New segregation analysis of panic disorder

Role of MicroRNAs in Anxiety and Anxiety-Related Disorders

MicroRNAs as critical regulators of gene expression important for functions including neuronal development, synapse formation, and synaptic plasticity have been linked with the regulation of neurobiological systems that underlie anxiety processing in the brain. In this chapter, we give an update on associative evidence linking regulation of microRNAs with anxiety- and trauma-related disorders. Moving beyond correlative research, functional studies have emerged recently that explore causal relationships between microRNA expression and anxiety-like behavior. It has been demonstrated that experimental up- or downregulation of the candidate microRNAs in important nodes of the anxiety neurocircuitry can indeed modulate anxiety-related behavior in animal models. Improved methodologies for assessing microRNA-mediated modulation have aided such functional studies, revealing a number of anxiety-regulating microRNAs including miR-15a, miR-17-92, miR-34, miR-101, miR-124, miR-135, and miR-155. Important functional target genes of these identified microRNAs are associated with specific neurotransmitter/neuromodulator signaling, neurotrophin (e.g., BDNF) expression and other aspects of synaptic plasticity, as well as with stress-regulatory/hypothalamic-pituitary-axis function. Furthermore, microRNAs have been revealed that are regulated in distinct brain regions following various anxiety-attenuating strategies. These include pharmacological treatments such as antidepressants and other drugs, as well as non-pharmacological interventions such as fear extinction/exposure therapy or positive stimuli such as exposure to environmental enrichment. These are first indications for a role for microRNAs in the mechanism of action of anxiolytic treatments. As research continues, there is much hope that a deeper understanding of the microRNA-mediated mechanisms underlying anxiety-related disorders could open up possibilities for future novel biomarker and treatment strategies.

Impairment of Working Memory, Decision-making, and Executive Function in the First-Degree Relatives of People with Panic Disorder: A Pilot Study

BACKGROUND

Panic disorder (PD) patients present impairments of working memory, decision-making, and executive function. However, whether the first-degree relatives (FDRs) of people with PD present abnormal characteristics, including clinical and neuropsychological aspects, in comparison to the general population, has not been studied. Investigation and understanding of the abnormal neuropsychological characteristics of the FDRs of people with PD will contribute to the prevention and treatment of PD.

OBJECTIVE

The purpose of this paper is to compare the working memory, decision-making, and executive function among people with PD, their FDRs, and controls.

MATERIALS AND METHODS

Neuropsychological functions of 30 people with PD, 30 FDRs of people with PD, and 30 controls were measured with a digit span task, Iowa Gambling Task (IGT), and Wisconsin Card Sorting Test (WCST).

RESULTS

Perseverative errors, failure to maintain set scores, and number of cards chosen from decks A, B, C, and D were higher for People with PD and their FDRs than those of controls. Furthermore, error rates for these tests were higher for people with PD than their FDRs. Forward scores and backward scores, percentage of conceptual level responses, the number of categories completed, choices from advantageous minus disadvantageous decks, and mean amount of money earned of people with PD and their FDRs were all lower than those of controls. Scores for these tests were also lower for people with PD than for their FDRs.

CONCLUSION

People with PD as well as their FDRs present different degrees of impairments of working memory, decision-making, and executive function. Impaired performance on three tasks appears to be associated with the diathesis for PD and may be a valuable indicator of susceptibility for this disorder.

Temperament characteristics in patients with panic disorder and their first-degree relatives

AIM

Panic disorder is one of the highly heritable anxiety disorders; and temperament characteristics are considered predicting liability to panic disorder. Accumulating evidence suggests temperament characteristics are intermediate phenotypes for clinical conditions. Given this background, we aimed to investigate temperament characteristics in patients with panic disorder, their first-degree relatives, and healthy controls.

METHOD

Study sample consisted of 60 patients with panic disorder, 37 first-degree relatives of these patients, and 37 age, gender, and education level matched healthy controls (HC). SCID-I, the Panic Agoraphobia Scale, and the State and Trait Anxiety Inventory were applied to assess clinical characteristics of the patient group. Temperament characteristics were assessed using the Temperament Evaluation of Memphis, Pisa, Paris, San Diego Autoquestionnaire (TEMPS-A).

RESULTS

Anxious, depressive, cyclothymic, and irritable temperament scores of patients were higher than those of HC. There was no difference between the patients and the relatives, with the exception of higher anxious temperament scores in patients.

CONCLUSION

Overall, our findings suggest that anxious temperament characteristic might be a trait marker for liability to panic disorder. Further research with a prospective design in a larger sample is required to confirm our findings.

Pro198Leu polymorphism in the oxidative stress gene, glutathione peroxidase-1, is associated with a gender-specific risk for panic disorder

OBJECTIVE

Panic disorder (PD) is an anxiety disorder characterized by sudden attacks of intense fear. Biochemical studies suggest that oxidative stress (OS) index is significantly higher in PD, and OS genes may participate in development of anxiety-like behavioral phenotypes. We aimed to investigate role of polymorphisms in OS gene, glutathione peroxidase-1 (GPX1), and DNA repair enzyme gene, 8-oxoguanine glycosylase-1 (OGG1), in PD patients.

METHODS

GPX1 Pro198Leu (rs1050450) and OGG1 Ser326Cys (rs1052133) polymorphisms of 127 patients with PD and 151 disease-free controls were analyzed with real-time polymerase chain reaction. Severity of PD symptoms was assessed by Panic and Agoraphobia Scale (PAS).

