Gene variations in the cholecystokinin system in patients with panic disorder

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

Cholecystokinin B receptor gene polymorphism (rs2941026) is associated with anxious personality and suicidal thoughts in a longitudinal study

OBJECTIVES

Cholecystokinin is a neuropeptide with a role in the neurobiology of adaptive behaviour that is implicated in anxiety disorders, while the underlying mechanisms currently remain insufficiently explained. The rs2941026 variation in the cholecystokinin B receptor gene has previously been associated with trait anxiety. Our aim was to investigate associations between the CCK_B receptor gene polymorphism rs2941026 with anxiety, personality, depressiveness and suicidality in a longitudinal study of late adolescence and early adulthood.

METHODS

We used reports on trait and state anxiety, depressiveness and suicidal thoughts, as well as Affective Neuroscience Personality Scales, from the two birth cohorts of the Estonian Children Personality, Behaviour and Health Study. We measured associations between the CCKBR gene rs2941026 and anxiety-related phenotypes both longitudinally and cross-sectionally at ages 15, 18, 25 and 33.

RESULTS

Homozygosity for both alleles of the CCKBR rs2941026 was associated with higher trait and state anxiety in the longitudinal analysis. Cross-sectional comparisons were statistically significant at ages 18 and 25 for trait anxiety and at ages 25 and 33 for state anxiety. Higher depressiveness and suicidal thoughts were associated with the A/A genotype at age 18. Additionally, homozygosity for the A-allele was related to higher FEAR and SADNESS in the Affective Neuroscience Personality Scales. The genotype effects were more apparent in females, who displayed higher levels of negative affect overall.

CONCLUSIONS

CCKBR genotype is persistently associated with negative affect in adolescence and young adulthood. The association of the CCKBR rs2941026 genotype with anxiety-related phenotypes is more pronounced in females.

Evaluation of MINOCA syndrome and HEART score in patients presenting to the emergency department with panic attack and chest pain complaints

BACKGROUND

Patients presenting with chest pain may or may not be experiencing a panic attack. Is chest pain caused by a panic attack or myocardial infarction with non-obstructive coronary arteries (MINOCA) syndrome?

AIM

In this study, we evaluated both MINOCA syndrome and HEART score in patients who presented to the emergency department with panic attacks and chest pain.

METHOD

Patients who applied to the emergency department with panic disorder and chest pain complaints were included. Patients who met the MINOCA diagnostic criteria were identified. The study was completed with 143 eligible patients out of a total of 217 patients evaluated. The patients were divided into two groups. The first group was those whose symptoms and test results were consistent with MINOCA. The second group was composed of those whose chest pain was considered non-specific. The HEART score of all patients was calculated. The demographic characteristics, symptoms, and HEART scores were compared between the groups.

RESULTS

Of the 143 patients evaluated in the study, 62 (43.3%) were male and 81 (56.7%) were female. While the mean HEART score was 4.7 ± 1.5 in the MINOCA group, it was 2.0 ± 1.0 in the non-cardiac group, a statistically significant difference.

CONCLUSION

Clinicians should pay attention to the patient's age, gender, number of attacks per week, HEART score, and which symptoms (palpitations, shortness of breath, and fear of death) are present in patients who meet the panic attack diagnostic criteria. Clinicians should be alert to the MINOCA syndrome in panic attack patients.

Cholecystokinin and Panic Disorder: Reflections on the History and Some Unsolved Questions

The classic gut hormone cholecystokinin (CCK) and its CCK2-receptor are expressed in almost all regions of the brain. This widespread expression makes CCK by far the most abundant peptidergic transmitter system in the brain. This CNS-ubiquity has, however, complicated the delineation of the roles of CCK peptides in normal brain functions and neuropsychiatric diseases. Nevertheless, the common panic disorder disease is apparently associated with CCK in the brain. Thus, the C-terminal tetrapeptide fragment of CCK (CCK-4) induces, by intravenous administration in a dose-related manner, panic attacks that are similar to the endogenous attacks in panic disorder patients. This review describes the history behind the discovery of the panicogenic effect of CCK-4. Subsequently, the review discusses three unsettled questions about the involvement of cerebral CCK in the pathogenesis of anxiety and panic disorder, including therapeutic attempts with CCK2-receptor antagonists.

