The present results appear at a first glance surprising since mutant mice heterozygous for either NRG1 or ErbB4 show a behavioral phenotype that resembles alterations seen in schizophrenia and, furthermore, NRG1 hypomorphs, expressing 50% of the normal levels of NRG1, have 16% fewer functional NMDARs than wild-type mice (26). Here, ERBB4 is linked to schizophrenia.