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Psychological disturbance (PD) or cerebral dysfunction (CD) covers several clinical areas, and has defining features of mental retardation. Recently, we conducted a study to investigate heritable heterogeneity in Pakistani consanguineous couples with recessive autosomal intellectual abnormalities. A cohort of three consanguineous families with multiple birth defects, belonging two to district lower Dir and one to district Lodhra, were selected for molecular analysis. All the affected individuals in the cohort showed autosomal recessive non-syndromic mental disturbances. DNA was extracted and subjected to Single tagged sequence (STS) marker analyses to all known non-syndromic autosomal recessive mental retardation (NS-ARMR) genes, while autozygosity mapping was performed by advanced SNP techniques. Fragment analyses of the NS-ARMR disease genes CRBN, CC2D2A, PRSS12, GRIK2, TUSC3, and CC2D1A using polymorphic STS markers confirmed these to be contender genes for the alteration. Mapping of autozygosity in all the study subjects using genome study revealed nine novel linkage intervals, i.e. four intervals for MR4, two intervals for MR8 and three intervals for MR13. In spite of being a monogenic condition, autosomal recessive mental retardation shows genetic heterogeneity and several genes are involved in different families; hence, there is a chance for involvement of separate gene in each family.

The purpose of this study was to analyze the gene-gene interactions of 70 polymorphic variants of six genes of the neurotrophin and neurexin system (BDNF, NTRK2, NTRK3, NGF, NXPH1, NRXN1) and nine genes of the neurotransmitter system (DRD2, DRD3, DRD4, COMT, GRM3, GRIK2, GRIA2, GRIN2B, RGS2) in determining the risk of developing paranoid schizophrenia in ethnic groups of Russians and Tatars.

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases. In most cases, the development of the disease is sporadic and is not associated with any currently known mutations associated with PD. It is believed that changes associated with the epigenetic regulation of gene expression may play an important role in the pathogenesis of this disease. The study of individuals with an almost identical genetic background, such as monozygotic twins, is one of the best approaches to the analysis of such changes. A whole-transcriptome analysis of dermal fibroblasts obtained from three pairs of monozygotic twins discordant for PD was carried out in this work. Twenty-nine differentially expressed genes were identified in the three pairs of twins. These genes were included in seven processes within two clusters, according to the results of an enrichment analysis. The cluster with the greatest statistical significance included processes associated with the regulation of the differentiation of fat cells, the action potential, and the regulation of glutamatergic synaptic transmission. The most significant genes, which occupied a central position in this cluster, were PTGS2, SCN9A, and GRIK2. These genes can be considered as potential candidate genes for PD. Electronic supplementary material The online version of this article (10.1007/s12031-019-01452-3) contains supplementary material, which is available to authorized users.

Aims The association of single nucleotide polymorphisms (SNPs) of glutamate receptor 2 (GRIK2) gene, as well as gene-gene interaction with the risk of early-onset epilepsy susceptibility, was studied in Chinese children. Methods Generalized multi-factor dimension reduction (GMDR) is used to identify the optimal linkage between interaction among four SNPs and early-onset epilepsy susceptibility. Logistic regression was performed to assess association between four SNPs within GRIK2 gene and the risk of epilepsy. Results The results show that the risk of epilepsy in the rs4840200-T allele carriers was significantly higher than CC (CT/TT vs CC), adjusted OR (95% CI) = 1.74 (1.31-2.20), and the carrier of rs3213607-A allele was also higher than CC (CG/GG vs CC) with adjusted OR (95% CI) = 1.61 (1.23-2.10). We did not detect significant association between rs9390754 and rs2235076 within GRIK2 gene and epilepsy risk. In the GMDR analysis for the gene/gene interaction (2-4 locus models), we found a significant two-locus model (P = 0.001) involving rs4840200 and rs9390754. The cross-validation consistency was 10/10, and the prediction error was 0.632. Participants with rs4840200-CT/TT and rs9390754-GA/AA genotype within GRIK2 gene have the highest epilepsy risk, compared to participants with rs4840200-CC and rs9390754-GG genotype within GRIK2 gene, OR (95% CI) = 2.42 (1.78-3.11), after covariates adjustment for age and gender. Conclusions Both rs4840200-T and rs3213607-A, and the interactions between rs4840200 and rs9390754 are related to the increased risk of epilepsy risk.

NETO1 and NETO2 are auxiliary subunits of kainate receptors (KARs). They interact with native KAR subunits to modulate multiple aspects of receptor function. Variation in KAR genes has been associated with psychiatric disorders in humans, and in mice, knockouts of the Grik1 gene have increased, while Grik2 and Grik4 knockouts have reduced anxiety-like behavior. To determine whether the NETO proteins regulate anxiety and fear through modulation of KARs, we undertook a comprehensive behavioral analysis of adult Neto1(-/-) and Neto2(-/-) mice. We observed no differences in anxiety-like behavior. However, in cued fear conditioning, Neto2(-/-), but not Neto1(-/-) mice, showed higher fear expression and delayed extinction compared to wild type mice. We established, by in situ hybridization, that Neto2 was expressed in both excitatory and inhibitory neurons throughout the fear circuit including the medial prefrontal cortex, amygdala, and hippocampus. Finally, we demonstrated that the relative amount of synaptosomal KAR GLUK2/3 subunit was 20.8% lower in the ventral hippocampus and 36.5% lower in the medial prefrontal cortex in Neto2(-/-) compared to the Neto2(+/+) mice. The GLUK5 subunit abundance was reduced 23.8% in the ventral hippocampus and 16.9% in the amygdala. We conclude that Neto2 regulates fear expression and extinction in mice, and that its absence increases conditionability, a phenotype related to post-traumatic stress disorder and propose that this phenotype is mediated by reduced KAR subunit abundance at synapses of fear-associated brain regions.

Background The aberrant regulation of growth and proliferation is a key feature of carcinoma cells. In order to use molecular strategies to correct these defects toward therapeutic purposes, it is important to characterize the entire spectrum of causative molecules. Materials and methods By using gene transfer technique, SKOV3 ovarian carcinoma cells were transduced with an expression construct of glutamate receptor 6 (glutamate ionotropic receptor kainate type subunit 2, GRIK2) in retroviral vector PQCXIP. The senescence of transduced cells was subsequently characterized. Results Our results demonstrated that retroviral transduction occurs with high frequency and transduced cells continue to proliferate, albeit at a significantly reduced rate, up to 39 days. Some transduced colonies stopped proliferating after 12 days, and none of the clones proliferated beyond 37 days. The doubling time for these transduced cells increased progressively until they reached a complete cell-cycle arrest. The proliferating cells were distinguished by bromodeoxyuridine incorporation and 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide assay. The growth and cell cycle arrest in transduced cells accompanied activation of senescence-associated β-galactosidase. Furthermore, we have demonstrated a decrease in the levels of active protein kinase B and increase in the abundance of inactive cyclin-dependent kinase 1. Conclusion These results indicate involvement of GRIK2 in senescence and suggests GRIK2 as a potential target for therapeutic intervention of cancer cells.

New motifs for phosphorylation sites associated with calcium-dependent protein kinases were developed using 494 sites experimentally proved in mammalians. Subsequent motif-based search revealed consensus regions in α-, β-, and γ-tubulin from Arabidopsis thaliana. The analysis of selected candidate sites and comparison of sequences and structures of homological mammalian and plant protein kinases were performed. Bioinformatic analysis reveals Arabidopsis protein kinases CPK20 (At2g38910), CPK21 (AT4G04720), and GRIK2 (At5g60550) as probable contributors of the plant tubulin code.

