ANK3 and CACNA1C--missing genetic link for bipolar disorder and major depressive disorder in two German case-control samples

Genetic Landscape of Major Depressive Disorder: Assessment of Potential Diagnostic and Antidepressant Response Markers

BACKGROUND

The clinical heterogeneity in major depressive disorder (MDD), variable treatment response, and conflicting findings limit the ability of genomics toward the discovery of evidence-based diagnosis and treatment regimen. This study attempts to curate all genetic association findings to evaluate potential variants for clinical translation.

METHODS

We systematically reviewed all candidates and genome-wide association studies for both MDD susceptibility and antidepressant response, independently, using MEDLINE, particularly to identify replicated findings. These variants were evaluated for functional consequences using different in silico tools and further estimated their diagnostic predictability by calculating positive predictive values.

RESULTS

A total of 217 significantly associated studies comprising 1200 variants across 545 genes and 128 studies including 921 variants across 412 genes were included with MDD susceptibility and antidepressant response, respectively. Although the majority of associations were confirmed by a single study, we identified 31 and 18 replicated variants (in at least 2 studies) for MDD and antidepressant response. Functional annotation of these 31 variants predicted 20% coding variants as deleterious/damaging and 80.6% variants with regulatory effect. Similarly, the response-related 18 variants revealed 25% coding variant as damaging and 88.2% with substantial regulatory potential. Finally, we could calculate the diagnostic predictability of 19 and 5 variants whose positive predictive values ranges from 0.49 to 0.66 for MDD and 0.36 to 0.66 for response.

CONCLUSIONS

The replicated variants presented in our data are promising for disease diagnosis and improved response outcomes. Although these quantitative assessment measures are solely directive of available observational evidence, robust homogenous validation studies are required to strengthen these variants for molecular diagnostic application.

Association of 11 variants of the dopaminergic and cognitive pathways genes with major depression, schizophrenia and bipolar disorder in the Pakistani population

Background: The dopaminergic pathways control neural signals that modulate mood and behaviour along and have a vital role in the aetiology of major depression (MDD), schizophrenia (SHZ) and bipolar disorder (BD). Genome-wide association studies (GWAS) have reported several dopaminergic and cognitive pathway genes association with these disorders however, no such comprehensive data was available regarding the Pakistani population.Objective: The present study was conducted to analyse the 11 genetic variants of dopaminergic and cognitive system genes in MDD, SHZ, and BD in the Pakistani population.Methods: A total of 1237 subjects [MDD n = 479; BD n = 222; SHZ n = 146; and controls n = 390], were screened for 11 genetic variants through polymerase chain reaction (PCR) techniques. Univariant followed by multivariant logistic regression analysis was applied to determine the genetic association.Results: Significant risk associations were observed for rs4532 and rs1799732 with MDD; and rs1006737 and rs2238056 with BD. However, after applying multiple test corrections rs4532 and rs1799732 association did not remain significant for MDD. Moreover, a protective association was found for three variants; DRD4-120bp, rs10033951 and rs2388334 in the current cohort.Conclusions: The present study revealed the risk association of single nucleotide polymorphisms (SNPs) rs1006737 and rs2238056 with BD and the protective effect of the DRD4-120bp variant in MDD and BD, of rs2388334 in BD and of rs10033951 in MDD, BD, and SHZ in the current Pakistani cohort. Thus, the study is valuable in understanding the genetic basis of MDD, BD and SHZ in the Pakistani population, which may pave the way for future functional studies.

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.

The role of genes affected by human evolution marker GNA13 in schizophrenia

Numerous variants associated with increased risk for SCZ have undergone positive selection and were associated with human brain development, but which brain regions and developmental stages were influenced by the positive selection for SCZ risk alleles are unclear. We analyzed SCZ using summary statistics from a genome-wide association study (GWAS) from the Psychiatric Genomics Consortium (PGC). Machine-learning scores were used to investigate two natural-selection scenarios: complete selection (loci where a selected allele has reached fixation) and incomplete selection (loci where a selected allele has not yet reached fixation). Based on the p value of single nucleotide polymorphisms (SNPs) with selection scores in the top 5%, we formed five subgroups: p < 0.0001, 0.001, 0.01, 0.05, or 0.1. We found that 48 and 29 genes (p < 0.0001) in complete and incomplete selection, respectively, were enrichedfor the transcriptionalco-expressionprofilein theprenatal dorsolateral prefrontal cortex (DFC), inferior parietal cortex (IPC), and ventrolateral prefrontal cortex (VFC). Core genes (GNA13, TBC1D19, and ZMYM4) involved in regulating early brain development were identified in these three brain regions. RNA sequencing for primary cortical neurons that were transfected Gna13 overexpressed lentivirus demonstrated that 135 gene expression levels changed in the Gna13 overexpressed groups compared with the controls. Gene-set analysis identified important associations among common variants of these 13 genes, which were associated with neurodevelopment and putamen volume [p = 0.031; family-wise error correction (FWEC)], SCZ (p = 0.022; FWEC). The study indicate that certain SCZ risk alleles were likely to undergo positive selection during human evolution due to their involvement in the development of prenatal DFC, IPC and VFC, and suggest that SCZ is related to abnormal neurodevelopment.

