Norepinephrine transporter gene (NET) variants in patients with panic disorder

Neuroinflammation-Associated Alterations of the Brain as Potential Neural Biomarkers in Anxiety Disorders

Stress-induced changes in the immune system, which lead to neuroinflammation and consequent brain alterations, have been suggested as possible neurobiological substrates of anxiety disorders, with previous literature predominantly focusing on panic disorder, agoraphobia, and generalized anxiety disorder, among the anxiety disorders. Anxiety disorders have frequently been associated with chronic stress, with chronically stressful situations being reported to precipitate the onset of anxiety disorders. Also, chronic stress has been reported to lead to hypothalamic–pituitary–adrenal axis and autonomic nervous system disruption, which may in turn induce systemic proinflammatory conditions. Preliminary evidence suggests anxiety disorders are also associated with increased inflammation. Systemic inflammation can access the brain, and enhance pro-inflammatory cytokine levels that have been shown to precipitate direct and indirect neurotoxic effects. Prefrontal and limbic structures are widely reported to be influenced by neuroinflammatory conditions. In concordance with these findings, various imaging studies on panic disorder, agoraphobia, and generalized anxiety disorder have reported alterations in structure, function, and connectivity of prefrontal and limbic structures. Further research is needed on the use of inflammatory markers and brain imaging in the early diagnosis of anxiety disorders, along with the possible efficacy of anti-inflammatory interventions on the prevention and treatment of anxiety disorders.

A functional genetic variation of SLC6A2 repressor hsa-miR-579-3p upregulates sympathetic noradrenergic processes of fear and anxiety

Increased sympathetic noradrenergic signaling is crucially involved in fear and anxiety as defensive states. MicroRNAs regulate dynamic gene expression during synaptic plasticity and genetic variation of microRNAs modulating noradrenaline transporter gene (SLC6A2) expression may thus lead to altered central and peripheral processing of fear and anxiety. In silico prediction of microRNA regulation of SLC6A2 was confirmed by luciferase reporter assays and identified hsa-miR-579-3p as a regulating microRNA. The minor (T)-allele of rs2910931 (MAF_cases = 0.431, MAF_controls = 0.368) upstream of MIR579 was associated with panic disorder in patients (p_allelic = 0.004, n_cases = 506, n_controls = 506) and with higher trait anxiety in healthy individuals (p_ASI = 0.029, p_ACQ = 0.047, n = 3112). Compared to the major (A)-allele, increased promoter activity was observed in luciferase reporter assays in vitro suggesting more effective MIR579 expression and SLC6A2 repression in vivo (p = 0.041). Healthy individuals carrying at least one (T)-allele showed a brain activation pattern suggesting increased defensive responding and sympathetic noradrenergic activation in midbrain and limbic areas during the extinction of conditioned fear. Panic disorder patients carrying two (T)-alleles showed elevated heart rates in an anxiety-provoking behavioral avoidance test (F(2, 270) = 5.47, p = 0.005). Fine-tuning of noradrenaline homeostasis by a MIR579 genetic variation modulated central and peripheral sympathetic noradrenergic activation during fear processing and anxiety. This study opens new perspectives on the role of microRNAs in the etiopathogenesis of anxiety disorders, particularly their cardiovascular symptoms and comorbidities.

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.

A Genetic Susceptibility Mechanism for Major Depression: Combinations of polymorphisms Defined the Risk of Major Depression and Subpopulations

Major Depression (MD) is a highly inherited psychiatric disorder. The norepinephrine transporter (NET) gene plays important role in pathophysiology of MD. This study attempted to examine the relationship between polymorphisms of NET gene and MD. Patients with MD and healthy controls were recruited and subgrouped. The T-182C and G1287A polymorphisms of NET gene were genotyped by direct sequencing. The genotypic and allelic frequencies were compared using the Pearson χ2 analysis. The linkage disequilibrium was analyzed using the UNPHASED program. Significant differences in genotypic and allelic frequencies of T-182C polymorphism were observed between MD subgroups and controls. When referenced by TT genotype, the OR value increased gradient from TC to CC genotype; when referenced by T allele, the odds ratio value of C allele also increased. Compared with those having both -182 T/T and 1287 G/G genotypes, in patients with MD, early-onset MD, and MD with suicide concept group, the -182 C/C and 1287 G/A combinatorial genotype has significant risk; yet in patients with MD family history, the -182 C/C and 1287 A/A combinatorial genotype has significant risk. Different combinations of T-182C and the G1287A polymorphisms of NET gene might increase morbidity risk of MD subpopulations.

