irritability and bipolar disorder. We draw on the research to make clinical recommendations and highlight important directions for future research.

Dopamine transporter 3'-UTR VNTR genotype and ADHD: a pharmaco-behavioural genetic study with methylphenidate

We sought to test the hypothesis that the variable number of tandem repeat (VNTR) polymorphism in the 3'-untranslated region (3'-UTR) of the SLC6A3 gene modulates behavior in children with ADHD and/or behavioral response to methylphenidate (MPH). One hundred and fifty-nine children with AHDH (6-12 years) were assessed with regard to the Conners' Global Index for parents (CGI-Parents) and teachers (CGI-Teachers) and the response of these behaviors to MPH (0.5 mg/kg/day) using a 2-week prospective within-subject (crossover) trial. Based on CGI-Parents, the profile of behavioral response to MPH as compared to placebo was not parallel in the three groups of children separated according to their genotype in the 3'-UTR VNTR polymorphism of SLC6A3, as indicated by a significant (p=0.017) genotype by treatment two-way interaction. Individuals having the 9/10 and 10/10 genotypes displayed a significant positive response to MPH as opposed to those homozygous for the 9-repeat allele. No genotype or genotype by treatment interaction was observed for CGI-Teachers. These findings support a role for the DAT gene 3'-UTR VNTR polymorphism in modulating the response of some behavioral dimensions to MPH in children with ADHD. They also suggest the presence of genetic heterogeneity that could be indexed by the quality of behavioral response to MPH.

The functional impact of SLC6 transporter genetic variation

Solute carrier 6 (SLC6) is a gene family of ion-coupled plasma membrane cotransporters, including transporters of neurotransmitters, amino acids, and osmolytes that mediate the movement of their substrates into cells to facilitate or regulate synaptic transmission, neurotransmitter recycling, metabolic function, and fluid homeostasis. Polymorphisms in transporter genes may influence expression and activity of transporters and contribute to behavior, traits, and disease. Determining the relationship between the monoamine transporters and complex psychiatric disorders has been a particular challenge that is being met by evolving approaches. Elucidating the functional consequences of and interactions among polymorphic sites is advancing our understanding of this relationship. Examining the influence of environmental influences, especially early-life events, has helped bridge the gap between genotype and phenotype. Refining phenotypes, through assessment of endophenotypes, specific behavioral tasks, medication response, and brain network properties has also improved detection of the impact of genetic variation on complex behavior and disease.

Association study of 5'-UTR polymorphisms of the human dopamine transporter gene with manic depression

OBJECTIVES

To determine the degree of association of five single nucleotide polymorphisms at the 5'-untranslated region (5'-UTR) of the human dopamine transporter gene (hSLC6A3; hDAT1) in bipolar affective disorder.

METHODS

In a case-control design study, the polymorphisms were genotyped for allelic and genotypic distribution between 105 index cases (50 males) with bipolar affective disorder according to DSM IV and 199 unaffected control subjects (120 males).

RESULTS

At the 5'-UTR locus of hSLC6A3, no significant allelic or genotypic differences were observed between index cases and controls. However, distinct 5-locus genotypes accumulated in subjects with bipolar affective disorder compared to control subjects (p = 0.029, odds ratio 1.84, 95% confidence interval 1.12-3.02).

CONCLUSIONS

In conclusion, our data do not provide evidence for a major role of the 5'-UTR of the dopamine transporter gene in bipolar affective disorder. A minor contribution of distinct genotypes may be possible and warrants replication in extended samples.

A 40-basepair VNTR polymorphism in the dopamine transporter (DAT1) gene and the rapid response to antidepressant treatment

