Genome-wide scan for genes involved in bipolar affective disorder in 70 European families ascertained through a bipolar type I early-onset proband: supportive evidence for linkage at 3p14

Lipid Biomarker Research in Bipolar Disorder: A Scoping Review of Trends, Challenges, and Future Directions

Bipolar disorder (BD) is a disabling disorder with heterogeneous symptom profiles and trajectories. Like many other neuropsychiatric disorders, clinical decision making related to diagnoses and choice of treatment is based on clinical assessments alone, and risk prediction for treatment success or resistance at an individual level remains sparse. An enormous effort to add biological markers to this risk prediction is ongoing. The role of lipids in normal brain functioning is well established, and several hypotheses about the role of lipids in the pathogenesis of neuropsychiatric disorders, including BD, have been made. The frequent comorbidity between neuropsychiatric disorders and cardiovascular disease, the genetic overlap of risk genes for severe mental disorders and genes involved in lipid regulation, and the lipid-altering effects of antipsychotics and mood stabilizers indicate that lipids could hold promise as biomarkers for neuropsychiatric disorders, including BD. To date, reviews of lipid biomarkers in schizophrenia and major depression have noted caveats for future investigations, while reviews of lipid biomarker research in BD is missing. In the current scoping review, we present a comprehensive overview of trends in previous research on lipid biomarkers in BD. The current literature varies greatly in the phenotypes investigated and study designs, leading to divergent findings. Small sample size; potential confounders related to physical activity, nutritional status, and medication use; and cross-sectional designs were frequently reported limitations. Future research may benefit from pivoting toward utilization of newer laboratory techniques such as lipidomics, but consistent use of study methods across cohorts is also needed.

Psychosocial markers of age at onset in bipolar disorder: a machine learning approach

BACKGROUND

Bipolar disorder is a chronic and severe mental health disorder. Early stratification of individuals into subgroups based on age at onset (AAO) has the potential to inform diagnosis and early intervention. Yet, the psychosocial predictors associated with AAO are unknown.

AIMS

We aim to identify psychosocial factors associated with bipolar disorder AAO.

METHOD

Using data from the Bipolar Disorder Research Network UK, we employed least absolute shrinkage and selection operator regression to identify psychosocial factors associated with bipolar disorder AAO. Twenty-eight factors were entered into our model, with AAO as our outcome measure.

RESULTS

We included 1022 participants with bipolar disorder (μ = 23.0, s.d. ± 9.86) in our model. Six variables predicted an earlier AAO: childhood abuse (β = -0.2855), regular cannabis use in the year before onset (β = -0.2765), death of a close family friend or relative in the 6 months before onset (β = -0.2435), family history of suicide (β = -0.1385), schizotypal personality traits (β = -0.1055) and irritable temperament (β = -0.0685). Five predicted a later AAO: the average number of alcohol units consumed per week in the year before onset (β = 0.1385); birth of a child in the 6 months before onset (β = 0.2755); death of parent, partner, child or sibling in the 6 months before onset (β = 0.3125); seeking work without success for 1 month or more in the 6 months before onset (β = 0.3505) and a major financial crisis in the 6 months before onset (β = 0.4575).

CONCLUSIONS

The identified predictor variables have the potential to help stratify high-risk individuals into likely AAO groups, to inform treatment provision and early intervention.

CADPS functional mutations in patients with bipolar disorder increase the sensitivity to stress

Bipolar disorder is a severe and chronic psychiatric disease resulting from a combination of genetic and environmental risk factors. Here, we identified a significant higher mutation rate in a gene encoding the calcium-dependent activator protein for secretion (CADPS) in 132 individuals with bipolar disorder, when compared to 184 unaffected controls or to 21,070 non-psychiatric and non-Finnish European subjects from the Exome Aggregation Consortium. We found that most of these variants resulted either in a lower abundance or a partial impairment in one of the basic functions of CADPS in regulating neuronal exocytosis, synaptic plasticity and vesicular transporter-dependent uptake of catecholamines. Heterozygous mutant mice for Cadps^+/- revealed that a decreased level of CADPS leads to manic-like behaviours, changes in BDNF level and a hypersensitivity to stress. This was consistent with more childhood trauma reported in families with mutation in CADPS, and more specifically in mutated individuals. Furthermore, hyperactivity observed in mutant animals was rescued by the mood-stabilizing drug lithium. Overall, our results suggest that dysfunction in calcium-dependent vesicular exocytosis may increase the sensitivity to environmental stressors enhancing the risk of developing bipolar disorder.

Bipolar disorder: Trimodal age-at-onset distribution

OBJECTIVE

Bipolar disorder (BD) is a chronic mental health disorder with significant morbidity and mortality. Age at onset (AAO) may be a key variable in delineating more homogeneous subgroups of BD patients. However, no known research has systematically assessed how BD age-at-onset subgroups should be defined.

METHODS

We systematically searched the following databases: Cochrane Central Register of Controlled Trials, PsycINFO, MEDLINE, Embase, CINAHL, Scopus, Proquest Dissertations and Theses, Google Scholar and BIOSIS Previews. Original quantitative English language studies investigating AAO in BD were sought.

RESULTS

A total of 9454 unique publications were identified. Twenty-one of these were included in data analysis (n = 22981 BD participants). Fourteen of these studies (67%, n = 13626 participants) found a trimodal AAO distribution: early-onset (µ = 17.3, σ = 1.19, 45% of sample), mid-onset (µ = 26.0, σ = 1.72, 35%), and late-onset (µ = 41.9, σ = 6.16, 20%). Five studies (24%, n = 1422 participants) described a bimodal AAO distribution: early-onset (µ = 24.3, σ = 6.57, 66% of sample) and late-onset (µ = 46.3, σ = 14.15, 34%). Two studies investigated cohort effects on BD AAO and found that when the sample was not split by cohort, a trimodal AAO was the winning model, but when separated by cohort a bimodal distribution fit the data better.

CONCLUSIONS

We propose that the field conceptualises bipolar disorder age-at-onset subgroups as referring broadly to life stages. Demarcating BD AAO groups can inform treatment and provide a framework for future research to continue to investigate potential mechanisms of disease onset.

Genome-wide association study of early-onset bipolar I disorder in the Han Taiwanese population

The search for susceptibility genes underlying the heterogeneous bipolar disorder has been inconclusive, often with irreproducible results. There is a hope that narrowing the phenotypes will increase the power of genetic analysis. Early-onset bipolar disorder is thought to be a genetically homogeneous subtype with greater symptom severity. We conducted a genome-wide association study (GWAS) for this subtype in bipolar I (BPI) disorder. Study participants included 1779 patients of Han Chinese descent with BPI disorder recruited by the Taiwan Bipolar Consortium. We conducted phenotype assessment using the Chinese version of the Schedules for Clinical Assessment in Neuropsychiatry and prepared a life chart with graphic depiction of lifetime clinical course for each of the BPI patient recruited. The assessment of onset age was based on this life chart with early onset defined as ≤20 years of age. We performed GWAS in a discovery group of 516 early-onset and 790 non-early-onset BPI patients, followed by a replication study in an independent group of 153 early-onset and 320 non-early-onset BPI patients and a meta-analysis with these two groups. The SNP rs11127876, located in the intron of CADM2, showed association with early-onset BPI in the discovery cohort (P = 7.04 × 10^-8) and in the test of replication (P = 0.0354). After meta-analysis, this SNP was demonstrated to be a new genetic locus in CADM2 gene associated with early-onset BPI disorder (P = 5.19 × 10^-8).

Age at onset in bipolar disorder: Investigation of the role of TaqIA polymorphism of DRD2 gene in a Sardinian sample

Bipolar disorder (BD) is a highly heterogeneous and heritable psychiatric illness. Age at onset has been shown to be a powerful tool for dissecting both the phenotypic and genetic complexity of BD. In this article, we present findings from an association study between the DRD2 TaqIA polymorphism and age at onset, showing that both alleles and genotypes at this locus associate with early onset BD.

