Genome-wide survey implicates the influence of copy number variants (CNVs) in the development of early-onset bipolar disorder

Beyond the Window of Risk? The Dutch Bipolar Offspring Study: 22-Year Follow-up

OBJECTIVE

Adolescent offspring of parents with bipolar disorder (BD) are at high risk to develop BD and other psychopathology, yet how this risk continues into middle adulthood remains unknown. This study aimed to determine the window of risk for BD and other psychopathology in offspring of parents with BD followed from adolescence into adulthood.

METHOD

This study reported on the 22-year follow-up assessment of the Dutch Bipolar Offspring Study, a fixed cohort study of 140 participants established in 1997. Offspring (n = 100; mean [SD] age = 38.28 [2.74] years) of parents with bipolar I disorder or bipolar II disorder were assessed at baseline and 1-, 5-, 12-, and 22-year follow-up.

RESULTS

No new BD onsets occurred since the 12-year follow-up (lifetime prevalence = 11%-13%; bipolar I disorder = 4%; bipolar II disorder = 7%). Lifetime prevalence of any mood disorder was 65%; for major depressive disorder, prevalence was 36%; and for recurrent mood episodes, prevalence was 37%. Prevalence of major depressive disorder more than doubled in the past decade. Point prevalence of any psychopathology peaked between 20 and 25 years (38%-46%), subsiding to 29% to 35% per year after age 30. Overall, 71% of offspring contacted mental health services since the last assessment.

CONCLUSION

The risk for homotypic transmission of BD in offspring of parents with BD is highest during adolescence. The heterotypic risk for mood disorder onset and recurrences continues over the life course. Severe mood disorders are often preceded by milder psychopathology, emphasizing the need for early identification and interventions. This study allows for better understanding of the onset and course of mood disorders and specific windows of risk in a familial high-risk population.

Copy Number Variations in Neuropsychiatric Disorders

Neuropsychiatric disorders are complex conditions that represent a significant global health burden with complex and multifactorial etiologies. Technological advances in recent years have improved our understanding of the genetic architecture of the major neuropsychiatric disorders and the genetic loci involved. Previous studies mainly investigated genome-wide significant SNPs to elucidate the cross-disorder and disorder-specific genetic basis of neuropsychiatric disorders. Although copy number variations represent a major source of genetic variations, they are known risk factors in developing a variety of human disorders, including certain neuropsychiatric diseases. In this review, we demonstrate the current understanding of CNVs contributing to liability for schizophrenia, bipolar disorder, and major depressive disorder.

The contribution of copy number variants to psychiatric symptoms and cognitive ability

Copy number variants (CNVs) are deletions and duplications of DNA sequence. The most frequently studied CNVs, which are described in this review, are recurrent CNVs that occur in the same locations on the genome. These CNVs have been strongly implicated in neurodevelopmental disorders, namely autism spectrum disorder (ASD), intellectual disability (ID), and developmental delay (DD), but also in schizophrenia. More recent work has also shown that CNVs increase risk for other psychiatric disorders, namely, depression, bipolar disorder, and post-traumatic stress disorder. Many of the same CNVs are implicated across all of these disorders, and these neuropsychiatric CNVs are also associated with cognitive ability in the general population, as well as with structural and functional brain alterations. Neuropsychiatric CNVs also show incomplete penetrance, such that carriers do not always develop any psychiatric disorder, and may show only mild symptoms, if any. Variable expressivity, whereby the same CNVs are associated with many different phenotypes of varied severity, also points to highly complex mechanisms underlying disease risk in CNV carriers. Comprehensive and longitudinal phenotyping studies of individual CNVs have provided initial insights into these mechanisms. However, more work is needed to estimate and predict the effect of non-recurrent, ultra-rare CNVs, which also contribute to psychiatric and cognitive outcomes. Moreover, delineating the broader phenotypic landscape of neuropsychiatric CNVs in both clinical and general population cohorts may also offer important mechanistic insights.

Cross-Disorder Analysis of Genic and Regulatory Copy Number Variations in Bipolar Disorder, Schizophrenia, and Autism Spectrum Disorder

BACKGROUND

We aimed to determine the similarities and differences in the roles of genic and regulatory copy number variations (CNVs) in bipolar disorder (BD), schizophrenia (SCZ), and autism spectrum disorder (ASD).

METHODS

Based on high-resolution CNV data from 8708 Japanese samples, we performed to our knowledge the largest cross-disorder analysis of genic and regulatory CNVs in BD, SCZ, and ASD.

RESULTS

In genic CNVs, we found an increased burden of smaller (<100 kb) exonic deletions in BD, which contrasted with the highest burden of larger (>500 kb) exonic CNVs in SCZ/ASD. Pathogenic CNVs linked to neurodevelopmental disorders were significantly associated with the risk for each disorder, but BD and SCZ/ASD differed in terms of the effect size (smaller in BD) and subtype distribution of CNVs linked to neurodevelopmental disorders. We identified 3 synaptic genes (DLG2, PCDH15, and ASTN2) as risk factors for BD. Whereas gene set analysis showed that BD-associated pathways were restricted to chromatin biology, SCZ and ASD involved more extensive and similar pathways. Nevertheless, a correlation analysis of gene set results indicated weak but significant pathway similarities between BD and SCZ or ASD (r = 0.25-0.31). In SCZ and ASD, but not BD, CNVs were significantly enriched in enhancers and promoters in brain tissue.

CONCLUSIONS

BD and SCZ/ASD differ in terms of CNV burden, characteristics of CNVs linked to neurodevelopmental disorders, and regulatory CNVs. On the other hand, they have shared molecular mechanisms, including chromatin biology. The BD risk genes identified here could provide insight into the pathogenesis of BD.

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.

dbBIP: a comprehensive bipolar disorder database for genetic research

Bipolar disorder (BIP) is one of the most common hereditary psychiatric disorders worldwide. Elucidating the genetic basis of BIP will play a pivotal role in mechanistic delineation. Genome-wide association studies (GWAS) have successfully reported multiple susceptibility loci conferring BIP risk, thus providing insight into the effects of its underlying pathobiology. However, difficulties remain in the extrication of important and biologically relevant data from genetic discoveries related to psychiatric disorders such as BIP. There is an urgent need for an integrated and comprehensive online database with unified access to genetic and multi-omics data for in-depth data mining. Here, we developed the dbBIP, a database for BIP genetic research based on published data. The dbBIP consists of several modules, i.e.: (i) single nucleotide polymorphism (SNP) module, containing large-scale GWAS genetic summary statistics and functional annotation information relevant to risk variants; (ii) gene module, containing BIP-related candidate risk genes from various sources and (iii) analysis module, providing a simple and user-friendly interface to analyze one’s own data. We also conducted extensive analyses, including functional SNP annotation, integration (including summary-data-based Mendelian randomization and transcriptome-wide association studies), co-expression, gene expression, tissue expression, protein–protein interaction and brain expression quantitative trait loci analyses, thus shedding light on the genetic causes of BIP. Finally, we developed a graphical browser with powerful search tools to facilitate data navigation and access. The dbBIP provides a comprehensive resource for BIP genetic research as well as an integrated analysis platform for researchers and can be accessed online at http://dbbip.xialab.info.