RESULTS

No significant relationship was found in genotype distributions of OGG1 Ser326Cys and GPX1 Pro198Leu polymorphisms between PD and control groups (p > 0.05). There was no significant relationship between OGG1 or GPX1 polymorphisms, and age of onset, agoraphobia, or PAS scores in PD group (p > 0.05). However, in GPX1 Pro198Leu polymorphism, C allele (Pro) was found to be more frequent in female subgroup of PD patients compared with that in males (p = 0.027).

CONCLUSIONS

GPX1 Pro198Leu and OGG1 Ser326Cys polymorphisms were not associated with PD risk in Turkish patients. However, a gender-specific effect of GPX1 Pro198Leu C allele may be associated with PD development.

Evidence for linkage and association of GABRB3 and GABRA5 to panic disorder

Panic disorder (PD) is a debilitating anxiety disorder characterized by episodes of intense fear with autonomic and psychological symptoms that lead to behavioral impairment. A convergence of genetic and biological evidence implicates gamma-aminobutyric acid type A receptor subunits on chromosome 15q12 as candidate genes for PD. This study investigated 120 Caucasian, multiplex PD pedigrees using regional microsatellites (chr15q11-13) and found support for linkage (logarithm of odds (LOD) ⩾2), with a prominent parent-of-origin effect. Genotyping with 10 single-nucleotide polymorphisms (SNPs) showed linkage to GABRB3 (rs11631421, LOD=4.6) and GABRA5 (rs2075716, LOD=2.2), and allelic association to GABRB3 (rs8024564, p=0.005; rs8025575, p=0.02) and GABRA5 (rs35399885, p=0.05). Genotyping of an independent Sardinian PD trio sample also supported association in the region, again with a parent-of-origin effect. These findings provide genetic evidence for the involvement of the genes GABRB3 and GABRA5 in the susceptibility to PD.

Effects of ADORA2A gene variation and caffeine on prepulse inhibition: a multi-level risk model of anxiety

The complex pathogenesis of anxiety and panic disorder in particular has been suggested to be influenced by genetic factors such as the adenosine A2A receptor gene (ADORA2A) 1976T>C polymorphism (rs5751876) as well as neuropsychological factors such as early information processing deficits. In 114 healthy individuals (males=57, females=57) controlled for anxiety sensitivity (AS), a multi-level risk model of the development of anxiety was applied: Genetic (ADORA2A 1976T>C variant) and biochemical (300 mg of caffeine citrate vs. placebo) factors were hypothesized to influence early information processing as measured by the prepulse inhibition/facilitation paradigm (stimulus onset asynchronies (SOAs) of 60, 120, 240, 480 and 2000ms between prepulses and startle stimuli). A fourfold interaction of genotype, intervention, gender, and SOAs was discerned. Stratification by SOAs revealed that at 120 ms and 240 ms SOAs in the caffeine condition, PPI was impaired in female ADORA2A 1976TT risk genotype carriers as compared to male ADORA2A 1976TT homozygotes, while no significant effects were observed in the ADORA2A 1976CC/CT non-risk genotype or placebo group. Only in high anxiety sensitive probands, a significant intervention effect was discerned with impaired prepulse facilitation (PPF) due to caffeine. The present results point to an impaired ability to selectively process very early information and to gate irrelevant sensory information, respectively, in female ADORA2A 1976TT homozygotes in response to caffeine, providing further evidence for the adenosinergic system to be involved in the pathogenesis of anxiety.

Are there anxious genes?

Anxiety comprises many clinical descriptions and phenotypes. A genetic predisposition to anxiety is undoubted; however, the nature and extent of that contribution is still unclear. Methods for the genetic analysis of such complex disorders is briefly reviewed, followed by a discussion of the comorbidity of anxiety with other psychiatric disorders and their possible common genetic etiology. Extensive genetic studies of the serotonin (5-hydroxytryptamine, 5-HT) transporter (5-HTT) gene have revealed how variation in gene expression can be correlated with anxiety phenotypes. Complete genome-wide linkage scans for panic disorder (PD) susceptibility genes have suggested a locus on chromosome arm 7p, and association studies have highlighted many candidate genes. A highly significant association between phobias, panic disorder, and a duplication at chromosomal region 15q24-26 is one of the most exciting findings to date. Emerging molecular genetic technologies and the use of increasingly sophisticated animal models of anxiety provide great promise for the future of the field.

Genetic polymorphism of angiotensin I-converting enzyme (ACE), but not angiotensin II type I receptor (ATr1), has a gender-specific role in panic disorder

AIMS

Angiotensins were shown to have some role in the development of panic disorder (PD). In this study, we aimed to determine the frequency of polymorphisms in two angiotensin-related genes, angiotensin I-converting enzyme (ACE) and angiotensin II type I receptor (ATr1), in a sample of Turkish patients with PD and to evaluate their association with PD development.

METHODS

Polymerase chain reaction and restriction fragment length polymorphism was used to analyze ATr1 A1166C polymorphism, and only polymerase chain reaction was used to analyze functional ACE insertion/deletion polymorphism in 123 patients with PD and in 169 similarly aged disease-free controls.

RESULTS

 There was no significant difference in the genotype distribution between PD patients and controls for each polymorphism (P>0.05). Allele frequency of ACE insertion/deletion was borderline statistically significant between the groups (P=0.055; odds ratio: 1.39; 95% confidence interval: 0.99-1.95), and allele frequency of ATr1 A1166C was not significantly different between the groups (P=0.32; odds ratio: 0.81; 95% confidence interval: 0.53-1.22).

CONCLUSION

This study suggests that polymorphisms of ACE I/D and ATr1 A1166C are not associated with risk of PD in Turkish patients. However, in ACE insertion/deletion polymorphism, the insertion allele was found to be more frequent in the male subgroup of patients (χ²=4.61, P=0.032) than in controls, suggesting a potential male-specific role of the less active ACE insertion allele in the pathogenesis of PD.

