C4A and psychotic disorder: In short, C4A expression was found to be elevated in schizophrenia, C4 was localised at synapses and neurons in the human brain, C4 deficiency produced a segregation deficit in the mouse RGC system (as did C1q), C4A expression was positively associated with schizophrenia symptoms (delusions and reduced memory performance), decreased C4b inhibiting protein levels were found in children preceding a psychotic disorder, and increased C4A repeats were associated with neuropil contraction in multiple brain regions of schizophrenic patients.