A case of severe autosomal recessive spinocerebellar ataxia type 18 with a novel nonsense variant in GRID2

GRID2 aberration leads to disturbance in neuroactive ligand-receptor interactions via changes to the species richness and composition of gut microbes

OBJECTIVE

To explore the association between phenotype and the gut microbiome following damage to the GRID2 gene.

METHODS

Ten wild-type (WT) mice and 11 GRID2 knockout heterozygous mice (GRID2(±)) of a similar age and weight were randomly selected. Fresh feces were collected from both groups of mice under specified pathogen-free (SPF) conditions. The bacterial genomes were extracted from the feces, the 16S rRNA genes were sequenced, and the data were analyzed to determine clustering, diversity, abundance, LEfSe, and functional differences. Differential expression and enrichment analyses of the RNA-seq and protein levels of the GRID2 gene were also performed using data in the GENE database and the new version of the Human Protein Atlas portal (www.proteinatlas.org).

RESULTS

The diversity analysis showed differences in species composition between the two groups at different levels. At phylum level, compared with the WT group, the distribution was more bacteriophages but showed a lower content of Tenericutes in the GRID2(±) group. At the order level, compared with the WT group, a higher content of Actinomycetales and Bacteriophages were found in the GRID2(±) group. The species difference analysis showed that 17 species, including E. faecalis and Paracoccus spp., showed differences in content between the two groups. LEfSe analysis showed that the abundance of Clostridiaceae, Allobaculum, and other groups decreased in the GRID2(±) group compared with the WT group, while Mycoplasma, Sphingomonas, and Alphaproteobacteria increased in abundance. Functional analysis revealed eight differential functions between the WT and GRID2(±) group (P < 0.05). The most significantly disrupted were neuroactive ligand-receptor interactions (P < 9.99e-4). In addition, the differential expression and enrichment analyses performed at RNA-seq and protein levels revealed that the GRID2 gene showed organ-specific expression and was mainly enriched in the brain tissue.

CONCLUSIONS

Compared with the WT group, the defective GRID2 gene affected the species richness and composition of gut microbes in the GRID2(±) mice, which in turn affected the function of gut microbes, leading to the disruption of neuroactive ligand-receptor interactions. Our findings indicate that the host gene, GRID2, can influence the abundance of a subset of gut microbes but the exact mechanisms still need further investigation.

Neurodevelopmental Syndrome with Intellectual Disability, Speech Impairment, and Quadrupedia Is Associated with Glutamate Receptor Delta 2 Gene Defect

Bipedalism, speech, and intellect are the most prominent traits that emerged in the evolution of Homo sapiens. Here, we describe a novel genetic cause of an "involution" phenotype in four patients, who are characterized by quadrupedal locomotion, intellectual impairment, the absence of speech, small stature, and hirsutism, observed in a consanguineous Brazilian family. Using whole-genome sequencing analysis and homozygous genetic mapping, we identified genes bearing homozygous genetic variants and found a homozygous 36.2 kb deletion in the gene of glutamate receptor delta 2 (GRID2) in the patients, resulting in the lack of a coding region from the fifth to the seventh exons. The GRID2 gene is highly expressed in the cerebellum cortex from prenatal development to adulthood, specifically in Purkinje neurons. Deletion in this gene leads to the loss of the alpha chain in the extracellular amino-terminal protein domain (ATD), essential in protein folding and transport from the endoplasmic reticulum (ER) to the cell surface. Then, we studied the evolutionary trajectories of the GRID2 gene. There was no sign of strong selection of the highly conservative GRID2 gene in ancient hominids (Neanderthals and Denisovans) or modern humans; however, according to in silico tests using the Mfold tool, the GRID2 gene possibly gained human-specific mutations that increased the stability of GRID2 mRNA.

Autosomal recessive spinocerebellar ataxia type 4 with a VPS13D mutation: A case report

BACKGROUND

Autosomal recessive spinocerebellar ataxia type 4 (SCAR4) is a type of SCA that is a group of hereditary diseases characterized by gait ataxia. The main clinical features of SCAR4 are progressive cerebellar ataxia, pyramidal signs, neuropathy, and macrosaccadic intrusions. To date, many gene dysfunctions have been reported to be associated with SCAR4.

CASE SUMMARY

Here, we report a novel compound heterozygous mutation, c.3288delA (p.Asp1097ThrfsTer6), in the VPS13D gene in a young female Chinese patient. The patient found something wrong with her legs about 10 years ago and presented with the typical characteristics of SCAR4 when she came to the hospital, including ataxia, neuropathy, and positive pyramidal signs. She was then diagnosed with SCAR4 and went home with symptomatic schemes.

CONCLUSION

SCAR4 is a hereditary disease characterized by ataxia, pyramidal signs, neuropathy, and macrosaccadic intrusions. We report a novel compound heterozygous mutation, c.3288delA (p.Asp1097ThrfsTer6), in the VPS13D gene, which enriches the gene mutation spectrum and provides additional information about SCAR4.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

Many physiologic effects of l-glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, are mediated via signaling by ionotropic glutamate receptors (iGluRs). These ligand-gated ion channels are critical to brain function and are centrally implicated in numerous psychiatric and neurologic disorders. There are different classes of iGluRs with a variety of receptor subtypes in each class that play distinct roles in neuronal functions. The diversity in iGluR subtypes, with their unique functional properties and physiologic roles, has motivated a large number of studies. Our understanding of receptor subtypes has advanced considerably since the first iGluR subunit gene was cloned in 1989, and the research focus has expanded to encompass facets of biology that have been recently discovered and to exploit experimental paradigms made possible by technological advances. Here, we review insights from more than 3 decades of iGluR studies with an emphasis on the progress that has occurred in the past decade. We cover structure, function, pharmacology, roles in neurophysiology, and therapeutic implications for all classes of receptors assembled from the subunits encoded by the 18 ionotropic glutamate receptor genes. SIGNIFICANCE STATEMENT: Glutamate receptors play important roles in virtually all aspects of brain function and are either involved in mediating some clinical features of neurological disease or represent a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of this class of receptors will advance our understanding of many aspects of brain function at molecular, cellular, and system levels and provide new opportunities to treat patients.

Structural biology and thermodynamics of GluD receptors

Glutamate delta (GluD) receptors are a functionally enigmatic subfamily of ionotropic glutamate receptors. Despite sharing similar sequences and structures with AMPA, NMDA, and kainate receptors, GluD receptors do not bind glutamate nor function as ligand-gated ion channels. Binding d-serine and engaging in transsynaptic protein-protein interactions, GluD receptors are thought to undergo complex conformational rearrangements for non-ionotropic signaling that regulates synaptic plasticity. Recent structural, biochemical, and computational studies have elucidated multiple conformational and thermodynamic factors governing the unique properties of GluD receptors. Here, we review advances in biophysical insights into GluD receptors and discuss the structural thermodynamic relationships that underpin their neurobiological functions.