DLG4 and schizophrenia: Indeed, large-scale gene expression examination indicates that presynaptic protein synaptophysin levels are decreased in the hippocampus, frontal cortex, and cingulate cortex in schizophrenia patients, while synaptic protein SNAP − 25, synapsin, rab3A, and PSD-95 are also reduced in the hippocampus in schizophrenia patients (Osimo et al., 2019).