Understanding the genetic basis of mood disorders: where do we stand?

Obsessive-Compulsive Disorder and Decision Making under Ambiguity: A Systematic Review with Meta-Analysis

In the last decade, decision-making has been proposed to have a central role in obsessive-compulsive disorder (OCD) aetiology, since patients show pathological doubt and an apparent inability to make decisions. Here, we aimed to comprehensively review decision making under ambiguity, as measured by the Iowa Gambling Task (IGT), in OCD, using a meta-analytic approach. According to PRISMA Guidelines, we selected 26 studies for a systematic review and, amongst them, 16 studies were included in a meta-analysis, comprising a total of 846 OCD patients and 763 healthy controls (HC). Our results show that OCD patients perform significantly lower than HC at the IGT, pointing towards the direction of a decision making impairment. In particular, this deficit seems to emerge mainly in the last three blocks of the IGT. IGT scores in OCD patients under the age of 18 were still significantly lower than in HC. Finally, no difference emerged between medicated and unmedicated patients, since they both scored significantly lower at the IGT compared to HC. In conclusion, our results are in line with the hypothesis according to which decision making impairment might represent a potential endophenotype lying between the clinical manifestation of OCD and its neurobiological aetiology.

Slow Binocular Rivalry as a Potential Endophenotype of Schizophrenia

Objectives: Binocular rivalry is a typical example of bistable perception that arises when two monocular images are simultaneously presented to each eye. Binocular rivalry is a heritable perceptual cognitive function that is impaired in patients with schizophrenia (SZ). Despite its potential suitability as a visual endophenotype, binocular rivalry has hardly been studied in the unaffected siblings of schizophrenia (SIB). There is also little research about whether binocular rivalry is a potential visual endophenotype between SZ and SIB. Methods: In our cross-sectional study, we included 40 SZ and their unaffected SIBs, as well as 40 age- and sex-matched healthy controls (HC). All subjects underwent the binocular rivalry test, the Positive and Negative Syndrome Scale (PANSS) and a battery of cognitive neuropsychological assessments evaluating attention, memory and executive function domains. Results: Our results demonstrate that the switching rate in SZ was significantly slower than in HC (p < 0.001), and compared to the SIB, the mean alternation rates were significantly different (p < 0.01). Moreover, there was a significant difference in mean switching rate between the SIB and the HC (p < 0.001). There was no significant correlation between the alternation rate of binocular rivalry and these cognitive tasks and the PANSS scores. Conclusion: The present study shows that SZ and SIB both exhibit changes in binocular rivalry, with SIB exhibiting intermediate performance compared with that of SZ and the HC. This supports the claim that the switching rate for SZ differs from that of SIB and suggests that binocular rivalry may qualify as a visual endophenotype for SZ.

Dissociation of decision making under ambiguity and decision making under risk: a neurocognitive endophenotype candidate for obsessive-compulsive disorder

Evidence in the literature suggests that executive dysfunction is regarded as an endophenotype candidate for obsessive-compulsive disorder (OCD). Decision making is an important domain of executive function. However, few studies that have investigated whether decision making is a potential endophenotype for OCD have produced inconsistent results. Differences in the findings across these studies may be attributed to several factors: different study materials, comorbidity, medication, etc. There are at least two types of decision making that differ mainly in the degree of uncertainty and how much useful information about consequences and their probabilities are provided to the decision maker: decision making under ambiguity and decision making under risk. The aim of the present study was to simultaneously examine decision making under ambiguity as assessed by the Iowa Gambling Task (IGT) and decision making under risk as measured by the Game of Dice Task (GDT) in OCD patients and their unaffected first-degree relative (UFDR) for the first time. The study analyzed 55 medication-naïve, non-depressed OCD patient probands, 55 UFDRs of the OCD patients and 55 healthy matched comparison subjects (CS) without a family history of OCD with the IGT, the GDT and a neuropsychological test battery. While the OCD patients and the UFDRs performed worse than the CS on the IGT, they were unimpaired on the GDT. Our study supports the claim that decision making under ambiguity differs from decision making under risk and suggests that dissociation of decision making under ambiguity and decision making under risk may qualify to be a neurocognitive endophenotypes for OCD.

