Lack of Associations of Neuregulin 1 Variations with Schizophrenia and Smooth Pursuit Eye Movement Abnormality in a Korean Population

Evidence for an Association Between a pH-Dependent Potassium Channel, TWIK-1, and the Accuracy of Smooth Pursuit Eye Movements

Purpose

Within the healthy population there is a large variation in the ability to perform smooth pursuit eye movements. Our purpose was to investigate the genetic and physiological bases for this variation.

Methods

We carried out a whole-genome association study, recording smooth pursuit movements for 1040 healthy volunteers by infrared oculography. The primary phenotypic measure was root mean square error (RMSE) of eye position relative to target position. Secondary measures were pursuit gain, frequency of catch-up saccades, and frequency of anticipatory saccades. Ten percent of participants, chosen randomly, were tested twice, giving estimates of test-retest reliability.

Results

No significant association was found with three genes previously identified as candidate genes for variation in smooth pursuit: DRD3, COMT, NRG1. A strong association (P = 3.55 × 10-11) was found between RMSE and chromosomal region 1q42.2. The most strongly associated marker (rs701232) lies in an intron of KCNK1, which encodes a two-pore-domain potassium ion channel TWIK-1 (or K2P1) that affects cell excitability. Each additional copy of the A allele decreased RMSE by 0.29 standard deviation. When a psychophysical test of visually perceived motion was used as a covariate in the regression analysis, the association with rs701232 did not weaken (P = 5.38 × 10-12).

Conclusions

Variation in the sequence or the expression of the pH-dependent ion channel TWIK-1 is a likely source of variance in smooth pursuit. The variance associated with TWIK-1 appears not to arise from sensory mechanisms, because the use of a perceptual covariate left the association intact.

Genetic network analysis indicate that individuals affected by neurodevelopmental conditions have genetic variations associated with ophthalmologic alterations: A critical review of literature

Changes in the nervous system are related to a wide range of mental disorders, which include neurodevelopmental disorders (NDD) that are characterized by early onset mental conditions, such as schizophrenia and autism spectrum disorders and correlated conditions (ASD). Previous studies have shown distinct genetic components associated with diverse schizophrenia and ASD phenotypes, with mostly focused on rescuing neural phenotypes and brain activity, but alterations related to vision are overlooked. Thus, as the vision is composed by the eyes that itself represents a part of the brain, with the retina being formed by neurons and cells originating from the glia, genetic variations affecting the brain can also affect the vision. Here, we performed a critical systematic literature review to screen for all genetic variations in individuals presenting NDD with reported alterations in vision. Using these restricting criteria, we found 20 genes with distinct types of genetic variations, inherited or de novo, that includes SNP, SNV, deletion, insertion, duplication or indel. The variations occurring within protein coding regions have different impact on protein formation, such as missense, nonsense or frameshift. Moreover, a molecular analysis of the 20 genes found revealed that 17 shared a common protein-protein or genetic interaction network. Moreover, gene expression analysis in samples from the brain and other tissues indicates that 18 of the genes found are highly expressed in the brain and retina, indicating their potential role in adult vision phenotype. Finally, we only found 3 genes from our study described in standard public databanks of ophthalmogenetics, suggesting that the other 17 genes could be novel target for vision diseases.

Association between schizophrenia risk allele dosage of rs6994992 and whole-brain structural and functional characteristics

The rs6994992 polymorphism has been reported as a candidate variant associated with schizophrenia (SZ). Neuroimaging studies have revealed that SZ is associated with widespread structural and functional alterations in brain. However, whether the allele dosage of rs6994992 is associated with brain structural or functional features is unclear. We aimed to investigate the association between the risk allele dosage of rs6994992 and whole-brain structural and functional characteristics and to further explore the relationship between these characteristics and cognition. Magnetic resonance images and the rs6994992 genotype were obtained from 53 healthy participants. A general linear model was used to determine the effects of risk allele dosage of rs6994992 on brain characteristics. Spearman correlation analysis was employed to calculate the correlation between altered brain characteristics and cognitive scores. Our results demonstrated that regions with significant differences in structural characteristics between groups with different dosages of rs6994992 were mainly located in the frontal and temporal lobes, hippocampus and angular gyrus. Moreover, significant regions of functional connectivity (FC) partly overlapped with the structural results. Measurements in those significant regions and FCs were correlated with the cognition scales. This association can inform our understanding of the mechanisms through which rs6994992 variants increase the risk for SZ.

BACE1-Dependent Neuregulin-1 Signaling: An Implication for Schizophrenia

Schizophrenia is a chronic psychiatric disorder with a lifetime prevalence of about 1% in the general population. Recent studies have shown that Neuregulin-1 (Nrg1) is a candidate gene for schizophrenia. At least 15 alternative splicing of NRG1 isoforms all contain an extracellular epidermal growth factor (EGF)-like domain, which is sufficient for Nrg1 biological activity including the formation of myelin sheaths and the regulation of synaptic plasticity. It is known that Nrg1 can be cleaved by β-secretase (BACE1) and the resulting N-terminal fragment (Nrg1-ntf) binds to receptor tyrosine kinase ErbB4, which activates Nrg1/ErbB4 signaling. While changes in Nrg1 expression levels in schizophrenia still remain controversial, understanding the BACE1-cleaved Nrg1-ntf and Nrg1/ErbB4 signaling in schizophrenia neuropathogenesis is essential and important. In this review paper, we included three major parts: (1) Nrg1 structure and cleavage pattern by BACE1; (2) BACE1-dependent Nrg1 cleavage associated with schizophrenia in human studies; and (3) Animal studies of Nrg1 and BACE1 mutations with behavioral observations. Our review will provide a better understanding of Nrg1 in schizophrenia and a potential strategy for using BACE1 cleavage of Nrg1 as a unique biomarker for diagnosis, as well as a new therapeutic target, of schizophrenia.

