Moreover, the subgroup analysis involving ethnicity revealed that low C4 GCNs were significantly associated with the risk of autoimmune diseases among Caucasian individuals (pooled OR = 1.91, 95% CI:1.42–2.56), while such an association was not confirmed in an Asian population (pooled OR = 1.13, 95% CI: 0.88–1.45). The gene discussed is C4A; the disease is autoimmune disease.