Genome-wide linkage survey for genetic loci that affect the risk of suicide attempts in families with recurrent, early-onset, major depression

Abelson Helper Integration Site 1 haplotypes and peripheral blood expression associates with lithium response and immunomodulation in bipolar patients

RATIONALE

In bipolar disorder (BD), immunological factors play a role in the pathogenesis and treatment of the illness. Studies showed the potential link between Abelson Helper Integration Site 1 (AHI1) protein, behavioural changes and innate immunity regulation. An immunomodulatory effect was suggested for lithium, a mood stabilizer used in BD treatment.

OBJECTIVES

We hypothesized that AHI1 may be an important mediator of lithium treatment response. Our study aimed to investigate whether the AHI1 haplotypes and expression associates with lithium treatment response in BD patients. We also examined whether AHI1 expression and lithium treatment correlate with innate inflammatory response genes.

RESULTS

We genotyped seven AHI1 single nucleotide polymorphisms in 97 euthymic BD patients and found that TG haplotype (rs7739635, rs9494332) was significantly associated with lithium response. We also showed significantly increased AHI1 expression in the blood of lithium responders compared to non-responders and BD patients compared to healthy controls (HC). We analyzed the expression of genes involved in the innate immune response and inflammatory response regulation (TLR4, CASP4, CASP5, NLRP3, IL1A, IL1B, IL6, IL10, IL18) in 21 lithium-treated BD patients, 20 BD patients treated with other mood stabilizer and 19 HC. We found significantly altered expression between BD patients and HC, but not between BD patients treated with different mood stabilizers.

CONCLUSIONS

Our study suggests the involvement of AHI1 in the lithium mode of action. Moreover, mood-stabilizing treatment associated with the innate immunity-related gene expression in BD patients and only the lithium-treated BD patients showed significantly elevated expression of anti-inflammatory IL10, suggesting lithium's immunomodulatory potential.

Genetics and epigenetics of self-injurious thoughts and behaviors: Systematic review of the suicide literature and methodological considerations

Suicide is a multifaceted and poorly understood clinical outcome, and there is an urgent need to advance research on its phenomenology and etiology. Epidemiological studies have demonstrated that suicidal behavior is heritable, suggesting that genetic and epigenetic information may serve as biomarkers for suicide risk. Here we systematically review the literature on genetic and epigenetic alterations observed in phenotypes across the full range of self-injurious thoughts and behaviors (SITB). We included 577 studies focused on genome-wide and epigenome-wide associations, candidate genes (SNP and methylation), noncoding RNAs, and histones. Convergence of specific genes is limited across units of analysis, although pathway-based analyses do indicate nervous system development and function and immunity/inflammation as potential underlying mechanisms of SITB. We provide suggestions for future work on the genetic and epigenetic correlates of SITB with a specific focus on measurement issues.

Relationship Between Affective Temperaments and Suicide Risk in Patients With First-Onset Major Depressive Disorder

Background

People may endorse suicidal behavior during a major depressive episode. Affective temperaments may play a role in this risk. We explored the relationship between affective temperaments and suicide and identified some traits that can predict suicide risk in depression.

Materials and Methods

We analyzed the results of the Temperament Evaluation of the Memphis, Pisa, Paris, and San Diego Auto-questionnaire (TEMPS-A) in 284 participants recruited from a psychiatric clinic and the community in Beijing and compared the subscale scores (temperaments of cyclothymic, dysthymic, anxious, irritable, and hyperthymic) among major depressive disorders (MDDs) vs. the general population as well as depressive patients with vs. without suicide risk, using Student's test, chi-square test, rank-sum test, and multivariable regression modeling.

Results

The incidence of suicidal risk in depressive subjects was 47.62% (80/168). Being unmarried (p < 0.001), unemployed (p = 0.007), and temperaments of dysthymic, cyclothymic, anxious, and irritable scores (all p < 0.001) were significantly more prevalent in patients with depression than in the general population. Young age (p < 0.001), female sex (p = 0.037), unmarried (p = 0.001), more severe depression (p < 0.001), and dysthymic, anxious, and cyclothymic temperament (all p < 0.05) were significantly more prevalent in patients with depressive disorder than those without suicide risk. The logistic regression analysis showed that younger age (odds ratio [OR] = 0.937, 95% CI 0.905∼0.970), female sex (OR = 2.606, 95% CI 1.142∼5.948), more severe depression (OR = 1.145, 95% CI 1.063∼1.234), cyclothymic temperament (OR = 1.275, 95% CI 1.102∼1.475), and dysthymic temperament (OR = 1.265, 95% CI 1.037∼1.542) were all independently associated with high suicidal risk in patients with first-onset major depression (p < 0.05).

Conclusion

Temperament traits differ between the general population and people suffering from MDD. Subjects with MDD who have much more severe depressive symptoms and a cyclothymic or dysthymic temperament were at a high risk of suicide.

Suicide Related Phenotypes in a Bipolar Sample: Genetic Underpinnings

Suicide in Bipolar Disorder (BD) is a relevant clinical concern. Genetics may shape the individual risk for suicide behavior in BD, together with known clinical factors. The lack of consistent replication in BD may be associated with its multigenetic component. In the present contribution we analyzed a sample of BD individuals (from STEP-BD database) to identify the genetic variants potentially associated with three different suicide-related phenotypes: (1) a feeling that the life was not worth living; (2) fantasies about committing a violent suicide; (3) previous attempted suicide. The sample under analysis included 1115 BD individuals. None of the SNPs reached genome-wide significance. However, a trend of association was evidenced for rs2767403, an intron variant of AOPEP gene, in association with phenotype #1 (p = 5.977 × 10⁻⁶). The molecular pathway analysis showed a significant enrichment in all the investigated phenotypes on pathways related to post synaptic signaling, neurotransmission and neurodevelopment. Further, NOTCH signaling or the γ-aminobutyric acid (GABA)-ergic signaling were found to be associated with specific suicide-related phenotypes. The present investigation contributes to the hypothesis that the genetic architecture of suicide behaviors in BD is related to alteration of entire pathways rather than single genes. In particular, our molecular pathway analysis points on some specific molecular events that could be the focus of further research in this field.

Genetic origins of suicidality? A synopsis of genes in suicidal behaviours, with regard to evidence diversity, disorder specificity and neurodevelopmental brain transcriptomics

With regard to suicidal behavior (SB) genetics, many novel genes have been implicated over the years, in particular by a variety of hypothesis-free genomic methods (e.g. GWAS and exome sequencing). In addition, many novel SB gene findings appear enigmatic in their biological relevance and have weak statistical support, e.g. lack direct replications. Adding to this is the comorbidity between psychiatric disorders and SB. Here we provide a synopsis of SB genes, by prioritization of 106 (out of ~2500) genes based on their highest level of evidence diversity across mainly five genetic evidence types (candidate/GWAS SNP, CNV, linkage and whole exome sequencing), supplemented by three functional categories. This is a representative set of both old and new SB gene candidates, implicated by all kinds of evidence. Furthermore, we define a subset of 40 SB "specific" genes, which are not found among ~3900 genes implicated in other neuropsychiatric disorders, e.g. Autism spectrum disorders (ASD) or Schizophrenia. Biological research of suicidality contains a major developmental focus, e.g. with regard to the gene-environment interactions and epigenetic effects during childhood. Less is known about early (fetal) development and SB genes. Inspired by huge efforts to understand the role early (fetal) neurodevelopment in e.g. ASD by using brain transcriptomic data, we here also characterize the 106 SB genes. We find interesting spatiotemporal expression differences and similarities between SB specific and non-specific genes during brain neurodevelopment. These aspects are of interest to investigate further, to better understand and counteract the genetic origins suicidality.

