Targeted genome screen of panic disorder and anxiety disorder proneness using homology to murine QTL regions

Fear extinction requires ASIC1a-dependent regulation of hippocampal-prefrontal correlates

Extinction of conditioned fear necessitates the dynamic involvement of hippocampus, medial prefrontal cortex (mPFC), and basolateral amygdala (BLA), but key molecular players that regulate these circuits to achieve fear extinction remain largely unknown. Here, we report that acid-sensing ion channel 1a (ASIC1a) is a crucial molecular regulator of fear extinction, and that this function requires ASIC1a in ventral hippocampus (vHPC), but not dorsal hippocampus, mPFC, or BLA. While genetic disruption or pharmacological inhibition of ASIC1a in vHPC attenuated the extinction of conditioned fear, overexpression of the channel in this area promoted fear extinction. Channelrhodopsin-2-assisted circuit mapping revealed that fear extinction involved an ASIC1a-dependent modification of the long-range hippocampal-prefrontal correlates in a projection-specific manner. Gene expression profiling analysis and validating experiments identified several neuronal activity-regulated and memory-related genes, including Fos, Npas4, and Bdnf, as the potential mediators of ASIC1a regulation of fear extinction. Mechanistically, genetic overexpression of brain-derived neurotrophic factor (BDNF) in vHPC or supplement of BDNF protein in mPFC both rescued the deficiency in fear extinction and the deficits on extinction-driven adaptations of hippocampal-prefrontal correlates caused by the Asic1a gene inactivation in vHPC. Together, these results establish ASIC1a as a critical constituent in fear extinction circuits and thus a promising target for managing adaptive behaviors.

Genome-wide QTL analysis for anxiety trait in bipolar disorder type I

BACKGROUND

Genetic studies have been consistent that bipolar disorder type I (BPI) runs in families and that this familial aggregation is strongly influenced by genes. In a preliminary study, we proved that anxiety trait meets endophenotype criteria for BPI.

METHODS

We assessed 619 individuals from the Central Valley of Costa Rica (CVCR) who have received evaluation for anxiety following the same methodological procedure used for the initial pilot study. Our goal was to conduct a multipoint quantitative trait linkage analysis to identify quantitative trait loci (QTLs) related to anxiety trait in subjects with BPI. We conducted the statistical analyses using Quantitative Trait Loci method (Variance-components models), implemented in Sequential Oligogenic Linkage Analysis Routines (SOLAR), using 5606 single nucleotide polymorphism (SNPs).

RESULTS

We identified a suggestive linkage signal with a LOD score of 2.01 at chromosome 2 (2q13-q14).

LIMITATIONS

Since confounding factors such as substance abuse, medical illness and medication history were not assessed in our study, these conclusions should be taken as preliminary.

CONCLUSIONS

We conclude that region 2q13-q14 may harbor a candidate gene(s) with an important role in the pathophysiology of BPI and anxiety.

Genetics of anxiety: would the genome recognize the DSM?

The nosology of anxiety disorders has undergone substantial evolution over the past several decades. The modern classification of these disorders dates to the publication of Diagnostic and Statistical Manual-III (DSM-III) in 1980, but the validity of the current diagnostic categories has been the subject of controversy. Genetic research can help clarify the boundaries of diagnostic categories by examining the etiologic relationships among them. The question posed in the title of this article asks to what degree the DSM-IV definitions of the anxiety disorders are supported by the evolving body of research on the genetic basis of pathologic anxiety. With DSM-V on the horizon, there is a renewed imperative to examine the structure of these disorders. In this article, we address this issue by, first, providing a brief update about the current status of genetic research on anxiety disorders and then considering whether the evidence suggests that genetic influences conform to or transcend DSM definitions. Finally, we discuss future directions for the genetic dissection of anxiety disorders.

The Genetics of Stress-Related Disorders: PTSD, Depression, and Anxiety Disorders

Research into the causes of psychopathology has largely focused on two broad etiologic factors: genetic vulnerability and environmental stressors. An important role for familial/heritable factors in the etiology of a broad range of psychiatric disorders was established well before the modern era of genomic research. This review focuses on the genetic basis of three disorder categories-posttraumatic stress disorder (PTSD), major depressive disorder (MDD), and the anxiety disorders-for which environmental stressors and stress responses are understood to be central to pathogenesis. Each of these disorders aggregates in families and is moderately heritable. More recently, molecular genetic approaches, including genome-wide studies of genetic variation, have been applied to identify specific risk variants. In this review, I summarize evidence for genetic contributions to PTSD, MDD, and the anxiety disorders including genetic epidemiology, the role of common genetic variation, the role of rare and structural variation, and the role of gene-environment interaction. Available data suggest that stress-related disorders are highly complex and polygenic and, despite substantial progress in other areas of psychiatric genetics, few risk loci have been identified for these disorders. Progress in this area will likely require analysis of much larger sample sizes than have been reported to date. The phenotypic complexity and genetic overlap among these disorders present further challenges. The review concludes with a discussion of prospects for clinical translation of genetic findings and future directions for research.

Acid-Sensing Ion Channels as Potential Pharmacological Targets in Peripheral and Central Nervous System Diseases

Acid-sensing ion channels (ASICs) are widely expressed in the body and represent good sensors for detecting protons. The pH drop in the nervous system is equivalent to ischemia and acidosis, and ASICs are very good detectors in discriminating slight changes in acidity. ASICs are important pharmacological targets being involved in a variety of pathophysiological processes affecting both the peripheral nervous system (e.g., peripheral pain, diabetic neuropathy) and the central nervous system (e.g., stroke, epilepsy, migraine, anxiety, fear, depression, neurodegenerative diseases, etc.). This review discusses the role played by ASICs in different pathologies and the pharmacological agents acting on ASICs that might represent promising drugs. As the majority of above-mentioned pathologies involve not only neuronal dysfunctions but also microvascular alterations, in the next future, ASICs may be also considered as potential pharmacological targets at the vasculature level. Perspectives and limitations in the use of ASICs antagonists and modulators as pharmaceutical agents are also discussed.

The RS685012 Polymorphism of ACCN2, the Human Ortholog of Murine Acid-Sensing Ion Channel (ASIC1) Gene, is Highly Represented in Patients with Panic Disorder

Panic disorder (PD) is a disabling anxiety disorder that is characterized by unexpected, recurrent panic attacks, associated with fear of dying and worrying about possible future attacks or other behavioral changes as a consequence of the attacks. The acid-sensing ion channels (ASICs) are a family of proton-sensing channels expressed throughout the nervous system. Their activity is linked to a variety of behaviors including fear, anxiety, pain, depression, learning, and memory. The human analog of ASIC1a is the amiloride-sensitive cation channel 2 (ACCN2). Adenosine A2A receptors are suggested to play an important role in different brain circuits and pathways involved in anxiety reactions. In this work we aimed to evaluate the distribution of ACCN2 rs685012 and ADORA2A rs2298383 polymorphisms in PD patients compared with healthy subjects. We found no association between ADORA2A polymorphism and PD. Instead, the C mutated allele for ACCN2 rs685012 polymorphism was significantly more frequent in patients than in controls. On the contrary, the TT homozygous wild-type genotype and also the ACCN2 TT/ADORA2A CT diplotype were significantly more represented in controls. These results are suggestive for a role of ACCN2 rs685012 polymorphism in PD development in Caucasian people.

The nature of individual differences in inhibited temperament and risk for psychiatric disease: A review and meta-analysis

What makes us different from one another? Why does one person jump out of airplanes for fun while another prefers to stay home and read? Why are some babies born with a predisposition to become anxious? Questions about individual differences in temperament have engaged the minds of scientists, psychologists, and philosophers for centuries. Recent technological advances in neuroimaging and genetics provide an unprecedented opportunity to answer these questions. Here we review the literature on the neurobiology of one of the most basic individual differences-the tendency to approach or avoid novelty. This trait, called inhibited temperament, is innate, heritable, and observed across species. Importantly, inhibited temperament also confers risk for psychiatric disease. Here, we provide a comprehensive review of inhibited temperament, including neuroimaging and genetic studies in human and non-human primates. We conducted a meta-analysis of neuroimaging findings in inhibited humans that points to alterations in a fronto-limbic-basal ganglia circuit; these findings provide the basis of a model of inhibited temperament neurocircuitry. Lesion and neuroimaging studies in non-human primate models of inhibited temperament highlight roles for the amygdala, hippocampus, orbitofrontal cortex, and dorsal prefrontal cortex. Genetic studies highlight a role for genes that regulate neurotransmitter function, such as the serotonin transporter polymorphisms (5-HTTLPR), as well as genes that regulate stress response, such as corticotropin-releasing hormone (CRH). Together these studies provide a foundation of knowledge about the genetic and neural substrates of this most basic of temperament traits. Future studies using novel imaging methods and genetic approaches promise to expand upon these biological bases of inhibited temperament and inform our understanding of risk for psychiatric disease.