Ankyrins in human health and disease - an update of recent experimental findings

Ankyrins are adaptor molecules that in eukaryotic cells form complexes with ion channel proteins, cell adhesion and signalling molecules and components of the cytoskeleton. They play a pivotal role as scaffolding proteins, in the structural anchoring to the muscle membrane, in muscle development, neurogenesis and synapse formation. Dysfunction of ankyrins is implicated in numerous diseases such as hereditary spherocytosis, neurodegeneration of Purkinje cells, cardiac arrhythmia, Brugada syndrome, bipolar disorders and schizophrenia, congenital myopathies and congenital heart disease as well as cancers. Detecting either down- or over-expression of ankyrins and ergo their use as biomarkers can provide a new paradigm in the diagnosis of these diseases. This paper provides an outline of knowledge about the structure of ankyrins, and by making use of recent experimental research studies critically discusses their role in several health disorders. Moreover, therapeutic options utilizing engineered ankyrins, designed ankyrin repeat proteins (DARPins), are discussed.

Quantitative separation of the depressive phase of bipolar disorder and major depressive disorder using electrovestibulography

Objectives: No electrophysiological, neuroimaging or genetic markers have been established that strongly relate to the diagnostic separation of bipolar disorder (BD) and major depressive disorder (MDD). This paper's objective is to describe the potential of features, extracted from the recording of electrical activity from the outer ear canal, in a process called electrovestibulography (EVestG), for identifying depressed and partly remitted/remitted MDD and BD patients from each other.Methods: From EVestG data four sensory vestibulo-acoustic features were extracted from both background (no movement) and using a single supine-vertical translation stimulus to distinguish 27 controls, 39 MDD and 43 BD patients.Results: Using leave-one-out-cross-validation, unbiased parametric and non-parametric classification routines resulted in 78-83% (2-3 features), 80-81% (1-2 features) and 66-68% (3 features) accuracies for separation of MDD from BD, controls from depressed (BD & MDD) and the 3-way separation of BD from MDD from control groups, respectively. The main limitations of this study were the inability to fully disentangle the impact of prescribed medication from the responses and also the limited sample size.Conclusions: EVestG features can reliably identify depressed and partly remitted/remitted MDD and BD patients from each other.

Association analysis of ANK3 variants with bipolar disorder in the Korean population

BACKGROUND

Bipolar disorder (BD) is a major psychiatric disorder characterized by alternating mood episodes, including major depressive, hypomanic, and manic episodes. Previous genetic studies of BD have reported several genes as potentially associated with BD. The ANK3 gene has been identified as a possible BD susceptibility gene in genome-wide association analyses.

AIMS

The goal of the present study was to evaluate the association of ANK3 variants with BD in the Korean population.

METHODS

Based on previous results, two single nucleotide polymorphisms (SNPs), rs1938526 and rs10994336, were selected in the ANK3 gene. The study included 287 BD patients and 340 healthy controls. Case-control association and case-control haplotype analyses of the two ANK3 variants were performed.

RESULTS

No significant association was found of either single SNP with BD by case-control association analysis. However, rs1938526 and rs10994336 showed a significant association (overall p = 3.6 × 10^-11; permutation p = 0) in a case-control haplotype analysis.

CONCLUSIONS

The haplotype analysis results suggest that ANK3 variants rs1938526 and rs10994336 may confer susceptibility for BD in the Korean population. Association analysis revealed a probable genetic difference between Korean and Caucasian populations in the degree of ANK3 involvement in BD pathogenesis.

