GRIN2B related syndrome is a genetic disorder that causes developmental delay and intellectual disability. Intellectual disability ranges from mild to severe. Other symptoms may include low muscle tone (hypotonia), seizures, behavior problems including autistic features, abnormal movements, a very small head (microcephaly), and developmental regression. Some children have brain malformations that can be seen in brain imaging exams. This disorder is caused by variations (mutations) in the GRIN2B gene, which plays a role in the transmission of signals in the brain. Inheritance is autosomal dominant. Treatment depends on the symptoms seen in each person. In some cases, the medication memantine was used with good results, but more studies are needed to know if it is broadly effective.