GRIN2A and developmental and/or epileptic encephalopathy with spike-wave activation in sleep: Landau–Kleffner syndrome (LKS), is a rare, poorly‐understood epileptic encephalopathy with spike–wave activation in sleep associated with mutations in GRIN2A, encoding the N‐Methyl‐D‐Aspartate receptor (NMDAR) GluN2A subunit.