Cholecystokinin peptide signaling is regulated by a TBX5-MEF2 axis in the heart

The procholecystokinin (proCCK) gene encodes a secreted peptide known to regulate the digestive, endocrine, and nervous systems. Though recently proposed as a biomarker for heart dysfunction, its physiological role in both the embryonic and adult heart is poorly understood, and there are no reports of tissue-specific regulators of cholecystokinin signaling in the heart or other tissues. In the present study, mRNA of proCCK was observed in cardiac tissues during mouse embryonic development, establishing proCCK as an early marker of differentiated cardiomyocytes which is later restricted to anatomical subdomains of the neonatal heart. Three-dimensional analysis of the expression of proCCK and CCKAR/CCKBR receptors was performed using in situ hybridization and optical projection tomography, illustrating chamber-specific expression patterns in the postnatal heart. Transcription factor motif analyses indicated developmental cardiac transcription factors TBX5 and MEF2C as upstream regulators of proCCK, and this regulatory activity was confirmed in reporter gene assays. proCCK mRNA levels were also measured in the infarcted heart and in response to cyclic mechanical stretch and endothelin-1, indicating dynamic transcriptional regulation which might be leveraged for improved biomarker development. Functional analyses of exogenous cholecystokinin octapeptide (CCK-8) administration were performed in differentiating mouse embryonic stem cells (mESCs), and the results suggest that CCK-8 does not act as a differentiation modulator of cardiomyocyte subtypes. Collectively, these findings indicate that proCCK is regulated at the transcriptional level by TBX5-MEF2 and neurohormonal signaling, informing use of proCCK as a biomarker and future strategies for upstream manipulation of cholecystokinin signaling in the heart and other tissues.

Association between genes on chromosome 19p13.2 and panic disorder

Panic disorder (PD) is a severe and disabling mental disorder, which is moderately heritable. In a previous study, we carried out a genome-wide association study using patients with PD and control individuals from the isolated population of the Faroe Islands and identified chromosome 19p13.2 as a candidate region. To further investigate this chromosomal region for association with PD, we analysed eight single nucleotide polymorphisms (SNPs) in three candidate genes - small-nuclear RNA activating complex, polypeptide 2 (SNAPC2), mitogen-activated protein kinase kinase 7 (MAP2K7) and leucine-rich repeat containing 8 family, member E (LRRC8E) - these genes have previously been directly or indirectly implicated in other mental disorders. A total of 511 patients with PD and 1029 healthy control individuals from the Faroe Islands, Denmark and Germany were included in the current study. SNPs covering the gene region of SNAPC2, MAP2K7 and LRRC8E were genotyped and tested for association with PD. In the Faroese cohort, rs7788 within SNAPC2 was significantly associated with PD, whereas rs3745383 within LRRC8E was nominally associated. No association was observed between the analysed SNPs and PD in the Danish cohorts. In the German women, we observed a nominal association between rs4804833 within MAP2K7 and PD. We present further evidence that chromosome 19p13.2 may harbour candidate genes that contribute towards the risk of developing PD. Moreover, the implication of the associated genes in other mental disorders may indicate shared genetic susceptibility between mental disorders. We show that associated variants may be sex specific, indicating the importance of carrying out a sex-specific association analysis of PD.

Biological markers for anxiety disorders, OCD and PTSD - a consensus statement. Part I: Neuroimaging and genetics

OBJECTIVES

Biomarkers are defined as anatomical, biochemical or physiological traits that are specific to certain disorders or syndromes. The objective of this paper is to summarise the current knowledge of biomarkers for anxiety disorders, obsessive-compulsive disorder (OCD) and post-traumatic stress disorder (PTSD).

METHODS

Findings in biomarker research were reviewed by a task force of international experts in the field, consisting of members of the World Federation of Societies for Biological Psychiatry Task Force on Biological Markers and of the European College of Neuropsychopharmacology Anxiety Disorders Research Network.

RESULTS

The present article (Part I) summarises findings on potential biomarkers in neuroimaging studies, including structural brain morphology, functional magnetic resonance imaging and techniques for measuring metabolic changes, including positron emission tomography and others. Furthermore, this review reports on the clinical and molecular genetic findings of family, twin, linkage, association and genome-wide association studies. Part II of the review focuses on neurochemistry, neurophysiology and neurocognition.

