Wcn26-2641 a Case of Sporadic Karyomegalic Interstitial Nephritis With a Novel Fan1 Gene Mutation: The First Report in East Asia

Karyomegalic interstitial nephritis (KIN) is a rare autosomal recessive disorder caused by pathogenic variants in FAN1, leading to chronic tubulointerstitial injury and progressive renal dysfunction. Its hallmark is karyomegaly—marked enlargement and atypia of tubular epithelial nuclei—resulting from defective DNA repair during regeneration. We report a Japanese patient with sporadic KIN diagnosed by biopsy, carrying compound heterozygous FAN1 frameshift mutations, one of which was novel. This represents the first genetically confirmed KIN case in East Asia involving a novel FAN1 mutation.