A mouse model of GRIN2D developmental and epileptic encephalopathy recapitulates the human disease.

A recurrent gain-of-function mutation in GRIN2D, which encodes an NMDA receptor subunit, causes developmental and epileptic encephalopathies. Mice carrying the orthologous mutation show premature death, spontaneous seizures, early motor deficits, and later cognitive impairment, closely mirroring the human disease. Electrophysiological recordings in cerebellar Purkinje neurons revealed developmental changes: reduced spontaneous firing in immature mice and augmented synaptic response to NMDA in older mice. Electrocorticography showed continuous abnormal brain activity with narrowband oscillations in theta, alpha, and beta bands, similar to a patient with the same variant. Low-dose ketamine had limited effect; higher doses caused seizures. Memantine and phenytoin produced small corrective effects on brain activity. These abnormal oscillations may serve as a biomarker for drug response.

Study at a glance

Abstract

Pathogenic variants in GRIN2D, encoding one of the subunits of the NMDA receptor (NMDAR), are associated with developmental and epileptic encephalopathies (DEEs). Unusual for de novo mutations, the recurrent, de-novo, gain of function, missense mutation c.1999G>A (p.Val667Ile) was discovered in multiple patients. We characterized a mouse model carrying the orthologous Grin2d mutation, using behavioral paradigms, electrophysiological recordings in acute brain slices focusing mainly on the activity of Purkinje neurons (PNs) in the cerebellum, and electrocorticography (ECoG) recordings monitoring brain activity and the response to several drugs. Grin2d mutant mice exhibit a range of phenotypes that closely mirror the human disease, including premature mortality, spontaneous seizures, and early onset of motor deficits followed by cognitive impairment. In addition, we observed complex developmental changes in PNs with reduced spontaneous firing in immature mice and augmented synaptic response to NMDA application in older mice. ECoG recordings demonstrated profound and continuous abnormal brain activity, with altered spectral properties and a prominent narrowband activity in the theta, alpha, and beta bands, paralleling the patterns seen in a patient with the same GRIN2D pathogenic variant. Acute administration of ketamine at a low dose (0.5 mg/kg) had a limited effect on the spectral properties, and higher dosages (4 or 10 mg/kg) caused seizures. Conversely, memantine (10 mg/kg) and phenytoin (30 mg/kg) demonstrated a small corrective effect on ECoG properties. Together, Grin2d mutant mice recapitulate key phenotypes of patients with pathogenic GRIN2D variants, including unique, abnormal brain oscillations, which may serve as a biomarker for quantifying drug responses and guiding future research efforts.