A 31-year-old woman from Fortaleza (Northeastern Brazil) diagnosed since 2009 with SLE and meeting the 2019 ACR/EULAR criteria for SLE (11) (arthritis, serositis, oral ulcers, alopecia, fever, hemolytic anemia associated low complement c3 and c4, and anti-DNA positivity), without adequate disease monitoring, presented at an emergency service with asthenia, anorexia, weight loss, progressive dyspnea and lipothymia, reportedly starting 4 months earlier, and was referred to a local tertiary-level facility. The gene discussed is C3; the disease is systemic lupus erythematosus.