Monotherapy With Major Antihypertensive Drug Classes and Risk of Hospital Admissions for Mood Disorders

Major depressive and bipolar disorders predispose to atherosclerosis, and there is accruing data from animal model, epidemiological, and genomic studies that commonly used antihypertensive drugs may have a role in the pathogenesis or course of mood disorders. In this study, we propose to determine whether antihypertensive drugs have an impact on mood disorders through the analysis of patients on monotherapy with different classes of antihypertensive drugs from a large hospital database of 525 046 patients with follow-up for 5 years. There were 144 066 eligible patients fulfilling the inclusion criteria: age 40 to 80 years old at time of antihypertensive prescription and medication exposure >90 days. The burden of comorbidity assessed by Charlson and Elixhauser scores showed an independent linear association with mood disorder diagnosis. The median time to hospital admission with mood disorder was 847 days for the 299 admissions (641 685 person-years of follow-up). Patients on angiotensin-converting enzyme inhibitors or angiotensin receptor blockers had the lowest risk for mood disorder admissions, and compared with this group, those on β-blockers (hazard ratio=2.11; [95% confidence interval, 1.12-3.98]; P=0.02) and calcium antagonists (2.28 [95% confidence interval, 1.13-4.58]; P=0.02) showed higher risk, whereas those on no antihypertensives (1.63 [95% confidence interval, 0.94-2.82]; P=0.08) and thiazide diuretics (1.56 [95% confidence interval, 0.65-3.73]; P=0.32) showed no significant difference. Overall, our exploratory findings suggest possible differential effects of antihypertensive medications on mood that merits further study: calcium antagonists and β-blockers may be associated with increased risk, whereas angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may be associated with a decreased risk of mood disorders.

Common variants in CACNA1C and MDD susceptibility: A comprehensive meta-analysis

Major depressive disorder (MDD) is one of the most common psychiatric disorders with a relatively high heritability (35-40%). Though rs1006737 in the CACNA1C gene showed significant association with MDD in a British large-scale candidate association study, most of the replication analyses with relatively small sample size reported negative association. Moreover, this locus has never been identified in previous genome-wide association studies (GWAS) for MDD. Here, we conducted a comprehensive meta-analysis of the association between CACNA1C variants and MDD risk by combining all published data. Genetic data from one European GWAS and five individual follow-up studies, which include up to 12,629 patients of MDD and 28,653 controls, that is, the largest sample size on CACNA1C to date, were collected. Rs1006737 showed significant association with MDD in the fixed-effect model (Z = 2.56, P = 0.011, OR = 1.08, 95%CI = 1.04-1.12) and the association remained after reanalyzing the data according to ethnicity. We additionally analyzed other 25 SNPs, genotyped in only one replication study, across the CACNA1C locus, and found that two SNPs, rs4765905 (P = 0.041, OR = 1.05, 95%CI 1.00-1.09) and rs4765937 (P = 0.025, OR = 1.05, 95%CI 1.01-1.09) showed nominal association with MDD, while rs2239073 (P = 0.002, OR = 1.07, 95%CI 1.02-1.11) exhibited significant association with MDD, which survived from multiple corrections. Our study provides support for positive association between CACNA1C and MDD; however, the current data suggest the necessity of replication analyses in a larger-scale sample. © 2016 Wiley Periodicals, Inc.

Evaluating the association between CACNA1C rs1006737 and schizophrenia risk: A meta-analysis

INTRODUCTION

Genetic analyses including genome-wide association studies have reported an intronic single nucleotide polymorphism (SNP) rs1006737 in CACNA1C gene (encoded calcium channel, voltage-dependent, L type, alpha 1C subunit) as a risk factor for schizophrenia in European populations. The replications in other ethnic populations such as East Asians have also been conducted, but the results were inconsistent, either likely due to the limited sample size of single study or genetic heterogeneity between continental populations on this locus.

METHODS

We performed a comprehensive meta-analysis of all available samples from existing studies of East Asian populations, including a total of 9,432 cases and 10,661 controls, to further confirm whether CACNA1C rs1006737 is an authentic risk SNP for schizophrenia in East Asian populations.

RESULTS

Our results revealed a significant association between rs1006737 and schizophrenia (allelic model, P = 4.39 × 10(-6) , pooled odds ratio [OR] = 1.20), and the results were much strengthened when the European and East Asian samples were combined together (P = 2.40 × 10(-17) , pooled OR = 1.12). There is no significant heterogeneity or publication bias between individual studies, and removal of any single study still remained significant associations between rs1006737 and schizophrenia.