Database URL:  http://dbbip.xialab.info

Parental age and the risk of bipolar disorder in the offspring: A systematic review and meta-analysis

OBJECTIVES

Whether parental age, i.e., paternal or maternal, at childbirth is associated with the risk of bipolar disorder (BD) in offspring remains unclear. We conducted a meta-analysis of observational studies to address this gap.

METHODS

PubMed, PsycINFO, Embase, and Web of Science were searched up to June 2021. Studies investigating the associations between parental age at childbirth (exposure) and the risk of BD in offspring (outcome) were eligible for inclusion in our study. Paternal and maternal age were examined separately. Odds ratio (OR) was used as the effect size index. Data were pooled through random-effects meta-analyses.

RESULTS

Seven studies involving 3,183,539 participants and 23,253 individuals with BD were included in our meta-analyses. Meta-analyses indicated an increased risk of BD in the offspring of the older paternal age groups (35-44 years old [k = 5; OR = 1.09; 95% CI 1.05, 1.14; p < 0.0001] and ≥45 years old [k = 5; OR = 1.44; 95% CI 1.19, 1.14; p = 0.0001]) in comparison with the reference category (25-34 years old). Meta-analysis also indicated an increased risk of BD in the offspring of the older maternal age group (≥40 years old [k = 3; OR = 1.20; 95% CI 1.10, 1.31; p < 0.0001]) in comparison with the reference category (20-29 years old).

CONCLUSIONS

Advanced paternal and maternal age were both associated with an increased risk of BD in offspring. Further studies are needed to investigate the mechanisms behind this association.

Genetic Pathways and Functional Subnetworks for the Complex Nature of Bipolar Disorder in Genome-Wide Association Study

Bipolar disorder is a complex psychiatric trait that is also recognized as a high substantial heritability from a worldwide distribution. The success in identifying susceptibility loci for bipolar disorder (BPD) has been limited due to its complex genetic architecture. Growing evidence from association studies including genome-wide association (GWA) studies points to the need of improved analytic strategies to pinpoint the missing heritability for BPD. More importantly, many studies indicate that BPD has a strong association with dementia. We conducted advanced pathway analytics strategies to investigate synergistic effects of multilocus within biologically functional pathways, and further demonstrated functional effects among proteins in subnetworks to examine mechanisms underlying the complex nature of bipolarity using a GWA dataset for BPD. We allowed bipolar susceptible loci to play a role that takes larger weights in pathway-based analytic approaches. Having significantly informative genes identified from enriched pathways, we further built function-specific subnetworks of protein interactions using MetaCore. The gene-wise scores (i.e., minimum p-value) were corrected for the gene-length, and the results were corrected for multiple tests using Benjamini and Hochberg’s method. We found 87 enriched pathways that are significant for BPD; of which 36 pathways were reported. Most of them are involved with several metabolic processes, neural systems, immune system, molecular transport, cellular communication, and signal transduction. Three significant and function-related subnetworks with multiple hotspots were reported to link with several Gene Ontology processes for BPD. Our comprehensive pathway-network frameworks demonstrated that the use of prior knowledge is promising to facilitate our understanding between complex psychiatric disorders (e.g., BPD) and dementia for the access to the connection and clinical implications, along with the development and progression of dementia.

Brain-derived neurotrophic factor in bipolar disorder: Associations with age at onset and illness duration

Bipolar disorder (BD) is a heterogeneous disorder that contains neurodevelopmental differences. Defining homogeneous subgroups of BD patients by using age at onset (AAO) as a specifier may promote the classification of biomarkers. This study compares peripheral BDNF levels between pediatric and adult BD patients to investigate the associations between BDNF levels, AAO, and illness duration. We enrolled two groups of euthymic patients, those with pediatric BD (n = 39) and those with adult BD (n = 31), as well as a group of healthy controls (HCs) (n = 90). Participants were assessed using clinical measures and BDNF serum levels were obtained using ELISA. We observed that BDNF levels were comparable between adult BD and HCs, but were clearly lower in pediatric BD than in HCs. In adult BD with AAO ≥30 years, BDNF levels were significantly higher than in adult BD with AAO <30 years. In pediatric BD, patients with prepubertal-onset had higher BDNF levels than those with pubertal-onset. BDNF levels demonstrated the accuracy of being able to distinguish pediatric BD from healthy controls in a receiver operating characteristic (ROC) curve analysis (area under the curve [AUC] = 0.792). In adult BD, higher BDNF levels were associated with later disease onset, but this was not the case in pediatric BD. Finally, reduced BDNF levels were associated with illness duration in adult BD. The findings indicate that BDNF levels in BD patients are associated with AAO. BDNF may, therefore, potentially serve as a developmental marker in BD, when AAO is taken into account.

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).

The "missing heritability"-Problem in psychiatry: Is the interaction of genetics, epigenetics and transposable elements a potential solution?

Psychiatric disorders exhibit an enormous burden on the health care systems worldwide accounting for around one-third of years lost due to disability among adults. Their etiology is largely unknown and diagnostic classification is based on symptomatology and course of illness and not on objective biomarkers. Most psychiatric disorders are moderately to highly heritable. However, it is still unknown what mechanisms may explain the discrepancy between heritability estimates and the present data from genetic analysis. In addition to genetic differences also epigenetic modifications are considered as potentially relevant in the transfer of susceptibility to psychiatric diseases. Though, whether or not epigenetic alterations can be inherited for many generations is highly controversial. In the present article, we will critically summarize both the genetic findings and the results from epigenetic analyses, including also those of noncoding RNAs. We will argue that one possible solution to the "missing heritability" problem in psychiatry is a potential role of retrotransposons, the exploration of which is presently only in its beginnings.

The Co-existence of ADHD With Autism in Saudi Children: An Analysis Using Next-Generation DNA Sequencing

Attention-deficit/hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders. Several studies have confirmed the co-existence of other neuropsychiatric disorders with ADHD. Out of 106 individuals suspected to have ADHD, eight Saudi Arabian pediatric patients were diagnosed with ADHD using a dual assessment procedure based on highly significant scores from the international criteria for diagnosis; (full form DMS) DSM-5. Then, these patients were examined for the co-existence of autism and ADHD using different international diagnostic protocols. Four patients with combined ADHD and autism and four ADHD patients without autism were examined for the presence of genetic variants. Six variants (chr1:98165091, chr6:32029183, chr6:32035603, chr6:32064098, chr8:2909992, chr16:84213434) were identified in 75% of the patients with ADHD and autism, indicating that these genes may have a possible role in causing autism. Five variants (The chr2:116525960, chr15:68624396, chr15:91452595, chr15:92647645, and chr16:82673047) may increase to the severity of ADHD. This study recommends screening these eleven variants in ADHD cases and their relevant controls to confirm the prevalence in the Saudi population. It is recommended that future studies examine the 11 variants in detail.