Targeted sequencing of the LRRTM gene family in suicide attempters with bipolar disorder

Glutamatergic signaling is the primary excitatory neurotransmission pathway in the brain, and its relationship to neuropsychiatric disorders is of considerable interest. Our previous attempted suicide genome-wide association study, and numerous studies investigating gene expression, genetic variation, and DNA methylation have implicated aberrant glutamatergic signaling in suicide risk. The glutamatergic pathway gene LRRTM4 was an associated gene identified in our attempted suicide genome-wide association study, with association support seen primarily in females. Recent evidence has also shown that glutamatergic signaling is partly regulated by sex-related hormones. The LRRTM gene family encodes neuronal leucine-rich transmembrane proteins that localize to and promote glutamatergic synapse development. In this study, we sequenced the coding and regulatory regions of all four LRRTM gene members plus a large intronic region of LRRTM4 in 476 bipolar disorder suicide attempters and 473 bipolar disorder nonattempters. We identified two male-specific variants, one female- and five male-specific haplotypes significantly associated with attempted suicide in LRRTM4. Furthermore, variants within significant haplotypes may be brain expression quantitative trait loci for LRRTM4 and some of these variants overlap with predicted hormone response elements. Overall, these results provide supporting evidence for a sex-specific association of genetic variation in LRRTM4 with attempted suicide.

Genetic influences on conduct disorder

Conduct disorder (CD) is a moderately heritable psychiatric disorder of childhood and adolescence characterized by aggression toward people and animals, destruction of property, deceitfulness or theft, and serious violation of rules. Genome-wide scans using linkage and association methods have identified a number of suggestive genomic regions that are pending replication. A small number of candidate genes (e.g., GABRA2, MAOA, SLC6A4, AVPR1A) are associated with CD related phenotypes across independent studies; however, failures to replicate also exist. Studies of gene-environment interplay show that CD genetic predispositions also contribute to selection into higher-risk environments, and that environmental factors can alter the importance of CD genetic factors and differentially methylate CD candidate genes. The field's understanding of CD etiology will benefit from larger, adequately powered studies in gene identification efforts; the incorporation of polygenic approaches in gene-environment interplay studies; attention to the mechanisms of risk from genes to brain to behavior; and the use of genetically informative data to test quasi-causal hypotheses about purported risk factors.

Replication of rs300774, a genetic biomarker near ACP1, associated with suicide attempts in patients with schizophrenia: Relation to brain cholesterol biosynthesis

The aim of this study was to determine if three biomarkers for suicide attempts previously identified and replicated in a genome-wide association (GWAS) study of bipolar disorder (BD) suicide attempters also predicted suicide attempts in patients prospectively diagnosed with schizophrenia (SCZ) or schizoaffective disorder (SAD). 162 genetically-verified Caucasian patients with SCZ or SAD were phenotyped for presence (45.7%) or absence of a lifetime suicide attempt. Three single nucleotide polymorphisms (SNPs) were genotyped or partially imputed from a GWAS dataset. After controlling for genetic architecture and gender, we replicated rs300774 (p = 0.012), near ACP1 (acid phosphatase 1), the top predictor of suicide attempts in the BD study. The result of Willour et al. (2012) was replicated in males (p = 0.046) but not in females (p = 0.205). The other two SNPs, rs7296262, and rs10437629, were not associated with suicide attempts in this study. rs300774 could be a cis-eQTL for ACP1, with minor allele carriers having lower expression levels (p = 0.002). This SNP also functioned as a trans-eQTL for genes related to cholesterol biosynthesis and the wnt-β-catenin pathway (p ≤ 0.0001). Further, co-expression analysis of candidate genes in brain suggested ACP1 is important to the regulation of a number of brain mechanisms linked to suicide, including cholesterol synthesis, β-catenin-mediated signaling pathway, serotonin, GABA, and the stress response via ARHGAP35 (p190rhogap), a repressor of glucocorticoid receptor (NR3C1) transcription. This study provides an additional validation of rs300774 as a potential transdiagnostic biomarker for suicide attempts and evidence that ACP1 may have an important role in regulation of the multiple systems associated with suicide.

Assessment of Whole-Exome Sequence Data in Attempted Suicide within a Bipolar Disorder Cohort

Suicidal behavior is a complex and devastating phenotype with a heritable component that has not been fully explained by existing common genetic variant analyses. This study represents the first large-scale DNA sequencing project designed to assess the role of rare functional genetic variation in suicidal behavior risk. To accomplish this, whole-exome sequencing data for ∼19,000 genes were generated for 387 bipolar disorder subjects with a history of suicide attempt and 631 bipolar disorder subjects with no prior suicide attempts. Rare functional variants were assessed in all exome genes as well as pathways hypothesized to contribute to suicidal behavior risk. No result survived conservative Bonferroni correction, though many suggestive findings have arisen that merit additional attention. In addition, nominal support for past associations in genes, such as BDNF, and pathways, such as the hypothalamic-pituitary-adrenal axis, was also observed. Finally, a novel pathway was identified that is driven by aldehyde dehydrogenase genes. Ultimately, this investigation explores variation left largely untouched by existing efforts in suicidal behavior, providing a wealth of novel information to add to future investigations, such as meta-analyses.

A targeted sequencing study of glutamatergic candidate genes in suicide attempters with bipolar disorder

Suicidal behavior has been shown to have a heritable component that is partly driven by psychiatric disorders [Brent and Mann, 2005]. However, there is also an independent factor contributing to the heritability of suicidal behavior. We previously conducted a genome-wide association study (GWAS) of bipolar suicide attempters and bipolar non-attempters to assess this independent factor [Willour et al., 2012]. This GWAS implicated glutamatergic neurotransmission in attempted suicide. In the current study, we have conducted a targeted next-generation sequencing study of the glutamatergic N-methyl-D-aspartate (NMDA) receptor, neurexin, and neuroligin gene families in 476 bipolar suicide attempters and 473 bipolar non-attempters. The goal of this study was to gather sequence information from coding and regulatory regions of these glutamatergic genes to identify variants associated with attempted suicide. We identified 186 coding variants and 4,298 regulatory variants predicted to be functional in these genes. No individual variants were overrepresented in cases or controls to a degree that was statistically significant after correction for multiple testing. Additionally, none of the gene-level results were statistically significant following correction. While this study provides no direct support for a role of the examined glutamatergic candidate genes, further sequencing in expanded gene sets and datasets will be required to ultimately determine whether genetic variation in glutamatergic signaling influences suicidal behavior. © 2016 Wiley Periodicals, Inc.

