Abstract
Karyomegalic interstitial nephritis is a rare progressive renal disease. We report a 36-year-old male patient who developed kidney failure due to this condition, underwent kidney transplantation from his sister, and developed the same condition in the graft. Genetic testing of the donor revealed autosomal recessive compound heterozygous mutation of Fanconi anemia-associated nuclease1 (FAN1) gene. Karyomegalic interstitial nephritis is most probably donor derived in our patient. It should not be mislabeled as viral nephropathy.