Accordingly, higher C4A expression was observed in brain samples from patients with schizophrenia compared to controls (Sekar et al., 2016) and a positive correlation was found between the copy numbers of C4 and neuropil contraction in different brain regions in patients (Prasad et al., 2018; Figure 1), which strongly suggest that increased C4 levels constitute a risk factor for schizophrenia. Here, C4A is linked to schizophrenia.