RGS2 ggenetic variation: association analysis with panic disorder and dimensional as well as intermediate phenotypes of anxiety

Accumulating evidence from mouse models points to the G protein-coupled receptor RGS2 (regulator of G-protein signaling 2) as a promising candidate gene for anxiety in humans. Recently, RGS2 polymorphisms were found to be associated with various anxiety disorders, e.g., rs4606 with panic disorder (PD), but other findings have been negative or inconsistent concerning the respective risk allele. To further examine the role of RGS2 polymorphisms in the pathogenesis of PD, we genotyped rs4606 and five additional RGS2 tag single nucleotide polymorphisms (SNPs; rs16834831, rs10801153, rs16829458, rs1342809, rs1890397) in two independent PD samples, comprising 531 matched case/control pairs. The functional SNP rs4606 was nominally associated with PD when both samples were combined. The upstream SNP rs10801153 displayed a Bonferroni-resistant significant association with PD in the second and the combined sample (P = 0.006 and P = 0.017). We furthermore investigated the effect of rs10801153 on dimensional anxiety traits, a behavioral avoidance test (BAT), and an index for emotional processing in the respective subsets of the total sample. In line with categorical results, homozygous risk (G) allele carriers displayed higher scores on the Agoraphobic Cognitions Questionnaire (ACQ; P = 0.015) and showed significantly more defensive behavior during fear provoking situations (P = 0.001). Furthermore, significant effects on brain activation in response to angry (P = 0.013), happy (P = 0.042) and neutral faces (P = 0.032) were detected. Taken together, these findings provide further evidence for the potential role of RGS2 as a candidate gene for PD.

Polymorphisms of IKBKE gene are associated with major depressive disorder and panic disorder

BACKGROUND

The immune system has been increasingly implicated in the development of mood and anxiety disorders. Inhibitor of kappa light polypeptide gene enhancer in B cells, kinase epsilon (IKBKE) gene encodes IKKε protein that is involved in innate immunity, predominantly antiviral response generation. It also bears pro-inflammatory properties that could affect psychiatric outcomes. In order to investigate the possible role of IKBKE gene in major depressive disorder (MDD) and panic disorder (PD), we conducted a case-control genetic association study concerning these disorders.

METHODS

In all, 14 SNPs of IKBKE gene were genotyped in groups of 391 patients with MDD and 190 patients with PD together with respective 389 and 371 healthy control individuals. The given groups were further divided by gender for additional analyses.

RESULTS

Substantial genetic associations were revealed between IKBKE SNPs and MDD (multiple testing adjusted P < 0.05) and suggestive associations in case of PD (P(adj) > 0.05). In addition, two SNPs that were only associated with PD among males, also displayed significantly different allele frequencies compared to PD females. This may indicate a specific role of these SNPs in male PD, but caution should be applied here due to the small size of the studied PD males group.

CONCLUSIONS

The results of this study confirm our initial findings and indicate a possible role of IKBKE gene in mood and anxiety disorders.

The human ortholog of acid-sensing ion channel gene ASIC1a is associated with panic disorder and amygdala structure and function

BACKGROUND

Individuals with panic disorder (PD) exhibit a hypersensitivity to inhaled carbon dioxide, possibly reflecting a lowered threshold for sensing signals of suffocation. Animal studies have shown that carbon dioxide-mediated fear behavior depends on chemosensing of acidosis in the amygdala via the acid-sensing ion channel ASIC1a. We examined whether the human ortholog of the ASIC1a gene, ACCN2, is associated with the presence of PD and with amygdala structure and function.

METHODS

We conducted a case-control analysis (n = 414 PD cases and 846 healthy controls) of ACCN2 single nucleotide polymorphisms and PD. We then tested whether variants showing significant association with PD are also associated with amygdala volume (n = 1048) or task-evoked reactivity to emotional stimuli (n = 103) in healthy individuals.

RESULTS

Two single nucleotide polymorphisms at the ACCN2 locus showed evidence of association with PD: rs685012 (odds ratio = 1.32, gene-wise corrected p = .011) and rs10875995 (odds ratio = 1.26, gene-wise corrected p = .046). The association appeared to be stronger when early-onset (age ≤ 20 years) PD cases and when PD cases with prominent respiratory symptoms were compared with controls. The PD risk allele at rs10875995 was associated with increased amygdala volume (p = .035) as well as task-evoked amygdala reactivity to fearful and angry faces (p = .0048).

CONCLUSIONS

Genetic variation at ACCN2 appears to be associated with PD and with amygdala phenotypes that have been linked to proneness to anxiety. These results support the possibility that modulation of acid-sensing ion channels may have therapeutic potential for PD.

Acid-sensing ion channels in pain and disease

Why do neurons sense extracellular acid? In large part, this question has driven increasing investigation on acid-sensing ion channels (ASICs) in the CNS and the peripheral nervous system for the past two decades. Significant progress has been made in understanding the structure and function of ASICs at the molecular level. Studies aimed at clarifying their physiological importance have suggested roles for ASICs in pain, neurological and psychiatric disease. This Review highlights recent findings linking these channels to physiology and disease. In addition, it discusses some of the implications for therapy and points out questions that remain unanswered.

The role of the serotonergic and GABA system in translational approaches in drug discovery for anxiety disorders

There is ample evidence that genetic factors play an important role in anxiety disorders. In support, human genome-wide association studies have implicated several novel candidate genes. However, illumination of such genetic factors involved in anxiety disorders has not resulted in novel drugs over the past decades. A complicating factor is the heterogeneous classification of anxiety disorders in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) and diverging operationalization of anxiety used in preclinical and clinical studies. Currently, there is an increasing focus on the gene × environment (G × E) interaction in anxiety as genes do not operate in isolation and environmental factors have been found to significantly contribute to the development of anxiety disorders in at-risk individuals. Nevertheless, extensive research on G × E mechanisms in anxiety has not resulted in major breakthroughs in drug discovery. Modification of individual genes in rodent models has enabled the specific study of anxiety in preclinical studies. In this context, two extensively studied neurotransmitters involved in anxiety are the gamma-aminobutyric acid (GABA) and 5-HT (5-hydroxytryptamine) system. In this review, we illustrate the complex interplay between genes and environment in anxiety processes by reviewing preclinical and clinical studies on the serotonin transporter (5-HTT), 5-HT1A receptor, 5-HT2 receptor, and GABAA receptor. Even though targets from the serotonin and GABA system have yielded drugs with known anxiolytic efficacy, the relation between the genetic background of these targets and anxiety symptoms and development of anxiety disorders is largely unknown. The aim of this review is to show the vast complexity of genetic and environmental factors in anxiety disorders. In light of the difficulty with which common genetic variants are identified in anxiety disorders, animal models with translational validity may aid in elucidating the neurobiological background of these genes and their possible role in anxiety. We argue that, in addition to human genetic studies, translational models are essential to map anxiety-related genes and to enhance our understanding of anxiety disorders in order to develop potentially novel treatment strategies.

Linkage analysis of alternative anxiety phenotypes in multiply affected panic disorder families

BACKGROUND

The choice of phenotype definitions for genetic studies of panic and phobic disorders is complicated by family, twin, and neurobiological data indicating both distinct and shared risk factors as well as heterogeneity within categories. We have previously reported a genome scan in 120 multiplex panic disorder (PD) families using a phenotype that closely adhered to the Diagnostic and Statistical Manual of Mental Disorders, 4th ed., PD definition. Here, we extend this work by carrying out exploratory linkage analyses in this same pedigree set using ten additional literature-based panic and phobia-related phenotypes that take into account aspects of these hypothesized complexities.