Insights into the genomics of affective disorders

Affective disorders, or mood disorders, are a group of neuropsychiatric illnesses that are characterized by a disturbance of mood or affect. Most genetic research in this field to date has focused on bipolar disorder and major depression. Symptoms of major depression include a depressed mood, reduced energy, and a loss of interest and enjoyment. Bipolar disorder is characterized by the occurrence of (hypo)manic episodes, which generally alternate with periods of depression. Formal and molecular genetic studies have demonstrated that affective disorders are multifactorial diseases, in which both genetic and environmental factors contribute to disease development. Twin and family studies have generated heritability estimates of 58–85 % for bipolar disorder and 40 % for major depression.

Large genome-wide association studies have provided important insights into the genetics of affective disorders via the identification of a number of common genetic risk factors. Based on these studies, the estimated overall contribution of common variants to the phenotypic variability (single-nucleotide polymorphism [SNP]-based heritability) is 17–23 % for bipolar disorder and 9 % for major depression. Bioinformatic analyses suggest that the associated loci and implicated genes converge into specific pathways, including calcium signaling. Research suggests that rare copy number variants make a lower contribution to the development of affective disorders than to other psychiatric diseases, such as schizophrenia or the autism spectrum disorders, which would be compatible with their less pronounced negative impact on reproduction. However, the identification of rare sequence variants remains in its infancy, as available next-generation sequencing studies have been conducted in limited samples. Future research strategies will include the enlargement of genomic data sets via innovative recruitment strategies; functional analyses of known associated loci; and the development of new, etiologically based disease models. Researchers hope that deeper insights into the biological causes of affective disorders will eventually lead to improved diagnostics and disease prediction, as well as to the development of new preventative, diagnostic, and therapeutic strategies. Pharmacogenetics and the application of polygenic risk scores represent promising initial approaches to the future translation of genomic findings into psychiatric clinical practice.

Contribution of Rare Copy Number Variants to Bipolar Disorder Risk Is Limited to Schizoaffective Cases

BACKGROUND

Genetic risk for bipolar disorder (BD) is conferred through many common alleles, while a role for rare copy number variants (CNVs) is less clear. Subtypes of BD including schizoaffective disorder bipolar type (SAB), bipolar I disorder (BD I), and bipolar II disorder (BD II) differ according to the prominence and timing of psychosis, mania, and depression. The genetic factors contributing to the combination of symptoms among these subtypes are poorly understood.

METHODS

Rare large CNVs were analyzed in 6353 BD cases (3833 BD I [2676 with psychosis, 850 without psychosis, and 307 with unknown psychosis history], 1436 BD II, 579 SAB, and 505 BD not otherwise specified) and 8656 controls. CNV burden and a polygenic risk score (PRS) for schizophrenia were used to evaluate the relative contributions of rare and common variants to risk of BD, BD subtypes, and psychosis.

RESULTS

CNV burden did not differ between BD and controls when treated as a single diagnostic entity. However, burden in SAB was increased relative to controls (p = .001), BD I (p = .0003), and BD II (p = .0007). Burden and schizophrenia PRSs were increased in SAB compared with BD I with psychosis (CNV p = .0007, PRS p = .004), and BD I without psychosis (CNV p = .0004, PRS p = 3.9 × 10^-5). Within BD I, psychosis was associated with increased schizophrenia PRSs (p = .005) but not CNV burden.

CONCLUSIONS

CNV burden in BD is limited to SAB. Rare and common genetic variants may contribute differently to risk for psychosis and perhaps other classes of psychiatric symptoms.

[Breakthrough in understanding the molecular causes of psychiatric disorders]

A long-established hypothesis is that genetic factors contribute to the development of psychiatric diseases, including common illnesses such as schizophrenia and the affective disorders; however, reliable molecular identification of these factors represents a far more recent innovation. This has been rendered possible by technological advances in the individual characterization of the human genome and the combining of large genetic datasets at the international level. For the first time, the results of genome-wide analyses provide researchers with systematic insights into disease-relevant biological mechanisms. Here, the integrated analysis of different omics level data generates important insights into the functional interpretation of the genetic findings. The results of genetic studies also demonstrated the degree of etiological overlap between differing psychiatric disorders, with the greatest commonality having been observed to date between schizophrenia and bipolar affective disorder. Although the translation of genetic findings into routine clinical practice is being pursued at various levels, elaborate follow-up studies are typically necessary. The diagnostic investigation of rare genomic deletions/duplications (so-called copy number variants) in patients with schizophrenia is likely to represent one of the first examples of routine clinical application. The necessary prerequisites for this are currently being defined.

Identification of potential genetic risk factors for bipolar disorder by whole-exome sequencing

This study aims at assessing the burden of rare (minor allele frequency < 1%) predicted damaging variants in the whole exome of 92 bipolar I disorder (BD) patients and 1051 controls of French ancestry. Patients exhibiting an extreme phenotype (earlier onset and family history of mood disorder) were preferentially included to increase the power to detect an association. A collapsing strategy was used to test the overall burden of rare variants in cases versus controls at the gene level. Only protein-truncating and predicted damaging missense variants were included in the analysis. Thirteen genes exhibited p values exceeding 10^-3 and could be considered as potential risk factors for BD. Furthermore, the validity of the association was supported when the Exome Aggregation Consortium database non-Finnish European population was used as controls for eight of them. Their gene products are involved in various cerebral processes, some of which were previously implicated in BD and belong to pathways implicated in the therapeutic effect of lithium, the main mood stabilizer. However, exome-wide threshold for association study was not reached, emphasizing that larger samples are needed.