Genome-wide study of immune biomarkers in cerebrospinal fluid and serum from patients with bipolar disorder and controls

Bipolar disorder is a common, chronic psychiatric disorder. Despite high heritability, there is a paucity of identified genetic risk factors. Immune biomarkers are under more direct genetic influence than bipolar disorder. To explore the genetic associations with immune biomarker levels in cerebrospinal fluid (CSF) and blood serum which previously showed differences in bipolar disorder, we performed a study involving 291 individuals (184 bipolar disorder patients and 107 controls). The biomarkers assayed in both CSF and serum were: chitinase-3-like protein-1 (YKL-40), monocyte chemoattractant protein-1 (MCP-1), soluble cluster of differentiation (sCD14), tissue inhibitor of metalloproteinases-1 and 2 (TIMP-1 and TIMP-2). C-reactive protein (CRP) was only quantified in serum, and interleukin 8 (IL-8) measures were only available in CSF. Genome-wide association studies were conducted using PLINK for each of three genotyping waves and incorporated covariates for population substructure, age, sex, and body mass index (BMI). Results were combined by meta-analysis. Genome-wide significant associations were detected for all biomarkers except TIMP-1 and TIMP-2 in CSF. The strongest association in CSF was found for markers within the CNTNAP5 gene with YKL-40 (rs150248456, P = 2.84 × 10^-10). The strongest association in serum was also for YKL-40 but localized to the FANCI gene (rs188263039, P = 5.80 × 10^-26). This study revealed numerous biologically plausible genetic associations with immune biomarkers in CSF and blood serum. Importantly, the genetic variants regulating immune biomarker levels in CSF and blood serum differ. These results extend our knowledge of how biomarkers showing alterations in bipolar disorder are genetically regulated.

Genome-wide QTL analysis for anxiety trait in bipolar disorder type I

BACKGROUND

Genetic studies have been consistent that bipolar disorder type I (BPI) runs in families and that this familial aggregation is strongly influenced by genes. In a preliminary study, we proved that anxiety trait meets endophenotype criteria for BPI.

METHODS

We assessed 619 individuals from the Central Valley of Costa Rica (CVCR) who have received evaluation for anxiety following the same methodological procedure used for the initial pilot study. Our goal was to conduct a multipoint quantitative trait linkage analysis to identify quantitative trait loci (QTLs) related to anxiety trait in subjects with BPI. We conducted the statistical analyses using Quantitative Trait Loci method (Variance-components models), implemented in Sequential Oligogenic Linkage Analysis Routines (SOLAR), using 5606 single nucleotide polymorphism (SNPs).

RESULTS

We identified a suggestive linkage signal with a LOD score of 2.01 at chromosome 2 (2q13-q14).

LIMITATIONS

Since confounding factors such as substance abuse, medical illness and medication history were not assessed in our study, these conclusions should be taken as preliminary.

CONCLUSIONS

We conclude that region 2q13-q14 may harbor a candidate gene(s) with an important role in the pathophysiology of BPI and anxiety.

The genetics of human personality

Personality traits are the relatively enduring patterns of thoughts, feelings and behaviors that reflect the tendency to respond in certain ways under certain circumstances. Twin and family studies have showed that personality traits are moderately heritable, and can predict various lifetime outcomes, including psychopathology. The Research Domain Criteria characterizes psychiatric diseases as extremes of normal tendencies, including specific personality traits. This implies that heritable variation in personality traits, such as neuroticism, would share a common genetic basis with psychiatric diseases, such as major depressive disorder. Despite considerable efforts over the past several decades, the genetic variants that influence personality are only beginning to be identified. We review these recent and increasingly rapid developments, which focus on the assessment of personality via several commonly used personality questionnaires in healthy human subjects. Study designs covered include twin, linkage, candidate gene association studies, genome-wide association studies and polygenic analyses. Findings from genetic studies of personality have furthered our understanding about the genetic etiology of personality, which, like neuropsychiatric diseases themselves, is highly polygenic. Polygenic analyses have showed genetic correlations between personality and psychopathology, confirming that genetic studies of personality can help to elucidate the etiology of several neuropsychiatric diseases.

Modeling prior information of common genetic variants improves gene discovery for neuroticism

Neuroticism reflects emotional instability, and is related to various mental and physical health issues. However, the majority of genetic variants associated with neuroticism remain unclear. Inconsistent genetic variants identified by different genome-wide association studies (GWAS) may be attributable to low statistical power. We proposed a novel framework to improve the power for gene discovery by incorporating prior information of single nucleotide polymorphisms (SNPs) and combining two relevant existing tools, relative enrichment score (RES) and conditional false discovery rate (FDR). Here, SNP's conditional FDR was estimated given its RES based on SNP prior information including linkage disequilibrium (LD)-weighted genic annotation scores, total LD scores and heterozygosity. A known significant locus in chromosome 8p was excluded before estimating FDR due to long-range LD structure. Only one significant LD-independent SNP was detected by analyses of unconditional FDR and traditional GWAS in the discovery sample (N = 59 225), and notably four additional SNPs by conditional FDR. Three of the five SNPs, all identified by conditional FDR, were replicated (P < 0.05) in an independent sample (N = 170 911). These three SNPs are located in intronic regions of CADM2, LINGO2 and EP300 which have been reported to be associated with autism, Parkinson's disease and schizophrenia, respectively. Our approach using a combination of RES and conditional FDR improved power of traditional GWAS for gene discovery providing a useful framework for the analysis of GWAS summary statistics by utilizing SNP prior information, and helping to elucidate the links between neuroticism and complex diseases from a genetic perspective.

Genetic Risk Score Analysis in Early-Onset Bipolar Disorder

OBJECTIVE

In this study, we performed a candidate genetic risk score (GRS) analysis of early-onset bipolar disorder (BD).

METHODS

Treatment of Early Age Mania (TEAM) study enrollment and sample collection took place from 2003 to 2008. Mayo Clinic Bipolar Biobank samples were collected from 2009 to 2013. Genotyping and analyses for the present study took place from 2013 to 2014. The diagnosis of BD was based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria. Eight single-nucleotide polymorphisms (SNPs), previously reported in genome-wide association studies to be associated with BD, were chosen for GRS analysis in early-onset bipolar disease. These SNPs map to 3 genes: CACNA1C (calcium channel, voltage-dependent, L type, alpha 1C subunit), ANK3 (ankyrin-3, node of Ranvier [ankyrin G]), and ODZ4 (teneurin transmembrane protein 4 [formerly "odz, odd Oz/10-m homolog 4 {Drosophila}, ODZ4"]). The 8 candidate SNPs were genotyped in patients from the TEAM study (n = 69); adult patients with BD (n = 732), including a subset with early-onset illness (n = 192); and healthy controls (n = 776). GRS analyses were performed to compare early-onset cases with controls. In addition, associations of early-onset BD with individual SNPs and haplotypes were explored.

RESULTS

GRS analysis revealed associations of the risk score with early-onset BD (P = .01). Gene-level haplotype analysis comparing TEAM patients with controls suggested association of early-onset BD with a CACNA1C haplotype (global test, P = .01). At the level of individual SNPs, comparison of TEAM cases with healthy controls provided nominally significant evidence for association of SNP rs10848632 in CACNA1C with early-onset BD (P = .017), which did not remain significant after correction for multiple comparisons.

CONCLUSIONS

These preliminary analyses suggest that previously identified BD risk loci, especially CACNA1C, have a role in early-onset BD, possibly with stronger effects than for late-onset BD.