DISCUSSION

Our results further confirmed that rs1006737 should be categorized as an authentic risk SNP for schizophrenia in the general populations.

Review of the genetic basis of emotion dysregulation in children and adolescents

Previous evidence suggests that emotion dysregulation may have different biological correlates between adults and children/adolescents. Although the role of genetic factors has been extensively studied in adult-onset emotion dysregulation, the genetic basis for pediatric-onset emotion dysregulation remains elusive. The current review article presents a summary of previous studies that have suggested a few genetic variants associated with pediatric emotion dysregulation. Among these candidate loci, many prior studies have been focused on serotonin transporter promoter gene polymorphism 5-HTTLPR. Certain alleles of the 5-HTTLPR gene polymorphism have been found to be associated with traits associated with emotion dysregulation, such as aggression, affect reactivity, and insecure attachment. Additionally, genetic variants involving dopamine and neurophysiological biomarkers like the COMT Val158Met (rs460) and dopamine receptor D2/ ankyrin repeat and kinase domain containing one polymorphisms may play a role in emotion dysregulation. Inconsistent findings have been noted, possibly due to the heterogeneity in study designs and characteristics of different populations. Further research on the role of genetic predetermination of emotion dysregulation in children and adolescents is warranted.

Toward a Deeper Understanding of the Genetics of Bipolar Disorder

Bipolar disorder is a common, complex psychiatric disorder characterized by mania and depression. The disease aggregates in families, but despite much effort, it has been difficult to delineate the basic genetic model or identify specific genetic risk factors. Not only single gene Mendelian transmission and common variant hypotheses but also multivariate threshold models and oligogenic quasi-Mendelian modes of inheritance have dominated the discussion at times. Almost complete sequence information of the human genome and falling sequencing costs now offer the opportunity to test these models in families in which the disorder is transmitted over several generations. Exome-wide sequencing studies have revealed an astonishing number of rare and potentially damaging mutations in brain-expressed genes that could have contributed to the disease manifestation. However, the statistical analysis of these data has been challenging, because genetic risk factors displayed a high degree of dissimilarity across families. This scenario is not unique to bipolar disorder, but similar results have also been found in schizophrenia, a potentially related psychiatric disorder. Recently, our group has published data which supported an oligogenic genetic model of transmission in a family with bipolar disorder. In this family, three affected siblings shared rare, damaging mutations in multiple genes, which were linked to stress response pathways. These pathways are also the target for drugs frequently used to treat bipolar disorder. This article discusses these findings in the context of previously proclaimed disease models and suggests future research directions, including biological confirmation and phenotype stratification as an approach to disease heterogeneity.

Gene-environment interaction in major depression: focus on experience-dependent biological systems

Major depressive disorder (MDD) is a multifactorial and polygenic disorder, where multiple and partially overlapping sets of susceptibility genes interact each other and with the environment, predisposing individuals to the development of the illness. Thus, MDD results from a complex interplay of vulnerability genes and environmental factors that act cumulatively throughout individual's lifetime. Among these environmental factors, stressful life experiences, especially those occurring early in life, have been suggested to exert a crucial impact on brain development, leading to permanent functional changes that may contribute to lifelong risk for mental health outcomes. In this review, we will discuss how genetic variants (polymorphisms, SNPs) within genes operating in neurobiological systems that mediate stress response and synaptic plasticity, can impact, by themselves, the vulnerability risk for MDD; we will also consider how this MDD risk can be further modulated when gene × environment interaction is taken into account. Finally, we will discuss the role of epigenetic mechanisms, and in particular of DNA methylation and miRNAs expression changes, in mediating the effect of the stress on the vulnerability risk to develop MDD. Taken together, we aim to underlie the role of genetic and epigenetic processes involved in stress- and neuroplasticity-related biological systems on the development of MDD after exposure to early life stress, thereby building the basis for future research and clinical interventions.

