Genome-wide linkage analyses of extended Utah pedigrees identifies loci that influence recurrent, early-onset major depression and anxiety disorders

Stress and the CRH System, Norepinephrine, Depression, and Type 2 Diabetes

Major depressive disorder (MDD) increases the risk of type 2 diabetes (T2D) by 60% in untreated patients, and hypercortisolism is common in MDD as well as in some patients with T2D. Patients with MDD, despite hypercortisolism, show inappropriately normal levels of corticotropin-releasing hormone (CRH) and plasma adrenocorticotropin (ACTH) in the cerebrospinal fluid, which might implicate impaired negative feedback. Also, a positive feedback loop of the CRH-norepinephrine (NE)-CRH system may be involved in the hypercortisolism of MDD and T2D. Dysfunctional CRH receptor 1 (CRHR1) and CRH receptor 2 (CRHR2), both of which are involved in glucose regulation, may explain hypercortisolism in MDD and T2D, at least in a subgroup of patients. CRHR1 increases glucose-stimulated insulin secretion. Dysfunctional CRHR1 variants can cause hypercortisolism, leading to serotonin dysfunction and depression, which can contribute to hyperglycemia, insulin resistance, and increased visceral fat, all of which are characteristics of T2D. CRHR2 is implicated in glucose homeostasis through the regulation of insulin secretion and gastrointestinal functions, and it stimulates insulin sensitivity at the muscular level. A few studies show a correlation of the CRHR2 gene with depressive disorders. Based on our own research, we have found a linkage and association (i.e., linkage disequilibrium [LD]) of the genes CRHR1 and CRHR2 with MDD and T2D in families with T2D. The correlation of CRHR1 and CRHR2 with MDD appears stronger than that with T2D, and per our hypothesis, MDD may precede the onset of T2D. According to the findings of our analysis, CRHR1 and CRHR2 variants could modify the response to prolonged chronic stress and contribute to high levels of cortisol, increasing the risk of developing MDD, T2D, and the comorbidity MDD-T2D. We report here the potential links of the CRH system, NE, and their roles in MDD and T2D.

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

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

OGDHL Variant rs2293239: A Potential Genetic Driver of Chinese Familial Depressive Disorder

Depressive disorders are a severe psychiatric and social problem that affect more than 4% of the global population. Depressive disorders have explicit hereditary characteristics; however, the precise driving genetic force behind these disorders has not yet been clearly illustrated. In the present study, we recruited a three-generation Chinese pedigree in which 5 of 17 members had long-term depression. We conducted whole-exome sequencing to identify the genetic mutation profiles of the family, and a list of susceptible genetic variations that were highly associated with depression onset was revealed via multiple omics analysis. In particular, a non-synonymous single nucleotide variation in the oxoglutarate dehydrogenase-like (OGDHL) gene, rs2293239 (p.Asn725Ser), was identified as one of the major driving genetic forces for depression onset in the family. This variant causes an important conformational change in the transketolase domain of OGDHL, thus reducing its binding affinity with the cofactor thiamine pyrophosphate and eventually resulting in the abnormal accumulation of glutamate in the brain. Brain imaging analysis further linked the rs2293239 variant with an enlarged amygdala and cerebellum in depressive family members. In summary, the present study enhances the current genetic understanding of depressive disorders. It also provides new options for prioritizing better clinical therapeutic regimens, as well as identifying a new protein target for the design of highly specific drugs to treat depressive disorders.

The genetic basis of major depression

Major depressive disorder (MDD) is a common, debilitating, phenotypically heterogeneous disorder with heritability ranges from 30% to 50%. Compared to other psychiatric disorders, its high prevalence, moderate heritability, and strong polygenicity have posed major challenges for gene-mapping in MDD. Studies of common genetic variation in MDD, driven by large international collaborations such as the Psychiatric Genomics Consortium, have confirmed the highly polygenic nature of the disorder and implicated over 100 genetic risk loci to date. Rare copy number variants associated with MDD risk were also recently identified. The goal of this review is to present a broad picture of our current understanding of the epidemiology, genetic epidemiology, molecular genetics, and gene-environment interplay in MDD. Insights into the impact of genetic factors on the aetiology of this complex disorder hold great promise for improving clinical care.

PDLIM5 improves depression-like behavior of prenatal stress offspring rats via methylation in male, but not female

OBJECTIVE

Prenatal stress (PS) contributes to depression-like behavior in the offspring. PDLIM5 is involved in the onset of mental disorders. This study is to investigate the role and mechanism of PDLIM5 in depression-like behavior of PS offspring rats.

METHODS

PS model was used to analyze the effects of different treatments to PS offspring rats with different sex, including PDLIM5, PDLIM5 shRNA and 5-aza-2' -deoxycytidine (5-azaD). The depression-like behavior was assessed by the sucrose preference test (SPT) and forced swimming test (FST). The mRNA and protein expression levels of PDLIM5 in the hippocampus of PS offspring rats were detected by qRT-PCR and western blot, respectively. The methylation of PDLIM5 promoter were analyzed by bisulfite sequencing.

RESULTS

Our data revealed that PS offspring rats showed a significant decrease in sucrose preference and a prolonged immobility time. Injection of PDLIM5 significantly improved the depression-like behavior in PS offspring rats, whereas administration of PDLIM5 shRNA aggravated it. In addition, PDLIM5 expression was decreased at the mRNA and protein levels, and the methylation level of PDLIM5 promoter was increased in hippocampus of PS male but not female offspring rats. Furthermore, microinjection of 5-azaD improved the PS induced depression-like behavior in offspring rats. Moreover, in male PS offspring rats, microinjection of 5-azaD reversed the effect of PS on PDLIM5 expression and promoter methylation.

CONCLUSION

PDLIM5 can significantly improve the depression-like behavior of both male and female PS offspring rats, while the PDLIM5 promoter methylation is only observed in male PS offspring rats. Our study may provide new mechanism for the pathogenesis of depression and experimental evidence for sex-based precise treatment.

Association between increased serum interleukin-6 levels and sustained attention deficits in patients with major depressive disorder

BACKGROUND

The pathophysiology of cognitive impairment in patients with the major depressive disorder (MDD) may involve neuroinflammation mediated by cytokines.

OBJECTIVE

The aim of this study was to examine the serum interleukin-6 (IL-6) levels, sustained attention, and their association in patients with MDD.

