GRIN2B and epilepsy: For example, the relative proportion of two protein subunits in the NMDA receptor alters with age due to the varying expression levels of the two genes, GRIN2A and GRIN2B, which can alter phenotypic expression of deleterious variants in these genes; prenatally expressed GRIN2B is linked with severe cognitive defects from birth, while postnatally expressed GRIN2A is linked with epilepsies in childhood and schizophrenia in adults (Strehlow et al., 2019).