C4A and systemic lupus erythematosus: While monogenic SLE (found in 7–8% of pediatric cases, compared to 1–4% of cases in adults) is caused by disruption of the genes involved in the complement pathway (C1q, C1r, C1s, C2, C4A and C4B), nucleic acid metabolism, apoptosis and immune tolerance reflected on the activity of B and T lymphocytes, the majority of SLE cases meet a coexistence of the involvement of genetics and additional factors in shaping the etiology.