SLC12A5 and schizophrenia: However, the authors of the paper suggest that the MMP-9-1562C/T polymorphism association with schizophrenia risk is not related to the polymorphism-driven changes in MMP-9 expression, but rather with its genomic linkage with a nearby schizophrenia predisposing SLC12A5 gene, encoding KCC2 (a neuronal specific K + -Cl– cotransporter) (Gregory et al., 2019).