Behavioral genetics of affective and anxiety disorders

As shown by clinical genetic studies, affective and anxiety disorders are complex genetic disorders with genetic and environmental factors interactively determining their respective pathomechanism. Advances in molecular genetic techniques including linkage studies, association studies, and genome-wide association studies allow for the detailed dissection of the genetic influence on the development of these disorders. Besides the molecular genetic investigation of categorical entities according to standardized diagnostic criteria, intermediate phenotypes comprising neurobiological or neuropsychological traits (e.g., neuronal correlates of emotional processing) that are linked to the disease of interest and that are heritable, have been proposed to be closer to the underlying genotype than the overall disease phenotype. These intermediate phenotypes are dimensional and more precisely defined than the categorical disease phenotype, and therefore have attracted much interest in the genetic investigation of affective and anxiety disorders. Given the complex genetic nature of affective and anxiety disorders with an interaction of multiple risk genes and environmental influences, the interplay of genetic factors with environmental factors is investigated by means of gene-environment interaction (GxE) studies. Pharmacogenetic studies aid in the dissection of the genetically influenced heterogeneity of psychotropic drug response and may contribute to the development of a more individualized treatment of affective and anxiety disorders. Finally, there is some evidence for genetic factors potentially shared between affective and anxiety disorders pointing to a possible overlapping phenotype between anxiety disorders and depression.

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.

Life events in panic disorder-an update on "candidate stressors"

Studies on gene-environment interactions in mental disorders are characterized by powerful genetic techniques and well defined "candidate genes," whereas a definition of "candidate stressors," in most cases assessed in the form of life events (LEs), is inconsistent or not even provided. This review addresses this problem, with particular attention to the clinical phenotype of panic disorder (PD), by providing an overview and critical discussion for which life events are known to contribute to the etiology of the disease and how they may be conceptualized. There is converging evidence for a significant impact of cumulative as well as specific life events, such as threat, interpersonal and health-related events in adulthood, and abuse or loss/separation experiences in childhood, respectively, on the pathogenesis of panic disorder with some overlapping effect across the anxiety disorder spectrum as well as on comorbid major depression. Besides genetic vulnerability factors, personality and behavioral characteristics, such as anxiety sensitivity, neuroticism, and cognitive appraisal might moderate the influence of LEs on the development of panic disorder. The present state of knowledge regarding the specification and conceptualization of LEs in PD within a more complex multifactorial model, involving mediating and moderating factors in between genes and the clinical phenotype, is hoped to aid in informing future gene-environment interaction studies in panic disorder.

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.

Association and linkage analysis of candidate genes GRP, GRPR, CRHR1, and TACR1 in panic disorder

Panic disorder (PD) is a debilitating anxiety disorder, characterized by recurrent episodes of intense fear that are accompanied by autonomic and psychological symptoms leading to behavioral impairment. Basic research implicates neuropeptide-signaling genes in the modulation of anxiety and stress. The genes encoding corticotropin releasing hormone receptor 1 (CRHR1), tachykinin receptor 1 (TACR1), gastrin releasing peptide (GRP), and gastrin releasing peptide receptor (GRPR) were selected as candidates for PD based on their biology. Linkage and association analysis in 120 multiplex U.S. PD pedigrees was performed using 21 single nucleotide polymorphisms (SNPs). Parametric and non-parametric linkage tests in pedigrees, for single point and multipoint analysis, revealed limited support for genetic linkage to TACR1 (parametric and non-parametric lod scores approximately 1). The family-based association test (FBAT) generated nominal support for allelic association in TACR1 (P = 0.02), and GRP (P = 0.02), findings which must be considered in the light of multiple comparisons. Further exploration of the GRP and TACR1 findings in large case-control PD samples may provide more definitive evidence implicating these loci in the genetic etiology of PD.

Meta-analysis of COMT val158met in panic disorder: ethnic heterogeneity and gender specificity

There is strong evidence for a genetic contribution to the pathogenesis of panic disorder, with the functional catechol-O-methyltransferase (COMT) val158met polymorphism having been suggested as a potential susceptibility factor. In the present study, a meta-analysis of six available case-control studies (557 patients with panic disorder and 763 healthy controls in total) on the role of the COMT val158met polymorphism in panic disorder was conducted in an attempt to reconcile previous conflicting results and to facilitate evaluation of the role of COMT gene variation in panic disorder. Overall, no significant association, but strong between-study heterogeneity, was discerned. Analysis of studies pooled by ancestry yielded a significant association of the COMT 158val allele with panic disorder in Caucasian samples and, conversely, a trend towards association of the COMT 158met allele with the disorder in Asian samples. Interestingly, stratification for gender as well as ethnicity revealed that association of the 158val allele in Caucasians and, reciprocally, the 158met allele in Asian samples was restricted to females. The present meta-analysis provides tentative support for the COMT val158met polymorphism as a possible risk factor for panic disorder, with differential effects in Caucasian and Asian populations, and suggests a female-specific effect. However, given the relatively small number of case-control studies presently available, several more association studies, preferably including a larger number of family-based studies, are warranted for conclusive evaluation of the COMT val158met polymorphism as a vulnerability factor in panic disorder.