Casting a wider fish net on animal models in neuropsychiatric research

Neuropsychiatric disorders, such as schizophrenia, are associated with abnormal brain development. In this review, we discuss how studying dimensional components of these disorders, or endophenotypes, in a wider range of animal models will deepen our understanding of how interactions between biological and environmental factors alter the trajectory of neurodevelopment leading to aberrant behavior. In particular, we discuss some of the advantages of incorporating studies of brain and behavior using a range of teleost fish species into current neuropsychiatric research. From the perspective of comparative neurobiology, teleosts share a fundamental pattern of neurodevelopment and functional brain organization with other vertebrates, including humans. These shared features provide a basis for experimentally probing the mechanisms of disease-associated brain abnormalities. Moreover, incorporating information about how behaviors have been shaped by evolution will allow us to better understand the relevance of behavioral variation to determine their physiological underpinnings. We believe that exploiting the conservation in brain development across vertebrate species, and the rich diversity of fish behavior in lab and natural populations will lead to significant new insights and a holistic understanding of the neurobiological systems implicated in neuropsychiatric disorders.

Cluster randomized controlled trial of a psycho-educational intervention for people with a family history of depression for use in general practice

BACKGROUND

The strongest risk factor for depression is having a family history of the condition. Many individuals with a family history of depression are concerned about their personal risk for depression and report unmet educational and psychological support needs. No supportive and/or educational interventions are currently available that target this group of individuals. In this study we will develop and evaluate the first online psycho-educational intervention targeted to individuals with a family history of depression. Genetic risk information and evidence-rated information on preventive strategies for depression will be provided to such individuals in a general practice setting. The intervention will also incorporate a risk assessment tool. The content and delivery of the intervention will be pilot-tested.

METHODS/DESIGN

The proposed intervention will be evaluated in the general practitioner (GPs) setting, using a cluster randomized controlled trial. GP practices will be randomized to provide either access to the online, targeted psycho-educational intervention or brief generic information about depression (control) to eligible patients. Eligibility criteria include having at least one first-degree relative with either major depressive disorder (MDD) or bipolar disorder (BD). The primary outcome measure is 'intention to adopt, or actual adoption of, risk-reducing strategies'. Secondary outcome measures include: depression symptoms, perceived stigma of depression, knowledge of risk factors for development of depression and risk-reducing strategies, and perceived risk of developing depression or having a recurrence of family history. Over the course of the study, participants will complete online questionnaires at three time points: at baseline, and two weeks and six months after receiving the intervention or control condition.

DISCUSSION

This novel psycho-educational intervention will provide individuals with a family history of depression with information on evidence-based strategies for the prevention of depression, thus, we hypothesize, enabling them to make appropriate lifestyle choices and implement behaviors designed to reduce their risk for depression. The online psycho-educational intervention will also provide a model for similar interventions aimed at individuals at increased familial risk for other psychiatric disorders.

TRIAL REGISTRATION

The study is registered with the Australian and New Zealand Clinical Trials Group (Registration no: ACTRN12613000402741).

Cross-species behavioural genetics: A starting point for unravelling the neurobiology of human psychiatric disorders

Identifying the genetic and neurobiological mechanisms underlying certain behavioural traits is an important strategy to understand the aetiology of various psychiatric disorders and to find potential new treatment possibilities. It has proven a great challenge to develop paradigms that allow translational research for behavioural phenotypes that are relevant for disorders across the psychiatric spectrum. Recently, there has been increasing attention for studies that implement rodent behavioural paradigms in the home cage to assess the association between genetic backgrounds and behavioural traits. The application of interspecies genetics to unravel these traits has revealed novel insights in the genetic mechanisms that are encoding phenotypes relevant to biological processes underlying psychiatric disorders. By means of two examples, namely the stress-induced hyperthermia paradigm and the home cage environment, this review aims to show that by using individual genetic variations with phenotypes obtained from mice and across categories of neuropsychiatric disorders, novel insights in the neurobiological trajectory of psychiatric disorders can be obtained.

