GRIA2 and microcephaly: Pathogenic variants in the glutamate Ionotropic Receptor AMPA Type Subunit 2 (GRIA2) cause a complex neurodevelopmental disorder in which, following a period of normal development, early-onset epilepsy/EE with microcephaly, hypotonia, DD with absent speech, ASD or repetitive behavior and a wide range of MDs, mainly hyperkinetic (dystonia, dyskinesia, startle, chorea, oculogyric crises, stereotypies) but also—less frequently—hypokinetic MD.