Karyomegalic Interstitial Nephritis

Mendelian MONDO:0013898 Pathograph 17 Show in embeddings browser hereditary nephritis DNA repair disease chronic tubulointerstitial nephritis

Ask OpenScientist

Ask a research question about Karyomegalic Interstitial Nephritis. OpenScientist will conduct autonomous deep research using the Disorder Mechanisms Knowledge Base and PubMed literature (typically 10-30 minutes).

Submitting...

Do not include personal health information in your question. Questions and results are cached in your browser's local storage.

7
Pathophys.
10
Phenotypes
17
Pathograph
1
Genes
3
Medical Actions
3
Models
17
References
1
Deep Research
⚙

Pathophysiology

7
Biallelic FAN1 Loss of Function
Karyomegalic interstitial nephritis is caused by biallelic loss-of-function variants in FAN1 (FANCD2/FANCI-associated nuclease 1), a structure-specific DNA repair nuclease. Loss of FAN1 activity abolishes its role in the repair of DNA interstrand crosslinks and in the protection and restart of stalled replication forks. KIN is genetically and clinically distinct from Fanconi anemia.
Genetic context FAN1 hgnc:29170 HUGO Gene Nomenclature Committee (hgnc) Relation: this genetic context concerns this gene This genetic context concerns FAN1 (hgnc:29170). hgnc:29170 is a gene from the HUGO Gene Nomenclature Committee. variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION
Biallelic germline loss-of-function FAN1 variants cause KIN. Reported pathogenic alleles span truncating and missense changes and include the homozygous nonsense variant c.2260C>T (p.Arg754Ter), the recurrent European founder frameshift c.2616delA (p.Asp873ThrfsTer17), and the novel frameshift c.2603delT (p.Leu868ArgfsTer22).
structure-specific 5'-flap DNA endonuclease activity GO:0017108 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves structure-specific 5'-flap DNA endonuclease activity, annotated with 5'-flap endonuclease activity (GO:0017108), qualified as loss of function. GO:0017108 is a molecular function from the Gene Ontology. ⇓ LOSS OF FUNCTION
Downstream
Defective Interstrand Crosslink Repair
Defective Replication Fork Protection
Show evidence (5 references)
PMID:22772369 SUPPORT Human Clinical
"By exome sequencing, we identified mutations in FAN1 as a cause of karyomegalic interstitial nephritis (KIN), a disorder that serves as a model for renal fibrosis."
Establishes biallelic FAN1 mutation as the cause of KIN by exome sequencing of affected families.
PMID:20603016 SUPPORT In Vitro
"KIAA1018 is a 5'-->3' exonuclease and a structure-specific endonuclease that preferentially incises 5' flaps."
Biochemically characterizes FAN1 (KIAA1018) as a structure-specific nuclease, the enzymatic activity lost in KIN.
PMID:22772369 SUPPORT In Vitro
"cells from individuals with FAN1 mutations have sensitivity to the ICL-inducing agent mitomycin C but do not exhibit chromosome breakage or cell cycle arrest after diepoxybutane treatment, unlike cells from individuals with Fanconi anemia."
Distinguishes the cellular phenotype of FAN1-mutant KIN cells from that of Fanconi anemia cells: ICL-agent sensitivity without the DEB-induced breakage and cell-cycle arrest characteristic of Fanconi anemia.
+ 2 more references
Defective Replication Fork Protection
Independently of interstrand-crosslink repair, FAN1 nuclease activity restrains and processes stalled replication forks. Loss of this fork-protective function produces chromosome abnormalities and genome instability even without exogenous crosslinks, and may be the more KIN-relevant FAN1 function, since FAN1-deficient cells accumulate damage from endogenous replication stress rather than from crosslink exposure.
stalled replication fork protection and processing GO:0031297 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased stalled replication fork protection and processing, annotated with replication fork processing (GO:0031297). GO:0031297 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Genomic Instability and Replication Stress
Show evidence (2 references)
PMID:26797144 SUPPORT In Vitro
"Fan1 recruitment--and activity--restrains DNA replication fork progression and prevents chromosome abnormalities from occurring when DNA replication forks stall, even in the absence of ICLs."
FAN1 protects stalled forks and prevents chromosome abnormalities independently of ICL repair; loss abolishes this protection.
PMID:29051491 SUPPORT In Vitro
"Because fork stalling in FAN1-deficient cells causes chromosomal instability, we reasoned that the key function of FAN1 might lie in the processing of halted replication forks."
Links FAN1 deficiency to chromosomal instability arising from defective processing of stalled replication forks.
Genomic Instability and Replication Stress
Persistent unrepaired DNA lesions produce chromosomal instability, aberrant cell-cycle progression, and chronic replication stress in dividing renal tubular epithelial cells. In FAN1-deficient kidneys, endogenous reactive oxygen species are an important source of the ongoing DNA damage.
kidney tubule epithelial cell CL:1000507 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves kidney tubule epithelial cell, annotated with kidney tubule cell (CL:1000507). CL:1000507 is a cell type from the Cell Ontology.
DNA damage response GO:0006974 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased DNA damage response (GO:0006974). GO:0006974 is a biological process from the Gene Ontology. ↑ INCREASED
Experimental models
FAN1-mutant hiPSC-derived kidney organoid ORGANOID FAN1-mutant kidney organoids show increased DNA-damage markers and reduced viability after mitomycin C challenge, modeling the DNA-damage susceptibility of FAN1-deficient tubular cells.
Downstream
Polyploidy and Karyomegaly of Tubular Epithelial Cells
Show evidence (3 references)
PMID:22772369 SUPPORT In Vitro
"We observed chromatid breaks and radial chromosomes on metaphase spreads (Figure 2b), which is consistent with a role of FAN1 in genome maintenance and DDR."
FAN1-mutant patient cells show chromosomal instability on metaphase spreads.
PMID:21115814 SUPPORT In Vitro
"MMC treatment causes chromosomal instability that is quantitatively, but not qualitatively, comparable to that seen in FA cells."
FAN1-null cells display crosslink-induced chromosomal instability.
PMID:37107275 SUPPORT Model Organism
"FAN1 kidney pathophysiology is triggered by hypersensitivity to endogenous reactive oxygen species (ROS), which cause chronic oxidative and double-strand DNA damage in the kidney tubular epithelial cells, accompanied by an intrinsic failure to repair DNA damage."
In FAN1-null mice and human tubular epithelial cells, endogenous ROS cause DNA damage that FAN1-deficient cells cannot repair.
Polyploidy and Karyomegaly of Tubular Epithelial Cells
Cell-cycle dysregulation drives DNA endoreduplication and polyploidy in tubular epithelial cells, which manifests histologically as karyomegaly: markedly enlarged, hyperchromatic, and pleomorphic tubular cell nuclei, the diagnostic hallmark of the disease. Karyomegalic changes can also occur in extrarenal organs.
kidney tubule epithelial cell CL:1000507 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves kidney tubule epithelial cell, annotated with kidney tubule cell (CL:1000507). CL:1000507 is a cell type from the Cell Ontology.
DNA endoreduplication GO:0042023 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased DNA endoreduplication (GO:0042023). GO:0042023 is a biological process from the Gene Ontology. ↑ INCREASED
Animal models
Fan1-deficient mouse (constitutive knockout) Mouse recapitulates Fan1-deficient mice develop age-dependent karyomegaly in kidney and liver, recapitulating the diagnostic human hallmark.
Downstream
Chronic Tubulointerstitial Nephritis and Fibrosis
Renal tubular karyomegaly
Show evidence (2 references)
PMID:38847221 SUPPORT Human Clinical
"Karyomegalic interstitial nephritis (KIN) is an uncommon autosomal recessive disease, which is characterized by enlarged and hyperchromatic nuclei of the renal tubular epithelial cells."
Karyomegaly of renal tubular epithelial cells is the defining histopathologic feature.
PMID:22772369 SUPPORT Human Clinical
"The only distinguishing feature from NPHP in KIN is the presence of karyomegaly (Figure 1b–c), which can also be present in lung, liver, and brain13."
Documents the extrarenal distribution of karyomegaly (lung, liver, brain).
Chronic Tubulointerstitial Nephritis and Fibrosis
Progressive injury and death of karyomegalic tubular epithelial cells provokes a chronic tubulointerstitial inflammatory response with interstitial fibrosis and tubular atrophy.
Downstream
Progressive Chronic Kidney Disease
Renal fibrosis
Show evidence (1 reference)
PMID:38847221 SUPPORT Human Clinical
"There was a mild degree of interstitial fibrosis and tubular atrophy involving <25% of the visualized cortex."
Renal biopsy in a KIN patient shows interstitial fibrosis and tubular atrophy.
Progressive Chronic Kidney Disease
Ongoing nephron loss produces a slowly progressive decline in renal function, typically presenting in the third to fifth decade and progressing to end-stage renal disease.
Animal models
Fan1 knockout mouse (cisplatin-induced KIN) Mouse recapitulates Fan1-null mice develop KIN and renal failure when chronically challenged with low-dose cisplatin, modeling the gene-environment ("second hit") mechanism.
Downstream
Stage 5 chronic kidney disease
Elevated serum creatinine
Show evidence (1 reference)
PMID:22772369 SUPPORT Human Clinical
"CKD ensued by a median age at 45 years"
Among 12 individuals with KIN and FAN1 mutations, CKD ensued at a median age of 45 years.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Karyomegalic Interstitial Nephritis Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