Polymorphisms in the serotonin receptor gene HTR2A are associated with quantitative traits in panic disorder

Anxiety disorders and specifically panic disorder (PD) are caused by complex interactions of environmental and genetic factors. The latter comprise many different genes, from which those involved in serotonergic neurotransmission have received particular attention. Here we report the results from an association candidate-gene approach, where we analyzed 15 single nucleotide polymorphisms (SNPs) within the gene coding for the serotonin-receptor 2A (HTR2A) in patients suffering from PD and a control sample. We found that the SNP rs2296972 shows an association between the number of T-alleles and severity of symptoms in PD. By performing tests according to the Fisher product method (FPM), an association between HTR2A and the personality trait reward dependence could be shown. Most pronounced effects were observable for the SNPs rs2770304, rs6313, and rs6311. Furthermore, the polymorphisms rs3742278, rs2296972, and rs2770292 form a haplotype, which may be associated with higher susceptibility for PD. These results further underline a possible important role of genetic variations within the system controlling serotonergic neurotransmission for the development and course of disease in PD.

Association of the Val158Met catechol O-methyltransferase genetic polymorphism with panic disorder

Genetic as well as clinical data suggest that catechol O-methyltransferase (COMT) is involved in multiple complex psychiatric conditions. Recent studies have described an association between the Val158Met COMT polymorphism and panic disorder. Other recent investigations provide evidence that there are other loci within or nearby the COMT gene that may contribute to the susceptibility to panic disorder. To further evaluate the influence of the Val158Met COMT polymorphism in panic disorder we genotyped this marker in the coding region of the COMT gene and two additional variants (rs737865 and rs165599) in the 5' and the 3' region, respectively, in two independent Canadian samples: 121 nuclear families, and 89 cases with matched controls. In the nuclear families, significant transmission disequilibrium for the valine allele was observed between the alleles of the Val158Met COMT polymorphism and panic disorder (p<0.01). A significant excess of the valine allele was found in analysis of the case-control sample (p<0.01). This effect was mainly derived from the subgroup of females. This finding, including the female effect, replicates earlier results in studies of the Val158Met polymorphism in panic disorder. No significant results were found for the other two markers. These results support the hypothesis that the valine allele of the Val158Met COMT polymorphism or a nearby locus is involved in the etiopathogenesis of panic disorder.

A third-pass genome scan in panic disorder: evidence for multiple susceptibility loci

BACKGROUND

Panic disorder (PD) is a common illness with a definite but "complex" genetic contribution and estimated heritability of 30-46%.

METHODS

We report a genome scan in 120 multiplex PD pedigrees consisting of 1591 individuals of whom 992 were genotyped with 371 markers at an average spacing of 9cM. Parametric two-point, multipoint, and nonparametric analyses were performed using three PD models (Broad, Intermediate, Narrow) and allowing for homogeneity or heterogeneity. The two-point analyses were also performed allowing for independent male and female recombination fractions (theta). Genome-wide significance was empirically evaluated using simulations of this dataset.

RESULTS

Evidence for linkage reached genome-wide significance in one region on chromosome 15q (near GABA-A receptor subunit genes) and was suggestive at loci on 2p, 2q and 9p using an averaged theta. Analyses allowing for sex-specific theta's were consistent except that support at one locus on 2q increased to genome-wide significance and an additional region of suggestive linkage on 12q was identified. However, differences in male and female recombination fractions predicted by the sex-specific approach were not consistent with current physical maps.

CONCLUSIONS

These data provide evidence for chromosomal regions on 15q and 2q that may be important in genetic susceptibility to panic disorder. Although we are encouraged by the findings of analyses using sex-specific recombination fractions, we also note that further understanding of this analytic strategy will be important.

Lack of association between the corticotrophin-releasing hormone receptor 2 gene and panic disorder

Panic disorder is classified as an anxiety disorder and affects 1-3% of the population. An individual suffering from such a disorder may experience unexpected recurrent panic attacks and fear of future attacks. Twin and family studies have pointed towards a strong heritability of the disorder. Stress response and anxiety are thought to be mediated, at least in part, by the corticotrophin-releasing hormone (CRH), which is known to be a regulator of the hypothalamic-pituitary-adrenal pathway. To search for markers conferring genetic susceptibility to panic disorder, we typed three polymorphisms of the CRHR2 gene - CRHR2(CA), CRHR2(GT), and CRHR2(GAT) - in 466 individuals, 183 of whom had DSM-IV panic disorder. Seventy-five case-controls and 101 triad families plus 13 siblings were examined. Case-control association analyses using chi(2) tests yielded no difference in the distribution of the alleles. Linkage analysis using the Transmission Disequilibrium Test showed no preferential transmission of alleles for any of the three markers. Haplotype analysis indicated that allele 7 of CRHR2 (GAT) and 8 of CRHR2 (GT) are in almost complete linkage disequilibrium (P = 0.000 000 1). Although both neurobiology and chromosomal location point to the CHRH2 receptor gene as a candidate for panic disorder, our study indicates that the CRHR2 polymorphisms examined do not confer susceptibility to panic disorder. Further studies investigating additional polymorphisms in this gene and other components of the CRH signalling system may prove useful.

Rgs 2 gene polymorphisms as modulators of anxiety in humans?

Rgs2 (regulator of G-protein signalling 2) gene recently was reported as a quantitative trait gene for anxious behaviour in mice and male Rgs2 knockout mice have been shown to be more anxious than wildtype mice. Therefore we investigated four non-coding single nucleotide polymorphisms in a sample of 173 patients with panic disorder and 173 matched controls of German descent. At the genotype level all four SNPs were associated with panic disorder (p = 0.02-0.05). At the haplotype level the strongest association was observed for a haplotype containing SNP3 and SNP 4 (subgroup men and men with agoraphobia: p = 0.01 and 0.03). This points towards a functional polymorphism at the 3' end of the gene. Our results support the hypothesis that variations of the Rgs2 gene play a role also for the development of anxiety in humans.