METHODS

Thirty patients with MDD and 30 healthy controls were enrolled in this case-control study. Sustained attention was measured using the Rapid Visual Information Processing (RVP) task in the Cambridge Neuropsychological Tests Automated Battery. The serum IL-6 levels of all subjects were assessed by sandwich enzyme-linked immunosorbent assays.

RESULTS

There were significant differences in the log10RVP total hits, log10RVP total misses, and log10RVP mean latency between patients with MDD and healthy controls (F = 6.04, p = 0.017; F = 19.77, p < 0.0001; F = 14.42, p < 0.0001, respectively). The serum levels of Log10IL-6 were significantly higher in patients with MDD than in healthy controls (F = 192.27, p < 0.0001). The log10IL-6 levels were also positively correlated with the log10RVP mean latency in patients with MDD (r = 0.45, p = 0.013). A further stepwise multivariate regression analysis indicated that the log10IL-6 levels were significantly associated with the log10RVP mean latency in patients with MDD (β = 0.31, t = 2.41, p = 0.025).

CONCLUSIONS

Our data suggested that increased IL-6 levels were associated with the psychopathology of MDD, and that abnormal IL-6 levels were implicated in the impairment of sustained attention in patients with MDD.

Genetics Factors in Major Depression Disease

Depressive disorders (DDs) are one of the most widespread forms of psychiatric pathology. According to the World Health Organization, about 350 million people in the world are affected by this condition. Family and twin studies have demonstrated that the contribution of genetic factors to the risk of the onset of DDs is quite large. Various methodological approaches (analysis of candidate genes, genome-wide association analysis, genome-wide sequencing) have been used, and a large number of the associations between genes and different clinical DD variants and DD subphenotypes have been published. However, in most cases, these associations have not been confirmed in replication studies, and only a small number of genes have been proven to be associated with DD development risk. To ascertain the role of genetic factors in DD pathogenesis, further investigations of the relevant conditions are required. Special consideration should be given to the polygenic characteristics noted in whole-genome studies of the heritability of the disorder without a pronounced effect of the major gene. These observations accentuate the relevance of the analysis of gene-interaction roles in DD development and progression. It is important that association studies of the inherited variants of the genome should be supported by analysis of dynamic changes during DD progression. Epigenetic changes that cause modifications of a gene's functional state without changing its coding sequence are of primary interest. However, the opportunities for studying changes in the epigenome, transcriptome, and proteome during DD are limited by the nature of the disease and the need for brain tissue analysis, which is possible only postmortem. Therefore, any association studies between DD pathogenesis and epigenetic factors must be supplemented through the use of different animal models of depression. A threefold approach comprising the combination of gene association studies, assessment of the epigenetic state in DD patients, and analysis of different "omic" changes in animal depression models will make it possible to evaluate the contribution of genetic, epigenetic, and environmental factors to the development of different forms of depression and to help develop ways to decrease the risk of depression and improve the treatment of DD.

Reduced ENA78 levels as novel biomarker for major depressive disorder and venlafaxine efficiency: Result from a prospective longitudinal study

Although lines of evidence demonstrated that cytokines play an important role in the pathogenesis of major depressive disorder (MDD), none of the them have been established as reliable biomarkers. We use our previous whole-genome cRNA microarray data to identify epithelial cell-derived neutrophil-activating peptide 78 (ENA78), the most differentially expressed cytokine in peripheral blood between MDD patients and healthy controls; and then we confirmed the result by the quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) for mRNA and protein level, respectively, in an independent drug-naïve first-episode sample set. In addition, to replicate the role of plasma ENA 78 in MDD, and determine the role of ENA78 on the venlafaxine efficiency, we further detected the plasma ENA78 in another independent 8- week follow-up sample set. We found that both of mRNA and plasma of ENA78 decreased in MDD patients, and displayed much lower after venlafaxine treatment. We also found that venlafaxine non-responders had lower level of peripheral plasma ENA78 prior to treatment than responders. Our findings for the first time provided strong evidence that the ENA78 may play a key role of mediator in pathogenesis of MDD and in the mechanism of vinlafaxine effects on MDD indicating that reduced ENA78 may be a potential biomarker for diagnosing of MDD and predicting of response to venlafaxine.

Exome-sequencing in a large population-based study reveals a rare Asn396Ser variant in the LIPG gene associated with depressive symptoms

Despite a substantial genetic component, efforts to identify common genetic variation underlying depression have largely been unsuccessful. In the current study we aimed to identify rare genetic variants that might have large effects on depression in the general population. Using high-coverage exome-sequencing, we studied the exonic variants in 1265 individuals from the Rotterdam study (RS), who were assessed for depressive symptoms. We identified a missense Asn396Ser mutation (rs77960347) in the endothelial lipase (LIPG) gene, occurring with an allele frequency of 1% in the general population, which was significantly associated with depressive symptoms (P-value=5.2 × 10^-08, β=7.2). Replication in three independent data sets (N=3612) confirmed the association of Asn396Ser (P-value=7.1 × 10^-03, β=2.55) with depressive symptoms. LIPG is predicted to have enzymatic function in steroid biosynthesis, cholesterol biosynthesis and thyroid hormone metabolic processes. The Asn396Ser variant is predicted to have a damaging effect on the function of LIPG. Within the discovery population, carriers also showed an increased burden of white matter lesions (P-value=3.3 × 10^-02) and a higher risk of Alzheimer's disease (odds ratio=2.01; P-value=2.8 × 10^-02) compared with the non-carriers. Together, these findings implicate the Asn396Ser variant of LIPG in the pathogenesis of depressive symptoms in the general population.

Identification of IL6 as a susceptibility gene for major depressive disorder

Our previous work implied that interleukin 6 (IL6) may be a biological marker for major depressive disorder (MDD). In this study, we performed a comprehensive genetic study to determine the association between the gene encoding IL6 (IL6) and MDD in Han Chinese. There were 50 drug-naïve MDD patients and 50 healthy controls undergoing an mRNA expression study. A sample of 772 patients with MDD and 759 healthy controls were used for genetic analysis. Next, we performed an eQTL analysis to identify whether risk SNP(s) is associated with IL6 expression in brain. Our results showed that patients with MDD have higher levels of IL6 than healthy controls (P = 0.008). The SNP rs1800797 has a significant association with MDD (P = 0.01) in a dominant model. The eQTL analysis showed a marginally significant association between the rs1800797 and IL6 expression in the frontal cortex (P = 0.087). Our preliminary findings are suggestive of an association between rs1800797 and the risk of MDD. Further investigations are required to evaluate this association in larger samples to increase statistical power, and to examine the correlation between rs1800797 and IL6 methylation patterns.

