In Case 2, the renal biopsy findings—notably enlarged glomeruli with diffuse basement membrane thickening—favored a diagnosis of secondary membranous nephropathy (SMN), given the absence of systemic IgG4-related disease manifestations, weak IgG4 deposition in renal tissue, and negative PLA2R staining. This evidence concerns the gene PLA2R1 and membranous glomerulonephritis.