CONCLUSIONS

Although at present, none of the putative biomarkers is sufficient and specific as a diagnostic tool, an abundance of high-quality research has accumulated that will improve our understanding of the neurobiological causes of anxiety disorders, OCD and PTSD.

Candidate genes in panic disorder: meta-analyses of 23 common variants in major anxiogenic pathways

The utilization of molecular genetics approaches in examination of panic disorder (PD) has implicated several variants as potential susceptibility factors for panicogenesis. However, the identification of robust PD susceptibility genes has been complicated by phenotypic diversity, underpowered association studies and ancestry-specific effects. In the present study, we performed a succinct review of case-control association studies published prior to April 2015. Meta-analyses were performed for candidate gene variants examined in at least three studies using the Cochrane Mantel-Haenszel fixed-effect model. Secondary analyses were also performed to assess the influences of sex, agoraphobia co-morbidity and ancestry-specific effects on panicogenesis. Meta-analyses were performed on 23 variants in 20 PD candidate genes. Significant associations after correction for multiple testing were observed for three variants, TMEM132D rs7370927 (T allele: odds ratio (OR)=1.27, 95% confidence interval (CI): 1.15-1.40, P=2.49 × 10(-6)), rs11060369 (CC genotype: OR=0.65, 95% CI: 0.53-0.79, P=1.81 × 10(-5)) and COMT rs4680 (Val (G) allele: OR=1.27, 95% CI: 1.14-1.42, P=2.49 × 10(-5)) in studies with samples of European ancestry. Nominal associations that did not survive correction for multiple testing were observed for NPSR1 rs324891 (T allele: OR=1.22, 95% CI: 1.07-1.38, P=0.002), TPH1 rs1800532 (AA genotype: OR=1.46, 95% CI: 1.14-1.89, P=0.003) and HTR2A rs6313 (T allele: OR=1.19, 95% CI: 1.07-1.33, P=0.002) in studies with samples of European ancestry and for MAOA-uVNTR in female PD (low-active alleles: OR=1.21, 95% CI: 1.07-1.38, P=0.004). No significant associations were observed in the secondary analyses considering sex, agoraphobia co-morbidity and studies with samples of Asian ancestry. Although these findings highlight a few associations, PD likely involves genetic variation in a multitude of biological pathways that is diverse among populations. Future studies must incorporate larger sample sizes and genome-wide approaches to further quantify the observed genetic variation among populations and subphenotypes of PD.

Exploring the association between a cholecystokinin promoter polymorphism (rs1799923) and posttraumatic stress disorder in combat veterans

BACKGROUND

Cholecystokinin (CCK) is a neuropeptide that has been implicated in understanding the acquisition and extinction of fear. Research on CCK in anxiety has primarily focused on understanding panic attacks and panic disorder. Emerging data suggests that CCK may also hold promise in understanding the development and maintenance of posttraumatic stress disorder (PTSD).

METHOD

The present study examined whether a single nucleotide polymorphism in the promoter region of the CCK gene (C>T; rs1799923) was associated with an increased prevalence of PTSD as well as with severity of PTSD symptoms among a sample of 457 combat veterans.

RESULTS

Results demonstrated that participants with either the heterozygous or homozygous T allele had an increased prevalence of PTSD relative to participants with the CC genotype (OR=2.17; 95% CI [1.37-3.43]).

LIMITATIONS

The relatively small sample size precluded examination of racial/ethnic differences. Findings were also limited by the absence of a systematic assessment of comorbid anxiety psychopathology.

CONCLUSIONS

These data offer preliminary evidence supporting an association between the rs1799923 polymorphism in the CCK gene and PTSD. Additional research is needed to better understand the nature of this relationship.

From neural to genetic substrates of panic disorder: Insights from human and mouse studies

Fear is an ancestral emotion, an intrinsic defensive response present in every organism. Although fear is an evolutionarily advantageous emotion, under certain pathologies such as panic disorder it might become exaggerated and non-adaptive. Clinical and preclinical work pinpoints that changes in cognitive processes, such as perception and interpretation of environmental stimuli that rely on brain regions responsible for high-level function, are essential for the development of fear-related disorders. This review focuses on the involvement of cognitive function to fear circuitry disorders. Moreover, we address how animal models are contributing to understand the involvement of human candidate genes to pathological fear and helping achieve progress in this field. Multidisciplinary approaches that integrate human genetic findings with state of the art genetic mouse models will allow to elucidate the mechanisms underlying pathology and to develop new strategies for therapeutic targeting.