Synapse and synapse-associated proteins (SAPs) play critical roles in various neurodegeneration diseases and brain tumors. However, in lower-grade gliomas (LGG), SAPs have not been explored systematically. Herein, we are going to explore SAPs expression profile and its clinicopathological significance in LGG which can offer new insights to glioma therapy. In the present study, we integrate a list of SAPs that covered 231 proteins with synaptogenesis activity and post synapse formation. The LGG RNA-seq data were downloaded from GEO, TCGA and CGGA database. The prognosis associated SAPs in key modules of PPI (protein–protein interaction networks) was regarded as hub SAPs. Western blot, quantitative reverse transcription PCR (qRT-PCR) and immunochemistry results from HPA database were used to verify the expression of hub SAPs. There were 68 up-regulated SAPs and 44 down-regulated SAPs in LGG tissue compared with normal brain tissue. Data from function enrichment analysis revealed functions of differentially expressed SAPs in synapse organization and glutamatergic receptor pathway in LGGs. Survival analysis revealed that four SAPs, GRIK2, GABRD, GRID2 and ARC were correlate with the prognosis of LGG patients. Interestingly, we found that GABRD were up-regulated in LGG patients with seizures, indicating that SAPs may link to the pathogenesis of seizures in glioma patients. The four-SAPs signature was revealed as an independent prognostic factor in gliomas. Our study presented a novel strategy to assess the prognostic risks of LGGs, based on the expression of SAPs.

In this study, we split 2156 individuals from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) data into two groups, establishing a phenotype of exceptional longevity & normal cognition versus cognitive impairment. We conducted a genome-wide association study (GWAS) to identify significant genetic variants and biological pathways that are associated with cognitive impairment and used these results to construct polygenic risk scores. We elucidated the important and robust factors, both genetic and non-genetic, in predicting the phenotype, using several machine learning models. The GWAS identified 28 significant SNPs at p-value $$< 3 \times 10^{-5}$$ < 3 × 10 - 5 significance level and we pinpointed four genes, ESR1, PHB, RYR3, GRIK2, that are associated with the phenotype though immunological systems, brain function, metabolic pathways, inflammation and diet in the CLHLS cohort. Using both genetic and non-genetic factors, four machine learning models have close prediction results for the phenotype measured in Area Under the Curve: random forest (0.782), XGBoost (0.781), support vector machine with linear kernel (0.780), and $$\ell _2$$ ℓ 2 penalized logistic regression (0.780). The top four important and congruent features in predicting the phenotype identified by these four models are: polygenic risk score, sex, age, and education.

Alzheimer's disease (AD) is the most common neurodegenerative disorder. The earliest neuropathology of AD appears in entorhinal cortex (EC) regions. Therapeutic strategies and preventive measures to protect against entorhinal degeneration would be of substantial value in the early stages of AD. In this study, transcriptome based on the Illumina RNA-seq and proteome based on TMT-labelling were performed for RNA and protein profiling on AD EC samples and non-AD control EC samples. Immunohistochemistry was used to validate proteins expressions. After integrated analysis, 57 genes were detected both in transcriptome and proteome data, including 51 in similar altering trends (7 upregulated, 44 downregulated) and 6 in inverse trends when compared AD vs. control. The top 6 genes (GABRG2, CACNG3, CACNB4, GABRB2, GRIK2, and SLC17A6) within the 51 genes were selected and related to "ion transport". Correlation analysis demonstrated negative relationship of protein expression level with the neuropathologic changes. In conclusion, the integrate transcriptome and proteome analysis provided evidence for dysregulation of ion transport across brain regions in AD, which might be a critical signaling pathway that initiates pathology. This study might provide new insight into the earliest changes occurring in the EC of AD and novel targets for AD prevention and treatment.

Background/aim Glutamate receptor GRIK2, previously designated as GluR6, is best described in neuronal cells. However, its biological relevance in non-neuronal cells is not well understood. We have investigated the expression of this important protein in normal human fibroblasts as a function of cell proliferation. Materials and methods We introduced expression constructs of all five isoforms (A-E) of GRIK2 in normal human fibroblasts and investigated the cells for the presence and localization of GRIK2, as well as for cell proliferation and senescence over a period of 24 days. Results The expression of GRIK2-A isoform led to immediate cessation of cell proliferation. However, the cell numbers increased by 1.5- to 9.0-fold in 24 days upon transfection with B, C, D and E isoforms, after which they entered a state of senescence. The decreased proliferation was reflected by incorporation of BrdU in only 2-8% of transfected cells even after culturing them for 16 days. Conclusion Our results are indicative of an association between GRIK2 and aging of fibroblasts.

Kainate receptors are members of the glutamate receptor family that function by both generating ionotropic currents through an integral ion channel pore and coupling to downstream metabotropic signaling pathways. They are highly expressed in the striatum, yet their roles in regulating striatal synapses are not known. Using mice of both sexes, we demonstrate that GluK2-containing kainate receptors expressed in direct pathway spiny projection neurons (dSPNs) inhibit glutamate release at corticostriatal synapses in the dorsolateral striatum. This inhibition requires postsynaptic kainate-receptor-mediated mobilization of a retrograde endocannabinoid (eCB) signal and activation of presynaptic CB1 receptors. This pathway can be activated during repetitive 25 Hz trains of synaptic stimulation, causing short-term depression of corticostriatal synapses. This is the first study to demonstrate a role for kainate receptors in regulating eCB-mediated plasticity at the corticostriatal synapse and demonstrates an important role for these receptors in regulating basal ganglia circuits.SIGNIFICANCE STATEMENTTheGRIK2gene, encoding the GluK2 subunit of the kainate receptor, has been linked to several neuropsychiatric and neurodevelopmental disorders including obsessive compulsive disorder (OCD). Perseverative behaviors associated with OCD are known to result from pathophysiological changes in the striatum and kainate receptor knock-out mice have striatal-dependent phenotypes. However, the role of kainate receptors in striatal synapses is not known. We demonstrate that GluK2-containing kainate receptors regulate corticostriatal synapses by mobilizing endocannabinoids from direct pathway spiny projection neurons. Synaptic activation of GluK2 receptors during trains of synaptic input causes short-term synaptic depression, demonstrating a novel role for these receptors in regulating striatal circuits.

Background The Trail Making Test (TMT) Part A (TMT-A) is a good measure of performance on cognitive processing speed. This study aimed to perform a genome-wide association study of TMT-A in Alzheimer's disease (AD). Methods A total of 757 individuals with TMT-A phenotypes and 620,901 single nucleotide polymorphisms (SNPs) were extracted from the Alzheimer's Disease Neuroimaging Initiative 1 (ADNI-1) cohort. AD related cognitive phenotypes include TMT-A, TMT-B, Functional Activities Questionnaire (FAQ), Clinical Dementia Rating Sum of Boxes (CDR-SB), and Alzheimer's Disease Assessment Scale–Cognitive Subscale 13 (ADAS13). Multivariable linear regression analysis of TMT-A was conducted using PLINK software. The most TMT-A associated gene was tested with Color Trails Test 1 Form A (CTTA), a culturally fair analog of the TMT-A. Functional annotation of SNPs was performed using the RegulomeDB and Genotype-Tissue Expression (GTEx) databases. Results The best signal with TMT-A was rs1108010 (p = 4.34 × 10−8) at 11p15.2 within INSC gene, which was also associated with TMT-B, FAQ, CDR-SB, and ADAS13 (p = 2.47 × 10−4, 8.56 × 10−3, 0.0127 and 0.0188, respectively). Furthermore, suggestive loci were identified such as FOXD2 and CLTA with TMT-A, GBP1/GBP3 with TMT-B, GRIK2 with FAQ, BAALC and CCDC146 with CDR-SB, BAALC and NKAIN2 with ADAS13. Additionally, the best SNP within INSC associated with CTTA was rs7931705 (p = 6.15 × 10−5). Several SNPs had significant eQTLs using GTEx. Conclusions We identified several genes/loci associated with TMT-A and AD related phenotypes. These findings offer the potential for new insights into the pathogenesis of cognitive function and Alzheimer's disease.

