Thrombotic microangiopathy and smoldering multiple myeloma after kidney transplant in a patient with MCP mutation

The most frequent cause of atypical hemolytic uremic syndrome (aHUS) is defective regulation of complement activation because of genetic anomalies. We present the case of 53-year-old man with a kidney transplant and stabilized kidney function (creatinine 2.5 mg/dL; proteinuria 0.4 g/24 h) with mycophenolate/tacrolimus/prednisone who was diagnosed of Thrombotic Microangiopathy (TMA). This diagnosis was associated with creatinine and proteinuria rise (3 mg/dL; 2.4 g/24 h) and a new monoclonal IgA/lambda component. Renal biopsy showed membranoproliferative glomerulonephritis; a pathogenic variant in the Membrane cofactor protein (MCP) gene with a polymorphism ggaac, typically associated to secondary aHUS, was identified. We suspected that immunoglobulin could be acting as a trigger for TMA in a genetically susceptible patient, so “clone-directed” therapy with bortezomib and dexamethasone was initiated.