PSD-Zip70 Deficiency Causes Prefrontal Hypofunction Associated with Glutamatergic Synapse Maturation Defects by Dysregulation of Rap2 Activity

Dysregulation of synapse formation and plasticity is closely related to the pathophysiology of psychiatric and neurodevelopmental disorders. The prefrontal cortex (PFC) is particularly important for executive functions such as working memory, cognition, and emotional control, which are impaired in the disorders. PSD-Zip70 (Lzts1/FEZ1) is a postsynaptic density (PSD) protein predominantly expressed in the frontal cortex, olfactory bulb, striatum, and hippocampus. Here we found that PSD-Zip70 knock-out (PSD-Zip70KO) mice exhibit working memory and cognitive defects, and enhanced anxiety-like behaviors. These abnormal behaviors are caused by impaired glutamatergic synapse transmission accompanied by tiny-headed immature dendritic spines in the PFC, due to aberrant Rap2 activation, which has roles in synapse formation and plasticity. PSD-Zip70 modulates the Rap2 activity by interacting with SPAR (spine-associated RapGAP) and PDZ-GEF1 (RapGEF) in the postsynapse. Furthermore, suppression of the aberrant Rap2 activation in the PFC rescued the behavioral defects in PSD-Zip70KO mice. Our data demonstrate a critical role for PSD-Zip70 in Rap2-dependent spine synapse development in the PFC and underscore the importance of this regulation in PFC-dependent behaviors.

SIGNIFICANCE STATEMENT

PSD-Zip70 deficiency causes behavioral defects in working memory and cognition, and enhanced anxiety due to prefrontal hypofunction. This study revealed that PSD-Zip70 plays essential roles in glutamatergic synapse maturation via modulation of the Rap2 activity in the PFC. PSD-Zip70 interacts with both SPAR (spine-associated RapGAP) and PDZ-GEF1 (RapGEF) and modulates the Rap2 activity in postsynaptic sites. Our results provide a novel Rap2-specific regulatory mechanism in synaptic maturation involving PSD-Zip70.

A genome-wide association study of suicide severity scores in bipolar disorder

BACKGROUND

Suicide claims one million lives worldwide annually, making it a serious public health concern. The risk for suicidal behaviour can be partly explained by genetic factors, as suggested by twin and family studies (reviewed in (Zai et al. 2012)). Recently, genome-wide association studies (GWASs) of suicide attempt on large samples of bipolar disorder (BD) patients from multiple sites have identified a number of novel candidate genes. GWASs of suicide behaviour severity, from suicidal ideation to serious suicide attempt, have not been reported for BD.

METHODS

We conducted a GWAS of suicide behaviour severity in three independent BD samples:212 small nuclear families with BD probands from Toronto, Canada, 428 BD cases from Toronto, and 483 BD cases from the UK. We carried out imputation with 1000 Genome Project data as reference using IMPUTE2. Quality control and data analysis was conducted using PLINK and R. We conducted the quantitative analyses of suicide behaviour severity in the three samples separately, and derived an overall significance by a meta-analysis using the METAL software.

RESULTS

We did not find genome-wide significant association of any tested markers in any of the BD samples, but we found a number of suggestive associations, including regions on chromosomes 8 and 10 (p < 1e-5).

CONCLUSIONS

Our GWAS findings suggest that likely many gene variants of small effects contribute collectively to the risk for suicidal behaviour severity in BD. Larger independent replications are required to strengthen the findings from the GWAS presented here.

Abelson helper integration site-1 gene variants on major depressive disorder and bipolar disorder

OBJECTIVE

The present study aimed to explore whether 4 single nucleotide polymorphisms (SNPs) within the AHI1 gene could be associated with major depressive disorder (MD) and bipolar disorder (BD), and whether they could predict clinical outcomes in mood disorders.

METHODS

One hundred and eighty-four (184) patients with MD, 170 patients with BD and 170 healthy controls were genotyped for 4 AHI1 SNPs (rs11154801, rs7750586, rs9647635 and rs9321501). Baseline and final clinical measures for MD patients were assessed through the Hamilton Rating Scale for Depression (HAM-D). Allelic and genotypic frequencies in MD and BD subjects were compared with those of each disorder and healthy group using the χ(2) statistics. Repeated measures ANOVA was used to test possible influences of SNPs on treatment efficacy.

RESULTS

The rs9647635 A/A was more represented in subjects with BD as compared with MD and healthy subjects together. The rs9647635 A/A was also more presented in patients with MD than in healthy subjects. With regard to the allelic analysis, rs9647635 A allele was more represented in subjects with BD compared with healthy subjects, while it was not observed between patients with MD and healthy subjects.

CONCLUSION

Our findings provide potential evidence of an association between some variants of AHI1 and mood disorders susceptibility but not with clinical outcomes. However, we will need to do more adequately-powered and advanced association studies to draw any conclusion due to clear limitations.

Common and rare variant analysis in early-onset bipolar disorder vulnerability

Bipolar disorder is one of the most common and devastating psychiatric disorders whose mechanisms remain largely unknown. Despite a strong genetic contribution demonstrated by twin and adoption studies, a polygenic background influences this multifactorial and heterogeneous psychiatric disorder. To identify susceptibility genes on a severe and more familial sub-form of the disease, we conducted a genome-wide association study focused on 211 patients of French origin with an early age at onset and 1,719 controls, and then replicated our data on a German sample of 159 patients with early-onset bipolar disorder and 998 controls. Replication study and subsequent meta-analysis revealed two genes encoding proteins involved in phosphoinositide signalling pathway (PLEKHA5 and PLCXD3). We performed additional replication studies in two datasets from the WTCCC (764 patients and 2,938 controls) and the GAIN-TGen cohorts (1,524 patients and 1,436 controls) and found nominal P-values both in the PLCXD3 and PLEKHA5 loci with the WTCCC sample. In addition, we identified in the French cohort one affected individual with a deletion at the PLCXD3 locus and another one carrying a missense variation in PLCXD3 (p.R93H), both supporting a role of the phosphatidylinositol pathway in early-onset bipolar disorder vulnerability. Although the current nominally significant findings should be interpreted with caution and need replication in independent cohorts, this study supports the strategy to combine genetic approaches to determine the molecular mechanisms underlying bipolar disorder.

