MR brain: Basal ganglion calcification  Renal biopsy:  IgA nephropathy  ANA–Positive  Anti dsDNA: 67.5 IU  C3/C4: 105 mg/dL/29.6 mg/dL  IgG: 3,590 mg/dl  IgA: 621 mg/dl  IgM: 60.9 mg/dl. The gene discussed is C3; the disease is IgA glomerulonephritis.