Finding predictors of the response to antidepressant therapy is a major goal of molecular psychiatry. The genes encoding the serotonin (SERT) and dopamine (DAT1) transporters are among the possible candidate genes modulating an individual's antidepressant response. In a naturalistic prospective cohort study with a total of 190 fully assessed patients, improvement of depression symptoms during the 3 weeks following initiation of antidepressant therapy was recorded using the 21-item Hamilton Depression Rating Scale (HDRS). The SLC6A3 3' UTR 40-bp variable number of tandem repeats (VNTR) and the SLC6A4 5' 44-bp insertion/deletion polymorphism were analyzed by polymerase chain reaction. There was a significantly smaller number of rapid responders among homozygous carriers of the DAT1 9-repeat allele (9/9) than among heterozygous (9/10) and homozygous (10/10) carriers of the 10-repeat allele (19 versus 37 versus 52%, respectively, P=0.0037). Median decline in HDRS score was 35, 40, and 52% in patients with the 9/9, 9/10, and 10/10 genotypes, respectively (P=0.013). The effect was found in all classes of medications (selective serotonin reuptake inhibitors (SSRIs), tricyclics, mirtazapine, venlafaxine) and statistically significant also within the subgroup of patients having received SSRIs. The serotonin promoter insertion/deletion genotype had no effect in the entire study group, but there was an insignificant trend of better response in the l/l and l/s carriers who received SSRIs or mirtazapine. In conclusion, the dopamine transporter VNTR polymorphism influenced rapid response to antidepressant therapy. Compared with homozygous carriers of the 10-repeat allele, carriers of the 9/10 genotype had an odds ratio (OR) calculated by logistic regression analysis of 1.6 (95% CI 0.8-3.2) and carriers of the 9/9 genotype had an OR of 6.0 (1.5-24.4) for no or poor response. Further studies are required to confirm this clinical association and to elucidate the underlying mechanisms.

Identification of additional variants within the human dopamine transporter gene provides further evidence for an association with bipolar disorder in two independent samples

The dopamine transporter (DAT) is the site of action of stimulants, and variations in the human DAT gene (DAT1) have been associated with susceptibility to several psychiatric disorders including attention deficit hyperactivity disorder (ADHD) and bipolar disorder. We have previously reported the association of bipolar disorder to novel SNPs in the 3' end of DAT1. We now report the identification of 20 additional SNPs in DAT1 for a total of 63 variants. We also report evidence for association to bipolar disorder in a second independent sample of families. Eight newly identified SNPs and 14 previously identified SNPs were analyzed in two independent samples of 50 and 70 families each using the transmission disequilibrium test. Two of the eight new SNPs, one in intron 8 and one in intron 13, were found to be moderately associated with bipolar disorder, each in one of the two independent samples. Analysis of haplotypes comprised of all 22 SNPs in sliding windows of five adjacent SNPs revealed an association to the region near introns 7 and 8 in both samples (empirical P-values 0.002 and 0.001, respectively, for the same window). The haplotype block structure observed in the gene in our previous study was confirmed in this sample with greater resolution allowing for discrimination of a third haplotype block in the middle of the gene. Together, these data are consistent with the presence of multiple variants in DAT1 that convey susceptibility to bipolar disorder.

A dopamine transporter mutation associated with bipolar affective disorder causes inhibition of transporter cell surface expression

The dopamine transporter (DAT) plays a crucial role in dopaminergic neurotransmission as it clears the extracellular space of dopamine (DA) and thus controls the concentration of active neurotransmitter. Genetic association studies have reported a variable number of tandem repeat polymorphisms in the 3'-noncoding region of the DAT gene implicating this protein in the development of various psychiatric disorders. In a sample of bipolar patients, two rare missense substitutions (A559V and E602G) have been identified, one of which (E602G) was inherited by the patient from her affected father. None of these mutations had been identified in any control subjects of this survey. Using a heterologous cellular expression system, we have analysed possible consequences of these mutations on functional properties of the encoded DAT protein. DA transport measurements and antagonist binding revealed that the A559V mutant protein is fully functional, whereas the E602G mutant is not. Further analyses by confocal microscopy showed that the E602G protein is transcribed and translated but not delivered to the cell surface. Taken together, our results suggest that this missense mutation has functional consequences thus supporting the need to screen larger samples of patients and their relatives for this rare but bipolar disorder-associated mutation in the DAT gene.