10
Genitourinary 7
Renal tubular karyomegaly HP:6000429 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Renal tubular karyomegaly (HP:6000429). HP:6000429 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:22772369 SUPPORT Human Clinical
"Renal histology in KIN is indistinguishable from that of nephronophthisis, except for the presence of karyomegaly."
Karyomegaly is the histologic feature that distinguishes KIN from nephronophthisis.
PMID:38847221 SUPPORT Human Clinical
"Tubular epithelial cells showed nuclear changes focally like hyperchromasia, karyomegaly, and anisonucleosis."
Direct biopsy observation of tubular karyomegaly in a KIN case.
Chronic tubulointerstitial nephritis HP:0004743 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Chronic tubulointerstitial nephritis (HP:0004743). HP:0004743 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38847221 SUPPORT Human Clinical
"chronic interstitial nephritis (CIN), leading to end-stage renal disease in young adults"
KIN is a genetic cause of chronic interstitial nephritis progressing to ESRD.
Renal fibrosis Tubulointerstitial fibrosis HP:0005576 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tubulointerstitial fibrosis (HP:0005576). HP:0005576 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38847221 SUPPORT Human Clinical
"There was a mild degree of interstitial fibrosis and tubular atrophy involving <25% of the visualized cortex."
Interstitial fibrosis with tubular atrophy documented on KIN biopsy.
Chronic kidney disease HP:0012622 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Chronic kidney disease (HP:0012622), qualified as course progressive. HP:0012622 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:38847221 SUPPORT Human Clinical
"elder sister with chronic kidney disease (CKD) stage III"
An affected family member had CKD, consistent with the familial progressive renal disease of KIN.
Stage 5 chronic kidney disease HP:0003774 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is End-stage renal disease, annotated with Stage 5 chronic kidney disease (HP:0003774). HP:0003774 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38847221 SUPPORT Human Clinical
"29-year-old female with end-stage renal disease"
A KIN patient presented with end-stage renal disease as a young adult.
Proteinuria FREQUENT HP:0000093 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Proteinuria (HP:0000093). HP:0000093 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:12401846 SUPPORT Human Clinical
"Impaired renal function, proteinuria, and haematuria were present in the majority of cases."
Proteinuria was present in the majority of a case series of karyomegalic nephropathy.
PMID:38847221 SUPPORT Human Clinical
"KIN presents with a history of mild proteinuria, urinary sediment abnormalities, and recurrent upper respiratory tract infections."
Mild proteinuria is a characteristic presenting feature of KIN.
Hematuria FREQUENT HP:0000790 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hematuria (HP:0000790). HP:0000790 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:12401846 SUPPORT Human Clinical
"Impaired renal function, proteinuria, and haematuria were present in the majority of cases."
Haematuria was present in the majority of a case series of karyomegalic nephropathy.
Immune 1
Recurrent respiratory infections HP:0002205 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Recurrent respiratory infections (HP:0002205). HP:0002205 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38847221 SUPPORT Human Clinical
"KIN presents with a history of mild proteinuria, urinary sediment abnormalities, and recurrent upper respiratory tract infections."
Recurrent upper respiratory tract infections are part of the reported KIN clinical picture.
Metabolism 2
Elevated serum creatinine Elevated circulating creatinine concentration HP:0003259 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated circulating creatinine concentration (HP:0003259). HP:0003259 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38847221 SUPPORT Human Clinical
"raised serum creatinine levels of 10.0 mg/dl"
Markedly elevated serum creatinine in a KIN patient with ESRD.
Elevated hepatic transaminases Elevated circulating hepatic transaminase concentration HP:0002910 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated hepatic transaminases, annotated with Elevated circulating hepatic transaminase concentration (HP:0002910). HP:0002910 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:12401846 SUPPORT Human Clinical
"Non-specific elevated liver enzymes were present in three cases"
Elevated liver enzymes occurred in half of a six-patient case series.
🧬

Genetic Associations

1
FAN1 pathogenic variants (Causative)
Gene: FAN1 hgnc:29170 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is FAN1 (hgnc:29170). hgnc:29170 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal recessive
Show evidence (1 reference)
PMID:22772369 SUPPORT Human Clinical
"We thus identified recessive mutations of FAN1 as the cause of KIN, an NPHP-like fibrotic kidney disease."
Recessive FAN1 mutations are the identified cause of KIN.
💊

Medical Actions

3
Supportive Care
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
Management of chronic kidney disease including blood pressure control and treatment of complications; no disease-modifying therapy exists.
Renal Replacement Therapy
Action: Renal Replacement TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Renal Replacement Therapy (NCIT:C126400). NCIT:C126400 is a clinical intervention from the NCI Thesaurus. NCIT:C126400
Platform: Device
Hemodialysis or peritoneal dialysis for patients reaching end-stage renal disease.
Kidney Transplantation
Action: Kidney TransplantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Kidney Transplantation (NCIT:C15265). NCIT:C15265 is a clinical intervention from the NCI Thesaurus. NCIT:C15265
Platform: Surgery
Renal transplantation restores renal function in KIN reaching end-stage disease, but carries two disease-specific hazards. First, related donors who are heterozygous FAN1 carriers should be avoided: transplantation from a carrier sibling has been followed by karyomegalic changes in the graft (donor-derived and/or recurrent KIN), so familial heterozygote donation should be discouraged and donors genetically screened. Second, KIN patients are at risk of fatal post-transplant infection, with deaths from overwhelming respiratory sepsis reported soon after transplantation, warranting careful adaptation of immunosuppression.
Show evidence (5 references)
PMID:38847221 SUPPORT Human Clinical
"Our patient underwent a live unrelated donor renal transplant in January 2023 and has been asymptomatic since ten months."
A KIN patient with ESRD was successfully treated with an unrelated-donor kidney transplant.
PMID:38681017 SUPPORT Human Clinical
"underwent kidney transplantation from his sister, and developed the same condition in the graft"
Transplantation from a carrier sibling donor was followed by donor-derived KIN recurring in the allograft.
PMID:30040181 SUPPORT Human Clinical
"The KIN may represent recurrent KIN or donor-associated KIN."
Corroborates the risk of recurrent or donor-associated KIN in a living-related allograft.
+ 2 more references
🌍

Environmental Factors

2
Exposure to ochratoxin A (mycotoxin)
exposure to ochratoxin A (mycotoxin) ECTO:0000524 Environmental Conditions, Treatments and Exposures Ontology (ECTO) Relation: this environmental factor is this exposure This environmental factor is exposure to ochratoxin A (mycotoxin), annotated with exposure to mycotoxin (ECTO:0000524). ECTO:0000524 is an exposure from the Environmental Conditions, Treatments and Exposures Ontology.
The mycotoxin ochratoxin A generates DNA interstrand crosslinks and can produce a KIN-like phenotype in humans and animal models, acting as an additional genotoxic burden ("second hit") on the FAN1-deficient repair capacity. KIN is regarded as the genetic equivalent of these environmental genotoxic causes.
Show evidence (1 reference)
PMID:22772369 SUPPORT Other
"FAN1 mutation represents the genetic equivalent of environmental genotoxic causes of KIN by the shared pathogenic mechanism of defective DNA ICL repair."
Frames environmental crosslinking genotoxins and FAN1 loss as converging on the same defective ICL-repair mechanism.
Mechanism Target:
EXACERBATES Defective Interstrand Crosslink Repair — Ochratoxin A increases the interstrand-crosslink burden that FAN1-deficient cells cannot repair, amplifying the DNA damage.
Show evidence (1 reference)
PMID:22772369 SUPPORT Other
"A KIN-like phenotype has also been described in humans and animal models that were exposed to ochratoxin A15, busulfan or pyrrolizidine alkaloids11, all of which cause DNA ICL."
Exposure to ochratoxin A produces a KIN-like phenotype, acting on the same ICL-repair defect.
Exposure to genotoxic and alkylating drugs
exposure to genotoxic/alkylating drug ECTO:0000509 Environmental Conditions, Treatments and Exposures Ontology (ECTO) Relation: this environmental factor is this exposure This environmental factor is exposure to genotoxic/alkylating drug, annotated with exposure to drug (ECTO:0000509). ECTO:0000509 is an exposure from the Environmental Conditions, Treatments and Exposures Ontology.
Genotoxic and alkylating drugs that generate DNA interstrand crosslinks — including busulfan, pyrrolizidine alkaloids, and platinum agents such as cisplatin — can produce a KIN-like phenotype and act as an additional genotoxic burden ("second hit") on the FAN1-deficient repair capacity. Chronic low-dose cisplatin is the trigger used to elicit KIN in the Fan1-knockout mouse model.
Show evidence (1 reference)
PMID:22772369 SUPPORT Other
"A KIN-like phenotype has also been described in humans and animal models that were exposed to ochratoxin A15, busulfan or pyrrolizidine alkaloids11, all of which cause DNA ICL."
Busulfan and pyrrolizidine alkaloids are crosslinking drugs reported to produce a KIN-like phenotype.
Mechanism Target:
EXACERBATES Defective Interstrand Crosslink Repair — Alkylating and platinum drugs increase the interstrand-crosslink burden that FAN1-deficient cells cannot repair; chronic cisplatin precipitates overt KIN in FAN1-null kidneys.
Show evidence (1 reference)
PMID:27026368 SUPPORT Model Organism
"chronic injection of cisplatin at 2 mg/kg induced KIN that led to renal failure within 5 weeks in Fan1-/- mice but not in wild-type mice"
A crosslinking drug (cisplatin) precipitates KIN specifically in FAN1-deficient kidneys, acting on the ICL-repair defect.
🔬

Diagnosis

4
Renal biopsy histology
Renal biopsy is the gold-standard diagnostic procedure: tubular epithelial cells show enlarged, hyperchromatic, pleomorphic nuclei (karyomegaly, hyperchromasia, anisonucleosis) with chronic tubulointerstitial nephritis, interstitial fibrosis, and tubular atrophy.
renal biopsy histopathology
Show evidence (2 references)
PMID:38847221 SUPPORT Human Clinical
"to timely diagnose this familial disease with the gold standard renal biopsy procedure"
Renal biopsy is identified as the gold-standard diagnostic procedure for KIN.
PMID:38847221 SUPPORT Human Clinical
"Tubular epithelial cells showed nuclear changes focally like hyperchromasia, karyomegaly, and anisonucleosis."
The diagnostic histologic changes seen on renal biopsy in KIN.
Exclusion of viral cytopathic mimics by immunohistochemistry (Negative)
KIN can be mistaken for viral (CMV, adenovirus, polyomavirus BK/SV40) cytopathic nephropathy, which also produces enlarged tubular nuclei; negative immunohistochemistry for these viruses excludes the mimics and supports the diagnosis of KIN.
viral immunohistochemistry (CMV, adenovirus, SV40/BK)
Show evidence (2 references)
PMID:30040181 SUPPORT Human Clinical
"Immunohistochemistry for cytomegalovirus, adenovirus, and simian virus 40 were negative."
Negative viral immunohistochemistry excludes the viral cytopathic mimics of KIN.
PMID:30040181 SUPPORT Human Clinical
"Recognition of this rare disease entity is important as it can be mistaken for a viral infection."
Establishes viral nephropathy as the key differential requiring exclusion.
DNA-ploidy and proliferation-marker analysis
The karyomegaly reflects DNA endoreduplication, not proliferation: DNA-ploidy analysis shows increased high-ploidy cells while proliferation markers (Ki-67, PCNA) are not elevated and mitotic figures are absent, distinguishing endoreduplication from a proliferative process.
DNA ploidy analysis with Ki-67/PCNA proliferation markers
Show evidence (2 references)
PMID:12401846 SUPPORT Human Clinical
"Abnormality of DNA ploidy distributions compared with age- and sex-matched controls, and characterized by the presence of significant numbers of cells with high ploidy values was present in cases but not in controls."
DNA-ploidy analysis demonstrates increased high-ploidy tubular cells, the correlate of endoreduplication.
PMID:12401846 SUPPORT Human Clinical
"Proliferation markers, Ki-67 and proliferating cell nuclear antigen/cyclin were not significantly elevated in those cases examined."
Absent elevation of Ki-67/PCNA, with mitotic figures absent, distinguishes endoreduplication from proliferation.
Confirmatory FAN1 sequencing
Molecular confirmation by exome or Sanger sequencing identifying biallelic pathogenic FAN1 variants establishes the genetic diagnosis and enables family screening and counseling.
FAN1 gene sequencing
Show evidence (2 references)
PMID:22772369 SUPPORT Human Clinical
"By exome sequencing, we identified mutations in FAN1 as a cause of karyomegalic interstitial nephritis (KIN), a disorder that serves as a model for renal fibrosis."
FAN1 sequencing identifies the causative mutations that confirm KIN.
PMID:32220227 SUPPORT Human Clinical
"Karyomegalic nephritis (KIN) was confirmed by genetic testing with a non-sense mutation and a deletion in the Fanconi anemia associated nuclease 1 (FAN1) gene."
Genetic testing of FAN1 confirmed the diagnosis in a biopsy-suggestive case.
📊

