Glutamate receptor metabotropic 7 (GRM7) gene polymorphisms in mood disorders and attention deficit hyperactive disorder

GRM7 deficiency, from excitotoxicity and neuroinflammation to neurodegeneration: Systematic review of GRM7 deficient patients

The metabotropic glutamate receptor 7 (mGluR7) is a presynaptic G-protein-coupled glutamate receptor that modulates neurotransmitter release and synaptic plasticity at presynaptic terminals. It is encoded by GRM7, and recently variants have been identified in patients with autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), developmental delay (DD), intellectual disability (ID), and brain malformations. To gain updated insights into the function of GRM7 and the phenotypic spectrum of genetic variations within this gene, we conducted a systematic review of relevant literature utilizing PubMed, Web of Science, and Scopus databases. Among the 14 articles meeting the inclusion criteria, a total of 42 patients (from 28 families) harboring confirmed mutations in the GRM7 gene have been documented. Specifically, there were 17 patients with heterozygous mutations, 20 patients with homozygous mutations, and 5 patients with compound heterozygous mutations. Common clinical features included intellectual behavioral disability, seizure/epilepsy, microcephaly, developmental delay, peripheral hypertonia and hypomyelination. Genotype-phenotype correlation was not clear and each variant had unique characteristics including gene dosage, mutant protein surface expression, and degradation pathway that result with a spectrum of phenotype manifestations through ASD or ADHD to severe DD/ID with brain malformations. Neuroinflammation may play a role in the development and/or progression of GRM7-related neurodegeneration along with excitotoxicity. The clinical and functional data presented here demonstrate that both autosomal dominant and recessive inheritance of GRM7 mutation can cause disease spectrum phenotypes through ASD or ADHD to severe DD/ID and seizure with brain malformations.

Analysis of single nucleotide polymorphisms of the metabotropic glutamate receptors in a transgender population

Introduction

Gender incongruence (GI) is characterized by a marked incongruence between an individual's experienced/expressed gender and the assigned sex at birth. It includes strong displeasure about his or her sexual anatomy and secondary sex characteristics. In some people, this condition produces a strong distress with anxiety and depression named gender dysphoria (GD). This condition appears to be associated with genetic, epigenetics, hormonal as well as social factors. Given that L-glutamate is the major excitatory neurotransmitter in the central nervous system, also associated with male sexual behavior as well as depression, we aimed to determine whether metabotropic glutamate receptors are involved in GD.

Methods

We analyzed 74 single nucleotide polymorphisms located at the metabotropic glutamate receptors (mGluR1, mGluR3, mGluR4, mGluR5, mGluR7 and mGluR8) in 94 transgender versus 94 cisgender people. The allele and genotype frequencies were analyzed by c2 test contrasting male and female cisgender and transgender populations. The strength of the associations was measured by binary logistic regression, estimating the odds ratio (OR) for each genotype. Measurement of linkage disequilibrium, and subsequent measurement of haplotype frequencies were also performed considering three levels of significance: P ≤ 0.05, P ≤ 0.005 and P ≤ 0.0005. Furthermore, false positives were controlled with the Bonferroni correction (P ≤ 0.05/74 = 0.00067).

Results

After analysis of allele and genotypic frequencies, we found twenty-five polymorphisms with significant differences at level P ≤ 0.05, five at P ≤ 0.005 and two at P ≤ 0.0005. Furthermore, the only two polymorphisms (rs9838094 and rs1818033) that passed the Bonferroni correction were both related to the metabotropic glutamate receptor 7 (mGluR7) and showed significant differences for multiple patterns of inheritance. Moreover, the haplotype T/G [OR=0.34 (0.19-0.62); P<0.0004] had a lower representation in the transgender population than in the cisgender population, with no evidence of sex cross-interaction.

Conclusion

We provide genetic evidence that the mGluR7, and therefore glutamatergic neurotransmission, may be involved in GI and GD.

