Gene-based SNP genetic association study of the corticotropin-releasing hormone receptor-2 (CRHR2) in major depression

Comorbidity of Novel CRHR2 Gene Variants in Type 2 Diabetes and Depression

The corticotropin-releasing hormone receptor 2 (CRHR2) gene encodes CRHR2, contributing to the hypothalamic–pituitary–adrenal stress response and to hyperglycemia and insulin resistance. CRHR2−/− mice are hypersensitive to stress, and the CRHR2 locus has been linked to type 2 diabetes and depression. While CRHR2 variants confer risk for mood disorders, MDD, and type 2 diabetes, they have not been investigated in familial T2D and MDD. In 212 Italian families with type 2 diabetes and depression, we tested 17 CRHR2 single nucleotide polymorphisms (SNPs), using two-point parametric-linkage and linkage-disequilibrium (i.e., association) analysis (models: dominant-complete-penetrance-D1, dominant-incomplete-penetrance-D2, recessive-complete-penetrance-R1, recessive-incomplete-penetrance-R2). We detected novel linkage/linkage-disequilibrium/association to/with depression (3 SNPs/D1, 2 SNPs/D2, 3 SNPs/R1, 3 SNPs/R2) and type 2 diabetes (3 SNPs/D1, 2 SNPs/D2, 2 SNPs/R1, 1 SNP/R2). All detected risk variants are novel. Two depression-risk variants within one linkage-disequilibrium block replicate each other. Two independent novel SNPs were comorbid while the most significant conferred either depression- or type 2 diabetes-risk. Although the families were primarily ascertained for type 2 diabetes, depression-risk variants showed higher significance than type 2 diabetes-risk variants, implying CRHR2 has a stronger role in depression-risk than type 2 diabetes-risk. In silico analysis predicted variants’ dysfunction. CRHR2 is for the first time linked to/in linkage-disequilibrium/association with depression-type 2 diabetes comorbidity and may underlie the shared genetic pathogenesis via pleiotropy.

Systems Approach to Identify Common Genes and Pathways Associated with Response to Selective Serotonin Reuptake Inhibitors and Major Depression Risk

Despite numerous studies on major depressive disorder (MDD) susceptibility, the precise underlying molecular mechanism has not been elucidated which restricts the development of etiology-based disease-modifying drug. Major depressive disorder treatment is still symptomatic and is the leading cause of (~30%) failure of the current antidepressant therapy. Here we comprehended the probable genes and pathways commonly associated with antidepressant response and MDD. A systematic review was conducted, and candidate genes/pathways associated with antidepressant response and MDD were identified using an integrative genetics approach. Initially, single nucleotide polymorphisms (SNPs)/genes found to be significantly associated with antidepressant response were systematically reviewed and retrieved from the candidate studies and genome-wide association studies (GWAS). Also, significant variations concerning MDD susceptibility were extracted from GWAS only. We found 245 (Set A) and 800 (Set B) significantly associated genes with antidepressant response and MDD, respectively. Further, gene set enrichment analysis revealed the top five co-occurring molecular pathways (p ≤ 0.05) among the two sets of genes: Cushing syndrome, Axon guidance, cAMP signaling pathway, Insulin secretion, and Glutamatergic synapse, wherein all show a very close relation to synaptic plasticity. Integrative analyses of candidate gene and genome-wide association studies would enable us to investigate the putative targets for the development of disease etiology-based antidepressant that might be more promising than current ones.

Antidepressant Outcomes Predicted by Genetic Variation in Corticotropin-Releasing Hormone Binding Protein

OBJECTIVE

Genetic variation within the hypothalamic-pituitary-adrenal (HPA) axis has been linked to risk for depression and antidepressant response. However, these associations have yet to produce clinical gains that inform treatment decisions. The authors investigated whether variation within HPA axis genes predicts antidepressant outcomes within two large clinical trials.

METHOD

The test sample comprised 636 patients from the International Study to Predict Optimized Treatment in Depression (iSPOT-D) who completed baseline and 8-week follow-up visits and for whom complete genotyping data were available. The authors tested the relationship between genotype at 16 candidate HPA axis single-nucleotide polymorphisms (SNPs) and treatment outcomes for three commonly used antidepressants (escitalopram, sertraline, and extended-release venlafaxine), using multivariable linear and logistic regression with Bonferroni correction. Response and remission were defined using the Hamilton Depression Rating Scale. Findings were then validated using the Predictors of Remission in Depression to Individual and Combined Treatments (PReDICT) study of outcome predictors in treatment-naive patients with major depression.

