Anti GBM antibodies are seen in
**Core Concept**
Anti-GBM (Glomerular Basement Membrane) antibodies are a type of autoantibody that targets the glomerular basement membrane, leading to a rapidly progressive glomerulonephritis. This condition is characterized by the formation of immune complexes and activation of the complement system, resulting in severe kidney damage.
**Why the Correct Answer is Right**
The presence of anti-GBM antibodies is a hallmark of Goodpasture syndrome, a rare autoimmune disorder. These antibodies bind to the alpha-3 chain of type IV collagen in the glomerular basement membrane, triggering an immune response that destroys the glomerular capillaries. The resulting inflammation and scarring lead to kidney failure and, if left untreated, can be fatal. The diagnosis of Goodpasture syndrome is confirmed by the detection of anti-GBM antibodies in the patient's serum.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because anti-GBM antibodies are not typically associated with Henoch-Schönlein purpura (HSP), a vasculitis that primarily affects small blood vessels. While HSP can cause kidney damage, it is not characterized by the presence of anti-GBM antibodies.
**Option B:** This option is incorrect because systemic lupus erythematosus (SLE) is a systemic autoimmune disease that can affect multiple organs, including the kidneys. However, SLE is associated with a wide range of autoantibodies, including anti-dsDNA and anti-Sm antibodies, but not typically anti-GBM antibodies.
**Option C:** This option is incorrect because membranous nephropathy is a type of kidney disease characterized by the deposition of immune complexes on the glomerular basement membrane. However, it is not associated with anti-GBM antibodies, but rather with antibodies against the M-type phospholipase A2 receptor (PLA2R).
**Clinical Pearl / High-Yield Fact**
The detection of anti-GBM antibodies is a critical diagnostic step in Goodpasture syndrome. A positive test result can be confirmed by immunofluorescence staining of the patient's kidney tissue, which shows linear deposition of IgG antibodies along the glomerular basement membrane.
**Correct Answer:** C. Membranous nephropathy