A Novel GRIN2A Mutation In Rolandic Epilepsy:functional Changes And Responses To Anti-epileptic Drugs

The N-methyl-D-aspartate receptor(NMDAR),a ligand-gated ion channel,plays a critical role in the functioning of the brain.Recent studies have identified an increasing number of GRIN2A(a gene encoding NMDAR GluN2A subunit)mutations in patients with epilepsy.Phenotypes ofGRIN2A mutations include epilepsy-aphasia disorders and other epileptic encephalopathies,which pose challenges in clinical treatment.We identified a novel heterozygous GRIN2A mutation(c.1341T>A,p.N447K)in a boy of Rolandic epilepsy without language or intelligent disability by whole-exome sequencing.He got seizure-free with a combination of valproate and lamotrigine.Whole-cell voltage clamp recording in transfected HEK cells was used to determine functional alteration and responses to antiepileptic drugs.The results showed that the NMDA receptor mutant had a relatively mild gain-of-function effect featured by 1.2-fold of increment in current amplitude,2-fold of enhanced glutamate potency,and reduced sensitivity to Mg2+ inhibition.The mild gain-of-function of N447K mutant corresponded with the mild clinical phenotype,suggesting a correlation between functional impact and phenotype severity.In addition,alternative substitution at residue N447 by alanine and glutamate(N447A and N447E)did not lead to changes in the receptor function,suggesting a mutation-selective association at this site with the receptor channel dysfunction.Aslo,this may partly explain the diverse functional consequences caused by GRIN2A mutant variants.Valproate and lamotrigine decreased the maximal current amplitude of NMDA receptors in a dose-dependent manner,whereas levetiracetam showed only subtle inhibition on the receptor.These different responses of NMDA receptors to anti-epileptic drugs would help precision management of patients with GRIN2A mutations.