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Ann Clin Transl Neurol
2021 Jul 01;87:1480-1494. doi: 10.1002/acn3.51406.
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Recurrent seizure-related GRIN1 variant: Molecular mechanism and targeted therapy.
Xu Y
,
Song R
,
Chen W
,
Strong K
,
Shrey D
,
Gedela S
,
Traynelis SF
,
Zhang G
,
Yuan H
.
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OBJECTIVE: Genetic variants in the GRIN genes that encode N-methyl-D-aspartate receptor (NMDAR) subunits have been identified in various neurodevelopmental disorders, including epilepsy. We identified a GRIN1 variant from an individual with early-onset epileptic encephalopathy, evaluated functional changes to NMDAR properties caused by the variant, and screened FDA-approved therapeutic compounds as potential treatments for the patient.
METHODS: Whole exome sequencing identified a missense variant in GRIN1. Electrophysiological recordings were made from Xenopus oocytes and transfected HEK cells to determine the NMDAR biophysical properties as well as the sensitivity to agonists and FDA-approved drugs that inhibit NMDARs. A beta-lactamase reporter assay in transfected HEK cells evaluated the effects of the variant on the NMDAR surface expression.
RESULTS: A recurrent de novo missense variant in GRIN1 (c.1923G>A, p.Met641Ile), which encodes the GluN1 subunit, was identified in a pediatric patient with drug-resistant seizures and early-onset epileptic encephalopathy. In vitro analysis indicates that GluN1-M641I containing NMDARs showed enhanced agonist potency and reduced Mg2+ block, which may be associated with the patient's phenotype. Results from screening FDA-approved drugs suggested that GluN1-M641I containing NMDARs are more sensitive to the NMDAR channel blockers memantine, ketamine, and dextromethorphan compared to the wild-type receptors. The addition of memantine to the seizure treatment regimen significantly reduced the patient's seizure burden.
INTERPRETATION: Our finding contributes to the understanding of the phenotype-genotype correlations of patients with GRIN1 gene variants, provides a molecular mechanism underlying the actions of this variant, and explores therapeutic strategies for treating GRIN1-related neurological conditions.
FIGURE 1. Brain MRI and EEG features of the patient with the M641I variant. (A) MRI of the brain at 3months of age was normal. (B) Ictal EEG at 9months of age showed electro decrement superimposed with fast activity and myogenic artifacts in a patient with typical epileptic spasms.
FIGURE 2. De novo GRIN1 c.1923G>A (GluN1 p.Met641Ile) variant. (A) A de novo GRIN1 missense variant (c.1923G>A, p.Met641Ile) was identified in a male patient using the nextgeneration wholeexome sequencing. (B) A linear schematic representation of the GluN1 subunit (the position of M641 is marked with red). The Methionine residue at position 641 is highly conserved across most of the subphylum Vertebrata. (C) A homology model of GluN1/GluN2A subunit built from the GluN1/GluN2B crystallographic data. 34 , 35 The GluN1M641I residue resides in the M3 transmembrane helix. The substitution of an amino acid (methionine to isoleucine) is shown as a stick model and marked with a different color.
FIGURE 3. GluN1M641I alters NMDAR pharmacological properties. (A and B) Composite concentrationresponse curves for glutamate (A, in the presence of 100mol/L glycine) and glycine (B, in the presence of 100mol/L glutamate) recorded at a holding potential of 40mV for WT GluN1 and GluN1M641I coexpressed with GluN2A (upper panels) or GluN2B (lower panels), respectively. (C) Summary of proton sensitivity evaluated by current ratio at pH 6.8 to pH 7.6 (in the presence of 100mol/L glutamate and 100mol/L glycine) at a holding potential of 40mV of the WT GluN1 and GluN1M641I when coexpressed with GluN2A (upper panel) and GluN2B (lower panel), respectively. (D) Composite concentrationresponse curves for Mg2+ in the presence of 100mol/L glutamate and 100mol/L glycine at a holding potential of 60mV of the WT GluN1 and GluN1M641I when coexpressed with GluN2A (left panel) and GluN2B (right panel), respectively. (E) Mg2+ currentvoltage (IV) curves for the WT GluN1 and GluN1M641I coexpressed with GluN2A. All current responses were normalized to the current recorded at +30mV. Composite data are shown as meanSEM. NMDAR, NmethylDaspartate receptor; WT, wildtype.
