Additionally, in support of the hypothesis that epilepsy is caused by gain-of-functionmutations in GRIN2B, truncating and thus predicted loss-of-function mutations haveonly been described in patients with ID and/or ASD so far.18These data suggest a distinct genotype–phenotype correlation, although more mutations andfunctional studies are needed to verify this assumption. The gene discussed is GRIN2B; the disease is epilepsy.