METHODS

Multiply affected families (>2 individuals with PD) were recruited from clinical and nonclinical sources, evaluated by a clinician-administered semistructured interview and a subsequent blind consensus best estimate procedure. Each phenotype was analyzed under dominant and recessive models using parametric two-point (homogeneity and heterogeneity), multipoint, and nonparametric methods. Empirically based permutations were used to estimate model-specific and global (across all phenotypes) P-values.

RESULTS

The highest score was a two-point lod (4.27, global P<0.08) on chromosome 13 (D13S793, 76 cM) for the phenotype 'specific or social phobia' under a recessive model and conditions of homogeneity. There was minimal support for linkage to any of the remaining nine phenotypes.

CONCLUSION

Although the interpretation of findings is limited by the sample size and the large number of phenotypes and models analyzed, these data suggest a region on chromosome 13 as a potential site for further exploration in relation to the risk for specific and social phobias.

Meta-analyses of genome-wide linkage scans of anxiety-related phenotypes

Genetic factors underlying trait neuroticism, reflecting a tendency towards negative affective states, may overlap genetic susceptibility for anxiety disorders and help explain the extensive comorbidity amongst internalizing disorders. Genome-wide linkage (GWL) data from several studies of neuroticism and anxiety disorders have been published, providing an opportunity to test such hypotheses and identify genomic regions that harbor genes common to these phenotypes. In all, 11 independent GWL studies of either neuroticism (n=8) or anxiety disorders (n=3) were collected, which comprised of 5341 families with 15 529 individuals. The rank-based genome scan meta-analysis (GSMA) approach was used to analyze each trait separately and combined, and global correlations between results were examined. False discovery rate (FDR) analysis was performed to test for enrichment of significant effects. Using 10 cM intervals, bins nominally significant for both GSMA statistics, P(SR) and P(OR), were found on chromosomes 9, 11, 12, and 14 for neuroticism and on chromosomes 1, 5, 15, and 16 for anxiety disorders. Genome-wide, the results for the two phenotypes were significantly correlated, and a combined analysis identified additional nominally significant bins. Although none reached genome-wide significance, an excess of significant P(SR)P-values were observed, with 12 bins falling under a FDR threshold of 0.50. As demonstrated by our identification of multiple, consistent signals across the genome, meta-analytically combining existing GWL data is a valuable approach to narrowing down regions relevant for anxiety-related phenotypes. This may prove useful for prioritizing emerging genome-wide association data for anxiety disorders.

Multivariate analysis of anxiety disorders yields further evidence of linkage to chromosomes 4q21 and 7p in panic disorder families

Replication has been difficult to achieve in linkage studies of psychiatric disease. Linkage studies of panic disorder have indicated regions of interest on chromosomes 1q, 2p, 2q, 3, 7, 9, 11, 12q13, 12q23, and 15. Few regions have been implicated in more than one study. We examine two samples, the Iowa (IA) and the Columba panic disorder families. We use the fuzzy-clustering method presented by Kaabi et al. [Kaabi et al. (2006); Am J Hum Genet 78: 543-553] to summarize liability to panic disorder, agoraphobia, simple phobia, and social phobia. Kaabi et al. applied this method to the Yale panic disorder linkage families and found evidence of linkage to chromosomes 4q21, 4q32, 7p, and 8. When we apply the same method to the IA families, we obtain overlapping evidence of linkage to chromosomes 4q21 and 7p. Additionally, we find evidence of linkage on chromosomes 1, 5, 6, 16, and 22. The Columbia (CO) data does not indicate linkage to any of the Kaabi et al. peaks, instead implicating chromosomes 2 and 22q11 (2 Mb from COMT). There is some evidence of overlapping linkage between the IA and CO datasets on chromosomes 1 and 14. While use of fuzzy clustering has not produced complete concordance across datasets, it has produced more than previously seen in analyses of panic disorder proper. We conclude that chromosomes 4q21 and 7p should be considered strong candidate regions for panic and fear-associated anxiety disorder loci. More generally, this suggests that analyses including multiple aspects of psychopathology may lead to greater consistency across datasets.

Prioritization and association analysis of murine-derived candidate genes in anxiety-spectrum disorders

BACKGROUND

Anxiety disorders are common psychiatric conditions that are highly comorbid with each other and related phenotypes such as depression, likely due to a shared genetic basis. Fear-related behaviors in mice have long been investigated as potential models of anxiety disorders, making integration of information from both murine and human genetic data a powerful strategy for identifying potential susceptibility genes for these conditions.

METHODS

We combined genome-wide association analysis of fear-related behaviors with strain distribution pattern analysis in heterogeneous stock mice to identify a preliminary list of 52 novel candidate genes. We ranked these according to three complementary sources of prior anxiety-related genetic data: 1) extant linkage and knockout studies in mice, 2) a meta-analysis of human linkage scans, and 3) a preliminary human genome-wide association study. We genotyped tagging single nucleotide polymorphisms covering the nine top-ranked regions in a two-stage association study of 1316 subjects from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders chosen for high or low genetic loading for anxiety-spectrum phenotypes (anxiety disorders, neuroticism, and major depression).

RESULTS

Multiple single nucleotide polymorphisms in the PPARGC1A gene demonstrated association in both stages that survived gene-wise correction for multiple testing.

CONCLUSIONS

Integration of genetic data across human and murine studies suggests PPARGC1A as a potential susceptibility gene for anxiety-related disorders.

The clinical implications of mouse models of enhanced anxiety

Mice are increasingly overtaking the rat model organism in important aspects of anxiety research, including drug development. However, translating the results obtained in mouse studies into information that can be applied in clinics remains challenging. One reason may be that most of the studies so far have used animals displaying 'normal' anxiety rather than 'psychopathological' animal models with abnormal (elevated) anxiety, which more closely reflect core features and sensitivities to therapeutic interventions of human anxiety disorders, and which would, thus, narrow the translational gap. Here, we discuss manipulations aimed at persistently enhancing anxiety-related behavior in the laboratory mouse using phenotypic selection, genetic techniques and/or environmental manipulations. It is hoped that such models with enhanced construct validity will provide improved ways of studying the neurobiology and treatment of pathological anxiety. Examples of findings from mouse models of enhanced anxiety-related behavior will be discussed, as well as their relation to findings in anxiety disorder patients regarding neuroanatomy, neurobiology, genetic involvement and epigenetic modifications. Finally, we highlight novel targets for potential anxiolytic pharmacotherapeutics that have been established with the help of research involving mice. Since the use of psychopathological mouse models is only just beginning to increase, it is still unclear as to the extent to which such approaches will enhance the success rate of drug development in translating identified therapeutic targets into clinical trials and, thus, helping to introduce the next anxiolytic class of drugs.

The genetic basis of panic disorder

Panic disorder is one of the chronic and disabling anxiety disorders. There has been evidence for either genetic heterogeneity or complex inheritance, with environmental factor interactions and multiple single genes, in panic disorder's etiology. Linkage studies have implicated several chromosomal regions, but no research has replicated evidence for major genes involved in panic disorder. Researchers have suggested several neurotransmitter systems are related to panic disorder. However, to date no candidate gene association studies have established specific loci. Recently, researchers have emphasized genome-wide association studies. Results of two genome-wide association studies on panic disorder failed to show significant associations. Evidence exists for differences regarding gender and ethnicity in panic disorder. Increasing evidence suggests genes underlying panic disorder overlap, transcending current diagnostic boundaries. In addition, an anxious temperament and anxiety-related personality traits may represent intermediate phenotypes that predispose to panic disorder. Future research should focus on broad phenotypes, defined by comorbidity or intermediate phenotypes. Genome-wide association studies in large samples, studies of gene-gene and gene-environment interactions, and pharmacogenetic studies are needed.