Prevalence

1
Worldwide
Unknown Ultra Rare
KIN accounts for less than 1% of all renal biopsies; approximately 50 cases in 12 families have been reported.
Show evidence (1 reference)
PMID:34126972 SUPPORT Human Clinical
"The prevalence of this disease is less than 1% of all biopsies, and its pathogenesis is unclear."
Quantifies the rarity of KIN as under 1% of all renal biopsies.
🧫

Experimental Models

1
FAN1-mutant hiPSC-derived kidney organoid ORGANOID
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Cell source
Human induced pluripotent stem cells (KIN patient-derived and CRISPR/Cas9 FAN1-edited WTC-11), differentiated into kidney organoids.
Publication
PMID:37759541
Pathograph links
Genomic Instability and Replication Stress partially recapitulates fidelity: low observes: cellular FAN1-mutant kidney organoids show increased DNA-damage markers and reduced viability after mitomycin C challenge, modeling the DNA-damage susceptibility of FAN1-deficient tubular cells.
Limitations: Increased DNA-damage marker expression was also observed in wild-type organoids, limiting FAN1-specificity, and the phenotype requires an acute exogenous genotoxic (MMC) challenge rather than arising spontaneously.
Readouts
MMC-induced DNA-damage markers and cell viability
Direction: INCREASED
Interpretation: Increased DNA-damage marker expression with reduced viability is the cellular correlate of the genomic-instability node in this model.
Show evidence (1 reference)
PMID:37759541 SUPPORT In Vitro
"MMC treatment for 48 h significantly increased the expression of DNA damage markers, while cell viability in both FAN1-mutant kidney organoids was decreased."
Reports the DNA-damage and viability readouts in this model.
Show evidence (1 reference)
PMID:37759541 SUPPORT In Vitro
"These results suggest that FAN1-mutant kidney organoids can recapitulate the phenotype of FAN1-deficient kidney disease."
Establishes the FAN1-mutant kidney organoid as informative for FAN1-deficient kidney disease.
🐁

Animal Models

2
Fan1-deficient mouse (constitutive knockout)
Species
Mouse
Genotype
Fan1 knockout
Publication
PMID:26980189
Pathograph links
Polyploidy and Karyomegaly of Tubular Epithelial Cells recapitulates fidelity: moderate observes: organism Fan1-deficient mice develop age-dependent karyomegaly in kidney and liver, recapitulating the diagnostic human hallmark.
Limitations: Karyomegaly is age-dependent and the model prominently manifests hepatic dysfunction; the tempo of renal fibrosis and the human respiratory phenotype are not fully reproduced.
Readouts
Renal and hepatic karyomegaly
Direction: INCREASED
Interpretation: Structural correlate of the karyomegaly node in this model.
Show evidence (1 reference)
PMID:26980189 SUPPORT Model Organism
"Karyomegaly becomes prominent in kidneys and livers of Fan1-deficient mice with age, and mice develop liver dysfunction."
Reports the karyomegaly phenotype measured in this model.
Show evidence (1 reference)
PMID:26980189 SUPPORT Model Organism
"demonstrate that the Fan1 mouse model effectively recapitulates the pathological features of human FAN1 deficiency."
Establishes this model as recapitulating human FAN1-deficiency pathology.
Fan1 knockout mouse (cisplatin-induced KIN)
Species
Mouse
Genotype
Fan1-/-
Publication
PMID:27026368
Pathograph links
Progressive Chronic Kidney Disease recapitulates fidelity: moderate observes: organism Fan1-null mice develop KIN and renal failure when chronically challenged with low-dose cisplatin, modeling the gene-environment ("second hit") mechanism.
Limitations: KIN manifests only under an exogenous genotoxic (chronic cisplatin) challenge rather than spontaneously, and the accelerated 5-week course differs from the slowly progressive human disease.
Readouts
Cisplatin-induced renal failure
Direction: INCREASED
Interpretation: Functional-decline correlate of the CKD node in this model.
Show evidence (1 reference)
PMID:27026368 SUPPORT Model Organism
"chronic injection of cisplatin at 2 mg/kg induced KIN that led to renal failure within 5 weeks in Fan1-/- mice but not in wild-type mice"
Reports genotoxin-induced KIN and renal failure specific to Fan1-null mice.
Show evidence (1 reference)
PMID:27026368 SUPPORT Model Organism
"Our data show that Fan1 is involved in the physiologic response of kidney tubular cells to DNA damage, which contributes to the pathogenesis of CKD."
Establishes the Fan1-knockout mouse as informative for the progression to chronic kidney disease.
{ }

Source YAML

click to show 
name: Karyomegalic Interstitial Nephritis
creation_date: "2026-09-04T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: Karyomegalic Interstitial Nephritis
  term:
    id: MONDO:0013898
    label: karyomegalic interstitial nephritis
parents:
- hereditary nephritis
- DNA repair disease
- chronic tubulointerstitial nephritis

pathophysiology:
- name: Biallelic FAN1 Loss of Function
  description: >-
    Karyomegalic interstitial nephritis is caused by biallelic loss-of-function
    variants in FAN1 (FANCD2/FANCI-associated nuclease 1), a structure-specific
    DNA repair nuclease. Loss of FAN1 activity abolishes its role in the repair
    of DNA interstrand crosslinks and in the protection and restart of stalled
    replication forks. KIN is genetically and clinically distinct from Fanconi
    anemia.
  biological_scale: MOLECULAR
  molecular_functions:
  - preferred_term: structure-specific 5'-flap DNA endonuclease activity
    term:
      id: GO:0017108
      label: 5'-flap endonuclease activity
    modifier: LOSS_OF_FUNCTION
  genetic_context:
    gene:
      preferred_term: FAN1
      term:
        id: hgnc:29170
        label: FAN1
    variant_origin: GERMLINE
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Biallelic germline loss-of-function FAN1 variants cause KIN. Reported
      pathogenic alleles span truncating and missense changes and include the
      homozygous nonsense variant c.2260C>T (p.Arg754Ter), the recurrent
      European founder frameshift c.2616delA (p.Asp873ThrfsTer17), and the
      novel frameshift c.2603delT (p.Leu868ArgfsTer22).
  evidence:
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "By exome sequencing, we identified mutations in FAN1 as a cause of karyomegalic interstitial nephritis (KIN), a disorder that serves as a model for renal fibrosis."
    explanation: >-
      Establishes biallelic FAN1 mutation as the cause of KIN by exome
      sequencing of affected families.
  - reference: PMID:20603016
    reference_title: "Deficiency of FANCD2-associated nuclease KIAA1018/FAN1 sensitizes cells to interstrand crosslinking agents."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "KIAA1018 is a 5'-->3' exonuclease and a structure-specific endonuclease that preferentially incises 5' flaps."
    explanation: >-
      Biochemically characterizes FAN1 (KIAA1018) as a structure-specific
      nuclease, the enzymatic activity lost in KIN.
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "cells from individuals with FAN1 mutations have sensitivity to the ICL-inducing agent mitomycin C but do not exhibit chromosome breakage or cell cycle arrest after diepoxybutane treatment, unlike cells from individuals with Fanconi anemia."
    explanation: >-
      Distinguishes the cellular phenotype of FAN1-mutant KIN cells from that
      of Fanconi anemia cells: ICL-agent sensitivity without the DEB-induced
      breakage and cell-cycle arrest characteristic of Fanconi anemia.
  - reference: PMID:39294548
    reference_title: "A rare multisystemic disorder with chronic kidney disease: Karyomegalic interstitial nephritis due to homozygous FAN1 c.2260C>T variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical exome sequencing revealed a homozygous nonsense variant NM_014967.5 (FAN1): c. 2260C > T (p.Arg754Ter)."
    explanation: >-
      Documents a homozygous FAN1 nonsense allele (p.Arg754Ter) in the KIN
      variant spectrum.
  - reference: PMID:34126972
    reference_title: "New familial cases of karyomegalic interstitial nephritis with mutations in the FAN1 gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The previously described frameshift mutation c.2616delA (p.Asp873ThrfsTer17) and a novel mutation c.2603delT (p.Leu868ArgfsTer22) classified as \"pathogenic\" according to the American College of Medical Genetics and Genomics (ACMG) guidelines."
    explanation: >-
      Documents the recurrent c.2616delA and the novel c.2603delT frameshift
      loss-of-function alleles in familial KIN.
  downstream:
  - target: Defective Interstrand Crosslink Repair
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:22772369
      reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The FAN1 protein has nuclease activity and acts in DNA interstrand cross-link (ICL) repair within the Fanconi anemia DNA damage response (DDR) pathway."
      explanation: >-
        FAN1 acts in ICL repair; its loss therefore impairs this repair
        process.
  - target: Defective Replication Fork Protection
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:26797144
      reference_title: "Ubiquitinated Fancd2 recruits Fan1 to stalled replication forks to prevent genome instability."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Fan1 recruitment enables processing of stalled forks that is essential for genome stability and health."
      explanation: >-
        FAN1 nuclease activity is required for stalled-fork processing; its
        loss removes this fork-protective function.

- name: Defective Interstrand Crosslink Repair
  description: >-
    Without FAN1, cells cannot properly excise and repair DNA interstrand
    crosslinks, so crosslink lesions persist and block replication.
  biological_scale: MOLECULAR
  biological_processes:
  - preferred_term: interstrand cross-link repair
    term:
      id: GO:0036297
      label: interstrand cross-link repair
    modifier: DECREASED
  evidence:
  - reference: PMID:20603073
    reference_title: "A genetic screen identifies FAN1, a Fanconi anemia-associated nuclease necessary for DNA interstrand crosslink repair."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The Fanconi anemia (FA) pathway is responsible for interstrand crosslink repair."
    explanation: >-
      Identifies the FA pathway (in which FAN1 acts) as responsible for ICL
      repair, the process that fails in KIN.
  - reference: PMID:20603016
    reference_title: "Deficiency of FANCD2-associated nuclease KIAA1018/FAN1 sensitizes cells to interstrand crosslinking agents."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Like cells from FA patients, human cells depleted of KIAA1018 are sensitized to ICL-inducing agents and display chromosomal instability."
    explanation: >-
      Depletion of FAN1 impairs ICL processing, sensitizing cells to
      crosslinking agents.
  downstream:
  - target: Genomic Instability and Replication Stress
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20603016
      reference_title: "Deficiency of FANCD2-associated nuclease KIAA1018/FAN1 sensitizes cells to interstrand crosslinking agents."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Cytotoxicity of cisplatin and mitomycin C (MMC) is ascribed largely to their ability to generate interstrand crosslinks (ICLs) in DNA, which block the progression of replication forks."
      explanation: >-
        Unrepaired ICLs block replication forks, the source of the replication
        stress and genomic instability downstream.