Interaction of serotonergic and noradrenergic gene variants in panic disorder

OBJECTIVE

Panic disorder is an anxiety disorder with an estimated heritability of 48%. Associations findings have been obtained with candidate genes from both serotonergic and noradrenergic pathways including regulatory and coding variants of the serotonin receptor 1A gene, the monoamine oxidase A gene, the catechol-O-methyltransferase gene and the norepinephrine transporter gene.

METHODS

In the present study, an analysis of interactions between the functional serotonin receptor 1A polymorphism, the norepinephrine transporter variants and the other respective polymorphisms of the above-mentioned genes is reported. The analysis is based on genotype results from 115 cases and 115 age and sex-matched controls.

RESULTS

A nominally significant (P=0.04) interaction between the serotonin receptor 1A and the catechol-O-methyltransferase polymorphisms was observed. Stratified analysis revealed that the odds ratio of each polymorphism was highest in the presence of the low-risk genotype(s) of the other polymorphism and low in the presence of the high-risk genotype(s) of the other polymorphism.

CONCLUSIONS

This is the first possible interaction of genetic variations in panic disorder that has been observed. As the sample size was small and no adjustment for multiple testing was made, the assessment of the interacting risk alleles needs replication in a larger sample with higher power.

Association study of serotonin-2A receptor gene polymorphism and panic disorder in patients from Canada and Germany

The T102C serotonin-2A (5-HT2A) receptor gene polymorphism has been studied extensively in a number of complex psychiatric conditions with mixed results. Recently a genetic association has been described between this polymorphism and panic disorder in a Japanese sample. To evaluate the impact of the T102C polymorphism in panic disorder we genotyped triad families (panic disorder patient and parents), and cases with controls in Canadian and German samples. No significant transmission disequilibrium was observed between the alleles of the T102C 5-HT2A receptor gene polymorphism and panic disorder, nor was a significant excess of either allele found in the case control analysis. Our data suggest thus that this polymorphism is unlikely to play a major role in the pathogenesis of panic disorder.

The genetics of panic disorder: state of the art

Panic disorder (PD) is a highly prevalent, debilitating disorder. The heritability of the disease has been estimated by twin studies to be between 30 and 60%. The vulnerability for PD overlaps with an increased risk of bipolar disorder in some families. Classical genetic methods such as linkage analysis and association studies have not yet identified genetic risk factors beyond doubt. However, two independent studies confirm linkage of a specific syndrome characterized by PD, bladder problems, severe headaches, mitral valve prolapse and thyroid dysfunction to genetic markers on chromosome 13q. Association studies, although showing divergent results, give some support to a causative role for the genes encoding for monoamine oxidase A (MAO-A), cholecystokinin (CCK) and catechol-O-methyltransferase (COMT). Finally, a somatic duplication of a 19-Mb region on chromosome 15 has been associated with PD, but this intriguing finding awaits confirmation.

Evidence for genetic linkage between a polymorphism in the adenosine 2A receptor and panic disorder

Data from clinical and behavioral pharmacological studies have implicated adenosine in anxiety behaviors, while genetic studies have suggested that adenosine receptors may be associated with panic disorder. We have undertaken an analysis of several DNA sequence variations in the adenosine 2A receptor (ADORA2A) in a large sample of panic disorder pedigrees. Individuals from 70 panic disorder pedigrees, and 83 child-parent 'trios', were genotyped at five single-nucleotide polymorphisms (SNPs) in and near the ADORA2A gene and were analyzed for genetic linkage and association. Linkage analysis revealed elevated LOD scores for a silent substitution (1083C/T, SNP-4) in the second coding exon. This SNP has been previously reported to be associated with panic disorder. We observed a maximal heterogeneity LOD score of 2.98 (theta=0) under a recessive genetic model and narrow diagnostic model. Other SNPs showed no evidence for linkage. Association tests were not significant for any of the five ADORA2A SNPs. When SNP haplotypes were assessed in the triads with TRANSMIT, one 3-marker haplotype (SNPs 1, 4, 5) was nominally significantly associated with panic disorder (p=0.029). Pairwise estimations of linkage disequilibrium between the SNPs showed strong patterns of linkage disequilibrium across the ADORA2A locus. Analyses carried out by broadening the panic disorder phenotype to include agoraphobia continued to support linkage to ADORA2A. Our findings provide evidence for a susceptibility locus for panic disorder, and possibly including agoraphobia, either within the ADORA2A gene or in a nearby region of chromosome 22, and serves as the first successful candidate gene replication study in panic disorder.

Cholecystokinin- and cholecystokinin-B-receptor gene polymorphisms in panic disorder

Panic disorder like other neuropsychiatric disorders is believed to be caused by multiple psychosocial and biological factors. Several lines of evidence point to a role for the peptide neurotransmitter cholecystokinin in the pathogenesis of panic disorder. We therefore determined the allele and genotype frequencies of a single nucleotide polymorphism in the CCK gene (-36C>T) and one CT repeat polymorphism in the CCK-B-receptor gene in a German panic disorder sample (n = 115 for CCK gene polymorphism, n = 111 for CCK-B-receptor polymorphism) and compared them with gender and age matched controls. The length of the polymorphic CT repeat alleles varies between 146 bp and 180 bp. We first analysed the results by a permutation test which provided evidence for heterogeneity between patients and controls (p=0.002). We then analysed the data as a di-allelic polymorphism with a short (146-162bp) and a long (164-180bp) allele and as a tetra-allelic polymorphism with 4 alleles (146-154bp, 156-162bp, 164-170bp, 172-180bp). In the di-allelic analysis as well as in the tetra-allelic analysis there was an excess of the longer allele (p = 0.001) or the two longer alleles (p = 0.041) respectively in patients with panic disorder. No difference between groups was observed for the -36C > T polymorphism. Our findings are consistent with the notion that genetic variation in the CCK neurotransmitter system contributes to the pathogenesis of panic disorder.