FIGURE 4. GluN1M641I alters NMDAR open probability and surface expression. (A) Representative recordings of the current response time course obtained from wholecell voltageclamp recordings of HEK cells transfected with the WT GluN1/GluN2A (Black) and GluN1M641I/GluN2A (Gray) at a holding potential of 60mV in response to rapid application of 1000mol/L glutamate in the presence of 100mol/L glycine. (B) The channel open probability was assessed by measuring the degree of MTSEA (0.2mmol/L) potentiation using TEVC recordings from Xenopus oocytes expressing the WT GluN1 or GluN1M641I coexpressed with GluN2AA650C (hereafter 2AA7C) in the presence of 100mol/L glutamate and glycine at a holding potential of 40mV. (C and D) Representative plots of nitrocefin absorbance (optical density, O.D.) versus time course are indicated for HEK cells transfected with the WT lacGluN1 and lacGluN1M641I when coexpressed with GluN2A (C) and GluN2B (D), respectively. The slopes of O.D. versus time were averaged as percentages of the WT NMDAR for the ratio of surface/total from five to six independent experiments. Data are presented as meanSEM, and were analyzed by unpaired ttest (*p<0.05, compared to WT). NMDAR, NmethylDaspartate receptor; WT, wildtype.
FIGURE 5. The effect of NMDAR antagonists, including FDAapproved drugs, on the WT and GluN1M641I NMDARs. Composite concentrationresponse curves of NMDAR antagonists were evaluated by TEVC recordings of Xenopus oocytes in the presence of 100mol/L glutamate and 100mol/L glycine (except for TCN201 with 3mol/L glycine) at a holding potential of 40mV. Curves are shown for (A) memantine, (B) ketamine, (C) dextromethorphan, (D) memantine, (E) amantadine, and (F) TCN201. Data are shown as mean SEM; SEM is shown when larger than symbol size. NMDAR, NmethylDaspartate receptor; TEVC, twoelectrode voltageclamp; WT, wildtype.
FIGURE 6. The effect of memantine on patients seizure frequency and EEG. (A) Addition of memantine to the anticonvulsant regimen reduced the seizure frequency significantly; the patient was also on Felbamate, Vigabatrin and Clobazam. Seizure frequency was determined by a parental observation log. The patient accidentally missed 2days of memantine after 3months of treatment, over which time the seizures increased significantly. One week after restarting memantine, the seizure frequency dropped significantly again. Six months after the memantine treatment, the seizures were still under good control. (BD) Routine EEG before and after memantine treatment. Before the treatment at 4months of age (B), the EEG showed hypsarrhythmia pattern and moderate slow background and abundant multifocal epileptiform discharges at 9months of age (C) However, after the treatment at 18months of age (D), the EEG only showed mild slow EEG background without epileptiform discharge.
Akazawa,
Differential expression of five N-methyl-D-aspartate receptor subunit mRNAs in the cerebellum of developing and adult rats.
1994, Pubmed
Akazawa,
Differential expression of five N-methyl-D-aspartate receptor subunit mRNAs in the cerebellum of developing and adult rats.
1994,
Pubmed
Amador,
Modelling and treating GRIN2A developmental and epileptic encephalopathy in mice.
2020,
Pubmed
Burnashev,
NMDA receptor subunit mutations in neurodevelopmental disorders.
2015,
Pubmed
Camp,
GRIN2D/GluN2D NMDA receptor: Unique features and its contribution to pediatric developmental and epileptic encephalopathy.
2020,
Pubmed
Chang,
The activation gate and gating mechanism of the NMDA receptor.
2008,
Pubmed
,
Xenbase
Chen,
Functional Evaluation of a De Novo GRIN2A Mutation Identified in a Patient with Profound Global Developmental Delay and Refractory Epilepsy.