Drug addiction and stress-response genetic variability: association study in African Americans

Stress is a significant risk factor in the development of drug addictions and in addiction relapse susceptibility. This hypothesis-driven study was designed to determine if specific SNPs in genes related to stress response are associated with heroin and/or cocaine addiction in African Americans. The analysis included 27 genes (124 SNPs) and was performed independently for each addiction. The sample consisted of former heroin addicts in methadone maintenance treatment (n = 314), cocaine addicts (n = 281), and controls (n = 208). Fourteen SNPs showed nominally significant association with heroin addiction (p < 0.05), including the African-specific, missense SNP rs5376 (Asn334Ser) in the galanin receptor type 1 gene (GALR1) and the functional FKBP5 intronic SNP rs1360780. Thirteen SNPs showed association with cocaine addiction, including the synonymous SNPs rs237902, in the oxytocin receptor gene (OXTR), and rs5374 in GALR1. No signal remained significant after correction for multiple testing. Four additional SNPs (GALR1 rs2717162, AVP rs2282018, CRHBP rs1875999, and NR3C2 rs1040288) were associated with both addictions and may indicate common liability. The study provides preliminary evidence for novel association of variants in several stress-related genes with heroin and/or cocaine addictions and may enhance the understanding of the interaction between stress and addictions.

Investigating the role of BDNF and CCK system genes in suicidality in a familial bipolar cohort

BACKGROUND

Suicidal behaviour is a phenotype widely associated with psychiatric disorders such as major depressive disorder and bipolar disorder. However, recent evidence indicates that part of the heritability of suicidal behaviour is independent of the heritability of individual psychiatric disorders. This allows investigation into genetic risk factors for suicidal behaviour within a disorder using a candidate gene association approach.

METHODS

We used family-based association testing in a cohort of 130 multiplex bipolar pedigrees, comprising 795 individuals, to look for associations between suicidal behaviour and 32 single nucleotide polymorphisms (SNPs) from across the genes brain-derived neurotrophic factor (BDNF), cholecystokinin (CCK) and the cholecystokinin beta-receptor (CCKBR).

RESULTS

We found associations (p≤0.05) between suicide attempt and 12 SNPs of CCKBR and five SNPs of BDNF. After correction for multiple testing, seven SNPs of CCKBR remained significantly associated. No association was found between CCK and suicidal behaviour.

LIMITATIONS

The study relied on retrospective self-reporting by individuals to determine phenotype, and the sample size was relatively small.

CONCLUSIONS

The results of the study support the hypothesis that some CCKBR polymorphisms may contribute to an underlying predisposition towards suicidal behaviour in bipolar disorder.

Variants in CCK and CCKAR genes to susceptibility to biliary tract cancers and stones: a population-based study in Shanghai, China

BACKGROUND AND AIM

Altered motility of the gallbladder is associated with an increased risk of gallstones and can result in biliary tract cancers. Cholecystokinin (CCK) is an important modulator of gallbladder motility which functions by activating CCK type-A receptor (CCKAR). The aim of this study was to determine whether genetic variants in CCK and CCKAR are associated with the risk of biliary tract cancers and stones.

METHODS

We investigated the associations between nine single nucleotide polymorphisms in CCK and CCKAR in a population-based case-control study, including 439 biliary tract cancer cases (253 gallbladder, 133 extrahepatic bile duct, and 53 ampulla of Vater cancer cases), 429 biliary stone cases, and 447 population controls in Shanghai, China.

RESULTS

We found that women with the CCKAR rs1800855 AA genotype had an increased risk of gallbladder cancer (odds ratio = 2.37, 95% confidence interval (CI): 1.36-4.14) compared with subjects with the TT genotype, and remained significant after Bonferroni correction (P = 0.0056). Additionally, female carriers of the CCKAR haplotype C-T-C-T (rs2071011-rs915889-rs3822222-rs1800855) had a reduced risk of gallbladder cancer (odds ratio = 0.61, 95% confidence interval: 0.43-0.86) compared with those with the G-C-C-A haplotype; the association also remained significant after Bonferroni correction.

CONCLUSIONS

These findings suggest that variants in the CCKAR gene may influence the risk of gallbladder cancer in women. Additional studies are needed to confirm our findings.