TMEM132D, a new candidate for anxiety phenotypes: evidence from human and mouse studies

The lifetime prevalence of panic disorder (PD) is up to 4% worldwide and there is substantial evidence that genetic factors contribute to the development of PD. Single-nucleotide polymorphisms (SNPs) in TMEM132D, identified in a whole-genome association study (GWAS), were found to be associated with PD in three independent samples, with a two-SNP haplotype associated in each of three samples in the same direction, and with a P-value of 1.2e-7 in the combined sample (909 cases and 915 controls). Independent SNPs in this gene were also associated with the severity of anxiety symptoms in patients affected by PD or panic attacks as well as in patients suffering from unipolar depression. Risk genotypes for PD were associated with higher TMEM132D mRNA expression levels in the frontal cortex. In parallel, using a mouse model of extremes in trait anxiety, we could further show that anxiety-related behavior was positively correlated with Tmem132d mRNA expression in the anterior cingulate cortex, central to the processing of anxiety/fear-related stimuli, and that in this animal model a Tmem132d SNP is associated with anxiety-related behavior in an F2 panel. TMEM132D may thus be an important new candidate gene for PD as well as more generally for anxiety-related behavior.

Association of RGS2 variants with panic disorder in a Japanese population

Panic disorder (PD) is a severe and chronic psychiatric disorder with significant genetic components underlying its etiology. The gene regulator of G protein signaling 2 (RGS2) has been reported to be associated with anxiety disorders. To confirm the association of RGS2 with PD, we investigated three single nucleotide polymorphisms (SNPs) of RGS2 (rs10801152, rs4606, and rs1819741) in 677 Japanese PD cases and 460 controls. The SNP rs10801152 was suggestive of an association with PD (allele P = 0.045 adjusted using sex and age as confounding factors). The three-SNP haplotype was significantly associated with PD (global permutation P = 4 × 10(-4)). The haplotypes T-G-C and T-C-T showed significant association and protective effect on PD (T-G-C, permutation P = 0.038, OR = 0.80, 95%CI = 0.68-0.95; T-C-T, permutation P = 0.004, OR = 0.38, 95%CI = 0.21-0.70). These results provide support for an association of RGS2 with PD in a Japanese population.

Convergent functional genomics of anxiety disorders: translational identification of genes, biomarkers, pathways and mechanisms

Anxiety disorders are prevalent and disabling yet understudied from a genetic standpoint, compared with other major psychiatric disorders such as bipolar disorder and schizophrenia. The fact that they are more common, diverse and perceived as embedded in normal life may explain this relative oversight. In addition, as for other psychiatric disorders, there are technical challenges related to the identification and validation of candidate genes and peripheral biomarkers. Human studies, particularly genetic ones, are susceptible to the issue of being underpowered, because of genetic heterogeneity, the effect of variable environmental exposure on gene expression, and difficulty of accrual of large, well phenotyped cohorts. Animal model gene expression studies, in a genetically homogeneous and experimentally tractable setting, can avoid artifacts and provide sensitivity of detection. Subsequent translational integration of the animal model datasets with human genetic and gene expression datasets can ensure cross-validatory power and specificity for illness. We have used a pharmacogenomic mouse model (involving treatments with an anxiogenic drug--yohimbine, and an anti-anxiety drug--diazepam) as a discovery engine for identification of anxiety candidate genes as well as potential blood biomarkers. Gene expression changes in key brain regions for anxiety (prefrontal cortex, amygdala and hippocampus) and blood were analyzed using a convergent functional genomics (CFG) approach, which integrates our new data with published human and animal model data, as a translational strategy of cross-matching and prioritizing findings. Our work identifies top candidate genes (such as FOS, GABBR1, NR4A2, DRD1, ADORA2A, QKI, RGS2, PTGDS, HSPA1B, DYNLL2, CCKBR and DBP), brain-blood biomarkers (such as FOS, QKI and HSPA1B), pathways (such as cAMP signaling) and mechanisms for anxiety disorders--notably signal transduction and reactivity to environment, with a prominent role for the hippocampus. Overall, this work complements our previous similar work (on bipolar mood disorders and schizophrenia) conducted over the last decade. It concludes our programmatic first pass mapping of the genomic landscape of the triad of major psychiatric disorder domains using CFG, and permitted us to uncover the significant genetic overlap between anxiety and these other major psychiatric disorders, notably the under-appreciated overlap with schizophrenia. PDE10A, TAC1 and other genes uncovered by our work provide a molecular basis for the frequently observed clinical co-morbidity and interdependence between anxiety and other major psychiatric disorders, and suggest schizo-anxiety as a possible new nosological domain.

Convergent functional genomic studies of ω-3 fatty acids in stress reactivity, bipolar disorder and alcoholism

Omega-3 fatty acids have been proposed as an adjuvant treatment option in psychiatric disorders. Given their other health benefits and their relative lack of toxicity, teratogenicity and side effects, they may be particularly useful in children and in females of child-bearing age, especially during pregnancy and postpartum. A comprehensive mechanistic understanding of their effects is needed. Here we report translational studies demonstrating the phenotypic normalization and gene expression effects of dietary omega-3 fatty acids, specifically docosahexaenoic acid (DHA), in a stress-reactive knockout mouse model of bipolar disorder and co-morbid alcoholism, using a bioinformatic convergent functional genomics approach integrating animal model and human data to prioritize disease-relevant genes. Additionally, to validate at a behavioral level the novel observed effects on decreasing alcohol consumption, we also tested the effects of DHA in an independent animal model, alcohol-preferring (P) rats, a well-established animal model of alcoholism. Our studies uncover sex differences, brain region-specific effects and blood biomarkers that may underpin the effects of DHA. Of note, DHA modulates some of the same genes targeted by current psychotropic medications, as well as increases myelin-related gene expression. Myelin-related gene expression decrease is a common, if nonspecific, denominator of neuropsychiatric disorders. In conclusion, our work supports the potential utility of omega-3 fatty acids, specifically DHA, for a spectrum of psychiatric disorders such as stress disorders, bipolar disorder, alcoholism and beyond.

Genetics of panic disorder: focus on association studies and therapeutic perspectives

There is evidence for either genetic heterogeneity or complex inheritance with an interaction of environmental factors and multiple single genes in the etiology of panic disorder. Although linkage analyses of panic disorder have implicated several chromosomal regions including 1q, 2q, 4q, 7p, 9q, 12q, 13q, 15q and 22q, they so far have not been able to identify a major gene responsible for panic disorder. Several genes of classical candidate neurotransmitter systems have been reported to be associated with panic disorder. Genetic variation in genes of monoamine oxidase A, catechol-O-methyltransferase, adenosine receptor (ADORA2A) and cholecystokinin B receptor have been inconsistently replicated. There are multiple lines of evidence for highly relevant effects of gender and ethnicity. Future research strategies might focus on broad phenotypes defined by comorbidity or intermediate phenotypes and include the use of animal models for identifying candidate genes, such as the regulator of G-protein signaling (RGS2) gene, genome-wide association studies in large samples, studies of gene-gene and gene-environment interactions and pharmacogenetic studies. The identification of novel pathophysiological pathways may provide the basis for the development of novel therapeutic interventions.

Advances in molecular genetics of panic disorder

The molecular genetic research on panic disorder (PD) has grown tremendously in the past decade. Although the data from twin and family studies suggest an involvement of genetic factors in the familial transmission of PD with the heritability estimate near 40%, the genetic substrate underlying panicogenesis is not yet understood. The linkage studies so far have suggested that chromosomal regions 13q, 14q, 22q, 4q31-q34, and probably 9q31 are associated with the transmission of PD phenotypes. To date, more than 350 candidate genes have been examined in association studies of PD, but most of these results remain inconsistent, negative, or not clearly replicated. Only Val158Met polymorphism of the catechol-O-methyltransferase gene has been implicated in susceptibility to PD by several studies in independent samples and confirmed in a recent meta-analysis. However, the specific role of this genetic variation in PD requires additional analysis considering its gender- and ethnicity-dependent effect and putative impact on cognitive functions. The recent advantages in bioinformatics and genotyping technologies, including genome-wide association and gene expression methods, provide the means for far more comprehensive discovery in PD. The progress in clinical and neurobiological concepts of PD may further guide genetic research through the current controversies to more definitive findings.

