Evidence for Association between the Brain-Derived Neurotrophic Factor Gene and Panic Disorder: A Novel Haplotype Analysis

Transcranial direct current stimulation and neuronal functional connectivity in MCI: role of individual factors associated to AD

Background

Alzheimer's disease (AD) encompasses a spectrum that may progress from mild cognitive impairment (MCI) to full dementia, characterized by amyloid-beta and tau accumulation. Transcranial direct current stimulation (tDCS) is being investigated as a therapeutic option, but its efficacy in relation to individual genetic and biological risk factors remains underexplored.

Objective

To evaluate the effects of a two-week anodal tDCS regimen on the left dorsolateral prefrontal cortex, focusing on functional connectivity changes in neural networks in MCI patients resulting from various possible underlying disorders, considering individual factors associated to AD such as amyloid-beta deposition, APOE ϵ4 allele, BDNF Val66Met polymorphism, and sex.

Methods

In a single-arm prospective study, 63 patients with MCI, including both amyloid-PET positive and negative cases, received 10 sessions of tDCS. We assessed intra- and inter-network functional connectivity (FC) using fMRI and analyzed interactions between tDCS effects and individual factors associated to AD.

Results

tDCS significantly enhanced intra-network FC within the Salience Network (SN) and inter-network FC between the Central Executive Network and SN, predominantly in APOE ϵ4 carriers. We also observed significant sex*tDCS interactions that benefited inter-network FC among females. Furthermore, the effects of multiple modifiers, particularly the interaction of the BDNF Val66Met polymorphism and sex, were evident, as demonstrated by increased intra-network FC of the SN in female Met non-carriers. Lastly, the effects of tDCS on FC did not differ between the group of 26 MCI patients with cerebral amyloid-beta deposition detected by flutemetamol PET and the group of 37 MCI patients without cerebral amyloid-beta deposition.

Conclusions

The study highlights the importance of precision medicine in tDCS applications for MCI, suggesting that individual genetic and biological profiles significantly influence therapeutic outcomes. Tailoring interventions based on these profiles may optimize treatment efficacy in early stages of AD.

Effects of transcranial direct current stimulation on cognition in MCI with Alzheimer's disease risk factors using Bayesian analysis

Despite the growing interest in precision medicine-based therapies for Alzheimer's disease (AD), little research has been conducted on how individual AD risk factors influence changes in cognitive function following transcranial direct current stimulation (tDCS). This study evaluates the cognitive effects of sequential tDCS on 63 mild cognitive impairment (MCI) patients, considering AD risk factors such as amyloid-beta deposition, APOE ε4, BDNF polymorphism, and sex. Using both frequentist and Bayesian methods, we assessed the interaction of tDCS with these risk factors on cognitive performance. Notably, we found that amyloid-beta deposition significantly interacted with tDCS in improving executive function, specifically Stroop Word-Color scores, with strong Bayesian support for this finding. Memory enhancements were differentially influenced by BDNF Met carrier status. However, sex and APOE ε4 status did not show significant effects. Our results highlight the importance of individual AD risk factors in modulating cognitive outcomes from tDCS, suggesting that precision medicine may offer more effective tDCS treatments tailored to individual risk profiles in early AD stages.

Impact of transcranial direct current stimulation on white matter microstructure integrity in mild cognitive impairment patients according to effect modifiers as risk factors for Alzheimer's disease

Background

Little research exists on how individual risk factors for Alzheimer's disease (AD) affect the intermediate phenotype after transcranial direct current stimulation (tDCS), despite the importance of precision medicine-based therapeutic approaches.

Objective

To determine how an application of sequential tDCS (2 mA/day, left dorsolateral prefrontal cortex, 10 sessions) affects changes in white matter (WM) microstructure integrity in 63 mild cognitive impairment (MCI) patients with effect modifiers such as Aβ deposition, APOE ε4 carrier status, BDNF Val66Met polymorphism status, and sex.

Methods

We examined individual effect modifier-by-tDCS interactions and multiple effect modifiers-by-tDCS interactions for diffusion metrics. We also evaluated the association between baseline Aβ deposition and changes in WM microstructure integrity following tDCS.