Ethnicity moderates the association between 5-HTTLPR and national suicide rates

The association between ethnicity, national suicide rates, and the functional serotonin transporter gene polymorphism (5-HTTLPR), under consideration of the role of economic indicators, national alcohol intake, and national happiness scores was analyzed with an ecologic analysis. Data on allelic frequencies of the short (s) allele from 38 countries from over 100,000 healthy screened or general population individuals were analyzed with multiple regression models. Allele frequency varied widely both within and across ethnicities and an ethnicity-based interaction between national suicide rates and 5-HTTLPR allele frequency was revealed with the s allele acting as protective factor in Caucasian and as a risk factor in non-Caucasian populations. This interaction effect underlines the importance of ethnicity as a moderating factor in the genetics of suicide.

A pilot genome wide association and gene expression array study of suicide with and without major depression

OBJECTIVES

Suicide is partly heritable but the responsible genes have not been identified. We conducted a gene-centric, low coverage single nucleotide polymorphism (SNP) pilot genome-wide association study (GWAS) seeking new candidate regions in suicides with and without depression, combined with gene expression assay of brain tissue.

METHODS

Ninety-nine Caucasian subjects, including 68 who completed suicide and 31 who died suddenly from other causes, were genotyped postmortem using GeneChip® Mapping 50K Xba. Clinical data were obtained from relatives. SNPs with Hardy-Weinberg equilibrium P values below 0.001 were excluded from analysis. Illumina chip expression arrays assayed the transcriptome in prefrontal cortex in a drug-free subgroup.

RESULTS

GWAS analysis (cutoff P < 0.001) yielded 58 SNPs, 22 of them in or near 19 known genes, with risk allele-associated odds ratios between 2.7 and 6.9. Diagnosis of mood disorder did not explain the associations. Some of the SNPs matched into four functional groups in gene ontology. Gene expression in the prefrontal and the anterior cingulate cortex for these 19 genes was measured on a separate, though overlapping, sample of suicides and seven of 19 genes showed altered expression in suicides as compared with controls, especially in immune system related genes.

CONCLUSIONS

Matching GWAS findings with expression data assesses functional effect of new candidate genes in suicide, and is an alternative form of confirmation or replication study. Results highlight a role for neuroimmunological effects in suicidal behaviour.

Association between DPYSL2 gene polymorphisms and alcohol dependence in Caucasian samples

The DPYSL2 gene at 8p22-p21 is expressed widely in neuronal tissues and has been implicated in multiple psychiatric disorders such as Alzheimer's disease and schizophrenia. We therefore hypothesized that DPYSL2 gene polymorphisms may play a role in alcohol dependence (AD). We investigated the genetic associations of 57 single-nucleotide polymorphisms (SNPs) within the DPYSL2 gene with AD using two Caucasian samples-the Collaborative Study on the Genetics of Alcoholism (COGA) sample (660 AD cases and 400 controls), and the Study of Addiction: Genetics and Environment (SAGE) sample (623 cases and 1,016 controls). The SNP rs11995227 was most significantly associated with AD (p = 0.000122) in the COGA sample while one flanking SNP rs7832576 revealed the second most significant association with AD (p = 0.00163) in the COGA sample and association with AD (p = 0.0195) in the SAGE sample. Meta-analysis of two samples showed both rs119952227 and rs7832576 were associated with AD (p = 0.000363 and 0.000184, respectively). Furthermore, the C-A haplotype from rs11995227 and rs7832576 revealed significant association with AD (p = 0.0000899) in the COGA sample while the T-G haplotype revealed association with AD both in the COGA and SAGE samples (p = 0.00098 and 0.021, respectively). These findings suggest that genetic variants in DPYSL2 may play a role in susceptibility to AD.

The serotonergic system in mood disorders and suicidal behaviour

A stress-diathesis explanatory model of suicidal behaviour has proved to be of heuristic value, and both clinical and neurobiological components can be integrated into such a model. A trait deficiency in serotonin input to the anterior cingulate and ventromedial prefrontal cortex is found in association with suicide, and more recently non-fatal suicidal behaviour, and is linked to decision-making and suicide intent by imaging and related studies in vivo. The same neural circuitry and serotonin deficiency may contribute to impulsive aggressive traits that are part of the diathesis for suicidal behaviour and are associated with early onset mood disorders and greater risk for suicidal behaviour. Other brain areas manifest deficient serotonin input, that is, a trait related to recurrent major depressive disorder and bipolar disorder. Thus the serotonin system is involved in both the diathesis for suicidal behaviour in terms of decision-making, and to a major stressor, namely episodes of major depression.

Association between a genetic variant in the serotonin transporter gene (SLC6A4) and suicidal behavior in patients with schizophrenia

Background

The serotonin (5-hydroxytryptamin; 5-HT) system has a central role in the circuitry of cognition and emotions. Multiple lines of evidence suggest that genetic variation in the serotonin transporter gene (SLC6A4; 5-HTT) is associated with schizophrenia and suicidal behavior. In this study, we wanted to elucidate whether SLC6A4 variations is involved in attempted suicide among patients with schizophrenia in a Scandinavian case–control sample.

Methods

Patients diagnosed with schizophrenia from three Scandinavian samples were assessed for presence or absence of suicide attempts, based on record reviews and interview data. Seven SLC6A4 single nucleotide polymorphisms (SNPs) were genotyped in 837 schizophrenia patients and 1,473 control individuals. Association analyses and statistical evaluations were performed with the program UNPHASED (version 3.0.9).

Results

We observed an allele association between the SNP rs16965628, located in intron one of SLC6A4, and attempted suicide (adjusted p-value 0.01), among patients with schizophrenia. No association was found to a diagnosis of schizophrenia, when patients were compared to healthy control individuals.

Conclusion

The gene SLC6A4 appears to be involved in suicidal ideation among patients with schizophrenia. Independent replication is needed before more firm conclusions can be drawn.

A genome-wide association study of attempted suicide

The heritable component to attempted and completed suicide is partly related to psychiatric disorders and also partly independent of them. Although attempted suicide linkage regions have been identified on 2p11-12 and 6q25-26, there are likely many more such loci, the discovery of which will require a much higher resolution approach, such as the genome-wide association study (GWAS). With this in mind, we conducted an attempted suicide GWAS that compared the single-nucleotide polymorphism (SNP) genotypes of 1201 bipolar (BP) subjects with a history of suicide attempts to the genotypes of 1497 BP subjects without a history of suicide attempts. In all, 2507 SNPs with evidence for association at P<0.001 were identified. These associated SNPs were subsequently tested for association in a large and independent BP sample set. None of these SNPs were significantly associated in the replication sample after correcting for multiple testing, but the combined analysis of the two sample sets produced an association signal on 2p25 (rs300774) at the threshold of genome-wide significance (P=5.07 × 10(-8)). The associated SNPs on 2p25 fall in a large linkage disequilibrium block containing the ACP1 (acid phosphatase 1) gene, a gene whose expression is significantly elevated in BP subjects who have completed suicide. Furthermore, the ACP1 protein is a tyrosine phosphatase that influences Wnt signaling, a pathway regulated by lithium, making ACP1 a functional candidate for involvement in the phenotype. Larger GWAS sample sets will be required to confirm the signal on 2p25 and to identify additional genetic risk factors increasing susceptibility for attempted suicide.