Clinical correlates of age at onset distribution in bipolar disorder: a comparison between diagnostic subgroups

Background

Admixture analysis of age at onset (AAO) has helped delineating the clinical profile of early onset (EO) bipolar disorder (BD). However, there is scarce evidence comparing the distributional properties of AAO as well as the clinical features of EO BD type 1 (BD1) with EO BD type 2 (BD2). To this end, we studied 515 BD patients (224 BD1, 279 BD2, and 12 BD not otherwise specified [NOS]) diagnosed according to DSM-IV-TR criteria.

Methods

AAO was defined as the first reliably diagnosed hypo/manic or depressive episode according to diagnostic criteria. We used normal distribution mixture analysis to identify subgroups of patients according to AAO. Models were chosen according to the Schwarz’s Bayesian information criteria (BIC). Clinical correlates of EO were analysed using univariate tests and multivariate logistic regression models.

Results

A two normal components model best fitted the observed distribution of AAO in BD1 (BIC = −1599.3), BD2 (BIC = −2158.4), and in the whole sample (BIC = −3854.9). A higher number of EO BD2 patients had a depression-(hypo)mania-free interval (DMI) course, while a higher rate of (hypo)mania-depression-free interval (MDI) course was found in EO BD1. EO BD2 had also a higher rate of comorbidity with alcohol dependence compared to EO BD1. The latter finding was confirmed by multivariate logistic regression analysis.

Conclusions

In conclusion, both BD1 and BD2 had bimodal AAO distributions, but EO subgroups had a diagnostic-specific clinical delineation.

A genome wide association study suggests the association of muskelin with early onset bipolar disorder: Implications for a GABAergic epileptogenic neurogenesis model

BACKGROUND

Although multiple genes have been implicated in bipolar disorder (BD), they explain only a small proportion of its heritability. Identifying additional BD risk variants may be impaired by phenotypic heterogeneity, which is usually not taken into account in genome-wide association studies (GWAS). BD with early age at onset is a more homogeneous familial form of the disorder associated with greater symptom severity.

METHODS

We conducted a GWAS of early-onset BD (onset of mania/hypomania ≤19 years old) in a discovery sample of 419 cases and 1034 controls and a replication sample of 181 cases and 777 controls. These two samples were meta-analyzed, followed by replication of one signal in a third independent sample of 141 cases and 746 controls.

RESULTS

No single nucleotide polymorphism (SNP) associations were genome-wide significant in the discovery sample. Of the top 15 SNPs in the discovery analysis, rs114034759 in the muskelin (MKLN1) gene was nominally significant in the replication analysis, and was among the top associations in the meta-analysis (p=2.63E-06, OR=1.9). In the third sample, this SNP was again associated with early-onset BD (p=0.036, OR=1.6). Gene expression analysis showed that the rs114034759 risk allele is associated with decreased hippocampal MKLN1 expression.

LIMITATIONS

The sample sizes of the early-onset BD subgroups were relatively small.

CONCLUSIONS

Our results suggest MKLN1 is associated with early-onset BD. MKLN1 regulates cellular trafficking of GABA-A receptors, which is involved in synaptic transmission and plasticity, and is implicated in the mechanism of action of a group of antiepileptic mood stabilizers. These results therefore indicate that GABAergic neurotransmission may be implicated in early-onset BD. We propose that an increase in GABA-A receptors in the hippocampus in BD patients due to lower MKLN1 expression might increase the excitability during the GABA-excited early phase of young neurons, leading to an increased risk of developing a manic/hypomanic episode. Further studies are needed to test this model.

A Rare Variant in CACNA1D Segregates with 7 Bipolar I Disorder Cases in a Large Pedigree

Whole-genome sequencing was performed on 3 bipolar I disorder (BPI) cases from a multiplex pedigree of European ancestry with 7 BPI cases. Within CACNA1D, a gene implicated by genome-wide association studies, a G to C nucleotide transversion at 53,835,340 base pairs (bps) was found predicting the substitution of proline for alanine at amino acid position 1751 (A1751P). Using Sanger sequencing, the DNA variant was shown to co-segregate with the remaining 4 BPI cases within the pedigree. A high-resolution DNA denaturing curve method was then used to screen for the presence of the A1751P change in 4,150 BPI cases from the NIMH Genetics Initiative. The A1751P variant was found in 4 BPI cases. A second variant within exon 43, a C to T nucleotide transition, was found in 1 case at 53,835,355 bps, predicting the substitution of tryptophan for arginine at amino acid position 1771 (R1771W). In the NHLBI Exome Sequencing Project database, the heterozygous A1751P variant was present in 3 of 4,300 subjects of European ancestry, and the R1771W change was not present in any subject. Given the rarity of these variants, large-scale case/control rare variant sequencing studies will be required for definitive conclusions.

A significant risk locus on 19q13 for bipolar disorder identified using a combined genome-wide linkage and copy number variation analysis

Background

The genetic background to bipolar disorder (BPD) has been attributed to different genetic and genomic risk factors. In the present study we hypothesized that inherited copy number variations (CNVs) contribute to susceptibility of BPD. We screened 637 BP-pedigrees from the NIMH Genetic Initiative and gave priority to 46 pedigrees. In this subsample we performed parametric and non-parametric genome-wide linkage analyses using ~21,000 SNP-markers. We developed an algorithm to test for linkage restricted to regions with CNVs that are shared within and across families.

Results

For the combined CNV and linkage analysis, one region on 19q13 survived correction for multiple comparisons and replicates a previous BPD risk locus. The shared CNV map to the pregnancy-specific glycoprotein (PSG) gene, a gene-family not previously implicated in BPD etiology. Two SNPs in the shared CNV are likely transcription factor binding sites and are linked to expression of an F-box binding gene, a key regulator of neuronal pathways suggested to be involved in BPD etiology.

Conclusions

Our CNV-weighted linkage approach identifies a risk locus for BPD on 19q13 and forms a useful tool to future studies to unravel part of the genetic vulnerability to BPD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13040-015-0076-y) contains supplementary material, which is available to authorized users.

The genetics of early-onset bipolar disorder: A systematic review

BACKGROUND

Early-onset bipolar disorder has been associated with a significantly worse prognosis than late-onset BD and has been hypothesized to be a genetically homogenous subset of BD. A sizeable number of studies have investigated early-onset BD through linkage-analyses, candidate-gene association studies, genome-wide association studies (GWAS), and analyses of copy number variants (CNVs), but this literature has not yet been reviewed.

METHODS

A systematic review was conducted using the PubMed database on articles published online before January 15, 2015 and after 1990. Separate searches were made for linkage studies, candidate gene-association studies, GWAS, and studies on CNVs.

RESULTS

Seventy-three studies were included in our review. There is a lack of robust positive findings on the genetics of early-onset BD in any major molecular genetics method.

LIMITATIONS

Early-onset populations were quite small in some studies. Variance in study methods hindered efforts to interpret results or conduct meta-analysis.

CONCLUSIONS

The field is still at an early phase for research on early-onset BD. The largely null findings mirror the results of most genetics research on BD. Although most studies were underpowered, the null findings could mean that early-onset BD may not be as genetically homogenous as has been hypothesized or even that early-onset BD does not differ genetically from adult-onset BD. Nevertheless, clinically the probabilistic developmental risk trajectories associated with early-onset that may not be primarily genetically determined continued to warrant scrutiny. Future research should dramatically expand sample sizes, use atheoretical research methods like GWAS, and standardize methods.

Association of brain-derived neurotrophic factor (BDNF) Val66Met polymorphism with early-onset bipolar disorder

OBJECTIVES

Brain-derived neurotrophic factor (BDNF) Val66Met (rs6265) functional polymorphism has been implicated in early-onset bipolar disorder. However, results of studies are inconsistent. We aimed to further explore this association.

