What lies in-between: C3 glomerulopathy with non-hemolytic renal microangiopathy and an ultra-rare C3 variant

We report a 36-year-old female with mixed nephritic-nephrotic syndrome and recurrent pancreatitis. Kidney biopsy showed a crescentic membranoproliferative glomerulonephritis with dominant C3 staining on immunofluorescence (IF) but only scant deposits on electron microscopy (EM) and instead, evidence of severe acute and chronic microangiopathy - endothelial swelling, sub-endothelial fluff, and segmental basement membrane remodeling. Her serum C3 was normal, Factor Ba, and serum Membrane attack complex (sMAC) levels were elevated, and Properdin was low. Genetic testing revealed a heterozygous ultra rare C3 variant of unknown significance (c.4838G>T, p.Gly1613Val) as well as a heterozygous deletion of CFHR3CFHR1. She showed an initial response to terminal complement blockade with eculizumab, but her renal disease progressed in the next year. Notably, our patient never demonstrated microangiopathic hemolysis, yet pancreatitis of unclear etiology recurred periodically. Our case suggests the existence of a C3G/aHUS overlap clinicopathologic syndrome and highlights the challenges of treating complement-mediated kidney disease. [Am J Med Sci 2023;365(3):286-293.]

Automated summary

We present a case of a female patient with mixed nephritic-nephrotic syndrome and recurrent pancreatitis. Kidney biopsy revealed crescentic membranoproliferative glomerulonephritis with dominant C3 staining on immunofluorescence. Genetic testing revealed a rare C3 variant and a deletion of CFHR3CFHR1. The case highlights the challenges of treating complement-mediated kidney disease and suggests the existence of a C3G/aHUS overlap syndrome.