Unravelling the genome: a review of molecular genetic research in schizophrenia

The Inflammatory Signals Associated with Psychosis: Impact of Comorbid Drug Abuse

Psychosis and substance use disorders are two diagnostic categories whose association has been studied for decades. In addition, both psychosis spectrum disorders and drug abuse have recently been linked to multiple pro-inflammatory changes in the central nervous system. We have carried out a narrative review of the literature through a holistic approach. We used PubMed as our search engine. We included in the review all relevant studies looking at pro-inflammatory changes in psychotic disorders and substance use disorders. We found that there are multiple studies that relate various pro-inflammatory lipids and proteins with psychosis and substance use disorders, with an overlap between the two. The main findings involve inflammatory mediators such as cytokines, chemokines, endocannabinoids, eicosanoids, lysophospholipds and/or bacterial products. Many of these findings are present in different phases of psychosis and in substance use disorders such as cannabis, cocaine, methamphetamines, alcohol and nicotine. Psychosis and substance use disorders may have a common origin in an abnormal neurodevelopment caused, among other factors, by a neuroinflammatory process. A possible convergent pathway is that which interrelates the transcriptional factors NFκB and PPARγ. This may have future clinical implications.

Genetic and functional analysis reveals TENM4 contributes to schizophrenia

TENM4, encoding a member of the teneurin protein family, is a risk gene shared by many types of mental diseases and is implicated in neuronal plasticity and signaling. However, the role and the mechanisms of TENM4 in schizophrenia (SCZ) remain unclear. We identified possible pathogenic mutations in the TENM4 gene through target sequencing of TENM4 in 68 SCZ families. We further demonstrated that aberrant expression of Ten-m leads to lower learning ability, sleep reduction, and increased aggressiveness in animal models. RNA sequencing showed that aberrant expression of Ten-m was related to stimulus perception and metabolic process, and Gene Ontology enrichment terms were neurogenesis and ATPase activity. This study provides strong evidence that TENM4 contributes to SCZ, and its functional mutations might be responsible for the impaired neural circuits and behaviors observed in SCZ.

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Possible pathogenic rare missense mutations in TENM4 gene contribute to SCZ

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Aberrant expression of Ten-m leads to behavioral disturbances related to SCZ symptoms

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Ten-m affects stimulation, metabolic process, neurogenesis, and ATPase activity

Two gene co-expression modules differentiate psychotics and controls

Schizophrenia (SCZ) and bipolar disorder (BD) are highly heritable psychiatric disorders. Associated genetic and gene expression changes have been identified, but many have not been replicated and have unknown functions. We identified groups of genes whose expressions varied together, that is co-expression modules, then tested them for association with SCZ. Using weighted gene co-expression network analysis, we show that two modules were differentially expressed in patients versus controls. One, upregulated in cerebral cortex, was enriched with neuron differentiation and neuron development genes, as well as disease genome-wide association study genetic signals; the second, altered in cerebral cortex and cerebellum, was enriched with genes involved in neuron protection functions. The findings were preserved in five expression data sets, including sets from three brain regions, from a different microarray platform, and from BD patients. From those observations, we propose neuron differentiation and development pathways may be involved in etiologies of both SCZ and BD, and neuron protection function participates in pathological process of the diseases.

Genetics in psychiatry: are the promises met?

OBJECTIVES

Psychiatric disorders are among the most heritable common disorders, and for more than 20 years researchers have tried to unravel genetic susceptibility genes. This review briefly outlines the pros and cons of genetic approaches, important advances and possible future directions for readers not familiar with genetic studies.

METHODS

In this article the results of 20 years molecular genetics in psychiatry are shortly and critically summarized on the basis of important reviews and meta-analyses of the last decade, without describing and enumerating the different findings (see special reviews).

RESULTS

Conventional linkage and candidate association studies revealed numerous, but also inconsistent and sometimes contradictory results. The reasons are assumed to include the complexity of the disorder with interaction of several genes of small effects, lack of a valid phenotype, and invalid statistical and methodological issues. Recent systematic genome-wide association studies (GWAS) have reported association of some common variants for schizophrenia and bipolar disorder. However, the risk conferred by these variants is small and genome-wide significance is rare. Also structural variations might be important, and interesting data are arising from copy-number-variations (CNVs).

CONCLUSIONS

Although the new data from GWAS are promising, they still do not meet our initial expectations, identifying a "susceptibility gene". However, they opened new aspects concerning aetiology of psychoses, and the incorporation of new approaches, as epigenetics, or gene-environment interaction, is needed in future study designs.

DNA sequencing by microchip electrophoresis using mixtures of high- and low-molar mass poly(N,N-dimethylacrylamide) matrices

Previous studies have reported that mixed molar mass polymer matrices show enhanced DNA sequencing fragment separation compared with matrices formulated from a single average molar mass. Here, we describe a systematic study to investigate the effects of varying the amounts of two different average molar mass polymers on the DNA sequencing ability of poly(N,N-dimethylacrylamide) (pDMA) sequencing matrices in microfluidic chips. Two polydisperse samples of pDMA, with weight-average molar masses of 3.5 MDa and 770 kDa, were mixed at various fractional concentrations while maintaining the overall polymer concentration at 5% w/v. We show that although the separation of short DNA fragments depends strongly on the overall solution concentration of the polymer, inclusion of the high-molar mass polymer is essential to achieve read lengths of interest (>400 bases) for many sequencing applications. Our results also show that one of the blended matrices, comprised of 3% 3.5 MDa pDMA and 2% 770 kDa pDMA, yields similar sequencing read lengths (>520 bases on average) to the high-molar mass matrix alone, while also providing a fivefold reduction in zero-shear viscosity. These results indicate that the long read lengths achieved in a viscous, high-molar mass polymer matrix are also possible to achieve in a tuned, blended matrix of high- and low-molar mass polymers with a much lower overall solution viscosity.