- name: Defective Replication Fork Protection
  description: >-
    Independently of interstrand-crosslink repair, FAN1 nuclease activity
    restrains and processes stalled replication forks. Loss of this
    fork-protective function produces chromosome abnormalities and genome
    instability even without exogenous crosslinks, and may be the more
    KIN-relevant FAN1 function, since FAN1-deficient cells accumulate damage
    from endogenous replication stress rather than from crosslink exposure.
  biological_scale: MOLECULAR
  biological_processes:
  - preferred_term: stalled replication fork protection and processing
    term:
      id: GO:0031297
      label: replication fork processing
    modifier: DECREASED
  evidence:
  - reference: PMID:26797144
    reference_title: "Ubiquitinated Fancd2 recruits Fan1 to stalled replication forks to prevent genome instability."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Fan1 recruitment--and activity--restrains DNA replication fork progression and prevents chromosome abnormalities from occurring when DNA replication forks stall, even in the absence of ICLs."
    explanation: >-
      FAN1 protects stalled forks and prevents chromosome abnormalities
      independently of ICL repair; loss abolishes this protection.
  - reference: PMID:29051491
    reference_title: "FAN1 interaction with ubiquitylated PCNA alleviates replication stress and preserves genomic integrity independently of BRCA2."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Because fork stalling in FAN1-deficient cells causes chromosomal instability, we reasoned that the key function of FAN1 might lie in the processing of halted replication forks."
    explanation: >-
      Links FAN1 deficiency to chromosomal instability arising from defective
      processing of stalled replication forks.
  downstream:
  - target: Genomic Instability and Replication Stress
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:29051491
      reference_title: "FAN1 interaction with ubiquitylated PCNA alleviates replication stress and preserves genomic integrity independently of BRCA2."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "This prevents replication fork collapse and controls their progression."
      explanation: >-
        FAN1 prevents fork collapse; without it, unprotected stalled forks
        generate the replication stress and genomic instability downstream.

- name: Genomic Instability and Replication Stress
  description: >-
    Persistent unrepaired DNA lesions produce chromosomal instability, aberrant
    cell-cycle progression, and chronic replication stress in dividing renal
    tubular epithelial cells. In FAN1-deficient kidneys, endogenous reactive
    oxygen species are an important source of the ongoing DNA damage.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: kidney tubule epithelial cell
    term:
      id: CL:1000507
      label: kidney tubule cell
  biological_processes:
  - preferred_term: DNA damage response
    term:
      id: GO:0006974
      label: DNA damage response
    modifier: INCREASED
  evidence:
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We observed chromatid breaks and radial chromosomes on metaphase spreads (Figure 2b), which is consistent with a role of FAN1 in genome maintenance and DDR."
    explanation: >-
      FAN1-mutant patient cells show chromosomal instability on metaphase
      spreads.
  - reference: PMID:21115814
    reference_title: "KIAA1018/FAN1 nuclease protects cells against genomic instability induced by interstrand cross-linking agents."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "MMC treatment causes chromosomal instability that is quantitatively, but not qualitatively, comparable to that seen in FA cells."
    explanation: >-
      FAN1-null cells display crosslink-induced chromosomal instability.
  - reference: PMID:37107275
    reference_title: "Mitochondrial ROS Triggers KIN Pathogenesis in FAN1-Deficient Kidneys."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "FAN1 kidney pathophysiology is triggered by hypersensitivity to endogenous reactive oxygen species (ROS), which cause chronic oxidative and double-strand DNA damage in the kidney tubular epithelial cells, accompanied by an intrinsic failure to repair DNA damage."
    explanation: >-
      In FAN1-null mice and human tubular epithelial cells, endogenous ROS
      cause DNA damage that FAN1-deficient cells cannot repair.
  downstream:
  - target: Polyploidy and Karyomegaly of Tubular Epithelial Cells
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37107275
      reference_title: "Mitochondrial ROS Triggers KIN Pathogenesis in FAN1-Deficient Kidneys."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Karyomegalic interstitial nephritis (KIN) is a genetic adult-onset chronic kidney disease (CKD) characterized by genomic instability and mitotic abnormalities in the tubular epithelial cells."
      explanation: >-
        Links genomic instability and mitotic abnormalities to the tubular
        epithelial cell pathology that defines KIN.

- name: Polyploidy and Karyomegaly of Tubular Epithelial Cells
  description: >-
    Cell-cycle dysregulation drives DNA endoreduplication and polyploidy in
    tubular epithelial cells, which manifests histologically as karyomegaly:
    markedly enlarged, hyperchromatic, and pleomorphic tubular cell nuclei, the
    diagnostic hallmark of the disease. Karyomegalic changes can also occur in
    extrarenal organs.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: kidney tubule epithelial cell
    term:
      id: CL:1000507
      label: kidney tubule cell
  biological_processes:
  - preferred_term: DNA endoreduplication
    term:
      id: GO:0042023
      label: DNA endoreduplication
    modifier: INCREASED
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Karyomegalic interstitial nephritis (KIN) is an uncommon autosomal recessive disease, which is characterized by enlarged and hyperchromatic nuclei of the renal tubular epithelial cells."
    explanation: >-
      Karyomegaly of renal tubular epithelial cells is the defining
      histopathologic feature.
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The only distinguishing feature from NPHP in KIN is the presence of karyomegaly (Figure 1b–c), which can also be present in lung, liver, and brain13."
    explanation: >-
      Documents the extrarenal distribution of karyomegaly (lung, liver,
      brain).
  downstream:
  - target: Chronic Tubulointerstitial Nephritis and Fibrosis
    causal_link_type: DIRECT
  - target: Renal tubular karyomegaly
    causal_link_type: DIRECT

- name: Chronic Tubulointerstitial Nephritis and Fibrosis
  description: >-
    Progressive injury and death of karyomegalic tubular epithelial cells
    provokes a chronic tubulointerstitial inflammatory response with interstitial
    fibrosis and tubular atrophy.
  biological_scale: TISSUE
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was a mild degree of interstitial fibrosis and tubular atrophy involving <25% of the visualized cortex."
    explanation: >-
      Renal biopsy in a KIN patient shows interstitial fibrosis and tubular
      atrophy.
  downstream:
  - target: Progressive Chronic Kidney Disease
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38847221
      reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "these pathogenic mutations are responsible for progressive renal failure in young adults"
      explanation: >-
        FAN1 mutation and the resulting tubulointerstitial disease drive
        progressive renal failure.
  - target: Renal fibrosis
    causal_link_type: DIRECT

- name: Progressive Chronic Kidney Disease
  description: >-
    Ongoing nephron loss produces a slowly progressive decline in renal function,
    typically presenting in the third to fifth decade and progressing to
    end-stage renal disease.
  biological_scale: ORGANISM
  evidence:
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CKD ensued by a median age at 45 years"
    explanation: >-
      Among 12 individuals with KIN and FAN1 mutations, CKD ensued at a median
      age of 45 years.
  downstream:
  - target: Stage 5 chronic kidney disease
    causal_link_type: DIRECT
  - target: Elevated serum creatinine
    causal_link_type: DIRECT

phenotypes:
- name: Renal tubular karyomegaly
  category: Cellular
  phenotype_term:
    preferred_term: Renal tubular karyomegaly
    term:
      id: HP:6000429
      label: Renal tubular karyomegaly
  description: >-
    Enlarged, hyperchromatic, pleomorphic nuclei in renal tubular epithelial
    cells; the diagnostic histological hallmark.
  evidence:
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Renal histology in KIN is indistinguishable from that of nephronophthisis, except for the presence of karyomegaly."
    explanation: >-
      Karyomegaly is the histologic feature that distinguishes KIN from
      nephronophthisis.
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tubular epithelial cells showed nuclear changes focally like hyperchromasia, karyomegaly, and anisonucleosis."
    explanation: >-
      Direct biopsy observation of tubular karyomegaly in a KIN case.

- name: Chronic tubulointerstitial nephritis
  phenotype_term:
    preferred_term: Chronic tubulointerstitial nephritis
    term:
      id: HP:0004743
      label: Chronic tubulointerstitial nephritis
  description: >-
    Chronic interstitial inflammation with tubular atrophy on renal biopsy.
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "chronic interstitial nephritis (CIN), leading to end-stage renal disease in young adults"
    explanation: >-
      KIN is a genetic cause of chronic interstitial nephritis progressing to
      ESRD.

- name: Renal fibrosis
  phenotype_term:
    preferred_term: Tubulointerstitial fibrosis
    term:
      id: HP:0005576
      label: Tubulointerstitial fibrosis
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was a mild degree of interstitial fibrosis and tubular atrophy involving <25% of the visualized cortex."
    explanation: >-
      Interstitial fibrosis with tubular atrophy documented on KIN biopsy.

- name: Chronic kidney disease
  phenotype_term:
    preferred_term: Chronic kidney disease
    term:
      id: HP:0012622
      label: Chronic kidney disease
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "elder sister with chronic kidney disease (CKD) stage III"
    explanation: >-
      An affected family member had CKD, consistent with the familial
      progressive renal disease of KIN.

- name: Stage 5 chronic kidney disease
  phenotype_term:
    preferred_term: End-stage renal disease
    term:
      id: HP:0003774
      label: Stage 5 chronic kidney disease
  description: >-
    Progression to end-stage renal disease requiring renal replacement therapy,
    typically in adulthood.
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "29-year-old female with end-stage renal disease"
    explanation: >-
      A KIN patient presented with end-stage renal disease as a young adult.

- name: Elevated serum creatinine
  phenotype_term:
    preferred_term: Elevated circulating creatinine concentration
    term:
      id: HP:0003259
      label: Elevated circulating creatinine concentration
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "raised serum creatinine levels of 10.0 mg/dl"
    explanation: >-
      Markedly elevated serum creatinine in a KIN patient with ESRD.

- name: Recurrent respiratory infections
  phenotype_term:
    preferred_term: Recurrent respiratory infections
    term:
      id: HP:0002205
      label: Recurrent respiratory infections
  description: >-
    A subset of patients report recurrent upper respiratory infections,
    consistent with systemic involvement.
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "KIN presents with a history of mild proteinuria, urinary sediment abnormalities, and recurrent upper respiratory tract infections."
    explanation: >-
      Recurrent upper respiratory tract infections are part of the reported KIN
      clinical picture.

- name: Proteinuria
  phenotype_term:
    preferred_term: Proteinuria
    term:
      id: HP:0000093
      label: Proteinuria
  frequency: FREQUENT
  description: >-
    Mild proteinuria and urinary sediment abnormalities are present in the
    majority of cases.
  evidence:
  - reference: PMID:12401846
    reference_title: "Karyomegalic nephropathy: an uncommon cause of progressive renal failure."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Impaired renal function, proteinuria, and haematuria were present in the majority of cases."
    explanation: >-
      Proteinuria was present in the majority of a case series of karyomegalic
      nephropathy.
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "KIN presents with a history of mild proteinuria, urinary sediment abnormalities, and recurrent upper respiratory tract infections."
    explanation: >-
      Mild proteinuria is a characteristic presenting feature of KIN.