RESULTS

The authors found that the rs28365143 variant within the corticotropin-releasing hormone binding protein (CRHBP) gene predicted antidepressant outcomes for remission, response, and symptom change. Patients homozygous for the G allele of rs28365143 had greater remission rates, response rates, and symptom reductions. These effects were specific to drug class. Patients homozygous for the G allele responded significantly better to the selective serotonin reuptake inhibitors escitalopram and sertraline than did A allele carriers. In contrast, rs28365143 genotype was not associated with treatment outcomes for the serotonin norepinephrine reuptake inhibitor venlafaxine. When patients were stratified by race, the overall effect of genotype on treatment response remained. In the validation sample, the GG genotype was again associated with favorable antidepressant outcomes, with comparable effect sizes.

CONCLUSIONS

These findings suggest that a specific CRHBP SNP, rs28365143, may have a role in predicting which patients will improve with antidepressants and which type of antidepressant may be most effective. The results add to the foundational knowledge needed to advance a precision approach to personalized antidepressant choices.

Corticotropin-Releasing Hormone Receptor 2 Gene Variants in Irritable Bowel Syndrome

Background

Corticotropin-releasing hormone (CRH) plays an important role in the pathophysiology of irritable bowel syndrome (IBS) and regulates the stress response through two CRH receptors (R1 and R2). Previously, we reported that a CRHR1 gene polymorphism (rs110402, rs242924, and rs7209436) and haplotypes were associated with IBS. However, the association between the CRHR2 gene and IBS was not investigated. We tested the hypothesis that genetic polymorphisms and haplotypes of CRHR2 are associated with IBS pathophysiology and negative emotion in IBS patients.

Methods

A total of 142 IBS patients and 142 healthy controls participated in this study. Seven single nucleotide polymorphisms (SNPs) of the CRHR2 gene (rs4722999, rs3779250, rs2240403, rs2267710, rs2190242, rs2284217, and rs2284220) were genotyped. Subjects' psychological states were evaluated using the Perceived-Stress Scale, the State-Trait Anxiety Inventory, and the Self-Rating Depression Scale.

Results

We found that rs4722999 and rs3779250, located in intronic region, were associated with IBS in terms of genotype frequency (rs4722999: P = 0.037; rs3779250: P = 0.017) and that the distribution of the major allele was significantly different between patients and controls. There was a significant group effect (controls vs. IBS), and a CRHR2 genotype effect was observed for three psychological scores, but the interaction was not significant. We found a haplotype of four SNPs (rs4722999, rs3779250, rs2240403, and rs2267710) and two SNPs (rs2284217 and rs2284220) in strong linkage disequilibrium (D′ > 0.90). We also found that haplotypes of the CRHR2 gene were significantly different between IBS patients and controls and that they were associated with negative emotion.

Conclusion

Our findings support the hypothesis that genetic polymorphisms and haplotypes of CRHR2 are related to IBS. In addition, we found associations between CRHR2 genotypes and haplotypes and negative emotion in IBS patients and controls. Further studies on IBS and the CRH system are warranted.

Relationship of cortisol levels and genetic polymorphisms to antidepressant response to placebo and fluoxetine in patients with major depressive disorder: a prospective study

BACKGROUND

Increased cortisol levels and genetic polymorphisms have been related to both major depressive disorder and antidepressant treatment outcome. The aim of this study is to evaluate the relationship between circadian salivary cortisol levels, cortisol suppression by dexamethasone and genetic polymorphisms in some HPA axis-related genes to the response to placebo and fluoxetine in depressed patients.

METHODS

The diagnosis and severity of depression were performed using the Mini International Neuropsychiatric Interview (M.I.N.I.) and Hamilton depression scale (HAM-D17), respectively. Euthyroid patients were treated with placebo (one week) followed by fluoxetine (20 mg) (two months). Severity of depression was re-evaluated after placebo, three weeks and two months of fluoxetine treatments. Placebo response was defined as HAM-D17 score reductions of at least 25% and to < 15. Early response and response were reductions of at least 50% after three weeks and two months, and remission with ≤ 7 after two months. Plasma TSH, free-T4, circadian salivary cortisol levels and cortisol suppression by dexamethasone were evaluated. Seven genetic polymorphisms located in the Corticotrophin-releasing-hormone-receptor-1 (rs242939, rs242941, rs1876828), Corticotrophin-releasing-hormone-receptor-2 (rs2270007), Glucocorticoid-receptor (rs41423247), FK506-binding-protein-5 (rs1360780), and Arginine-vasopressin (rs3729965) genes were determined. Association analyses between response to placebo/fluoxetine and polymorphism were performed by chi-square or Fisher exact test. Cortisol levels were compared by t-test, ANOVA and the general linear model for repeated measures.

