Genetic tests of biologic systems in affective disorders

Clinical experiences with intranasal esketamine for major depressive disorder resistant to treatment and with a psychiatric emergency: case presentations

Recently, esketamine became availableas an intranasal formulation, proposed for treatment-resistant depression (TRD). Three cases of TRD are presented, two with features of a psychiatric emergency. The first case is a 35-year-old man with MDD onset at the age of 27 years, with five previous failed therapies. The second patient is a middle-aged man with a 21-year MDD onset and six previous antidepressant treatments discontinued for poor therapeutic effects and tolerability. He also presented suicidal ideation with intent and a history of a failed suicide attempt by self-cutting his forearms. The third case is a 28-year-old female with a first MDD episode in 2020, treated first with amitriptyline and then with intravenous clomipramine. She had a history of a previous suicide attempt by self-cutting and, by her admission, showed active suicidal ideation with intent. In all three cases, a rapid reduction of depressive symptoms was observed with a subsequent complete resolution of suicidal ideation and intent in the two patients with such risk. Intranasal esketamine treatment was carried out with concomitant oral antidepressant therapy. The third patient reported the only recorded side effect: dissociation 20 min after every esketamine administration. Our preliminary experience proved esketamine's effectiveness on TRD symptoms and successful outcomes in psychiatric emergencies such as suicide risk.

Prediction of complex human diseases from pathway-focused candidate markers by joint estimation of marker effects: case of chronic fatigue syndrome

Background

The current practice of using only a few strongly associated genetic markers in regression models results in generally low power in prediction or accounting for heritability of complex human traits.

Purpose

We illustrate here a Bayesian joint estimation of single nucleotide polymorphism (SNP) effects principle to improve prediction of phenotype status from pathway-focused sets of SNPs. Chronic fatigue syndrome (CFS), a complex disease of unknown etiology with no laboratory methods for diagnosis, was chosen to demonstrate the power of this Bayesian method. For CFS, such a genetic predictive model in combination with clinical evidence might lead to an earlier diagnosis than one based solely on clinical findings.

Methods

One of our goals is to model disease status using Bayesian statistics which perform variable selection and parameter estimation simultaneously and which can induce the sparseness and smoothness of the SNP effects. Smoothness of the SNP effects is obtained by explicit modeling of the covariance structure of the SNP effects.

Results

The Bayesian model achieved perfect goodness of fit when tested within the sampled data. Tenfold cross-validation resulted in 80 % accuracy, one of the best so far for CFS in comparison to previous prediction models. Model reduction aspects were investigated in a computationally feasible manner. Additionally, genetic variation estimates provided by the model identified specific genetic markers for their biological role in the disease pathophysiology.

Conclusions

This proof-of-principle study provides a powerful approach combining Bayesian methods, SNPs representing multiple pathways and rigorous case ascertainment for accurate genetic risk prediction modeling of complex diseases like CFS and other chronic diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s40246-015-0030-6) contains supplementary material, which is available to authorized users.

[The role of genotype in the intergenerational transmission of experiences of childhood adversity]

The prevalence of childhood abuse and maltreatment is estimated to lie at about 15% in the overall German population. Previous research suggested that about one third of all individuals who had experienced childhood adversity subsequently maltreated their own children or responded insensitively to their children's needs. Empirical studies imply that interindividual differences in the responsiveness to childhood adversity can partially be explained by gene-environment interactions. This article discusses the potential interplay of genes and environment in the context of transmitting maltreating behavior and (in)sensitive parenting against the background of current challenges in genetic research. Selected studies on gene × environment interactions are presented and relevant gene polymorphisms are identified. Overall, previous studies reported interactions between polymorphisms of the serotonergic, dopaminergic, oxytocin-related, and arginine vasopressin-related systems and childhood experiences of care and abuse in the prediction of social behaviors during mother-child interactions. The results indicate a differential susceptibility toward both negative and positive environments which is dependent on genetic characteristics. Future research should thus investigate the effects of children's presumed risk gene variants toward negative as well as positive parenting. This could contribute to a deeper understanding of the underlying mechanisms of the intergenerational transmission of abusive and beneficial parenting behavior and help to avoid false stigmatizations.

