We initially selected 35 cases (pilot cohort) of PLA2R-negative MN on kidney biopsy for analysis by tandem mass spectrometry (MS/MS), and detected the unique protein, NELL-1,

BackgroundIn membranous nephropathy (MN), which is characterized by deposition of immune complexes along the glomerular basement membrane (GBM), phospholipase A2 receptor (PLA2R) and thrombospondin type 1 domain–containing 7A are target antigens in approximately 70% and 1%–5% of cases of primary MN, respectively. In other cases of primary MN and in secondary MN, the target antigens are unknown.MethodsWe studied 224 cases of biopsy-proven PLA2R-negative MN and 102 controls (including 47 cases of PLA2R-associated MN) in pilot and discovery cohorts. We also evaluated 48 cases of PLA2R-negative presumed primary MN and lupus MN in a validation cohort. We used laser microdissection and mass spectrometry to identify new antigens, which were localized by immunohistochemistry.ResultsMass spectrometry detected exostosin 1 (EXT1) and exostosin 2 (EXT2) in 21 cases of PLA2R-negative MN, but not in PLA2R-associated MN and control cases. Immunohistochemistry staining revealed bright granular GBM staining for EXT1 and EXT2. Clinical and biopsy findings showed features of autoimmune disease, including lupus, in 80.7% of the 26 EXT1/EXT2-associated MN cases we identified. In the validation cohort, we confirmed that EXT1/EXT2 staining was detected in pure class 5 lupus nephritis (eight of 18 patients) and in presumed primary MN associated with signs of autoimmunity (three of 16 patients); only one of the 14 cases of mixed class 5 and 3/4 lupus nephritis was positive for EXT1/EXT2. Tests in seven patients with EXT1/EXT2-associated MN found no circulating anti-exostosin antibodies.ConclusionsA subset of MN is associated with accumulation of EXT1 and EXT2 in the GBM. Autoimmune disease is common in this group of patients.

Histiocytic neoplasms, a rare and heterogeneous group of disorders, primarily include Erdheim-Chester disease, Langerhans cell histiocytosis, and Rosai-Dorfman disease. Due to their diverse clinical manifestations, the greatest challenge posed by these neoplasms is the establishment of a diagnosis, which often leads to a delay in institution of appropriate therapy. Recent insights into their genomic architecture demonstrating mitogen-activated protein kinase/extracellular signaleregulated kinase pathway mutations have now enabled potential treatment with targeted therapies in most patients. This consensus statement represents a joint document from a multidisciplinary group of physicians at Mayo Clinic who specialize in the management of adult histiocytic neoplasms. It consists of evidence-and consensus-based recommendations on when to suspect these neoplasms and what tests to order for the diagnosis and initial evaluation. In addition, it also describes the histopathologic and individual organ manifestations of these neoplasms to help the clinicians in identifying their key features. With uniform guidelines that aid in identifying these neoplasms, we hope to improve the awareness that may lead to their timely and correct diagnosis.

Rosai-Dorfman disease is a rare subtype of non-Langerhans cell histiocytosis. With the last major report published in 1990, there is a paucity of contemporary data on this disease. Our objective was to report the clinicopathological features, treatments and outcomes of patients seen at a tertiary referral center. Sixty-four patients with histopathological diagnosis of Rosai-Dorfman disease were identified from 1994 to 2017 (median age 50 years; range, 2-79). The median duration from symptom onset to diagnosis was seven months (range, 0-128), which was also reflected in the number of biopsies required to establish the diagnosis (median 2; range, 1-6). The most common presentation was subcutaneous masses (40%). Of the 64 patients, 8% had classical (nodal only) and 92% had extra-nodal disease (67% extra-nodal only). The most common organs involved were skin and subcutaneous tissue (52%), followed by lymph nodes (33%). Three patients had an overlap with Erdheim-Chester disease, which had not been described before. Two of these were found to have MAP2K1 mutations. Commonly utilized first line treatments were surgical excision (38%) and systemic corticosteroids (27%). Corticosteroids led to a response in 56% of the cases. Of those treated initially, 15 (30%) patients developed recurrent disease. The most commonly used systemic agent was cladribine (n=6), with 67% overall response rate. Our study demonstrates that Rosai-Dorfman disease has diverse clinical manifestations and outcomes. While this disease has been historically considered a benign entity, a subset of patients endures an aggressive course necessitating the use of systemic therapies.

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