SP4 and schizophrenia: Genes containing the GC-boxes in the proximal promoter region are significantly over-represented in the susceptibility genes for schizophrenia from both the SCHEMA and the GWAS studies, suggesting that Sp4 is not only a high-risk gene for schizophrenia, but may also act as a hub of network in the regulation of many other schizophrenia-risk genes via these GC-boxes in neuronal cells.