Serotonin transporter-linked polymorphic region (5-HTTLPR) genotype is associated with cortisol responsivity to naloxone challenge

RATIONALE

The serotonergic and opioidergic neurotransmitter systems are critical regulators of the hypothalamic-pituitary-adrenal (HPA) axis through their respective excitatory and inhibitory inputs. Serotonin transporter (5-HTT) genotype has been studied as a marker of HPA axis dysregulation and for predicting risk of psychopathology, with mixed findings.

OBJECTIVES

We stimulated the HPA axis with naloxone, an opioid receptor antagonist, to examine cortisol reactivity based on 5-HTT-linked polymorphic region (5-HTTLPR) genotypes.

METHODS

Healthy community volunteers (N = 78) received intravenous (IV) placebo followed by sequential doses of IV naloxone (50, 100, 200, and 400 μg/kg) every 30 min. Plasma cortisol was measured every 15 min. Participants were genotyped for the long (L) and short (S) alleles of the 5-HTT gene and for rs25531 (A/G) in the 5-HTTLPR repetitive element and compared by the 5-HTTLPR/rs25531 genotype (triallele) and by the 5-HTTLPR genotype (biallele) classification.

RESULTS

In triallele analyses, individuals with one or more L(A) alleles showed higher cortisol response to naloxone compared with individuals with no L(A) alleles. In biallele analyses, less robust effects were found, although individuals with two L alleles showed a higher cortisol response compared with other genotypes.

CONCLUSIONS

Naloxone blockade leads to a greater activation of the HPA axis among individuals with the L(A) allele. Including rs25531 in the analysis with the 5-HTTLPR genotype appears more sensitive in detecting genetic differences in naloxone-induced cortisol than when using only the 5-HTTLPR genotype. Future research should investigate the interactive effects between the serotonergic and opioidergic systems on HPA axis dysregulation and psychopathophysiology.

Common and specific liability to addiction: approaches to association studies of opioid addiction

BACKGROUND

Opioid addiction, whether to opiates such as heroin and morphine, and/or to non-medical use of opioids, is a major problem worldwide. Although drug-induced and environmental factors are essential for the liability to develop opioid addiction, the genetic background of an individual is now known also to play a substantial role.

METHODS

The overall goal of this article is to address the common and specific liabilities to addiction in the context of approaches to studies of one addiction, opioid addiction. Literature on identifying genetic variants that may play a role in the development of opioid addiction was reviewed.

RESULTS

A substantial number of genetic variants have been reported to be associated with opioid addiction. No single variant has been found in any of the reported GWAS studies with a substantial effect size on the liability to develop heroin addiction. It appears that there is a complex interaction of a large number of variants, some rare, some common, which interact with the environment and in response to specific drugs of abuse to increase the liability of developing opioid addiction.

CONCLUSIONS

In spite of the inherent difficulties in obtaining large well-phenotyped cohorts for genetic studies, new findings have been reported that are being used to develop testable hypotheses into the biological basis of opioid addiction.

Genome-wide association study identifies genes that may contribute to risk for developing heroin addiction

OBJECTIVES

We have used genome-wide association studies to identify variants that are associated with vulnerability to develop heroin addiction.

METHODS

DNA from 325 methadone stabilized, former severe heroin addicts and 250 control individuals were pooled by ethnicity (Caucasian and African-American) and analyzed using the Affymetrix GeneChip Mapping 100 K Set. Genome-wide association tests were conducted.

RESULTS

The strongest association with vulnerability to develop heroin addiction, with experiment-wise significance (P=0.035), was found in Caucasians with the variant rs10494334, a variant in an unannotated region of the genome (1q23.3). In African Americans, the variant most significantly associated with the heroin addiction vulnerability was rs950302, found in the cytosolic dual specificity phosphatase 27 gene DUSP27 (point-wise P=0.0079). Furthermore, analysis of the top 500 variants with the most significant associations (point-wise P< or =0.0036) in Caucasians showed that three of these variants are clustered in the regulating synaptic membrane exocytosis protein 2 gene RIMS2. Of the top 500 variants in African-Americans (point-wise P< or =0.0238), three variants are in the cardiomyopathy associated 3 gene CMYA3.