Glucocorticoid receptor gene haplotype predicts increased risk of hospital admission for depressive disorders in the Helsinki birth cohort study

BACKGROUND

Although glucocorticoid receptors (GR) are involved in mediating hypothalamic-pituitary-adrenal-axis functioning, which is altered in acute depression, data on associations between GR gene (NR3C1) polymorphisms and depression are scarce. We examined if single nucleotide polymorphisms (SNPs) and their haplotypes spanning the entire NR3C1 are associated with depressive disorders and with self-reported depressive symptoms in adulthood.

METHODS

We successfully genotyped 10 SNPs spanning the NR3C1, and performed SNP and haplotype analyses in 1,075 women and 928 men participating in the Helsinki birth cohort study. Diagnoses of depressive disorders were extracted from the Finnish Hospital Discharge Register covering a 35-year period from early to late adulthood. In addition, depressive symptoms were self-reported with standardized questionnaire in late adulthood.

RESULTS

In comparison to the most common haplotype, one haplotype in the regulatory region of the NR3C1 was associated with increased risk of hospital admission (OR: 3.35; 95% confidence interval 1.5 to 7.3) for depressive disorders after adjusting for sex, birth year, and education. The association was statistically significant after Bonferroni correction for multiple testing. There were no other significant associations.

CONCLUSIONS

Haplotypic variation in the regulatory region of the NR3C1 may increase vulnerability to depressive disorders requiring hospital admission, but is not associated with self-reported symptoms.

X chromosome and suicide

Suicide completion rates are significantly higher in males than females in most societies. Although gender differences in suicide rates have been partially explained by environmental and behavioral factors, it is possible that genetic factors, through differential expression between genders, may also help explain gender moderation of suicide risk. This study investigated X-linked genes in suicide completers using a two-step strategy. We first took advantage of the genetic structure of the French-Canadian population and genotyped 722 unrelated French-Canadian male subjects, of whom 333 were suicide completers and 389 were non-suicide controls, using a panel of 37 microsatellite markers spanning the entire X chromosome. Nine haplotype windows and several individual markers were associated with suicide. Significant results aggregated primarily in two regions, one in the long arm and another in the short arm of chromosome X, limited by markers DXS8051 and DXS8102, and DXS1001 and DXS8106, respectively. The second stage of the study investigated differential brain expression of genes mapping to associated regions in Brodmann areas 8/9, 11, 44 and 46, in an independent sample of suicide completers and controls. Six genes within these regions, Rho GTPase-activating protein 6, adaptor-related protein complex 1 sigma 2 subunit, glycoprotein M6B, ribosomal protein S6 kinase 90  kDa polypeptide 3, spermidine/spermine N(1)-acetyltransferase 1 and THO complex 2, were found to be differentially expressed in suicide completers.

A genomewide linkage study on suicidality in major depressive disorder confirms evidence for linkage to 2p12

Suicidal behavior is commonly associated with depression. Twin studies indicate that both suicidality and major depressive disorder (MDD) are heritable. However, epidemiological evidence suggests that the inheritance of suicidality is likely to be independent of the underlying psychiatric disorder, implying a distinct genetic contribution to suicidality. We conducted a genomewide linkage search aiming to detect genomic loci that may harbor susceptibility genes contributing to risk for suicidality in recurrent MDD. Affected sibling pair (ASP) variance components analysis was performed using the Depression Network cohort of 971 ASPs. The quantitative trait measuring suicidality as a broad phenotype, encompassing ideation and suicide attempts, was established from Schedules for Clinical Assessment in Neuropsychiatry interview items. We examined 1,060 genotyped microsatellite markers with an average spacing of 3.3 cM. Empirical thresholds for linkage evidence were set by whole-genome simulations (LOD = 2.71 for genomewide significance, 1.71 for suggestive linkage). No genomewide significant findings were found. Marker D3S1234 on 3p14 achieved suggestive linkage and yielded a maximum LOD of 1.853 (P = 0.0017), loci 9p24.3 and 18q22-q23 achieved LOD scores >1.5. We found some support for linkage to 2p12 (LOD = 1.2, P = 0.0087) which was previously implicated in linkage studies of suicidality. Our follow-up meta-analysis of five studies showed strong linkage to this region (P = 2 × 10(-6) ). In conclusion, this study analyzed suicidality as a continuous trait in MDD. We found modest evidence for linkage on 3p14. Our meta-analysis supports previous evidence of linkage to suicidality on 2p12. Some candidate genes in these regions may plausibly be implicated in suicidality. © 2010 Wiley-Liss, Inc.

Evidence for genes on chromosome 2 contributing to alcohol dependence with conduct disorder and suicide attempts

Twin studies provide strong evidence that there is a shared genetic liability that predisposes to a number of different psychiatric outcomes related to behavioral disinhibition. Further, alcohol dependence comorbid with other disinhibitory disorders is particularly heritable. Chromosome 2p14-2q14.3 has been linked to multiple psychiatric conditions related to behavioral undercontrol. In the Collaborative Study on the Genetics of Alcoholism (COGA), we previously reported linkage to this region with alcohol dependence (AD), suicide attempts (SUI), and conduct disorder (CD). In this study, we follow-up on these previous reports of linkage by combining the phenotypes in analyses that jointly consider the presence of multiple conditions. Linkage analyses of the combined phenotype of AD with CD or SUI results in a maximum LOD score of 5.4 in this region. In addition to this primary linkage peak, independent samples have reported linkage to other alcohol-related phenotypes across chromosome 2. Accordingly, we followed-up these linkage signals by testing for association with SNPs across chromosome 2 in a case-control sample, in which a subset of the cases consisted of alcohol-dependent probands from the linkage sample. We find evidence of association with the combined AD with CD or SUI phenotype, with 23 genes surviving permutation testing. The number of associated genes across the chromosome may explain the persistent linkage findings reported on chromosome 2 across a number of independent studies of alcohol and disinhibitory phenotypes. Further, none of the genes were located directly under the primary COGA linkage peak, which has implications for association tests following-up linkage peaks.

Analysis of two polymorphisms of the manganese superoxide dismutase gene (Ile-58Thr and Ala-9Val) in patients with recurrent depressive disorder

Reactive oxygen species (ROS) may contribute to the pathogenesis of depressive disorder (DD). Functional genetic polymorphisms of manganese superoxide dismutase (MnSOD) are candidates for DD susceptibility. The study examined the relationship between MnSOD gene polymorphisms (Ala-9Val, Ile-58Thr) and DD in the Polish population. The association study was conducted in a case-control design in DD patients (n=149) and healthy controls (CG; n=149) by genotyping. Assessment of Ala-9Val genotype distribution and disease odds ratio demonstrated a statistically significant difference between the compared groups only in the female subgroup. The obtained results suggest a role of the MnSOD polymorphism in the development and course of depression.