Results

We found that APOE ε4 carrier status and sex had a significant interaction with tDCS, resulting in increased fractional anisotropy (FA) in the right uncinate fasciculus (UF) after stimulation. Additionally, we observed multiple effect modifiers-by-tDCS interactions on WM integrity of the right UF, leading to a more pronounced increase in FA values in APOE ε4 carriers and females with Val66 homozygotes. Finally, baseline Aβ deposition was positively associated with a difference in FA of the left cingulum in the hippocampal area, which showed a positive association with the changes in the score for delayed memory.

Conclusion

Our study shows the differential impact of individual AD risk factors on changes in the early intermediate phenotype after sequential tDCS in MCI patients. This research emphasizes the importance of precision medicine approaches in tDCS for the prodromal stages of AD.

Predicting the diagnosis of various mental disorders in a mixed cohort using blood-based multi-protein model: a machine learning approach

The lack of objective diagnostic methods for mental disorders challenges the reliability of diagnosis. The study aimed to develop an easily accessible and useable objective method for diagnosing major depressive disorder (MDD), schizophrenia (SZ), bipolar disorder (BPD), and panic disorder (PD) using serum multi-protein. Serum levels of brain-derived neurotrophic factor (BDNF), VGF (non-acronymic), bicaudal C homolog 1 (BICC1), C-reactive protein (CRP), and cortisol, which are generally recognized to be involved in different pathogenesis of various mental disorders, were measured in patients with MDD (n = 50), SZ (n = 50), BPD (n = 55), and PD along with 50 healthy controls (HC). Linear discriminant analysis (LDA) was employed to construct a multi-classification model to classify these mental disorders. Both leave-one-out cross-validation (LOOCV) and fivefold cross-validation were applied to validate the accuracy and stability of the LDA model. All five serum proteins were included in the LDA model, and it was found to display a high overall accuracy of 96.9% when classifying MDD, SZ, BPD, PD, and HC groups. Multi-classification accuracy of the LDA model for LOOCV and fivefold cross-validation (within-study replication) reached 96.9 and 96.5%, respectively, demonstrating the feasibility of the blood-based multi-protein LDA model for classifying common mental disorders in a mixed cohort. The results suggest that combining multiple proteins associated with different pathogeneses of mental disorders using LDA may be a novel and relatively objective method for classifying mental disorders. Clinicians should consider combining multiple serum proteins to diagnose mental disorders objectively.

Pathoclinical associations between panic disorders and the brain-derived neurotrophic factor Val66Met polymorphism: an updated meta-analysis

Prior studies have indicated the pathological role of brain-derived neurotrophic factor (BDNF) gene polymorphism in panic disorders (PD). A functionally less active BDNF Val66Met mutant was previously detected in PD patients with different ethnic backgrounds. However, the results remain inconclusive or inconsistent. A meta-analysis was used to explore the consistency of the BDNF Val66Met mutant's association with PD irrespective of the subject's ethnicity. Relevant case-controlled full-length clinical and preclinical reports were retrieved by database searching, and 11 articles involving 2203 cases and 2554 controls were systematically selected per the standard inclusion criteria. Eleven articles were finally included that explored the relationship between the Val66Met polymorphism and PD risk susceptibility. Statistical analysis revealed a significant genetic association of the mutation, allele frequencies, and genotype distributions of BDNF with PD onset. Our findings demonstrated that the BDNF Val66Met is a susceptibility factor of PD.

The Relationship Among BDNF Val66Met Polymorphism, Plasma BDNF Level, and Trait Anxiety in Chinese Patients With Panic Disorder

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a candidate for susceptibility locus of Panic disorder (PD). However, the findings about the role of the BDNF Val66Met variant in PD were not consistent. Till now, the relationship between BDNF Val66Met polymorphism and anxiety-related traits in PD patients has been rarely explored. This study aimed to explore the relationship among BDNF Val66Met polymorphism, plasma BDNF level and anxiety-related trait in Chinese PD patients.

METHOD

This multi-center study included 116 PD patients and 99 health controls. We detected single-nucleotide polymorphism (SNP) of BDNF rs6265 (Val66Met) and BDNF plasma level in the two groups. In addition, PD patients were administered the State-Trait Anxiety Inventory (STAI), Panic Disorder Severity Scale-Chinese Version (PDSS-CV) and Hamilton Anxiety Rating Scale (HAMA-14). Quantitative comparison of the differences of BDNF concentration among subjects with different genotypes and association between BDNF Val66Met genotype and trait anxiety were performed.