METHODS

DNA samples from the Treatment of Early Age Mania (TEAM) and Mayo Clinic Bipolar Disorder Biobank were investigated for association of rs6265 with early-onset bipolar disorder. Bipolar cases were classified as early onset if the first manic or depressive episode occurred at age ≤19 years (versus adult-onset cases at age >19 years). After quality control, 69 TEAM early-onset bipolar disorder cases, 725 Mayo Clinic bipolar disorder cases (including 189 early-onset cases), and 764 controls were included in the analysis of association, assessed with logistic regression assuming log-additive allele effects.

RESULTS

Comparison of TEAM cases with controls suggested association of early-onset bipolar disorder with the rs6265 minor allele [odds ratio (OR) = 1.55, p = 0.04]. Although comparison of early-onset adult bipolar disorder cases from the Mayo Clinic versus controls was not statistically significant, the OR estimate indicated the same direction of effect (OR = 1.21, p = 0.19). When the early-onset TEAM and Mayo Clinic early-onset adult groups were combined and compared with the control group, the association of the minor allele rs6265 was statistically significant (OR = 1.30, p = 0.04).

CONCLUSIONS

These preliminary analyses of a relatively small sample with early-onset bipolar disorder are suggestive that functional variation in BDNF is implicated in bipolar disorder risk and may have a more significant role in early-onset expression of the disorder.

Meta-analysis of Genome-wide Association Studies for Neuroticism, and the Polygenic Association With Major Depressive Disorder

IMPORTANCE

Neuroticism is a pervasive risk factor for psychiatric conditions. It genetically overlaps with major depressive disorder (MDD) and is therefore an important phenotype for psychiatric genetics. The Genetics of Personality Consortium has created a resource for genome-wide association analyses of personality traits in more than 63,000 participants (including MDD cases).

OBJECTIVES

To identify genetic variants associated with neuroticism by performing a meta-analysis of genome-wide association results based on 1000 Genomes imputation; to evaluate whether common genetic variants as assessed by single-nucleotide polymorphisms (SNPs) explain variation in neuroticism by estimating SNP-based heritability; and to examine whether SNPs that predict neuroticism also predict MDD.

DESIGN, SETTING, AND PARTICIPANTS

Genome-wide association meta-analysis of 30 cohorts with genome-wide genotype, personality, and MDD data from the Genetics of Personality Consortium. The study included 63,661 participants from 29 discovery cohorts and 9786 participants from a replication cohort. Participants came from Europe, the United States, or Australia. Analyses were conducted between 2012 and 2014.

MAIN OUTCOMES AND MEASURES

Neuroticism scores harmonized across all 29 discovery cohorts by item response theory analysis, and clinical MDD case-control status in 2 of the cohorts.

RESULTS

A genome-wide significant SNP was found on 3p14 in MAGI1 (rs35855737; P = 9.26 × 10-9 in the discovery meta-analysis). This association was not replicated (P = .32), but the SNP was still genome-wide significant in the meta-analysis of all 30 cohorts (P = 2.38 × 10-8). Common genetic variants explain 15% of the variance in neuroticism. Polygenic scores based on the meta-analysis of neuroticism in 27 cohorts significantly predicted neuroticism (1.09 × 10-12 < P < .05) and MDD (4.02 × 10-9 < P < .05) in the 2 other cohorts.

CONCLUSIONS AND RELEVANCE

This study identifies a novel locus for neuroticism. The variant is located in a known gene that has been associated with bipolar disorder and schizophrenia in previous studies. In addition, the study shows that neuroticism is influenced by many genetic variants of small effect that are either common or tagged by common variants. These genetic variants also influence MDD. Future studies should confirm the role of the MAGI1 locus for neuroticism and further investigate the association of MAGI1 and the polygenic association to a range of other psychiatric disorders that are phenotypically correlated with neuroticism.

A genome-wide linkage scan of bipolar disorder in Latino families identifies susceptibility loci at 8q24 and 14q32

A genome-wide nonparametric linkage screen was performed to localize Bipolar Disorder (BP) susceptibility loci in a sample of 3757 individuals of Latino ancestry. The sample included 963 individuals with BP phenotype (704 relative pairs) from 686 families recruited from the US, Mexico, Costa Rica, and Guatemala. Non-parametric analyses were performed over a 5 cM grid with an average genetic coverage of 0.67 cM. Multipoint analyses were conducted across the genome using non-parametric Kong & Cox LOD scores along with Sall statistics for all relative pairs. Suggestive and significant genome-wide thresholds were calculated based on 1000 simulations. Single-marker association tests in the presence of linkage were performed assuming a multiplicative model with a population prevalence of 2%. We identified two genome-wide significant susceptibly loci for BP at 8q24 and 14q32, and a third suggestive locus at 2q13-q14. Within these three linkage regions, the top associated single marker (rs1847694, P = 2.40 × 10(-5)) is located 195 Kb upstream of DPP10 in Chromosome 2. DPP10 is prominently expressed in brain neuronal populations, where it has been shown to bind and regulate Kv4-mediated A-type potassium channels. Taken together, these results provide additional evidence that 8q24, 14q32, and 2q13-q14 are susceptibly loci for BP and these regions may be involved in the pathogenesis of BP in the Latino population.

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.

Allelic association, DNA resequencing and copy number variation at the metabotropic glutamate receptor GRM7 gene locus in bipolar disorder

Genetic markers at the GRM7 gene have shown allelic association with bipolar disorder (BP) in several case-control samples including our own sample. In this report, we present results of resequencing the GRM7 gene in 32 bipolar samples and 32 random controls selected from 553 bipolar cases and 547 control samples (UCL1). Novel and potential etiological base pair changes discovered by resequencing were genotyped in the entire UCL case-control sample. We also report on the association between GRM7 and BP in a second sample of 593 patients and 642 controls (UCL2). The three most significantly associated SNPs in the original UCL1 BP GWAS sample were genotyped in the UCL2 sample, of which none were associated. After combining the genotype data for the two samples only two (rs1508724 and rs6769814) of the original three SNP markers remained significantly associated with BP. DNA sequencing revealed mutations in three cases which were absent in control subjects. A 3'-UTR SNP rs56173829 was found to be significantly associated with BP in the whole UCL sample (P = 0.035; OR = 0.482), the rare allele being less common in cases compared to controls. Bioinformatic analyses predicted a change in the centroid secondary structure of RNA and alterations in the miRNA binding sites for the mutated base of rs56173829. We also validated two deletions and a duplication within GRM7 using quantitative-PCR which provides further support for the pre-existing evidence that copy number variants at GRM7 may have a role in the etiology of BP.

Relationship between clinical features and inflammation-related monocyte gene expression in bipolar disorder - towards a better understanding of psychoimmunological interactions

OBJECTIVES

Existing and previously published datasets were examined for associations between illness and treatment characteristics and monocyte pro-inflammatory gene expression in patients with bipolar disorder (BD). We hypothesized a priori that increased monocyte pro-inflammatory gene expression would be found more frequently in patients with a lifetime history of psychotic symptoms.

METHODS

Monocyte quantitative polymerase chain reaction and symptom data from 64 patients with BD were collected from three Dutch studies. Regression analyses were performed to analyze the various associations between pro-inflammatory gene expression and clinical features, from which feature-expression heat maps were drawn.

RESULTS

No associations were found between pro-inflammatory gene expression and lifetime psychotic symptoms, whereas a positive association was identified between subcluster 2 genes and manic symptoms. For several subcluster 1a genes, a negative association was found with age at onset. For most subcluster 2 genes, a positive association was found with the duration of illness. Current use of antidepressants and of anti-epileptic agents was associated with subcluster 2 gene expression, and current use of lithium and antipsychotic agents with subcluster 1a gene expression.