Case-control association study of TGOLN2 in attempted suicide

Family, twin, and adoption studies provide convincing evidence for a genetic contribution to suicidal behavior. The heritability for suicidal behavior depends in part on the transmission of psychiatric disorders, such as mood disorders and substance use disorders, but is also partly independent of them. Three linkage studies using the attempted suicide phenotype in pedigrees with bipolar disorder, major depression, or alcoholism have provided consistent evidence that 2p11-12 harbors a susceptibility gene for attempted suicide. A microarray expression study using postmortem brain samples has implicated a gene from the 2p11-12 candidate region, the trans-Golgi network protein 2 (TGOLN2) gene, as being consistently up-regulated in suicide cases as compared to controls. Here, we present a TGOLN2 case-control association study using nine single nucleotide polymorphisms (SNPs). These nine SNPs, which include seven tag SNPs and two coding SNPs, have been genotyped in 517 mood disorder subjects with a history of attempted suicide and 515 normal controls. Allelic and genotypic analyses of the case-control sample did not provide evidence for association with the attempted suicide phenotype. Eight of the nine SNPs provided supportive evidence for association (P-values ranging from 0.008 to 0.03) when we compared the attempted suicide cases with a history of alcoholism to the attempted suicide cases without a history of alcoholism. However, this association finding was not replicated in an independent sample. Taken together, these analyses do not provide support for the hypothesis that common genetic variation in TGOLN2 contributes significantly to the risk for attempted suicide in subjects with major mood disorders.

Association of genetic variants in the neurotrophic receptor-encoding gene NTRK2 and a lifetime history of suicide attempts in depressed patients

CONTEXT

A consistent body of evidence supports a role of reduced neurotrophic signaling in the pathophysiology of major depressive disorder (MDD) and suicidal behavior. Especially in suicide victims, lower postmortem brain messenger RNA and protein levels of neurotrophins and their receptors have been reported.

OBJECTIVE

To determine whether the brain-derived neurotrophic factor (BDNF) gene or its high-affinity receptor gene, receptor tyrosine kinase 2 (NTRK2), confer risk for suicide attempt (SA) and MDD by investigating common genetic variants in these loci.

DESIGN

Eighty-three tagging single-nucleotide polymorphisms (SNPs) covering the genetic variability of these loci in European populations were assessed in a case-control association design.

SETTING

Inpatients and screened control subjects.

PARTICIPANTS

The discovery sample consisted of 394 depressed patients, of whom 113 had SA, and 366 matched healthy control subjects. The replication studies comprised 744 German patients with MDD and 921 African American nonpsychiatric clinic patients, of whom 152 and 119 were positive for SA, respectively.

INTERVENTIONS

Blood or saliva samples were collected from each participant for DNA extraction and genotyping.

MAIN OUTCOME MEASURES

Associations of SNPs in BDNF and NTRK2 with SA and MDD.

RESULTS

Independent SNPs within NTRK2 were associated with SA among depressed patients of the discovery sample that could be confirmed in both the German and African American replication samples. Multilocus interaction analysis revealed that single SNP associations within this locus contribute to the risk of SA in a multiplicative and interactive fashion (P = 4.7 x 10(-7) for a 3-SNP model in the combined German sample). The effect size was 4.5 (95% confidence interval, 2.1-9.8) when patients carrying risk genotypes in all 3 markers were compared with those without any of the 3 risk genotypes.

CONCLUSIONS

Our results suggest that a combination of several independent risk alleles within the NTRK2 locus is associated with SA in depressed patients, further supporting a role of neurotrophins in the pathophysiology of suicide.

Sex-specific association of depression and a haplotype in leukotriene A4 hydrolase gene

OBJECTIVE

To assess whether genetic variants involved in inflammation play a role in the sex difference in depression. Depression is, in part, genetically determined and inflammation has been implicated. Women are twice as likely to develop depression as men.

METHODS

We examined the association, separately in men and women, between seven single nucleotide polymorphisms (SNPs) in the arachidonate 5-lipoxygenase-activating protein (ALOX5AP) gene and 12 SNPs in the leukotriene A4 hydrolase (LTA4H) gene and depression in 1368 white subjects (30.4% female) referred for cardiovascular evaluation. Depression was defined as a score of >or=10 in the Patient Health Questionnaire 9. Single marker analysis was assessed by the chi(2) test. Haplotype-specific associations were performed, using likelihood ratio tests. Empirical significance levels were determined by permutation tests.

RESULTS

Depressed individuals, comprising 14.5% of the total, were more likely to be female, current smokers, have a history of diabetes and myocardial infarction. None of the SNPs in the ALOX5AP gene, either singly or in combination, was associated with depression. The 12 SNPs in the LTA4H gene were not individually associated with depression. However, a six-SNP haplotype in LTA4H gene, named HapE, showed a significant protective effect on depression in women, but not in men, after correcting for cardiovascular effects. The interaction between HapE and sex on depression was statistically significant.

CONCLUSION

This study provides the first evidence for a sex-specific association of a novel haplotype in the LTA4H gene on depression. Although replication is needed, our study suggests that genetic variations may underlie sex differences in depression.

Chromosome 8p as a potential hub for developmental neuropsychiatric disorders: implications for schizophrenia, autism and cancer

Defects in genetic and developmental processes are thought to contribute susceptibility to autism and schizophrenia. Presumably, owing to etiological complexity identifying susceptibility genes and abnormalities in the development has been difficult. However, the importance of genes within chromosomal 8p region for neuropsychiatric disorders and cancer is well established. There are 484 annotated genes located on 8p; many are most likely oncogenes and tumor-suppressor genes. Molecular genetics and developmental studies have identified 21 genes in this region (ADRA1A, ARHGEF10, CHRNA2, CHRNA6, CHRNB3, DKK4, DPYSL2, EGR3, FGF17, FGF20, FGFR1, FZD3, LDL, NAT2, NEF3, NRG1, PCM1, PLAT, PPP3CC, SFRP1 and VMAT1/SLC18A1) that are most likely to contribute to neuropsychiatric disorders (schizophrenia, autism, bipolar disorder and depression), neurodegenerative disorders (Parkinson's and Alzheimer's disease) and cancer. Furthermore, at least seven nonprotein-coding RNAs (microRNAs) are located at 8p. Structural variants on 8p, such as copy number variants, microdeletions or microduplications, might also contribute to autism, schizophrenia and other human diseases including cancer. In this review, we consider the current state of evidence from cytogenetic, linkage, association, gene expression and endophenotyping studies for the role of these 8p genes in neuropsychiatric disease. We also describe how a mutation in an 8p gene (Fgf17) results in a mouse with deficits in specific components of social behavior and a reduction in its dorsomedial prefrontal cortex. We finish by discussing the biological connections of 8p with respect to neuropsychiatric disorders and cancer, despite the shortcomings of this evidence.

Genome-wide linkage analysis of multiple measures of neuroticism of 2 large cohorts from Australia and the Netherlands

CONTEXT

People meeting diagnostic criteria for anxiety or depressive disorders tend to score high on the personality scale of neuroticism. Studying this personality dimension can give insights into the etiology of these important psychiatric disorders.

