Fibronectin Glomerulopathy

A renal biopsy was performed in a 32-year-old female with microscopic hematuria and nephrotic range proteinuria of 4 grams per day. Serologic workup for autoimmune disease was negative. The glomeruli show extensive mesangial and subendothelial deposition of PAS-positive (A) and silver-negative material (B and C) by light microscopy. The immunofluorescence showed segmental glomerular staining for C3 (1-2+). An immunoperoxidase stain for fibronectin was diffusely positive in glomeruli (D) and electron microscopy showed massive electron dense deposits replacing the mesangium that were also present along the subendothelial aspect of basement membranes (E). These findings are consistent with fibronectin glomerulopathy. Approximately 40% of patients with fibronectin glomerulopathy have pathogenic variants in the FN1 gene (AD pattern of inheritance).