FAN1 mutation and karyomegalic nephropathy in chronic kidney disease.

Karyomegalic Interstitial Nephritis (KIN) is a rare hereditary cause of chronic kidney disease (CKD), resulting from autosomal recessive mutations in the FAN1 gene. Renal biopsy typically reveals severe interstitial fibrosis, tubular injury and glomerulosclerosis. Early and accurate diagnosis can guide appropriate management. We present a middle-aged euglycaemic, normotensive female who underwent renal biopsy, which revealed tubular vacuolisation, patchy acute injury and enlarged, bizarre nuclei (karyomegaly) with occasional intranuclear cytoplasmic inclusions. Clinical exome sequencing confirmed a homozygous one-base-pair deletion in exon 9 of the FAN1 gene, classified as pathogenic. The patient was managed conservatively and her renal function remained stable at 6-month follow-up.