GRIN1 and Neurodevelopmental delay: GRIN-related neurodevelopmental disorders (GRIN-NDD) comprise a phenotypic spectrum caused by pathogenic variants in one of the four GRIN genes (GRIN1, GRIN2A, GRIN2B, and GRIN2D), all of which encode different subunits of the N-methyl-D-aspartate receptor (NMDAR) for glutamate [102].