Therapeutic Potential for Metabotropic Glutamate Receptor 7 Modulators in Cognitive Disorders

Metabotropic glutamate receptor 7 (mGlu7) is the most highly conserved and abundantly expressed mGlu receptor in the human brain. The presynaptic localization of mGlu7, coupled with its low affinity for its endogenous agonist, glutamate, are features that contribute to the receptor's role in modulating neuronal excitation and inhibition patterns, including long-term potentiation, in various brain regions. These characteristics suggest that mGlu7 modulation may serve as a novel therapeutic strategy in disorders of cognitive dysfunction, including neurodevelopmental disorders that cause impairments in learning, memory, and attention. Primary mutations in the GRM7 gene have recently been identified as novel causes of neurodevelopmental disorders, and these patients exhibit profound intellectual and cognitive disability. Pharmacological tools, such as agonists, antagonists, and allosteric modulators, have been the mainstay for targeting mGlu7 in its endogenous homodimeric form to probe effects of its function and modulation in disease models. However, recent research has identified diversity in dimerization, as well as trans-synaptic interacting proteins, that also play a role in mGlu7 signaling and pharmacological properties. These novel findings represent exciting opportunities in the field of mGlu receptor drug discovery and highlight the importance of further understanding the functions of mGlu7 in complex neurologic conditions at both the molecular and physiologic levels. SIGNIFICANCE STATEMENT: Proper expression and function of mGlu7 is essential for learning, attention, and memory formation at the molecular level within neural circuits. The pharmacological targeting of mGlu7 is undergoing a paradigm shift by incorporating an understanding of receptor interaction with other cis- and trans- acting synaptic proteins, as well as various intracellular signaling pathways. Based upon these new findings, mGlu7's potential as a drug target in the treatment of cognitive disorders and learning impairments is primed for exploration.

Associations between GRM7 polymorphisms and obesity in patients selected for sleeve gastrectomy

Obesity is a worldwide problem in which genetic factors have a prominent role. We have selected two single nucleotide polymorphisms (SNPs) within glutamate metabotropic receptor 7 (GRM7) gene, namely rs6782011 and rs779867 to weigh their association with obesity in an Iranian cohort. The distribution of rs6782011 alleles was significantly different in the obese patients from normal controls (P < 0.0001; 434 obese patients vs. 297 normal controls). Distribution of alleles was also measured between sex-based groups of obese patients and controls. We detected remarkable differences between female obese cases and female control subjects (P < 0.0001; 374 female obese cases vs. 216 female normal controls); nevertheless, the difference in allele distribution was not significant for male cases compared with corresponding normal controls (p = 0.47; 60 male patients vs. 81 normal males). Contrariwise, distribution of rs779867 alleles was not significantly different between total obese patients compared with normal controls (P = 0.21; 434 obese patients vs. 297 normal BMI controls). There was also no significant difference for female and male obese patients compared with female and male normal BMI controls. Thus, GRM7 can be considered as a risk locus for obesity.

GRM7 gene mutations and consequences for neurodevelopment

The metabotropic glutamate receptor 7 (mGlu7), encoded by the GRM7 gene in humans, is a presynaptic, G protein-coupled glutamate receptor that is essential for modulating neurotransmission. Mutations in or reduced expression of GRM7 have been identified in different genetic neurodevelopmental disorders (NDDs), and rare biallelic missense variants have been proposed to underlie a subset of NDDs. Clinical GRM7 variants have been associated with a range of symptoms consistent with neurodevelopmental molecular features, including hypomyelination, brain atrophy and defects in axon outgrowth. Here, we review the newest findings regarding the cellular and molecular defects caused by GRM7 variants in NDD patients.

