Atypical Antiglomerular Basement Membrane Disease With IgG1-κ Staining

INTRODUCTION A ntiglomerular basement membrane (GBM) disease is an autoimmune disease that classically presents as a rapidly progressive crescentic glomerulonephritis, with or without pulmonary hemorrhage, and typically does not relapse. The anti-GBM autoantibodies, typically polyclonal IgG1 and IgG4, bind to the noncollagenous 1 domain of the alpha-3 chain of type IV collagen that is present on alveolar and glomerular basement membranes. Kidney biopsies in patients with anti-GBM disease reveal a crescentic and necrotizing glomerulonephritis on light microscopy with diffuse linear staining of the glomerular basement membrane for IgG on immunofluorescence (IF) microscopy. Anti-GBM antibodies are detectable in the serum of w90% of patients using conventional enzyme-linked immunosorbent assays. Atypical antiGBM disease is a rare entity defined by uncharacteristic histologic features on light microscopy and/or linear GBM staining for an antibody other than the typical polyclonal IgG on IF. Here we describe a case of relapsing, atypical IgG1-k anti-GBM glomerulonephritis.