Positive association between panic disorder and polymorphism of the serotonin 2A receptor gene

Family and twin studies have shown that genetic factors play an important role in the etiology of panic disorder. However, linkage and association studies using DNA markers have yielded inconclusive results. Increased serotonin neurotransmission may cause or be related to panic disorder. Assuming that genes regulating the serotonin system are involved in the pathogenesis of panic disorder, the authors searched for a genetic association of panic disorder with the serotonin 1A (HTR1A), 2A (HTR2A), and 2C (HTR2C) receptor genes. HTR1A, HTR2A and HTR2C polymorphisms were detected by the polymerase chain reaction method with analysis of restriction fragment-length polymorphisms (PCR-RFLP). The subjects were 63 biologically unrelated patients with panic disorder and 100 biologically unrelated normal control subjects who were native Japanese living in the western area of Japan. HTR1A and HTR2C showed no significant association with panic disorder. However, the frequency of the MspI A2 allele of HTR2A was significantly higher in the patients than in the normal control subjects. The study showed a positive association between panic disorder and the HTR2A gene, suggesting that HTR2A plays an important role in the pathogenesis of panic disorder.

Human nuclear transcription factor gene CREM: genomic organization, mutation screening, and association analysis in panic disorder

Panic disorder is an anxiety disorder with an estimated heritability of 48%. Variation in the gene of the nuclear transcription factor "cAMP-responsive element modulator" (CREM) might contribute to its pathogenesis. CREM knock-out mice exhibit significantly less anxiety behavior than wild-type mice and the alternative CREM gene product "inducible cAMP early repressor" (ICER) plays a pivotal role in the hypothalamo-pituitary-adrenal (HPA) axis, which is disturbed in panic disorder. We characterized the genomic organization of the human CREM gene and performed a systematic mutation screening by means of single stranded conformational analysis (SSCA) in a sample of 40 German patients with panic disorder (DSM-III-R). Four novel single nucleotide polymorphisms in CREM promoters P 1 and P 4, one trinucleotide (ATT)-repeat polymorphism in CREM promoter P 2-generating the ICER isoform-and a rare amino acid substitution in CREM exon glut 2 were identified. Association analysis in an extended sample of German patients (n = 88) revealed a significant excess of the shorter CREM P 2 promoter eight-repeat trinucleotide allele and of genotypes containing the eight-repeat trinucleotide allele in panic disorder (P = 0.02), in particular in panic disorder without agoraphobia (P = 0.001). A replication study in independent Italian (n = 76) and Spanish (n = 62) samples, however, failed to confirm this observation. This suggests that the CREM P 2 promoter trinucleotide polymorphism is not a major susceptibility factor in the pathogenesis of panic disorder. Functional analysis of the observed CREM P 2 promoter polymorphism as well as studies in independent panic disorder samples are necessary.

Attachment and panic disorder

A dysfunctional relationship between parents and children can influence cognitive and emotional development and contribute to the development of psychiatric disorders, particularly panic disorder (PD). With the aim of exploring childhood experiences of parenting in PD patients, we compared subjectively perceived climate and objective recall by administering the Parental Bonding Instrument and 10 adjunctive items to 22 out-patients and 22 matched controls. Our analysis showed that DSM-III-R-diagnosed PD patients reported their parents to be significantly less caring than did the control group, while there was no significant difference in objective recall of parenting experiences.

Relative risk for genetic associations: the case-parent triad as a variant of case-cohort design

The contribution of this paper is to conceptualize the case-parent triad within an epidemiological framework. We propose that the case-parent triad design is a variant of the case-cohort design. The affected offspring of case-parent triads come from a source cohort of all offspring of parents in a population. We first demonstrate that if the source cohort is restricted to offspring of a certain parental mating type then the relative risk in relation to genetic exposure can be estimated simply from the ratio of the number of exposed to the number of unexposed affected offspring. We then extend the logic to studies including offspring of all parental mating types; provided that the allele frequencies and possible parental mating types are specified, a valid relative risk can still be estimated. Compared to prior descriptions of the case-parent triad design, the proposed approach is readily understandable, epidemiologically meaningful and provides a relatively simple perspective for estimating valid measure of effect. Also, by allowing the potential sources of selection bias to be revealed more easily the design is made more accessible both conceptually and practically to epidemiologists.

Linkage genome scan for loci predisposing to panic disorder or agoraphobia

We conducted a 10 cM linkage genome scan in a set of 20 American pedigrees (153 subjects), ascertained through probands with panic disorder (PD). Several anxiety disorders segregate in these families; they were diagnosed on the basis of Schedule for Affective Disorders and Schizophrenia interview. In this article, we describe results for panic disorder and agoraphobia, which are closely related, common, heritable anxiety disorders. This is the first complete linkage genome scan for agoraphobia and the third for PD. A total of 407 markers (389 autosomal, 18 X chromosome) were genotyped. Multipoint LOD score and NPL analysis were completed using GENEHUNTER2. For PD, two genomic regions meet criteria for suggestive linkage. One of these regions is on chromosome 1 (LOD score = 2.04). This region coincides with a region that generated a LOD score of 1.1 in a previous genome scan by Crowe et al. [2001: Am J Med Genet (Neuropsychiatr Genet) 105:105-109]. The other (LOD score = 2.01) is located on chromosome 11p and occurs at marker CCKBR, one of eight candidate genes examined. For agoraphobia, the most promising potential linkage was on chromosome 3 (NPL score = 2.75; P = 0.005). This was accounted for primarily by a single family that by itself generated an NPL score of 10.01 (P = 0.0039) and a LOD score of 2.10. These results provide initial evidence for a genetic locus on chromosome 3 that contributes to risk for agoraphobia. They also support suggestive linkage to two risk loci for panic disorder. Additional potential loci were identified with lesser statistical support; several of these were consistent with previously reported panic disorder linkage results. Overall, the results presented here suggest that PD and agoraphobia are complex traits that share some, but not all, of their susceptibility loci. Published 2001 Wiley-Liss, Inc.