CONCLUSIONS

Our hypothesis that lifetime psychotic features would be associated with pro-inflammatory monocyte gene expression was not confirmed. In an explorative analysis we found: (i) a possible relationship between pro-inflammatory gene expression and manic symptomatology; (ii) a differential immune activation related to age at onset and duration of illness; and (iii) support for the concept of an immune suppressive action of some of the mood-regulating medications.

Family with sequence similarity 107: A family of stress responsive small proteins with diverse functions in cancer and the nervous system (Review)

Under conditions of acute stress, rapid adaptation is crucial for maximizing biological survival. The responses to environmental stress are often complex, involving numerous genes and integrating events at the cellular and organismal levels. The heat shock proteins (HSPs) are a family of highly conserved proteins that play critical roles in maintaining cell homeostasis and protecting cells under chronic and acute stress conditions. The genes for these stress-responding proteins are widely distributed in organisms, tissues and cells. HSPs participate in a variety of physiological processes and are associated with various types of disease. In this review, we focused on family with sequence similarity 107 (FAM107), a novel unique protein family that exhibits functional similarity with HSPs during the cellular stress response. This review aimed to summarize the biological properties of FAM107 in cancer and the nervous system.

Assessment of Response to Lithium Maintenance Treatment in Bipolar Disorder: A Consortium on Lithium Genetics (ConLiGen) Report

OBJECTIVE

The assessment of response to lithium maintenance treatment in bipolar disorder (BD) is complicated by variable length of treatment, unpredictable clinical course, and often inconsistent compliance. Prospective and retrospective methods of assessment of lithium response have been proposed in the literature. In this study we report the key phenotypic measures of the "Retrospective Criteria of Long-Term Treatment Response in Research Subjects with Bipolar Disorder" scale currently used in the Consortium on Lithium Genetics (ConLiGen) study.

MATERIALS AND METHODS

Twenty-nine ConLiGen sites took part in a two-stage case-vignette rating procedure to examine inter-rater agreement [Kappa (κ)] and reliability [intra-class correlation coefficient (ICC)] of lithium response. Annotated first-round vignettes and rating guidelines were circulated to expert research clinicians for training purposes between the two stages. Further, we analyzed the distributional properties of the treatment response scores available for 1,308 patients using mixture modeling.

RESULTS

Substantial and moderate agreement was shown across sites in the first and second sets of vignettes (κ = 0.66 and κ = 0.54, respectively), without significant improvement from training. However, definition of response using the A score as a quantitative trait and selecting cases with B criteria of 4 or less showed an improvement between the two stages (ICC1 = 0.71 and ICC2 = 0.75, respectively). Mixture modeling of score distribution indicated three subpopulations (full responders, partial responders, non responders).

CONCLUSIONS

We identified two definitions of lithium response, one dichotomous and the other continuous, with moderate to substantial inter-rater agreement and reliability. Accurate phenotypic measurement of lithium response is crucial for the ongoing ConLiGen pharmacogenomic study.

[Early onset bipolar disorder: validation from admixture analyses and biomarkers]

OBJECTIVES

Bipolar affective disorder (BD) is a multifactorial disorder with heterogeneous clinical presentations, in particular according to age at onset (AAO). The relevance of such an indicator has been discussed as a potential specifier in future nosographical classification.

METHOD

We summarize available evidence of admixture analyses and biomarkers in early onset BD.

RESULTS

Numerous clinical arguments have led us to conclude that the early onset BD subgroup is clinically homogeneous, with particular, recurrent, and severe characteristics.Eight admixture studies have demonstrated the existence of 3 subgroups of patients with BD according to AAO (early, intermediate, and late AAO), with 2 cut-off points of 21 (21.33) [SD 1.41]) and 35 years (34.67 [SD 5.52]). Differential clinical features and outcome measures characterize the early onset subgroup: higher rate of suicide attempts, rapid cycling, alcohol and drugs misuse, psychotic symptoms, and comorbid anxiety disorders. This may partially explain the delayed diagnosis and late initiation of mood stabilizers. Genetic, biological, imaging, and cognitive arguments may be considered as potential markers in providing external validity of the existence of this early onset subgroup. Implementation of AAO in the algorithms of treatment may be discussed, although the level of proof for focused medication strategies remains to be consolidated.

CONCLUSION

Given the high frequency (44.80%) of early onset BD, awareness of clinicians should be stimulated to provide an early and accurate detection, preventive strategies, and possibly specific treatments.The forthcoming DSM-5 should include AAO as a specifier, given its relevance for course and outcome.

Long-term cortisol in bipolar disorder: associations with age of onset and psychiatric co-morbidity

INTRODUCTION

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is hypothesized to play a role in the pathogenesis of bipolar disorder (BD). Conflicting results have been reported when saliva or serum was used to measure cortisol levels. A recently developed method is to measure cortisol in scalp hair, with 1cm of scalp hair representing 1 month. We studied whether there are differences in long-term hair cortisol levels between BD patients and healthy individuals and whether there are associations between hair cortisol and disease characteristics.

METHODS

Hair samples were collected in 100 BD patients and 195 healthy controls. Long-term cortisol levels were determined in 3 cm hair segments. Saliva samples were collected on two consecutive evenings. Documented disease characteristics were disease state, age of onset and psychiatric co-morbidity.

RESULTS

Hair cortisol levels were not statistically different in BD patients compared to healthy controls (p=0.233) and were not associated with the disease state at the moment of sample collection (p=0.978). In the subgroup of patients with age of onset ≥ 30 years, hair cortisol levels were significantly elevated compared to the subgroup with age of onset <30 years and to healthy controls (p=0.004). Psychiatric co-morbidity was associated with elevated cortisol levels (44.87 versus 31.41 pg/mg hair; p=0.021), with the exclusion of panic disorder, which was associated with decreased cortisol levels (22.13 versus 34.67 pg/mg hair; p=0.019).

CONCLUSIONS

Elevated long-term cortisol levels might play a role in a subgroup of patients with BD. There may be differences in pathogenesis of younger and older onset BD suggesting two different disease entities.

Genetic heterogeneity according to age at onset in bipolar disorder: a combined positional cloning and candidate gene approach

This study is the first that formally tests for genetic heterogeneity of bipolar disorder (BD) according to age at onset (AAO) sub-groups by combining positional cloning and candidate gene approaches. Our previous genome-wide linkage-scan identified five genomic regions linked to early-onset form of BD. The present study uses association analysis to test genetic heterogeneity of candidate genes located in these five regions in a sample of 443 unrelated bipolar patients and 1,731 controls. The study involved the following steps: (1) test of heterogeneity by comparing early-onset BD patients versus later-onset BD patients; and (2) for significant results in step 1, comparison of early-onset BD patients and later-onset BD patients separately to controls. Two types of analyses were used: the single SNP test and the gene-based association test. We provide evidence for genetic heterogeneity within the ADRB2 (beta-2adrenoreceptor) gene region that is specifically associated with the early onset form of BD with an OR of 1.8. Unfortunately, the genotyping coverage of ADRB2 in the Wellcome Trust Case Control Consortium sample meant undermined our efforts to undertake a replication. However, as the ADRB2 gene product directly interacts with the CACNA1C gene product, and is known to be implicated in BD susceptibility, we conclude that further exploration of the relationships between ADRB2 and BD needs to be undertaken.

