In a report in which renal biopsies were performed on 48 patients with SLE without abnormal urinalysis and renal impairment, 36 patients had lupus nephritis (class I or II, 72%; class III or IV, 17%; and type V, 11%), and hypocomplementemia (low titers of CH50 and C3) and a high titer of anti-Sm antibodies were identified as predictive factors for silent lupus nephritis. The gene discussed is C3; the disease is lupus nephritis.