RESULTS

There were no significant differences in the genotype frequency (p = 0.79) or allele frequency (p = 0.88) between PD patients and health controls. BDNF plasma levels of PD patients were significantly lower than those in control group (p = 0.003). BDNF plasma levels of the Met/Met genotype were significantly lower than those of Val/Met genotype in PD patients (p = 0.033). PD patients carried Met/Met genotype showed significantly higher scores in STAI trait compared to those carried Val/Val genotype (p = 0.045) and Val/Met genotype (p = 0.018). STAI trait scores of PD patients with agoraphobia were significantly higher than those of patients without agoraphobia (p < 0.05). The ANCOVA showed that the dependent variable STAI trait score was significantly affected by factor "genotype" (Val/Val, Val/Met, Met/Met, p = 0.029), and covariate "agoraphobia" (p = 0.008). In this model, 11.5% of the variance of the STAI trait score was explained by the BDNF genotype. Contrast analysis showed STAI trait scores of Met/Met subjects were significantly higher than those of Val/Met (p = 0.018) and Val/Val individuals (p = 0.045).

CONCLUSION

We found that anxiety trait was associated with the BDNF polymorphism in PD patients. BDNF Met/Met genotype may decrease plasma BDNF level and increase trait anxiety in panic disorder.

Genotype-expression interactions for BDNF across human brain regions

Background

Genetic variations in brain-derived neurotrophic factor (BDNF) are associated with various psychiatric disorders including depression, obsessive-compulsive disorder, substance use disorders, and schizophrenia; altered gene expression triggered by these genetic variants may serve to create these phenotypes. But genotype-expression interactions for this gene have not been well-studied across brain regions relevant for psychiatric disorders.

Results

At false discovery rate (FDR) of 10% (q < 0.1), a total of 61 SNPs were associated with BDNF expression in cerebellum (n = 209), 55 SNPs in cortex (n = 205), 48 SNPs in nucleus accumbens (n = 202), 47 SNPs in caudate (n = 194), and 58 SNPs in cerebellar hemisphere (n = 175). We identified a set of 30 SNPs in 2 haplotype blocks that were associated with alterations in expression for each of these 5 regions. The first haplotype block included variants associated in the literature with panic disorders (rs16917204), addiction (rs11030104), bipolar disorder (rs16917237/rs2049045), and obsessive-compulsive disorder (rs6265). Likewise, variants in the second haplotype block have been previously associated with disorders such as nicotine addiction, major depressive disorder (rs988748), and epilepsy (rs6484320/rs7103411).

Conclusions

This work supports the association of variants within BDNF for expression changes in these key brain regions that may contribute to common behavioral phenotypes for disorders of compulsion, impulsivity, and addiction. These SNPs should be further investigated as possible therapeutic and diagnostic targets to aid in management of these and other psychiatric disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07525-1.

CREB1 and BDNF gene polymorphisms are associated with early treatment response to escitalopram in panic disorder

OBJECTIVES

Increasing evidence shows that the alternations under escitalopram treatment for Panic disorder (PD) patients are related to the cAMP response element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF). We aimed to explore the single nucleotide polymorphisms (SNPs) of genes BDNF and CREB1 in the treatment response to escitalopram on PD.

METHODS

There were 80 PD patients with DSM-5 diagnosis and 78 healthy controls. All PD patients have received escitalopram treatment for consecutive 8 weeks. The Chinese version of Panic Disorder Severity Scale (PDSS-CV) and the Hamilton Anxiety Scale (HAMA-14) were used to evaluate the severity of panic and anxious symptoms for PD patients at baseline, week-2, week-4, and week-8, respectively. Four SNPs (rs11904814, rs6740584, rs2253206, and rs2551941) in CREB1 gene and rs6265 in BDNF gene were genotyped using matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF MS). Quantitative and binary genetic associations between SNPs and escitalopram treatment response were performed.

RESULTS

The comparisons of three genotypes in CREB1 SNPs rs11904814 and rs2551941 among the PDSS-CV responders showed significant differences at the end of week-2 (both p<0.05). The results remained significant after Bonferroni corrections. For candidate genes in our present study, the gene CREB1 SNP rs11904814 (p=0.007) was significantly associated with changes of PDSS-CV scores under escitalopram treatment for 12 weeks in PD patients. And the result was still significant after adjusting age and gender.

CONCLUSIONS

The findings provide preliminary evidence supporting the potential role of BDNF and CREB1 on a rapid response after escitalopram intervention in PD patients.