CONCLUSION

This study identifies new genes and variants that may increase an individual's vulnerability to develop heroin addiction.

New findings in the genetics of major psychoses

Schizophrenia and bipolar disorder have a largely unknown pathophysiology and etiology, but they are highly heritable. Although linkage and association studies have identified a series of chromosomal regions likely to contain susceptibility genes, progress in identifying causative genes has been largely disappointing. However, rapid technological advances are beginning to lead to new insights. Systematic genome-wide association and follow-up studies have reported genome-wide significant association findings of common variants for schizophrenia and bipolar disorder. The risk conferred by individual variants is small, and some variants confer a risk for both disorders. In addition, recent studies have identified rare, large structural variants (copy number variants) that confer a greater risk for schizophrenia. This review summarizes recent developments in genetic research into schizophrenia and bipolar disorder, and discusses possible future directions in this field.

Strong genetic evidence for a selective influence of GABAA receptors on a component of the bipolar disorder phenotype

Despite compelling evidence for a major genetic contribution to risk of bipolar mood disorder, conclusive evidence implicating specific genes or pathophysiological systems has proved elusive. In part this is likely to be related to the unknown validity of current phenotype definitions and consequent aetiological heterogeneity of samples. In the recent Wellcome Trust Case Control Consortium genome-wide association analysis of bipolar disorder (1868 cases, 2938 controls) one of the most strongly associated polymorphisms lay within the gene encoding the GABA(A) receptor beta1 subunit, GABRB1. Aiming to increase biological homogeneity, we sought the diagnostic subset that showed the strongest signal at this polymorphism and used this to test for independent evidence of association with other members of the GABA(A) receptor gene family. The index signal was significantly enriched in the 279 cases meeting Research Diagnostic Criteria for schizoaffective disorder, bipolar type (P=3.8 x 10(-6)). Independently, these cases showed strong evidence that variation in GABA(A) receptor genes influences risk for this phenotype (independent system-wide P=6.6 x 10(-5)) with association signals also at GABRA4, GABRB3, GABRA5 and GABRR3. [corrected] Our findings have the potential to inform understanding of presentation, pathogenesis and nosology of bipolar disorders. Our method of phenotype refinement may be useful in studies of other complex psychiatric and non-psychiatric disorders.

Clock genes may influence bipolar disorder susceptibility and dysfunctional circadian rhythm

Several previous studies suggest that dysfunction of circadian rhythms may increase susceptibility to bipolar disorder (BP). We conducted an association study of five circadian genes (CRY2, PER1-3, and TIMELESS) in a family collection of 36 trios and 79 quads (Sample I), and 10 circadian genes (ARNTL, ARNTL2, BHLHB2, BHLHB3, CLOCK, CRY1, CSNK1D, CSNK1E, DBP, and NR1D1) in an extended family collection of 70 trios and 237 quads (Sample II), which includes the same 114 families but not necessarily the same individuals as Sample I. In Sample II, the Sibling-Transmission Disequilibrium Test (sib-tdt) analysis showed nominally significant association of BP with three SNPs within or near the CLOCK gene (rs534654, P = 0.0097; rs6850524, P = 0.012; rs4340844, P = 0.015). In addition, SNPs in the ARNTL2, CLOCK, DBP, and TIMELESS genes and haplotypes in the ARNTL, CLOCK, CSNK1E, and TIMELESS genes showed suggestive evidence of association with several circadian phenotypes identified in BP patients. However, none of these associations reached gene-wide or experiment-wide significance after correction for multiple-testing. A multi-locus interaction between rs6442925 in the 5' upstream of BHLHB2, rs1534891 in CSNK1E, and rs534654 near the 3' end of the CLOCK gene, however, is significantly associated with BP (P = 0.00000172). It remains significant after correcting for multiple testing using the False Discovery Rate method. Our results indicate an interaction between three circadian genes in susceptibility to bipolar disorder.