OBJECTIVES

To undertake a comprehensive genome-wide linkage study of neuroticism using large study samples that have been measured multiple times and to compare the results between countries for replication and across time within countries for consistency.

DESIGN

Genome-wide linkage scan.

SETTING

Twin individuals and their family members from Australia and the Netherlands.

PARTICIPANTS

Nineteen thousand six hundred thirty-five sibling pairs completed self-report questionnaires for neuroticism up to 5 times over a period of up to 22 years. Five thousand sixty-nine sibling pairs were genotyped with microsatellite markers.

METHODS

Nonparametric linkage analyses were conducted in MERLIN-REGRESS for the mean neuroticism scores averaged across time. Additional analyses were conducted for the time-specific measures of neuroticism from each country to investigate consistency of linkage results.

RESULTS

Three chromosomal regions exceeded empirically derived thresholds for suggestive linkage using mean neuroticism scores: 10p 5 Kosambi cM (cM) (Dutch study sample), 14q 103 cM (Dutch study sample), and 18q 117 cM (combined Australian and Dutch study sample), but only 14q retained significance after correction for multiple testing. These regions all showed evidence for linkage in individual time-specific measures of neuroticism and 1 (18q) showed some evidence for replication between countries. Linkage intervals for these regions all overlap with regions identified in other studies of neuroticism or related traits and/or in studies of anxiety in mice.

CONCLUSIONS

Our results demonstrate the value of the availability of multiple measures over time and add to the optimism reported in recent reviews for replication of linkage regions for neuroticism. These regions are likely to harbor causal variants for neuroticism and its related psychiatric disorders and can inform prioritization of results from genome-wide association studies.

The genetics of suicide: a critical review of molecular studies

Genetic epidemiology research has shown that genes contribute to suicide risk. Unfortunately, the first 30 years of candidate-based association studies have provided little information about the specific genetic contributors. This article reviews genetic association studies of suicidal phenotypes published to date. Possible theoretical, methodological, and operational challenges accounting for the modest success of association studies in the field are also discussed. The authors conclude that future research may benefit from using a more systematic and comprehensive selection of candidate genes and variants, examining gene-environment and gene-gene interactions, and investigating higher-order moderators.

Linkage analysis in a large family from Pakistan with depression and a high incidence of consanguineous marriages

OBJECTIVES

A genome wide scan for linkage was performed in a five generation family with a high incidence of depression and high average coefficient of inbreeding ascertained in a rural area of Pakistan. The effect of inbreeding on linkage analysis in an extended pedigree is discussed.

METHODS

372 microsatellite markers were used in a genome wide linkage study. Inbreeding coefficients were measured by two methods using both genealogical and genotype data.

RESULTS

Of 111 family members with phenotypic information, 82 were diagnosed with recurrent major depression. Linkage analysis using the program Superlink online generated LOD scores of less than one at all loci. A model free analysis with SimWalk did not result in any significant linkage score. The mean inbreeding coefficient was 0.038 estimated from genealogical data and 0.02 estimated from the genotype data. These results did not differ significantly. The effects of inbreeding included a reduction in the polymorphism information content of markers and an overestimate of marker allele frequencies.

CONCLUSION

The analysis of very large families is computationally demanding. Problems encountered in this analysis, including loss of power due to reduced polymorphism information content and sensitivity of the LOD score method to estimates of allele frequencies, severely limited the chance of detecting linkage.

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.

Gene expression profiling of post-mortem orbitofrontal cortex in violent suicide victims

The neurobiological basis of suicidal behaviour is multifactorial and complex. Several lines of evidence indicate that environmental factors as well as multiple genes and interactions of both are implicated in its aetiology. The aim of this study was to establish the transcriptomic expression profile of post-mortem brain tissue of suicide victims in order to identify new candidate genes and biological patterns for suicidal behaviour. Post-mortem orbitofrontal cortex tissue was derived from 11 suicide victims and 10 non-psychiatric controls carefully selected from a brain bank of over 150 brains, and the expression of more than 23000 messenger RNAs was assessed in this case-control study. Validation experiments were carried out using quantitative RT-PCR as an independent method. A classification of the differentially expressed genes according to their biological function and statistical analyses of the data were performed in order to identify biological pathways that are over-represented in the suicide group. In total, 124 transcripts demonstrated significant changes (fold changes > or = 1.3, p value < or = 0.01), with 59 showing under-, and 65 over-expression in the suicide group. The results could be validated for nine particularly interesting transcripts (CDCA7L, CDH12, EFEMP1, MLC1, PCDHB5, PTPRR, S100A13, SCN2B, and ZFP36). The pathway analysis showed that the Gene Ontology categories 'central nervous system development', 'homophilic cell adhesion', 'regulation of cell proliferation' and 'transmission of nerve impulse' were significantly enriched. The differentially expressed genes and significant biological processes might be involved in the pathophysiology of suicide and warrant further attention.

Attempted suicide in bipolar disorder pedigrees: evidence for linkage to 2p12

BACKGROUND

We are interested in identifying susceptibility genes that predispose subjects to attempted suicide.

METHODS

We conducted a secondary analysis of genome-wide linkage data from 162 bipolar pedigrees that incorporated attempted suicide as a clinical covariate.

RESULTS

The strongest covariate-based linkage signal was seen on 2p12 at marker D2S1777. The logarithm of odds (LOD) score at marker D2S1777 rose from 1.56 to 3.82 after inclusion of the suicide covariate, resulting in significant chromosome-wide empirically derived p-values for the overall linkage finding (p = .01) and for the change in LOD score after the inclusion of the covariate (p = .02).

CONCLUSIONS

The finding on chromosome 2 replicates results from two previous studies of attempted suicide in pedigrees with alcohol dependence and in pedigrees with recurrent early-onset depression. Combined, these three studies provide compelling evidence for a locus influencing attempted suicide on 2p12.

Molecular genetic findings in suicidal behavior: what is beyond the serotonergic system?

Various studies provide consistent evidence for a genetic component in suicidal behavior. First molecular genetic studies concentrated on genes of the serotonergic system based on the biochemical evidence that serotonergic neurotransmission is implicated in this behavior. Furthermore, genes of the dopaminergic and noradrenergic neurotransmitter systems have also been the subjects of investigations in this context. Some epidemical and clinical studies showed that low serum cholesterol levels are associated with suicidal behavior and genes involved in these pathways have been investigated. Microarray experiments provide the possibility of genome-wide gene expression analysis and help to investigate associated molecular mechanisms. The aim of this article is to review molecular genetic studies in suicidal behavior and to emphasize findings on new genes.