A haplotype in the 5'-upstream region of the NDUFV2 gene is associated with major depressive disorder in Han Chinese

BACKGROUND

There is ample evidence supporting the idea that mitochondrial dysfunction and altered expression of complex I subunits play important roles in the pathophysiology of mental disorders. Early literature reports have implicated NDUFV2, a nuclear-encoded mitochondrial complex I subunit gene, in bipolar disorder and schizophrenia. There has been no genetic study to investigate whether there is an association between NDUFV2 and major depressive disorder (MDD).

METHODS

This study recruited 744 patients with MDD and 767 well-matched healthy controls in a Chinese Han population, and genotyped 9 SNPs within NDUFV2.

RESULTS

Initial analysis showed statistically significant differences for 2 SNPs (rs4798765 and rs12964485) in the genotypic distribution and for 1 SNP (rs4797356) in the allelic distribution between the case and control groups. Nevertheless, no significance was demonstrated following multiple testing corrections. Haplotype analysis showed that the T-C haplotype, consisting of rs12457810 and rs12964485, was significantly associated with MDD (P=0.005, corrected P=0.04 after a 10,000 permutation test). We performed an eQTL analysis and found that rs12964485 was significantly associated with NDUFV2 expression in the occipital cortex (P=0.036), albeit this significance did not survive after Bonferroni correction.

LIMITATION

This is a preliminary investigation with a relatively modest sample size.

CONCLUSION

Our findings provided preliminary evidence that a haplotype T-C consisting of rs12457810 and rs12964485 in the 5'-upstream region of NDUFV2 may be a protective factor for the development of MDD in Han Chinese.

Evidence for the role of corticotropin-releasing factor in major depressive disorder

Major depressive disorder (MDD) is a devastating disease affecting over 300 million people worldwide, and costing an estimated 380 billion Euros in lost productivity and health care in the European Union alone. Although a wealth of research has been directed toward understanding and treating MDD, still no therapy has proved to be consistently and reliably effective in interrupting the symptoms of this disease. Recent clinical and preclinical studies, using genetic screening and transgenic rodents, respectively, suggest a major role of the CRF1 gene, and the central expression of CRF1 receptor protein in determining an individual's risk of developing MDD. This gene is widely expressed in brain tissue, and regulates an organism's immediate and long-term responses to social and environmental stressors, which are primary contributors to MDD. This review presents the current state of knowledge on CRF physiology, and how it may influence the occurrence of symptoms associated with MDD. Additionally, this review presents findings from multiple laboratories that were presented as part of a symposium on this topic at the annual 2014 meeting of the International Behavioral Neuroscience Society (IBNS). The ideas and data presented in this review demonstrate the great progress that has been made over the past few decades in our understanding of MDD, and provide a pathway forward toward developing novel treatments and detection methods for this disorder.

The genetics of major depression

Major depression is the commonest psychiatric disorder and in the U.S. has the greatest impact of all biomedical diseases on disability. Here we review evidence of the genetic contribution to disease susceptibility and the current state of molecular approaches. Genome-wide association and linkage results provide constraints on the allele frequencies and effect sizes of susceptibility loci, which we use to interpret the voluminous candidate gene literature. We consider evidence for the genetic heterogeneity of the disorder and the likelihood that subtypes exist that represent more genetically homogenous conditions than have hitherto been analyzed.

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

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

Influence of BCL2 gene in major depression susceptibility and antidepressant treatment outcome

BACKGROUND

Our recent work indicated that low-expression of the anti-apoptotic protein B-cell/lymphoma 2 (Bcl-2) mRNA was observed among untreated major depressive disorder (MDD) patients, and the subsequent altered level of Bcl-2 was found to be close to the antidepressant treatment outcome. The primary aim of this present study was to examine whether a particular gene, encoding Bcl-2 (BCL2) confers risk to MDD, and likewise to investigate whether this gene acts as an indicator of antidepressant treatment outcome.

METHODS

We enrolled 178 treatment-resistant depression (TRD) and 612 non-treatment-resistant depression (NTRD) patients as well as 725 healthy controls. In total, three selected tagging SNPs (tagSNPs) of BCL2 (rs2279115, rs1801018 and rs1564483) were genotyped to test for possible association. Using TaqMan relative quantitative real-time polymerase chain reaction (PCR), we analyzed leukocytic expression of BCL2 mRNA in 47 healthy subjects.

RESULTS

Of the three SNPs, we observed no significant differences in genotype and allele frequencies between the MDD and control groups as well as between the TRD and NTRD groups. However, we found a significant association between the rs2279115C allele and TRD in males (corrected P=0.048) but not in females. Further real-time quantitative PCR analysis in healthy subjects revealed that the rs2279115 polymorphism significantly influenced BCL2 mRNA expression (P=0.03).

LIMITATIONS

This is a preliminary investigation with relatively small sample size and cross-sectional design.

CONCLUSIONS

These initial findings strengthen the hypothesis that BCL2 may play an important role in mediating the outcome of antidepressant treatment, a result that may further be confirmed by future genetic studies from large-scale populations that can overcome the limited sample size of this preliminary finding.

Mood disorders in individuals with distal 18q deletions

We examined 36 participants at least 4 years old with hemizygous distal deletions of the long arm of Chromosome 18 (18q-) for histories of mood disorders and to characterize these disorders clinically. Since each participant had a different region of 18q hemizygosity, our goal was also to identify their common region of hemizygosity associated with mood disorders; thereby identifying candidate causal genes in that region. Lifetime mood and other psychiatric disorders were determined by semi-structured interviews of patients and parents, supplemented by reviews of medical and psychiatric records, and norm-referenced psychological assessment instruments, for psychiatric symptoms, cognitive problems, and adaptive functioning. Sixteen participants were identified with lifetime mood disorders (ages 12-42 years, 71% female, 14 having had unipolar depression and 2 with bipolar disorders). From the group of 20 who did not meet criteria for a mood disorder; a comparison group of 6 participants were identified who were matched for age range and deletion size. Mood-disordered patients had high rates of anxiety (75%) and externalizing behavior disorders (44%), and significant mean differences from comparison patients (P < 0.05), including higher overall and verbal IQs and lower autistic symptoms. A critical region was defined in the mood-disordered group that included a hypothetical gene, C18orf62, and two known genes, ZADH2 and TSHZ1. We conclude that patients having terminal deletions of this critical region of the long arm of Chromosome 18 are highly likely to have mood disorders, which are often comorbid with anxiety and to a lesser extent with externalizing disorders.