Prenatal diagnosis and molecular cytogenetic characterization of a de novo proximal interstitial deletion of chromosome 4p (4p15.2→p14)

We present prenatal diagnosis of de novo proximal interstitial deletion of chromosome 4p (4p15.2→p14) and molecular cytogenetic characterization of the deletion using uncultured amniocytes. We review the phenotypic abnormalities of previously reported patients with similar proximal interstitial 4p deletions, and we discuss the functions of the genes of RBPJ, CCKAR, STIM2, PCDH7 and ARAP2 that are deleted within this region.

Identification and analysis of the human hyaluronan synthase 1 gene promoter reveals Smad3- and Sp3-mediated transcriptional induction

The ubiquitous mammalian extracellular matrix glycosaminoglycan hyaluronan (HA) plays a pivotal role in the regulation of cell phenotype in fibrosis and scarring. Transforming growth factor-beta 1 (TGF-β1) and interleukin-1 beta (IL-1β) up-regulate hyaluronan synthase (HAS) 1 and HAS2 in dermal fibroblasts and renal proximal tubular epithelial cells, and subsequent HA synthesis regulates cell phenotype. In the present study, we investigated the mechanism of HAS1 transcriptional up-regulation in response to these cytokines. We used 5'-rapid amplification of cDNA ends analysis to identify the 5' end of HAS1 transcripts, resulting in an increase of 26 nucleotides to the HAS1 exon 1 sequence of reference sequence NM_001523. Constitutive luciferase activity of upstream DNA sequences was shown in luciferase reporter assays, but our reporter vector signals were refractory to the addition of TGF-β1 and IL-1β. Using siRNAs to knockdown transcription factor mRNAs, we showed that TGF-β1 up-regulation of HAS1 transcription was mediated via Smad3 but not Smad2, while HAS1 induction by IL-1β was Sp3, not Sp1, dependent.

Neuronal network of panic disorder: the role of the neuropeptide cholecystokinin

Panic disorder (PD) is characterized by panic attacks, anticipatory anxiety and avoidance behavior. Its pathogenesis is complex and includes both neurobiological and psychological factors. With regard to neurobiological underpinnings, anxiety in humans seems to be mediated through a neuronal network, which involves several distinct brain regions, neuronal circuits and projections as well as neurotransmitters. A large body of evidence suggests that the neuropeptide cholecystokinin (CCK) might be an important modulator of this neuronal network. Key regions of the fear network, such as amygdala, hypothalamus, peraqueductal grey, or cortical regions seem to be connected by CCKergic pathways. CCK interacts with several anxiety-relevant neurotransmitters such as the serotonergic, GABA-ergic and noradrenergic system as well as with endocannabinoids, NPY and NPS. In humans, administration of CCK-4 reliably provokes panic attacks, which can be blocked by antipanic medication. Also, there is some support for a role of the CCK system in the genetic pathomechanism of PD with particularly strong evidence for the CCK gene itself and the CCK-2R (CCKBR) gene. Thus, it is hypothesized that genetic variants in the CCK system might contribute to the biological basis for the postulated CCK dysfunction in the fear network underlying PD. Taken together, a large body of evidence suggests a possible role for the neuropeptide CCK in PD with regard to neuroanatomical circuits, neurotransmitters and genetic factors. This review article proposes an extended hypothetical model for human PD, which integrates preclinical and clinical findings on CCK in addition to existing theories of the pathogenesis of PD.

Replication and meta-analysis of TMEM132D gene variants in panic disorder

A recent genome-wide association study in patients with panic disorder (PD) identified a risk haplotype consisting of two single-nucleotide polymorphisms (SNPs) (rs7309727 and rs11060369) located in intron 3 of TMEM132D to be associated with PD in three independent samples. Now we report a subsequent confirmation study using five additional PD case-control samples (n = 1670 cases and n = 2266 controls) assembled as part of the Panic Disorder International Consortium (PanIC) study for a total of 2678 cases and 3262 controls in the analysis. In the new independent samples of European ancestry (EA), the association of rs7309727 and the risk haplotype rs7309727-rs11060369 was, indeed, replicated, with the strongest signal coming from patients with primary PD, that is, patients without major psychiatric comorbidities (n = 1038 cases and n = 2411 controls). This finding was paralleled by the results of the meta-analysis across all samples, in which the risk haplotype and rs7309727 reached P-levels of P = 1.4e-8 and P = 1.1e-8, respectively, when restricting the samples to individuals of EA with primary PD. In the Japanese sample no associations with PD could be found. The present results support the initial finding that TMEM132D gene contributes to genetic susceptibility for PD in individuals of EA. Our results also indicate that patient ascertainment and genetic background could be important sources of heterogeneity modifying this association signal in different populations.