Neurotransmission and bipolar disorder: a systematic family-based association study

Neurotransmission pathways/systems have been proposed to be involved in the pathophysiology and treatment of bipolar disorder for over 40 years. In order to test the hypothesis that common variants of genes in one or more of five neurotransmission systems confer risk for bipolar disorder, we analyzed 1,005 tag single nucleotide polymorphisms in 90 genes from dopaminergic, serotonergic, noradrenergic, GABAergic, and glutamatergic neurotransmitter systems in 101 trios and 203 quads from Caucasian bipolar families. Our sample has 80% power to detect ORs >or= 1.82 and >or=1.57 for minor allele frequencies of 0.1 and 0.5, respectively. Nominally significant allelic and haplotypic associations were found for genes from each neurotransmission system, with several reaching gene-wide significance (allelic: GRIA1, GRIN2D, and QDPR; haplotypic: GRIN2C, QDPR, and SLC6A3). However, none of these associations survived correction for multiple testing in an individual system, or in all systems considered together. Significant single nucleotide polymorphism associations were not found with sub-phenotypes (alcoholism, psychosis, substance abuse, and suicide attempts) or significant gene-gene interactions. These results suggest that, within the detectable odds ratios of this study, common variants of the selected genes in the five neurotransmission systems do not play major roles in influencing the risk for bipolar disorder or comorbid sub-phenotypes.

Genomic imprinting in the development and evolution of psychotic spectrum conditions

I review and evaluate genetic and genomic evidence salient to the hypothesis that the development and evolution of psychotic spectrum conditions have been mediated in part by alterations of imprinted genes expressed in the brain. Evidence from the genetics and genomics of schizophrenia, bipolar disorder, major depression, Prader-Willi syndrome, Klinefelter syndrome, and other neurogenetic conditions support the hypothesis that the etiologies of psychotic spectrum conditions commonly involve genetic and epigenetic imbalances in the effects of imprinted genes, with a bias towards increased relative effects from imprinted genes with maternal expression or other genes favouring maternal interests. By contrast, autistic spectrum conditions, including Kanner autism, Asperger syndrome, Rett syndrome, Turner syndrome, Angelman syndrome, and Beckwith-Wiedemann syndrome, commonly engender increased relative effects from paternally expressed imprinted genes, or reduced effects from genes favouring maternal interests. Imprinted-gene effects on the etiologies of autistic and psychotic spectrum conditions parallel the diametric effects of imprinted genes in placental and foetal development, in that psychotic spectrum conditions tend to be associated with undergrowth and relatively-slow brain development, whereas some autistic spectrum conditions involve brain and body overgrowth, especially in foetal development and early childhood. An important role for imprinted genes in the etiologies of psychotic and autistic spectrum conditions is consistent with neurodevelopmental models of these disorders, and with predictions from the conflict theory of genomic imprinting.

Emotion-induced retrograde amnesia is determined by a 5-HTT genetic polymorphism

A polymorphism in the human serotonin transporter (5-HTT) gene is implicated in susceptibility to anxiety and depression and in enhanced emotion-induced activation in the amygdala. A role for 5-HTT polymorphism in the emotional modulation of human episodic memory has yet to be demonstrated. Here, we demonstrate that whereas emotional memory for aversive events per se is not influenced by 5-HTT polymorphism, an emotion-induced retrograde amnesia is expressed solely in the presence of the short allele. The findings indicate a critical role for the serotonin system in emotion-mediated memory disruption.

Association analysis of monoamine oxidase A gene and bipolar affective disorder in Han Chinese

Background

Monoamine oxidase A (MAOA) is a mitochondrial enzyme involved in degrading several different biological amines, including serotonin. Although several pieces of evidence suggested that MAOA is important in the etiology of bipolar affective disorder (BPD), associations for markers of the MAOA gene with BPD were not conclusive and the association has not been investigated in Taiwanese population. This study was designed to illustrate the role of MAOA in the etiology of BPD in Han Chinese.