An examination of multiple classes of rare variants in extended families with bipolar disorder

Bipolar disorder (BD) is a complex psychiatric condition with high heritability, the genetic architecture of which likely comprises both common variants of small effect and rare variants of higher penetrance, the latter of which are largely unknown. Extended families with high density of illness provide an opportunity to map novel risk genes or consolidate evidence for existing candidates, by identifying genes carrying pathogenic rare variants. We performed whole-exome sequencing (WES) in 15 BD families (117 subjects, of whom 72 were affected), augmented with copy number variant (CNV) microarray data, to examine contributions of multiple classes of rare genetic variants within a familial context. Linkage analysis and haplotype reconstruction using WES-derived genotypes enabled exclusion of false-positive single-nucleotide variants (SNVs), CNV inheritance estimation, de novo variant identification and candidate gene prioritization. We found that rare predicted pathogenic variants shared among ≥3 affected relatives were overrepresented in postsynaptic density (PSD) genes (P = 0.002), with no enrichment in unaffected relatives. Genome-wide burden of likely gene-disruptive variants was no different in affected vs. unaffected relatives (P = 0.24), but correlated significantly with age of onset (P = 0.017), suggesting that a high disruptive variant burden may expedite symptom onset. The number of de novo variants was no different in affected vs. unaffected offspring (P = 0.89). We observed heterogeneity within and between families, with the most likely genetic model involving alleles of modest effect and reduced penetrance: a possible exception being a truncating X-linked mutation in IRS4 within a family-specific linkage peak. Genetic approaches combining WES, CNV and linkage analyses in extended families are promising strategies for gene discovery.

Bipolar disorders

Bipolar disorders are chronic and recurrent disorders that affect >1% of the global population. Bipolar disorders are leading causes of disability in young people as they can lead to cognitive and functional impairment and increased mortality, particularly from suicide and cardiovascular disease. Psychiatric and nonpsychiatric medical comorbidities are common in patients and might also contribute to increased mortality. Bipolar disorders are some of the most heritable psychiatric disorders, although a model with gene-environment interactions is believed to best explain the aetiology. Early and accurate diagnosis is difficult in clinical practice as the onset of bipolar disorder is commonly characterized by nonspecific symptoms, mood lability or a depressive episode, which can be similar in presentation to unipolar depression. Moreover, patients and their families do not always understand the significance of their symptoms, especially with hypomanic or manic symptoms. As specific biomarkers for bipolar disorders are not yet available, careful clinical assessment remains the cornerstone of diagnosis. The detection of hypomanic symptoms and longtudinal clinical assessment are crucial to differentiate a bipolar disorder from other conditions. Optimal early treatment of patients with evidence-based medication (typically mood stabilizers and antipsychotics) and psychosocial strategies is necessary.

Genetic and molecular risk factors within the newly identified primate-specific exon of the SAP97/DLG1 gene in the 3q29 schizophrenia-associated locus

The synapse-associated protein 97/discs, large homolog 1 of Drosophila (DLG1) gene encodes synaptic scaffold PDZ proteins interacting with ionotropic glutamate receptors including the N-methyl-D-aspartate type glutamate receptor (NMDAR) that is presumed to be hypoactive in brains of patients with schizophrenia. The DLG1 gene resides in the chromosomal position 3q29, the microdeletion of which confers a 40-fold increase in the risk for schizophrenia. In the present study, we performed genetic association analyses for DLG1 gene using a Japanese cohort with 1808 schizophrenia patients and 2170 controls. We detected an association which remained significant after multiple comparison testing between schizophrenia and the single nucleotide polymorphism (SNP) rs3915512 that is located within the newly identified primate-specific exon (exon 3b) of the DLG1 gene and constitutes the exonic splicing enhancer sequence. When stratified by onset age, although it did not survive multiple comparisons, the association was observed in non-early onset schizophrenia, whose onset-age selectivity is consistent with our recent postmortem study demonstrating a decrease in the expression of the DLG1 variant in early-onset schizophrenia. Although the present study did not demonstrate the previously reported association of the SNP rs9843659 by itself, a meta-analysis revealed a significant association between DLG1 gene and schizophrenia. These findings provide a valuable clue for molecular mechanisms on how genetic variations in the primate-specific exon of the gene in the schizophrenia-associated 3q29 locus affect its regulation in the glutamate system and lead to the disease onset around a specific stage of brain development.

Schizophrenia and the neurodevelopmental continuum:evidence from genomics

The idea that disturbances occurring early in brain development contribute to the pathogenesis of schizophrenia, often referred to as the neurodevelopmental hypothesis, has become widely accepted. Despite this, the disorder is viewed as being distinct nosologically, and by implication pathophysiologically and clinically, from syndromes such as autism spectrum disorders, attention-deficit/hyperactivity disorder (ADHD) and intellectual disability, which typically present in childhood and are grouped together as "neurodevelopmental disorders". An alternative view is that neurodevelopmental disorders, including schizophrenia, rather than being etiologically discrete entities, are better conceptualized as lying on an etiological and neurodevelopmental continuum, with the major clinical syndromes reflecting the severity, timing and predominant pattern of abnormal brain development and resulting functional abnormalities. It has also been suggested that, within the neurodevelopmental continuum, severe mental illnesses occupy a gradient of decreasing neurodevelopmental impairment as follows: intellectual disability, autism spectrum disorders, ADHD, schizophrenia and bipolar disorder. Recent genomic studies have identified large numbers of specific risk DNA changes and offer a direct and robust test of the predictions of the neurodevelopmental continuum model and gradient hypothesis. These findings are reviewed in detail. They not only support the view that schizophrenia is a disorder whose origins lie in disturbances of brain development, but also that it shares genetic risk and pathogenic mechanisms with the early onset neurodevelopmental disorders (intellectual disability, autism spectrum disorders and ADHD). They also support the idea that these disorders lie on a gradient of severity, implying that they differ to some extent quantitatively as well as qualitatively. These findings have important implications for nosology, clinical practice and research.

Genomic Disorders in Psychiatry-What Does the Clinician Need to Know?

PURPOSE OF REVIEW

The purpose of this review is to summarize the role of genomic disorders in various psychiatric conditions and to highlight important recent advances in the field that are of potential clinical relevance.

RECENT FINDINGS

Genomic disorders are caused by large rare recurrent deletions and duplications at certain chromosomal "hotspots" (e.g., 22q11.2, 16p11.2, 15q11-q13, 1q21.1, 15q13.3) across the genome. Most overlap multiple genes, affect development, and are associated with variable cognitive and other neuropsychiatric expression. Although individually rare, genomic disorders collectively account for a significant minority of intellectual disability, autism spectrum disorder, and schizophrenia. Genome-wide chromosomal microarray analysis is capable of detecting all genomic disorders in a single test, offering the first opportunity for routine clinical genetic testing in psychiatric practice.