Risk and information evaluation of prioritized genes for complex traits: application to bipolar disorder

Many susceptibility genes for complex traits were identified without conclusive findings. There is a strong need to integrate rapidly accumulated genomic data from multi-dimensional platforms, and to conduct risk evaluation for potential therapeutic and diagnostic usages. We set up an algorithm to computationally search for optimal weight-vector for various data sources, while minimized potential noises. Through gene-prioritization framework, combined scores for the resulting prioritized gene-set were calculated using a genome-wide association (GWA) dataset, following with evaluation using weighted genetic risk score and risk-attributed information using an independent GWA dataset. The significance of association of GWA data was corrected for gene length. Enriched functional pathways were identified for the prioritized gene-set using the Gene Ontology analysis. We illustrated our framework with bipolar disorder. 233 prioritized genes were identified from 10,830 candidates that curated from six platforms. The prioritized genes were significantly enriched (P(adjusted) < 1 × 10(-5)) in 18 biological functions and molecular mechanisms including membrane, synaptic transmission, transmission of nerve impulse, integral to membrane, and plasma membrane. Our risk evaluation demonstrated higher weighted genetic risk score in bipolar patients than controls (P-values ranged from 0.002 to 3.8 × 10(-6)). Substantial risk-information (71%) was extracted from prioritized genes for bipolar illness than other candidate-gene sets. Our evidence-based prioritized gene-set provides opportunity to explore the complex network and to conduct follow-up basic and clinical studies for complex traits.

Analysis of ANK3 and CACNA1C variants identified in bipolar disorder whole genome sequence data

OBJECTIVES

Genetic markers in the genes encoding ankyrin 3 (ANK3) and the α-calcium channel subunit (CACNA1C) are associated with bipolar disorder (BP). The associated variants in the CACNA1C gene are mainly within intron 3 of the gene. ANK3 BP-associated variants are in two distinct clusters at the ends of the gene, indicating disease allele heterogeneity.

METHODS

In order to screen both coding and non-coding regions to identify potential aetiological variants, we used whole-genome sequencing in 99 BP cases. Variants with markedly different allele frequencies in the BP samples and the 1,000 genomes project European data were genotyped in 1,510 BP cases and 1,095 controls.

RESULTS

We found that the CACNA1C intron 3 variant, rs79398153, potentially affecting an ENCyclopedia of DNA Elements (ENCODE)-defined region, showed an association with BP (p = 0.015). We also found the ANK3 BP-associated variant rs139972937, responsible for an asparagine to serine change (p = 0.042). However, a previous study had not found support for an association between rs139972937 and BP. The variants at ANK3 and CACNA1C previously known to be associated with BP were not in linkage disequilibrium with either of the two variants that we identified and these are therefore independent of the previous haplotypes implicated by genome-wide association.

CONCLUSIONS

Sequencing in additional BP samples is needed to find the molecular pathology that explains the previous association findings. If changes similar to those we have found can be shown to have an effect on the expression and function of ANK3 and CACNA1C, they might help to explain the so-called 'missing heritability' of BP.

Cognitive effects of the ANK3 risk variants in patients with bipolar disorder and healthy individuals

BACKGROUND

Genetic variants within the ankyrin 3 gene (ANK3) have been identified as a risk factor for bipolar disorder. ANK3 influences action potential generation by clustering sodium gated channels and plays an integral role in neurotransmission. Thus, this gene may influence cognition, a process compromised in bipolar disorder. We investigated whether genetic variants of ANK3 would be associated with an array of cognitive functions in patients with bipolar disorder and healthy individuals.

METHODS

In a sample of 49 patients with bipolar disorder and 633 healthy subjects, we examined possible effects of 2 risk variants within ANK3, rs10994336 and rs10761482, on 7 neurocognitive domains.

RESULTS

Compared to healthy subjects, patients with bipolar disorder demonstrated significantly poorer performance on most of the cognitive domains examined. The risk C-allele of rs10761482 was significantly associated with worse performance on verbal comprehension, logical memory and processing speed in patients. This allele was significantly associated with worse performance on executive function and visual memory in healthy individuals. No significant association was observed between rs10994336 and cognition either in patients or healthy individuals.

LIMITATIONS

The sample size of patients with bipolar disorder was small, and most of the patients were on psychotropic medication.

CONCLUSIONS

These results indicate that a risk variant within ANK3 may have an impact on neurocognitive function, suggesting a mechanism by which ANK3 confers risk for bipolar disorder.

