The presence of a skin rash, leukopenia, hemolytic anemia, proteinuria, blood ANA 1:1280 positive, anti-dsDNA 1:1000 positive, poor complement (C3 and C4), and serositis (recurrent pericardial effusion) matches the 2019 EULAR/ACR diagnostic criteria for systemic lupus erythematosus. The gene discussed is C3; the disease is exanthem.