RESULTS

208 depressed patients were recruited, 187 of whom were euthyroid. Placebo responders, fluoxetine responders and remitters exhibited significantly lower circadian cortisol levels than those who did not respond (p-values of 0.014, 0.008 and 0.021 respectively). Patients who abandoned treatment before the third week also exhibited a trend to low cortisol levels (p = 0.057). The polymorphisms rs242939 (CRHR1) and rs2270007 (CRHR2) were not in Hardy-Weinberg equilibrium. Only the rs242939 polymorphism (CRHR1) exhibited association with early response (three weeks) to fluoxetine (p-value = 0.043). No other association between outcomes and polymorphisms was observed.

CONCLUSIONS

These results support the clinical relevance of low salivary cortisol levels as a predictor of antidepressant response, either to placebo or to fluoxetine. Only one polymorphism in the CRHR1 gene was associated with the early response. Other factors may be involved in antidepressant response, although further studies are needed to identify them.

Hypothesis of the neuroendocrine cortisol pathway gene role in the comorbidity of depression, type 2 diabetes, and metabolic syndrome

Depression, type 2 diabetes (T2D), and metabolic syndrome (MetS) are often comorbid. Depression per se increases the risk for T2D by 60%. This risk is not accounted for by the use of antidepressant therapy. Stress causes hyperactivation of the hypothalamic–pituitary–adrenal (HPA) axis, by triggering the hypothalamic corticotropin-releasing hormone (CRH) secretion, which stimulates the anterior pituitary to release the adrenocorticotropin hormone (ACTH), which causes the adrenal secretion of cortisol. Depression is associated with an increased level of cortisol, and CRH and ACTH at inappropriately “normal” levels, that is too high compared to their expected lower levels due to cortisol negative feedback. T2D and MetS are also associated with hypercortisolism. High levels of cortisol can impair mood as well as cause hyperglycemia and insulin resistance and other traits typical of T2D and MetS. We hypothesize that HPA axis hyperactivation may be due to variants in the genes of the CRH receptors (CRHR1, CRHR2), corticotropin receptors (or melanocortin receptors, MC1R-MC5R), glucocorticoid receptor (NR3C1), mineralocorticoid receptor (NR3C2), and of the FK506 binding protein 51 (FKBP5), and that these variants may be partially responsible for the clinical association of depression, T2D and MetS. In this review, we will focus on the correlation of stress, HPA axis hyperactivation, and the possible genetic role of the CRHR1, CRHR2, MCR1–5, NR3C1, and NR3C2 receptors and FKBP5 in the susceptibility to the comorbidity of depression, T2D, and MetS. New studies are needed to confirm the hypothesized role of these genes in the clinical association of depression, T2D, and MetS.

Corticotropin releasing hormone receptor 2 (CRHR-2) gene is associated with decreased risk and severity of posttraumatic stress disorder in women

BACKGROUND

The corticotropin releasing hormone (CRH) system has been implicated in a variety of anxiety and mood-based symptoms and disorders. CRH receptor-2 (CRHR-2) plays a role in attenuating biological responses to stressful life events and trauma, making the CRHR-2 gene a strong candidate to study in relationship to PTSD.

METHODS

The sample was 491 trauma-exposed white non-Hispanic veterans and their cohabitating intimate partners assessed via structured interview for lifetime DSM-IV PTSD; just over 60% met criteria for the disorder. Thirty-one single nucleotide polymorphisms (SNPs) in and near CRHR-2, obtained from an array of 2.5 million markers, were tested for association with PTSD diagnosis and symptom severity in the whole sample and in men and women separately.

RESULTS

Ten SNPs showed nominally significant evidence of association with PTSD in the full sample and two SNPs (rs8192496 and rs2190242) were significant after permutation-based multiple testing correction (uncorrected ps = .0004 and .0005, odds ratios = .60 and .58, respectively). Analyses stratified by sex revealed that the effect was specific to women, who comprised 35% of the sample (uncorrected ps = .0003 and .0002, odds ratios = .41 and .35, respectively). Two additional SNPs (rs2267715 and rs2284218) also showed significant association with PTSD in women (both uncorrected ps = .001, both odds ratios = .48).

CONCLUSIONS

Results suggest that CRHR-2 variants may affect risk for PTSD in women by attenuating the stress response and reducing symptoms of the disorder.

