Case Report: Recurrent Deposition in Renal Allografts: A Rare Case of Fibronectin Glomerulopathy Overlooked in Native Kidneys.

Fibronectin glomerulopathy (FNG) is a rare inherited kidney disease characterized by extensive deposition of fibronectin in the glomeruli, especially in the mesangial and subendothelial regions. The disease progresses slowly and eventually leads to kidney failure in 15-20 years. Here, we report an interesting case. The patient presented with proteinuria and was diagnosed with immune complex-mediated glomerulonephritis, and lupus nephritis was suspected. This patient progressed to end-stage renal disease after 18 years and received an allogeneic kidney transplant. However, proteinuria recurred 27 months after kidney transplantation. The renal biopsy found extensive deposition in glomeruli, and the patient was diagnosed with FNG using mass spectrometry analysis and confirmed by immunohistochemistry in both the native and transplanted kidneys. Gene sequencing revealed that a missense mutation in the fibronectin 1 (FN1) gene caused reduced binding to heparin, endothelial cells, and podocytes and impaired stress fiber formation. The patient had stable renal function but persistent nephrotic proteinuria after 6 months of follow-up. Given the persistence of abnormal circulating fibronectin levels, FNG can relapse following renal transplantation. The circulating fibronectin deposits on grafts, and renal function progressively deteriorates after recurrence. Therefore, whether renal transplantation is an acceptable treatment for FNG is still debatable.