The current state of play on the molecular genetics of depression

BACKGROUND

It has been well established that both genes and non-shared environment contribute substantially to the underlying aetiology of major depressive disorder (MDD). A comprehensive overview of genetic research in MDD is presented. Method Papers were retrieved from PubMed up to December 2011, using many keywords including: depression, major depressive disorder, genetics, rare variants, gene-environment, whole genome, epigenetics, and specific candidate genes and variants. These were combined in a variety of permutations.

RESULTS

Linkage studies have yielded some promising chromosomal regions in MDD. However, there is a continued lack of consistency in association studies, in both candidate gene and genome-wide association studies (GWAS). Numerous factors may account for variable results including the use of different diagnostic approaches, small samples in early studies, population stratification, epigenetic phenomena, copy number variation (CNV), rare variation, and phenotypic and allelic heterogeneity. The conflicting results are also probably, in part, a consequence of environmental factors not being considered or controlled for.

CONCLUSIONS

Each research group has to identify what issues their sample may best address. We suggest that, where possible, more emphasis should be placed on the environment in molecular behavioural genetics to identify individuals at environmental high risk in addition to genetic high risk. Sequencing should be used to identify rare and alternative variation that may act as a risk factor, and a systems biology approach including gene-gene interactions and pathway analyses would be advantageous. GWAS may require even larger samples with reliably defined (sub)phenotypes.

Homozygosity mapping of depressive disorder in a large family from Pakistan: significant linkage on chromosome 6 and 9

A large family with a high prevalence of recurrent major depression and high average inbreeding coefficient was ascertained from rural Pakistan. Subjects were interviewed and diagnosed by a trained psychiatrist, 370 microsatellite markers were genotyped and the program FEstim was used for homozygosity mapping. Significant linkage was found on Chromosome 9 and Chromosome 6 after fine mapping. These regions on Chromosome 6 and 9 may harbor genes which predispose to depression.

Genomic structural variation in psychiatric disorders

Copy number variants (CNVs) are submicroscopic deletions and duplications of genomic material that were previously thought to be rare phenomena. They have now been robustly associated with a variety of disorders such as autism, schizophrenia, and attention-deficit/hyperactivity disorder through an emerging research base in affective disorders. A complex picture is emerging of a polygenic, heterogeneous model of disease, with CNVs conferring broad susceptibility to a variety of neurodevelopmental disorders, rather than specific disorders per se. Although the insights gleaned thus far only represent a small piece of a much larger puzzle, progress has been rapid and new technologies promise even more insights into these hitherto opaque brain disorders. We will discuss CNVs, the current state of evidence for their role in the pathogenesis of classical psychiatric disorders, and the application of such knowledge in clinical settings.

Associations between LSAMP gene polymorphisms and major depressive disorder and panic disorder

The purpose of this case-control genetic association study was to explore potential relationships between polymorphisms in the limbic system-associated membrane protein (LSAMP) gene and mood and anxiety disorders. A total of 21 single-nucleotide polymorphisms (SNPs) from the LSAMP gene were analyzed in 591 unrelated patients with the diagnoses of major depressive disorder (MDD) or panic disorder (PD) and in 384 healthy control subjects. The results showed a strong association between LSAMP SNPs and MDD, and a suggestive association between LSAMP SNPs and PD. This is the first evidence of a possible role of LSAMP gene in mood and anxiety disorders in humans.

Meta-analyses of genome-wide linkage scans of anxiety-related phenotypes

Genetic factors underlying trait neuroticism, reflecting a tendency towards negative affective states, may overlap genetic susceptibility for anxiety disorders and help explain the extensive comorbidity amongst internalizing disorders. Genome-wide linkage (GWL) data from several studies of neuroticism and anxiety disorders have been published, providing an opportunity to test such hypotheses and identify genomic regions that harbor genes common to these phenotypes. In all, 11 independent GWL studies of either neuroticism (n=8) or anxiety disorders (n=3) were collected, which comprised of 5341 families with 15 529 individuals. The rank-based genome scan meta-analysis (GSMA) approach was used to analyze each trait separately and combined, and global correlations between results were examined. False discovery rate (FDR) analysis was performed to test for enrichment of significant effects. Using 10 cM intervals, bins nominally significant for both GSMA statistics, P(SR) and P(OR), were found on chromosomes 9, 11, 12, and 14 for neuroticism and on chromosomes 1, 5, 15, and 16 for anxiety disorders. Genome-wide, the results for the two phenotypes were significantly correlated, and a combined analysis identified additional nominally significant bins. Although none reached genome-wide significance, an excess of significant P(SR)P-values were observed, with 12 bins falling under a FDR threshold of 0.50. As demonstrated by our identification of multiple, consistent signals across the genome, meta-analytically combining existing GWL data is a valuable approach to narrowing down regions relevant for anxiety-related phenotypes. This may prove useful for prioritizing emerging genome-wide association data for anxiety disorders.

Behavioral genetics of affective and anxiety disorders

As shown by clinical genetic studies, affective and anxiety disorders are complex genetic disorders with genetic and environmental factors interactively determining their respective pathomechanism. Advances in molecular genetic techniques including linkage studies, association studies, and genome-wide association studies allow for the detailed dissection of the genetic influence on the development of these disorders. Besides the molecular genetic investigation of categorical entities according to standardized diagnostic criteria, intermediate phenotypes comprising neurobiological or neuropsychological traits (e.g., neuronal correlates of emotional processing) that are linked to the disease of interest and that are heritable, have been proposed to be closer to the underlying genotype than the overall disease phenotype. These intermediate phenotypes are dimensional and more precisely defined than the categorical disease phenotype, and therefore have attracted much interest in the genetic investigation of affective and anxiety disorders. Given the complex genetic nature of affective and anxiety disorders with an interaction of multiple risk genes and environmental influences, the interplay of genetic factors with environmental factors is investigated by means of gene-environment interaction (GxE) studies. Pharmacogenetic studies aid in the dissection of the genetically influenced heterogeneity of psychotropic drug response and may contribute to the development of a more individualized treatment of affective and anxiety disorders. Finally, there is some evidence for genetic factors potentially shared between affective and anxiety disorders pointing to a possible overlapping phenotype between anxiety disorders and depression.

