Four genes encoding NMDAR subunits (GRIN1, GRIN2A, GRIN2B, and GRIN2D) have so far been linked to human disease; GRIN2A appears to be associated with the broadest and best characterized phenotypic spectrum, including a variety of disorders of the epilepsy aphasia spectrum and developmental and epileptic encephalopathy, such as Landau-Kleffner syndrome and epileptic encephalopathy with continuous spike-and-wave during slow-wave sleep (CSWS) (Lemke et al., 2013, Lesca et al., 2013; Carvill et al., 2013). Here, GRIN2A is linked to developmental and/or epileptic encephalopathy with spike-wave activation in sleep.