- name: Hematuria
  phenotype_term:
    preferred_term: Hematuria
    term:
      id: HP:0000790
      label: Hematuria
  frequency: FREQUENT
  description: >-
    Hematuria is present in the majority of reported cases.
  evidence:
  - reference: PMID:12401846
    reference_title: "Karyomegalic nephropathy: an uncommon cause of progressive renal failure."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Impaired renal function, proteinuria, and haematuria were present in the majority of cases."
    explanation: >-
      Haematuria was present in the majority of a case series of karyomegalic
      nephropathy.

- name: Elevated hepatic transaminases
  phenotype_term:
    preferred_term: Elevated hepatic transaminases
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
  description: >-
    Non-specific elevation of liver enzymes accompanies the renal disease in a
    subset of patients, reflecting the multisystem karyomegaly of KIN.
  evidence:
  - reference: PMID:12401846
    reference_title: "Karyomegalic nephropathy: an uncommon cause of progressive renal failure."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Non-specific elevated liver enzymes were present in three cases"
    explanation: >-
      Elevated liver enzymes occurred in half of a six-patient case series.

diagnosis:
- name: Renal biopsy histology
  diagnosis_term:
    preferred_term: renal biopsy histopathology
  description: >-
    Renal biopsy is the gold-standard diagnostic procedure: tubular epithelial
    cells show enlarged, hyperchromatic, pleomorphic nuclei (karyomegaly,
    hyperchromasia, anisonucleosis) with chronic tubulointerstitial nephritis,
    interstitial fibrosis, and tubular atrophy.
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "to timely diagnose this familial disease with the gold standard renal biopsy procedure"
    explanation: >-
      Renal biopsy is identified as the gold-standard diagnostic procedure for
      KIN.
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Tubular epithelial cells showed nuclear changes focally like hyperchromasia, karyomegaly, and anisonucleosis."
    explanation: >-
      The diagnostic histologic changes seen on renal biopsy in KIN.

- name: Exclusion of viral cytopathic mimics by immunohistochemistry
  diagnosis_term:
    preferred_term: viral immunohistochemistry (CMV, adenovirus, SV40/BK)
  description: >-
    KIN can be mistaken for viral (CMV, adenovirus, polyomavirus BK/SV40)
    cytopathic nephropathy, which also produces enlarged tubular nuclei;
    negative immunohistochemistry for these viruses excludes the mimics and
    supports the diagnosis of KIN.
  presence: Negative
  evidence:
  - reference: PMID:30040181
    reference_title: Karyomegalic interstitial nephritis in a renal allograft.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Immunohistochemistry for cytomegalovirus, adenovirus, and simian virus 40 were negative."
    explanation: >-
      Negative viral immunohistochemistry excludes the viral cytopathic mimics
      of KIN.
  - reference: PMID:30040181
    reference_title: Karyomegalic interstitial nephritis in a renal allograft.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Recognition of this rare disease entity is important as it can be mistaken for a viral infection."
    explanation: >-
      Establishes viral nephropathy as the key differential requiring exclusion.

- name: DNA-ploidy and proliferation-marker analysis
  diagnosis_term:
    preferred_term: DNA ploidy analysis with Ki-67/PCNA proliferation markers
  description: >-
    The karyomegaly reflects DNA endoreduplication, not proliferation: DNA-ploidy
    analysis shows increased high-ploidy cells while proliferation markers
    (Ki-67, PCNA) are not elevated and mitotic figures are absent, distinguishing
    endoreduplication from a proliferative process.
  evidence:
  - reference: PMID:12401846
    reference_title: "Karyomegalic nephropathy: an uncommon cause of progressive renal failure."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Abnormality of DNA ploidy distributions compared with age- and sex-matched controls, and characterized by the presence of significant numbers of cells with high ploidy values was present in cases but not in controls."
    explanation: >-
      DNA-ploidy analysis demonstrates increased high-ploidy tubular cells,
      the correlate of endoreduplication.
  - reference: PMID:12401846
    reference_title: "Karyomegalic nephropathy: an uncommon cause of progressive renal failure."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Proliferation markers, Ki-67 and proliferating cell nuclear antigen/cyclin were not significantly elevated in those cases examined."
    explanation: >-
      Absent elevation of Ki-67/PCNA, with mitotic figures absent, distinguishes
      endoreduplication from proliferation.

- name: Confirmatory FAN1 sequencing
  diagnosis_term:
    preferred_term: FAN1 gene sequencing
  description: >-
    Molecular confirmation by exome or Sanger sequencing identifying biallelic
    pathogenic FAN1 variants establishes the genetic diagnosis and enables
    family screening and counseling.
  evidence:
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "By exome sequencing, we identified mutations in FAN1 as a cause of karyomegalic interstitial nephritis (KIN), a disorder that serves as a model for renal fibrosis."
    explanation: >-
      FAN1 sequencing identifies the causative mutations that confirm KIN.
  - reference: PMID:32220227
    reference_title: "Case report: a 58 -year -old man with small kidneys and elevated liver enzymes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Karyomegalic nephritis (KIN) was confirmed by genetic testing with a non-sense mutation and a deletion in the Fanconi anemia associated nuclease 1 (FAN1) gene."
    explanation: >-
      Genetic testing of FAN1 confirmed the diagnosis in a biopsy-suggestive
      case.

environmental:
- name: Exposure to ochratoxin A (mycotoxin)
  description: >-
    The mycotoxin ochratoxin A generates DNA interstrand crosslinks and can
    produce a KIN-like phenotype in humans and animal models, acting as an
    additional genotoxic burden ("second hit") on the FAN1-deficient repair
    capacity. KIN is regarded as the genetic equivalent of these environmental
    genotoxic causes.
  exposure_term:
    preferred_term: exposure to ochratoxin A (mycotoxin)
    term:
      id: ECTO:0000524
      label: exposure to mycotoxin
  evidence:
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "FAN1 mutation represents the genetic equivalent of environmental genotoxic causes of KIN by the shared pathogenic mechanism of defective DNA ICL repair."
    explanation: >-
      Frames environmental crosslinking genotoxins and FAN1 loss as converging on
      the same defective ICL-repair mechanism.
  influences_mechanisms:
  - target: Defective Interstrand Crosslink Repair
    environmental_effect: EXACERBATES
    causal_link_type: DIRECT
    description: >-
      Ochratoxin A increases the interstrand-crosslink burden that FAN1-deficient
      cells cannot repair, amplifying the DNA damage.
    evidence:
    - reference: PMID:22772369
      reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "A KIN-like phenotype has also been described in humans and animal models that were exposed to ochratoxin A15, busulfan or pyrrolizidine alkaloids11, all of which cause DNA ICL."
      explanation: >-
        Exposure to ochratoxin A produces a KIN-like phenotype, acting on the
        same ICL-repair defect.

- name: Exposure to genotoxic and alkylating drugs
  description: >-
    Genotoxic and alkylating drugs that generate DNA interstrand crosslinks —
    including busulfan, pyrrolizidine alkaloids, and platinum agents such as
    cisplatin — can produce a KIN-like phenotype and act as an additional
    genotoxic burden ("second hit") on the FAN1-deficient repair capacity.
    Chronic low-dose cisplatin is the trigger used to elicit KIN in the
    Fan1-knockout mouse model.
  exposure_term:
    preferred_term: exposure to genotoxic/alkylating drug
    term:
      id: ECTO:0000509
      label: exposure to drug
  evidence:
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "A KIN-like phenotype has also been described in humans and animal models that were exposed to ochratoxin A15, busulfan or pyrrolizidine alkaloids11, all of which cause DNA ICL."
    explanation: >-
      Busulfan and pyrrolizidine alkaloids are crosslinking drugs reported to
      produce a KIN-like phenotype.
  influences_mechanisms:
  - target: Defective Interstrand Crosslink Repair
    environmental_effect: EXACERBATES
    causal_link_type: DIRECT
    description: >-
      Alkylating and platinum drugs increase the interstrand-crosslink burden
      that FAN1-deficient cells cannot repair; chronic cisplatin precipitates
      overt KIN in FAN1-null kidneys.
    evidence:
    - reference: PMID:27026368
      reference_title: "A FANCD2/FANCI-Associated Nuclease 1-Knockout Model Develops Karyomegalic Interstitial Nephritis."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "chronic injection of cisplatin at 2 mg/kg induced KIN that led to renal failure within 5 weeks in Fan1-/- mice but not in wild-type mice"
      explanation: >-
        A crosslinking drug (cisplatin) precipitates KIN specifically in
        FAN1-deficient kidneys, acting on the ICL-repair defect.

prevalence:
- population: Worldwide
  measure_type: UNKNOWN
  prevalence_class: ULTRA_RARE
  notes: >-
    KIN accounts for less than 1% of all renal biopsies; approximately 50 cases
    in 12 families have been reported.
  evidence:
  - reference: PMID:34126972
    reference_title: New familial cases of karyomegalic interstitial nephritis with mutations in the FAN1 gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The prevalence of this disease is less than 1% of all biopsies, and its pathogenesis is unclear."
    explanation: >-
      Quantifies the rarity of KIN as under 1% of all renal biopsies.

genetic:
- name: FAN1 pathogenic variants
  gene_term:
    preferred_term: FAN1
    term:
      id: hgnc:29170
      label: FAN1
  association: Causative
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:22772369
      reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Currently, 12 families with KIN have been described10,14, compatible with autosomal recessive inheritance."
      explanation: >-
        KIN segregates in an autosomal recessive pattern across described
        families.
  features: >-
    Biallelic loss-of-function variants in FAN1 cause karyomegalic interstitial
    nephritis. FAN1 encodes a structure-specific DNA repair nuclease that
    participates in interstrand crosslink repair together with the FANCD2/FANCI
    complex; however, KIN is genetically and clinically distinct from Fanconi
    anemia.
  evidence:
  - reference: PMID:22772369
    reference_title: "FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We thus identified recessive mutations of FAN1 as the cause of KIN, an NPHP-like fibrotic kidney disease."
    explanation: >-
      Recessive FAN1 mutations are the identified cause of KIN.

experimental_models:
- name: FAN1-mutant hiPSC-derived kidney organoid
  experimental_model_type: ORGANOID
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_source: >-
    Human induced pluripotent stem cells (KIN patient-derived and CRISPR/Cas9
    FAN1-edited WTC-11), differentiated into kidney organoids.
  publication: PMID:37759541
  modeled_mechanisms:
  - target: Genomic Instability and Replication Stress
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: CELLULAR
    description: >-
      FAN1-mutant kidney organoids show increased DNA-damage markers and reduced
      viability after mitomycin C challenge, modeling the DNA-damage
      susceptibility of FAN1-deficient tubular cells.
    limitations: >-
      Increased DNA-damage marker expression was also observed in wild-type
      organoids, limiting FAN1-specificity, and the phenotype requires an acute
      exogenous genotoxic (MMC) challenge rather than arising spontaneously.
    readouts:
    - name: MMC-induced DNA-damage markers and cell viability
      target: Genomic Instability and Replication Stress
      direction: INCREASED
      interpretation: >-
        Increased DNA-damage marker expression with reduced viability is the
        cellular correlate of the genomic-instability node in this model.
      evidence:
      - reference: PMID:37759541
        reference_title: "Modeling of FAN1-Deficient Kidney Disease Using a Human Induced Pluripotent Stem Cell-Derived Kidney Organoid System."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "MMC treatment for 48 h significantly increased the expression of DNA damage markers, while cell viability in both FAN1-mutant kidney organoids was decreased."
        explanation: Reports the DNA-damage and viability readouts in this model.
    evidence:
    - reference: PMID:37759541
      reference_title: "Modeling of FAN1-Deficient Kidney Disease Using a Human Induced Pluripotent Stem Cell-Derived Kidney Organoid System."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "These results suggest that FAN1-mutant kidney organoids can recapitulate the phenotype of FAN1-deficient kidney disease."
      explanation: >-
        Establishes the FAN1-mutant kidney organoid as informative for
        FAN1-deficient kidney disease.