Stability and change in reported age of onset of depression, back pain, and smoking over 29 years in a prospective cohort study

Accurate age of onset (AOO) measurement is vital to etiologic and preventive research. While AOO reports are known to be subject to recall error, few population-based studies have been used to investigate agreement in AOO reports over more than a decade. We examined AOO reports for depression, back/neck pain, and daily smoking, in a population-based cohort spanning 29 years. A stratified sample of participants from Zurich, Switzerland (n = 591) completed a psychiatric and physical health interview 7 times between 1979, at ages 20 (males) and 21 (females), and 2008. We used one-way ANOVA to estimate intraclass correlations (ICCs) and weighted mixed models to estimate mean change over time and test for interactions with sex and clinical characteristics. Stratum-specific ICCs among those with 2 + reports were 0.19 and 0.29 for depression, 0.46 and 0.35 for back pain, and 0.66 and 0.75 for smoking. The average yearly increases in AOO report from the wave of first 12-month diagnosis or reported smoking, estimated in mixed models, were 0.57 years (95% confidence interval: 0.35, 0.79) for depression, 0.44 (95%CI: 0.28, 0.59) years for back pain, and 0.08 (95%CI: 0.03, 0.14) years for smoking. Initial impairment and frequency of treatment were associated with differences in average yearly change for depression. There is substantial variability in AOO reports over time and systematic increase with age. The degree of increase may differ by outcome, and for some outcomes, by participant clinical characteristics. Future studies should identify predictors of AOO report stability to ultimately benefit etiologic and preventive research.

Copy number variation in bipolar disorder

Large (>100 kb), rare (<1% in the population) copy number variants (CNVs) have been shown to confer risk for schizophrenia (SZ), but the findings for bipolar disorder (BD) are less clear. In a new BD sample from the United Kingdom (n=2591), we have examined the occurrence of CNVs and compared this with previously reported samples of 6882 SZ and 8842 control subjects. When combined with previous data, we find evidence for a contribution to BD for three SZ-associated CNV loci: duplications at 1q21.1 (P=0.022), deletions at 3q29 (P=0.03) and duplications at 16p11.2 (P=2.3 × 10(-4)). The latter survives multiple-testing correction for the number of recurrent large CNV loci in the genome. Genes in 20 regions (total of 55 genes) were enriched for rare exonic CNVs among BD cases, but none of these survives correction for multiple testing. Finally, our data provide strong support for the hypothesis of a lesser contribution of very large (>500 kb) CNVs in BD compared with SZ, most notably for deletions >1 Mb (P=9 × 10(-4)).

Association of age-of-onset groups with GWAS significant schizophrenia and bipolar disorder loci in Romanian bipolar I patients

We investigated the influence of the age-of-onset (AO) on the association of 45 loci conferring risk for bipolar disorder (BP) and schizophrenia with BP-type-I in a Romanian sample (461 patients, 436 controls). The AO-analysis implicated the EGFR gene, as well as loci in other genes, in the AO variation of BP-type-I and revealed for the first time the link between BP-type-I and risk variants considered specific to schizophrenia (polymorphisms in MMP16/RIPK2 and CNNM2 genes).

Interaction between SLC6A4 promoter variants and childhood trauma on the age at onset of bipolar disorders

Age at onset (AAO) of bipolar disorders (BD) could be influenced both by a repeat length polymorphism (5HTTLPR) in the promoter region of the serotonin transporter gene (SLC6A4) and exposure to childhood trauma. We assessed 308 euthymic patients with BD for the AAO of their first mood episode and childhood trauma. Patients were genotyped for the 5HTTLPR (long/short variant) and the rs25531. Genotypes were classified on functional significance (LL, LS, SS). A sample of 126 Brazilian euthymic patients with BD was used for replication. In the French sample, the correlation between AAO and trauma score was observed only among 'SS' homozygotes (p = 0.002) but not among 'L' allele carriers. A history of at least one trauma decreased the AAO only in 'SS' homozygotes (p = 0.001). These results remained significant after correction using FDR. Regression models suggested an interaction between emotional neglect and 'SS' genotype on the AAO (p = 0.009) and no further interaction with other trauma subtypes. Partial replication was obtained in the Brazilian sample, showing an interaction between emotional abuse and 'LS' genotype on the AAO (p = 0.02). In conclusion, an effect of childhood trauma on AAO of BD was observed only in patients who carry a specific stress responsiveness-related SLC6A4 promoter genotype.

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.

Genetic and childhood trauma interaction effect on age of onset in bipolar disorder: An exploratory analysis

INTRODUCTION

This study investigated whether early life trauma mediates genetic effects on the age at onset (AAO) of bipolar disorder.

METHOD

Data from the BiGS Consortium case samples (N=1119) were used. Childhood traumatic events were documented using the Childhood Life Events Scale (CLES). Interaction between occurrence of childhood trauma and common genetic variants throughout the genome was tested to identify single nucleotide polymorphic gene variants (SNPs) whose effects on bipolar AAO differ between individuals clearly exposed (CLES≥2) and not exposed (CLES=0) to childhood trauma.

RESULTS

The modal response to the CLES was 0 (N=480), but an additional 276 subjects had CLES=1, and 363 subjects reported 2 or more traumatic lifetime events. The distribution of age at onset showed a broad peak between ages 12 and 18, with the majority of subjects having onset during that period, and a significant decrease in age of onset with the number of traumatic events. No single SNP showed a statistically significant interaction with the presence of traumatic events to impact bipolar age at onset. However, SNPs in or near genes coding for calcium channel activity-related proteins (Gene Ontology: 0005262) were found to be more likely than other SNPs to show evidence of interaction using the INRICH method (p<0.001).

LIMITATIONS

Retrospective ascertainment of trauma and AAO.

CONCLUSION

Interaction effects of early life trauma with genotype may have a significant effect on the development and manifestation of bipolar disorder. These effects may be mediated in part by genes involved in calcium signaling.

Assessment of copy number variations in the brain genome of schizophrenia patients

Background

Cytogenomic mutations and chromosomal abnormality are implicated in the neuropathology of several brain diseases. Cell heterogeneity of brain tissues makes their detection and validation difficult, however. In the present study, we analyzed gene dosage alterations in brain DNA of schizophrenia patients and compared those with the copy number variations (CNVs) identified in schizophrenia patients as well as with those in Asian lymphocyte DNA and attempted to obtain hints at the pathological contribution of cytogenomic instability to schizophrenia.

Results

Brain DNA was extracted from postmortem striatum of schizophrenia patients and control subjects (n = 48 each) and subjected to the direct two color microarray analysis that limits technical data variations. Disease-associated biases of relative DNA doses were statistically analyzed with Bonferroni’s compensation on the premise of brain cell mosaicism. We found that the relative gene dosage of 85 regions significantly varied among a million of probe sites. In the candidate CNV regions, 26 regions had no overlaps with the common CNVs found in Asian populations and included the genes (i.e., ANTXRL, CHST9, DNM3, NDST3, SDK1, STRC, SKY) that are associated with schizophrenia and/or other psychiatric diseases. The majority of these candidate CNVs exhibited high statistical probabilities but their signal differences in gene dosage were less than 1.5-fold. For test evaluation, we rather selected the 10 candidate CNV regions that exhibited higher aberration scores or larger global effects and were thus confirmable by PCR. Quantitative PCR verified the loss of gene dosage at two loci (1p36.21 and 1p13.3) and confirmed the global variation of the copy number distributions at two loci (11p15.4 and 13q21.1), both indicating the utility of the present strategy. These test loci, however, exhibited the same somatic CNV patterns in the other brain region.

