EXT2 transition in adolescent membranous nephritis.

Membranous nephropathy (MN) is the cause of 3% of pediatric nephrotic syndrome, with increasing incidence in adolescents. It was historically divided into primary and secondary forms but is increasingly described by antigen. The direct clinical value of knowing the MN antigen often depends on the strength of association between antigen and various underlying conditions, prognostic potential, and the presence of commercially available serum antibody testing. In this case, we describe an adolescent with PLA2R-, NELL1-, THSD7A-, and EXT2-negative MN who responded to B-cell depleting therapy. Three years later, he developed proliferative lupus nephritis and ongoing membranous nephritis with newly detected EXT2-positive deposits on kidney biopsy. This discordant MN antigen result demonstrates (1) the potential for apparent change in MN antigen detection over time and (2) that EXT1/2 negativity does not exclude the possibility of later development of lupus nephritis in an adolescent with MN.