Heterozygous Variants in a Patient with Karyomegalic Interstitial Nephritis

Karyomegalic interstitial nephritis (KIN) is a rare kidney disease marked by large tubular nuclei, interstitial inflammation, tubular atrophy, and interstitial fibrosis. The current study presented the case of a 39-year-old man with deteriorating kidney function and a serum creatinine level of 2.08 mg/dL. The renal biopsy revealed that the main pathological features of renal tubular epithelial cells were obvious enlargement, irregular shape, and hyperchromatic nuclei. The genetic analysis of the patient revealed two heterozygous variants in the FAN1 gene, c.2485c>T, and c.2928dupT, located in exons 10 and 13, respectively. A diagnosis of KIN was rendered. The two variations of the proband are identified in separate alleles from the father and mother, respectively, according to his family's sequencing. This phenotype is consistent with an autosomal recessive pattern of inheritance. The patient was treated with the Chinese patent medicine Niaoduqing Particles. After 38 months of follow-up, renal function was barely changed with a serum creatinine of 1.73 mg/dL.