C4A and schizophrenia: The higher C4A copy number has been found to be associated with higher schizophrenia risk, while the C4-BS allele is a protective factor of schizophrenia.16 A recent study further demonstrated the overexpression of C4A gene promotes the excessive synaptic loss and abnormal behaviour in mice.48 Interestingly, they found that the loss of C4 does not affect the normal developmental synaptic pruning.48 At the nominal level of the significance threshold, C4-BS was associated with the increased cortical TH and grey matter volume across different brain regions especially the prefrontal cortex.