The genetic basis of depression

Since the publication of the working draft of the human genome just over a decade ago, there have been dramatic advances in our understanding of the role genetics play in both normal human functioning as well as in disease. The identification of genes, which influence an individual's susceptibility to depression, is not only an intriguing scientific endeavour in its own right, but further, if a gene can be confidently implicated in depression, then this could shed light on the aetiological processes involved in the disease. Moreover, a genetic association with depression may identify targets for consideration in the development of novel treatments for the illness. This chapter will summarise the current research into the genetic basis of depression. A number of genes of interest have been highlighted, although a genetic variant, that is unequivocally associated with increased risk for the disease, is yet to be identified. However, technologies and methodologies are evolving rapidly, and genetic approaches have helped shape how we conceptualise depression as an illness.

A genomewide linkage scan of cocaine dependence and major depressive episode in two populations

Cocaine dependence (CD) and major depressive episode (MDE) frequently co-occur with poorer treatment outcome and higher relapse risk. Shared genetic risk was affirmed; to date, there have been no reports of genomewide linkage scans (GWLSs) surveying the susceptibility regions for comorbid CD and MDE (CD-MDE). We aimed to identify chromosomal regions and candidate genes susceptible to CD, MDE, and CD-MDE in African Americans (AAs) and European Americans (EAs). A total of 1896 individuals were recruited from 384 AA and 355 EA families, each with at least a sibling-pair with CD and/or opioid dependence. Array-based genotyping of about 6000 single-nucleotide polymorphisms was completed for all individuals. Parametric and non-parametric genomewide linkage analyses were performed. We found a genomewide-significant linkage peak on chromosome 7 at 183.4 cM for non-parametric analysis of CD-MDE in AAs (lod=3.8, genomewide empirical p=0.016; point-wise p=0.00001). A nearly genomewide significant linkage was identified for CD-MDE in EAs on chromosome 5 at 14.3 cM (logarithm of odds (lod)=2.95, genomewide empirical p=0.055; point-wise p=0.00012). Parametric analysis corroborated the findings in these two regions and improved the support for the peak on chromosome 5 so that it reached genomewide significance (heterogeneity lod=3.28, genomewide empirical p=0.046; point-wise p=0.00053). This is the first GWLS for CD-MDE. The genomewide significant linkage regions on chromosomes 5 and 7 harbor four particularly promising candidate genes: SRD5A1, UBE3C, PTPRN2, and VIPR2. Replication of the linkage findings in other populations is warranted, as is a focused analysis of the genes located in the linkage regions implicated here.

Bcl-2 SNP rs956572 associates with disrupted intracellular calcium homeostasis in bipolar I disorder

OBJECTIVES

Disrupted intracellular calcium (Ca(2+) ) homeostasis (ICH) related to mitochondrial and/or endoplasmic reticulum (ER) dysfunction has been implicated in bipolar disorder (BD). The anti-apoptotic protein B-cell CLL/lymphoma 2 (Bcl-2), encoded in a putative BD susceptibility locus, modulates ER-Ca(2+) dynamics. Recently, an intronic single-nucleotide polymorphism (SNP) in the Bcl-2 gene, rs956572, was suggested as a functionally active SNP that influences its messenger RNA (mRNA) and protein level as well as human gray matter volume. We sought to evaluate the impact of this variant on ICH in BD.

METHODS

Basal intracellular Ca(2+) concentrations ([Ca(2+) ](B) ) and rs956572 genotypes were determined in B lymphoblast cell lines (BLCLs) from bipolar I disorder (BD-I) (n=150), bipolar II disorder (BD-II) (n=65), and major depressive disorder (n=30) patients, and from healthy subjects (n=70). Bcl-2 mRNA and protein levels were determined by quantitative reverse transcriptase polymerase chain reaction and immunoblotting, respectively. Functional interactions of rs956572 with ICH were assessed by thapsigargin- and lysophosphatidic acid (LPA)-stimulated Ca(2+) responses.

RESULTS

Although rs956572 variation was not significantly associated with BD, BD-I, or BD-II, BLCL [Ca(2+) ](B) was significantly higher in BD-I G/G patients compared with other genotypes and with healthy subjects. Bcl-2 mRNA and protein levels were lowest in BD-I G/G patients. Compared with A carriers, BD-I patients with G/G variants showed a modest enhancing effect on thapsigargin- and LPA-stimulated Ca(2+) responses.

CONCLUSIONS

These findings support the notion that genetic variation in Bcl-2 affecting its expression impacts ICH in BD. Moreover, we show here for the first time that this interactive effect is diagnostically specific to BD-I.

Overview of the genetics of major depressive disorder

Major depressive disorder (MDD) is a common psychiatric illness with high levels of morbidity and mortality. Despite intensive research during the past several decades, the neurobiological basis and pathophysiology of depressive disorders remain unknown. Genetic factors play important roles in the development of MDD, as indicated by family, twin, and adoption studies, and may reveal important information about disease mechanisms. This article describes recent developments in the field of psychiatric genetics, with a focus on MDD. Early twin studies, linkage studies, and association studies are discussed. Recent findings from genome-wide association studies are reviewed and future directions discussed. Despite all efforts, thus far, no single genetic variation has been identified to increase the risk of depression substantially. Genetic variants are expected to have only small effects on overall disease risk, and multiple genetic factors in conjunction with environmental factors are likely necessary for the development of MDD. Future large-scale studies are needed to dissect this complex phenotype and to identify pathways involved in the etiology of MDD.