The norepinephrine transporter gene is associated with the retardation symptoms of major depressive disorder in the Han Chinese population

The norepinephrine transporter plays an important role in the pathophysiology and pharmacological treatment of major depressive disorder. Consequently, the norepinephrine transporter gene is an attractive candidate in major depressive disorder research. In the present study, we evaluated the depression symptoms of subjects with major depressive disorder, who were all from the North of China and of Han Chinese origin, using the Hamilton Depression Scale. We examined the relationship between two single nucleotide polymorphisms in the norepinephrine transporter, rs2242446 and rs5569, and the retardation symptoms of major depressive disorder using quantitative trait testing with the UNPHASED program. rs5569 was associated with depressed mood, and the GG genotype may be a risk factor for this; rs2242446 was associated with work and interest, and the TT genotype may be a risk factor for loss of interest. Our findings suggest that rs2242446 and rs5569 in the norepinephrine transporter gene are associated with the retardation symptoms of depression in the Han Chinese population.

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.

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.

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.

The role of central noradrenergic dysregulation in anxiety disorders: evidence from clinical studies

The nature of the noradrenergic dysregulation in clinical anxiety disorders remains unclear. In panic disorder, the predominant view has been that central noradrenergic neuronal networks and/or the sympathetic nervous system was normal in patients at rest, but hyper-reactive to specific stimuli, for example carbon dioxide. These ideas have been extended to other anxiety disorders, which share with panic disorder characteristic subjective anxiety and physiological symptoms of excess sympathetic activity. For example, Generalized Anxiety Disorder is characterized by chronic free-floating anxiety, muscle tension, palpitation and insomnia. It has been proposed that there is chronic central hypersecretion of noradrenaline in Generalized Anxiety Disorder, with consequent hyporesponsiveness of central post-synaptic receptors. With regards to other disorders, it has been suggested that there is noradrenergic involvement or derangement, but a more specific hypothesis has not been enunciated. This paper reviews the evidence for noradrenergic dysfunction in anxiety disorders, derived from indirect measures of noradrenergic function in clinical populations.

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.

Norepinephrine transporter polymorphisms T-182C and G1287A are not associated with alcohol dependence and its clinical subgroups

Several studies have suggested that the norepinephrine transporter (NET) may play an important role in the pathogenesis of alcohol dependence. Additional studies have shown that the polymorphisms of T-182C (rs2242446) and G1287A (rs5569) in NET gene (hSLC6A2) may affect the NET function. Therefore, in this study, we examined whether these hSLC6A2 gene polymorphisms are a susceptibility factor for alcohol dependence or its clinical subgroup(s). A total of 690 Han Chinese subjects (408 alcohol dependent patients and 282 controls) in Taiwan were recruited for this study. Individuals with alcohol dependence were classified into several clinical subgroups to reduce the clinical heterogeneity. All subjects were interviewed with identical methods, and the mental disorders were diagnosed according to DSM-IV criteria. The polymorphisms of T-182C and G1287A in hSLC6A2 gene were analyzed by using a standard method. No significant differences in genotype and allele frequencies of hSLC6A2 polymorphisms were found between controls and total alcohol dependence or between more homogeneous subgroups with alcohol dependence and controls. This study suggests that the polymorphisms of T-182C and G1287A in hSLC6A2 gene are not major risk factors in increasing susceptibility to either alcohol dependence or its clinical subtypes.

No association of the G1287A polymorphism in the norepinephrine transporter gene and susceptibility to major depressive disorder in a Japanese population

Norepinephrinergic neurotransmission in the central nervous system have a major impact on the symptomatology in major depressive disorder (MDD), and genetic polymorphisms of norepinephrine transporter (NET) have a possibility to be involved in susceptibility to MDD. We investigated the association of the G1287A (rs5569) polymorphism of the NET gene and susceptibility to MDD by comparing 145 major depressive patients with 164 healthy individuals first in a Japanese population. The genotype frequencies in depressed patients and health volunteers of the NET G1287A polymorphism were 52.4% (G/G), 39.3% (G/A) and 8.3% (A/A) in depressed patients, 61.6% (G/G), 29.9% (G/A allele) and 8.5% (A/A) in healthy volunteers, respectively. The allele frequencies in depressed patients and health volunteers of the NET G1287A polymorphism were 72.1% (G allele) and 27.9% (A allele) in depressed patients, 76.5% (G allele) and 23.5% (A allele) in healthy volunteers, respectively. The genotype distribution and allele frequencies were not significantly different between major depressive patients and healthy volunteers. NET G1287A polymorphism appears not to be an important factor in susceptibility to MDD in a Japanese population.

