Clinically Suspected Focal Segmental Glomerulosclerosis Caused by a Novel INF2 Variant in a Korean Patient Undergoing Renal Transplantation: A Case Report and Literature Review

Introduction: Heterozygous pathogenic/likely pathogenic (P/LP) variants in the inverted formin-2 (INF2) gene are recognized causes of focal segmental glomerulosclerosis (FSGS), a rare glomerular disorder often leading to rapid renal failure. Whereas some variants produce a combined FSGS and Charcot-Marie-Tooth disease phenotype, others manifest exclusively with renal pathology. Case Presentation: We report an 18-year-old Korean male with clinically suspected FSGS attributable to a sporadic INF2 P/LP variant. He initially presented with nephrotic-range proteinuria and bilaterally atrophic kidneys and subsequently progressed to end-stage renal disease. Exome sequencing identified a novel heterozygous in-frame duplication in exon 4 of INF2 (NM_022489.4:c.582_608dup;p.(Thr196_Val204dup)), confirmed as de novo by Sanger sequencing. Despite three HLA mismatches and an ABO-incompatible donor-recipient pair, living donor kidney transplantation from his mother was performed successfully, with stable graft function at 4 months of follow-up. Conclusion: To our knowledge, this is the first Korean case in which the p.(Thr196_Val204dup) variant is linked to clinically suspected FSGS without neurological involvement. Our findings highlight the importance of INF2 molecular testing even in sporadic presentations and demonstrate that transplantation is a viable therapeutic option when conventional immunosuppressive therapy fails.