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.

Serotonin transporter gene-linked polymorphic region: possible pharmacogenetic implications of rare variants

A functional insertion/deletion (*l/*s) repeat polymorphism within the promoter region of the serotonin transporter (5-HTTLPR) has been described. An association between *l variant and a better and faster response to serotonin selective reuptake inhibitors in depressed patients was reported in Caucasians. The value of the explained variance due to the 5-HTTLPR, however, was 7% only, and different *l and *s variants were reported according to the nucleotide sequence of repeats. In this study, we investigated the antidepressant response to fluvoxamine in individuals carrying different *l and *s variants according to the Nakamura findings. Two hundred and twenty-eight patients affected by bipolar disorder and major depression were administered a daily dose of fluvoxamine up to 300 mg and evaluated at baseline and weekly thereafter until week 7, using the 21-item Hamilton Rating Scale for Depression. We found a marginally significant difference in genotype and allele (P=0.04, data not shown) distribution (*l and *s traditional variants) according to diagnosis (bipolar disorder vs. major depression). We confirmed a better and faster response in our depressed patients bearing the *l variant, but we also found significant differences in response among *l carriers according to the type of *l allele. In fact, 16F *l carriers showed only a partial response, while 16D *l carriers showed a marginally significantly better response than 16A *l allele carriers. These results, although very preliminary, can represent a further step toward a better understanding of the molecular genetics of antidepressant response.

A review of bipolar disorder in adults

OBJECTIVE

This article reviews the epidemiology, etiology, assessment, and management of bipolar disorder. Special attention is paid to factors that complicate treatment, including nonadherence, comorbid disorders, mixed mania, and depression.

METHODS

A Medline search was conducted from January of 1990 through December of 2005 using key terms of bipolar disorder, diagnosis, and treatment. Papers selected for further review included those published in English in peer-reviewed journals, with preference for articles based on randomized, controlled trials and consensus guidelines. Citations de-emphasized original mania trials as these are generally well known.

RESULTS

Bipolar disorder is a major public health problem, with diagnosis often occurring years after onset of the disorder. comorbid conditions are common and difficult to treat. Management includes a lifetime course of medication, usually more than one, and attention to psychosocial issues for patients and their families. Management of mania is well-established. Research is increasing regarding management of depressive, mixed and cycling episodes, as well as combination therapy.

CONCLUSIONS

Bipolar disorder is a complex psychiatric disorder to manage, even for psychiatrists, because of its many episodes and comorbid disorders and nonadherence to treatment.

Transmission distortion of BDNF variants to bipolar disorder type I patients from a South American population isolate

Recent reports have implicated polymorphisms in the brain derived neurotrophic factor (BDNF) gene region in the etiology of several psychiatric phenotypes, including bipolar disorder. Significant disease association has been reported for the G allele at SNP rs6265, which encodes for Valine at position 66 of BDNF (Val66Met), an apparently functional variant of this key BDNF. Here we examined a sample of 224 bipolar type I patients and available parents (comprising a total of 212 nuclear families) ascertained in a South American population isolate (Antioquia, Colombia). We tested for transmission distortion to bipolar patients of alleles at the rs6265 polymorphism and at a microsatellite marker 1.3 kb away from this SNP. Significant excess transmission of the rs6265 G allele to cases was observed (chi(2) = 10.77, d.f. = 1, P = 0.001). Two-locus haplotype analysis showed a significant global transmission distortion (chi(2) = 16.059, d.f. = 7, P = 0.025) with an excess transmission of a haplotype comprising the rs6265 G allele and microsatellite allele 227. These results are consistent with previous studies pointing to a role for BDNF in susceptibility to mood disorders.

Endophenotypes for psychiatric disorders: ready for primetime?