Genetics of anxiety disorders: the complex road from DSM to DNA

Anxiety disorders are among the most common psychiatric disorders, affecting one in four individuals over a lifetime. Although our understanding of the etiology of these disorders is incomplete, familial and genetic factors are established risk factors. However, identifying the specific casual genes has been difficult. Within the past several years, advances in molecular and statistical genetic methods have made the genetic dissection of complex disorders a feasible project. Here we provide an overview of these developments, with a focus on their implications for genetic studies of anxiety disorders. Although the genetic and phenotypic complexity of the anxiety disorders present formidable challenges, advances in neuroimaging and experimental animal models of anxiety and fear offer important opportunities for discovery. Real progress in identifying the genetic basis of anxiety disorders will require integrative approaches that make use of these biologic tools as well as larger-scale genomic studies. If successful, such efforts may yield novel and more effective approaches for the prevention and treatment of these common and costly disorders.

Panic disorder is associated with the serotonin transporter gene (SLC6A4) but not the promoter region (5-HTTLPR)

Panic disorder (PD) and social anxiety disorder (SAD) are moderately heritable anxiety disorders. We analyzed five genes, derived from pharmacological or translational mouse models, in a new case-control study of PD and SAD in European Americans: (1) the serotonin transporter (SLC6A4), (2) the serotonin receptor 1A, (3) catechol-O-methyltransferase, (4) a regulator of g-protein signaling and (5) the gastrin-releasing peptide receptor. Cases were interviewed using the schedule for affective disorders and schizophrenia and were required to have a probable or definite lifetime diagnosis of PD (N=179), SAD (161) or both (140), with first onset by age 31 and a family history of anxiety. Final diagnoses were determined using the best estimate procedure, blind to genotyping data. Controls were obtained from the National Institute of Mental Health Human Genetics Initiative; only subjects above 25 years of age who screened negative for all psychiatric symptoms were included (N=470). A total of 45 single nucleotide polymorphisms were successfully genotyped over the five selected genes using Applied Biosystems SNPlex protocol. SLC6A4 provided strong and consistent evidence of association with the PD and PD+SAD groups, with the most significant association in both groups being at rs140701 (chi(2)=10.72, P=0.001 with PD and chi(2)=8.59, P=0.003 in the PD+SAD group). This association remained significant after multiple test correction. Those carrying at least one copy of the haplotype A-A-G constructed from rs3794808, rs140701 and rs4583306 have 1.7 times the odds of PD than those without the haplotype (95% confidence interval: 1.2-2.3). The SAD only group did not provide evidence of association, suggesting a PD-driven association. The findings remained after adjustment for age and sex, and there was no evidence that the association was due to population stratification. The promoter region of the gene, 5-HTTLPR, did not provide any evidence of association, regardless of whether analyzed as a triallelic or biallelic locus, nor did any of the other four candidate genes tested. Our findings suggest that the serotonin transporter gene may play a role in PD; however, the findings require replication. Future studies should attend to the entire genetic region rather than the promoter.

Insertion/deletion polymorphism in the gene for angiotensin converting enzyme (ACE) in panic disorder: A gender-specific effect?

Family, twin, and segregation analytic studies indicate a complex genetic contribution to panic disorder with an estimated heritability of 48%. Angiotensin-converting enzyme (ACE) degrades substance P, which has been implicated in anxiety-related behaviour. ACE has been suggested as a potential risk factor in the pathogenesis of panic attacks. A functional insertion deletion (I/D) polymorphism in the ACE gene was suggested to be associated with panic disorder in a potentially gender-specific way ( Olsson et al. 2004 ). The present study aimed to replicate this finding and thereby to further elucidate the role of ACE gene variation in the pathomechanism of panic disorder. The ACE I/D polymorphism was genotyped in a sample of 102 German patients with panic disorder with or without agoraphobia as well as a healthy German control group matched with regard to age and sex (n = 102). In the male subgroup (n = 43) of panic patients a significant association of the ACE I allele (P = 0.0474) and genotypes containing the I allele (P = 0.0195), respectively, was observed. The present results provide further support for a potentially male-specific role of the less active ACE I allele in the pathogenesis of panic disorder, possibly by altering substance P levels.

Replication of a genome-wide association study of panic disorder in a Japanese population

Panic disorder (PD) is an anxiety disorder characterized by recurrent and unexpected panic attacks, subsequent worry and phobic avoidance. Although a number of association and linkage studies have been conducted, no gene has been identified as a susceptibility locus. We previously conducted a genome-wide association analysis of PD in 200 Japanese patients and the same number of controls, using a 500 K single nucleotide polymorphisms (SNPs) chip. In this study, we report a replication analysis of PD using the DigTag2 assay. The second stage sample consisted of 558 Japanese patients and 566 controls. Thirty-two markers were tested in a replication sample. As a result, no significant association was found after correction for multiple testing. However, the difference was observed at the nominal allele P-value <0.05 for two SNPs (rs6733840 and rs132617). We also conducted haplotype analyses of SNPs in the APOL3 and CLU genes. Our results failed to show any significant association with PD in these genes. Further studies on these variants with a larger sample size may be worth testing to confirm the results.

Evidence for an interaction of schizophrenia susceptibility loci on chromosome 6q23.3 and 10q24.33-q26.13 in Arab Israeli families

A genome scan for schizophrenia related loci in Arab Israeli families by Lerer et al. [Lerer et al. (2003); Mol Psychiatry 8:488-498] detected significant evidence for linkage at chromosome 6q23. Subsequent fine mapping [Levi et al. (2005); Eur J Hum Genet 13:763-771], association [Amann-Zalcenstein et al. (2006); Eur J Hum Genet 14:1111-1119] and replication studies [Ingason et al. (2007); Eur J Hum Genet 15:988-991] identified AHI1 as a putative susceptibility gene. The same genome scan revealed suggestive evidence for a schizophrenia susceptibility locus in the 10q23-26 region. Genes at these two loci may act independently in the pathogenesis of the disease in our homogeneous sample of Arab Israeli families or may interact with each other and with other factors in a common biological pathway. The purpose of our current study was to test the hypothesis of genetic interaction between these two loci and to identify the type of interaction between them. The initial stage of our study focused on the 10q23-q26 region which has not been explored further in our sample. The second stage of the study included a test for possible genetic interaction between the 6q23.3 locus and the refined 10q24.33-q26.13 locus. A final candidate region of 19.9 Mb between markers D10S222 (105.3 Mb) and D10S587 (125.2 Mb) was found on chromosome 10 by non-parametric and parametric linkage analyses. These linkage findings are consistent with previous reports in the same chromosomal region. Two-locus multipoint linkage analysis under three complex disease inheritance models (heterogeneity, multiplicative, and additive models) yielded a best maximum LOD score of 7.45 under the multiplicative model suggesting overlapping function of the 6q23.3 and 10q24.33-q26.13 loci.

Suggestive linkage on chromosome 2, 8, and 17 for lifetime major depression

It is well established that major depressive disorder (MDD) is partly heritable. We present a genome-wide linkage study aiming to find regions on the genome that influence the vulnerability for MDD. Our sample consists of 110 Australian and 23 Dutch pedigrees with two or more siblings affected with MDD (total N = 278). Linkage analysis was carried out in MERLIN. Three regions showed suggestive linkage signals. The highest LOD-score of 2.1 was found on chromosome 17 at 52.6 cM along with LOD scores of 1.9 and 1.7 on chromosome 8 at 2.7 cM and chromosome 2 at 90.6 cM, respectively. The result on chromosome 8 seems most promising as two previous studies also found linkage in this region, once suggestive and once significant. The linkage peak on chromosome 17 harbors the serotonin transporter gene. In the Australian and Dutch sample, the serotonin transporter length polymorphism did not show evidence for association, thus other genes in this region or other polymorphisms in the serotonin transporter gene might be associated with MDD. Further replication is needed to establish the relevance of our linkage finding on chromosome 2.