Methods

Two markers, a dinucleotide polymorphism in exon 2 and a functional uVNTR on the promoter of the MAOA gene, were used to study the genetic association in 108 unrelated patients with BPD and 103 healthy controls. Allelic distributions of two polymorphisms were analyzed and, caused the MAOA located at X chromosome, haplotype association was performed using haplotype unambiguously assigned in male participants.

Results

While no difference in allelic distributions of two MAOA polymorphisms was found, the risk haplotype 114S was associated with BPD in male patients (P = 0.03). The significance, however, was not found in female patients with 114S haplotype.

Conclusion

Results from this study suggest that MAOA may have a gender-specific and small effect on the etiology of BPD in Taiwan. Due to the limited sample size, results from this study need to be confirmed in replicates.

Genotype patterns that contribute to increased risk for or protection from developing heroin addiction

A genome-wide association study was conducted using microarray technology to identify genes that may be associated with the vulnerability to develop heroin addiction, using DNA from 104 individual former severe heroin addicts (meeting Federal criteria for methadone maintenance) and 101 individual control subjects, all Caucasian. Using separate analyses for autosomal and X chromosomal variants, we found that the strongest associations of allele frequency with heroin addiction were with the autosomal variants rs965972, located in the Unigene cluster Hs.147755 (experiment-wise q=0.053), and rs1986513 (q=0.187). The three variants exhibiting the strongest association with heroin addiction by genotype frequency were rs1714984, located in an intron of the gene for the transcription factor myocardin (P=0.000022), rs965972 (P=0.000080) and rs1867898 (P=0.000284). One genotype pattern (AG-TT-GG) was found to be significantly associated with developing heroin addiction (odds ratio (OR)=6.25) and explained 27% of the population attributable risk for heroin addiction in this cohort. Another genotype pattern (GG-CT-GG) of these variants was found to be significantly associated with protection from developing heroin addiction (OR=0.13), and lacking this genotype pattern explained 83% of the population attributable risk for developing heroin addiction. Evidence was found for involvement of five genes in heroin addiction, the genes coding for the mu opioid receptor, the metabotropic receptors mGluR6 and mGluR8, nuclear receptor NR4A2 and cryptochrome 1 (photolyase-like). This approach has identified several new genes potentially associated with heroin addiction and has confirmed the role of OPRM1 in this disease.

Translational research in late-life mood disorders: implications for future intervention and prevention research

Clinical and epidemiological studies have consistently observed the heterogeneous symptomatology and course of geriatric depression. Given the importance of genetic and environmental risk factors, aging processes, neurodegenerative and cerebrovascular disease processes, and medical comorbidity, the integration of basic and clinical neuroscience research approaches is critical for the understanding of the variability in illness course, as well as the development of prevention and intervention strategies that are more effective. These considerations were the impetus for a workshop, sponsored by the Geriatrics Research Branch in the Division of Adult Translational Research and Treatment Development of the National Institute of Mental Health that was held on September 7-8, 2005. The primary goal of the workshop was to bring together investigators in geriatric psychiatry research with researchers in specific topic areas outside of geriatric mental health to identify priority areas to advance translational research in geriatric depression. As described in this report, the workshop focused on a discussion of the development and application of integrative approaches combining genetics and neuroimaging methods to understand such complex issues as treatment response variability, the role of medical comorbidity in depression, and the potential overlap between depression and dementia. Future directions for integrative research were identified. Understanding the nature of geriatric depression requires the application of translational research and interdisciplinary research approaches. Geriatric depression could serve as a model for translational research integrating basic and clinical neuroscience approaches that would have implications for the study of other neuropsychiatric disorders.

Enrichment of HapMap recombination hotspot predictions around human nervous system genes: evidence for positive selection ?

