Abstract: A young male presented with bilateral lower extremity edema. Laboratory tests indicated mass proteinuria, glomerular originated hematuria, normal renal function, decreased complement 3 (C3) and positive C3NeF. The pathological manifestations were membranoproliferative glomerular lesions accompanied by electron⁃dense deposits in the mesangial area, within the basal membrane, at the subendothelial and epithelial side. Immunofluorescence revealed granular and diffuse deposition of C3+++ and IgG+ in the mesangial area and capillary loops. Gene sequencing identified a compound heterozygous mutation of CFI, and both parents were heterozygous. The final diagnosis was C3 glomerulonephritis with compound⁃heterozygous mutation of CFI and positive C3NeF. The treatment with prednisone acetate, mycophenolate mofetil and losartan was initially well controlled, but the condition progressed later.

Key words: CFI mutation, C3 nephritic factor, C3 glomerulonephritis