Anxiety in mice and men: a comparison

Anxiety is one of the most fundamental emotions required to survive or to cope with potential threatening stimuli. Under certain circumstances, it can change to excessive or maladaptive response and might manifest in anxious personality or even anxiety disorders. Genetic studies provide a number of promising candidate genes that, however, account for only a few percent of the phenotypic variance. Social and material environmental effects such as stressful life events, drugs or chemicals and particular behavioural influences such as parental care are suggested to interact with gene effects presumably involving epigenetic processes. Such interaction probably modifies an individual's predisposition, personality and susceptibility to develop normal or low anxiety or even maladaptive or excessive anxiety. Since human anxiety involves complex emotions as well as cognitions, unique experiences and an individual genetic make-up, studies trying to clarify the complex and functionally interwoven pathogenesis of anxious personality or anxiety disorders often adopt a reductionistic, simplifying approach. Therein, mice constitute an invaluable tool for modelling human anxiety in its various forms as they display remarkable similarities on anatomical, physiological, biochemical, molecular and behavioural levels. This review aims to fit observations and results obtained from men and mice on behavioural, genetic and environmental levels in response to different threatening stimuli elucidating different genetic and epigenetic effects.

Variant in RGS2 moderates posttraumatic stress symptoms following potentially traumatic event exposure

Polymorphisms in the RGS2 (regulator of G-protein signaling 2) gene were found to be associated with anxious behavior in mice and anxiety in humans. We examined whether rs4606, a single nucleotide polymorphism (SNP) of RGS2, and social support moderated risk for PTSD in an epidemiologic sample. The study examines 607 adults from the 2004 Florida Hurricanes study who returned buccal DNA samples via mail. rs4606 was associated with increased symptoms of posthurricane PTSD symptoms under conditions of high hurricane exposure and low social support (P<.05). Further, this polymorphism was associated with lifetime PTSD symptoms under conditions of lifetime exposure to a potentially traumatic event, and low social support (P<.001). These gene by environment interactions remained significant after adjustment for sex, ancestry, and age. RGS2 rs4606 modifies risk of postdisaster and lifetime PTSD symptoms under conditions of high stressor exposure. This is the first demonstration of gene-environment interaction for this locus.

RGS2 and generalized anxiety disorder in an epidemiologic sample of hurricane-exposed adults

BACKGROUND

Generalized anxiety disorder (GAD) is a common and sometimes disabling condition often associated with stressful life events that involve significant loss or danger. The disorder appears moderately heritable. Polymorphisms in the RGS2 (regulator of G-protein signaling 2) gene were recently associated with anxious behavior in mice and panic disorder and trait anxiety in humans. We examined whether rs4606, a single nucleotide polymorphism (SNP) in the 3' UTR of RGS2, was associated with GAD in an epidemiologic sample of adults exposed to the 2004 Florida Hurricanes.

METHODS

The sample for the current study is 607 adults from the 2004 Florida Hurricane Study who returned buccal DNA samples via mail. Participants were selected via random digit dial procedures and interviewed via telephone about hurricane exposure, social support, and GAD symptoms. The outcome measure was DSM-IV diagnosis of GAD derived from structured interviews.

RESULTS

RGS2 SNP rs4606 was significantly associated with GAD in this sample. In logistic regression analyses, each C allele was associated with a 100% (P=.026) increased risk of GAD after controlling for age, sex, ancestry, hurricane exposure, and social support.

CONCLUSIONS

These findings are consistent with a previously published study showing a higher prevalence of the C allele among panic disorder patients than controls. This study points toward a relevant polymorphism for GAD at the 3' end of the RGS2 gene; and suggests that studying a recently disaster-exposed sample is both feasible and may improve power to find gene-disorder associations.

An association analysis of murine anxiety genes in humans implicates novel candidate genes for anxiety disorders

BACKGROUND

Human anxiety disorders are complex diseases with largely unknown etiology. We have taken a cross-species approach to identify genes that regulate anxiety-like behavior with inbred mouse strains that differ in their innate anxiety levels as a model. We previously identified 17 genes with expression levels that correlate with anxiety behavior across the studied strains. In the present study, we tested their 13 known human homologues as candidate genes for human anxiety disorders with a genetic association study.

METHODS

We describe an anxiety disorder study sample derived from a Finnish population-based cohort and consisting of 321 patients and 653 carefully matched control subjects, all interviewed to obtain DSM-IV diagnoses. We genotyped altogether 208 single nucleotide polymorphisms (SNPs) (all non-synonymous SNPs, SNPs that alter potential microRNA binding sites, and gap-filling SNPs selected on the basis of HapMap information) from the investigated anxiety candidate genes.

RESULTS

Specific alleles and haplotypes of six of the examined genes revealed some evidence for association (p < or = .01). The most significant evidence for association with different anxiety disorder subtypes were: p = .0009 with ALAD (delta-aminolevulinate dehydratase) in social phobia, p = .009 with DYNLL2 (dynein light chain 2) in generalized anxiety disorder, and p = .004 with PSAP (prosaposin) in panic disorder.

CONCLUSIONS

Our findings suggest that variants in these genes might predispose to specific human anxiety disorders. These results illustrate the potential utility of cross-species approaches in identification of candidate genes for psychiatric disorders.

Combined effects of exonic polymorphisms in CRHR1 and AVPR1B genes in a case/control study for panic disorder

Accumulating evidence from animal studies suggests that the corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) neuropeptide systems, contribute to anxiety behavior. To investigate whether polymorphisms in the genes regulating these two systems may alter susceptibility to anxiety disorders in humans, we genotyped 71 single nucleotide polymorphisms (SNPs) in CRH, CRHR1, CRHR2, AVP, AVPR1A, AVPR1B in a German sample from Munich with patients suffering from panic disorder and matched healthy controls (n = 186/n = 299). Significant associations were then replicated in a second German sample with 173 patients with panic disorder and 495 controls. In both samples separately and the combined sample, SNPs within CHRH1 and AVPR1B were nominally associated with panic disorder. We then tested two locus multiplicative and interaction effects of polymorphisms of these two genes on panic disorder. Fifteen SNP pairs showed significant multiplicative effects in both samples. The SNP pair with the most significant association in the combined sample (P = 0.00057), which withstood correction for multiple testing, was rs878886 in CRHR1 and rs28632197 in AVPR1B. Both SNPs are of potential functional relevance as rs878886 is located in the 3' untranslated region of the CRHR1 and rs28632197 leads to an arginine to histidine amino acid exchange at position 364 of AVPR1B which is located in the intracellular C-terminal domain of the receptor. These data suggest that polymorphisms in the AVPR1B and the CRHR1 genes alter the susceptibility to panic disorder.

Genome-wide linkage analysis of multiple measures of neuroticism of 2 large cohorts from Australia and the Netherlands

CONTEXT

People meeting diagnostic criteria for anxiety or depressive disorders tend to score high on the personality scale of neuroticism. Studying this personality dimension can give insights into the etiology of these important psychiatric disorders.

OBJECTIVES

To undertake a comprehensive genome-wide linkage study of neuroticism using large study samples that have been measured multiple times and to compare the results between countries for replication and across time within countries for consistency.

DESIGN

Genome-wide linkage scan.

SETTING

Twin individuals and their family members from Australia and the Netherlands.

PARTICIPANTS

Nineteen thousand six hundred thirty-five sibling pairs completed self-report questionnaires for neuroticism up to 5 times over a period of up to 22 years. Five thousand sixty-nine sibling pairs were genotyped with microsatellite markers.

METHODS

Nonparametric linkage analyses were conducted in MERLIN-REGRESS for the mean neuroticism scores averaged across time. Additional analyses were conducted for the time-specific measures of neuroticism from each country to investigate consistency of linkage results.

RESULTS

Three chromosomal regions exceeded empirically derived thresholds for suggestive linkage using mean neuroticism scores: 10p 5 Kosambi cM (cM) (Dutch study sample), 14q 103 cM (Dutch study sample), and 18q 117 cM (combined Australian and Dutch study sample), but only 14q retained significance after correction for multiple testing. These regions all showed evidence for linkage in individual time-specific measures of neuroticism and 1 (18q) showed some evidence for replication between countries. Linkage intervals for these regions all overlap with regions identified in other studies of neuroticism or related traits and/or in studies of anxiety in mice.

CONCLUSIONS

Our results demonstrate the value of the availability of multiple measures over time and add to the optimism reported in recent reviews for replication of linkage regions for neuroticism. These regions are likely to harbor causal variants for neuroticism and its related psychiatric disorders and can inform prioritization of results from genome-wide association studies.