The genetics of panic disorder

Of the anxiety disorders, panic disorder (PD) has been the most extensively studied from a genetic standpoint. Results of family studies have consistently demonstrated that PD runs in families, and twin studies indicate that genes contribute to this familiality. However, phenotypic and genetic complexity has made finding the specific genes involved in PD a challenge. There is still uncertainty about how best to define the phenotype for genetic studies and whether it is the clinical phenotype of PD or more latent psychologic and biologic traits that are inherited. To date, molecular genetic studies have suggested some chromosomal regions and genes that may contribute to risk, but none of these have been established. We review the genetic epidemiology of PD as well as recent molecular genetic studies of the disorder, and conclude with a discussion of promising strategies that attempt to uncover specific genetic loci involved in the etiology of PD.

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

Family and twin studies have indicated that genes influence susceptibility to panic and phobic anxiety disorders, but the location of the genes involved remains unknown. Animal models can simplify gene-mapping efforts by overcoming problems that complicate human pedigree studies including genetic heterogeneity and high phenocopy rates. Homology between rodent and human genomes can be exploited to map human genes underlying complex traits. We used regions identified by quantitative trait locus (QTL)-mapping of anxiety phenotypes in mice to guide a linkage analysis of a large multiplex pedigree (99 members, 75 genotyped) segregating panic disorder/agoraphobia. Two phenotypes were studied: panic disorder/agoraphobia and a phenotype ("D-type") designed to capture early-onset susceptibility to anxiety disorders. A total of 99 markers across 11 chromosomal regions were typed. Parametric lod score analysis provided suggestive evidence of linkage (lod = 2.38) to a locus on chromosome 10q under a dominant model with reduced penetrance for the anxiety-proneness (D-type) phenotype. Nonparametric (NPL) analysis provided evidence of linkage for panic disorder/agoraphobia to a locus on chromosome 12q13 (NPL = 4.96, P = 0.006). Modest evidence of linkage by NPL analysis was also found for the D-type phenotype to a region of chromosome 1q (peak NPL = 2.05, P = 0.035). While these linkage results are merely suggestive, this study illustrates the potential advantages of using mouse gene-mapping results and exploring alternative phenotype definitions in linkage studies of anxiety disorder.

No association or linkage between polymorphisms in the genes encoding cholecystokinin and the cholecystokinin B receptor and panic disorder

Growing animal data implicate cholecystokinin in the regulation of anxiety, while human clinical research confirms the role of cholecystokinin in the provocation of panic attacks. Antipanic medications suppress the ability of cholecystokinin to induce panic attacks, and may alter the expression of the cholecystokinin gene. Thus, there is increased interest in understanding the molecular genetic component of these observations. Recent association studies using persons with panic disorder described some association between polymorphisms in the genes encoding cholecystokinin and the cholecystokinin B-receptor and panic disorder. In this study, we used a family-based design, employing 596 individuals in 70 panic disorder pedigrees, as well as 77 haplotype relative risk 'triads'. Subjects were genotyped for two polymorphisms: the polymorphic microsatellite marker in the CCK-BR locus using PCR-based genotyping and at a single nucleotide polymorphism in the CCK promoter using a fluorescence polarization detection assay, and the data were analyzed for genetic association and linkage. Employing a variety of diagnostic and genetic models, linkage analysis produced no significant lod scores at either locus. Family-based tests of association, the haplotype-based haplotype relative risk statistic and the transmission disequilibrium test, were likewise non-significant. The results reported here provide little support for the role of these polymorphisms in panic disorder.

Potential panic disorder syndrome: clinical and genetic linkage evidence

This paper reports evidence for a possible "chromosome 13 syndrome," which includes panic disorder, kidney or bladder problems, serious headaches, thyroid problems (usually hypothyroid), and/or mitral valve prolapse (MVP). In the course of a genetic linkage study of panic disorder, we noted these medical conditions in individual family members. (We were blind to family relationships and marker data.) We hypothesized that there may exist a subgroup of panic families with these medical conditions, which for simplicity we called it the "syndrome." Subsequently we reclassified the families as with or without the "syndrome" and extended the phenotype for analysis to include the above medical conditions. All these classifications were also done before the analysis and blind to marker data. We then examined our linkage results, looking for significant differences between families with and without the "syndrome" (using several definitions of the "syndrome")-i.e., testing for genetic heterogeneity. When the families with and without bladder/kidney problems were separated from each other, one marker-D13S779 (ATA26D07)-yielded a lod score of over 3 in the families with bladder/kidney problems. This lod score went up to 4.2 in these families when we diagnosed any individual with any one of the "syndrome" conditions as affected. These results were statistically significant even after applying an extremely overconservative Bonferroni correction for multiple tests. We present these results in order to alert other investigators working on panic disorder, for replication. If replicated, one may hypothesize that a candidate gene for the syndrome should be expressed in CNS, kidney, gut, thyroid, etc. We also noted that two independent studies report recent linkage findings between schizophrenia and the same region on chromosome 13. No connection between schizophrenia and panic disorder has ever been reported. Finally, we suggest that genetic studies of psychiatric disorders might prove more fruitful if phenotypes were expanded to include possible manifestations of the disorder in medical (non-mental) symptoms. Am. J. Med. Genet.(Neuropsychiatr. Genet.) 96:24-35, 2000.