Channels and developmental genes belong to the molecular key players in the human central nervous system (CNS). Mutations in these genes often cause monogenic neurological disease and interspecies comparisons had shown reduced divergence. On the other hand, accelerated evolution of genes with roles in neurotransmission and development had indicated widespread positive selection in hominids. In the present study, we hypothesized that recombination hotspots could be enriched at genes with particularly important role in the CNS, because at those loci beneficial mutations may occur on a highly constrained background and consequently increased recombination could promote their fixation. To test this hypothesis, we retrieved CNS genes based on keyword search, expression data and expert knowledge. Consistent with our hypothesis, we find an enrichment of hotspot predictions around genes that are retrieved by all three strategies. Moreover, when comparing human genes based on their Gene Ontology annotations, we find hotspot predictions preferentially located around channels and neurodevelopmental genes. Taken together with the distinct sequence evolution that was reported by comparative genomic studies, this finding indicates continued positive selection at many CNS gene loci. In support of this interpretation, we also find an enrichment of recombination hotspot predictions around conserved noncoding regions that were reported to display a signature of accelerated evolution in the human lineage. Widespread positive selection acting on CNS gene loci could relate to the high prevalence of human nervous system disorders with genetically complex inheritance, potentially under an ancestral susceptibility allele model.

Bioinformatic analysis of human CNS-expressed ion channels as candidates for episodic nervous system disorders

As monogenic forms of episodic nervous system disorders are often caused by ion channel mutations, we looked for features of human central nervous system (CNS) expressed ion channels that further our understanding of those phenotypes. To this end, we compared human ion channels with other CNS-expressed genes, which we categorized according to the existence of transmembrane domains. When looking at the phylogenetic distribution of these genes, we observed an increased percentage of ion channels that exist in vertebrate genomes while missing in invertebrate genomes. Because we hypothesized that this pattern may relate to a more specific expression, we searched for characteristics of ion channels that indicate a tighter expression regulation. We found that ion channels have longer intron and protein sequences, features typical of genes with more specific expression. In addition, ion channels have increased human-rodent conservation around their transcription start site, as indicated by a higher fraction of conserved noncoding regions. This points to a high relevance of mutations that regulate ion channel expression. When we finally asked whether vertebrate-specific diversification is also displayed by non-ion channel genes with important roles in the CNS, we found a similar phylogenetic distribution. This concordant phylogenetic pattern suggests that vertebrate-specific adaptations may account for a large part of the shared genetic basis of episodic CNS disorders, including monogenic and genetically complex disease manifestations. Consequently, this phylogenetic pattern may contribute to the prioritization of candidate genes in human genetic studies of episodic CNS disorders.

Dopamine D2-like receptors and the antidepressant response

Converging lines of evidence suggest a role for the mesolimbic dopamine system in the response to somatic antidepressant therapies. Here, we review evidence suggesting that antidepressant treatments of different types share the effect of increasing the sensitivity of dopamine D2-like receptors in the nucleus accumbens, clinical studies suggesting that activation of these receptors has antidepressant efficacy, as well as relevant imaging and genetic data on the role of this system in the antidepressant response. We then attempt to reconcile this data with evidence of a common target of antidepressant drugs in the cyclic adenosine monophosphate (cAMP) response element binding protein-brain-derived neurotrophic factor (CREB-BDNF) pathway in a model that suggests potential directions for future inquiry.

Gene-environment interactions in psychiatry: joining forces with neuroscience

Gene-environment interaction research in psychiatry is new, and is a natural ally of neuroscience. Mental disorders have known environmental causes, but there is heterogeneity in the response to each causal factor, which gene-environment findings attribute to genetic differences at the DNA sequence level. Such findings come from epidemiology, an ideal branch of science for showing that a gene-environment interactions exist in nature and affect a significant fraction of disease cases. The complementary discipline of epidemiology, experimental neuroscience, fuels gene-environment hypotheses and investigates underlying neural mechanisms. This article discusses opportunities and challenges in the collaboration between psychiatry, epidemiology and neuroscience in studying gene-environment interactions.