It is increasingly accepted that the imprecision of categorical psychiatric diagnoses can be a limiting factor in understanding the genetic basis of human behavioral abnormalities. Genetic investigation of endophenotypes--more precisely defined quantitative traits hypothesized to underlie disease syndromes--offers great promise as an alternative or complement to studies of categorical disease phenotypes. However, there is not yet standardization of the methods by which candidate endophenotypes should be chosen and applied. Fruitful endophenotype studies depend on the selection of heritable, quantitative traits that can be objectively and reliably measured. In this article, we propose guidelines for such investigations for psychiatric disorders, using endophenotypes previously proposed for bipolar disorder as particular examples. Gene expression studies and non-human primate models are recent developments in which an endophenotype approach might prove particularly valuable.

Implications of genetic risk information in families with a high density of bipolar disorder: an exploratory study

While major susceptibility genes for bipolar disorder are yet to be identified, the opportunity exists to systematically ascertain the important issues and societal implications of genetic risk determination for bipolar disorder prior to these technological advances becoming widely available. This study explores, in a sample of families with a high density of bipolar disorder: (i) attitudes to predictive genetic and prenatal testing, using different risk frames; (ii) attributions for bipolar disorder, in particular the degree to which a genetic model is endorsed; and (iii) the impact of these attributions on the perceived stigma of bipolar disorder. A qualitative methodology was selected as most appropriate as no previous research has examined this issue. Participants were ascertained through a molecular genetics study of bipolar disorder. In-depth interviews were conducted with 21 members of families with a high density of bipolar disorder. Most participants reported being interested in genetic testing if it gave a definitive answer, while expressed interest in testing was lower if it gave a probable answer only. Almost all stressed that a genetic susceptibility and environmental factors interacted. Most participants felt that a genetic explanation was likely to decrease the stigma associated with bipolar disorder as it shifted the locus of control and responsibility away from the individual towards the role of heredity. Findings indicate that expressed interest in genetic testing depends on the certainty imparted by the test. Results suggest that families with bipolar disorder are likely to benefit psychologically from information about the genetic basis of bipolar disorder.

The epidemiology of mood disorders

This review provides an overview of the epidemiology, risk factors, and genetic epidemiology of mood disorders in adults and children. The magnitude and impact of mood disorders in the community outweighs that of most other chronic diseases. Although there is substantial knowledge regarding the sociodemographic risk factors for mood disorders, our understanding of the pathogenesis and classification still is evolving. Comorbidity of mood disorders with anxiety disorders and substance abuse has been documented widely. Whereas substance abuse and mood disorders seem to be independent etiologically, anxiety and mood disorders result from partially common etiologic factors. The results of family, twin, and adoption studies reveal that a positive family history is the most potent risk factor for mood disorders, particularly bipolar disorder. However, the specific factors that are transmitted in families still are unknown. The two areas that will inform future genetic research include phenomenologic studies that refine the validity of the current phenotypic classification of mood disorders, and application of study designs to elucidate specific factors that may explain the familial transmission of these disorders.

Ancient DNA in anthropology: methods, applications, and ethics

Anthropologists were quick to recognize the potential of new techniques in molecular biology to provide additional lines of evidence on questions long investigated in anthropology, as well as those questions that, while always of interest, could not have been addressed by more traditional techniques. The earliest ancient DNA studies, both within anthropology and in other fields, lacked rigorous hypothesis testing. However, more recently the true value of ancient DNA studies is being realized, and methods are being applied to a wide variety of anthropological questions. We review the most common methods and applications to date, and describe promising avenues of future research. We find that ancient DNA analyses have a valuable place in the array of anthropological techniques, but argue that such studies must not be undertaken merely to demonstrate that surviving DNA is present in organic remains, and that no such work should be performed before a careful consideration of the possible ethical ramifications of the research is undertaken.

