A young woman was diagnosed with SLE at the age of 24 years due to polyarthritis, malar rash, photosensitivity, leukopenia, lymphopenia, thrombocytopenia, non-scarring alopecia, Raynaud’s phenomenon, erythema nodosum, cutaneous vasculitis, and compatible serological abnormalities including antinuclear antibodies (ANA) at a titer of 1:640; anti-dsDNA, anti-Smith, and anti-SSB autoantibodies; low levels of serum complement fractions C3/C4; and positive direct Coombs. The gene discussed is C3; the disease is Erythema nodosum.