Identification of novel autism candidate regions through analysis of reported cytogenetic abnormalities associated with autism

The identification of the candidate genes for autism through linkage and association studies has proven to be a difficult enterprise. An alternative approach is the analysis of cytogenetic abnormalities associated with autism. We present a review of all studies to date that relate patients with cytogenetic abnormalities to the autism phenotype. A literature survey of the Medline and Pubmed databases was performed, using multiple keyword searches. Additional searches through cited references and abstracts from the major genetic conferences from 2000 onwards completed the search. The quality of the phenotype (i.e. of the autism spectrum diagnosis) was rated for each included case. Available specific probe and marker information was used to define optimally the boundaries of the cytogenetic abnormalities. In case of recurrent deletions or duplications on chromosome 15 and 22, the positions of the low copy repeats that are thought to mediate these rearrangements were used to define the most likely boundaries of the implicated 'Cytogenetic Regions Of Interest' (CROIs). If no molecular data were available, the sequence position of the relevant chromosome bands was used to obtain the approximate molecular boundaries of the CROI. The findings of the current review indicate: (1) several regions of overlap between CROIs and known loci of significant linkage and/or association findings, and (2) additional regions of overlap among multiple CROIs at the same locus. Whereas the first finding confirms previous linkage/association findings, the latter may represent novel, not previously identified regions containing genes that contribute to autism. This analysis not only has confirmed the presence of several known autism risk regions but has also revealed additional previously unidentified loci, including 2q37, 5p15, 11q25, 16q22.3, 17p11.2, 18q21.1, 18q23, 22q11.2, 22q13.3 and Xp22.2-p22.3.

Genetics of suicide

The concept that genetic factors contribute to the complex trait of suicidal behaviour has stimulated much work aimed at identifying susceptibility genes. So far molecular genetic studies focused on the serotonergic pathway as the intent to die and the lethality of suicide acts were related to the serotonergic system. Two genes have so far emerged as being involved in the vulnerability for suicidality: first, the intronic polymorphisms (A218C or A779C) of the tryptophan hydroxylase 1 (TPH1) gene, which was suggested as a quantitative risk factor for suicidal behaviour; second, the insertion/deletion polymorphism of the serotonin transporter gene (5-HTTLPR), which does not seem to be involved in general suicidal behaviour, but in violent and repeated suicide attempts. The data have further shown that the MAOA gene, which is consistently associated with impulsive-aggressive personality traits, is not related to suicide but might induce violent methods in subjects with other suicide risk factors. Predominantly negative were the findings with any type of the serotonin receptors and inconsistent with catecholamine-synthesizing and -metabolizing enzymes or with the dopaminergic receptors. This paper reviews the status of current knowledge in this area, points to the weakness of the investigations and presents new approaches beyond the serotonergic system.

Differential Gender-Related Vulnerability to Depression Induction and Converging Antidepressant Responses in Rats

Vulnerability of females to depression among humans has not previously been reflected in animal models. Here, we show, by using a novel animal model of depression, that young female Wistar rats are clearly more vulnerable to depression induction than the males. This differential female vulnerability follows estrous cycle stages, is associated with cognitive impairment, and can be markedly transformed with sex hormones. Male hormone reduces vulnerability in females, whereas female hormone increases vulnerability in males. The induced depressive behavior in both sexes, however, is sensitive to imipramine and to the antagonism of the glucocorticoid receptors within a hormonal pathway previously implicated in human depression. Anisomycin, a protein synthesis inhibitor, eliminates the antidepressive effects of both antidepressants and male hormone but does not affect depression induction and estradiol-induced higher vulnerability. Moreover, direct cerebroventricular administration of brain-derived neurotrophic factor (BDNF), whose mRNA levels in the hippocampus and frontal cortex reach its lowest levels when estrogen levels are highest, is sufficient to rescue the antidepressive effects in the presence of the protein synthesis inhibitor. A selective enhancement of BDNF expression and/or BDNF signal cascades in the neural circuits controlling mood may represent an effective strategy for the development of novel antidepressants for both sexes, whereas blocking the gender-related higher vulnerability to potentially depressogenic events may lead to the development of specific antidepressants for the females.