Conclusions

The present study lists the candidate regions potentially representing cytogenomic CNVs in the brain of schizophrenia patients, although the significant but modest alterations in their brain genome doses largely remain to be characterized further.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-015-0144-5) contains supplementary material, which is available to authorized users.

A common microdeletion affecting a hippocampus- and amygdala-specific isoform of tryptophan hydroxylase 2 is not associated with affective disorders

OBJECTIVES

Copy number variants (CNVs) have been shown to affect susceptibility for neuropsychiatric disorders. To date, studies implicating the serotonergic system in complex conditions have just focused on single nucleotide polymorphisms (SNPs). We therefore sought to identify novel common genetic copy number polymorphisms affecting genes of the serotonergic system, and to assess their putative role in bipolar affective disorder (BPAD) and major depressive disorder (MDD).

METHODS

A selection of 41 genes of the serotonergic system encoding receptors, the serotonin transporter, metabolic enzymes and chaperones were investigated using a paired-end mapping (PEM) approach on next-generation sequencing data from the pilot project of the 1000 Genomes Project. For association testing, 593 patients with MDD, 1,145 patients with BPAD, and 1,738 healthy controls were included in the study.

RESULTS

PEM led to the identification of a microdeletion in the gene encoding tryptophan hydroxylase 2 (TPH2), affecting an amygdala- and hippocampus-specific isoform. It was not associated with BPAD or MDD using a case-control association approach.

CONCLUSIONS

We did not find evidence for a role of the TPH2 microdeletion in the pathoetiology of affective disorders. Further studies examining its putative role in behavioral traits regulated by the limbic system are warranted.

Commingling analysis of age-of-onset in bipolar I disorder and the morbid risk for major psychoses in first degree relatives of bipolar I probands

BACKGROUND

Age-of-onset (AO) is increasingly used in molecular genetics of bipolar I disorder (BP-I) as a phenotypic specifier with the goal of reducing genetic heterogeneity. However, questions regarding the cut-off age for defining early onset (EO), as well as the number of onset groups characterizing BP-I have emerged over the last decade with no definite conclusion. The aims of this paper are: 1) to see whether a mixture of three distributions better describes the AO of BP-I than a mixture of two distributions in different independent samples; 2) to compare the morbid risk (MR) for BP-I and for major affective disorders and schizophrenia in first degree relatives of BP-I probands by proband onset group derived from commingling analysis, since the MR to relatives is a trait with strong genetic background.

METHODS

We applied commingling (admixture) analysis to the AO of three BP-I samples from Romania (n=621), Germany (n=882), and Poland (n=354). Subsequently, the morbid risk (MR) for BP-I and for major psychoses (BP-I, BP-II, Mdd-UP, schizoaffective disorders, schizophrenia) was estimated in first degree relatives by proband AO-group derived from admixture analysis in the Romanian sample.

RESULTS

In the three independent samples and in the combined sample two- and three-AO-group distributions fitted the empirical data equally well. The upper EO limit varied between 21 and 25 years from sample to sample. The MR for both BP-I and for all major psychoses was similar in first degree relatives of EO probands (AO≤21) and in relatives of intermediate-onset probands (AO=22-34). Significant MR differences appeared only when comparing the EO group to the late-onset (LO) group (AO>34). Similar to Mdd-UP and schizophrenia, a significant MR decrease in proband first degree relatives was visible after proband AO of 34 years. Under the three-AO-group classification the MR for both BP-I and all major psychoses in first degree relatives did not differ by relative sex in any proband AO-group. Under the two-AO-group classification female relatives of LO probands (AO>24) had a significantly higher MR for all major psychoses than male relatives, while there was no sex difference for the relatives of EO probands.

LIMITATIONS

MR was not computed in the German and Polish samples because family data were not available and 34% of the relatives of the Romanian probands were not available for direct interview.

CONCLUSION

Similar to other clinical traits, the MR for major psychoses to relatives failed to support a three-AO-group classification in BP-I suggesting that this is not more useful for the molecular analysis than a two-AO-group classification.

De novo CNVs in bipolar affective disorder and schizophrenia

An increased rate of de novo copy number variants (CNVs) has been found in schizophrenia (SZ), autism and developmental delay. An increased rate has also been reported in bipolar affective disorder (BD). Here, in a larger BD sample, we aimed to replicate these findings and compare de novo CNVs between SZ and BD. We used Illumina microarrays to genotype 368 BD probands, 76 SZ probands and all their parents. Copy number variants were called by PennCNV and filtered for frequency (<1%) and size (>10 kb). Putative de novo CNVs were validated with the z-score algorithm, manual inspection of log R ratios (LRR) and qPCR probes. We found 15 de novo CNVs in BD (4.1% rate) and 6 in SZ (7.9% rate). Combining results with previous studies and using a cut-off of >100 kb, the rate of de novo CNVs in BD was intermediate between controls and SZ: 1.5% in controls, 2.2% in BD and 4.3% in SZ. Only the differences between SZ and BD and SZ and controls were significant. The median size of de novo CNVs in BD (448 kb) was also intermediate between SZ (613 kb) and controls (338 kb), but only the comparison between SZ and controls was significant. Only one de novo CNV in BD was in a confirmed SZ locus (16p11.2). Sporadic or early onset cases were not more likely to have de novo CNVs. We conclude that de novo CNVs play a smaller role in BD compared with SZ. Patients with a positive family history can also harbour de novo mutations.

Copy number variant study of bipolar disorder in Canadian and UK populations implicates synaptic genes

Genome-wide single nucleotide polymorphism (SNP) data from 936 bipolar disorder (BD) individuals and 940 psychiatrically healthy comparison individuals of North European descent were analyzed for copy number variation (CNV). Using multiple CNV calling algorithms, and validating using in vitro molecular analyses, we identified CNVs implicating several candidate genes that encode synaptic proteins, such as DLG1, DLG2, DPP6, NRXN1, NRXN2, NRXN3, SHANK2, and EPHA5, as well as the neuronal splicing regulator RBFOX1 (A2BP1), and neuronal cell adhesion molecule CHL1. We have also identified recurrent CNVs on 15q13.3 and 16p11.2-regions previously reported as risk loci for neuropsychiatric disorders. In addition, we performed CNV analysis of individuals from 215 BD trios and identified de novo CNVs involving the NRXN1 and DRD5 genes. Our study provides further evidence of the occasional involvement of genomic mutations in the etiology of BD, however, there is no evidence of an increased burden of CNVs in BD. Further, the identification of CNVs at multiple members of the neurexin gene family in BD individuals, supports the role of synaptic disruption in the etiology of BD.