Sex, stress, and mood disorders: at the intersection of adrenal and gonadal hormones

The risk for neuropsychiatric illnesses has a strong sex bias, and for major depressive disorder (MDD), females show a more than 2-fold greater risk compared to males. Such mood disorders are commonly associated with a dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis. Thus, sex differences in the incidence of MDD may be related with the levels of gonadal steroid hormone in adulthood or during early development as well as with the sex differences in HPA axis function. In rodents, organizational and activational effects of gonadal steroid hormones have been described for the regulation of HPA axis function and, if consistent with humans, this may underlie the increased risk of mood disorders in women. Other developmental factors, such as prenatal stress and prenatal overexposure to glucocorticoids can also impact behaviors and neuroendocrine responses to stress in adulthood and these effects are also reported to occur with sex differences. Similarly, in humans, the clinical benefits of antidepressants are associated with the normalization of the dysregulated HPA axis, and genetic polymorphisms have been found in some genes involved in controlling the stress response. This review examines some potential factors contributing to the sex difference in the risk of affective disorders with a focus on adrenal and gonadal hormones as potential modulators. Genetic and environmental factors that contribute to individual risk for affective disorders are also described. Ultimately, future treatment strategies for depression should consider all of these biological elements in their design.

Association of CRHR1 and CRHR2 with major depressive disorder and panic disorder in a Japanese population

Major depressive disorder (MDD) and panic disorder (PD) are common and disabling medical disorders with stress and genetic components. Dysregulation of the stress response of the hypothalamic-pituitary-adrenal axis, including the corticotrophin-releasing hormone (CRH) signaling via primary receptors (CRHR1 and CRHR2), is considered to play a major role for onset and recurrence in MDD and PD. To confirm the association of CRHR1 and CRHR2 with MDD and PD, we investigated 12 single nucleotide polymorphisms (SNPs) (rs4076452, rs7209436, rs110402, rs242924, rs242940, and rs173365 for CRHR1 and rs4722999, rs3779250, rs2267710, rs1076292, rs2284217, and rs226771 for CRHR2) in MDD patients (n = 173), PD patients (n = 180), and healthy controls (n = 285). The SNP rs110402 and rs242924 in the CRHR1 gene and the rs3779250 in the CRHR2 gene were associated with MDD. The SNP rs242924 in the CRHR1 gene was also associated with PD. The T-A-T-G-G haplotype consisting of rs7209436 and rs173365 in CRHR1 was positively associated with MDD. The T-A haplotype consisting of rs7209436 and rs110402 in CRHR1 was positively associated with MDD. The C-C haplotype consisting of rs4722999 and rs37790 in CRHR1 was associated with PD. These results provide support for an association of CRHR1 and CRHR2 with MDD and PD.

Biomarkers for major depression and its delineation from neurodegenerative disorders

Major depressive disorders (MDD) are among the most debilitating diseases worldwide and occur with a high prevalence in elderly individuals. Neurodegenerative diseases (in particular Alzheimer's disease, AD) do also show a strong age-dependent increase in incidence and prevalence among the elderly population. A high number of geriatric patients with MDD show cognitive deficits and a very high proportion of AD patients present co-morbid MDD, which poses difficult diagnostic and prognostic questions. Especially in prodromal and in very early stages of AD, it is almost impossible to differentiate between pure MDD and MDD with underlying AD. Here, we give a comprehensive review of the literature on the current state of candidate biomarkers for MDD ("positive MDD markers") and briefly refer to established and validated diagnostic AD biomarkers in order to rule out underlying AD pathophysiology in elderly MDD subjects with cognitive impairments ("negative MDD biomarkers"). In summary, to date there is no evidence for positive diagnostic MDD biomarkers and the only way to delineate MDD from AD is to use "negative MDD" biomarkers. Because of this highly unsatisfactory current state of MDD biomarker research, we propose a research strategy targeting to detect and validate positive MDD biomarkers, which is based on a complex (genetic, molecular and neurophysiological) biological model that incorporates current state of the art knowledge on the pathobiology of MDD. This model delineates common pathways and the intersection between AD and MDD. Applying these concepts to MDD gives hope that positive MDD biomarkers can be successfully identified in the near future.

Gene-environment interactions in geriatric depression

In older adults, several environmental challenges can potentially trigger the onset of an episode of major depression. Vulnerability to these challenges can be influenced by genetics. There is accumulating evidence for an interaction between stress and a serotonin transporter polymorphism, though there is also heterogeneity among studies. Other relevant genes include those encoding for the neuroendocrine stress axis, growth factors, and other monoaminergic systems. Each of these may interact with either predisposing traumas in early childhood or precipitating events later in life.