Gene admixture in the Costa Rican population

The general population of Costa Rica has sometimes been considered to be the product of an amalgamation of groups of diverse origin. To determine the magnitude of accumulated admixture since Spanish colonization, 11 classic genetic markers were analyzed in a total of 2196 individuals originating from five distinct regions of the country. A maximum likelihood approach was used. The proportions of genes of European, Amerindian and African ancestry were found to be 61%, 30% and 9% of the total population, respectively. Variation was observed at a regional level, with an increased European influence in the North (66%) and Central (65%) regions. Meanwhile an increase in Amerindian ancestry was found in the South (38%), and a higher incidence in the contribution of African genes was detected in the coastal regions (13% in the Atlantic and 14% in the North Pacific). A principal component (PC) analysis showed that 76% of the existing variability can be explained by the first two PCs, which is in agreement with the variations observed in the admixture process by geographic area. It has been concluded that the Costa Rican population is truly trihybrid, similar to populations in other Latin American countries; however, it differs from them fundamentally by the proportion of gene flow from ancestral populations.

Future of genetics of mood disorders research

This report summarizes the deliberations of a panel with representation from diverse disciplines of relevance to the genetics of mood disorders. The major charge to the panel was to develop a strategic plan to employ the tools of genetics to advance the understanding, treatment, and outcomes for mood disorders. A comprehensive review of the evidence for the role of genetic factors in the etiology of mood disorders was conducted, and the chief impediments for progress in gene identification were identified. The National Institute of Mental Health (NIMH) portfolios in the Genetics Research Branch and the Division of Mental Disorders, Behavioral Sciences, AIDS, and all genetics training activities were reviewed. Despite some promising leads, there are still no confirmed linkage findings for mood disorders. Impediments to gene finding include the lack of phenotypic validity, variation in ascertainment sources and methodology across studies, and genetic complexity. With respect to linkage, the committee recommended that a large-scale, integrated effort be undertaken to examine existing data from linkage and association studies of bipolar disorders using identical phenotypes and statistical methods across studies to determine whether the suggestive linkage findings at some loci can be confirmed. Confirmation would justify more intensive approaches to gene finding. The committee recommended that the NIMH support continued efforts to identify the most heritable subtypes and endophenotypes of major depression using the tools of genetic epidemiology, neuroscience, and behavioral science. The field of genetic epidemiology was identified as an important future direction because population-based, epidemiologic studies of families and unrelated affected individuals assume increasing importance for common chronic diseases. To prepare for shifts to more complex genetic models, the committee recommended that the NIMH develop new interdisciplinary training strategies to prepare for the next generation of genetics research.

Fine-scale mapping of a locus for severe bipolar mood disorder on chromosome 18p11.3 in the Costa Rican population

We have searched for genes predisposing to bipolar disorder (BP) by studying individuals with the most extreme form of the affected phenotype, BP-I, ascertained from the genetically isolated population of the Central Valley of Costa Rica (CVCR). The results of a previous linkage analysis on two extended CVCR BP-I pedigrees, CR001 and CR004, and of linkage disequilibrium (LD) analyses of a CVCR population sample of BP-I patients implicated a candidate region on 18p11.3. We further investigated this region by creating a physical map and developing 4 new microsatellite and 26 single-nucleotide polymorphism markers for typing in the pedigree and population samples. We report the results of fine-scale association analyses in the population sample, as well as evaluation of haplotypes in pedigree CR001. Our results suggest a candidate region containing six genes but also highlight the complexities of LD mapping of common disorders.

Molecular targets of lithium action

Lithium is highly effective in the treatment of bipolar disorder and also has multiple effects on embryonic development, glycogen synthesis, hematopoiesis, and other processes. However, the mechanism of lithium action is still unclear. A number of enzymes have been proposed as potential targets of lithium action, including inositol monophosphatase, a family of structurally related phosphomonoesterases, and the protein kinase glycogen synthase kinase-3. These potential targets are widely expressed, require metal ions for catalysis, and are generally inhibited by lithium in an uncompetitive manner, most likely by displacing a divalent cation. Thus, the challenge is to determine which target, if any, is responsible for a given response to lithium in cells. Comparison of lithium effects with genetic disruption of putative target molecules has helped to validate these targets, and the use of alternative inhibitors of a given target can also lend strong support for or against a proposed mechanism of lithium action. In this review, lithium sensitive enzymes are discussed, and a number of criteria are proposed to evaluate which of these enzymes are involved in the response to lithium in a given setting.