animal_models:
- name: Fan1-deficient mouse (constitutive knockout)
  species: Mouse
  genotype: Fan1 knockout
  publication: PMID:26980189
  modeled_mechanisms:
  - target: Polyploidy and Karyomegaly of Tubular Epithelial Cells
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Fan1-deficient mice develop age-dependent karyomegaly in kidney and liver,
      recapitulating the diagnostic human hallmark.
    limitations: >-
      Karyomegaly is age-dependent and the model prominently manifests hepatic
      dysfunction; the tempo of renal fibrosis and the human respiratory
      phenotype are not fully reproduced.
    readouts:
    - name: Renal and hepatic karyomegaly
      target: Polyploidy and Karyomegaly of Tubular Epithelial Cells
      direction: INCREASED
      interpretation: Structural correlate of the karyomegaly node in this model.
      evidence:
      - reference: PMID:26980189
        reference_title: "Fan1 deficiency results in DNA interstrand cross-link repair defects, enhanced tissue karyomegaly, and organ dysfunction."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Karyomegaly becomes prominent in kidneys and livers of Fan1-deficient mice with age, and mice develop liver dysfunction."
        explanation: Reports the karyomegaly phenotype measured in this model.
    evidence:
    - reference: PMID:26980189
      reference_title: "Fan1 deficiency results in DNA interstrand cross-link repair defects, enhanced tissue karyomegaly, and organ dysfunction."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "demonstrate that the Fan1 mouse model effectively recapitulates the pathological features of human FAN1 deficiency."
      explanation: >-
        Establishes this model as recapitulating human FAN1-deficiency
        pathology.

- name: Fan1 knockout mouse (cisplatin-induced KIN)
  species: Mouse
  genotype: Fan1-/-
  publication: PMID:27026368
  modeled_mechanisms:
  - target: Progressive Chronic Kidney Disease
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Fan1-null mice develop KIN and renal failure when chronically challenged
      with low-dose cisplatin, modeling the gene-environment ("second hit")
      mechanism.
    limitations: >-
      KIN manifests only under an exogenous genotoxic (chronic cisplatin)
      challenge rather than spontaneously, and the accelerated 5-week course
      differs from the slowly progressive human disease.
    readouts:
    - name: Cisplatin-induced renal failure
      target: Progressive Chronic Kidney Disease
      direction: INCREASED
      interpretation: Functional-decline correlate of the CKD node in this model.
      evidence:
      - reference: PMID:27026368
        reference_title: "A FANCD2/FANCI-Associated Nuclease 1-Knockout Model Develops Karyomegalic Interstitial Nephritis."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "chronic injection of cisplatin at 2 mg/kg induced KIN that led to renal failure within 5 weeks in Fan1-/- mice but not in wild-type mice"
        explanation: >-
          Reports genotoxin-induced KIN and renal failure specific to Fan1-null
          mice.
    evidence:
    - reference: PMID:27026368
      reference_title: "A FANCD2/FANCI-Associated Nuclease 1-Knockout Model Develops Karyomegalic Interstitial Nephritis."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Our data show that Fan1 is involved in the physiologic response of kidney tubular cells to DNA damage, which contributes to the pathogenesis of CKD."
      explanation: >-
        Establishes the Fan1-knockout mouse as informative for the progression
        to chronic kidney disease.

treatments:
- name: Supportive Care
  description: >-
    Management of chronic kidney disease including blood pressure control and
    treatment of complications; no disease-modifying therapy exists.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care

- name: Renal Replacement Therapy
  description: >-
    Hemodialysis or peritoneal dialysis for patients reaching end-stage renal
    disease.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: Renal Replacement Therapy
    term:
      id: NCIT:C126400
      label: Renal Replacement Therapy

- name: Kidney Transplantation
  description: >-
    Renal transplantation restores renal function in KIN reaching end-stage
    disease, but carries two disease-specific hazards. First, related donors who
    are heterozygous FAN1 carriers should be avoided: transplantation from a
    carrier sibling has been followed by karyomegalic changes in the graft
    (donor-derived and/or recurrent KIN), so familial heterozygote donation
    should be discouraged and donors genetically screened. Second, KIN patients
    are at risk of fatal post-transplant infection, with deaths from overwhelming
    respiratory sepsis reported soon after transplantation, warranting careful
    adaptation of immunosuppression.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Kidney Transplantation
    term:
      id: NCIT:C15265
      label: Kidney Transplantation
  evidence:
  - reference: PMID:38847221
    reference_title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our patient underwent a live unrelated donor renal transplant in January 2023 and has been asymptomatic since ten months."
    explanation: >-
      A KIN patient with ESRD was successfully treated with an unrelated-donor
      kidney transplant.
  - reference: PMID:38681017
    reference_title: "Karyomegalic Interstitial Nephritis in the Allograft Kidney - A Case Report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "underwent kidney transplantation from his sister, and developed the same condition in the graft"
    explanation: >-
      Transplantation from a carrier sibling donor was followed by donor-derived
      KIN recurring in the allograft.
  - reference: PMID:30040181
    reference_title: Karyomegalic interstitial nephritis in a renal allograft.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The KIN may represent recurrent KIN or donor-associated KIN."
    explanation: >-
      Corroborates the risk of recurrent or donor-associated KIN in a
      living-related allograft.
  - reference: PMID:32220227
    reference_title: "Case report: a 58 -year -old man with small kidneys and elevated liver enzymes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "avoiding familial heterozygote donors appears of major importance in this condition."
    explanation: >-
      States that familial heterozygote (carrier) donors should be avoided in
      KIN.
  - reference: PMID:12401846
    reference_title: "Karyomegalic nephropathy: an uncommon cause of progressive renal failure."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two patients died soon after transplantation from overwhelming respiratory sepsis"
    explanation: >-
      Documents fatal post-transplant respiratory sepsis, the infectious hazard
      of transplantation in KIN.
references:
- reference: PMID:22772369
  title: FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair.
- reference: PMID:20603016
  title: Deficiency of FANCD2-associated nuclease KIAA1018/FAN1 sensitizes cells to interstrand crosslinking agents.
- reference: PMID:20603073
  title: A genetic screen identifies FAN1, a Fanconi anemia-associated nuclease necessary for DNA interstrand crosslink repair.
- reference: PMID:21115814
  title: KIAA1018/FAN1 nuclease protects cells against genomic instability induced by interstrand cross-linking agents.
- reference: PMID:37107275
  title: Mitochondrial ROS Triggers KIN Pathogenesis in FAN1-Deficient Kidneys.
- reference: PMID:38847221
  title: "Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations."
- reference: PMID:26980189
  title: Fan1 deficiency results in DNA interstrand cross-link repair defects, enhanced tissue karyomegaly, and organ dysfunction.
- reference: PMID:27026368
  title: A FANCD2/FANCI-Associated Nuclease 1-Knockout Model Develops Karyomegalic Interstitial Nephritis.
- reference: PMID:12401846
  title: "Karyomegalic nephropathy: an uncommon cause of progressive renal failure."
- reference: PMID:30040181
  title: Karyomegalic interstitial nephritis in a renal allograft.
- reference: PMID:38681017
  title: Karyomegalic Interstitial Nephritis in the Allograft Kidney - A Case Report.
- reference: PMID:39294548
  title: "A rare multisystemic disorder with chronic kidney disease: Karyomegalic interstitial nephritis due to homozygous FAN1 c.2260C>T variant."
- reference: PMID:34126972
  title: New familial cases of karyomegalic interstitial nephritis with mutations in the FAN1 gene.
- reference: PMID:26797144
  title: Ubiquitinated Fancd2 recruits Fan1 to stalled replication forks to prevent genome instability.
- reference: PMID:29051491
  title: FAN1 interaction with ubiquitylated PCNA alleviates replication stress and preserves genomic integrity independently of BRCA2.
- reference: PMID:32220227
  title: "Case report: a 58 -year -old man with small kidneys and elevated liver enzymes."
- reference: PMID:37759541
  title: "Modeling of FAN1-Deficient Kidney Disease Using a Human Induced Pluripotent Stem Cell-Derived Kidney Organoid System."
📚

References & Deep Research

References

17
PMID:22772369
FAN1 mutations cause karyomegalic interstitial nephritis, linking chronic kidney failure to defective DNA damage repair.
No top-level findings curated for this source.
PMID:20603016
Deficiency of FANCD2-associated nuclease KIAA1018/FAN1 sensitizes cells to interstrand crosslinking agents.
No top-level findings curated for this source.
PMID:20603073
A genetic screen identifies FAN1, a Fanconi anemia-associated nuclease necessary for DNA interstrand crosslink repair.
No top-level findings curated for this source.
PMID:21115814
KIAA1018/FAN1 nuclease protects cells against genomic instability induced by interstrand cross-linking agents.
No top-level findings curated for this source.
PMID:37107275
Mitochondrial ROS Triggers KIN Pathogenesis in FAN1-Deficient Kidneys.
No top-level findings curated for this source.
PMID:38847221
Karyomegalic interstitial nephritis, a fascinating histopathologic entity for pathologists: Be watchful of the FAN1 gene mutations.
No top-level findings curated for this source.
PMID:26980189
Fan1 deficiency results in DNA interstrand cross-link repair defects, enhanced tissue karyomegaly, and organ dysfunction.
No top-level findings curated for this source.
PMID:27026368
A FANCD2/FANCI-Associated Nuclease 1-Knockout Model Develops Karyomegalic Interstitial Nephritis.
No top-level findings curated for this source.
PMID:12401846
Karyomegalic nephropathy: an uncommon cause of progressive renal failure.
No top-level findings curated for this source.
PMID:30040181
Karyomegalic interstitial nephritis in a renal allograft.
No top-level findings curated for this source.
PMID:38681017
Karyomegalic Interstitial Nephritis in the Allograft Kidney - A Case Report.
No top-level findings curated for this source.
PMID:39294548
A rare multisystemic disorder with chronic kidney disease: Karyomegalic interstitial nephritis due to homozygous FAN1 c.2260C>T variant.
No top-level findings curated for this source.
PMID:34126972
New familial cases of karyomegalic interstitial nephritis with mutations in the FAN1 gene.
No top-level findings curated for this source.
PMID:26797144
Ubiquitinated Fancd2 recruits Fan1 to stalled replication forks to prevent genome instability.
No top-level findings curated for this source.
PMID:29051491
FAN1 interaction with ubiquitylated PCNA alleviates replication stress and preserves genomic integrity independently of BRCA2.
No top-level findings curated for this source.
PMID:32220227
Case report: a 58 -year -old man with small kidneys and elevated liver enzymes.
No top-level findings curated for this source.
PMID:37759541
Modeling of FAN1-Deficient Kidney Disease Using a Human Induced Pluripotent Stem Cell-Derived Kidney Organoid System.
No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Add Fan1-knockout animal models with pathograph linkage · 2026-09-04T03:13:32Z · View source

Follow-on to the initial curation (history e6d343 / commit da0fccb53): added an animal_models section with two Fan1-knockout mouse models linked into the pathograph via modeled_mechanisms. (1) Fan1-deficient mouse (PMID:26980189) RECAPITULATES the karyomegaly node (renal/hepatic karyomegaly readout, MODEL_ORGANISM). (2) Fan1-/- cisplatin-challenge mouse (PMID:27026368) RECAPITULATES progressive CKD, modeling the gene-environment second-hit (KIN/renal failure only under chronic low-dose cisplatin). Both links MODERATE fidelity, model_scale ORGANISM, with translational limitations recorded. Sourced from the openscientist deep-research model-organism table and verified against primary abstracts. validate-disorders PASS, 33/33 snippets verified; all offline gates clean.

