Recurrence of proteinuria following renal transplantation in congenital nephrotic syndrome of the Finnish type

We report a Caucasian boy of Italian descent with congenital nephrotic syndrome of the Finnish type (NPHS1, CNF, MIM 256300) who developed recurrence of proteinuria and hypoalbuminemia on the seventh post-operative day following living related renal transplantation from his paternal aunt. The allograft biopsy was normal except for effacement of podocyte foot processes on electron microscopy. He was treated by the substitution of mycophenolate mofetil with cyclophosphamide for 12 weeks, in addition to cyclosporine, prednisone and daclizumab. His proteinuria resolved quickly following the initiation of cyclophosphamide treatment, and he remains in remission 4 years after receiving his transplant. His native and allograft kidneys were evaluated for nephrin expression by immunohistochemistry, DNA analysis for the NPHS1 mutation, serum for the presence of auto-antibodies to nephrin by both enzyme-linked immunosorbent assay (ELISA) and fetal glomeruli immunofluorescence assay, and serum for glomerular permeability to albumin (Palb) activity using a functional in vitro assay for Palb. Nephrin expression was completely absent in the native kidney, while it was decreased in the allograft compared with normal. DNA analysis of the NPHS1 gene revealed mutations 3248G>T and 3250delG in exon 24, causing G1083V and 1084Vfs, respectively, inherited from his father, and 3478C>T in exon 27, that leads to R1160X, inherited from his mother. Serum was negative for auto-antibodies to nephrin. Interestingly, the Palb activity was increased at the time of recurrence of proteinuria following transplantation (Palb 0.73±0.10) and remained elevated when retested more than 3 years later (Palb 0.54±0.09). This is the first report of increased Palb activity in recurrence of proteinuria following transplantation in NPHS1. We speculate the role of increased Palb activity in the recurrence of proteinuria following transplantation in NPHS1.