The diagnosis of SLE was established according to the 2019 European League Against Rheumatism (EULAR) criteria, based on the combination of inflammatory polyarthralgia, lymphopenia, a high titer of anti-nuclear antibodies, specific anti-Sm and anti-DNA antibodies, and consumption of C3 and C4 complement fractions. The gene discussed is C4A; the disease is systemic lupus erythematosus.