GRIN2B and Global developmental delay: For example, two GRIN2A mutations leading to GluN2A-A548T and GluN2A-P552R were identified in patients with seizure disorders and intellectual disability [20,21], a GRIN2B mutation encoding GluN2B-P553L was found in a patient with severe developmental delay [20], and two GRIN1 mutations corresponding to GluN1-D552E and GluN1-P557R were identified in patients with intellectual disability and/or epilepsy [22,23].