Correlation between variants of the CREB1 and GRM7 genes and risk of depression

The pathogenesis of depression involves cAMP-response element binding protein1 (CREB1) and metabotropic glutamate receptor 7 (GRM7), and their genetic polymorphisms may affect susceptibility to depression. The purpose of this study was to investigate whether the CREB1 polymorphisms rs2253206 and rs10932201 and the GRM7 polymorphism rs162209 are associated with the risk of depression. Using polymerase chain reaction-restriction fragment length polymorphism and DNA sequencing, we analyzed the rs2253206, rs10932201, and rs162209 frequencies in 479 patients with depression and 329 normal controls. The results showed that the rs2253206 and rs10932201 polymorphisms were significantly associated with an increased risk of depression. However, no association was found between rs162209 and depression risk. When the data were stratified for several disease-related variables, none of the three polymorphisms were found to be correlated to onset, disease severity, family history, or suicidal tendency. Thus, the present findings indicate that the CREB1 polymorphisms rs2253206 and rs10932201 may be related to the occurrence of depression.

Correlation research of susceptibility single nucleotide polymorphisms and the severity of clinical symptoms in attention deficit hyperactivity disorder

OBJECTIVE

To analyze the correlation between susceptibility single nucleotide polymorphisms (SNPs) and the severity of clinical symptoms in children with attention deficit hyperactivity disorder (ADHD), so as to supplement the clinical significance of gene polymorphism and increase our understanding of the association between genetic mutations and ADHD phenotypes.

METHODS

193 children with ADHD were included in our study from February 2017 to February 2020 in the Children's ADHD Clinic of the author's medical institution. 23 ADHD susceptibility SNPs were selected based on the literature, and multiple polymerase chain reaction (PCR) targeted capture sequencing technology was used for gene analysis. A series of ADHD-related questionnaires were used to reflect the severity of the disease, and the correlation between the SNPs of specific sites and the severity of clinical symptoms was evaluated. R software was used to search for independent risk factors by multivariate logistic regression and the "corplot" package was used for correlation analysis.

RESULTS

Among the 23 SNP loci of ADHD children, no mutation was detected in 6 loci, and 2 loci did not conform to Hardy-Weinberg equilibrium. Of the remaining 15 loci, there were 9 SNPs, rs2652511 (SLC6A3 locus), rs1410739 (OBI1-AS1 locus), rs3768046 (TIE1 locus), rs223508 (MANBA locus), rs2906457 (ST3GAL3 locus), rs4916723 (LINC00461 locus), rs9677504 (SPAG16 locus), rs1427829 (intron) and rs11210892 (intron), correlated with the severity of clinical symptoms of ADHD. Specifically, rs1410739 (OBI1-AS1 locus) was found to simultaneously affect conduct problems, control ability and abstract thinking ability of children with ADHD.

CONCLUSION

There were 9 SNPs significantly correlated with the severity of clinical symptoms in children with ADHD, and the rs1410739 (OBI1-AS1 locus) may provide a new direction for ADHD research. Our study builds on previous susceptibility research and further investigates the impact of a single SNP on the severity of clinical symptoms of ADHD. This can help improve the diagnosis, prognosis and treatment of ADHD.

Evaluating endophenotypes for bipolar disorder

BACKGROUND

Phenotypic heterogeneity is a major impediment to the elucidation of the neurobiology and genetics of bipolar disorder. Endophenotype could help in reducing heterogeneity by defining biological traits that are more direct expressions of gene effects. The aim of this review is to examine the recent literature on clinical, epidemiological, neurobiological, and genetic findings and to select and evaluate candidate endophenotypes for bipolar disorder. Evaluating putative endophenotype could be helpful in better understanding the neurobiology of bipolar disorder by improving the definition of bipolar-related phenotypes in genetic studies. In this manner, research on endophenotypes could be useful to improve psychopathological diagnostics in the long-run by dissecting psychiatric macro phenotypes into biologically valid components.

MAIN BODY

The associations among the psychopathological and biological endophenotypes are discussed with respect to specificity, temporal stability, heritability, familiarity, and clinical and biological plausibility. Numerous findings regarding brain function, brain structure, neuropsychology and altered neurochemical pathways in patients with bipolar disorder and their relatives deserve further investigation. Overall, major findings suggest a developmental origin of this disorder as all the candidate endophenotypes that we have been able to select are present both in the early stages of the disorder as well as in subjects at risk.