Lack of association between VNTR polymorphism of dopamine transporter gene (SLC6A3) and schizophrenia in a Brazilian sample

A role of dopaminergic dysfunction has been postulated in the aetiology of schizophrenia. We hypothesized that variations in the dopamine transporter gene (SLC6A3) may be associated with schizophrenia. We conducted case-control and family based analysis on the polymorphic SLC6A3 variable number tandem repeat (VNTR) in a sample of 220 schizophrenic patients, 226 gender and ethnic matched controls, and 49 additional case-parent trios. No differences were found in allelic or genotypic distributions between cases and controls and no significant transmission distortions from heterozygous parents to schizophrenic offspring were detected. Thus, our results do not support an association of the SLC6A3 VNTR with schizophrenia in our sample.

Human dopamine transporter gene variation: effects of protein coding variants V55A and V382A on expression and uptake activities

The human dopamine transporter (DAT, SLC6A3) is an important 15 exon gene for dopamine neurotransmission and dopamine recycling. Common exon 15 variable number tandem repeat variants can be associated with attention deficit/hyperactivity disorder. Rarer single nucleotide polymorphisms produce missense variants including V55A and V382A. We now report studies of the functional influences of these DAT protein-coding variants. In COS cell transient-expression assays, V382A displays about half of the dopamine uptake velocity Vmax and cocaine analog binding Bmax values of wildtype DAT. V382A lowers dopamine's potency in inhibiting cocaine analog binding by six-fold. Cells expressing V382A or mixtures of V382A and wildtype DAT both display reduced plasma membrane and increased perinuclear expression, consistent with dominant effects of V328A on expression. V55A expresses normally but reveals a 1.7-fold-lower Km for dopamine uptake. Individuals with these human DAT protein variants could display altered dopamine systems.

Promoter and intronic variants affect the transcriptional regulation of the human dopamine transporter gene

We have attempted to identify regions involved in the transcriptional regulation of the DAT1 (HUGO approved symbol SLC6A3) gene that may harbor functional variants predisposing to several neuropsychiatric disorders by examining haplotypes of various 5' and intronic regions for their effect on expression in a dopaminergic cell line. A 1.5-fold difference in regulatory activity was observed between haplotypes of the proximal promoter/intron 1 region, representing the two previously identified 5' clades. Although we found no effect on transcription with inclusion of the 9- and 10-repeat alleles of the 3' VNTR, introns 9, 12, and 14 appear to contain enhancer elements capable of increasing expression approximately 2-fold with respect to the promoter constructs. Differences in expression were also observed between two alleles of intron 14. These results thus suggest that it may be the particular combination of polymorphisms in a haplotype across the gene that ultimately affects DAT1 gene expression.

Genome-wide scan of bipolar disorder in 65 pedigrees: supportive evidence for linkage at 8q24, 18q22, 4q32, 2p12, and 13q12

The purpose of this study was to assess 65 pedigrees ascertained through a Bipolar I (BPI) proband for evidence of linkage, using nonparametric methods in a genome-wide scan and for possible parent of origin effect using several analytical methods. We identified 15 loci with nominally significant evidence for increased allele sharing among affected relative pairs. Eight of these regions, at 8q24, 18q22, 4q32, 13q12, 4q35, 10q26, 2p12, and 12q24, directly overlap with previously reported evidence of linkage to bipolar disorder. Five regions at 20p13, 2p22, 14q23, 9p13, and 1q41 are within several Mb of previously reported regions. We report our findings in rank order and the top five markers had an NPL>2.5. The peak finding in these regions were D8S256 at 8q24, NPL 3.13; D18S878 at 18q22, NPL 2.90; D4S1629 at 4q32, NPL 2.80; D2S99 at 2p12, NPL 2.54; and D13S1493 at 13q12, NPL 2.53. No locus produced statistically significant evidence for linkage at the genome-wide level. The parent of origin effect was studied and consistent with our previous findings, evidence for a locus on 18q22 was predominantly from families wherein the father or paternal lineage was affected. There was evidence consistent with paternal imprinting at the loci on 13q12 and 1q41.

Valproate attenuates hyperactive and perseverative behaviors in mutant mice with a dysregulated dopamine system

BACKGROUND

Dopamine transporter (DAT) knockdown (KD) mice, with approximately 90% loss of expression of the DAT, allow for the examination of the behavioral consequences of a chronically dysregulated dopamine system. The DAT KD mice have hyperdopaminergic tone, are hyperactive, and show impaired response inhibition in a number of paradigms. We hypothesized that the DAT KD mice would also display deficits in prepulse inhibition (PPI) and would be perseverative in their locomotor behavior.