// Ryuta Inoue 1, 2 , Yoshihiko Hirohashi 1 , Hiroshi Kitamura 3 , Sachiyo Nishida 1, 2 , Aiko Murai 1 , Akari Takaya 1 , Eri Yamamoto 1 , Masahiro Matsuki 1, 2 , Toshiaki Tanaka 2 , Terufumi Kubo 1 , Munehide Nakatsugawa 1 , Takayuki Kanaseki 1 , Tomohide Tsukahara 1 , Noriyuki Sato 1 , Naoya Masumori 2 , Toshihiko Torigoe 1 1 Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan 2 Department of Urology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan 3 Department of Urology, Graduate School of Medicine and Pharmaceutical Science for Research, University of Toyama, Toyama-Shi 930-0194, Japan Correspondence to: Yoshihiko Hirohashi, email: hirohash@sapmed.ac.jp Toshihiko Torigoe, email: torigoe@sapmed.ac.jp Keywords: cancer stem-like cells, ALDH1, GRIK2, urothelial carcinoma Received: June 29, 2016 Accepted: February 20, 2017 Published: March 16, 2017 ABSTRACT Cancer stem-like cells (CSCs)/cancer-initiating cells (CICs) are small sub-population of cancer cells that are endowed with higher tumor-initiating ability, self-renewal ability and differentiation ability. CSCs/CICs could be isolated as high aldehyde dehydrogenase 1 activity cells (ALDH1 high ) from various cancer samples. In this study, we isolated urothelial carcinoma CSCs/CICs as ALDH high cells and investigated the molecular aspects. ALDH1 high cells showed greater sphere-forming ability and higher tumor-initiating ability in immune-deficient mice than those of ALDH1 low cells, indicating that CSCs/CICs were enriched in ALDH1 high cells. cDNA microarray analysis revealed that an ionotropic glutamate receptor glutamate receptor, ionotropic, kainate 2 (GRIK2) was expressed in ALDH1 high cells at a higher level than that in ALDH1 low cells. GRIK2 gene knockdown by siRNAs decreased the sphere-forming ability and invasion ability, whereas GRIK2 overexpression increased the sphere-forming ability, invasion ability and tumorigenicity, indicating that GRIK2 has a role in the maintenance of CSCs/CICs. Immunohistochemical staining revealed that higher levels of GRIK2 and ALDH1 expression were related to poorer prognosis in urinary tract carcinoma cases. The findings indicate that GRIK2 has a role in the maintenance of urothelial CSCs/CICs and that GRIK2 and ALDH1 can be prognosis prediction markers for urinary tract carcinomas.

Впервые проведен анализ транскриптома фибробластов, полученных от близнецов, дискордантных по спорадической форме БП. Полученные данные свидетельствуют о потенциале исследования фибробластов больных БП для понимания процессов, участвующих в патогенезе БП, а также обращают внимание на три потенциально значимых гена-кандидата БП - GRIK2, PTGS2 и SCN9A. Analysis of transcriptome of fibroblasts, derived from twins, discordant in sporadic form of PD, have been conducted for the first time. We have obtained the evidence for potential utility of fibroblast studies for undrestanding the processes, underlying the PD pathogenesis. Also, our data highlights 3 possible candidate PD genes - GRIK2, PTGS2 & SCN9A.

Seizures that occur during early development are associated with adverse neurodevelopmental outcomes. Causation and mechanisms are currently under investigation. Induction of an early life seizure by kainic acid (KA) in immature rats on post-natal day (P) 7 results in behavioral changes in the adult rat that reflect social and intellectual deficits without overt cellular damage. Our previous work also demonstrated increased expression of CA1 hippocampal long-term potentiation (LTP) and reduced desensitization of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type ionotropic glutamate receptors (AMPA-R) one week following a kainic acid induced seizure (KA-ELS). Here we used RNA sequencing (RNAseq) of mRNA from dorsal hippocampal CA1 to probe changes in mRNA levels one week following KA-ELS as a means to investigate the mechanisms for these functional changes. Ingenuity pathway analysis (IPA) confirmed our previous results by predicting an up-regulation of the synaptic LTP pathway. Differential gene expression results revealed significant differences in 7 gene isoforms. Additional assessments included AMPA-R splice variants and adenosine deaminase acting on RNA 2 (ADAR2) editing sites as a means to determine the mechanism for reduced AMPA-R desensitization. Splice variant analysis demonstrated that KA-ELS result in a small, but significant decrease in the "flop" isoform of Gria3, and editing site analysis revealed significant changes in the editing of a kainate receptor subunit, Grik2, and a serotonin receptor, Htr2c. While these specific changes may not account for altered AMPA-R desensitization, the differences indicate that KA-ELS alters gene expression in the hippocampal CA1 one week after the insult.

Sex differences in opioid dependence (OD) are genetically influenced. We conducted genomewide gene-by-sex interaction scans for the DSM-IV diagnosis of OD in 8,387 African-American (AA) or European-American subjects (43.6% women; 4,715 OD subjects). Among AAs, 9 SNPs were genome-wide significant at ADGRV1 (adhesion G-protein-coupled receptor V1, lead-SNP rs2366929*(C/T), p = 1.5 × 10−9) for sex-different risk of OD, with the rs2366929*C-allele increasing OD risk only for men. The top co-expressions in brain were between ADGRV1 and GRIK2 in substantia nigra and medullary inferior olivary nucleus, and between ADGRV1 and EFHC2 in frontal cortex and putamen. Significant sex-differential ADGRV1 expression from GTEx was detected in breast (Bonferroni-corrected-p p p ADGRV1 co-expression and disease-enrichment analysis identifying the top 10 diseases showed strikingly sexually dimorphic risks. The enrichment and transcriptome analyses provided convergent support that ADGRV1 exerts a sex-different effect on OD risk. This is the first study to identify genetic variants contributing to sex differences in OD. It shows that ADGRV1 contributes to OD risk only in AA men, a finding that warrants further study.

Background: Osteoarthritis (OA) is a complex and heterogeneous condition, and one of the most common degenerative joint diseases. A standardized OA classification based on molecular criteria has yet to be defined. We performed transcriptomic profiling to determine the different molecular signatures associated with knee OA phenotypes. Methods: Five centres clinical research with next-generation sequencing was carried out using 201 samples from patients with knee osteoarthritis. Transcriptomic analysis and unsupervised clustering methods were performed on 131 cartilage samples. To investigate tissue crosstalk of the whole knee microenvironment, transcriptomic analysis was performed in 60 synovia and 65 subchondral bone samples. Findings: We identified four OA subgroups with distinct biological signatures: 1) the glycosaminoglycan metabolic disorder subgroup highly expressed ACAN, lowly expressed VCAN, and was enriched with glycosaminoglycan metabolic functions; 2) the collagen metabolic disorder subgroup presented with osteophyte formation, highly expressed COL1A1 and COL6A1, and was enriched with collagen catabolic functions; 3) the sensory neurons activated subgroup highly expressed GRIK2 and GRM7, and was enriched with synapse assembly functions; and 4) the immunogenic subgroup presented with high inflammation and narrow joint space, highly expressed IL1AŸ and CD34, and was enriched with immune responses. We also explored immune cell composition and tissue crosstalk for three identified metabolic disorder subgroups. Interpretation: These findings challenge the classical diagnosis model based on medical imaging, revealing distinct molecular subgroups in knee OA patients, and opening the door to precision diagnosis and treatment of OA. Funding Statement: This work was financially supported by the National Key R&D Program of China (2017YFA0104902), the National Natural Science Foundation of China (81630065, 31830029, 81802195) grants and China Postdoctoral Science Foundation (2017M621913). Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: Informed consent was obtained from all the participants. The study was approved by the local clinical ethics committees of Zhejiang University School of Medicine and the affiliated hospital of Wenzhou Medical University (2017KYLL11).

