Abstract
Introduction: GRIN-related developmental-epileptic encephalopathies are rare genetic conditions caused by heterozygous mutations in Glutamate ionotropic receptors (GluNRs, NMDARs), ligand-gated ion channels with important roles in learning, memory and synaptic plasticity. NMDARs are heterotetramer and are composed of GluN1, GluN2 and GluN3 subunits. The C-terminal domains of subunits play an important role in their localization and synaptic function. We searched for “GRIN mutations” as targeted study. Research based on rare variants identified in patients is a powerful approach to study receptor function. Materials and methods: We identified de novo heterozygous pathogenic mutation in GRIN2B gene - p.Glu839Ter. To study how this mutation alters receptor expression and biophysical properties we combined patch-clamp recordings, BRET experiments and immunocytochemistry, using HEK cells expressing wild type or mutated NMDA receptors subunits or patient fibroblasts reprogrammed into induced pluripotent stem cells (iPSCs) and differentiated into neurons. Results: This mutation leads to truncation of the entire cytosolic C-tail of GluN2B subunits. The mutated GluN2B correctly interacts with wild type GluN2B and GluN1 subunits forming functional receptor. However, compared to wild type NMDAR, mutated one is less expressed at the cell surface and display a reduced NMDA current amplitude with higher sensitivity to magnesium blockade.Conclusion: Ongoing experiments on patient-derived neurons might be a future platform for personal treatment of diseases with a broad spectrum of mutation. Functional analysis of the identified variants is an important step to interpret the clinical consequences of genetic variants and search for specific treatment for GRIN-related neuropathologies.