Since the identification of the first pathogenic mutations in NMDA receptors [17,18], more than 60 grin2b variants have been reported in the literature and identified in individuals with a variety of neurodevelopmental disorders, including ID, developmental delay (DD), ASD, epileptic encephalopathy (EE), schizophrenia (SCZ), and, to a lesser extent, attention deficit hyperactivity disorder (ADHD), cerebral visual impairment (CVI), and Alzheimer's disease (AD) [10]. The gene discussed is GRIN2B; the disease is ethylmalonic encephalopathy.