Associations between brain-derived neurotrophic factor and cognitive impairment in panic disorder

INTRODUCTION

Our study was designed to examine the relationship between Brain-Derived Neurotrophic Factor (BDNF) genotypes (rs6265, Val66Met), BDNF plasma levels, and cognitive impairment in Chinese patients with panic disorder (PD).

METHODS

Total 85 patients with PD and 91 healthy controls finally completed all assessments. The severity of panic symptoms and whole anxiety of PD was measured by Panic Disorder Severity Scale-Chinese Version (PDSS-CV) and Hamilton Anxiety Scale (HAMA-14). Montreal Cognitive Assessment (MoCA) and some neurocognitive measures were conducted to evaluate the cognitive performance. All participants were detected for the plasma BDNF levels and BDNF Val66Met polymorphism before assessment and treatment.

RESULTS

No significant differences were found in the BDNF allele frequencies and the BDNF genotype distributions between healthy controls and PD patients. BDNF Met/Met genotype was associated with lower BDNF plasma levels in PD patients, and PD patients with BDNF Met/Met genotype had the lower scores in the attention and speed of processing domains compared to those with Val/Val and Met/Val genotype (p's < .05). Among PD patients, the BDNF plasma levels showed moderate positive correlations with Stroop interference (r = .60, p < .001). Using the MoCA data, the BDNF plasma levels were correlated with delayed memory (r = .50, p < .001), verbal learning (r = .45, p < .001), and total scores of MoCA (r = .51, p < .001).

CONCLUSIONS

The BDNF Met/Met genotype may be associated with lower BDNF plasma levels and cognitive impairments in PD patients.

Peripheral blood levels of brain-derived neurotrophic factor in patients with post-traumatic stress disorder (PTSD): A systematic review and meta-analysis

BACKGROUND

Brain-derived neurotrophic factor (BDNF) plays a crucial role in the survival, differentiation, growth, and plasticity of the central nervous system (CNS). Post-traumatic stress disorder (PTSD) is a complex syndrome that affects CNS function. Evidence indicates that changes in peripheral levels of BDNF may interfere with stress. However, the results are mixed. This study investigates whether blood levels of BDNF in patients with post-traumatic stress disorder (PTSD) are different.

METHODS

We conducted a systematic search in the major electronic medical databases from inception through September 2019 and identified Observational studies that measured serum levels of BDNF in patients with PTSD compared to controls without PTSD.

RESULTS

20 studies were eligible to be included in the present meta-analysis. Subjects with PTSD (n = 909) showed lower BDNF levels compared to Non-PTSD controls (n = 1679) (SMD = 0.52; 95% confidence interval: 0.18 to 0.85). Subgroup meta-analyses confirmed higher levels of BDNF in patients with PTSD compared to non-PTSD controls in plasma, not serum, and in studies that used sandwich ELISA, not ELISA, for BDNF measurement. Meta-regressions showed no significant effect of age, gender, NOS, and sample size.

CONCLUSIONS

PTSD patients had increased serum BDNF levels compared to healthy controls. Our finding of higher BDNF levels in patients with PTSD supports the notion that PTSD is a neuroplastic disorder.

Genetic Biomarkers of Panic Disorder: A Systematic Review

(1) Background: Although panic disorder (PD) is one of the most common anxiety disorders severely impacting quality of life, no effective genetic testing exists; known data on possible genetic biomarkers is often scattered and unsystematic which complicates further studies. (2) Methods: We used PathwayStudio 12.3 (Elsevier, The Netherlands) to acquire literature data for further manual review and analysis. 229 articles were extracted, 55 articles reporting associations, and 32 articles reporting no associations were finally selected. (3) Results: We provide exhaustive information on genetic biomarkers associated with PD known in the scientific literature. Data is presented in two tables. Genes COMT and SLC6A4 may be considered the most promising for PD diagnostic to date. (4) Conclusions: This review illustrates current progress in association studies of PD and may indicate possible molecular mechanisms of its pathogenesis. This is a possible basis for data analysis, novel experimental studies, or developing test systems and personalized treatment approaches.