Identifying Potential Regions of Copy Number Variation for Bipolar Disorder

Bipolar disorder is a complex psychiatric disorder with high heritability, but its genetic determinants are still largely unknown. Copy number variation (CNV) is one of the sources to explain part of the heritability. However, it is a challenge to estimate discrete values of the copy numbers using continuous signals calling from a set of markers, and to simultaneously perform association testing between CNVs and phenotypic outcomes. The goal of the present study is to perform a series of data filtering and analysis procedures using a DNA pooling strategy to identify potential CNV regions that are related to bipolar disorder. A total of 200 normal controls and 200 clinically diagnosed bipolar patients were recruited in this study, and were randomly divided into eight control and eight case pools. Genome-wide genotyping was employed using Illumina Human Omni1-Quad array with approximately one million markers for CNV calling. We aimed at setting a series of criteria to filter out the signal noise of marker data and to reduce the chance of false-positive findings for CNV regions. We first defined CNV regions for each pool. Potential CNV regions were reported based on the different patterns of CNV status between cases and controls. Genes that were mapped into the potential CNV regions were examined with association testing, Gene Ontology enrichment analysis, and checked with existing literature for their associations with bipolar disorder. We reported several CNV regions that are related to bipolar disorder. Two CNV regions on chromosome 11 and 22 showed significant signal differences between cases and controls (p < 0.05). Another five CNV regions on chromosome 6, 9, and 19 were overlapped with results in previous CNV studies. Experimental validation of two CNV regions lent some support to our reported findings. Further experimental and replication studies could be designed for these selected regions.

Epigenomic and transcriptomic signatures of a Klinefelter syndrome (47,XXY) karyotype in the brain

Klinefelter syndrome (KS) is the most common sex-chromosome aneuploidy in humans. Most affected individuals carry one extra X-chromosome (47,XXY karyotype) and the condition presents with a heterogeneous mix of reproductive, physical and psychiatric phenotypes. Although the mechanism(s) by which the supernumerary X-chromosome determines these features of KS are poorly understood, skewed X-chromosome inactivation (XCI), gene-dosage dysregulation, and the parental origin of the extra X-chromosome have all been implicated, suggesting an important role for epigenetic processes. We assessed genomic, methylomic and transcriptomic variation in matched prefrontal cortex and cerebellum samples identifying an individual with a 47,XXY karyotype who was comorbid for schizophrenia and had a notably reduced cerebellum mass compared with other individuals in the study (n = 49). We examined methylomic and transcriptomic differences in this individual relative to female and male samples with 46,XX or 46,XY karyotypes, respectively, and identified numerous locus-specific differences in DNA methylation and gene expression, with many differences being autosomal and tissue-specific. Furthermore, global DNA methylation, assessed via the interrogation of LINE-1 and Alu repetitive elements, was significantly altered in the 47,XXY patient in a tissue-specific manner with extreme hypomethylation detected in the prefrontal cortex and extreme hypermethylation in the cerebellum. This study provides the first detailed molecular characterization of the prefrontal cortex and cerebellum from an individual with a 47,XXY karyotype, identifying widespread tissue-specific epigenomic and transcriptomic alterations in the brain.

Reduced burden of very large and rare CNVs in bipolar affective disorder

OBJECTIVES

Large, rare chromosomal copy number variants (CNVs) have been shown to increase the risk for schizophrenia and other neuropsychiatric disorders including autism, attention-deficit hyperactivity disorder, learning difficulties, and epilepsy. Their role in bipolar disorder (BD) is less clear. There are no reports of an increase in large, rare CNVs in BD in general, but some have reported an increase in early-onset cases. We previously found that the rate of such CNVs in individuals with BD was not increased, even in early-onset cases. Our aim here was to examine the rate of large rare CNVs in BD in comparison with a new large independent reference sample from the same country.

METHODS

We studied the CNVs in a case-control sample consisting of 1,650 BD cases (reported previously) and 10,259 reference individuals without a known psychiatric disorder who took part in the original Wellcome Trust Case Control Consortium (WTCCC) study. The 10,259 reference individuals were affected with six non-psychiatric disorders (coronary artery disease, types 1 and 2 diabetes, hypertension, Crohn's disease, and rheumatoid arthritis). Affymetrix 500K array genotyping data were used to call the CNVs.

RESULTS

The rate of CNVs > 100 kb was not statistically different between cases and controls. The rate of very large (defined as > 1 Mb) and rare (< 1%) CNVs was significantly lower in patients with BD compared with the reference group. CNV loci associated with schizophrenia were not enriched in BD and, in fact, cases of BD had the lowest number of such CNVs compared with any of the WTCCC cohorts; this finding held even for the early-onset BD cases.

CONCLUSIONS

Schizophrenia and BD differ with respect to CNV burden and association with specific CNVs. Our findings support the hypothesis that BD is etiologically distinct from schizophrenia with respect to large, rare CNVs and the accompanying associated neurodevelopmental abnormalities.

Association study of 83 candidate genes for bipolar disorder in chromosome 6q selected using an evidence-based prioritization algorithm

BACKGROUND

Prior genome-scans of bipolar disorder have revealed chromosome 6q22 as a promising candidate region. However, linkage disequilibrium (LD) mapping studies have yet to identify replicated susceptibility loci.

METHODS

We analyzed 1,422 LD-tagging single nucleotide polymorphisms (SNPs) in 83 genes to test single-marker and locus-wide evidence of association with bipolar disorder in the NIMH Genetics Initiative bipolar pedigrees and the Portuguese Island Collection (PIC) (N = 1,093 in 528 informative pairs). Both studies previously demonstrated significant evidence of linkage to 6q. SNPs were genotyped using an Illumina iSelect genotyping array which employs the Infinium assay. Evidence of single-marker association was assessed using the generalized disequilibrium test (GDT). Empirical estimates of gene-wide significance were obtained by permutation (via 100,000 gene-dropping simulations) of Fisher's combined test of P-values for each locus.

RESULTS

No single variant yielded significant experiment-wide evidence of association, for either the combined sample or in each subsample. Our gene-dropping simulations identified nominally significant gene-wide associations with multiple loci, of which NT5DC1 in the NIMH subsample and CCNC in the PIC were the strongest candidates. However, no one gene consistently exceeded empirical significance criteria in both independent samples or survived Bonferroni correction for the number of genes tested.