Both bipolar disorder (BD) and major depressive disorder (MDD) have high morbidity and share a genetic background. Treatment options for these mood disorders are currently suboptimal for many patients; however, specific genetic variables may be involved in both pathophysiology and response to treatment. Agents such as the glutamatergic modulator ketamine are effective in treatment-resistant mood disorders, underscoring the potential importance of the glutamatergic system as a target for improved therapeutics. Here we review genetic studies linking the glutamatergic system to the pathophysiology and therapeutics of mood disorders. We screened 763 original genetic studies of BD or MDD that investigated genes encoding targets of the pathway/mediators related to the so-called tripartite glutamate synapse, including pre- and post-synaptic neurons and glial cells; 60 papers were included in this review. The findings suggest the involvement of glutamate-related genes in risk for mood disorders, treatment response, and phenotypic characteristics, although there was no consistent evidence for a specific gene. Target genes of high interest included GRIA3 and GRIK2 (which likely play a role in emergent suicidal ideation after antidepressant treatment), GRIK4 (which may influence treatment response), and GRM7 (which potentially affects risk for mood disorders). There was stronger evidence that glutamate-related genes influence risk for BD compared with MDD. Taken together, the studies show a preliminary relationship between glutamate-related genes and risk for mood disorders, suicide, and treatment response, particularly with regard to targets on metabotropic and ionotropic receptors.

INTRODUCTION: The male-predominant sex difference through the spectrum of erosive esophagitis to Barrett's esophagus is widely known. We conducted a genome-wide association study (GWAS) stratified by sex for identifying factors that can predict the endoscopically diagnosed erosive esophagitis. METHODS: Erosive esophagitis was diagnosed by endoscopy and assessed for severity. We identified genetic factors associated with erosive esophagitis that accounted for the sex differences in a cohort of 4,242 participants via a GWAS. After quality control and imputation, genetic associations with erosive esophagitis were investigated by multivariate linear regression in 3,620 subjects. Single-nucleotide polymorphisms (SNPs) with P < 5.0 × 10−8 were considered significant genome wide, and a genetic risk score was constructed for the prediction of erosive esophagitis risk. RESULTS: Six genome-wide significant SNPs near the GRIK2 gene on chromosome 6 were found to be associated with erosive esophagitis only in male subjects. These were predictive of severity through a genetic risk score (P < 0.05), and the findings were validated in a cohort of 622 subjects (P < 0.05). DISCUSSION: This is the first GWAS of erosive esophagitis, and we identified 6 genome-wide significant SNPs in male subjects. These SNPs could help explain the pathogenesis of erosive esophagitis and contribute to the understanding of sex differences. Further genetic investigation could allow for the prediction of high risk for erosive esophagitis and development of new treatment options.

Kainate receptors (KARs) regulate neuronal excitability and network function. Most KARs contain the subunit GluK2 (also known as GRIK2), and the properties of these receptors are determined in part by ADAR2 (also known as ADARB1)-mediated mRNA editing of GluK2, which changes a genomically encoded glutamine residue into an arginine residue (Q/R editing). Suppression of synaptic activity reduces ADAR2-dependent Q/R editing of GluK2 with a consequential increase in GluK2-containing KAR surface expression. However, the mechanism underlying this reduction in GluK2 editing has not been addressed. Here, we show that induction of KAR upscaling, a phenomenon in which surface expression of receptors is increased in response to a chronic decrease in synaptic activity, results in proteasomal degradation of ADAR2, which reduces GluK2 Q/R editing. Because KARs incorporating unedited GluK2(Q) assemble and exit the ER more efficiently, this leads to an upscaling of KAR surface expression. Consistent with this, we demonstrate that partial ADAR2 knockdown phenocopies and occludes KAR upscaling. Moreover, we show that although the AMPA receptor (AMPAR) subunit GluA2 (also known as GRIA2) also undergoes ADAR2-dependent Q/R editing, this process does not mediate AMPAR upscaling. These data demonstrate that activity-dependent regulation of ADAR2 proteostasis and GluK2 Q/R editing are key determinants of KAR, but not AMPAR, trafficking and upscaling. This article has an associated First Person interview with the first author of the paper.

Impulsivity, the predisposition to act prematurely without foresight, is associated with a number of neuropsychiatric disorders, including attention-deficit/hyperactivity disorder (ADHD). Identifying genetic underpinnings of impulsive behavior may help decipher the complex etiology and neurobiological factors of disorders marked by impulsivity. To identify potential genetic factors of impulsivity, we examined common differentially expressed genes (DEGs) in the prefrontal cortex (PFC) of adolescent SHR/NCrl and Wistar rats, which showed marked decrease in preference for the large but delayed reward, compared with WKY/NCrl rats, in the delay discounting task. Of these DEGs, we examined drug-responsive transcripts whose mRNA levels were altered following treatment (in SHR/NCrl and Wistar rats) with drugs that alleviate impulsivity, namely, the ADHD medications methylphenidate and atomoxetine. Prefrontal cortical genetic overlaps between SHR/NCrl and Wistar rats in comparison with WKY/NCrl included genes associated with transcription (e.g., Btg2, Fos, Nr4a2), synaptic plasticity (e.g., Arc, Homer2), and neuron apoptosis (Grik2, Nmnat1). Treatment with methylphenidate and/or atomoxetine increased choice of the large, delayed reward in SHR/NCrl and Wistar rats and changed, in varying degrees, mRNA levels of Nr4a2, Btg2, and Homer2, genes with previously described roles in neuropsychiatric disorders characterized by impulsivity. While further studies are required, we dissected potential genetic factors that may influence impulsivity by identifying genetic overlaps in the PFC of “impulsive” SHR/NCrl and Wistar rats. Notably, these are also drug-responsive transcripts which may be studied further as biomarkers to predict response to ADHD drugs, and as potential targets for the development of treatments to improve impulsivity.

Schizophrenia is a severe mental disorder that affects approximately 1% of the global population, leading to disability and social deadaptation. One of the main neurobiological mechanisms hypothesized for the disease suggests a defect in glutamatergic neurotransmission. Changes in affinity of glutamate receptors, transcription of their genes, and expression of their subunits in the prefrontal cortex, hippocampus, and thalamus have been revealed in schizophrenics in post mortem studies. Association studies of the genes for kainate and AMPA ionotropic glutamate receptors have yielded discrepant results. In this study, GRIA2 and GRIK2 polymorphisms were tested for association with paranoid schizophrenia (PSZ) and response to haloperidol treatment in Russians and Tatars (257 patients and 349 healthy subjects) from Bashkortostan. Higher PSZ risk was associated with GRIK2*ATG (OR = 3.5) and GRIK2*TGG (OR = 3.12) in Tatars and GRIA2*CCC (OR = 9.60) in Russians. The markers of lower PSZ risk were genotype GRIA2*T/T (rs43025506) (OR = 0.34) in Tatars and GRIA2*CCT (OR = 0.481) in Russians. Genotypes GRIK2*T/T (rs2227281) and GRIA2*C/C in Russians and GRIK2*A/A (rs995640) in Tatars were identified as markers of a low efficacy of haloperidol treatment in improving both negative (NEGAT; flat affect, alogia, and anhedonia) and positive (POSIT; delusions, hallucinations, and disorganized thinking) symptoms. Genotype GRIA2*C/Cy was associated with low efficacy of haloperidol treatment in improving positive symptoms in Russians; such markers were not identified in Tatars. The findings support the hypothesis that glutamate receptor genes are involved in the etiology and pathogenesis of schizophrenia. Interethnic differences in genetic risk factors were observed.

