Genetic polymorphisms in the SCN8A gene are associated with suicidal behavior in psychiatric disorders in the Chinese population

Genetics of suicide ideation. A role for inflammation and neuroplasticity?

Suicide is a leading cause of death worldwide. Suicide ideation (SI) is a known risk factor for suicide behaviour (SB). The current psychobiology and genetic predisposition to SI and SB are poorly defined. Despite convincing relevance of a genetic background for SI, there is no current implementable knowledge about the genetic makeup that identifies subjects at risk for it. One of the possible reasons for the absence of a clear-cut evidence is the polygenetic nature of SI along with the very large sample sizes that are needed to observe significant genetic association result. The CATIE sample was instrumental to the analysis. SI was retrieved as measured by the Calgary test. Clinical possible covariates were identified by a nested regression model. A principal component analysis helped in defining the possible genetic stratification factors. A GWAS analysis, polygenic risk score associated with a random forest analysis and a molecular pathway analysis were undertaken to identify the genetic contribution to SI. As a result, 741 Schizophrenic individuals from the CATIE were available for the genetic analysis, including 166,325 SNPs after quality control and pruning. No GWAS significant result was found. The random forest analysis conducted by combining the polygenic risk score and several clinical variables resulted in a possibly overfitting model (OOB error rate < 1%). The molecular pathway analysis revealed several molecular pathways possibly involved in SI, of which those involved in microglia functioning were of particular interest. A medium-small sample of SKZ individuals was analyzed to shed a light on the genetic of SI. As an expected result from the underpowered sample, no GWAS positive result was retrieved, but the molecular pathway analysis indicated a possible role of microglia and neurodevelopment in SI.

Voltage-gated Sodium Channels and Blockers: An Overview and Where Will They Go?

Voltage-gated sodium (Nav) channels are critical players in the generation and propagation of action potentials by triggering membrane depolarization. Mutations in Nav channels are associated with a variety of channelopathies, which makes them relevant targets for pharmaceutical intervention. So far, the cryoelectron microscopic structure of the human Nav1.2, Nav1.4, and Nav1.7 has been reported, which sheds light on the molecular basis of functional mechanism of Nav channels and provides a path toward structure-based drug discovery. In this review, we focus on the recent advances in the structure, molecular mechanism and modulation of Nav channels, and state updated sodium channel blockers for the treatment of pathophysiology disorders and briefly discuss where the blockers may be developed in the future.

Alterations of Electrophysiological Properties and Ion Channel Expression in Prefrontal Cortex of a Mouse Model of Schizophrenia

Maternal immune activation (MIA) and juvenile social isolation (SI) are two most prevalent and widely accepted environmental insults that could increase the propensity of psychiatric illnesses. Using a two-hit mouse model, we examined the impact of the combination of these two factors on animal behaviors, neuronal excitability and expressions of voltage-gated sodium (Nav) and small conductance calcium-activated potassium (SK) channels in the prefrontal cortex (PFC). We found that MIA-SI induced a number of schizophrenia-related behavioral deficits. Patch clamp recordings revealed alterations in electrophysiological properties of PFC layer-5 pyramidal cells, including hyperpolarized resting membrane potential (RMP), increased input resistance and enhanced medium after-hyperpolarization (mAHP). MIA-SI also increased the ratio of the maximal slope of somatodendritic potential to the peak slope of action potential upstroke, indicating a change in perisomatic Nav availability. Consistently, MIA-SI significantly increased the expression level of Nav1.2 and SK3 channels that contribute to the somatodendritic potential and the mAHP, respectively. Together, these changes may alter neuronal signaling in the PFC and behavioral states, representing a molecular imprint of environmental insults associated with neuropsychiatric illnesses.

The association of attempted suicide with genetic variants in the SLC6A4 and TPH genes depends on the definition of suicidal behavior: a systematic review and meta-analysis

The global prevalence of suicide has increased substantially over the last four decades. Suicidal behavior manifests owing to a combination of biological, behavioral and social factors; however, the etiology of suicidality remains elusive. Even though twin studies have reported a significant heritability of 30-50%, meta-analyses have not highlighted a common genetic variant associated with the spectrum of suicidal behavior. Here, we performed a systematic review of the literature (n = 112) to assess the association between serotonergic and non-serotonergic genetic polymorphisms and suicidal behavior. Using an inverse variance random-effects model, we developed pooled odds ratios for the 10 most commonly studied genetic variants related to suicidal behavior, each with at least five independent studies that met our stringent inclusion criteria. Our pooled results indicate no significant correlation between genetic polymorphisms and overall suicidal behavior. However, subgroups of suicide attempts demonstrated actual significance with the serotonin transporter (SLC6A4) 5HTTLPR (OR = 1.13 (95% confidence interval = 1.05-1.21), P = 0.001) and reached nominal significance with the tryptophan hydroxylase rs1800532 (1.22 (1.05-1.41), P = 0.007) variant. Subgroups of suicidal behavior (completions and attempts) displayed reduced heterogeneity compared with the overall suicidal behavior spectrum. Our findings suggest that the 5HTTLPR and rs1800532 polymorphisms are significantly associated with suicide attempts, but not associated with completed suicides. The high degree of heterogeneity in past studies may be attributed to the lack of a phenotypic distinction between suicidal attempts and completions. Consequently, we have identified an important source of phenotypic heterogeneity that provides a rationale for the current lack of a common genetic variant associated with suicidal behavior.

Suicidal ideation during antidepressant treatment: do genetic predictors exist?

Suicidal thoughts during antidepressant treatment have recently been the focus of several candidate gene and genome-wide association studies. Although the clinical risk factors for such events are well known, unfortunately they do not help to predict who will have a suicidal event during antidepressant treatment and who will not. Pharmacogenomic studies have therefore attempted to use genetic variants to predict individual susceptibility to treatment-related suicidal ideation. In this perspective, several genetic predictors have been highlighted, the majority of which relate to common mechanisms of antidepressant action: genes involved in the neurotrophic and synaptic plasticity systems (CREB1, and BDNF and its receptor NTRK2), noradrenergic system (ADRA2A), glutamatergic system (GRIA3, GRIK2 and GDA), inflammatory and hypothalamic-pituitary-adrenal (HPA) axis systems (IL28RA and FKBP5) and in other brain functions (PAPLN, APOO, KCNIP4 and ELP3). Although some of these genes may be of interest in predicting antidepressant-induced suicidal ideation, they still need to be validated in better phenotypically designed samples. Several methodological factors are indeed responsible for the problems involved in implicating these findings in the causation of a clinically relevant phenotype. These include discrepancies between studies in defining phenotypes, with several different thresholds used to establish significant suicidal ideation; the use of scales not truly designed to measure suicidal ideation; and the paucity of true suicidal events (suicide attempts and/or completion) in pharmacogenomic studies. In conclusion, pharmacogenomic studies are far from fulfilling their promise. There is a need for future pharmacogenetic studies targeting events that are clinically significant in order to find associated variants that will help clinicians to improve their treatment strategies. While awaiting these genetic predictors, clinicians need to bear in mind that all studies in this field support a beneficial effect of antidepressants on suicidal ideation. This should therefore encourage them to prescribe antidepressant medication even in patients with suicidal ideation.