IgA Nephropathy With Membranoproliferative Pattern and Resistance to Immunosuppressive Therapy in Two Patients With Cofactor I Pathogenic Variant.

Complement system (CS) overactivation is one of the main causes of kidney damage in IgA nephropathy (IgAN), and it mainly involves the alternative pathway (AP). Additionally, pathogenic complement variants in CS-related genes are reported in IgAN with associated thrombotic microangiopathy (TMA). Here we report two patients with IgAN presenting membranoproliferative pattern, isolated C3 hypocomplementemia, resistance to multiple lines of immunosuppressive therapy, familiarity for proteinuric chronic kidney disease and pathogenic rare variants in cofactor I (CFI). To the best of our knowledge, no other cases of IgAN patients with a similar phenotype and genotype were previously reported in the literature. This work highlights the essential role of deep phenotyping and genotyping in providing tailored treatment strategies in IgAN patients.