The typical pathological characteristic was found to be membranous nephropathy, presenting as glomerular mesangial-cell hyperplasia; basement membrane thickening (BMT); and depositions of intraglomerular IgG, IgM, C3, and C4, suggesting that syphilitic nephropathy is an immune complex–mediated injury. The gene discussed is C4A; the disease is membranous glomerulonephritis.