METHODS

Basal levels of PPI and patterns of locomotor behavior were measured in two cohorts of DAT KD mice. In addition, measurements of locomotor behavior were recorded after pretreatment with 100 mg/kg valproate in both DAT KD and wildtype mice.

RESULTS

The DAT KD mice were hyperactive and displayed perseverative motor behavior but had normal levels of PPI. The clinically effective antimania drug valproate significantly attenuated the hyperactivity and perseverative locomotor behavior in the DAT KD mice and had no effect in control mice.

CONCLUSIONS

The DAT KD mice appear to provide a model of some aspects of manic behavior. With limited models of bipolar disorder, the DAT KD mice might provide a vehicle to screen for new psychiatric therapies to treat mania and its related symptoms.

Monoamine transporter gene structure and polymorphisms in relation to psychiatric and other complex disorders

The norepinephrine, dopamine and serotonin transporters (NET, DAT and SERT, respectively), limit cellular signaling by recapturing released neurotransmitter, and serve as targets for antidepressants and drugs of abuse, emphasizing the integral role these molecules play in neurotransmission and pathology. This has compelled researchers to search for polymorphisms in monoamine (MA) transporter genes. Studies support linkage and association of MA transporter genetic variation in psychiatric and other complex disorders. Understanding the contribution of MA transporter polymorphisms to human behavior, disease susceptibility and response to pharmacotherapies will involve further progress in linkage and association that will be aided by both definition of highly selective phenotypes and utilization of a large number of polymorphic markers. The relationship of polymorphisms to alterations in transport capacity, likely a complex interaction, involving genetic background, disease state, and medication, will elucidate the means by which MA transporter genetic variability contributes to our individuality.

Support for the presence of bipolar disorder susceptibility loci on chromosome 5: heterogeneity in a homogeneous population in Quebec

A very large pedigree derived from the Saguenay-Lac-St-Jean region of Quebec contains a branch where a distal chromosome 5q haplotype seems to cosegregate with bipolar affective disorder. The authors used a diagnosis model where Bipolar Types I and II and schizoaffective disorder bipolar type were considered as affected, while single or recurrent episode major depression was classified as unknown and all the others diagnoses as unaffected. Model-free two-point LOD score values of 3.41 and 2.21 were observed at D5S432 in the 5p region with sib_ibd and sib_phase from the ASPEX package, but simulation studies did not permit the conclusion of a significant linkage because associated empirical P values were equal to .0026 and .0037. A parametric LOD score value of 2.15 was obtained at locus D5S412 in the distal chromosome 5q area. In order to investigate heterogeneity in the single multigenerational family, the pedigree was divided into five branches. Our simulation study suggested that the five branches of the Saguenay-Lac-St-Jean bipolar pedigree had low power to detect linkage under intrapedigree heterogeneity in this region.

World Federation of Societies of Biological Psychiatry (WFSBP) guidelines for biological treatment of bipolar disorders. Part I: Treatment of bipolar depression

These practice guidelines for the biological, mainly pharmacological treatment of bipolar depression were developed by an international task force of the World Federation of Societies of Biological Psychiatry (WFSBP). Their purpose is to supply a systematic overview of all scientific evidence pertaining to the treatment of bipolar depression. The data used for these guidelines have been extracted from a MEDLINE and EMBASE search, and from recent proceedings of key conferences and various national and international treatment guidelines. Their scientific rigor was categorised into four levels of evidence (A-D). As these guidelines are intended for clinical use, the scientific evidence was not only graded, but also commented on by the experts of the task force to ensure practicability.