The genetic basis of panic and phobic anxiety disorders

Panic disorder and phobic anxiety disorders are common disorders that are often chronic and disabling. Genetic epidemiologic studies have documented that these disorders are familial and moderately heritable. Linkage studies have implicated several chromosomal regions that may harbor susceptibility genes; however, candidate gene association studies have not established a role for any specific loci to date. Increasing evidence from family and genetic studies suggests that genes underlying these disorders overlap and transcend diagnostic boundaries. Heritable forms of anxious temperament, anxiety-related personality traits and neuroimaging assays of fear circuitry may represent intermediate phenotypes that predispose to panic and phobic disorders. The identification of specific susceptibility variants will likely require much larger sample sizes and the integration of insights from genetic analyses of animal models and intermediate phenotypes.

Human-mouse quantitative trait locus concordance and the dissection of a human neuroticism locus

BACKGROUND

Exploiting synteny between mouse and human disease loci has been proposed as a cost-effective method for the identification of human susceptibility genes. Here we explore its utility in an analysis of a human personality trait, neuroticism, which can be modeled in mice by tests of emotionality. We investigated a mouse emotionality locus on chromosome 1 that contains no annotated genes but abuts four regulators of G protein signaling, one of which (rgs2) has been previously identified as a quantitative trait gene for emotionality. This locus is syntenic with a human region that has been consistently implicated in the genetic aetiology of neuroticism.

METHODS

The functional candidacy of 29 murine sequence variants was tested by a combination of gel shift and transient transfection assays. Murine sequences that contained functional variants and exhibited significant cross-species conservation were prioritized for investigation in humans. Genetic association with neuroticism was tested in 1869 high and 2032 low unrelated individuals scored for neuroticism, selected from the extremes of 88,141 people from southwest England.

RESULTS

Fifteen sequence variants contributed to variation in the expression of rgs18, the gene lying at the edge of the quantitative trait loci (QTL) interval. There was no evidence of association between neuroticism and single nucleotide polymorphisms (SNPs) lying in the human regions homologous to those of mouse functional variants. One SNP, rs6428058, in a region of sequence conservation 644 kb upstream of RGS18, showed significant association (p = .000631).

CONCLUSIONS

It is unlikely that a single variant is responsible for the mouse emotionality locus on chromosome 1. This level of underlying genetic complexity means that although cross-species QTL concordance may be invaluable for the identification of human disease loci, it is unlikely to be as informative in the identification of human disease-causing variants.

Lack of association between the amiloride-sensitive cation channel 2 (ACCN2) gene and anxiety spectrum disorders

OBJECTIVE

Ion channels are involved in a wide range of central nervous system functions and have been implicated in several neuropsychiatric disorders. Rodent studies suggest that the acid-sensing ion channel, ASIC1, may play a role in fear conditioning, a model for human anxiety disorders. In this study, we examined, for the first time, the human analog of ASIC1, the amiloride-sensitive cation channel 2 (ACCN2) gene, for its association with genetic risk across a range of anxiety spectrum phenotypes.

METHODS

Using multivariate structural equation modeling, we selected twin pairs scoring at the extremes of a latent genetic risk factor that underlies susceptibility to neuroticism, major depression, generalized anxiety disorder, panic disorder, agoraphobia, and social phobia, from the population-based Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. One member from each selected pair for whom DNA was available was entered into a 2-stage, case-control association study for the ACCN2 gene. In the resulting sample of 589 cases and 539 controls, a total of seven single nucleotide polymorphisms that represented the major allelic variation across the ACCN2 locus were screened in stage 1, the positive results of which were tested for replication in stage 2.

RESULTS

Although several markers or haplotypic combinations met threshold significance criteria in stage 1, their association was not replicated in stage 2. Post hoc analyses did not reveal significant association to the specific psychiatric phenotypes.

CONCLUSIONS

Although the ACCN2 gene may play a role in rodent fear conditioning, we could not detect association with genetic risk shared among human anxiety spectrum disorders.

Phenomic, convergent functional genomic, and biomarker studies in a stress-reactive genetic animal model of bipolar disorder and co-morbid alcoholism

We had previously identified the clock gene D-box binding protein (Dbp) as a potential candidate gene for bipolar disorder and for alcoholism, using a Convergent Functional Genomics (CFG) approach. Here we report that mice with a homozygous deletion of DBP have lower locomotor activity, blunted responses to stimulants, and gain less weight over time. In response to a chronic stress paradigm, these mice exhibit a diametric switch in these phenotypes. DBP knockout mice are also activated by sleep deprivation, similar to bipolar patients, and that activation is prevented by treatment with the mood stabilizer drug valproate. Moreover, these mice show increased alcohol intake following exposure to stress. Microarray studies of brain and blood reveal a pattern of gene expression changes that may explain the observed phenotypes. CFG analysis of the gene expression changes identified a series of novel candidate genes and blood biomarkers for bipolar disorder, alcoholism, and stress reactivity.

Chromosomal assignment of quantitative trait loci influencing modified hole board behavior in laboratory mice using consomic strains, with special reference to anxiety-related behavior and mouse chromosome 19

Male mice from a panel of chromosome substitution strains (CSS, also called consomic strains or lines)--in which a single full-length chromosome from the A/J inbred strain has been transferred onto the genetic background of the C57BL/6J inbred strain--and the parental strains were examined in the modified hole board test. This behavioral test allows to assess for a variety of different motivational systems in parallel (i.e. anxiety, risk assessment, exploration, memory, locomotion, and arousal). Such an approach is essential for behavioral characterization since the motivational system of interest is strongly influenced by other behavioral systems. Both univariate and bivariate analyses, as well as a factor analysis, were performed. The C57BL/6J and A/J mouse parental inbred strains differed in all motivational systems. The chromosome substitution strain survey indicated that nearly all mouse chromosomes (with the exception of chromosome 2) each contain at least one quantitative trait locus (QTL) that is involved in modified hole board behavior. The results agreed well with previous reports of QTLs for anxiety-related behavior using the A/J and C57BL/6J as parental strains. The present study confirmed that mouse chromosomes 5, 8, 10, 15, 18 and 19 likely contain at least one anxiety QTL. There was also evidence for a novel anxiety QTL on the Y chromosome. With respect to anxiety-related avoidance behavior towards an unprotected area, we have special interest for mouse chromosome 19. CSS-19 (C57BL/6J-Chr19(A)/NaJ) differed in avoidance behavior from the C57BL/6J, but not in locomotion. Thus pleiotropic contribution of locomotion could be excluded.

Linkage on chromosome 14 in a genome-wide linkage study of a broad anxiety phenotype

Several linkage studies on anxiety have been carried out in samples ascertained through probands with panic disorder. The results indicated that using a broad anxiety phenotype instead of a DSM-IV anxiety disorder diagnosis might enhance the chance of finding a linkage signal. In the current study, a genome-wide linkage analysis was performed on anxiety measured with a self-report questionnaire whose scores are highly correlated with DSM-IV anxiety disorders. The self-report questionnaire was included in five surveys of a longitudinal study of the Netherlands Twin Register. Genotype and phenotype data were available for 1602 twins and siblings. To estimate identity by descent , additional genotype data for 564 parents and 22 siblings were used. Linkage analyses were carried out using MERLIN-regress on the average anxiety scores across time. A linkage signal (logarithm of odds score 3.4, empirical P-value 0.07) was obtained at chromosome 14 for marker D14S65 at 105 cM (90% confidence interval, 99-115 cM bounded by markers D14S1434 and D14S985). This finding replicates a linkage finding for a broad anxiety phenotype in a clinically based sample, indicating that the region might harbor a quantitative trait locus associated with the whole spectrum of general anxiety, that is from the normal to the clinical range. Moreover, genome-wide linkage and association studies on emotionality in mice obtained significant results in a syntenic region on mouse chromosome 12. Two homolog genes lie in this region -Dlk1 (delta-like 1 homolog, Drosophila) and Rtl1 (retrotransposon-like 1). Future association studies of these genes are warranted.