A systematic meta-analysis of the association of Neuregulin 1 (NRG1), D-amino acid oxidase (DAO), and DAO activator (DAOA)/G72 polymorphisms with schizophrenia

The glutamate hypothesis of schizophrenia is related to the proposed dysregulation of D-amino acid oxidase (DAO), DAO activator (DAOA)/G72, and Neuregulin 1 (NRG1) genes. Genetic studies have shown significant associations between DAO, DAOA, NRG1 single-nucleotide polymorphisms (SNPs), and schizophrenia. The systematic literature search yielded 6, 5, and 18 new studies for DAO, DAOA, and NRG1 published after 2011 and not included in the previous SchizophreniaGene (SZGene) meta-analysis. We conducted meta-analyses of 20, 23, and 48 case-control studies, respectively, to comprehensively evaluate the association of 8 DAO, 12 DAOA, and 14 NRG1 SNPs with schizophrenia. The updated meta-analyses resulted in the following findings: the C-allele of DAO rs4623951 was associated with schizophrenia across all pooled studies [Odds ratio (OR) = 0.88, 95% confidence interval (CI) = 0.79-0.98, p = 0.02, N = 3143]; however, no new reports could be included. The G-allele of DAOA rs778293 was associated with schizophrenia in Asian patients (OR = 1.17, 95% CI = 1.08-1.27, p = 0.00008, N = 6117), and the T-allele of DAOA rs3916971 was associated with schizophrenia across all studies (OR = 0.84, 95% CI = 0.73-0.96, p = 0.01, N = 1765). Again, for both SNPs, no new eligible studies were available. After adding new reports, the T-allele of NRG1 SNP8NRG241930 (rs62510682) across all studies (OR = 0.95, 95% CI = 0.91-0.997, p = 0.04, N = 22,898) and in Caucasian samples (OR = 0.95, 95% CI = 0.90-0.99, p = 0.03, N = 16,014), and the C-allele of NRG1 rs10503929 across all studies (OR = 0.89, 95% CI = 0.81-0.97, p = 0.01, N = 6844) and in Caucasian samples (OR = 0.89, 95% CI = 0.81-0.98, p = 0.01, N = 6414) were protective against schizophrenia. Our systematic meta-analysis is the most updated one for the association of DAO, DAOA, and NRG1 SNPs with schizophrenia.

Consensus paper of the WFSBP Task Force on Biological Markers: Criteria for biomarkers and endophenotypes of schizophrenia part II: Cognition, neuroimaging and genetics

OBJECTIVES

Schizophrenia is a group of severe psychiatric disorders with high heritability but only low odds ratios of risk genes. Despite progress in the identification of pathophysiological processes, valid biomarkers of the disease are still lacking.

METHODS

This comprehensive review summarises recent efforts to identify genetic underpinnings, clinical and cognitive endophenotypes and symptom dimensions of schizophrenia and presents findings from neuroimaging studies with structural, functional and spectroscopy magnetic resonance imaging and positron emission tomography. The potential of findings to be biomarkers of schizophrenia is discussed.

RESULTS

Recent findings have not resulted in clear biomarkers for schizophrenia. However, we identified several biomarkers that are potential candidates for future research. Among them, copy number variations and links between genetic polymorphisms derived from genome-wide analysis studies, clinical or cognitive phenotypes, multimodal neuroimaging findings including positron emission tomography and magnetic resonance imaging, and the application of multivariate pattern analyses are promising.

CONCLUSIONS

Future studies should address the effects of treatment and stage of the disease more precisely and apply combinations of biomarker candidates. Although biomarkers for schizophrenia await validation, knowledge on candidate genomic and neuroimaging biomarkers is growing rapidly and research on this topic has the potential to identify psychiatric endophenotypes and in the future increase insight on individual treatment response in schizophrenia.

Association of chromosome 5q21.3 polymorphisms with the exploratory eye movement dysfunction in schizophrenia

Schizophrenia patients show abnormalities in many eye movement tasks. Among them, exploratory eye movements (EEM) dysfunction seems to be specific to schizophrenia. However the mechanism of EEM disturbances in schizophrenia patients remains elusive. We investigate the relationship between EEM and single nucleotide polymorphisms (SNPs) or genes to identify susceptibility loci for EEM in schizophrenia. We firstly performed EEM test, then performed a genome-wide association study (GWAS) and gene-based association study of EEM in 128 individuals with schizophrenia and 143 healthy control subjects. Comparing to healthy controls, schizophrenia patients show significant decrease in NEF (22.99 ± 3.96 vs. 26.02 ± 5.72, P <0.001), TESL (368.78 ± 123.57 vs. 603.12 ± 178.63, P <0.001), MESL (16.86 ± 5.27 vs. 24.42 ± 6.46, P <0.001), RSS (8.22 ± 1.56 vs. 10.92 ± 1.09, P <0.001), and CSS (5.06 ± 0.97 vs. 6.64 ± 0.87, P <0.001). Five SNPs of the MAN2A1, at 5q21.3, were associated with EEM abnormalities (deceased CSS) and satisfied the criteria of GWAS significance threshold. One is localized near 5'-UTR (rs17450784) and four are in intron (rs1438663, rs17162094, rs6877440 and rs10067856) of the gene. Our findings suggest that the identified loci may control the schizophrenia-related quantitative EEM trait. And the identified gene, associated with the EEM phenotype, may lead to new insights into the etiology of schizophrenia.