Cholecystokinin system genes: associations with panic and other psychiatric disorders

BACKGROUND

The cholecystokinin (CCK) system has long been hypothesised to have a role in the pathogenesis of panic attacks. Previous research into genetic variation within the CCK gene and the genes for its two receptors, CCKAR and CCKBR, has produced mixed results. We aimed to clarify this association by investigating multiple variants within each gene and multiple phenotypes associated with panic that may have confounded the previous studies' findings.

METHODS

Variants were selected for the three genes based on HapMap CEU data. Individuals from a family based cohort (n=563) were genotyped for these variations and this data was analysed in FBAT.

RESULTS

CCKBR showed the strongest association with panic, having multiple variants with p<0.05 (lowest: p=0.007). In CCKAR, some evidence was found for an association with panic, though further analysis suggested that the co-morbid bipolar-panic phenotype was most strongly associated. No variants in CCK were associated with panic but broader anxiety phenotypes did show associations.

LIMITATIONS

Small sample size prevented thorough investigation of phenotypes, particularly pure disorders, and no correction was made for the multiple phenotypes analysed.

CONCLUSIONS

Our findings support the involvement of variation in the CCK system, particularly CCKBR, in the pathogenesis of panic. Our data suggest that variation in CCK may be involved in several anxiety phenotypes and CCKAR may be involved in the development of panic co-morbid with bipolar disorder. These latter findings require further investigation and highlight the importance of clearly defined phenotypes when investigating psychiatric genetics.

A genome-wide study of panic disorder suggests the amiloride-sensitive cation channel 1 as a candidate gene

Panic disorder (PD) is a mental disorder with recurrent panic attacks that occur spontaneously and are not associated to any particular object or situation. There is no consensus on what causes PD. However, it is recognized that PD is influenced by environmental factors, as well as genetic factors. Despite a significant hereditary component, genetic studies have only been modestly successful in identifying genes of importance for the development of PD. In this study, we conducted a genome-wide scan using microsatellite markers and PD patients and control individuals from the isolated population of the Faroe Islands. Subsequently, we conducted a fine mapping, which revealed the amiloride-sensitive cation channel 1 (ACCN1) located on chromosome 17q11.2-q12 as a potential candidate gene for PD. The further analyses of the ACCN1 gene using single-nucleotide polymorphisms (SNPs) revealed significant association with PD in an extended Faroese case-control sample. However, analyses of a larger independent Danish case-control sample yielded no substantial significant association. This suggests that the possible risk alleles associated in the isolated population are not those involved in the development of PD in a larger outbred population.

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.

The norepinephrine transporter gene is a candidate gene for panic disorder

Panic disorder (PD) is an anxiety disorder characterized by recurrent panic attacks with a lifetime prevalence of 4.7%. Genetic factors are known to contribute to the development of the disorder. Several lines of evidence point towards a major role of the norepinephrine system in the pathogenesis of PD. The SLC6A2 gene is located on chromosome 16q12.2 and encodes the norepinephrine transporter (NET), responsible for the reuptake of norepinephrine into presynaptic nerve terminals. The aim of the present study was to analyze genetic variants located within the NET gene for association with PD. The case-control sample consisted of 449 patients with PD and 279 ethnically matched controls. All cases fulfilled the ICD-10 diagnostic criteria for PD. Genotyping was performed using the Sequenom platform (Sequenom, Inc, San Diego, USA). To test for allelic and haplotypic association, the PLINK software was used, and COMBASSOC was applied to test for gene-wise association. After quality control 29 single nucleotide polymorphisms (SNPs) spanning the gene-region were successfully analyzed. Seven SNPs located within the 5' end of the gene were significantly associated with PD. Furthermore, the NET gene showed overall evidence for association with the disease (P = 0.000035). In conclusion, the present study indicates that NET could be a susceptibility gene for PD.

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.