Cultural influences on diagnosis and perception of Tourette syndrome in Costa Rica

BACKGROUND AND OBJECTIVES

Tourette syndrome (TS) is a neuropsychiatric disorder in which the pattern of symptom presentation can vary greatly between individuals. Although globally described, TS has not been well characterized in many parts of the world. Differences in individual and cultural perceptions of TS may impact its expression and recognition in some countries, confounding the identification of affected individuals. This study examines the phenomenology and presentation of TS in Costa Rica.

METHOD

Clinical data on 85 Costa Rican subjects with TS (aged 5-29 years) initially recruited for a genetic study between 1996 and early 2000 were obtained by direct interview and review of medical records.

RESULTS

The clinical characteristics of TS were similar to that found elsewhere. The gender ratio was 4.6:1, the mean age of onset was 6.1 years, and 20% of subjects had coprolalia. However, the perceived impact of TS was different. Many subjects denied that their TS caused impairment or distress, even when objective evidence of impairment was available.

CONCLUSIONS

TS in Costa Rica is phenomenologically similar to TS seen in other parts of the world, but differs in perceived impairment. In other countries where cultural forces affect disease definition, close scrutiny of symptom expression and possible adjustment of phenotype definition may be important.

Genome screening for linkage disequilibrium in a Costa Rican sample of patients with bipolar-I disorder: a follow-up study on chromosome 18

Linkage disequilibrium (LD) methods offer great promise for mapping complex traits, but have thus far been applied sparingly. In this paper we describe an LD mapping study of severe bipolar disorder (BP-I) in the genetically isolated population of the Central Valley of Costa Rica. This study provides the first complete screen of a chromosome for a complex trait using LD mapping and presents the first application of a new LD mapping statistic (ancestral haplotype reconstruction (AHR)) that evaluates haplotype sharing among affected individuals. The results of this chromosome-wide analysis are instructive for genome-wide LD mapping in isolated populations. Furthermore, the analysis continues to support a possible BP-I locus on 18pter, suggested by previous analyses in this population. Evidence for a possible BP-I locus on 18q12.2 is also described.

An association study of bipolar mood disorder (type I) with the 5-HTTLPR serotonin transporter polymorphism in a human population isolate from Colombia

The short variant of a functional length polymorphism in the promoter region of the serotonin transporter has been associated with several behavioural and psychiatric traits, including bipolar mood disorder. The same short allele has also been implicated as a modifier of the bipolar phenotype. Here we evaluate the etiologic/modifier role of this polymorphism in a case (N=103) / control (N=112) sample for bipolar mood disorder (type I) collected from an isolated South American population. We did not detect an association between bipolar disorder and the 5-HTT promoter polymorphism in this sample. However, an excess of the short allele was seen in younger cases and in cases with psychotic symptoms. When combined with data from the literature, the increased frequency of the short allele in patients with psychotic symptoms was statistically significant.

Support for the availability of prenatal testing for neurological and psychiatric conditions in the psychiatric community

Faculty and residents of the University of Michigan Department of Psychiatry, members of the Alliance for the Mentally Ill (AMI), and university students were surveyed to elicit attitudes toward the availability of prenatal testing and genetic therapy or enhancement for early- and late-onset psychiatric diseases compared to neurological disorders and human traits. They were asked to complete a written questionnaire designed to assess their opinions as to whether prenatal testing and genetic therapy or enhancement should be applied to 16 selected "disease" phenotypes or human traits: eight early- and late-onset psychiatric conditions, four neurological disorders, and four human traits. Twenty-two percent returned the written survey. The majority of all respondents supported the availability of prenatal testing for well-defined, serious psychiatric or neurological phenotypes and found testing for human traits less desirable. The percentages of respondents supporting availability of testing increased if in utero curative gene therapy was available. Response to the survey differed on the basis of gender and age, as well as personal versus professional familiarity with the condition. The results of this pilot study suggest that a majority of the population, including psychiatrists, will support the public availability of prenatal diagnosis for serious psychiatric or neurological phenotypes, even if no in utero curative therapy is available. Support for testing for human traits was not strongly endorsed.