Poor replication of candidate genes for major depressive disorder using genome-wide association data

Data from the Genetic Association Information Network (GAIN) genome-wide association study (GWAS) in major depressive disorder (MDD) were used to explore previously reported candidate gene and single-nucleotide polymorphism (SNP) associations in MDD. A systematic literature search of candidate genes associated with MDD in case-control studies was performed before the results of the GAIN MDD study became available. Measured and imputed candidate SNPs and genes were tested in the GAIN MDD study encompassing 1738 cases and 1802 controls. Imputation was used to increase the number of SNPs from the GWAS and to improve coverage of SNPs in the candidate genes selected. Tests were carried out for individual SNPs and the entire gene using different statistical approaches, with permutation analysis as the final arbiter. In all, 78 papers reporting on 57 genes were identified, from which 92 SNPs could be mapped. In the GAIN MDD study, two SNPs were associated with MDD: C5orf20 (rs12520799; P=0.038; odds ratio (OR) AT=1.10, 95% CI 0.95-1.29; OR TT=1.21, 95% confidence interval (CI) 1.01-1.47) and NPY (rs16139; P=0.034; OR C allele=0.73, 95% CI 0.55-0.97), constituting a direct replication of previously identified SNPs. At the gene level, TNF (rs76917; OR T=1.35, 95% CI 1.13-1.63; P=0.0034) was identified as the only gene for which the association with MDD remained significant after correction for multiple testing. For SLC6A2 (norepinephrine transporter (NET)) significantly more SNPs (19 out of 100; P=0.039) than expected were associated while accounting for the linkage disequilibrium (LD) structure. Thus, we found support for involvement in MDD for only four genes. However, given the number of candidate SNPs and genes that were tested, even these significant may well be false positives. The poor replication may point to publication bias and false-positive findings in previous candidate gene studies, and may also be related to heterogeneity of the MDD phenotype as well as contextual genetic or environmental factors.

Associations between common arginine vasopressin 1b receptor and glucocorticoid receptor gene variants and HPA axis responses to psychosocial stress in a child psychiatric population

On the one hand, a suitable response to daily stressors is crucial for adequate functioning in any natural environment. On the other hand, depending on the individual's genetic makeup, prolonged stress that is accompanied by an inappropriate level of responsiveness may lead to physiological and psychiatric disorders. Several psychiatric conditions have been linked with stress and alterations in hypothalamic-pituitary-adrenal (HPA) activity. While stress is a general phenomenon, illness is only seen in a proportion of individuals, suggesting that genetic factors may play a role in the ability to cope with stress. In children, relatively little research has been conducted to determine the impact of genetic factors on the variability in HPA axis functioning. In the present exploratory investigation, 106 prepubertal children were studied to estimate the impact of four glucocorticoid receptor gene (NR3C1) polymorphisms (NR3C1-1 [rs10482605], ER22/23EK [rs6190], N363S [rs6195], N766N [rs6196]) and five arginine vasopressin (AVP) receptor 1b gene (AVPR1b) polymorphisms (AVPR1b_s1 [rs28536160], AVPR1b_s2 [rs28373064], AVPR1b_s3 [rs33976516], AVPR1b_s4 [rs33985287], AVPR1b_s5 [rs33933482]) on cortisol responses after a psychosocial stress test (public speaking task). ER22/23EK carriers had significantly lower cortisol responses to psychosocial stress compared with noncarriers. These findings provide evidence for the relevance of the ER22/23EK polymorphism in childhood HPA axis regulation. However, the small number of ER22/23EK subjects does not allow us to draw definitive conclusions about the genotypic effect.

The CRF system, stress, depression and anxiety-insights from human genetic studies

A concatenation of findings from preclinical and clinical studies support a preeminent function for the corticotropin-releasing factor (CRF) system in mediating the physiological response to external stressors and in the pathophysiology of anxiety and depression. Recently, human genetic studies have provided considerable support to several long-standing hypotheses of mood and anxiety disorders, including the CRF hypothesis. These data, reviewed in this report, are congruent with the hypothesis that this system is of paramount importance in mediating stress-related psychopathology. More specifically, variants in the gene encoding the CRF(1) receptor interact with adverse environmental factors to predict risk for stress-related psychiatric disorders. In-depth characterization of these variants will likely be important in furthering our understanding of the long-term consequences of adverse experience.

An intronic polymorphism in the corticotropin-releasing hormone receptor 2 gene increases susceptibility to HBV-related hepatocellular carcinoma in Chinese population

Corticotropin-releasing hormone receptor 2 (CRHR2) plays a role in both the central nervous system (CNS) and the peripheral nervous system. CRHR2 together with its ligands, urocortins (Ucns) and corticotropin-releasing hormone (CRH), functions as a mediator of inflammatory response and inhibitor of angiogenesis. Recently, it has been reported to be expressed in many human cancers. An association between rs2267716 polymorphism in the CRHR2 gene and susceptibility to hepatocellular carcinoma (HCC) was found in patients with chronic hepatitis C virus (HCV) infection. In the present study we analyzed, using a polymerase chain reaction-ligation detection reaction (PCR-LDR), the rs2267716 polymorphism in 364 hepatitis B virus (HBV)-related HCC patients, 196 non-HCC patients with HBV infection, and 404 healthy controls. The aim was to detect the possible association of this single-nucleotide polymorphism (SNP) with susceptibility to HBV-related HCC. Significant differences of rs2267716 allele were detected between HBV-related HCC patients and healthy controls (OR = 1.55, 95% CI 1.13-2.15, P = 0.007) or non-HCC patients with HBV infection (OR = 1.61, 95% CI 1.13-2.31, P = 0.009). These results suggest that the rs2267716 polymorphism in the CRHR2 gene might influence the risk of developing HCC in patients with HBV infection in Chinese population.

