THSD7A staining of membranous glomerulopathy in clinical practice reveals cases with dual autoantibody positivity

Thrombospondin type I domain-containing 7A (THSD7A) is a known antigenic target of autoantibodies leading to primary membranous glomerulopathy and was reported to account for ~10% of phospholipase A2 receptor (PLA2R)-negative membranous glomerulopathy. It has been proposed that PLA2R and THSD7A autoantibodies are mutually exclusive in membranous glomerulopathy. We validated an immunohistochemical assay to investigate for THSD7A-associated membranous glomerulopathy and utilized it in 258 consecutive native kidney biopsies, which showed membranous glomerulopathy in our laboratory, with the exception of membranous lupus nephritis. Membranous glomerulopathy stained positive for THSD7A-only in 7 (3%) cases, PLA2R-only in 141 (55%) cases, and showed dual positivity for THSD7A and PLA2R in 2 (1%) cases. Serologic testing for antibodies to PLA2R and THSD7A was performed in a subset of these patients. There was 100% correlation between positive THSD7A and/or PLA2R tissue staining and the presence of the corresponding autoantibodies in the serum including the two cases with dual positive THSD7A and PLA2R antibodies. We describe and provide a protocol for detection of THSD7A-associated membranous glomerulopathy in clinical practice. The cases with dual THSD7A and PLA2R positivity show that these autoantibodies are not mutually exclusive. They also emphasize the importance of using a panel-based approach when subtyping membranous glomerulopathy as a patient could conceptually be identified and treated based on anti-PLA2R titers, but still have anti-THSD7A antibodies driving persistent disease.