CONCLUSIONS

Among the stronger candidate endophenotypes, we suggest circadian rhythm instability, dysmodulation of emotion and reward, altered neuroimmune state, attention and executive dysfunctions, anterior cingulate cortex thickness and early white matter abnormalities. In particular, early white matter abnormalities could be the result of a vulnerable brain on which new stressors are added in young adulthood which favours the onset of the disorder. Possible pathways that lead to a vulnerable brain are discussed starting from the data about molecular and imaging endophenotypes of bipolar disorder.

Targeting the dysfunction of glutamate receptors for the development of novel antidepressants

Increasing evidence indicates that dysfunction of glutamate receptors is involved in the pathophysiology of major depressive disorder (MDD). Although accumulating efforts have been made to elucidate the applications and mechanisms underlying antidepressant-like effects of ketamine, a non-selective antagonist of N-methyl-d-aspartate receptor (NMDAR), the role of specific glutamate receptor subunit in regulating depression is not completely clear. The current review aims to discuss the relationships between glutamate receptor subunits and depressive-like behaviors. Research literatures were searched from inception to July 2020. We summarized the alterations of glutamate receptor subunits in patients with MDD and animal models of depression. Animal behaviors in response to dysfunction of glutamate receptor subunits were also surveyed. To fully understand mechanisms underlying antidepressant-like effects of modulators targeting glutamate receptors, we discussed effects of each glutamate receptor subunit on serotonin system, synaptic plasticity, neurogenesis and neuroinflammation. Finally, we collected most recent clinical applications of glutamate receptor modulators and pointed out the limitations of these candidates in the treatment of MDD.

Association between the group III metabotropic glutamate receptor gene polymorphisms and attention-deficit/hyperactivity disorder and functional exploration of risk loci

Existing evidence suggests that the group III metabotropic glutamate receptor (mGluR) gene variations are involved in attention-deficit/hyperactivity disorder (ADHD), but few studies have fully explored this association. We conducted a case-control study with 617 cases and 636 controls to investigate the association between functional single-nucleotide polymorphisms (SNPs) from the group III mGluR gene polymorphisms (GRM4, GRM7, GRM8) and ADHD in the Chinese Han population and initially explored the function of positive SNPs. The GRM4 rs1906953 T genotype showed a significant association with a decreased risk of ADHD (TT:CC, OR = 0.55, 95% CI = 0.40-0.77; recessive model, OR = 0.58, 95% CI = 0.43-0.78). GRM7 rs9826579 C showed a significant association with an increased risk of ADHD (TC:TT, OR = 1.81, 95% CI = 1.39-2.36; dominant model, OR = 1.74, 95% CI = 1.35-2.24; additive model, OR = 1.56, 95% CI = 1.24-1.97). In addition, compared with subjects with the rs1906953 TT genotype, subjects with of the CC genotype showed more obvious attention deficit behaviours and hyperactivity/impulsive behaviours. Dual-luciferase reporter gene assays showed that a promoter reporter with the rs1906953 TT genotype significantly decreased luciferase activity compared with the CC genotype. According to electrophoretic mobility shift assays, the binding capacity of rs1906953 T probe with nucleoprotein was lower than that of the rs1906953 C probe. Our results revealed the association of GRM4 rs1906953 and GRM7 rs9826579 with ADHD. Moreover, we found that rs1906953 disturbs the transcriptional activity of GRM4.

