Anti-PLA₂R Antibody Development During NELL1-Associated Membranous Glomerulonephritis Treatment: A Case Report

A Japanese man in his early 70s was referred to our hospital because of massive proteinuria. Analysis of his kidney biopsy demonstrated glomerular subepithelial immune deposits containing immunoglobulin (Ig)G, which was dominant for the IgG1 subclass. Immunoperoxidase staining for neural epidermal growth factor-like 1 protein (NELL1) was positive on the glomerular capillary walls, whereas neither serum anti-phospholipase A2 receptor (PLA₂R) antibodies nor immunofluorescence staining for PLA₂R was positive. Detailed investigation revealed no associated conditions, including underlying malignancies, and thus he was diagnosed as having NELL1-associated idiopathic membranous nephropathy (MN). The patient was treated with steroids, which substantially improved his nephrotic syndrome. Interestingly, serum anti-NELL1 as well as anti-PLA₂R antibodies became positive during his clinical course. Serology-based approaches are currently proposed for the treatment of patients suspected of having MN; however, an accurate diagnosis of the present patient would have been difficult if such an approach was performed only at a later phase of the disease. Several target antigens for the glomerular immune deposits observed in patients with MN have recently been identified, and dual positivity of antibodies to these antigens reportedly occurs in some patients. Further accumulation and analyses of such patients are needed to establish more appropriate diagnostic approaches for MN.