Candidate genes for panic disorder: insight from human and mouse genetic studies

Panic disorder is a major cause of medical attention with substantial social and health service cost. Based on pharmacological studies, research on its etiopathogenesis has been focused on the possible dysfunction of specific neurotransmitter systems. However, recent work has related the genes involved in development, synaptic plasticity and synaptic remodeling to anxiety disorders. This implies that learning processes and changes in perception, interpretation and behavioral responses to environmental stimuli are essential for development of complex anxiety responses secondary to the building of specific brain neural circuits and to adult plasticity. The focus of this review is on progress achieved in identifying genes that confer increased risk for panic disorder through genetic epidemiology and the use of genetically modified mouse models. The integration of human and animal studies targeting behavioral, systems-level, cellular and molecular levels will most probably help identify new molecules with potential impact on the pathogenetic aspects of the disease.

The functional impact of SLC6 transporter genetic variation

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

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.

Human genetics and pharmacology of neurotransmitter transporters

Biogenic amine neurotransmitters are released from nerve terminals and activate pre- and postsynaptic receptors. Released neurotransmitters are sequestered by transporters into presynaptic neurons, a major mode of their inactivation in the brain. Genetic studies of human biogenic amine transporter genes, including the dopamine transporter (hDAT; SLC6A3), the serotonin transporter (hSERT; SLC6A4), and the norepinephrine transporter (hNET; SLC6A2) have provided insight into how genomic variations in these transporter genes influence pharmacology and brain physiology. Genetic variants can influence transporter function by various mechanisms, including substrate affinities, transport velocity, transporter expression levels (density), extracellular membrane expression, trafficking and turnover, and neurotransmitter release. It is increasingly apparent that genetic variants of monoamine transporters also contribute to individual differences in behavior and neuropsychiatric disorders. This chapter summarizes current knowledge of transporters with a focus on genomic variations, expression variations, pharmacology of protein variants, and known association with human diseases.

Positive association between T-182C polymorphism in the norepinephrine transporter gene and susceptibility to major depressive disorder in a japanese population

Norepinephrinergic neurotransmission in the central nervous system appears to have a major impact on the symptomatology in major depressive disorder and the human norepinephrine transporter (NET) gene is one of the key candidates for genetic studies in major depressive disorder. The authors established a new allele-specific PCR-based genotyping procedure and examined whether the NET T-182C polymorphism was associated with the susceptibility to major depressive disorder in a Japanese population. This study included 145 patients with major depressive disorder (according to DSM-IV) and 164 healthy volunteers. There was a significant difference in the genotype distribution between major depressive disorder patients and healthy volunteers (p = 0.02), and the C/C genotype was associated with lesser susceptibility to major depressive disorder. The NET T-182C polymorphism may be in part related to the pathophysiology of major depressive disorder in a Japanese population.

Norepinephrine transporter (NET) promoter and 5'-UTR polymorphisms: association analysis in panic disorder

Several biochemical and pharmacological studies suggest that the catecholaminergic system involving the norepinephrine transporter (NET) is relevant for the pathogenesis of panic disorder. Three single nucleotide polymorphisms in the promoter or untranslated 5' region of the NET gene were investigated by means of RFLP analysis in a sample of 115 German patients with panic disorder and 115 matched controls. Statistical analysis failed to show association with the overall diagnosis of panic disorder. In the subgroup of patients with panic disorder without agoraphobia, however, two polymorphisms were found to be associated with the disease (G/C (rs2397771): p < 0.05; T/C (rs2242446): p < 0.01). While our data do not support a major function of the NET gene in the development of panic disorder, it may play a role in the subgroup of panic disorder without agoraphobia.

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.