Meta-analyses of genetic studies on major depressive disorder

The genetic basis of major depressive disorder (MDD) has been investigated extensively, but the identification of MDD genes has been hampered by conflicting results from underpowered studies. We review all MDD case-control genetic association studies published before June 2007 and perform meta-analyses for polymorphisms that had been investigated in at least three studies. The study selection and data extraction were performed in duplicate by two independent investigators. The 183 papers that met our criteria studied 393 polymorphisms in 102 genes. Twenty-two polymorphisms (6%) were investigated in at least three studies. Seven polymorphisms had been evaluated in previous meta-analyses, 5 of these had new data available. Hence, we performed meta-analyses for 20 polymorphisms in 18 genes. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Statistically significant associations were found for the APOE varepsilon2 (OR, 0.51), GNB3 825T (OR, 1.38), MTHFR 677T (OR, 1.20), SLC6A4 44 bp Ins/Del S (OR, 1.11) alleles and the SLC6A3 40 bpVNTR 9/10 genotype (OR, 2.06). To date, there is statistically significant evidence for six MDD susceptibility genes (APOE, DRD4, GNB3, MTHFR, SLC6A3 and SLC6A4).

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.

Genetic variability at HPA axis in major depression and clinical response to antidepressant treatment

BACKGROUND

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis has been observed in major depression. Normalization of HPA axis has been suggested to play a role in the mechanisms of action of antidepressants. Our aim was to investigate the influence of genetic variants in CRHR1, CRHR2, CRH-BP and FKBP5 genes on both the vulnerability for depression and the response to antidepressant treatment.

METHODS

The sample consisted of 159 depressive outpatients and 96 healthy controls of Spanish origin. Patients were assessed for clinical features including, among others, age of onset, seasonality or suicidal behavior. The episode was treated with citalopram and followed along 12 weeks. Severity of symptoms was evaluated at the inclusion and then monthly along the follow-up using a 21-item Hamilton Depression Rating Score (HDRS). SNPs were assayed using Applied Biosystems SNaP-Shot and TaqMan technology.

RESULTS

rs110402, in CRHR1 gene, was associated with an increased risk to present a seasonal pattern and an early age of onset of the first depressive episode. Allele G carriers of rs2270007 of CRHR2 gene, showed a worse overall response to citalopram along time of follow-up (Genotype effect F=7.45, P=0.007). G allele carriers showed 2.93 increased risk (95% CI [1.24-6.90]) for non-responding at 4th week to citalopram treatment (chi(2)=7.59, df=1, P=0.006).

LIMITATIONS

On the light of the moderate sample size, associations based on the mentioned polymorphisms need to be considered with caution and require further replication studies in other samples.

CONCLUSIONS

Variability at genes encoding proteins with a pivotal role in HPA axis regulation seems to influence i) the expression of severity variables of the depressive spectrum including early age of onset or a seasonal pattern and ii) the interindividual variation in clinical response to SSRI antidepressants.

Consensus paper of the WFSBP Task Force on Biological Markers: biological markers in depression

Biological markers for depression are of great interest to aid in elucidating the causes of major depression. We assess currently available biological markers to query their validity for aiding in the diagnosis of major depression. We specifically focus on neurotrophic factors, serotonergic markers, biochemical markers, immunological markers, neuroimaging, neurophysiological findings, and neuropsychological markers. We delineate the most robust biological markers of major depression. These include decreased platelet imipramine binding, decreased 5-HT1A receptor expression, increase of soluble interleukin-2 receptor and interleukin-6 in serum, decreased brain-derived neurotrophic factor in serum, hypocholesterolemia, low blood folate levels, and impaired suppression of the dexamethasone suppression test. To date, however, none of these markers are sufficiently specific to contribute to the diagnosis of major depression. Thus, with regard to new diagnostic manuals such as DSM-V and ICD-11 which are currently assessing whether biological markers may be included in diagnostic criteria, no biological markers for major depression are currently available for inclusion in the diagnostic criteria.

