Recurrent seizure‐related GRIN1 variant: Molecular mechanism and targeted therapy

Abstract

Objective: Genetic variants in the GRIN genes that encode N-methyl-Daspartate 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 FDAapproved 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 Mg 2+ 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.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

“…"Others" includes largescale chromosomal deletion, translocation, inversion, and duplication. NMDA receptor channel blockers and negative allosteric modulators has been evaluated for potency and efficacy at function-altering variants (Pierson et al, 2014;Li et al, 2016a;Swanger et al, 2016;Chen et al, 2017b;Mullier et al, 2017;Ogden et al, 2017;Platzer et al, 2017;XiangWei et al, 2019;Amador et al, 2020;Chen et al, 2020a;Xu et al, 2021). Some of these channel blockers (memantine, dextromethorphan) appear to be safe in pediatric patients (Chez et al, 2007).…”

“…Some of these channel blockers (memantine, dextromethorphan) appear to be safe in pediatric patients (Chez et al, 2007). However, different gain-of-function GRIN variants showed differential sensitivity to the channel blockers (Chen et al, 2017b;Ogden et al, 2017;Pierson et al, 2014;Xu et al, 2021), demonstrating the necessity to determine the sensitivity of each variant to any therapeutic agent contemplated as a potential treatment. Several NMDA receptor PAMs (i.e., endogenous neurosteroid 24(S)-HC, pregnenolone sulfate, and FDA-approved aminoglycosides) and coagonists at the glycine-binding site (i.e., D-serine, L-serine, and D-cycloserine) potentiate responses from NMDA receptors with loss-of-function GRIN1, GRIN2A, and GRIN2B variants identified in patients with neurodevelopmental and neuropsychiatric disorders (Swanger et al, 2016;Addis et al, 2017;Vyklicky et al, 2018;Soto et al, 2019;Tang et al, 2020).…”

Imprecision in Precision Medicine: Differential Response of a Disease-Linked GluN2A Mutant to NMDA Channel Blockers

“…The identification and in vitro characterization of human disease-linked GRIN mutations has led to the successful implementation of personalized medicine for several pediatric patients. More specifically, patients with GRIN mutations and intractable epilepsy have been treated with FDA-approved NMDAR blockers, including ketamine, memantine, and dextromethorphan (Supplementary Table S1), which led to a reduction in seizure burden in the majority of patients treated with these targeted therapies (Pierson et al, 2014;Li et al, 2016;Platzer et al, 2017;Amador et al, 2020;Xu et al, 2021). The results of these n of one clinical trials have important clinical implications for patients with GRIN-associated epileptic encephalopathies, as refractory epileptic activity in these disorders is thought to contribute to the co-morbid, and often progressive, cognitive impairments (Khan and Al Baradie, 2012;Auvin et al, 2016).…”

“…Mutations in NMDAR subunits have been increasingly implicated in neurological and neurodevelopmental diseases, including intellectual disability, autism spectrum disorders, developmental delay, and epilepsy (Myers et al, 2019). The identification of GRIN variants in pediatric patients is significant, as individuals GRIN mutations and epilepsy refractory to standard anti-convulsants have been successfully treated with the FDA-approved NMDAR antagonists memantine, ketamine, and dextromethorphan (Pierson et al, 2014;Li et al, 2016;Amador et al, 2020;Xu et al, 2021). Although mutations in four genes encoding NMDAR subunits (GRIN1, GRIN2A, GRIN2B, and GRIN2D) have been linked to human disease (Carvill et al, 2013;Li et al, 2016;Liu et al, 2017;Li et al, 2019;Bahry et al, 2021;Xu et al, 2021), mutations in GRIN2A account for the majority of disease-linked variants (46%) (Myers et al, 2019;Strehlow et al, 2019).…”

“…The identification of GRIN variants in pediatric patients is significant, as individuals GRIN mutations and epilepsy refractory to standard anti-convulsants have been successfully treated with the FDA-approved NMDAR antagonists memantine, ketamine, and dextromethorphan (Pierson et al, 2014;Li et al, 2016;Amador et al, 2020;Xu et al, 2021). Although mutations in four genes encoding NMDAR subunits (GRIN1, GRIN2A, GRIN2B, and GRIN2D) have been linked to human disease (Carvill et al, 2013;Li et al, 2016;Liu et al, 2017;Li et al, 2019;Bahry et al, 2021;Xu et al, 2021), mutations in GRIN2A account for the majority of disease-linked variants (46%) (Myers et al, 2019;Strehlow et al, 2019). Pathogenic variants cluster in the highly conserved agonist binding domains as well as transmembrane and linker domains, which are highly intolerant to genetic variation (Swanger et al, 2016;Ogden et al, 2017;Strehlow et al, 2019).…”