Common variants at 2q11.2, 8q21.3, and 11q13.2 are associated with major mood disorders

Human mood disorder risk gene Synaptotagmin-14 contributes to mania-like behaviors in mice

Bipolar disorder (BD) and major depressive disorder (MDD) are the most prevalent mood disorders and cause considerable burden worldwide. Compelling evidence suggests a pronounced overlap between these two disorders in clinical symptoms, treatment strategies, and genetic etiology. Here we leverage a BD GWAS (1822 cases and 4650 controls) and a MDD GWAS (5303 cases and 5337 controls), followed by independent replications, to investigate their shared genetic basis among Han Chinese. We have herein identified a lead SNP rs126277 at the 1q32.2 locus, which also exhibited nominal associations with mood disorders and several relevant sub-clinical phenotypes (e.g., mania) in European populations. Bulk tissue and single-cell eQTL analyses suggest that the risk G-allele of rs126277 predicted lower SYT14 mRNA expression in human brains. We generated mice lacking Syt14 (Syt14-/-) and mice with insufficient expression of Syt14 in the hippocampus (Syt14-KD), and found that depletion of Syt14 resulted in mania-like behaviors including hyperactivity and anti-depressive behaviors, resembling aspects of mood disorders. We also confirmed that deficiency of this gene in the hippocampus was sufficient to induce hyperactivity in mice. RNA-sequencing analyses of the hippocampus of Syt14-/- mice revealed significant upregulation of Per1 as well as downregulation of Slc7a11 and Ptprb. Ultrastructural analyses showed significant alteration of the number of vesicles within 50 nm to the active zone and the width of synaptic cleft in the ventral hippocampus of Syt14-/- mice compared with the control mice. Overall, we have identified a novel mood disorder risk gene SYT14, and confirmed its impact on mania-like behaviors. While the current study identifies an essential mood disorder risk gene, further investigations elucidating the detailed mechanisms by which SYT14 contributes to the pathogenesis of the illnesses are needed.

Therapy response prediction in major depressive disorder: current and novel genomic markers influencing pharmacokinetics and pharmacodynamics

Major depressive disorder is connected with high rates of functional disability and mortality. About a third of the patients are at risk of therapy failure. Several pharmacogenetic markers especially located in CYP450 genes such as CYP2D6 or CYP2C19 are of relevance for therapy outcome prediction in major depressive disorder but a further optimization of predictive tools is warranted. The article summarizes the current knowledge on pharmacogenetic variants, therapy effects and side effects of important antidepressive therapeutics, and sheds light on new methodological approaches for therapy response estimation based on genetic markers with relevance for pharmacokinetics, pharmacodynamics and disease pathology identified in genome-wide association study analyses, highlighting polygenic risk score analysis as a tool for further optimization of individualized therapy outcome prediction.

Integrating genome-wide association study and expression quantitative trait loci data identifies NEGR1 as a causal risk gene of major depression disorder

BACKGROUND

Genome-wide association studies (GWAS) have identified several genetic variants associated with major depression disorder (MDD). However, pinpointing the causal variants which are responsible for the association signal at a risk locus remains a major challenge.

METHODS

We used Summary data-based Mendelian Randomization (SMR) with Psychiatric Genomics Consortium (PGC) GWAS summary and brain expression quantitative trait loci (eQTL) data to identify genes whose expression levels are causally associated with MDD. Then we performed differential expression analysis, methylation quantitative trait loci analysis, and cognitive genetics analysis to investigate the potential roles of risk genes in the pathogenesis of MDD.

RESULTS

Through SMR integrative analysis, we identified the SNP rs10789336 located in Neuronal growth regulator 1 (NEGR1) gene significantly affected the expression level of RPL31P12 in brain tissues and contributed to the risk of MDD (P = 1.96 × 10^-6). Consistently, the SNP rs10789336 was associated with the methylation levels of three nearby DNA methylation sites, including cg09256413 (NEGR1, P=1.72 × 10^-10), cg11418303 (prostaglandin E receptor 3 [PTGER3], P = 4.78 × 10^-6), and cg23032215 (ZRANB2 antisense RNA 2 [ZRANB2-AS2], P = 1.23 × 10^-4). Differential expression analysis suggested that the NEGR1 gene was upregulated in prefrontal cortex (P = 5.14 × 10^-3). Cognitive genetics analysis showed that the SNP rs10789336 was associated with cognitive performance (P = 2.41 × 10^-16), educational attainment (P = 1.75 × 10^-14), general cognitive function (P = 2.65 × 10^-12), and verbal numerical reasoning (P = 1.36 × 10^-12).

CONCLUSION

Collectively, our results revealed that the SNP rs10789336 in NEGR1 might confer risk to MDD. Further investigation of the roles of NEGR1 in the pathogenesis of MDD is warranted.

Genetic Advance in Depressive Disorder

Major depressive disorder (MDD) and bipolar disorder (BPD) are both chronic, severe mood disorder with high misdiagnosis rate, leading to substantial health and economic burdens to patients around the world. There is a high misdiagnosis rate of bipolar depression (BD) just based on symptomology in depressed patients whose previous manic or mixed episodes have not been well recognized. Therefore, it is important for psychiatrists to identify these two major psychiatric disorders. Recently, with the accumulation of clinical sample sizes and the advances of methodology and technology, certain progress in the genetics of major depression and bipolar disorder has been made. This article reviews the candidate genes for MDD and BD, genetic variation loci, chromosome structural variation, new technologies, and new methods.