Molecular genetics of anxiety in mice and men

Human anxiety disorders represent one of the most common mental illnesses. They are complex diseases with both genetic and environmental factors affecting their predisposition. Since the basic neuronal mechanisms are shared across mammalian species, the same set of genes may regulate critical aspects of anxiety in humans and in lower species. In this review, we first summarize findings from human molecular genetic approaches to anxiety disorders or anxiety-related personality traits: genome-wide scans and candidate gene studies in large families or case-control cohorts. We then discuss recent studies that have used genome-wide methods in mouse strains to identify genes that regulate anxiety-like behavior. Although it has been difficult to pinpoint specific susceptibility genes for anxiety disorders, ongoing efforts to collect larger study cohorts and to develop new genetic tools should help in this task. Studies in animals have shown that novel quantitative trait locus (QTL) and functional genomics approaches might lead to the identification of regulators of anxiety in mice, and that these genes can be tested for their involvement in human anxiety disorders. Finally, breakthroughs are expected in the fine-mapping of human and mouse genetic linkage regions and in the identification of novel candidate genes using genome-wide methods in mouse models of anxiety.

Targeting ASIC1a reduces innate fear and alters neuronal activity in the fear circuit

BACKGROUND

The molecular mechanisms underlying innate fear are poorly understood. Previous studies indicated that the acid sensing ion channel ASIC1a influences fear behavior in conditioning paradigms. However, these differences may have resulted from an ASIC1a effect on learning, memory, or the expression of fear.

METHODS

To test the hypothesis that ASIC1a influences the expression of fear or anxiety independent of classical conditioning, we examined the effects of disrupting the mouse ASIC1a gene on unconditioned fear in the open field test, unconditioned acoustic startle, and fear evoked by the predator odor trimethylthiazoline (TMT). In addition, we tested the effects of acutely inhibiting ASIC1a with PcTx, an ASIC1a antagonist in tarantula venom. Our immunohistochemistry suggested ASIC1a is expressed in the bed nucleus of the stria terminalis, medial amygdala, and periaqueductal gray, which are thought to play important roles in the generation and expression of innate fear. Therefore, we also tested whether ASIC1a disruption altered c-fos expression in these structures following TMT exposure.

RESULTS

We found that the loss of ASIC1a reduced fear in the open field test, reduced acoustic startle, and inhibited the fear response to TMT. Similarly, intracerebroventricular administration of PcTx reduced TMT-evoked freezing in ASIC1a(+/+) mice but not ASIC1a(-/-) mice. In addition, loss of ASIC1a altered TMT-evoked c-fos expression in the medial amydala and dorsal periaqueductal gray.

CONCLUSIONS

These findings suggest that ASIC1a modulates activity in the circuits underlying innate fear. Furthermore, the data indicate that targeting the ASIC1a gene or acutely inhibiting ASIC1a suppresses fear and anxiety independent of conditioning.

Porcine maternal infanticide as a model for puerperal psychosis

Childbirth is a period of substantial rapid biological and psychological change and a wide range of psychotic disorders can occur ranging from mild 'baby blues' to severe episodes of psychotic illnesses. Puerperal psychosis is the most extreme form of postnatal psychosis, occurring in 1 in 1,000 births. In this study, we have used the pig as an animal model for human postnatal psychiatric illness. Our aim was to identify quantitative trait loci (QTL) associated with maternal (infanticide) sow aggression. This is defined by sows attacking and killing their own newborn offspring, within 24 hr of birth. An affected sib pair whole genome linkage analysis was carried out with 80 microsatellite markers covering the 18 porcine autosomes and the X chromosome, with the aim of identifying chromosomal regions responsible for this abnormal behavior. Analysis was carried out using the non-parametric linkage test of Whittemore and Halpern, as implemented in the Merlin software. The results identified 4 QTL mapping on Sus scrofa chromosomes 2 (SSC2), 10 (SSC10), and X (SSCX). The peak regions of these QTL are syntenic to HSA 5q14.3-15, 1q32, Xpter-Xp2.1, and Xq2.4-Xqter, respectively. Several potential candidate genes lie in these regions in addition to relevant abnormal behavioral QTL, found in humans and rodents.

Genetic determinants of emotionality and stress response in AcB/BcA recombinant congenic mice and in silico evidence of convergence with cardiovascular candidate genes

Genomic loci bearing stress-related phenotypes were dissected in recombinant congenic strains (RCS) of mice with C57BL/6J (B6) and A/J progenitors. Adult male mice from 14 A/J and 22 B6 background lines were evaluated for emotional reactivity in open-field (OF) and elevated plus-maze tests. Core temperature was monitored by radio telemetry during immobilization and on standard as well as salt-enriched diets. In addition, urinary electrolytes were measured. Genome-wide linkage analysis of the parameters revealed over 20 significant quantitative trait loci (QTL). The highest logarithm of odds (LOD) scores were within the previously-reported OF emotionality locus on Chr 1 (LOD = 4.6), in the dopa decarboxylase region on Chr 11 for the plus-maze (LOD = 4.7), and within a novel region of calmodulin 1 on Chr 12 for Ca++ excretion after a 24-h salt load (LOD = 4.6). RCS stress QTL overlapped with several candidate loci for cardiovascular (CV) disease. In silico evidence of functional polymorphisms by comparative sequence analysis of progenitor strains assisted to ascertain this convergence. The anxious BcA70 strain showed down regulation of Atp1a2 gene expression in the heart (P < 0.001) and brain (P < 0.05) compared with its parental B6 strain, compatible with the enhanced emotionality described in knock out animals for this gene, also involved in the salt-sensitive component of hypertension. Functional polymorphisms in regulatory elements of candidate genes of the CV/inflammatory/immune systems support the hypothesis of genetically-altered environmental susceptibility in CV disease development.

Association of a Met88Val diazepam binding inhibitor (DBI) gene polymorphism and anxiety disorders with panic attacks

Several lines of evidence suggest that anxiety disorders have a strong genetic component, but so far only few susceptibility genes have been identified. There is preclinical and clinical evidence for a dysregulation of the central gamma-aminobutyric acid (GABA)-ergic tone in the pathophysiology of anxiety disorders. Diazepam binding inhibitor (DBI) has been suggested to play a pivotal role in anxiety disorders through direct and indirect, i.e. via synthesis of neuroactive steroids, modulation of GABA(A) receptor function. These findings suggest that the DBI gene can be postulated as a candidate for a genetic association study in this disorder. Thus, single nucleotide polymorphisms (SNPs) of the DBI gene were investigated for putative disease associations in a German sample of anxiety disorder patients suffering from panic attacks and matched controls. We were able to detect a significant association between a non-synonymous coding variant of DBI with anxiety disorders with panic attacks. The rare allele of this polymorphism was more frequent in controls than in patients (OR=0.43; 95% CI: 0.19-0.95). In conclusion, these results suggest a central role of DBI genetic variants in the susceptibility for the development of anxiety disorders that are characterized by the occurrence of panic attacks.

Genetik der Angsterkrankungen

The authors give an overview of the present state of knowledge on the genetics of anxiety disorders. According to ICD-10 or DSM III/IV classification, anxiety disorders comprise panic disorder, generalized anxiety, phobias, and post-traumatic stress disorder. In the context of the conceptual change from psychodynamic anxiety neuroses to complex, multifactorial anxiety disorders, a summary of biological hypotheses of the pathogenesis of anxiety derived from pharmacotherapy, challenge tests, and animal model disorders is provided. The relevant findings from clinical genetic studies (twin and family) and molecular genetic studies (linkage and association) are presented in detail. The most data now available are on panic disorder, though with regard to molecular genetics these are still preliminary. In addition, genetic findings on anxiety as a personality dimension are reviewed, taking into account the present phenotype discussion (category vs dimension). Finally, ethical and therapeutic implications of genetic research on complex, polygenic disorders are discussed.

Identifying the genetic determinants of emotionality in humans; insights from rodents

The identification of human quantitative trait genes underlying variation in emotionality has proved to be both difficult and expensive. Whilst several QTL have been consistently identified and independently replicated across both phenotypes and populations, little progression has been made towards the identification of underlying genes or even variants. In this review we discuss the potential for using cross-species QTL concordance as a tool for QTL dissection in behaviour genetics, using an affect-related locus mapped to human chromosome 1 as an example.