5HTTLPR Genetic Variant and Major Depressive Disorder: A Review

Major Depressive Disorder (MDD) is a disease that involves biological, psychological, and social interactions. Studies have shown the importance of genetics contribution to MDD development. The SCL6A4 protein (5HTTLPR) functions transporting serotonin, a neurotransmitter linked to mood and emotion, to the synaptic cleft. Hence, this study seeks, through a literature review, a better comprehension of the 5HTTLPR genetic variant association with MDD. For this purpose, a search was performed on the Virtual Health Library Portal for articles that related 5HTTLPR to MDD. Most of the articles found were conducted in the American continent, with one (1) study implemented in Brazil. 5HTTLPR associations were found regarding changes in the nervous system, pharmacology, and risk factors seen in MDD patients. When verifying the allelic distribution, the S allele had a higher frequency in most of the studies analyzed. Despite not finding a commonality in the different studies, the tremendous genetic variation found demonstrates the MDD complexity. For this reason, further studies in diverse populations should be conducted to assist in the understanding and treatment of the disease.

Peripheral Biomarkers in DSM-5 Anxiety Disorders: An Updated Overview

Anxiety disorders are prevalent and highly disabling mental disorders. In recent years, intensive efforts focused on the search for potential neuroimaging, genetic, and peripheral biomarkers in order to better understand the pathophysiology of these disorders, support their diagnosis, and characterize the treatment response. Of note, peripheral blood biomarkers, as surrogates for the central nervous system, represent a promising instrument to characterize psychiatric disorders, although their role has not been extensively applied to clinical practice. In this report, the state of the art on peripheral biomarkers of DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th edition) Anxiety Disorders is presented, in order to examine their role in the pathogenesis of these conditions and their potential application for diagnosis and treatment. Available data on the cerebrospinal fluid and blood-based biomarkers related to neurotransmitters, neuropeptides, the hypothalamic-pituitary-adrenal axis, neurotrophic factors, and the inflammation and immune system are reviewed. Despite the wide scientific literature and the promising results in the field, only a few of the proposed peripheral biomarkers have been defined as a specific diagnostic instrument or have been identified as a guide in the treatment response to DSM-5 Anxiety Disorders. Therefore, further investigations are needed to provide new biological insights into the pathogenesis of anxiety disorders, to help in their diagnosis, and to tailor a treatment.

Functional rs6265 polymorphism in the brain-derived neurotrophic factor gene confers protection against neurocognitive dysfunction in posttraumatic stress disorder among Chinese patients with hepatocellular carcinoma

Posttraumatic stress disorder (PTSD) is a psychiatric disorder that plagues trauma survivors. Evidence shows that brain-derived neurotrophic factor (BDNF) may be involved in the occurrence and development of PTSD. Here we tried to demonstrate whether BDNF gene polymorphisms are correlated with neurocognitive function following PTSD in patients with hepatocellular carcinoma (HCC). This study included 102 patients with HCC complicated with PTSD, 146 HCC patients, and 152 healthy volunteers. Initially, we evaluated the neurocognitive function of the study subjects. Next, we measured BDNF G11757C and rs6265 polymorphisms by polymerase chain reaction-restriction fragment length polymorphism. The correlation of BDNF polymorphisms and BDNF level with HCC complicated with PTSD was evaluated. The results revealed that HCC complicated with PTSD showed decreased serum BDNF level and Mini-mental state examination (MMSE) score. Serum BDNF level of HCC and HCC complicated with PTSD was positively correlated with MMSE score. GA + AA allele and A allele of rs6265 increased the risk of PTSD among patients with HCC. GA and AA genotypes of rs6265 were correlated with the decreased MMSE score of HCC complicated with PTSD. Haplotype GA of rs6265 and G11757C increased the risk of PTSD for HCC, while haplotype CG decreased this risk. Lastly, the logistic regression analysis suggested that low BDNF level was a contributor to HCC complicated with PTSD, while GG genotype of rs6265 served as a protective factor. Collectively, this study defines the GG genotype of BDNF rs6265 polymorphism as a protector to HCC complicated with PTSD. In addition, these results provided a promising target for PTSD prevention in patients with HCC.