Genetics of bipolar disorder

Bipolar disorder is a common, complex genetic disorder, but the mode of transmission remains to be discovered. Many researchers assume that common genomic variants carry some risk for manifesting the disease. The research community has celebrated the first genome-wide significant associations between common single nucleotide polymorphisms (SNPs) and bipolar disorder. Currently, attempts are under way to translate these findings into clinical practice, genetic counseling, and predictive testing. However, some experts remain cautious. After all, common variants explain only a very small percentage of the genetic risk, and functional consequences of the discovered SNPs are inconclusive. Furthermore, the associated SNPs are not disease specific, and the majority of individuals with a "risk" allele are healthy. On the other hand, population-based genome-wide studies in psychiatric disorders have rediscovered rare structural variants and mutations in genes, which were previously known to cause genetic syndromes and monogenic Mendelian disorders. In many Mendelian syndromes, psychiatric symptoms are prevalent. Although these conditions do not fit the classic description of any specific psychiatric disorder, they often show nonspecific psychiatric symptoms that cross diagnostic boundaries, including intellectual disability, behavioral abnormalities, mood disorders, anxiety disorders, attention deficit, impulse control deficit, and psychosis. Although testing for chromosomal disorders and monogenic Mendelian disorders is well established, testing for common variants is still controversial. The standard concept of genetic testing includes at least three broad criteria that need to be fulfilled before new genetic tests should be introduced: analytical validity, clinical validity, and clinical utility. These criteria are currently not fulfilled for common genomic variants in psychiatric disorders. Further work is clearly needed before genetic testing for common variants in psychiatric disorders should be established.

Polygenic risk and white matter integrity in individuals at high risk of mood disorder

BACKGROUND

Bipolar disorder (BD) and major depressive disorder (MDD) are highly heritable and genetically overlapping conditions characterized by episodic elevation and/or depression of mood. Both demonstrate abnormalities in white matter integrity, measured with diffusion tensor magnetic resonance imaging, that are also heritable. However, it is unclear how these abnormalities relate to the underlying genetic architecture of each disorder. Genome-wide association studies have demonstrated a significant polygenic contribution to BD and MDD, where risk is attributed to the summation of many alleles of small effect. Determining the effects of an overall polygenic risk profile score on neuroimaging abnormalities might help to identify proxy measures of genetic susceptibility and thereby inform models of risk prediction.

METHODS

In the current study, we determined the extent to which common genetic variation underlying risk to mood disorders (BD and MDD) was related to fractional anisotropy, an index of white matter integrity. This was conducted in unaffected individuals at familial risk of mood disorder (n = 70) and comparison subjects (n = 62). Polygenic risk scores were calculated separately for BD and MDD on the basis of genome-wide association study data from the Psychiatric GWAS Consortia.

RESULTS

We report that a higher polygenic risk allele load for MDD was significantly associated with decreased white matter integrity across both groups in a large cluster, with a peak in the right-sided superior longitudinal fasciculus.

CONCLUSIONS

These findings suggest that the polygenic approach to examining brain imaging data might be a useful means of identifying traits linked to the genetic risk of mood disorders.

Ankyrin 3: genetic association with bipolar disorder and relevance to disease pathophysiology

Bipolar disorder (BD) is a multi-factorial disorder caused by genetic and environmental influences. It has a large genetic component, with heritability estimated between 59-93%. Recent genome-wide association studies (GWAS) using large BD patient populations have identified a number of genes with strong statistical evidence for association with susceptibility for BD. Among the most significant and replicated genes is ankyrin 3 (ANK3), a large gene that encodes multiple isoforms of the ankyrin G protein. This article reviews the current evidence for genetic association of ANK3 with BD, followed by a comprehensive overview of the known biology of the ankyrin G protein, focusing on its neural functions and their potential relevance to BD. Ankyrin G is a scaffold protein that is known to have many essential functions in the brain, although the mechanism by which it contributes to BD is unknown. These functions include organizational roles for subcellular domains in neurons including the axon initial segment and nodes of Ranvier, through which ankyrin G orchestrates the localization of key ion channels and GABAergic presynaptic terminals, as well as creating a diffusion barrier that limits transport into the axon and helps define axo-dendritic polarity. Ankyrin G is postulated to have similar structural and organizational roles at synaptic terminals. Finally, ankyrin G is implicated in both neurogenesis and neuroprotection. ANK3 and other BD risk genes participate in some of the same biological pathways and neural processes that highlight several mechanisms by which they may contribute to BD pathophysiology. Biological investigation in cellular and animal model systems will be critical for elucidating the mechanism through which ANK3 confers risk of BD. This knowledge is expected to lead to a better understanding of the brain abnormalities contributing to BD symptoms, and to potentially identify new targets for treatment and intervention approaches.