Brain Branched-Chain Amino Acids in Maple Syrup Urine Disease: Implications for Neurological Disorders

Maple syrup urine disease (MSUD) is an autosomal recessive disorder caused by decreased activity of the branched-chain α-ketoacid dehydrogenase complex (BCKDC), which catalyzes the irreversible catabolism of branched-chain amino acids (BCAAs). Current management of this BCAA dyshomeostasis consists of dietary restriction of BCAAs and liver transplantation, which aims to partially restore functional BCKDC activity in the periphery. These treatments improve the circulating levels of BCAAs and significantly increase survival rates in MSUD patients. However, significant cognitive and psychiatric morbidities remain. Specifically, patients are at a higher lifetime risk for cognitive impairments, mood and anxiety disorders (depression, anxiety, and panic disorder), and attention deficit disorder. Recent literature suggests that the neurological sequelae may be due to the brain-specific roles of BCAAs. This review will focus on the derangements of BCAAs observed in the brain of MSUD patients and will explore the potential mechanisms driving neurologic dysfunction. Finally, we will discuss recent evidence that implicates the relevance of BCAA metabolism in other neurological disorders. An understanding of the role of BCAAs in the central nervous system may facilitate future identification of novel therapeutic approaches in MSUD and a broad range of neurological disorders.

Anabolic-androgenic steroids and brain injury: miRNA evaluation in users compared to cocaine abusers and elderly people

Anabolic-androgenic steroids (AASs) can be used to treat both hormonal diseases and other pathologies characterized by muscle loss (aging, cancer, and AIDS). Even if the adverse effects related to the misuse of AASs have been well studied in different systems and apparatuses, knowledge about brain damage is poor.In this scenario, this experimental study aimed to analyze the role of several microRNAs (miRNAs) in brain damage after AAS misuse, to better comprehend the underlying mechanisms. The research hypothesis at the base of this experimental study is that the chronic use of AASs may be associated to brain damage with a dysregulation of these miRNAs. Moreover, miRNA expression values were compared among three different groups, "AAS" group, "Cocaine" group and "Aging" group, in order to define if AAS brain damage can be compared with the brain impairment linked to aging and/or cocaine assumption.This experimental study revealed that the tested miRNAs (hsa-miR-21-5p, hsa-miR-34a-5p, hsa-miR-124-5p, hsa-miR-132-3p, and hsa-miR-144-3p) were overexpressed in all enrolled groups. In the light of the presented results, the identification of specific circulating and/or tissue biomarkers is challenging for the scientific community. Further studies with larger samples are needed to confirm these interesting findings.

Phenotypic profiling of mGlu7 knockout mice reveals new implications for neurodevelopmental disorders

Neurodevelopmental disorders are characterized by deficits in communication, cognition, attention, social behavior and/or motor control. Previous studies have pointed to the involvement of genes that regulate synaptic structure and function in the pathogenesis of these disorders. One such gene, GRM7, encodes the metabotropic glutamate receptor 7 (mGlu₇ ), a G protein-coupled receptor that regulates presynaptic neurotransmitter release. Mutations and polymorphisms in GRM7 have been associated with neurodevelopmental disorders in clinical populations; however, limited preclinical studies have evaluated mGlu₇ in the context of this specific disease class. Here, we show that the absence of mGlu₇ in mice is sufficient to alter phenotypes within the domains of social behavior, associative learning, motor function, epilepsy and sleep. Moreover, Grm7 knockout mice exhibit an attenuated response to amphetamine. These findings provide rationale for further investigation of mGlu₇ as a potential therapeutic target for neurodevelopmental disorders such as idiopathic autism, attention deficit hyperactivity disorder and Rett syndrome.

GRM7 polymorphisms are not associated with ischemic stroke in Iranian population

Objectives: Ischemic stroke is the main neurological cause of acquired incapability in adults and a prominent cause of mortality. Several association studies have been conducted to explore the role of candidate genes in this neurological condition.Methods: In the present study, we aimed at identification of association between Glutamate Metabotropic Receptor 7 (GRM7) and risk of ischemic stroke in Iranian population. Two intronic variants within this gene (rs6782011 and rs779867) were genotyped in 318 sporadic ischemic stroke cases and 300 unrelated, healthy controls individuals.Results: No significant difference was found in allele, genotype or haplotype frequencies of these SNPs between cases and controls after correction for multiple comparisons.Conclusion: Consequently, the assessed GRM7 variants are not implicated in risk of ischemic stroke in Iranian population.