A new mouse model for mania shares genetic correlates with human bipolar disorder

Bipolar disorder (BPD) is a debilitating heritable psychiatric disorder. Contemporary rodent models for the manic pole of BPD have primarily utilized either single locus transgenics or treatment with psychostimulants. Our lab recently characterized a mouse strain termed Madison (MSN) that naturally displays a manic phenotype, exhibiting elevated locomotor activity, increased sexual behavior, and higher forced swimming relative to control strains. Lithium chloride and olanzapine treatments attenuate this phenotype. In this study, we replicated our locomotor activity experiment, showing that MSN mice display generationally-stable mania relative to their outbred ancestral strain, hsd:ICR (ICR). We then performed a gene expression microarray experiment to compare hippocampus of MSN and ICR mice. We found dysregulation of multiple transcripts whose human orthologs are associated with BPD and other psychiatric disorders including schizophrenia and ADHD, including: Epor, Smarca4, Cmklr1, Cat, Tac1, Npsr1, Fhit, and P2rx7. RT-qPCR confirmed dysregulation for all of seven transcripts tested. Using a novel genome enrichment algorithm, we found enrichment in genome regions homologous to human loci implicated in BPD in replicated linkage studies including homologs of human cytobands 1p36, 3p14, 3q29, 6p21–22, 12q24, 16q24, and 17q25. Using a functional network analysis, we found dysregulation of a gene system related to chromatin packaging, a result convergent with recent human findings on BPD. Our findings suggest that MSN mice represent a polygenic model for the manic pole of BPD showing much of the genetic systems complexity of the corresponding human disorder. Further, the high degree of convergence between our findings and the human literature on BPD brings up novel questions about evolution by analogy in mammalian genomes.

MAGI1 copy number variation in bipolar affective disorder and schizophrenia

BACKGROUND

Bipolar affective disorder (BPAD) and schizophrenia (SZ) are devastating psychiatric disorders that each affect about 1% of the population worldwide. Identification of new drug targets is an important step toward better treatment of these poorly understood diseases.

METHODS

Genome-wide copy number variation (CNV) was assessed and variants were ranked by co-occurrence with disease in 48 BPAD families. Additional support for involvement of the highest-ranking CNV from the family-based analysis in psychiatric disease was obtained through analysis of 4084 samples with BPAD, SZ, or schizoaffective disorder. Finally, a pooled analysis of in-house and published datasets was carried out including 10,925 cases with BPAD, SZ, or schizoaffective disorder and 16,747 controls.

RESULTS

In the family-based analysis, an approximately 200 kilobase (kb) deletion in the first intron of the MAGI1 gene was identified that segregated with BPAD in a pedigree (six out of six affected individuals; parametric logarithm of the odds score = 1.14). In the pooled analysis, seven additional insertions or deletions over 100 kb were identified in MAGI1 in cases, while only two such CNV events were identified in the same gene in controls (p = .023; Fisher's exact test). Because earlier work had identified a CNV in the close relative MAGI2 in SZ, the study was extended to include MAGI2. In the pooled analysis of MAGI2, two large deletions were found in cases, and two duplications were detected in controls.

CONCLUSIONS

Results presented herein provide further evidence for a role of MAGI1 and MAGI2 in BPAD and SZ etiology.

Comprehensive gene-based association study of a chromosome 20 linked region implicates novel risk loci for depressive symptoms in psychotic illness

BACKGROUND

Prior genomewide scans of schizophrenia support evidence of linkage to regions of chromosome 20. However, association analyses have yet to provide support for any etiologically relevant variants.

METHODS

We analyzed 2988 LD-tagging single nucleotide polymorphisms (SNPs) in 327 genes on chromosome 20, to test for association with schizophrenia in 270 Irish high-density families (ISHDSF, N = 270 families, 1408 subjects). These SNPs were genotyped using an Illumina iSelect genotyping array which employs the Infinium assay. Given a previous report of novel linkage with chromosome 20p using latent classes of psychotic illness in this sample, association analysis was also conducted for each of five factor-derived scores based on the Operational Criteria Checklist for Psychotic Illness (delusions, hallucinations, mania, depression, and negative symptoms). Tests of association were conducted using the PDTPHASE and QPDTPHASE packages of UNPHASED. Empirical estimates of gene-wise significance were obtained by adaptive permutation of a) the smallest observed P-value and b) the threshold-truncated product of P-values for each locus.

RESULTS

While no single variant was significant after LD-corrected Bonferroni-correction, our gene-dropping analyses identified loci which exceeded empirical significance criteria for both gene-based tests. Namely, R3HDML and C20orf39 are significantly associated with depressive symptoms of schizophrenia (P(emp)<2×10⁻⁵) based on the minimum P-value and truncated-product methods, respectively.

CONCLUSIONS

Using a gene-based approach to family-based association, R3HDML and C20orf39 were found to be significantly associated with clinical dimensions of schizophrenia. These findings demonstrate the efficacy of gene-based analysis and support previous evidence that chromosome 20 may harbor schizophrenia susceptibility or modifier loci.

Comparative linkage meta-analysis reveals regionally-distinct, disparate genetic architectures: application to bipolar disorder and schizophrenia

New high-throughput, population-based methods and next-generation sequencing capabilities hold great promise in the quest for common and rare variant discovery and in the search for ”missing heritability.” However, the optimal analytic strategies for approaching such data are still actively debated, representing the latest rate-limiting step in genetic progress. Since it is likely a majority of common variants of modest effect have been identified through the application of tagSNP-based microarray platforms (i.e., GWAS), alternative approaches robust to detection of low-frequency (1–5% MAF) and rare (<1%) variants are of great importance. Of direct relevance, we have available an accumulated wealth of linkage data collected through traditional genetic methods over several decades, the full value of which has not been exhausted. To that end, we compare results from two different linkage meta-analysis methods—GSMA and MSP—applied to the same set of 13 bipolar disorder and 16 schizophrenia GWLS datasets. Interestingly, we find that the two methods implicate distinct, largely non-overlapping, genomic regions. Furthermore, based on the statistical methods themselves and our contextualization of these results within the larger genetic literatures, our findings suggest, for each disorder, distinct genetic architectures may reside within disparate genomic regions. Thus, comparative linkage meta-analysis (CLMA) may be used to optimize low-frequency and rare variant discovery in the modern genomic era.

Convergent functional genomic studies of ω-3 fatty acids in stress reactivity, bipolar disorder and alcoholism

Omega-3 fatty acids have been proposed as an adjuvant treatment option in psychiatric disorders. Given their other health benefits and their relative lack of toxicity, teratogenicity and side effects, they may be particularly useful in children and in females of child-bearing age, especially during pregnancy and postpartum. A comprehensive mechanistic understanding of their effects is needed. Here we report translational studies demonstrating the phenotypic normalization and gene expression effects of dietary omega-3 fatty acids, specifically docosahexaenoic acid (DHA), in a stress-reactive knockout mouse model of bipolar disorder and co-morbid alcoholism, using a bioinformatic convergent functional genomics approach integrating animal model and human data to prioritize disease-relevant genes. Additionally, to validate at a behavioral level the novel observed effects on decreasing alcohol consumption, we also tested the effects of DHA in an independent animal model, alcohol-preferring (P) rats, a well-established animal model of alcoholism. Our studies uncover sex differences, brain region-specific effects and blood biomarkers that may underpin the effects of DHA. Of note, DHA modulates some of the same genes targeted by current psychotropic medications, as well as increases myelin-related gene expression. Myelin-related gene expression decrease is a common, if nonspecific, denominator of neuropsychiatric disorders. In conclusion, our work supports the potential utility of omega-3 fatty acids, specifically DHA, for a spectrum of psychiatric disorders such as stress disorders, bipolar disorder, alcoholism and beyond.

