A neurodevelopmental disorder caused by variation in the GRIN1 gene. It is characterized by mild-to-profound developmental delay/intellectual disability (DD/ID) in all affected individuals. Other common manifestations are epilepsy, muscular hypotonia, movement disorders, spasticity, feeding difficulties, and behavior issues. A subset of individuals show a malformation of cortical development consisting of extensive and diffuse bilateral polymicrogyria. The disease is Monarch Disease Ontology id MONDO_1060123 (GRIN1-related complex neurodevelopmental disorder). Also known as: GRIN1-related developmental and epileptic encephalopathy, GRIN1-related neurodevelopmental disorder.