Mental retardation (MR)/ intellectual disability (ID) is a neuro-developmental disorder characterized by a low intellectual quotient (IQ) and deficits in adaptive behavior related to everyday life tasks such as delayed language acquisition, social skills or self-help skills with onset before age 18. To date, a few genes (PRSS12, CRBN, CC2D1A, GRIK2, TUSC3, TRAPPC9, TECR, ST3GAL3, MED23, MAN1B1, NSUN1) for autosomal-recessive forms of non syndromic MR (NS-ARMR) have been identified and established in various families with ID. The recently reported candidate gene TRAPPC9 was selected for computational analysis to explore its potentially important role in pathology as it is the only gene for ID reported in more than five different familial cases worldwide. YASARA (12.4.1) was utilized to generate three dimensional structures of the candidate gene TRAPPC9. Hybrid structure prediction was employed. Crystal Structure of a Conserved Metalloprotein From Bacillus Cereus (3D19-C) was selected as best suitable template using position-specific iteration-BLAST. Template (3D19-C) parameters were based on E-value, Z-score and resolution and quality score of 0.32, -1.152, 2.30°A and 0.684 respectively. Model reliability showed 93.1% residues placed in the most favored region with 96.684 quality factor, and overall 0.20 G-factor (dihedrals 0.06 and covalent 0.39 respectively). Protein-Protein docking analysis demonstrated that TRAPPC9 showed strong interactions of the amino acid residues S(253), S(251), Y(256), G(243), D(131) with R(105), Q(425), W(226), N(255), S(233), its functional partner 1KBKB. Protein-protein interacting residues could facilitate the exploration of structural and functional outcomes of wild type and mutated TRAPCC9 protein. Actively involved residues can be used to elucidate the binding properties of the protein, and to develop drug therapy for NS-ARMR patients.

Autism is a complex neurodevelopmental disorder with high heritability. grik2 (which encodes the GluK2 subunit of kainate receptors) has been identified as a susceptibility gene in Autism Spectrum Disorders (ASD), but its role in the core and associated symptoms of ASD still remains elusive. We used mice lacking GluK2 (GluK2 KO) to examine their endophenotype with a view to modeling aspects of autism, including social deficits, stereotyped and repetitive behavior and decreased cognitive abilities. Anxiety was recorded in the elevated plus maze, social behavior in a three-chamber apparatus, and cognition in different water maze protocols. Deletion of the GluK2 gene reduced locomotor activity and sociability as indicated by the social interaction task. In addition, GluK2 KO mice learnt to locate a hidden platform in a water maze surrounded by a curtain with hanging cues faster than wild-type mice. They maintained a bias toward the target quadrant when some of these cues were removed, at which point wild-types orthogonalized the behavior and showed no memory. However, GluK2 KO mice were impaired in spatial reversal learning. These behavioral data together with previously published electrophysiology showing severe anomalies in CA3 network activity, suggest a computational shift in this network for enhanced propensity of pattern completion that would explain the loss of behavioral flexibility in GluK2 KO mice. Although a single mutation cannot recapitulate the entire core symptoms of ASD, our data provide evidence for glutamatergic dysfunction underlying a number of social- and cognition-related phenotypes relevant to ASD.

Astrocytes are glial cells specific to the central nervous system and involved in numerous brain functions, including regulation of synaptic transmission and of immune reactions. There is mounting evidence suggesting astrocytic dysfunction in psychopathologies such as major depression, however, little is known about the underlying etiological mechanisms. Here we report a two-stage study investigating genome-wide DNA methylation associated with astrocytic markers in depressive psychopathology. We first characterized prefrontal cortex samples from 121 individuals (76 who died during a depressive episode and 45 healthy controls) for the astrocytic markers GFAP, ALDH1L1, SOX9, GLUL, SCL1A3, GJA1 and GJB6. A subset of 22 cases with consistently downregulated astrocytic markers was then compared with 17 matched controls using methylation binding domain-2 (MBD2) sequencing followed by validation with high-resolution melting and bisulfite Sanger sequencing. With these data, we generated a genome-wide methylation map unique to altered astrocyte-associated depressive psychopathology. The map revealed differentially methylated regions (DMRs) between cases and controls, the majority of which displayed reduced methylation levels in cases. Among intragenic DMRs, those found in GRIK2 (glutamate receptor, ionotropic kainate 2) and BEGAIN (brain-enriched guanylate kinase-associated protein) were most significant and also showed significant correlations with gene expression. Cell-sorted fractions were investigated and demonstrated an important non-neuronal contribution of methylation status in BEGAIN. Functional cell assays revealed promoter and enhancer-like properties in this region that were markedly decreased by methylation. Furthermore, a large number of our DMRs overlapped known Encyclopedia of DNA elements (ENCODE)-identified regulatory elements. Taken together, our data indicate significant differences in the methylation patterns specific to astrocytic dysfunction associated with depressive psychopathology, providing a potential framework for better understanding this disease phenotype.

Background Copy number variations play a significant role in the aetiology of developmental disabilities including non-syndromic intellectual disability and autism. Case presentation We describe a 19-year old patient with intellectual disability and autism for whom chromosomal microarray (CMA) analysis showed the unusual finding of two de novo microdeletions in cis position on chromosome 6q16.1q16.2 and 6q16.3. The two deletions span 10 genes, including FBXL4, POU3F2, PRDM13, CCNC, COQ3 and GRIK2. We compared phenotypes of patients with similar deletions and looked at the involvement of the genes in neuronal networks in order to determine the pathogenicity of our patient’s deletions. Conclusions We suggest that both deletions on 6q are causing his disease phenotype since they harbour several genes which are implicated in pathways of neuronal development and function. Further studies regarding the interaction between PRDM13 and GRIK2 specifically may be interesting.

Kainate receptors, a subtype of ionotropic glutamate receptors, perform important functions in the spinal cord. This study aimed to examine the expression pattern of various kainate receptor subunits in the spinal cord over different stages of development. The regional distribution and levels of Grik1-5 mRNAs, which encode kainate receptor subunits, were examined in the spinal cord of embryonic, perinatal, and adult mice using in-situ hybridization and real-time PCR. At different developmental stages, the expression of Grik1-5 genes showed different regional distributions in the spinal cord. At E16.5, Grik2 and Grik3 were mainly expressed in the dorsal horns whereas Grik5 was expressed in the entire spinal cord. At P0 and P7, Grik2 expression accumulated at laminae II-IV, whereas Grik1 accumulated at the superficial laminae of the dorsal horns. At P30 and P60, the expression of Grik1-5 was concentrated in the superficial laminae of the dorsal horns. Development-related changes were observed in the expression pattern of Grik1-5. Grik5 was expressed in the entire spinal cord up to the perinatal period, whereas from P7 to adult stages, Grik5 expression was almost exclusively restricted to the dorsal horns. Similar observations were present with Grik1, Grik2, and Grik3. Consistently, quantitative determination of the expression levels of Grik1-5 was in accordance with the in-situ hybridization results. This age-related dynamic expression of kainate receptors may act as one driving force for the development of the anatomofunctional pattern and the maturation of the somatosensory circuitry in the spinal cord.

Computational Analysis and Polymorphism study of Tumor Suppressor Candidate Gene-3 for Non Syndromic Autosomal Recessive Mental Retardation Mental Retardation (MR) is regarded as a neuronal malfunction characterized by a low Intellectual Quotient (IQ). To date, few genes (GRIK2, TUSC3, TRAPPC9, TECR, ST3GAL3, MED23, MAN1B1, NSUN1 PRSS12, CRBN, CC2D1A) for autosomal-recessive non syndromic MR (NS-ARMR) have been identified and established in various families with MR. The recently reported candidate gene “Tumor Suppressor Candidate Gene-3 (TUSC3)” was selected for computational analysis to explore its potential role in pathology as it is the only gene for MR reported in more than five different familial cases worldwide. TUSC3 gene located at chromosome 8p22 contains 11 exons and encodes a protein involved in the vertebrate plasma membrane magnesium ion transport system. Three dimensional structures of the candidate gene TUSC3 and its mutated structure with Q55X were generated. Template parameters were based on Z-score, E value, resolution and quality. Present study demonstrates the reliability of 3D model which satisfies the overall quality of the model constructed, employing both physiochemical and statistical model evaluation. Previously a homozygous 163C-T transition in exon 2 of the TUSC3 gene, resulting in a gln55-to-ter (Q55X) substitution has been reported. And here we predicted by PHD-SNP that X could be either proline (P) or Aspartic acid (D) causing deleterious effect. As mutation at 55 position was responsible for non-syndromic autosomal recessive mental retardation, so it was assumed that mutation was either by proline or aspartic acid. Further, MUPRO, PROVEAN, I-Mutant, Predict SNP, Meta SNP, Panther, SIFT, SNPs 3D confirmed that deleterious mutation was Q55P transition... .