Whole Exome Sequencing Identifies a Novel Predisposing Gene, MAPKAP1, for Familial Mixed Mood Disorder

Background: Mood disorder is ranked seventh among the worldwide causes of non-fatal disease burden and is generally believed to be a heritable disease. However, there is still a substantial portion of the heritability yet to be discovered, despite the success of genome-wide association studies (GWAS) for mood disorder. A proportion of the missing heritability may be accounted for by rare coding variants segregating in families enriched with mood disorder.

Methods: To identify novel variants segregating with mood disorder, we performed whole-exome sequencing on genomic DNA for a multigenerational family with nine members affected with mood disorder. We prioritized potential causal variants within the family based on segregation with mood disorder, predicted functional effects, and prevalence in human populations. In addition, for the top-ranked candidate variant, we conducted validation in vivo to explore the pathogenesis of mood disorder.

Results: We identified and ranked 26 candidate variants based on their segregation pattern and functional annotations. The top-ranked variant, rs78809014, is located in intron 7 of the MAPKAP1 gene. The expression levels of MAPKAP1 in peripheral blood of both major depression disorder (MDD) patients and depressive-like mice ventral dentate gyrus were significantly higher than that in the corresponding controls. In addition, the expression level of MAPKAP1 were correlated with antidepressant response.

Conclusions: Although the exact mechanisms in the family remain to be elucidated, our data strongly indicate a probable role of the variant, rs78809014, in the regulatory process of the expression of MAPKAP1 and thus in the development of mood disorder in familial mood disorder.

Neuropeptide and Small Transmitter Coexistence: Fundamental Studies and Relevance to Mental Illness

Neuropeptides are auxiliary messenger molecules that always co-exist in nerve cells with one or more small molecule (classic) neurotransmitters. Neuropeptides act both as transmitters and trophic factors, and play a role particularly when the nervous system is challenged, as by injury, pain or stress. Here neuropeptides and coexistence in mammals are reviewed, but with special focus on the 29/30 amino acid galanin and its three receptors GalR1, -R2 and -R3. In particular, galanin's role as a co-transmitter in both rodent and human noradrenergic locus coeruleus (LC) neurons is addressed. Extensive experimental animal data strongly suggest a role for the galanin system in depression-like behavior. The translational potential of these results was tested by studying the galanin system in postmortem human brains, first in normal brains, and then in a comparison of five regions of brains obtained from depressed people who committed suicide, and from matched controls. The distribution of galanin and the four galanin system transcripts in the normal human brain was determined, and selective and parallel changes in levels of transcripts and DNA methylation for galanin and its three receptors were assessed in depressed patients who committed suicide: upregulation of transcripts, e.g., for galanin and GalR3 in LC, paralleled by a decrease in DNA methylation, suggesting involvement of epigenetic mechanisms. It is hypothesized that, when exposed to severe stress, the noradrenergic LC neurons fire in bursts and release galanin from their soma/dendrites. Galanin then acts on somato-dendritic, inhibitory galanin autoreceptors, opening potassium channels and inhibiting firing. The purpose of these autoreceptors is to act as a 'brake' to prevent overexcitation, a brake that is also part of resilience to stress that protects against depression. Depression then arises when the inhibition is too strong and long lasting - a maladaption, allostatic load, leading to depletion of NA levels in the forebrain. It is suggested that disinhibition by a galanin antagonist may have antidepressant activity by restoring forebrain NA levels. A role of galanin in depression is also supported by a recent candidate gene study, showing that variants in genes for galanin and its three receptors confer increased risk of depression and anxiety in people who experienced childhood adversity or recent negative life events. In summary, galanin, a neuropeptide coexisting in LC neurons, may participate in the mechanism underlying resilience against a serious and common disorder, MDD. Existing and further results may lead to an increased understanding of how this illness develops, which in turn could provide a basis for its treatment.

VRK2, a Candidate Gene for Psychiatric and Neurological Disorders

Recent large-scale genetic approaches, such as genome-wide association studies, have identified multiple genetic variations that contribute to the risk of mental illnesses, among which single nucleotide polymorphisms (SNPs) within or near the vaccinia related kinase 2 (VRK2) gene have gained consistent support for their correlations with multiple psychiatric and neurological disorders including schizophrenia (SCZ), major depressive disorder (MDD), and genetic generalized epilepsy. For instance, the genetic variant rs1518395 in VRK2 showed genome-wide significant associations with SCZ (35,476 cases and 46,839 controls, p = 3.43 × 10-8) and MDD (130,620 cases and 347,620 controls, p = 4.32 × 10-12) in European populations. This SNP was also genome-wide significantly associated with SCZ in Han Chinese population (12,083 cases and 24,097 controls, p = 3.78 × 10-13), and all associations were in the same direction of allelic effects. These studies highlight the potential roles of VRK2 in the central nervous system, and this gene therefore might be a good candidate to investigate the shared genetic and molecular basis between SCZ and MDD, as it is one of the few genes known to show genome-wide significant associations with both illnesses. Furthermore, the VRK2 gene was found to be involved in multiple other congenital deficits related to the malfunction of neurodevelopment, adding further support for the involvement of this gene in the pathogenesis of these neurological and psychiatric illnesses. While the precise function of VRK2 in these conditions remains unclear, preliminary evidence suggests that it may affect neuronal proliferation and migration via interacting with multiple essential signaling pathways involving other susceptibility genes/proteins for psychiatric disorders. Here, we have reviewed the recent progress of genetic and molecular studies of VRK2, with an emphasis on its role in psychiatric illnesses and neurological functions. We believe that attention to this important gene is necessary, and further investigations of VRK2 may provide hints into the underlying mechanisms of SCZ and MDD.