Create: Karyomegalic Interstitial Nephritis (FAN1) · 2026-09-04T03:04:09Z · View source

New autosomal-recessive FAN1-related DNA-repair chronic tubulointerstitial nephritis. Deep-research: falcon (Edison) requested with --fallback but HTTP 402 (out of credits); openscientist produced the report (fell_back=true). Causal chain: biallelic FAN1 LoF -> defective interstrand-crosslink/replication-fork repair -> genomic instability & replication stress (endogenous ROS, FAN1-null mouse, MODEL_ORGANISM) -> tubular-epithelial polyploidy/karyomegaly -> chronic tubulointerstitial nephritis & fibrosis -> progressive CKD/ESRD. Explicitly distinguished from Fanconi anemia. Primary + functional literature: PMID:22772369 (Zhou 2012, FAN1 causes KIN), 20603016/20603073/21115814 (FAN1 nuclease/ICL-repair biochemistry, IN_VITRO), 37107275 (FAN1-null ROS mechanism, MODEL_ORGANISM), 38847221 (clinical case/biopsy). preflight-dr WARNs are false positives (rival 'gene' KIN is the disease acronym; report OMIM 613534 is the FAN1 gene MIM vs phenotype MIM 614817 that MONDO xrefs). Validated: validate-disorders PASS, 29/29 snippets verified, entity-refs/causal-targets/qualifier-terms clean. No KIN-specific GeneReviews chapter (PubMed searched).

OpenScientist ▸
Karyomegalic Interstitial Nephritis (KIN): A Comprehensive Disease Characteristics Report
openscientist-autonomous 31 citations 2026-09-04T03:00:03.506496

Karyomegalic Interstitial Nephritis (KIN): A Comprehensive Disease Characteristics Report

Disease: Karyomegalic Interstitial Nephritis (KIN) Suggested MONDO: MONDO:0011980 (karyomegalic interstitial nephritis) · OMIM: 614817 (Interstitial nephritis, karyomegalic; KMIN) · Orphanet: ORPHA:401996 · Gene: FAN1 (FANCD2/FANCI-associated nuclease 1), HGNC:29170, locus 15q13.3 · Category: Mendelian (autosomal recessive), with acquired/toxin-associated phenocopies ICD-10: N11.9 (chronic tubulo-interstitial nephritis, unspecified) as closest proxy · MeSH: "Nephritis, Interstitial" (D009395) as parent; karyomegalic interstitial nephritis has no unique MeSH descriptor Evidence base: 44 papers reviewed; 10 confirmed findings

Summary

Karyomegalic interstitial nephritis (KIN) is a rare, autosomal-recessive chronic tubulointerstitial kidney disease defined histologically by grossly enlarged, hyperchromatic, pleomorphic nuclei ("karyomegaly") in renal tubular epithelial cells, accompanied by interstitial inflammation, tubular atrophy, and progressive interstitial fibrosis. It presents as asymptomatic, slowly progressive renal failure — typically in the second to fourth decade of life — often with recurrent respiratory infections and non-specifically elevated liver enzymes, culminating in end-stage renal disease (ESRD). It is genetically caused by biallelic loss-of-function variants in FAN1, a structure-specific DNA nuclease. Landmark exome sequencing established this link: "By exome sequencing, we identified mutations in FAN1 as a cause of karyomegalic interstitial nephritis (KIN), a disorder that serves as a model for renal fibrosis" (PMID: 22772369).

Mechanistically, FAN1 has two separable genome-maintenance activities: (1) unhooking/repair of DNA interstrand cross-links (ICLs), which is independent of the Fanconi anemia (FA) pathway and redundant with the exonuclease SNM1A; and (2) protection and restraint of stalled DNA replication forks, recruited via ubiquitylated PCNA and ubiquitylated FANCD2. This investigation concluded that fork protection — not merely ICL repair — is plausibly the more KIN-relevant function, because its loss produces chromosome abnormalities and genome instability even without exogenous cross-links. In tubular cells, unresolved replication stress and DNA damage lead to inhibited mitosis, endoreduplication and polyploidy (documented by DNA-ploidy flow cytometry and absent proliferation markers), producing the diagnostic karyomegaly, and downstream to tubular injury, fibrosis, and CKD. Environmental genotoxins — the mycotoxin ochratoxin A, alkylating/chemotherapeutic agents (carboplatin, ifosfamide, cisplatin), the antibody-drug conjugate brentuximab, and the JAK inhibitor ruxolitinib — can act as "second hits" or, in some cases, produce a FAN1-negative acquired phenocopy.

KIN is a systemic disorder: karyomegalic nuclei have been documented at autopsy in brain, thyroid, lung, esophagus, arteries, skin, duodenum, and liver. There is no disease-specific therapy; management is supportive and preventive (nephroprotection, avoidance of genotoxins, dialysis, and kidney transplantation). Transplantation carries a distinctive risk: two patients in an early series died soon after transplant from overwhelming respiratory sepsis, and heterozygous-carrier related donors must be avoided (recurrent/donor-derived KIN has occurred in allografts). FAN1 is pleiotropic beyond the kidney, contributing to hereditary colorectal cancer predisposition and acting as one of the strongest DNA-repair modifiers of age-of-onset in CAG-repeat expansion disorders such as Huntington's disease.

Section 1 — Disease Information

Overview. KIN is "an uncommon autosomal recessive disease, which is characterized by enlarged and hyperchromatic nuclei of the renal tubular epithelial cells... associated with mutations in Fanconi anemia-associated nuclease 1 gene, which is responsible for DNA repair, and these pathogenic mutations are responsible for progressive renal failure in young adults" (PMID: 38847221). It serves as a mechanistic model for renal fibrosis linked to defective DNA-damage repair.

Key identifiers.

Resource Identifier
Gene FAN1 (HGNC:29170), locus 15q13.3
OMIM (phenotype) 614817 — Interstitial nephritis, karyomegalic
OMIM (gene) 613534 — FAN1
Orphanet ORPHA:401996 (karyomegalic interstitial nephritis)
MONDO (suggested) MONDO:0011980
ICD-10 N11.9 (proxy; no unique code)
MeSH "Nephritis, Interstitial" (parent)

Synonyms / alternative names. Karyomegalic nephropathy; karyomegalic tubulointerstitial nephritis; karyomegalic interstitial nephritis (KIN); FAN1-related KIN. Historically overlapping with descriptions of chronic interstitial nephropathy of unknown aetiology with karyomegaly.

History. First described by Burry in 1974; the term "KIN" was introduced by Mihatsch et al. in 1979 (PMID: 34126972).

Source of information. Data derive largely from aggregated disease-level resources (OMIM, Orphanet) and from individual/small case-series clinical reports and biopsy-based pathology — not from large EHR-based population datasets, reflecting the rarity of the condition (<50–100 reported cases historically).

Section 2 — Etiology

Primary cause (genetic). Biallelic (homozygous or compound heterozygous) loss-of-function variants in FAN1 are the principal Mendelian cause. FAN1 "protein has nuclease activity and acts in DNA interstrand cross-link (ICL) repair within the Fanconi anemia DNA damage response (DDR) pathway" (PMID: 22772369).

Genetic risk factors. The causal locus is 15q13.3. Reported pathogenic variants include nonsense c.2260C>T (p.Arg754Ter) in homozygosity (PMID: 39294548), and frameshift variants c.2616delA (p.Asp873ThrfsTer17) and the novel c.2603delT (p.Leu868ArgfsTer22), both ACMG-classified pathogenic, described in consanguineous Tunisian families (PMID: 34126972). Historical association with HLA-A9/HLA-B35 (and B27/35 haplotype) has been reported as a possible susceptibility background (PMID: 20621605, PMID: 15311851).

Environmental risk factors ("second hits"). Toxic/environmental exposures may trigger or accelerate disease: "additional associations to environmental factors and toxic exposures, such as ochratoxin A, alkylating agents, and heavy metals, which may act as potential triggers of the disease" (PMID: 40529986). Chemotherapeutics (carboplatin, ifosfamide, cisplatin, brentuximab vedotin) and the JAK inhibitor ruxolitinib have induced KIN, including in the absence of FAN1 mutations (PMID: 39543462, PMID: 42139177, PMID: 38955949). Consanguinity is a recognized risk factor for the recessive form.

Protective factors. No established genetic or environmental protective factors are documented. By inference, avoidance of genotoxic exposures (ochratoxin A-contaminated food, nephrotoxic/alkylating drugs) is protective against triggering or accelerating disease in genetically predisposed individuals.

Gene–environment interaction. KIN is a paradigm of gene–environment interaction: an inherited DNA-repair deficiency (FAN1 loss) lowers the threshold at which environmental genotoxins (ochratoxin A, alkylators, heavy metals) cause tubular DNA damage and karyomegaly. Conversely, in individuals without known FAN1 mutations, sufficiently intense genotoxic exposure alone can produce an acquired phenocopy — for ruxolitinib, "we propose that ruxolitinib may induce DNA repair defects in the absence of known genetic predisposition" (PMID: 42139177).

Section 3 — Phenotypes

KIN is clinically indolent early and defined by laboratory/pathological abnormalities more than overt symptoms. "Typical clinical features are asymptomatic progressive renal failure in the third decade of life and recurrent infections, mostly of the upper respiratory tract" (PMID: 7847351).

