A case of anti-nephrin antibody-positive, steroid-dependent nephrotic syndrome with successful discontinuation of immunosuppressants following rituximab.

Minimal change nephrotic syndrome (MCNS) is a major cause of nephrotic syndrome in children and adults. Recent studies identified circulating anti-nephrin antibodies in 30%-50% of patients, linking them to severe proteinuria and frequent relapses. We describe a Japanese woman in her 40s with steroid-dependent nephrotic syndrome (SDNS). Anti-nephrin antibodies were identified in serum obtained at disease onset by immunoprecipitation and ELISA, and kidney biopsy showed punctate IgG colocalizing with nephrin. Before rituximab (RTX), she experienced relapses accompanied by increased anti-nephrin antibody reactivity. A low-dose RTX regimen (200 mg every 6 months for seven doses) enabled maintenance of complete remission and discontinuation of prednisolone and cyclosporine, with B-cell depletion confirmed by CD19 monitoring. She has maintained remission for two years after RTX discontinuation, without re-elevation of anti-nephrin antibody reactivity. This case supports a possible role of anti-nephrin antibodies in disease activity and suggests that low-dose RTX may contribute to durable remission.