Editing by ADAR enzymes is essential for mammalian life. Still, knowledge of the spatio-temporal editing patterns in mammals is limited. By use of 454 amplicon sequencing we examined the editing status of 12 regionally extracted mRNAs from porcine developing brain encompassing a total of 64 putative ADAR editing sites. In total 24 brain tissues, dissected from up to five regions from embryonic gestation day 23, 42, 60, 80, 100 and 115, were examined for editing. Generally, editing increased during embryonic development concomitantly with an increase in ADAR2 mRNA level. Notably, the Gria2 (GluR-B) Q/R site, reported to be ~100% edited in previous studies, is only 54% edited at embryonic day 23. Transcripts with multiple editing sites in close proximity to each other exhibit coupled editing and an extraordinary incidence of long-range coupling of editing events more than 32 kb apart is observed for the kainate glutamate receptor 2 transcript, Grik2. Our study reveals complex spatio-temporal ADAR editing patterns of coordinated editing events that may play important roles in the development of the mammalian brain.

Huntington's disease is a neurodegenerative disorder caused by an expanded CAG trinucleotide repeat whose length is the major determinant of age at onset but remaining variation appears to be due in part to the effect of genetic modifiers. GRIK2, which encodes GluR6, a mediator of excitatory neurotransmission in the brain, has been suggested in several studies to be a modifier gene based upon a 3′ untranslated region TAA trinucleotide repeat polymorphism. Prior to investing in detailed studies of the functional impact of this polymorphism, we sought to confirm its effect on age at onset in a much larger dataset than in previous investigations. We genotyped the HD CAG repeat and the GRIK2 TAA repeat in DNA samples from 2,911 Huntington's disease subjects with known age at onset, and tested for a potential modifier effect of GRIK2 using a variety of statistical approaches. Unlike previous reports, we detected no evidence of an influence of the GRIK2 TAA repeat polymorphism on age at motor onset. Similarly, the GRIK2 polymorphism did not show significant modifier effect on psychiatric and cognitive age at onset in HD. Comprehensive analytical methods applied to a much larger sample than in previous studies do not support a role for GRIK2 as a genetic modifier of age at onset of clinical symptoms in Huntington's disease.

Several studies support a genetic influence on obsessive-compulsive disorder (OCD) etiology. The role of glutamate as an important neurotransmitter affecting OCD pathophysiology has been supported by neuroimaging, animal model, medication, and initial candidate gene studies. Genes involved in glutamatergic pathways, such as the glutamate receptor, ionotropic, kainate 2 (GRIK2), have been associated with OCD in previous studies. This study examines GRIK2 as a candidate gene for OCD susceptibility in a family-based approach. Probands had full DSM-IV diagnostic criteria for OCD. Forty-seven OCD probands and their parents were recruited from tertiary care OCD specialty clinics from France and USA. Genotypes of single nucleotide polymorphism (SNP) markers and related haplotypes were analyzed using Haploview and FBAT software. The polymorphism at rs1556995 (P= 0.0027; permuted P-value = 0.03) was significantly associated with the presence of OCD. Also, the two marker haplotype rs1556995/rs1417182, was significantly associated with OCD (P= 0.0019, permuted P-value = 0.01). This study supports previously reported findings of association between proximal GRIK2 SNPs and OCD in a comprehensive evaluation of the gene. Further study with independent samples and larger sample sizes is required.

To determine the phenotypic significance of copy number changes (CNCs) in the human genome, we performed genome-wide segmental aneuploidy profiling by BAC-based array-CGH of 278 unrelated patients with multiple congenital abnormalities and mental retardation (MCAMR) and in 48 unaffected family members. In 20 patients, we found de novo CNCs composed of multiple consecutive probes. Of the 125 probes making up these probably pathogenic CNCs, 14 were also found as single CNCs in other patients and 5 in healthy individuals. Thus, these CNCs are not by themselves pathogenic. Almost one out of five patients and almost one out of six healthy individuals in our study cohort carried a gain or a loss for any one of the recently discovered microdeletion/microduplication loci, whereas seven patients and one healthy individual showed losses or gains for at least two different loci. The pathogenic burden resulting from these CNCs may be limited as they were found with similar frequencies among patients and healthy individuals (P = 0.165; Fischer's exact test), and several individuals showed CNCs at multiple loci. CNCs occurring specifically in our study cohort were enriched for components of the glutamate receptor family (GRIA2, GRIA4, GRIK2 and GRIK4) and genes encoding proteins involved in guiding cell localization during development (ATP1A2, GIRK3, GRIA2, KCNJ3, KCNJ10, KCNK17 and KCNK5). This indicates that disease cohort-specific compilations of CNCs may aid in identifying loci, genes and biological processes that contribute to the phenotype of patients. European Journal of Human Genetics (2010) 18, 39-46; doi:10.1038/ejhg.2009.120; published online 22 July 2009

We describe the clinical, radiographic, and genetic features of a large consanguineous Moroccan family in which bilateral occipital polymicrogyria segregated as an autosomal recessive trait. Six affected members of the family had partial complex seizures often associated with behavioral abnormalities. On MRI, three patients had a thickened irregular cortex in the lateral occipital lobes with small gyri. A high-density genome-wide scan with 10,000 SNPs established linkage by homozygosity mapping to a 14-Mb region on chromosome 6q16-q22. Candidate genes by function (TUBE1, GRIK2, GPRC6A, GPR6, NR2E1, MICAL1, and MARCKS) in this locus were screened for mutations.

Recent studies have shown that autosomal recessive mental retardation (ARMR) is extremely heterogeneous, and there is reason to believe that the number of underlying gene defects goes into the thousands. To date, however, only four genes have been implicated in nonsyndromic ARMR (NS-ARMR): PRSS12 (neurotrypsin), CRBN (cereblon), CC2D1A, and GRIK2. As part of an ongoing systematic study aiming to identify ARMR genes, we investigated a large consanguineous family comprising seven patients with nonsyndromic ARMR in four sibships. Genome-wide SNP typing enabled us to map the relevant genetic defect to a 4.6 Mbp interval on chromosome 8. Haplotype analyses and copy-number studies led to the identification of a homozygous deletion partly removing TUSC3 (N33) in all patients. All obligate carriers of this family were heterozygous, but none of 192 unrelated healthy individuals from the same population carried this deletion. We excluded other disease-causing mutations in the coding regions of all genes within the linkage interval by sequencing; moreover, we verified the complete absence of a functional TUSC3 transcript in all patients through RT-PCR. TUSC3 is thought to encode a subunit of the endoplasmic reticulum-bound oligosaccharyltransferase complex that catalyzes a pivotal step in the protein N-glycosylation process. Our data suggest that in contrast to other genetic defects of glycosylation, inactivation of TUSC3 causes nonsyndromic MR, a conclusion that is supported by a separate report in this issue of AJHG. TUSC3 is only the fifth gene implicated in NS-ARMR and the first for which mutations have been reported in more than one family.