Association study between the corticotropin-releasing hormone receptor 2 gene and suicidality in bipolar disorder

Family, adoption and twin studies show that genetics influences suicidal behavior, but does not indicate specific susceptibility variants. Stress response is thought to be mediated by the corticotrophin-releasing hormone (CRH), which is known to be a regulator of the hypothalamic-pituitary-adrenal pathway (HPA). Alterations in HPA system have been related to impulsivity, aggression and suicidal behaviour, that are common features in Bipolar Disorder (BD). CRH is a hypothalamic factor that stimulates the pituitary gland. Two CRH receptors are known, CRHR1 and CRHR2. To search for markers conferring genetic susceptibility to suicide, we typed three polymorphisms of the CRHR2 gene, CRHR2(CA), CRHR2(GT), and CRHR2(GAT), in 312 families where at least one subject had DSM-IV bipolar disorder. Family based association analyses in the suicide attempters using FBAT yielded no difference in the distribution of the alleles for all three markers. HBAT analysis for quantitative measures on suicide-related traits showed association between haplotype 5-2-3 and higher severity. The current results show that haplotype variation at the CRHR2 locus is associated with suicidal behaviour. This is to our knowledge the first investigation on suicidal behavior and genetic variation at the CRHR2 locus, an important regulator of the HPA axis.

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

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

Association between corticotropin-releasing hormone receptor 2 (CRHR2) gene polymorphism and personality traits

Corticotropin-releasing hormone (CRH) has been implicated in the pathophysiology of anxiety disorders and depression. Corticotropin-releasing hormone receptor 2 (CRHR2) is one of the receptors that mediate CRH signal. The purpose of the present study was to investigate the association between the CRHR2 gene and personality traits, evaluated using the Revised NEO Personality Inventory (NEO PI-R), in 243 healthy Japanese subjects. As a result, significant association was observed between the polymorphism in intron 2 (rs2267717) and Openness (P = 0.004, uncorrected, anova), while no relationship was observed concerning Neuroticism. The present result suggests an association between CRHR2 and the personality trait of Openness.

Glucocorticoid receptor gene-based SNP analysis in patients with recurrent major depression

Dysregulation of the hypothalamic-pituitary-adrenal axis, one of the stress-response systems, is one of the key neurobiological features of major depression (MDD). Data supporting the notion that glucocorticoid-mediated feedback inhibition is impaired in MDD come from a multitude of studies demonstrating nonsuppression of cortisol secretion following administration of the synthetic glucocorticoid dexamethasone. We examined whether genetic variations in the glucocorticoid receptor gene (Nuclear Receptor Subfamily 3, Group C, Member 1; NR3C1) could be associated with increased susceptibility for MDD using a whole gene-based association analysis of single nucleotide polymorphisms (SNPs). Four SNPs were identified in NR3C1 and genotyped in two well-diagnosed samples of patients with MDD ascertained in Belgium and northern Sweden, and matched control samples. In total, 314 MDD patients and 354 control individuals were included in the study. In the Belgian sample, we observed significant allele (p=0.02) and genotype (p=0.02) association with an SNP in the promoter region (NR3C1-1); in the Swedish sample, we observed significant allele (p=0.02) and genotype (p=0.02) association with the R23K SNP. The haplotype association studies showed modest evidence for an involvement of the 5' region of the NR3C1 gene in the genetic vulnerability for MDD. This study suggests that polymorphisms in the 5' region of the NR3C1 gene may play a role in the genetic vulnerability for MDD.

A psychobiological perspective on genetic determinants of hypothalamus-pituitary-adrenal axis activity

From the perspective of psychobiological stress research we present a brief overview of findings documenting a significant impact of genetic factors on the activity of the hypothalamus-pituitary-adrenal (HPA) axis. Quantitative genetic studies in twins as well as association studies, primarily on polymorphisms in the glucocorticoid receptor gene, are depicted. Recent findings suggest that the collaboration of psychobiology and molecular genetics is a promising interdisciplinary approach that will significantly contribute to the understanding of the mechanisms underlying the link between stress, the HPA axis, and HPA-related clinical states.

Hardy–Weinberg equilibrium in genetic association studies: an empirical evaluation of reporting, deviations, and power

We evaluated the testing and reporting of Hardy-Weinberg equilibrium (HWE) in recent genetic association studies, detected how frequently HWE was violated and estimated the power for HWE testing in this literature. Genetic association studies published in 2002 in Nature Genetics, American Journal of Human Genetics, and American Journal of Medical Genetics were assessed. Data were analyzed on 239 biallelic associations using 154 distinct genotype distribution data sets where HWE could be tested. Any information on HWE was given only for 150 (62.8%) associations (92 (59.7%) data sets). Reanalysis of the data showed significant deviation from HWE in the disease-free controls of 20 associations (13 data sets), but only four of them (two data sets) were admitted in the published articles. Another four deviations (in two data sets) were observed in the combined sample of cases and controls of studies where both cases and controls were diseased, and none were reported in the papers. In all six tested multiallelic associations (six data sets), there was violation of HWE, but this was not admitted in the published articles. Power calculations showed that most studies conforming to HWE simply were largely underpowered to detect HWE deviation; for example, power to detect an inbreeding of magnitude F=0.10 exceeded 80% in only 11 (7%) of the data sets being tested. This empirical evidence suggests that, even in high profile genetics journals, testing and reporting for HWE is often neglected and deviations are rarely admitted in the published reports. Moreover, power is limited for HWE testing in most current genetic association studies.