European collaborative study of early-onset bipolar disorder: Evidence for genetic heterogeneity on 2q14 according to age at onset

Bipolar disorder has a genetic component, but the mode of inheritance remains unclear. A previous genome scan conducted in 70 European families led to detect eight regions linked to bipolar disease. Here, we present an investigation of whether the phenotypic heterogeneity of the disorder corresponds to genetic heterogeneity in these regions using additional markers and an extended sample of families. The MLS statistic was used for linkage analyses. The predivided sample test and the maximum likelihood binomial methods were used to test genetic homogeneity between early-onset bipolar type I (cut-off of 22 years) and other types of the disorder (later onset of bipolar type I and early-onset bipolar type II), using a total of 138 independent bipolar-affected sib-pairs. Analysis of the extended sample of families supports linkage in four regions (2q14, 3p14, 16p23, and 20p12) of the eight regions of linkage suggested by our previous genome scan. Heterogeneity testing revealed genetic heterogeneity between early and late-onset bipolar type I in the 2q14 region (P = 0.0001). Only the early form of the bipolar disorder but not the late form appeared to be linked to this region. This region may therefore include a genetic factor either specifically involved in the early-onset bipolar type I or only influencing the age at onset (AAO). Our findings illustrate that stratification according to AAO may be valuable for the identification of genetic vulnerability polymorphisms. © 2010 Wiley-Liss, Inc.

Implication of synapse-related genes in bipolar disorder by linkage and gene expression analyses

Several chromosomal regions have been linked to bipolar disorder (BD). However, the search for specific genes has been hampered by inconsistent findings, partly due to genetic and phenotypic heterogeneity. We focused on lithium-responsive bipolar patients, a subgroup thought to be more homogeneous and conducted a multistage study including an initial linkage study followed up by fine mapping and gene expression. Our sample consisted of 36 families (275 genotyped individuals, 132 affected) recruited through probands who were responders to long-term lithium treatment. We conducted a genome-wide scan with 811 microsatellite markers followed by fine mapping. Gene expression studies of candidate regions were conducted on six post-mortem prefrontal brain regions of 20 individuals (8 BD and 12 controls). We identified regions 3p25, 3p14 and 14q11 as showing the highest genome-wide linkage signal (LOD 2.53, 2.04 and 3.19, respectively). Fine mapping provided further support for 3p25, while only modest support was found in the other two regions. We identified a group of synaptic, mitochondrial and apoptotic genes with altered expression patterns in BD. Analysis of an independent microarray dataset supported the implication of synapse-related and mitochondrial genes in BD. In conclusion, using two complementary strategies, we found evidence of linkage to lithium-responsive BD on 3p25, 3p14 and 14q11 as well as significantly dysregulated genes on these regions suggesting altered synaptic and mitochondrial function in BD. Further studies are warranted to demonstrate the functional role of these genes in BD.

Mixture regression analysis on age at onset in bipolar disorder patients: investigation of the role of serotonergic genes

Bipolar Disorder (BPD) is a complex psychiatric disease with a relevant underlying genetic basis. HTR2A T102C, HTR2C Cys23Ser, SLC6A4 5-HTTLPR and rs25531 polymorphisms were genotyped in 230 BPD patients and inserted as covariates in a mixture regression model of age at onset (AAO). 5-HTTLPR polymorphism associated with early onset component under recessive and additive model. HTR2A T102C, HTR2C Cys23Ser and 5-HTTLPR interaction terms associated with early onset component under dominant, recessive and additive model. These findings suggest a role of genes codifying for elements of the serotonergic system in influencing the AAO in BPD.

A SNAP25 promoter variant is associated with early-onset bipolar disorder and a high expression level in brain

Bipolar disorder (BD) is one of the most common and persistent psychiatric disorders. Early-onset BD has been shown to be the most severe and familial form. We recently carried out a whole-genome linkage analysis on sibpairs affected by early-onset BD and showed that the 20p12 region was more frequently shared in our families than expected by chance. The synaptosomal-associated protein SNAP25 is a presynaptic plasma membrane protein essential for the triggering of vesicular fusion and neurotransmitter release, and for which abnormal protein levels have been reported in postmortem studies of bipolar patients. We hypothesised that variations in the gene encoding SNAP25, located on chromosome 20p12, might influence the susceptibility to early-onset BD. We screened SNAP25 for mutations and performed a case-control association study in 197 patients with early-onset BD, 202 patients with late-onset BD and 136 unaffected subjects. In addition, we analysed the expression level of the two SNAP25 isoforms in 60 brains. We showed that one variant, located in the promoter region, was associated with early-onset BD but not with the late-onset subgroup. In addition, individuals homozygous for this variant showed a significant higher SNAP25b expression level in prefrontal cortex. These results show that variations in SNAP25, associated with an increased gene expression level in prefrontal cortex, might predispose to early-onset BD. Further analyses of this gene, as well as analysis of genes encoding for the SNAP25 protein partners, are required to understand the impact of such molecular mechanisms in BD.

Coming to grips with complex disorders: genetic risk prediction in bipolar disorder using panels of genes identified through convergent functional genomics

We previously proposed and provided proof of principle for the use of a complementary approach, convergent functional genomics (CFG), combining gene expression and genetic data, from human and animal model studies, 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 [Le-Niculescu et al., 2009b]. CFG provides a fit-to-disease prioritization of genes that leads to generalizability in independent cohorts, and counterbalances the fit-to-cohort prioritization inherent in classic genetic-only approaches, which have been plagued by poor reproducibility across cohorts. We have now extended our previous work to include more datasets of GWAS, and more recent evidence from other lines of work. In essence our analysis is the most comprehensive integration of genetics and functional genomics to date in the field of bipolar disorder. Biological pathway analyses identified top canonical pathways, and epistatic interaction testing inside these pathways has identified genes that merit future follow-up as direct interactors (intra-pathway epistasis, INPEP). Moreover, we have put together a panel of best P-value single nucleotide polymorphisms (SNPs), based on the top candidate genes we identified. We have developed a genetic risk prediction score (GRPS) based on our panel, and demonstrate how in two independent test cohorts the GRPS differentiates between subjects with bipolar disorder and normal controls, in both European-American and African-American populations. Lastly, we describe a prototype of how such testing could be used to categorize disease risk in individuals and aid personalized medicine approaches, in psychiatry and beyond.

A genome-wide linkage study of bipolar disorder and co-morbid migraine: replication of migraine linkage on chromosome 4q24, and suggestion of an overlapping susceptibility region for both disorders on chromosome 20p11

Migraine and Bipolar Disorder (BPAD) are clinically heterogeneous disorders of the brain with a significant, but complex, genetic component. Epidemiological and clinical studies have demonstrated a high degree of co-morbidity between migraine and BPAD. Several genome-wide linkage studies in BPAD and migraine have shown overlapping regions of linkage on chromosomes, and two functionally similar voltage-dependent calcium channels CACNA1A and CACNA1C have been identified in familial hemiplegic migraine and recently implicated in two whole genome BPAD association studies, respectively. We hypothesized that using migraine co-morbidity to look at subsets of BPAD families in a genetic linkage analysis would prove useful in identifying genetic susceptibility regions in both of these disorders. We used BPAD with co-morbid migraine as an alternative phenotype definition in a re-analysis of the NIMH Bipolar Genetics Initiative wave 4 data set. In this analysis we selected only those families in which at least two members were diagnosed with migraine by a doctor according to patients' reports. Nonparametric linkage analysis performed on 31 families segregating both BPAD and migraine identified a linkage signal on chromosome 4q24 for migraine (but not BPAD) with a peak LOD of 2.26. This region has previously been implicated in two independent migraine linkage studies. In addition we identified a locus on chromosome 20p11 with overlapping elevated LOD scores for both migraine (LOD=1.95) and BPAD (LOD=1.67) phenotypes. This region has previously been implicated in two BPAD linkage studies, and, interestingly, it harbors a known potassium dependant sodium/calcium exchanger gene, SLC24A3, that plays a critical role in neuronal calcium homeostasis. Our findings replicate a previously identified migraine linkage locus on chromosome 4 (not co-segregating with BPAD) in a sample of BPAD families with co-morbid migraine, and suggest a susceptibility locus on chromosome 20, harboring a gene for the migraine/BPAD phenotype. Together these data suggest that some genes may predispose to both bipolar disorder and migraine.