The effects of 5-HTTLPR and BDNF Val66Met polymorphisms on neurostructural changes in major depressive disorder

The serotonin-transporter-linked polymorphic region (5-HTTLPR) and brain-derived neurotrophic factor (BDNF) Val66Met polymorphism have been implicated in the pathophysiology of major depressive disorder (MDD). We aimed to investigate the effects of genetic variants of the 5-HTTLPR and BDNF Val66Met polymorphisms and their interactions with MDD on cortical volume and white matter integrity. Ninety-five patients with MDD and 65 healthy participants aged 20-65 years were recruited. The subjects were genotyped for the 5-HTTLPR and BDNF Val66Met polymorphisms and scanned with T1-weighted and diffusion tensor imaging. The gray matter volumes of 24 gyri in the prefrontal and anterior cingulate cortices and the fractional anisotropy values of nine white matter tracts in both hemispheres were determined. In the pooled sample of subjects from both groups, 5-HTTLPR L-allele carriers had significantly decreased cortical volume in the right anterior midcingulate gyrus compared to S-allele homozygotes. A significant effect of the interaction of the BDNF Val66Met polymorphism and MDD on the fractional anisotropy values of the right uncinate fasciculus was observed. Our results suggested that these genetic polymorphisms play important roles in the neurostructural changes of emotion-processing regions in subjects with MDD.

"DNA Methylation signatures in panic disorder"

Panic disorder (PD) affects about four million Europeans, with women affected twice as likely as men, causing substantial suffering and high economic costs. The etiopathogenesis of PD remains largely unknown, but both genetic and environmental factors contribute to risk. An epigenome-wide association study (EWAS) was conducted to compare medication-free PD patients (n = 89) with healthy controls (n = 76) stratified by gender. Replication was sought in an independent sample (131 cases, 169 controls) and functional analyses were conducted in a third sample (N = 71). DNA methylation was assessed in whole blood using the Infinium HumanMethylation450 BeadChip. One genome-wide association surviving FDR of 5% (cg07308824, P = 1.094 × 10-7, P-adj = 0.046) was identified in female PD patients (N = 49) compared to controls (N = 48). The same locus, located in an enhancer region of the HECA gene, was also hypermethylated in female PD patients in the replication sample (P = 0.035) and the significance of the association improved in the meta-analysis (P-adj = 0.004). Methylation at this CpG site was associated with HECA mRNA expression in another independent female sample (N = 71) both at baseline (P = 0.046) and after induction by dexamethasone (P = 0.029). Of 15 candidates, 5 previously reported as associated with PD or anxiety traits also showed differences in DNA methylation after gene-wise correction and included SGK1, FHIT, ADCYAP1, HTR1A, HTR2A. Our study examines epigenome-wide differences in peripheral blood for PD patients. Our results point to possible sex-specific methylation changes in the HECA gene for PD but overall highlight that this disorder is not associated with extensive changes in DNA methylation in peripheral blood.

Is the Val66Met polymorphism of the brain-derived neurotrophic factor gene associated with panic disorder? A meta-analysis

Although emerging evidence has suggested an association between the Val66Met (rs6265) polymorphisms in brain-derived neurotrophic factor (BDNF) gene and the panic disorder, the conclusion is inclusive given the mixed results. This meta-analysis reviewed and analyzed the recent studies addressing the potential association between the Val66Met polymorphisms and panic disorder susceptibility. Related case-control studies were retrieved by database searching and selected according to established inclusion criteria. Six articles were identified, which explored the association between the BDNF Val66Met polymorphism and panic disorder. Statistical analyses revealed no association for the allele contrast and the dominant model. However, the recessive model showed a significant association between the BDNF Val66Met polymorphism and panic disorder (odds ratio = 1.26, 95% confidence interval = 1.04-1.52, z = 2.39, P = 0.02). Despite of some limitations, this meta-analysis suggests that the Val66Met polymorphism of BDNF gene is a susceptibility factor for panic disorder.

Treatment-resistant panic disorder: clinical significance, concept and management

Panic disorder is commonly prevalent in the population, but the treatment response for panic disorder in clinical practice is much less effective than that in our imagination. Increasing evidence suggested existence of a chronic or remitting-relapsing clinical course in panic disorder. In this systematic review, we re-examine the definition of treatment-resistant panic disorder, and present the potential risk factors related to the treatment resistance, including the characteristics of panic disorder, other psychiatric and physical comorbidities, and psychosocial stresses. Furthermore, we summarize the potential pathophysiologies, such as genetic susceptibility, altered brain functioning, brain-derived neurotrophic factor, and long-term inflammation, to explain the treatment resistance. Finally, we conclude the current therapeutic strategies for treating treatment-resistant panic disorder from pharmacological and non-pharmacological views.

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.