A segregation study of panic disorder in families of panic patients responsive to the 35% CO2 challenge

BACKGROUND

A genetic component has a role in the etiology of Panic Disorder (PD) and a familial association between PD and CO2 hypersensitivity have been repeatedly described.

METHODS

Complex segregation analysis was performed on a sample of 165 families of PD probands and on the subgroup homogeneous for CO2 hypersensitivity, using Regressive Logistic Models. The only relatives considered to be affected were those with PD. Relatives have been diagnosed according to Family History Method.

RESULTS

A Mendelian hypothesis was compatible with our data, without distinction between different models of transmission. The Akaike's Information Criterion values indicated that the Additive model was the most parsimonious, with a gene frequency of .0005, incomplete penetrance and a phenocopy rate of .00029. By subdividing the families according to the probands' responses to CO2 inhalations, probands of 134 families were hypersensitive to CO2. The analysis performed on this subgroup supported the existence of a SML with a best fit for a Dominant model.

CONCLUSIONS

A SML account for genetic transmission in PD families and 35% CO2 challenge test may individuate a genetically homogeneous subgroup of patients with PD.

The genetics of anxiety disorders

The common denominator of anxiety disorders is that they share inappropriate levels of emotions and cognitions that affect rather than enable adaptive behaviours. The variety of symptoms include 'spontaneous' panic attacks with mental and physical symptoms, stimulus bound anxiety associated with avoidance behaviour, and almost constant 'generalized' anxious feelings. According to the DSM-IV criteria the anxiety disorders are classified as shown in Table I.

Excess of high activity monoamine oxidase A gene promoter alleles in female patients with panic disorder

A genetic contribution to the pathogenesis of panic disorder has been demonstrated by clinical genetic studies. Molecular genetic studies have focused on candidate genes suggested by the molecular mechanisms implied in the action of drugs utilized for therapy or in challenge tests. One class of drugs effective in the treatment of panic disorder is represented by monoamine oxidase A inhibitors. Therefore, the monoamine oxidase A gene on chromosome X is a prime candidate gene. In the present study we investigated a novel repeat polymorphism in the promoter of the monoamine oxidase A gene for association with panic disorder in two independent samples (German sample, n = 80; Italian sample, n = 129). Two alleles (3 and 4 repeats) were most common and constituted >97% of the observed alleles. Functional characterization in a luciferase assay demonstrated that the longer alleles (3a, 4 and 5) were more active than allele 3. Among females of both the German and the Italian samples of panic disorder patients (combined, n = 209) the longer alleles (3a, 4 and 5) were significantly more frequent than among females of the corresponding control samples (combined, n = 190, chi2 = 10.27, df = 1, P = 0.001). Together with the observation that inhibition of monoamine oxidase A is clinically effective in the treatment of panic disorder these findings suggest that increased monoamine oxidase A activity is a risk factor for panic disorder in female patients.

Heritability of anxiety sensitivity: a twin study

OBJECTIVE

In attempting to explain the familial predisposition to panic disorder, most studies have focused on the heritability of physiologic characteristics (e.g., CO2 sensitivity). A heretofore unexplored possibility is that a psychological characteristic that predisposes to panic-anxiety sensitivity-might be inherited. In this study, the authors examined the heritability of anxiety sensitivity through use of a twin group.

METHOD

Scores on the Anxiety Sensitivity Index were examined in a group of 179 monozygotic and 158 dizygotic twin pairs. Biometrical model fitting was conducted through use of standard statistical methods.

RESULTS

Broad heritability estimate of the Anxiety Sensitivity Index as a unifactorial construct was 45%. Additive genetic effects and unique environmental effects emerged as the primary influences on anxiety sensitivity. There was no evidence of genetic discontinuity between normal and extreme scores on the Anxiety Sensitivity Index.

CONCLUSIONS

This study suggests that one psychological risk factor for the development of panic disorder-anxiety sensitivity-may have a heritable component. As such, anxiety sensitivity should be considered in future research on the heritability of panic disorder.

Results of a genome-wide genetic screen for panic disorder

Panic disorder is characterized by spontaneous and recurrent panic attacks, often accompanied by agoraphobia. The results of family, twin, and segregation studies suggest a genetic role in the etiology of the illness. We have genotyped up to 23 families that have a high density of panic disorder with 540 microsatellite DNA markers in a first-pass genomic screen. The thirteen best families (ELOD > 6.0 under the dominant genetic model) have been genotyped with an ordered set of markers encompassing all the autosomes, at an average marker density of 11 cM. Over 110,000 genotypes have been generated on the whole set of families, and the data have been analyzed under both a dominant and a recessive model, and with the program SIBPAIR. No lod scores exceed 2.0 for either parametric model. Two markers give lod scores over 1.0 under the dominant model (chromosomes 1p and 20p), and four do under the recessive model (7p, 17p, 20q, and X/Y). One of these (20p) may be particularly promising. Analysis with SIBPAIR yielded P values equivalent to a lod score of 1.0 or greater (i.e., P < .016, one-sided, uncorrected for multiple tests) for 11 marker loci (2, 7p, 8p, 8q, 9p, 11q, 12q, 16p, 20p and 20q).