Segmental linkage disequilibrium within the dopamine transporter gene

The dopamine transporter gene (DAT) has been implicated in a variety of disorders, including bipolar disorder, attention-deficit hyperactivity disorder, cocaine-induced paranoia, Tourette's syndrome, and Parkinson's disease. As no clear functional polymorphism has been identified to date, studies rely on linkage disequilibrium (LD) to assess the possible genetic contribution of DAT to the various disorders. A better understanding of the complex structure of LD across the gene is thus critical for an accurate interpretation of the results of such studies, and may facilitate the mapping of the actual functional variants. In the process of characterizing the extent of variation within the DAT gene, we have identified a number of single nucleotide polymorphisms (SNPs) suitable for LD studies, 14 of which have been analyzed, along with a 3' repeat polymorphism, in a sample of 120 parent-proband triads. Calculations of pairwise LD between the SNPs in the parental haplotypes revealed a high degree of LD (P < 0.00001) in the 5' (distal promoter through intron 6) and 3' (exon 9 through exon 15) regions of DAT. This segmental LD pattern is maintained over approximately 27 kb and 20 kb in these two regions, respectively, with very little significant LD between them, possibly due to the presence of a recombination hotspot located near the middle of the gene. These analyses of the DAT gene thus reveal a complex structure resulting from both recombination and mutation, knowledge of which may be invaluable to the design of future studies.

Dopamine transporter gene (DAT1) VNTR polymorphism in major psychiatric disorders: family-based association study in the Bulgarian population

OBJECTIVE

A 40-bp variable number tandem repeat in the 3'-UTR of dopamine transporter gene (DAT1) has been examined for association with major psychiatric disorders in several case-control studies. No significant results have been found. We used a new collection of parent-offspring trios to test for association with schizophrenia (SZ), bipolar 1 disorder (BPI) and schizoaffective (SA) disorder.

METHOD

We genotyped trios from Bulgarian origin where the proband had SZ (178 trios), BPI (77 trios) and SA (29 trios). Alleles ranging from 5 to 11 repeats were observed. The results were analysed with the extended TDT (ETDT).

RESULTS

No preferential transmission of alleles was observed for any diagnostic group. The presence of allele DAT*10 was associated with the severity and frequency of auditory hallucinations, however, this result is not significant if corrected for multiple testing.

CONCLUSION

Our results are in agreement with previous reports of a lack of association between this polymorphism and major psychiatric disorders.

Bornavirus tropism and targeted pathogenesis: virus-host interactions in a neurodevelopmental model

Animal models provide unique opportunities to explore interactions between host and environment. Two models have been established based on Bornavirus infection that provide new insights into mechanisms by which neurotropic agents and/or immune factors may impact developing or mature CNS circuitry to effect complex disturbances in movement and behavior. Distinct losses in DA pathways in the adult infection model, and the associated dramatic movement disorder that accompanies it, make it an intriguing model for tardive dyskinesia and dystonic syndromes. The neuropathologic, physiologic, and neurobehavioral features of BDV infection of neonates indicate that it not only provides a useful model for exploring the mechanisms by which viral and immune factors may damage developing neurocircuitry, but also has significant links to the range of biologic, neurostructural, locomotor, cognitive, and social deficits observed in serious neuropsychiatric illnesses such as autism.

Population isolates: their special value for locating genes for bipolar disorder

OBJECTIVES

Population isolates offer several advantages for those hoping to identify predisposition genes for bipolar disorder (BP). In this review article, the rationale for performing gene mapping studies in this type of population and the results of genetic mapping studies performed to date in population isolates are presented.

METHODS

This article begins with a brief review of the concepts involved in mapping genes for BP. The concept of populations that show some degree of historical isolation and their special utility for certain types of gene mapping is presented. Methods of statistical analysis particularly relevant for gene mapping of complex diseases like BP are presented. Finally, several BP gene studies conducted to date in several population isolates are reviewed.

RESULTS

Genetic mapping studies of BP have occurred thus far in several isolates or sub-isolates, including the Amish population, Costa Ricans, Finnish, and Canadians (in Quebec), and significant linkage scores have been identified in the latter three isolates.

CONCLUSIONS

Possible greater homogeneity and greater consistency of diagnosis are factors that have been cited in several studies of BP done in isolates to date. Another special advantage of working in certain types of population isolate is their appropriateness for using certain types of association or linkage disequilibrium-based approaches at both the genome screening and fine mapping stages. These tests include mapping by linkage disequilibrium analyses, an approach that allows mapping to occur at the population, rather than the pedigree, level.