A unified theory of autism revisited: linkage evidence points to chromosome X using a high-risk subset of AGRE families

Zhao et al. [2007] in their "Unified Theory of Autism" hypothesized that incidence of autism in males could be explained by essentially two types of family structures: majority of autism cases are from low-risk autism families with de novo mutations, and a minority of cases are from high-risk multiplex families, where risk to male offspring approximates 50% consistent with a dominant model and high penetrance. Using the Autism Genetic Resource Exchange (AGRE) data set, Zhao et al. identified 86 high-risk families with likely dominant transmission. As genotype data are now available for many members of the AGRE resource, the objective of this manuscript was to determine if dominant linkage evidence for an autism predisposition gene exists in these 86 high-risk families. HumanHap550K Illumina SNP data were available for 92% of 455 total family members in these 86 high-risk families. We performed a linkage analysis using a pruned subset of markers where markers in high linkage disequilibrium were removed. We observed a single suggestive peak (maximum LOD 2.01, maximum HLOD 2.08) under a dominant model on chromosome Xp22.11-p21.2 that encompasses the IL1RAPL1 gene. Mutations or deletions in IL1RAPL1 have been previously reported in three families with autism. In our study, 11 families contributed nominally (P<0.05, HLOD>0.588) to the chromosome X peak. These results demonstrate that identification of a more homogeneous subset of autism cases, which was based on family structure in this study, may help to identify, localize and further our understanding of autism predisposition genes.

A genome-wide screen for depression in two independent Dutch populations

BACKGROUND

Depression has a strong genetic component but candidate gene studies conducted to date have not shown consistent associations.

METHODS

We conducted a genome-wide parametric and nonparametric linkage analysis in a large-scale family-based study including 115 individuals with depression who were identified based on the Hospital Anxiety Depression Scale, Center for Epidemiologic Studies Depression Rating Scale, or use of antidepressive medication. Further, we investigated the most promising chromosomal regions found in the genome-wide linkage analysis with an association analysis in 734 individuals in the family-based study and 2373 individuals in the population-based study.

RESULTS

Our study demonstrated evidence for significant linkage of depression to chromosome 2p16.1-15 (logarithm of odds [LOD] = 5.13; parametric analysis) and suggestive evidence for linkage in nonparametric analysis to chromosome 5p15.33 (LOD = 2.14), 11q25 (LOD = 2.27), and 19p13.3 (LOD = 2.66). The subsequent association analysis in the family-based study showed region-wide significant association in intron 1 of the OPCML gene on chromosome 11q25 (empirical p value = .04). The association analysis in the population-based study did not show any region-wide significant association, yet showed suggestive association in intron 1 of the APLP2 gene on chromosome 11q25.

CONCLUSIONS

Our linkage and association studies suggest a locus for depression on chromosomes 2p16.1-15 and 11q25. The linkage to chromosome 11q25 may be, in part, explained by the OPCML or the APLP2 gene. Further, there is evidence for a role of the GNG7 gene (chromosome 19p13.3).

Genome-wide linkage scans for major depression in individuals with alcohol dependence

Major depression is more prevalent among individuals with alcoholism than in the general population. Twin studies have found a moderate degree of genetic correlation for alcohol dependence (AD) and major depression (MD), suggesting the existence of loci that confer susceptibility to both disorders. The aim of the present study was to conduct genome-wide linkage analyses to identify loci and to replicate prior evidence for linkage to MD, and to search for linkage regions that may confer risk to the co-occurrence of depression and alcoholism in a sample of sib-pairs affected with AD. A set of 1020 microsatellite markers (average marker spacing of 4cM) were genotyped in 1289 subjects, which consisted of 473 informative families for analysis of depressive traits and 626 sibling pairs for analysis of symptoms of MD and AD. For univariate linkage results for depression, there were six regions (1q, 2p, 4q, 12q, 13q, and 22q) with multipoint LOD scores in excess of 1.00; the highest peak was on chromosome 4q32.3 near marker D4S2952 (LOD=2.17, p=0.0008) for symptoms of MD. Bivariate linkage analysis of symptoms of MD and AD identified only one region at 22q11.21 with LOD>1, which overlapped with the region for symptoms of MD. Several of these regions replicate previously reported linkage results for major depression and emotion-related traits and events, such as neuroticism and suicide attempts. These identified genomic locations, together with results from prior studies, indicate potential regions of interests that may contain susceptibility loci to the risk of depression among individuals with alcohol dependence.

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

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

Psychiatric syndromes in individuals with chromosome 18 abnormalities

Chromosome 18 abnormalities are associated with a range of physical abnormalities such as short stature and hearing impairments. Psychiatric manifestations have also been observed. This study focuses on the presentations of psychiatric syndromes as they relate to specific chromosomal abnormalities of chromosome 18. Twenty-five subjects (13 with an 18q deletion, 9 with 18p tetrasomy, and 3 with an 18p deletion), were interviewed by psychiatrists (blind to specific chromosomal abnormality) using the DIGS (subjects 18 and older) or KSADS-PL (subjects under 18). A consensus best estimation diagnostic process was employed to determine psychiatric syndromes. Oligonucleotide Array Comparative Genomic Hybridization (Agilent Technologies) was utilized to define specific regions of chromosome 18 that were deleted or duplicated. These data were further analyzed to determine critical regions of the chromosome as they relate to phenotypic manifestations in these subjects. 58.3% of the chromosome 18q- deletion subjects had depressive symptoms, 58.3% had anxiety symptoms, 25% had manic symptoms, and 25% had psychotic symptoms. 66.6% of the chromosome 18p- deletion subjects had anxiety symptoms, and none had depressive, manic, or psychotic symptoms. Fifty percent of the chromosome 18p tetrasomy subjects had anxiety symptoms, 12.5% had psychotic symptoms, and 12.5% had a mood disorder. All three chromosomal disorders were associated with high anxiety rates. Psychotic, manic and depressive disorders were seen mostly in 18q- subjects and this may be helpful in narrowing regions for candidate genes for these psychiatric conditions.

The genetics of major depression: moving beyond the monoamine hypothesis

Efforts to unlock the biology of major depressive disorder (MDD) are proceeding on multiple fronts. In this article, the authors review the current understanding of epidemiological evidence for a heritable component to MDD risk, as well as recent advances in linkage, candidate gene, and genome-wide association analyses of MDD and related disease subtypes and endophenotypes. While monoamine signaling has preoccupied the bulk of scientific investigation to date, nontraditional gene candidates such as PCLO and GRM7 are now emerging and beginning to change the landscape for future human and animal research on depression.

