Nucleic acids comprising the neuregulin 1 gene (NRG1) and encoding NRG1 polypeptides are disclosed. Also described are related nucleic acids encoding NRG1 polypeptides; NRG1 polypeptides; antibodies that bind to NRG1 polypeptides; methods of diagnosis of susceptibility to schizophrenia; assays for agents that alter the activity of NRG1 polypeptide or which identify NRG1 binding agents, and the gents or binding agents identified by the assays; NRG1 therapeutic agents, including the NRG1 nucleic acids, NRG1 polypeptides, or agents that alter the activity of an NRG1 polypeptides; pharmaceutical compositions comprising the NRG1 therapeutic agents; as well as methods of therapy of schizophrenia. Novel haplotypes with a common core haplotype in affected individuals are described, as well as their use in methods for screening for susceptibility to schizophrenia. Also described are hypomorphic mice for use in identifying phenotypes associated with schizophrenia, as well as for use in assessing agents of interest for neuroleptic activity and for potential therapeutic use for treatment of schizophrenia.