The glutamate receptor 6 (GluR6 or GRIK2, one of the kainate receptors) gene resides in a genetic linkage region (6q21) associated with bipolar disorder (BPD), but its function in affective regulation is unknown. Compared with wild-type (WT) and GluR5 knockout (KO) mice, GluR6 KO mice were more active in multiple tests and super responsive to amphetamine. In a battery of specific tests, GluR6 KO mice also exhibited less anxious or more risk-taking type behavior and less despair-type manifestations, and they also had more aggressive displays. Chronic treatment with lithium, a classic antimanic mood stabilizer, reduced hyperactivity, aggressive displays and some risk-taking type behavior in GluR6 KO mice. Hippocampal and prefrontal cortical membrane levels of GluR5 and KA-2 receptors were decreased in GluR6 KO mice, and chronic lithium treatment did not affect these decreases. The membrane levels of other glutamatergic receptors were not significantly altered by GluR6 ablation or chronic lithium treatment. Together, these biochemical and behavioral results suggest a unique role for GluR6 in controlling abnormalities related to the behavioral symptoms of mania, such as hyperactivity or psychomotor agitation, aggressiveness, driven or increased goal-directed pursuits, risk taking and supersensitivity to psychostimulants. Whether GluR6 perturbation is involved in the mood elevation or thought disturbance of mania and the cyclicity of BPD are unknown. The molecular mechanism underlying the behavioral effects of lithium in GluR6 KO mice remains to be elucidated.

Nonsyndromic mental retardation is one of the most important unresolved problems in genetic health care. Autosomal forms are far more common than X-linked forms, but, in contrast to the latter, they are still largely unexplored. Here, we report a complex mutation in the ionotropic glutamate receptor 6 gene (GRIK2, also called "GLUR6") that cosegregates with moderate-to-severe nonsyndromic autosomal recessive mental retardation in a large, consanguineous Iranian family. The predicted gene product lacks the first ligand-binding domain, the adjacent transmembrane domain, and the putative pore loop, suggesting a complete loss of function of the GLU(K6) protein, which is supported by electrophysiological data. This finding provides the first proof that GLU(K6) is indispensable for higher brain functions in humans, and future studies of this and other ionotropic kainate receptors will shed more light on the pathophysiology of mental retardation.

Obsessive-compulsive disorder (OCD) is a psychiatric condition characterized by intrusive thoughts and urges and repetitive, intentional behaviors that cause significant distress and impair functioning. The OCD Collaborative Genetics Association Study (OCGAS) is comprised of comprehensively assessed OCD patients with an early age of OCD onset. After application of a stringent quality control protocol, a total of 1065 families (containing 1406 patients with OCD), combined with population-based samples (resulting in a total sample of 5061 individuals), were studied. An integrative analyses pipeline was utilized, involving association testing at single-nucleotide polymorphism (SNP) and gene levels (via a hybrid approach that allowed for combined analyses of the family- and population-based data). The smallest P-value was observed for a marker on chromosome 9 (near PTPRD, P=4.13 × 10(-)(7)). Pre-synaptic PTPRD promotes the differentiation of glutamatergic synapses and interacts with SLITRK3. Together, both proteins selectively regulate the development of inhibitory GABAergic synapses. Although no SNPs were identified as associated with OCD at genome-wide significance level, follow-up analyses of genome-wide association study (GWAS) signals from a previously published OCD study identified significant enrichment (P=0.0176). Secondary analyses of high-confidence interaction partners of DLGAP1 and GRIK2 (both showing evidence for association in our follow-up and the original GWAS study) revealed a trend of association (P=0.075) for a set of genes such as NEUROD6, SV2A, GRIA4, SLC1A2 and PTPRD. Analyses at the gene level revealed association of IQCK and C16orf88 (both P

Studies analysing the effects of acute treatments on animal behaviour and brain biochemistry frequently use pairwise comparisons between sham-treated and -untreated animals. In this study, we analyse expression of tPA, Grik2, Smarca2 and the transcription factor, Sp1, in mouse cerebellum following acute ethanol treatment. Expression is compared to saline-injected and -untreated control animals. We demonstrate that acute i.p. injection of saline may alter gene expression in a gene-specific manner and that ethanol may modify the effects of sham treatment on gene expression, as well as inducing specific effects independent of any handling related stress. In addition to demonstrating the complexity of gene expression in response to physical and environmental stress, this work raises questions on the interpretation and validity of studies relying on pairwise comparisons.

The glutamatergic dysfunction hypothesis suggests that genes involved in the glutamate neurotransmitter system are candidates for schizophrenia-susceptibility genes. We have been doing systematic studies of the association of schizophrenia with each member of the glutamate receptor gene family. In this review, we summarize our results of association studies of five glutamate receptor genes, two of which are metabotropic, GRM2 and GRM3, whereas the other four are ionotropic, GRIA4, GRIK1, GRIK2 and GRIN1. Haplotype analyses using combinations of SNPs evenly distributed across the relevant genes showed significant associations of GRM3 and GRIA4 with schizophrenia. We discuss the possible involvement of glutamate receptor genes in the pathogenesis of schizophrenia, on the basis of association as well as linkage and postmortem studies previously reported. Replication of positive associations using different populations and the family-based study are necessary to confirm the results. Generation of gene-manipulated mice to represent endophenotypes of schizophrenia would be an alternative way to verify susceptibility genes. Some members of the glutamate receptor family may be promising targets for schizophrenia drugs. Drug Dev. Res. 60:137–151, 2003. © 2003 Wiley-Liss, Inc.

The glutamatergic dysfunction hypothesis of schizophrenia suggests genes involved in glutamatergic transmission as candidates for schizophrenia-susceptibility genes. The GluR6 kainate receptor gene GRIK2 is located on chromosome 6q16.3–q21, a schizophrenia susceptibility region, as suggested by multiple linkage studies. We examined 15 SNPs evenly distributed in the entire GRIK2 region (>700 kb) in Japanese patients with schizophrenia ( n =100) and controls ( n =100). Neither genotype nor allele frequency showed a significant association with the disorder. We constructed 2-SNP haplotypes from the 15 SNPs. Although we observed three long linkage disequilibrium blocks (>150 kb) within the GRIK2 region, none of the pairwise haplotypes showed a significant association with the disorder. Therefore, we conclude that GRIK2 does not play a major role in the pathogenesis of schizophrenia in the Japanese population.

Osteosarcoma is a primary, malignant bone tumour mainly affecting young adults with a five-year survival rate of 60-70% depending on presentation of metastasis at diagnosis. Tumours are marked by genetic instability and heterogeneity and for this reason, molecular subtypes have yet to be characterized. Survival rates have remained consistent over the past few decades and novel molecular targets for treatment are needed. Current genomic strategies have identified recurrent copy number alterations. In a study of 44 flash frozen osteosarcoma tumours which were obtained at the time of biopsy and 25 blood-matched samples we identified recurrent copy number losses including a region at 6q16.3 in 14% of tumours. Focal deletions were observed in the 5’ intergenic space and first intron of the GRIK2 gene and do not overlap with any coding sequence. The relationship between alterations in this region and osteosarcoma tumourigenesis has yet to be explored in depth. GRIK2 encodes an ionotropic glutamate receptor that has been implicated as a tumour suppressor in gastric cancer. An interesting feature of the tumours was the overlap of focal deletions with a SETDB1 histone methyltransferase binding site indicating a potential connection with epigenetic regulation of GRIK2. The goal of this study is to examine the effects of non-coding, focal deletions on GRIK2 gene expression, function and regulation in osteosarcoma cells. GRIK2 transcript levels were measured in osteosarcoma tumours and cell lines using qRT-PCR. Functional assays were performed to characterize the role of GRIK2 in osteosarcoma cell proliferation, migration and apoptosis in vitro. Gene editing with CRISPR/cas9 was performed to examine the link between non-coding deletions and GRIK2 expression. GRIK2 transcript levels varied in tumours; several tumours with focal deletions had increased transcript levels relative to cell lines which demonstrated low expression levels. Due to the observation of low transcript levels, a gain of function approach was employed to examine GRIK2 function in vitro. Overexpression of GRIK2 decreased proliferation, migration and increased apoptosis in osteosarcoma cells. Gene editing of the SETDB1 binding site resulted in increased GRIK2 transcript levels relative to untreated cells. This study suggests that non-coding focal deletions are linked to high expression levels of GRIK2 which may confer a less aggressive phenotype and are involved in epigenetic regulation of the gene. Citation Format: Justin G. Mayers, Nalan Gokgoz, Jay S. Wunder, Irene L. Andrulis. Investigation of the effects of alterations in the glutamate receptor, GRIK2 on osteosarcoma tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5507. doi:10.1158/1538-7445.AM2017-5507