CONCLUSIONS

Using a gene-based approach to family-based association, we identified gene-wide associations with several genes, though no single locus was significantly associated with bipolar disorder in both cohorts. This suggests that chromosome 6q may harbor multiple susceptibility loci or that complex patterns of LD in this region may confound approaches based on common SNPs. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Alterations in mitochondrial DNA copy number and the activities of electron transport chain complexes and pyruvate dehydrogenase in the frontal cortex from subjects with autism

Autism is a neurodevelopmental disorder associated with social deficits and behavioral abnormalities. Recent evidence suggests that mitochondrial dysfunction and oxidative stress may contribute to the etiology of autism. This is the first study to compare the activities of mitochondrial electron transport chain (ETC) complexes (I-V) and pyruvate dehydrogenase (PDH), as well as mitochondrial DNA (mtDNA) copy number in the frontal cortex tissues from autistic and age-matched control subjects. The activities of complexes I, V and PDH were most affected in autism (n=14) being significantly reduced by 31%, 36% and 35%, respectively. When 99% confidence interval (CI) of control group was taken as a reference range, impaired activities of complexes I, III and V were observed in 43%, 29% and 43% of autistic subjects, respectively. Reduced activities of all five ETC complexes were observed in 14% of autistic cases, and the activities of multiple complexes were decreased in 29% of autistic subjects. These results suggest that defects in complexes I and III (sites of mitochondrial free radical generation) and complex V (adenosine triphosphate synthase) are more prevalent in autism. PDH activity was also reduced in 57% of autistic subjects. The ratios of mtDNA of three mitochondrial genes ND1, ND4 and Cyt B (that encode for subunits of complexes I and III) to nuclear DNA were significantly increased in autism, suggesting a higher mtDNA copy number in autism. Compared with the 95% CI of the control group, 44% of autistic children showed higher copy numbers of all three mitochondrial genes examined. Furthermore, ND4 and Cyt B deletions were observed in 44% and 33% of autistic children, respectively. This study indicates that autism is associated with mitochondrial dysfunction in the brain.

Copy number variants in German patients with schizophrenia

Large rare copy number variants (CNVs) have been recognized as significant genetic risk factors for the development of schizophrenia (SCZ). However, due to their low frequency (1∶150 to 1∶1000) among patients, large sample sizes are needed to detect an association between specific CNVs and SCZ. So far, the majority of genome-wide CNV analyses have focused on reporting only CNVs that reached a significant P-value within the study cohort and merely confirmed the frequency of already-established risk-carrying CNVs. As a result, CNVs with a very low frequency that might be relevant for SCZ susceptibility are lost for secondary analyses. In this study, we provide a concise collection of high-quality CNVs in a large German sample consisting of 1,637 patients with SCZ or schizoaffective disorder and 1,627 controls. All individuals were genotyped on Illumina's BeadChips and putative CNVs were identified using QuantiSNP and PennCNV. Only those CNVs that were detected by both programs and spanned ≥30 consecutive SNPs were included in the data collection and downstream analyses (2,366 CNVs, 0.73 CNVs per individual). The genome-wide analysis did not reveal a specific association between a previously unknown CNV and SCZ. However, the group of CNVs previously reported to be associated with SCZ was more frequent in our patients than in the controls. The publication of our dataset will serve as a unique, easily accessible, high-quality CNV data collection for other research groups. The dataset could be useful for the identification of new disease-relevant CNVs that are currently overlooked due to their very low frequency and lack of power for their detection in individual studies.

[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.

Schizophrenia two-hit hypothesis in velo-cardio facial syndrome

Deletion of chr22q11 gives rise to velo-cardio facial syndrome (VCFS) and increases schizophrenia risk. The source of this elevated risk although unknown could result from stochastic, environmental, or genetic factors, the latter encompassing a range of complexity from polygenic mechanisms to "second-hit" mutations. For this study we tested the two-hit hypothesis where additional risk is conferred through a second CNV. We identified large (>100 kb) CNVs in 48 VCFS cases (23 with psychosis--25 without) and show in the psychotic VCFS group there is a significant (P = 0.02) increase in the average size of CNVs (354-227 kb). To identify second-hit loci we focused on individuals possessing gene-centric CNVs and through literature mining identified 4 (31%) psychotic VCFS individuals (n = 13) that overlapped loci previously implicated in neuropsychiatric disorders compared to 1 (10%) from the non-psychotic VCFS individuals (n = 10). For replication 17 VCFS patients with schizophrenia from the molecular genetics of schizophrenia dataset were used to identify further CNVs. Thirteen individuals possessing gene-centric CNVs were identified including 3 (23%) individuals possessing a potential second-hit, taking the overall total in the psychotic VCFS group (n = 26) to 7 (27%) potential second-hit loci. Notably a deletion in a psychotic VCFS patient at 2q23.1 hit the gene MBD5 which when deleted gives rise to intellectual disability, epilepsy, and autistic features. Through this study we potentially extend this phenotypic spectrum to include schizophrenia. Our results suggest the two-hit hypothesis may be relevant to a proportion of VCFS patients with psychosis but sample sizes are small and further studies warranted.

No association between general cognitive ability and rare copy number variation

There is increasing evidence for the role of rare copy-number variation (CNV) in the development of neuropsychiatric disorders. It is likely that such variants also have an effect on the variation of cognition in what is considered the "normal" phenotypic range. The role of rare CNV (>20 KB in length; frequency <5 %) on general cognitive ability is investigated in a sample of 800 individuals (mean age = 16.5, SD = 1.2) using copy-number variants called from the Illumina 610K SNP genotyping array with the software QuantiSNP. We assessed three measures of CNV burden--total CNV length, number of CNV and average CNV length--for both deletions and duplications in combination and separately. No correlation was found between any of the measures of CNV burden and IQ, or when comparing the top and bottom 10 % of the sample for IQ, both on a genome-wide scale and at individual positions across the genome.

A new paradigm emerges from the study of de novo mutations in the context of neurodevelopmental disease

The study of de novo point mutations (new germline mutations arising from the gametes of the parents) remained largely static until the arrival of next-generation sequencing technologies, which made both whole-exome sequencing (WES) and whole-genome sequencing (WGS) feasible in practical terms. Single nucleotide polymorphism genotyping arrays have been used to identify de novo copy-number variants in a number of common neurodevelopmental conditions such as schizophrenia and autism. By contrast, as point mutations and microlesions occurring de novo are refractory to analysis by these microarray-based methods, little was known about either their frequency or impact upon neurodevelopmental disease, until the advent of WES. De novo point mutations have recently been implicated in schizophrenia, autism and mental retardation through the WES of case-parent trios. Taken together, these findings strengthen the hypothesis that the occurrence of de novo mutations could account for the high prevalence of such diseases that are associated with a marked reduction in fecundity. De novo point mutations are also known to be responsible for many sporadic cases of rare dominant mendelian disorders such as Kabuki syndrome, Schinzel-Giedion syndrome and Bohring-Opitz syndrome. These disorders share a common feature in that they are all characterized by intellectual disability. In summary, recent WES studies of neurodevelopmental and neuropsychiatric disease have provided new insights into the role of de novo mutations in these disorders. Our knowledge of de novo mutations is likely to be further accelerated by WGS. However, the collection of case-parent trios will be a prerequisite for such studies. This review aims to discuss recent developments in the study of de novo mutations made possible by technological advances in DNA sequencing.