Nogo A, B and C expression in schizophrenia, depression and bipolar frontal cortex, and correlation of Nogo expression with CAA/TATC polymorphism in 3′-UTR

Schizophrenia may result from altered gene expression leading to abnormal neurodevelopment. In a search for genes with altered expression in schizophrenia, our previous work on human frontal cerebral cortex found the mRNA of Nogo, a myelin-associated protein which inhibits the outgrowth of neurites and nerve terminals, to be overexpressed in schizophrenia. Because those earlier results did not examine tissues for the separate Nogo A, B and C isoforms from age- and sex-matched individuals, we repeated the study for all three isoforms, using a new set of tissues from matched individuals, and using the more accurate method of quantitative real-time PCR (polymerase chain reaction). We found Nogo C to be overexpressed by 26% in the schizophrenia tissues, which is in accordance with our earlier results. The expression of Nogo B was statistically significantly reduced by 17% in the frontal cortices from individuals who had been diagnosed as having had severe depression. Furthermore, we show that there is a direct correlation between the expression of Nogo A and C and the presence of alleles with a CAA insert, irrespective of disease status. While upregulation of Nogo C expression may play a role in schizophrenia, altered Nogo B may contribute to the clinical condition of depression. Nogo A showed a statistically non-significant increase in expression in schizophrenia.

Manganese superoxide dismutase (MnSOD: Ala-9Val) gene polymorphism and mood disorders: a preliminary study

This study examined the relationship between a MnSOD gene (MnSOD) polymorphism (Ala-9Val) and mood disorders such as major depressive disorder (MDD) and bipolar I disorder (BD). Eighty patients with BD, 61 patients with MDD and 106 healthy controls were enrolled in this study and genotyped using a polymerase chain reaction-based method. The patients with MDD and BD, and the controls had a similar distribution of the genotypes and alleles in the Ala-9Val MnSOD polymorphism. The combined analysis (MDD plus BD) also failed to find any association between the Ala-9Val MnSOD polymorphism and mood disorders. Subgroup analyses according to the clinical variables such as the family history, age at onset, psychotic features and suicide history failed to identify any association with the Ala-9Val MnSOD polymorphism. This preliminary data suggests that at least in the Korean population, the Ala-9Val MnSOD polymorphism is not associated with the development of mood disorders or their clinical parameters. However, more study with a larger population sample will be needed.

Genome-wide linkage scan in a large bipolar disorder sample from the National Institute of Mental Health genetics initiative suggests putative loci for bipolar disorder, psychosis, suicide, and panic disorder

We conducted a 9-cM genome scan in a large bipolar pedigree sample from the National Institute of Mental Health genetics initiative (1060 individuals from 154 multiplex families). We performed parametric and nonparametric analyses using both standard diagnostic models and comorbid conditions thought to identify phenotypic subtypes: psychosis, suicidal behavior, and panic disorder. Our strongest linkage signals (genome-wide significance) were observed on chromosomes 10q25, 10p12, 16q24, 16p13, and 16p12 using standard diagnostic models, and on 6q25 (suicidal behavior), 7q21 (panic disorder) and 16p12 (psychosis) using phenotypic subtypes. Several other regions were suggestive of linkage, including 1p13 (psychosis), 1p21 (psychosis), 1q44, 2q24 (suicidal behavior), 2p25 (psychosis), 4p16 (psychosis, suicidal behavior), 5p15, 6p25 (psychosis), 8p22 (psychosis), 8q24, 10q21, 10q25 (suicidal behavior), 10p11 (psychosis), 13q32 and 19p13 (psychosis). Over half the implicated regions were identified using phenotypic subtypes. Several regions - 1p, 1q, 6q, 8p, 13q and 16p - have been previously reported to be linked to bipolar disorder. Our results suggest that dissection of the disease phenotype can enrich the harvest of linkage signals and expedite the search for susceptibility genes. This is the first large-scale linkage scan of bipolar disorder to analyze simultaneously bipolar disorder, psychosis, suicidal behavior, and panic disorder.

Excitement and confusion on chromosome 6q: the challenges of neuropsychiatric genetics in microcosm

The search for genes that are implicated in the pathogenesis of schizophrenia (SCZ), bipolar disorder (BPD) and other complex neuropsychiatric phenotypes has yielded a plethora of positive findings, but has also engendered a substantial degree of confusion. Exciting findings include positive linkage results in a number of chromosomal regions and the identification of several genes that have been associated with SCZ and to a lesser extent with BPD. Confusing aspects include the difference between studies in localization of linkage peaks in the same chromosomal regions, raising the possibility that these regions may harbor more than one gene, the fact that positive linkage findings as well as associated genes appear in several cases to be shared by more than one disorder, and the failure to identify thus far the precise pathogenic variants in associated genes. Recent findings of linkage and association studies on chromosome 6q illustrate the current status of neuropsychiatric genetics in intriguing microcosm. Positive findings from linkage and association studies are reviewed in order to identify approaches that may help to settle apparent contradictions and allow an interpretation of the results that may prove useful in application to findings from other chromosomal regions. Not only SCZ and BPD but also other psychiatric and neurological phenotypes are considered. Taking a topographic approach, we identify five foci of positive findings on chromosome 6q and suggest that each may harbor gene(s) that confer susceptibility to SCZ or BPD or may modify their onset or clinical course. We further suggest that in searching for these genes the possibility that they may be implicated in more than one disorder should be taken into account. We also discuss the potential contribution of rare genetic variants identified in homogeneous, isolated populations to the subsequent identification of common variants in the same gene that contribute to disease susceptibility in outbred populations.

Dissecting the genetic etiology of major depressive disorder using linkage analysis

Major depressive disorder (MDD) is clinically and genetically heterogeneous. Studies suggest that recurrence, early onset and comorbid phenotypes define more genetically homogeneous sub-samples. The concordance of linkage findings in recent studies using such approaches is encouraging. Sex-specific analyses and broader phenotypes have also yielded interesting results. These findings indicate that future research should consider comorbid disorders and sex-specific analyses. However, this direction must be approached with caution, owing to the complex multiple-testing issues that arise when considering numerous related phenotypes. With appropriate interpretation, these findings indicate a new potential for positional cloning efforts to locate genes in consensus regions. Genes found might influence specific subtypes of MDD or broader phenotypes, leading to enhanced clinical characterization and management of MDD.

Approaches to detecting gene × gene interaction in Genetic Analysis Workshop 14 pedigrees

Whether driven by the general lack of success in finding single-gene contributions to complex disease, by increased knowledge about the potential involvement of specific biological interactions in complex disease, or by recent dramatic increases in computational power, a large number of approaches to detect locus x locus interactions were recently proposed and implemented. The six Genetic Analysis Workshop 14 (GAW14) papers summarized here each applied either existing or refined approaches with the goal of detecting gene x gene, or locus x locus, interactions in the GAW14 data. Five of six papers analyzed the simulated data; the other analyzed the Collaborative Study on the Genetics of Alcoholism data. The analytic strategies implemented for detecting interactions included multifactor dimensionality reduction, conditional linkage analysis, nonparametric linkage correlation, two-locus parametric linkage analysis, and a joint test of linkage and association. Overall, most of the groups found limited success in consistently detecting all of the simulated interactions due, in large part, to the nature of the generating model.