Objective:To identify inherited or de novo mutations associated with a suite of neurodevelopmental abnormalities in a 10-year-old patient displaying ataxia, motor and speech delay, and intellectual disability.Methods:We performed whole-exome sequencing of the proband and her parents. A pathogenic gene variant was identified as damaging based on sequence conservation, gene function, and association with disorders having similar phenotypic profiles. Functional characterization of the mutated protein was performed in vitro using a heterologous expression system.Results:A single de novo point mutation in the GRIK2 gene was identified as causative for the neurologic symptoms of the proband. The mutation is predicted to change a codon for alanine to that of a threonine at position 657 (A657T) in the GluK2 kainate receptor (KAR) subunit, a member of the ionotropic glutamate receptor gene family. Whole-cell voltage-clamp recordings revealed that KARs incorporating the GluK2(A657T) subunits show profoundly altered channel gating and are constitutively active in nominally glutamate-free extracellular media.Conclusions:In this study, we associate a de novo gain-of-function mutation in the GRIK2 gene with deficits in motor and higher order cognitive function. These results suggest that disruption of physiologic KAR function precludes appropriate development of the nervous system.

Clinical observations indicate that atypical antipsychotics, especially clozapine, induce obsessive–compulsive (OC) symptoms in schizophrenia patients. Recent data from neuroimaging and clinical trials suggest a role for altered glutamate neurotransmission in the etiology of OC disorder (OCD), and SLC1A1, GRIN2B, and GRIK2 have all been reported to regulate glutamate transmission and affect OCD pathophysiology. This study aimed to determine whether SLC1A1, GRIN2B, and GRIK2 are associated with clozapine-induced OC symptoms. A total of 250 clinically stable schizophrenia patients receiving clozapine treatment were recruited. The Yale-Brown Obsessive Compulsive Scale (Y-BOCS) was used to evaluate the severity of OC symptoms. Based on their Y-BOCS scores, 250 patients were divided into the OC and non-OC groups (patients with or without OC symptoms, respectively). Additionally, three reported OCD susceptibility polymorphisms, SLC1A1 (rs2228622), GRIN2B (rs890), and GRIK2 (rs1556995), were genotyped. Trends of association with OC symptoms were observed in rs2228622A and rs890T alleles. SLC1A1 and GRIN2B interaction was found in the significant two-locus gene–gene interaction model (p = 0.0021), using the multifactor dimensionality reduction method. Further analysis showed a significant interaction between SLC1A1 and GRIN2B on the Y-BOCS score (F 6, 137 = 7.650, p

Purpose: Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus (DM). The susceptibility genes responsible for increasing the risk for DR in type 2 diabetes (T2D) were sought in this study. Methods: A case-control study was carried out, comprising 749 unrelated T2D individuals with (n = 174) and without (n = 575) DR. Genotypic distributions of single nucleotide polymorphisms (SNPs) were determined for subjects with and without DR. Results: Eight chromosome 6 SNPs, having the most significant differences, were delineated: rs10499298, rs10499299, rs17827966, rs1224329, rs1150790, rs713050, rs2518344 and rs487083; all were associated with genes TMEM217, MRPL14 and GRIK2. After adjusting for the duration of DM and levels of hemoglobin A1c, the TT genotype of rs713050, and the AG + AA genotypes of rs2518344 and rs10499298, differed significantly between those with and without DR. Haplotype analysis revealed haplotype C-A-C, residing in rs10499299, rs10499298 and rs17827966, to have significant linkage disequilibrium. Conclusions: We identified new loci on chromosome 6 associated to DR; all loci showed high levels of linkage disequilibrium.

For the identification of genes associated with smoking initiation and current smoking, genome-wide association analyses were carried out in 3497 subjects. Significant genes that replicated in three independent samples (n = 405, 5810, and 1648) were visualized into a biologically meaningful network showing cellular location and direct interaction of their proteins. Several interesting groups of proteins stood out, including glutamate receptors (e.g., GRIN2B, GRIN2A, GRIK2, GRM8), proteins involved in tyrosine kinase receptor signaling (e.g., NTRK2, GRB14), transporters (e.g., SLC1A2, SLC9A9) and cell-adhesion molecules (e.g., CDH23). We conclude that a network-based genome-wide association approach can identify genes influencing smoking behavior. © 2009 The American Society of Human Genetics.

The glutamate pathways are involved in diverse processes such as learning and memory, epilepsy, and they play important roles in neural plasticity, neural development, and neurodegeneration. It has been proposed that autism could be a hypoglutamatergic disorder. Recently, Jamain et al. reported that the glutamate receptor 6 (GluR6 or GRIK2) is in linkage disequilibrium with autism. In the present study, the transmission disequilibrium test (TDT) and the haplotype transmission were performed to analyze the four SNPs (SNP1: rs995640; SNP2: rs2227281; SNP3: rs2227283; SNP4: rs2235076) of GluR6 in 174 Chinese Han parent-offspring trios. The TDT demonstrated that the two SNPs (SNP2 and SNP3) showed preferential transmission (TDT P = 0.032). The global chi(2) test for haplotype transmission also revealed an association between GluR6 and autism (chi(2) = 10.78, df = 3, P = 0.013). Our results suggested that GluR6 is in linkage disequilibrium with autism.

Schizophrenia is characterized by thought disorders, hallucinations and delusions. Genetic studies have shown a high linkage at chromosome 6q16-21. Among the genes located in this region is the glutamate receptor ionotropic kainate 2 gene (GRIK2 or GLUR6), a functional candidate for susceptibility to schizophrenia. In this study, transmission of GRIK2 was evaluated in 356 schizophrenic patients from three different clinical centers. Whereas paternal transmission shows equilibrium, we observed maternal transmission disequilibrium of GRIK2 in the largest population (p=0.03), which was still significant when all populations were added (p=0.05). These results are similar to the maternal GRIK2 transmission disequilibrium previously reported for autism, and support the presence of a susceptibility gene for schizophrenia at 6q16.

Several lines of evidence suggest that obsessive compulsive disorder (OCD) could be the consequence of glutamatergic dysfunction. We performed a case-control study in 156 patients and 141 controls and the transmission disequilibrium test in 124 parent-offspring trios to search for association between OCD and two kainate receptors, GRIK2 and GRIK3. Using three single nucleotide polymorphisms (SNP) in GRIK2 and one in GRIK3, we found no evidence for association in case-control or family-based analyses. Only the GRIK2 SNP 1867, recently associated with autism, was less transmitted than expected (p < 0.03), supporting a functional role for this variant. These findings suggest the need for further investigation of the role of GRIK2 in OCD.

A new autosomal recessive mouse mutation characterized by deafness and circling behavior was recovered during mutagenesis experiments with chlorambucil (CHL). On the basis of allelism tests and linkage analyses, this mutation appears to represent a new allele of waltzer (v) that maps to mouse Chromosome (Chr) 10. We have designated this new allele, Albany waltzer (vAlb). A high-resolution map of the region around v was constructed from data from two intersubspecific backcrosses involving Mus musculus castaneus. The analysis of 648 backcross mice has allowed vAlb to be localized 1.1 +/- 0.4 cM distal to D10Mit60 and 0.2 +/- 0.2 cM proximal to a cluster of four markers, D10Mit172, D10Mit112, D10Mit48, and D10Mit196. An independent backcross was used to confirm the map order and distances in the vAlb backcross. The two linkage maps were consistent, indicating that the lesion in vAlb, which is presumed to be a deletion based on the known action of CHL, is small and has not significantly altered the map at this level of detection. Additionally, three genes (Ros1, Grik2, and Zfa) were eliminated as possible candidates for vAlb, and several SSLP markers were separated genetically.