Association study of clock gene (CLOCK) and schizophrenia and mood disorders in the Japanese population

Recently the clock genes have been reported to play some roles in neural transmitter systems, including the dopamine system, as well as to regulate circadian rhythms. Abnormalities in both of these mechanisms are thought to be involved in the pathophysiology of major mental illness such as schizophrenia and mood disorders including bipolar disorder (BP) and major depressive disorder (MDD). Recent genetic studies have reported that CLOCK, one of the clock genes, is associated with these psychiatric disorders. Therefore, we investigated the association between the six tagging SNPs in CLOCK and the risk of these psychiatric disorders in Japanese patients diagnosed with schizophrenia (733 patients), BP (149) and MDD (324), plus 795 Japanese controls. Only one association, with schizophrenia in females, was detected in the haplotype analysis (P = 0.0362). However, this significance did not remain after Bonferroni correction (P = 0.0724). No significant association was found with BP and MDD. In conclusion, we suggest that CLOCK may not play a major role in the pathophysiology of Japanese schizophrenia, BP and MDD patients. However, it will be important to replicate and confirm these findings in other independent studies using large samples.

Genome scan in sibling pairs with juvenile-onset mood disorders: Evidence for linkage to 13q and Xq

Mood disorders (bipolar and depressive disorders) in children and adolescents are associated with significant morbidity and mortality. Twin and family studies, for the most part, indicate higher familiality and heritability for mood disorders that onset in childhood/adolescence than those that onset in adulthood. To identify the genetic contribution to mood disorders that onset in childhood/adolescence, we performed a genome scan on 146 nuclear families from Hungary containing an affected proband and affected siblings. In total, the pedigrees contained 303 affected children: 146 probands, 137 siblings with a first episode of mood disorder before 14.9 years of age, and 20 siblings with onset of their first episode after 14.9 years of age but before the age of 18. The results of the genome scan using 405 microsatellite markers did not provide evidence for linkage at the recommended genome wide significance level for any novel loci. However, markers on two chromosomes, 13q and Xq, provided evidence for linkage in regions previously identified as linked to bipolar disorder in multiple studies. For the marker on chromosome 13q the peak non-parametric multipoint LOD score was at the marker D13S779 (LOD = 1.5, P = 0.004). On chromosome Xq, evidence for linkage was observed across a large region spanning two regions previously linked to bipolar disorder; Xq24 to Xq28, with a peak at marker TTTA062 (LOD 2.10, P = 0.0009) in Xq28. Results for these regions exceed the recommended P-value for a replication study of P < 0.01 and thus provide evidence for these two loci as contributing to mood disorders with juvenile onset.

A high-density SNP genome-wide linkage scan in a large autism extended pedigree

We performed a high-density, single nucleotide polymorphism (SNP), genome-wide scan on a six-generation pedigree from Utah with seven affected males, diagnosed with autism spectrum disorder. Using a two-stage linkage design, we first performed a nonparametric analysis on the entire genome using a 10K SNP chip to identify potential regions of interest. To confirm potentially interesting regions, we eliminated SNPs in high linkage disequilibrium (LD) using a principal components analysis (PCA) method and repeated the linkage results. Three regions met genome-wide significance criteria after controlling for LD: 3q13.2-q13.31 (nonparametric linkage (NPL), 5.58), 3q26.31-q27.3 (NPL, 4.85) and 20q11.21-q13.12 (NPL, 5.56). Two regions met suggestive criteria for significance 7p14.1-p11.22 (NPL, 3.18) and 9p24.3 (NPL, 3.44). All five chromosomal regions are consistent with other published findings. Haplotype sharing results showed that five of the affected subjects shared more than a single chromosomal region of interest with other affected subjects. Although no common autism susceptibility genes were found for all seven autism cases, these results suggest that multiple genetic loci within these regions may contribute to the autism phenotype in this family, and further follow-up of these chromosomal regions is warranted.

Significant evidence for linkage to chromosome 5q13 in a genome-wide scan for asthma in an extended pedigree resource

Asthma is a multifactorial disease with undetermined genetic factors. We performed a genome-wide scan to identify predisposition loci for asthma. The asthma phenotype consisted of physician-confirmed presence or absence of asthma symptoms. We analyzed 81 extended Utah pedigrees ranging from three to six generations, including 742 affected individuals, ranging from 2 to 40 per pedigree. We performed parametric multipoint linkage analyses with dominant and recessive models. Our analysis revealed genome-wide significant evidence of linkage to region 5q13 (log of the odds ratio (LOD)=3.8, recessive model), and suggestive evidence for linkage to region 6p21 (LOD=2.1, dominant model). Both the 5q13 and 6p21 regions indicated in these analyses have been previously identified as regions of interest in other genome-wide scans for asthma-related phenotypes. The evidence of linkage at the 5q13 region represents the first significant evidence for linkage on a genome-wide basis for this locus. Linked pedigrees localize the region to approximately between 92.3-105.5 Mb.

Significant linkage evidence for a predisposition gene for pelvic floor disorders on chromosome 9q21

Predisposition factors for pelvic floor disorders (PFDs), including pelvic organ prolapse (POP), stress urinary incontinence (SUI), urge urinary incontinence (UUI), and hernias, are not well understood. We assessed linkage evidence for PFDs in mostly sister pairs who received treatment for moderate-to-severe POP. We genotyped 70 affected women of European descent from 32 eligible families with at least two affected cases by using the Illumina 1 million single-nucleotide polymorphism (SNP) marker set. Parametric linkage analysis with general dominant and recessive models was performed by the Markov chain Monte Carlo linkage analysis method, MCLINK, and a set of SNPs was formed, from which those in high linkage disequilibrium were eliminated. Significant genome-wide evidence for linkage was identified on chromosome 9q21 with a HLOD score of 3.41 under a recessive model. Seventeen pedigrees (53%) had at least nominal evidence for linkage on a by-pedigree basis at this region. These results provide evidence for a predisposition gene for PFDs on chromosome 9q.