2017,
Pubmed
Chez,
Memantine as adjunctive therapy in children diagnosed with autistic spectrum disorders: an observation of initial clinical response and maintenance tolerability.
2007,
Pubmed
Erickson,
A retrospective study of memantine in children and adolescents with pervasive developmental disorders.
2007,
Pubmed
Fry,
De novo mutations in GRIN1 cause extensive bilateral polymicrogyria.
2018,
Pubmed
Hansen,
Structure, function, and allosteric modulation of NMDA receptors.
2018,
Pubmed
Helbig,
Diagnostic exome sequencing provides a molecular diagnosis for a significant proportion of patients with epilepsy.
2016,
Pubmed
Jones,
The NMDA receptor M3 segment is a conserved transduction element coupling ligand binding to channel opening.
2002,
Pubmed
,
Xenbase
Karakas,
Crystal structure of a heterotetrameric NMDA receptor ion channel.
2014,
Pubmed
Kearney,
Precision Medicine: NMDA Receptor-Targeted Therapy for GRIN2D Encephalopathy.
2017,
Pubmed
Lau,
NMDA receptor trafficking in synaptic plasticity and neuropsychiatric disorders.
2007,
Pubmed
Lee,
NMDA receptor structures reveal subunit arrangement and pore architecture.
2014,
Pubmed
,
Xenbase
Lemke,
Delineating the GRIN1 phenotypic spectrum: A distinct genetic NMDA receptor encephalopathy.
2016,
Pubmed
,
Xenbase
Li,
GRIN2D Recurrent De Novo Dominant Mutation Causes a Severe Epileptic Encephalopathy Treatable with NMDA Receptor Channel Blockers.
2016,
Pubmed
Mullier,
GRIN2B gain of function mutations are sensitive to radiprodil, a negative allosteric modulator of GluN2B-containing NMDA receptors.
2017,
Pubmed
,
Xenbase
Ogden,
Molecular Mechanism of Disease-Associated Mutations in the Pre-M1 Helix of NMDA Receptors and Potential Rescue Pharmacology.
2017,
Pubmed
,
Xenbase
Ohba,
GRIN1 mutations cause encephalopathy with infantile-onset epilepsy, and hyperkinetic and stereotyped movement disorders.
2015,
Pubmed
Paoletti,
NMDA receptor subunit diversity: impact on receptor properties, synaptic plasticity and disease.
2013,
Pubmed
Pierson,
GRIN2A mutation and early-onset epileptic encephalopathy: personalized therapy with memantine.
2014,
Pubmed
,
Xenbase
Platzer,
GRIN2B encephalopathy: novel findings on phenotype, variant clustering, functional consequences and treatment aspects.
2017,
Pubmed
Richards,
Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology.
2015,
Pubmed
Sobolevsky,
X-ray structure, symmetry and mechanism of an AMPA-subtype glutamate receptor.
2009,
Pubmed
Swanger,
Mechanistic Insight into NMDA Receptor Dysregulation by Rare Variants in the GluN2A and GluN2B Agonist Binding Domains.
2016,
Pubmed
Traynelis,
Glutamate receptor ion channels: structure, regulation, and function.
2010,
Pubmed
XiangWei,
De Novo Mutations and Rare Variants Occurring in NMDA Receptors.
2018,
Pubmed
XiangWei,
Heterogeneous clinical and functional features of GRIN2D-related developmental and epileptic encephalopathy.
2019,
Pubmed
Yuan,
Ionotropic GABA and Glutamate Receptor Mutations and Human Neurologic Diseases.
2015,
Pubmed
Yuan,
Conserved structural and functional control of N-methyl-D-aspartate receptor gating by transmembrane domain M3.
2005,
Pubmed
Yuste,
Mechanisms of calcium influx into hippocampal spines: heterogeneity among spines, coincidence detection by NMDA receptors, and optical quantal analysis.
1999,
Pubmed
Zehavi,
De novo GRIN1 mutations: An emerging cause of severe early infantile encephalopathy.
2017,
Pubmed