Candidate genes for antidepressant response to selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) can safely and successfully treat major depression, although a substantial number of patients benefit only partially or not at all from treatment. Genetic polymorphisms may play a major role in determining the response to SSRI treatment. Nonetheless, it is likely that efficacy is determined by multiple genes, with individual genetic polymorphisms having a limited effect size. Initial studies have identified the promoter polymorphism in the gene coding for the serotonin reuptake transporter as moderating efficacy for several SSRIs. The goal of this review is to suggest additional plausible polymorphisms that may be involved in antidepressant efficacy. These include genes affecting intracellular transductional cascades; neuronal growth factors; stress-related hormones, such as corticotropin-releasing hormone and glucocorticoid receptors; ion channels and synaptic efficacy; and adaptations of monoaminergic pathways. Association analyses to examine these candidate genes may facilitate identification of patients for targeted alternative therapies. Determining which genes are involved may also assist in identifying future, novel treatments.

Corticotropin-releasing hormone (CRH) in psychiatry: from stress to psychopathology

Corticotropin-releasing hormone (CRH) plays a central role in the adaptation of the organism to stress. It serves as the main regulating hormone of the hypothalamic pituitary adrenal (HPA) axis, which is activated within seconds after exposure to acute stress. Furthermore, it acts as a neurotransmitter in numerous other brain regions. Globally, CRH leads to a number of metabolic, neuroendocrine and autonomic adaptations, which are vitally important for an adequate reaction to acute stress, but can lead to pathological somatic and psychological effects in chronic stress situations. The adequate functioning of CRH is a delicate equilibrium, which can be permanently disturbed by early experiences of physical or sexual abuse, leading to psychopathology in adulthood. This review discusses the physiological functions of CRH as the stress response hormone. Subsequently, the emerging data on the disruptive effects of early trauma on the CRH system are summarized. The third part is devoted to CRH and HPA axis abnormalities in major depression and other psychiatric disorders. This rapidly accumulating evidence will change our understanding of psychopathology, and might challenge the established classification of psychiatric disorders.

CRH, Stress, and Major Depression: A Psychobiological Interplay

Major depressive disorder (MDD) is a complex disease and is one of the leading causes of disability in our society. The provoking factors are multiple; acute and chronic psychological stress, severe early trauma experiences, somatic disease, and genetic factors all play a role. This review focuses on hyperdrive of corticotropin-releasing hormone (CRH) as the fundamental neurobiological correlate of MDD. CRH plays a key role in the adaptation to acute stress, but chronic CRH hyperdrive leads to a number of disadvantageous emotional and somatic effects. The evidence that the HPA axis is hyperactive in MDD, probably as a result of a primary hyperdrive of CRH, comes from multiple sources: biochemical studies, functional HPA axis tests, neuroimaging and postmortem studies, and clinical trials with HPA axis-related compounds. The liability to develop CRH hyperdrive is probably partly genetic. For a number of relevant genes, transgenic animal studies and human association studies indicate a role in HPA axis regulation and the liability to develop CRH hyperdrive. These data are reviewed. Finally, early adverse experience can produce a lasting effect on HPA axis regulation as well, probably leading to a lifelong tendency to develop chronic CRH hyperdrive in response to stress. This has been shown in a number of animal studies, and recently some data in humans with early trauma have become available as well. Taken together, these findings allow formulating an integrative hypothesis, with CRH hyperdrive at the core, bridging the old dichotomy between biology and psychology in our thinking about MDD.

Genetic animal models of anxiety

The focus of this review is on progress achieved in identifying specific genes conferring risk for anxiety disorders through the use of genetic animal models. We discuss gene-finding studies as well as those manipulating a candidate gene. Both human and animal studies thus far support the genetic complexity of anxiety. Clinical manifestations of these diseases are likely related to multiple genes. While different anxiety disorders and anxiety-related traits all appear to be genetically influenced, it has been difficult to ascertain genetic influences in common. Mouse studies have provisionally mapped several loci harboring genes that affect anxiety-related behavior. The growing array of mutant mice is providing valuable information about how genes and environment interact to affect anxious behavior via multiple neuropharmacological pathways. Classical genetic methods such as artificial selection of rodents for high or low anxiety are being employed. Expression array technologies have as yet not been employed, but can be expected to implicate novel candidates and neurobiological pathways.