Suggestive linkage on chromosome 2, 8, and 17 for lifetime major depression

It is well established that major depressive disorder (MDD) is partly heritable. We present a genome-wide linkage study aiming to find regions on the genome that influence the vulnerability for MDD. Our sample consists of 110 Australian and 23 Dutch pedigrees with two or more siblings affected with MDD (total N = 278). Linkage analysis was carried out in MERLIN. Three regions showed suggestive linkage signals. The highest LOD-score of 2.1 was found on chromosome 17 at 52.6 cM along with LOD scores of 1.9 and 1.7 on chromosome 8 at 2.7 cM and chromosome 2 at 90.6 cM, respectively. The result on chromosome 8 seems most promising as two previous studies also found linkage in this region, once suggestive and once significant. The linkage peak on chromosome 17 harbors the serotonin transporter gene. In the Australian and Dutch sample, the serotonin transporter length polymorphism did not show evidence for association, thus other genes in this region or other polymorphisms in the serotonin transporter gene might be associated with MDD. Further replication is needed to establish the relevance of our linkage finding on chromosome 2.

A genome-wide scan for Eysenckian personality dimensions in adolescent twin sibships: psychoticism, extraversion, neuroticism, and lie

We report the first genome-wide scan of adolescent personality. We conducted a genome-wide scan to detect linkage for measures of adolescent Psychoticism, Extraversion, Neuroticism, and Lie from the Junior Eysenck Personality Questionnaire. Data are based on 1,280 genotyped Australian adolescent twins and their siblings. The highest linkage peaks were found on chromosomes 16 and 19 for Neuroticism, on chromosomes 1, 7, 10, 13 m, and 18 for Psychoticism, and on chromosomes 2 and 3 for Extraversion.

Convergent functional genomics of genome-wide association data for bipolar disorder: comprehensive identification of candidate genes, pathways and mechanisms

Given the mounting convergent evidence implicating many more genes in complex disorders such as bipolar disorder than the small number identified unambiguously by the first-generation Genome-Wide Association studies (GWAS) to date, there is a strong need for improvements in methodology. One strategy is to include in the next generation GWAS larger numbers of subjects, and/or to pool independent studies into meta-analyses. We propose and provide proof of principle for the use of a complementary approach, convergent functional genomics (CFG), as a way of mining the existing GWAS datasets for signals that are there already, but did not reach significance using a genetics-only approach. With the CFG approach, the integration of genetics with genomics, of human and animal model data, and of multiple independent lines of evidence converging on the same genes offers a way of extracting signal from noise and prioritizing candidates. In essence our analysis is the most comprehensive integration of genetics and functional genomics to date in the field of bipolar disorder, yielding a series of novel (such as Klf12, Aldh1a1, A2bp1, Ak3l1, Rorb, Rora) and previously known (such as Bdnf, Arntl, Gsk3b, Disc1, Nrg1, Htr2a) candidate genes, blood biomarkers, as well as a comprehensive identification of pathways and mechanisms. These become prime targets for hypothesis driven follow-up studies, new drug development and personalized medicine approaches.

Identifying blood biomarkers for mood disorders using convergent functional genomics

There are to date no objective clinical laboratory blood tests for mood disorders. The current reliance on patient self-report of symptom severity and on the clinicians' impression is a rate-limiting step in effective treatment and new drug development. We propose, and provide proof of principle for, an approach to help identify blood biomarkers for mood state. We measured whole-genome gene expression differences in blood samples from subjects with bipolar disorder that had low mood vs those that had high mood at the time of the blood draw, and separately, changes in gene expression in brain and blood of a mouse pharmacogenomic model. We then integrated our human blood gene expression data with animal model gene expression data, human genetic linkage/association data and human postmortem brain data, an approach called convergent functional genomics, as a Bayesian strategy for cross-validating and prioritizing findings. Topping our list of candidate blood biomarker genes we have five genes involved in myelination (Mbp, Edg2, Mag, Pmp22 and Ugt8), and six genes involved in growth factor signaling (Fgfr1, Fzd3, Erbb3, Igfbp4, Igfbp6 and Ptprm). All of these genes have prior evidence of differential expression in human postmortem brains from mood disorder subjects. A predictive score developed based on a panel of 10 top candidate biomarkers (five for high mood and five for low mood) shows sensitivity and specificity for high mood and low mood states, in two independent cohorts. Our studies suggest that blood biomarkers may offer an unexpectedly informative window into brain functioning and disease state.

An exploration of attitudes among black Americans towards psychiatric genetic research

With increasing emphasis on understanding genetic contribution to disease, inclusion of all racial and ethnic groups in molecular genetic research is necessary to ensure parity in distribution of research benefits. Blacks are underrepresented in large-scale genetic studies of psychiatric disorders. In an effort to understand the reasons for the underrepresentation, this study explored black participants' attitudes towards genetic research of psychiatric disorders. Twenty-six adults, the majority of whom were black (n = 18) were recruited from a New York City community to participate in six 90-minute focus groups. This paper reports findings about respondents' understanding of genetics and genetic research, and opinions about psychiatric genetic research. Primary themes revealed participants' perceived lack of knowledge about genetics, concerns about potentially harmful study procedures, and confidentiality surrounding mental illness in families. Participation incentives included provision of treatment or related service, monetary compensation, and reporting of results to participants. These findings suggest that recruitment of subjects into genetic studies should directly address procedures, privacy, benefits and follow-up with results. Further, there is critical need to engage communities with education about genetics and mental illness, and provide opportunities for continued discussion about concerns related to genetic research.

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.

A genome-wide linkage study in families with major depression and co-morbid unexplained swelling

Major depressive disorder (MDD) is a common heritable condition. The diversity of the phenotype coupled with aetiological and genetic heterogeneity present formidable obstacles in the search for causative genetic loci. Studies of large families with many affected individuals, and the selection of well-defined clinical subgroups of depression, are two ways to reduce this complexity. Unexplained swelling symptoms (USS) are common in women and many patients give a strong personal and family history of depression. Co-morbid depression and swelling symptoms define a useful sub-phenotype for investigating genetic factors in depression. We have completed a genome-wide linkage analysis using 371 microsatellite markers in four families where MDD is co-morbid with USS. Of 47 affected individuals, 28 had both MDD and unexplained swelling, 11 had symptoms of swelling alone, and 8 had MDD alone. Parametric marker-specific analysis identified one suggestive locus, D8S260 (LOD = 2.02) and non-parametric multipoint variance component analysis identified a region on 7p (LOD = 2.10). A 47 cM suggestive linkage region on chromosome 14q (identified by both parametric and non-parametric methods) was identified and investigated further with fine-mapping markers but the evidence for linkage to this region decreased with increased marker information content.

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.