Mutations of N-Methyl-D-Aspartate Receptor Subunits in Epilepsy

Epilepsy is one of the most common neurological diseases. Of all cases, 70%–80% are considered to be due to genetic factors. In recent years, a large number of genes have been identified as being involved in epilepsy.Among them, N-methyl-D-aspartate receptor（NMDAR）subunit-encoding genes represent a large proportion, suggesting an important role for NMDARs in epilepsy. In this review, we summarize and analyze the genotypes, functional alterations, and clinical aspects of NMDAR subunit mutations/variants identified from patients with epilepsy.These data will help to throw light upon the pathogenicity of these NMDAR mutations and advance our understanding of the subtle and complicated role of NMDARs in epilepsy. It will also offer new insights into precision therapy for this disorder.

Functional Investigation of a GRIN2A Variant Associated with Rolandic Epilepsy

N-methyl-D-aspartate receptors（NMDARs）, a subtype of glutamate-gated ion channels, play a central role in epileptogenesis. Recent studies have identified an increasing number of GRIN2 A（a gene encoding the NMDAR GluN2A subunit） mutations in patients with epilepsy. Phenotypes of GRIN2 A mutations include epilepsy-aphasia disorders and other epileptic encephalopathies, which pose challenges in clinical treatment. Here we identified a heterozygous GRIN2 A mutation（c.1341 T[A, p.N447 K） from a boy with Rolandic epilepsy by whole-exome sequencing. The patient became seizurefree with a combination of valproate and lamotrigine.Functional investigation was carried out using recombinant NMDARs containing a GluN2A-N447 K mutant that is located in the ligand-binding domain of the GluN2A subunit. Whole-cell current recordings in HEK 293 T cells revealed that the N447 K mutation increased the NMDAR current density by;.2-fold, enhanced the glutamate potency by 2-fold, and reduced the sensitivity to Mg;inhibition. These results indicated that N447 K is a gain-offunction mutation. Interestingly, alternative substitutions by alanine and glutamic acid at the same residue（N447 A and N447 E） did not change NMDAR function, suggesting a residual dependence of this mutation in altering NMDAR function. Taken together, this study identified human GluN2A N447 K as a novel mutation associated with epilepsy and validated its functional consequences in vitro.Identification of this mutation is also helpful for advancing our understanding of the role of NMDARs in epilepsy and provides new insights for precision therapeutics in epilepsy.