Heritability of age of onset of psychosis in schizophrenia

Schizophrenia is a genetically complex illness with heterogeneous clinical presentation, including variable age of onset. In this study, the heritability, or proportion of variation in age of onset of psychotic symptoms due to genetic factors, was estimated using a maximum likelihood method. The subjects were 717 members of families with more than one member affected with schizophrenia from Mexican and Central American populations. Age of onset of psychosis was determined by best-estimate consensus diagnosis based on the Diagnostic Interview for Genetic Studies, Family Interview for Genetic Studies, and each subject's medical records. Mean age of onset was 21.44 years (SD 8.07); 20.55 years for males (SD 6.90), and 22.67 for females (SD 9.34). Variance components were estimated using a polygenic model in the SOLAR software package. The sex of the participant was a significant covariate (P = 0.010) accounting for 0.02 of the total variance in age of onset. The heritability of age of onset of psychosis was 0.33 (SE = 0.09; P = 0.00004). These findings suggest that genetic factors significantly contribute to the age of onset of psychotic symptoms in individuals with schizophrenia and that sex influences this trait as well.

A narrow and highly significant linkage signal for severe bipolar disorder in the chromosome 5q33 region in Latin American pedigrees

We previously reported linkage of bipolar disorder to 5q33-q34 in families from two closely related population isolates, the Central Valley of Costa Rica (CVCR) and Antioquia, Colombia (CO). Here we present follow up results from fine-scale mapping in large CVCR and CO families segregating severe bipolar disorder, BP-I, and in 343 population trios/duos from CVCR and CO. Employing densely spaced SNPs to fine map the prior linkage peak region increases linkage evidence and clarifies the position of the putative BP-I locus. We performed two-point linkage analysis with 1134 SNPs in an approximately 9 Mb region between markers D5S410 and D5S422. Combining pedigrees from CVCR and CO yields a LOD score of 4.9 at SNP rs10035961. Two other SNPs (rs7721142 and rs1422795) within the same 94 kb region also displayed LOD scores greater than 4. This linkage peak coincides with our prior microsatellite results and suggests a narrowed BP-I susceptibility regions in these families. To investigate if the locus implicated in the familial form of BP-I also contributes to disease risk in the population, we followed up the family results with association analysis in duo and trio samples, obtaining signals within 2 Mb of the peak linkage signal in the pedigrees; rs12523547 and rs267015 (P = 0.00004 and 0.00016, respectively) in the CO sample and rs244960 in the CVCR sample and the combined sample, with P = 0.00032 and 0.00016, respectively. It remains unclear whether these association results reflect the same locus contributing to BP susceptibility within the extended pedigrees.

Case-control association study of 65 candidate genes revealed a possible association of a SNP of HTR5A to be a factor susceptible to bipolar disease in Bulgarian population

BACKGROUND

Bipolar affective disorder (BAD) is a psychiatric illness characterized by episodes of mania and depression. Although the etiology is not clear, epidemiological studies suggest it is a result of an interaction of genetic and environmental factors. Despite of enormous efforts and abundant studies conducted, none has yet been identified definitively a gene susceptible to bipolar disorder.

METHODS

Ninety-four Bulgarian patients diagnosed with bipolar disorder and 184 Bulgarian healthy individuals, were used for genotyping of 191 single nucleotide polymorphisms (SNPs) by TaqMan and/or Invader assays. Seventeen SNPs that revealed P value less than 0.05 in the first screening were genotyped using an additional independent set of samples, consisting of 78 BAD cases and 372 controls.

RESULTS

After applying the Bonferonni correction on genotyping results of 172 cases and 556 controls, only one SNP, rs1800883, in the HTR5A gene revealed a significant level of P value (P=0.000097; odds ratio=1.80 (95%CI, 1.27-2.54); corrected P=0.017).

CONCLUSIONS

Our findings suggest that HTR5A gene could play an important role in the pathogenesis of bipolar disorder in our population. However these findings should be viewed with caution and replication studies in other populations are necessary in support of these findings.

Premorbid adjustment: a phenotype highlighting a distinction rather than an overlap between schizophrenia and bipolar disorder

BACKGROUND

Premorbid adjustment (PMA) in schizophrenia (SZ) has been widely studied and shown to be worse in individuals who develop SZ as compared to controls. It has been proposed as a predictor of clinical presentation and outcome, and may delineate a specific SZ phenotype for genetic and other biological studies. Research into PMA in BD has been scarce and inconclusive.

AIMS

The authors compared PMA in individuals suffering from BD with that of healthy controls and investigated whether levels of PMA in BD patients correlate with specific phenotypic features.

METHODS

The authors investigated 344 BD patients and 137 population-based controls. Retrospective PMA assessment was performed using the Premorbid Adjustment Scale (PAS). An overall score as well as sub-scores for age ranges and functional domains were obtained.

RESULTS

Patients had a better overall PAS score than controls and outperformed controls during early and late adolescence. They scored significantly better than controls in the functional domains "sociability and withdrawal" and "adaptation to school". No differences were observed for the other subscales and there were no differences between groups during childhood. No association was observed between PMA and any of the phenotype characteristics investigated.

CONCLUSIONS

In the largest study to date on PMA in BD, PMA was shown to be better in bipolar patients than in healthy controls. PMA in BD is not a simple proxy for commonly studied phenotypic markers of severity. PMA emerges as a phenotype in its own right, and highlights an aspect of disparity rather than overlap between SZ and BD.

Family and genetic association studies of bipolar disorder in children

The risk of bipolar disorder (BPD) (15-42%) in first-degree relatives of children with BPD are consistently larger than the 8.7% estimate of recurrence risk of BPD in first-degree relatives of adult BPD cases. There have been no family linkage studies of pediatric BPD, but secondary analyses of adult linkage samples suggest that early-onset BPD both increases the strength of associations in linkage studies. Positive associations with pediatric BPD and the BDNF gene (Vall66), the GAD1 gene (4s2241165), and the dopamine transporter gene (rs41084) have been reported but none of these associations have been replicated in independent samples. The number of informative families examined so far is quite small and studies were vastly underpowered to detect small effects. An adequately powered sample will likely require collaborative ascertainment of cases and families from multiple sites using valid and accepted measures of pediatric BPD.

Clinical perspectives on the genetics of schizophrenia: a bottom-up orientation

Phenomenology has been the reference point that investigators have used in their efforts to understand schizophrenia. Although symptoms and signs are crucial for the diagnosis of schizophrenia, there is an ongoing debate since Kraepelin attempted to group symptoms to understand the etiology of schizophrenia. Several operational criteria have been developed to establish the diagnosis of schizophrenia, making it obvious that there are no precise symptomatological boundaries. There is little clear indication which of the systems is valid for genetic and other biological research. Despite the enormous effort to find a linkage between schizophrenia and one or more loci, the results are far from conclusive. Another approach is the search for candidate genes of which DICS1 and 22q11 deletion syndrome are examples. In all studies into the genetic underpinnings of schizophrenia, however, the clinical vantage point is neglected in that a broad clinical phenotype with respect to, e.g., developmental issues, symptoms and comorbidity is narrowed down to one categorical diagnosis. This is illustrated by the lack of exclusion criteria in genetic studies and by the occurrence of schizophrenia-like psychoses in a broad array of genetic syndromes. In case of 22q11 deletion syndrome, the psychotic symptoms emerge in the context of brain anomalies, a plethora of somatic abnormalities and specific neurocognitive deficits. Prader-Willi syndrome is a hypothalamic disorder in which psychotic symptoms may occur that resemble schizophrenia. It is concluded that not only schizophrenia is a highly variable disease but that the genetic samples are even much more heterogeneous.