TCF4 and schizophrenia: Interestingly, associations of TCF4 mutations occurring outside the bHLH domain with schizophrenia have been reported; common variants in human Tcf4 were among the first genes to reach significance in genome-wide association studies of schizophrenia [30], and rare coding Tcf4 variants outside of the bHLH domain have been identified in individual schizophrenia patients via deep sequencing [31, 32].