Sethi et. al have reported new markers Exostocin 1 & Exostocin 2, which are particularly useful for diagnosing PLA2R/THSD7A negative cases of Membranous nephropathy. In approximately 70%–80% of cases of primary membranous nephropathy (MN), phospholipase A2 receptor (PLA2R)/Thrombospondin Type-1 Domain–Containing 7A (THSD7A) and anti-PLA2R/THSD7A antibodies form immune complexes along the glomerular basement membrane (GBM) that characterize the condition. In other cases of primary MN and all secondary MN, the target antigen is unknown. Using proteomics and immunohistochemistry, Sethi et. al detected two proteins, exostosin 1 (EXT1) and exostosin 2 (EXT2), in the GBM of PLA2R-negative MN. EXT1 and EXT2 were absent in all cases of PLA2R-associated MN and controls. Clinical and biopsy findings showed features of autoimmune disease, including membranous lupus nephritis, in 81% of the 26 EXT1/EXT2-associated MN cases the authors identified. These findings suggest that EXT1/EXT2-associated MN represents a distinct subtype of MN, most commonly associated with autoimmune diseases (secondary MN).
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