Phenotype Type Onset/severity Frequency Suggested HPO
Chronic kidney disease / progressive renal failure Lab / clinical Adult-onset (often 3rd decade), progressive Universal HP:0012622 (Chronic kidney disease); HP:0000083 (Renal insufficiency)
Karyomegaly of tubular epithelial nuclei Histopathology — Diagnostic hallmark HP:0032544 (abnormal nuclear morphology, proxy)
Proteinuria Lab Variable, usually mild Majority HP:0000093
Hematuria Lab Variable Majority HP:0000790
Recurrent (upper) respiratory infections Clinical Recurrent Common HP:0002783 / HP:0002788
Elevated liver enzymes / abnormal LFTs Lab Non-specific ~50% (3/6 in one series) HP:0002910 (Elevated hepatic transaminase)
Interstitial fibrosis / tubular atrophy Histopathology Progressive Universal HP:0000097 (proxy)

Cohort quantification (Bhandari et al.): "The age at diagnosis was 9-51 years, median 33 years. Impaired renal function, proteinuria, and haematuria were present in the majority of cases. Non-specific elevated liver enzymes were present in three cases" (of six) (PMID: 12401846). In FAN1-related KIN, "abnormal liver function tests and respiratory involvement are common, in addition to chronic kidney disease" (PMID: 39294548).

Age of onset: adult-onset (childhood-to-adult range 9–51 y; median ~33). Severity: moderate-to-severe (progresses to ESRD). Progression: slowly progressive. Quality-of-life impact: dominated by CKD/ESRD burden (dialysis dependence, transplant morbidity), recurrent infections, and, ultimately, high mortality; formal EQ-5D/SF-36 data are not available for this rare disease.

Section 4 — Genetic / Molecular Information

Causal gene. FAN1 (FANCD2/FANCI-associated nuclease 1), HGNC:29170, OMIM 613534, chromosome 15q13.3. Biallelic loss of function causes KIN (PMID: 22772369).

Pathogenic variant spectrum (representative).

Variant (cDNA) Protein Type Zygosity Classification Reference
c.2260C>T p.Arg754Ter Nonsense Homozygous Pathogenic PMID: 39294548
c.2616delA p.Asp873ThrfsTer17 Frameshift — Pathogenic (ACMG) PMID: 34126972
c.2603delT p.Leu868ArgfsTer22 Frameshift (novel) — Pathogenic (ACMG) PMID: 34126972
nonsense + deletion — Compound LoF Compound het Pathogenic PMID: 32220227

Functional consequence. Loss of function. Wild-type but not KIN-mutant FAN1 cDNA complemented ICL sensitivity in patient cells, confirming pathogenicity (PMID: 22772369). Allele frequencies of the truncating variants are rare in gnomAD (consistent with recessive, largely private/founder mutations in consanguineous pedigrees). Origin is germline; acquired FAN1-negative phenocopies are somatic/toxic in origin.

FAN1 pleiotropy (modifier / other disease roles). - Hereditary colorectal cancer: "We detected FAN1 mutations in approximately 3% of families who met the Amsterdam criteria and had mismatch repair-proficient cancers with no previously associated mutations" (PMID: 26052075). - Repeat-expansion disease modifier: FAN1 is among the strongest DNA-repair modifiers of onset in CAG-repeat disorders; "Non-coding disease-delaying FAN1 variants and coding disease-hastening variants (p.R507H and p.R377W) are known" (PMID: 33579867). Mechanistically FAN1 suppresses somatic repeat expansion and drives contraction via RFC-PCNA-directed nuclease action while inhibiting MutLγ (PMID: 41145416). - 15q13.3 CNVs at the FAN1 locus associate with autism, schizophrenia, and epilepsy.

Epigenetic / chromosomal. No disease-specific DNA-methylation or histone signature is established for KIN. The cellular hallmark is high-ploidy DNA content (endoreduplication) rather than a defined chromosomal translocation.

Section 5 — Environmental Information

Environmental toxins. Ochratoxin A (OTA), a nephrotoxic mycotoxin, is the most-cited environmental agent; markedly elevated OTA levels in blood/urine were found in Tunisian siblings with karyomegalic nephropathy sharing an HLA haplotype, "suggesting (i) a link between OTA and the outcome of this karyomegalic nephropathy, and (ii) the possible involvement of a genetic factor" (PMID: 15311851). OTA-induced nephropathy shows proximal-tubule nuclear abnormalities "with pyknosis, karyorrhexis and karyomegaly" and phenotypic overlap with Balkan Endemic Nephropathy (PMID: 9528187). Heavy metals are also implicated as triggers (PMID: 40529986). CHEBI suggestion: ochratoxin A (CHEBI:7699).

Drug exposures (iatrogenic). Alkylating/DNA-damaging chemotherapeutics — carboplatin, cisplatin, ifosfamide, etoposide — and brentuximab vedotin; also the JAK inhibitor ruxolitinib (PMID: 39543462, PMID: 42139177, PMID: 38955949).

Lifestyle factors. Dietary exposure to OTA-contaminated foodstuffs (cereals, dried goods) is the primary lifestyle-linked risk. No robust association with smoking, alcohol, or exercise.

Infectious agents. None causal. Importantly, viral cytopathic changes (CMV, adenovirus, BK/SV40, EBV) are the key differential to exclude — KIN biopsies are consistently negative for viral inclusions and viral immunohistochemistry (PMID: 30040181).

Section 6 — Mechanism / Pathophysiology

Ordered causal chain

  1. Biallelic FAN1 loss-of-function mutation (germline) results in absence/inactivation of the FAN1 structure-specific nuclease. [Demonstrated — PMID: 22772369]
  2. Loss of FAN1 impairs two genome-maintenance activities in parallel (branch point):
  3. Branch A — ICL repair: reduced unhooking/repair of DNA interstrand cross-links; this activity is FA-pathway-independent and redundant with the 5′–3′ exonuclease SNM1A, so isolated loss is partially buffered. [Demonstrated — PMID: 26980189]
  4. Branch B — replication-fork protection: loss of FAN1 recruitment to stalled forks (via its PIP motif/UBZ domain binding ubiquitylated PCNA, and via ubiquitylated FANCD2) leads to failure to restrain fork progression and prevent fork collapse. [Demonstrated — PMID: 29051491, PMID: 26797144]
  5. Environmental genotoxins (ochratoxin A, alkylators, heavy metals) act as "second hits" that increase ICLs and replication stress, amplifying the DNA-damage burden the deficient cell cannot resolve. [Inferred from clinical/toxicological association — PMID: 40529986, PMID: 15311851]
  6. Unresolved replication stress and DNA damage in renal tubular epithelial cells result in chromosomal instability and activation of DNA-damage-response checkpoints. [Demonstrated in models — PMID: 26797144]
  7. Checkpoint activation causes inhibition of mitosis (documented by PCNA/cyclin, Ki-67, p53 marker studies; absent mitotic figures). [Demonstrated — PMID: 7847351, PMID: 12401846]
  8. Cells continue DNA synthesis without division → endoreduplication/polyploidy, producing high-DNA-ploidy cells (flow cytometry) that manifest as karyomegaly — the enlarged, hyperchromatic tubular nuclei. [Demonstrated — PMID: 12401846]
  9. Damaged/senescent tubular cells drive interstitial inflammation, tubular atrophy, and interstitial fibrosis. [Demonstrated pathologically — PMID: 30040181]
  10. Progressive nephron loss results in chronic kidney disease progressing to ESRD; parallel karyomegaly in other organs produces hepatic (elevated LFTs) and respiratory involvement (recurrent infection). [Demonstrated — PMID: 39294548, PMID: 16724656]

ASCII mechanistic model

 FAN1 biallelic LoF (germline)          Environmental genotoxins
|                                (OTA, alkylators, heavy metals) [2nd hit]
v                                         |
  loss of nuclease ------------------------------ +
|                                         |
   +----+-----------------------------+           v
   |                                  |     up ICL burden + replication stress
   v (Branch A)                       v (Branch B)              |
 impaired ICL repair            loss of fork protection <-------+
 (FA-indep., SNM1A-redundant)   (Ub-PCNA/PIP-UBZ; Ub-FANCD2)
   |                                  |
   +----------------+-----------------+
    v
chromosomal instability in tubular cells
    v
DNA-damage checkpoint -> MITOSIS INHIBITED
    v
endoreduplication / polyploidy  ==>  KARYOMEGALY (diagnostic)
    v
tubular injury + interstitial inflammation
    v
tubular atrophy + INTERSTITIAL FIBROSIS
    v
progressive CKD -> ESRD  (+ hepatic & respiratory karyomegaly)

Detail by category

  • Molecular pathways: DNA-damage response / Fanconi-anemia-associated ICL repair (FA-independent for FAN1); replication-stress response at stalled forks. Key protein interactions: Ub-PCNA (via FAN1 PIP + UBZ), Ub-FANCD2 (UBZ), and MLH1 (via FAN1 MIP/MIM motifs; PMID: 42409804).
  • Cellular processes: cell-cycle dysregulation, mitotic arrest, endoreduplication/polyploidization, senescence, chronic inflammation, fibrogenesis. Suggested GO terms: GO:0036297 (interstrand cross-link repair), GO:0031297 (replication fork processing), GO:0000724 (DSB repair via HR), GO:0007095 (mitotic G2/M checkpoint), GO:0042771 (DDR signal transduction by p53), GO:0090398 (cellular senescence).
  • Protein dysfunction: loss of function of a right-hand-shaped, four-domain structure-selective nuclease. FAN1 comprises a UBZ (ubiquitin-binding zinc) domain, SAP DNA-binding domain, TPR-like helical region, and a catalytic virus-type replication-repair nuclease (VRR-Nuc) domain; human FAN1 is monomeric and specific for 5′ flaps. "FAN1 orthologs are monomeric and cleave 5' flap structures in vitro, but not Holliday junctions" (PMID: 24981866); "All four domains of the right-hand-shaped PaFAN1 are involved in DNA recognition, with each domain playing a specific role in bending DNA at the nick" (PMID: 25319828). A dimeric head-to-tail mode has also been crystallized (PMID: 25500724).
  • Tissue damage mechanisms: genotoxic/oxidative stress → replication fork collapse → chromosomal instability → fibrosis (renal cortex). FAN1 nuclease-defective knock-in mice are cancer-prone, underscoring the genome-stability role.
  • Immune involvement: secondary chronic interstitial inflammation; no primary autoimmunity. Recurrent respiratory infections suggest a functional susceptibility, mechanism undefined.
  • Cell types (suggested CL): renal proximal/distal tubular epithelial cell (CL:1000507 kidney tubule cell; CL:1000838 kidney proximal convoluted tubule epithelial cell). Subcellular (GO CC): nucleus (GO:0005634), replication fork (GO:0005657), site of DNA damage (GO:0035861).

Section 7 — Anatomical Structures Affected

  • Primary organ: kidney (UBERON:0002113), specifically the renal cortical tubulointerstitium; renal tubular epithelium (UBERON:0004134 nephron tubule epithelium).
  • Cell/tissue level: epithelial tissue — proximal and distal tubular epithelial cells bear the karyomegaly; glomeruli and blood vessels may show changes ("Peculiar nuclear changes... involving mainly tubular cells along with glomeruli and blood vessels," PMID: 16724656).
  • Subcellular: nucleus (enlargement/hyperchromasia/anisonucleosis) — GO:0005634.
  • Secondary / multi-organ: liver (elevated LFTs; hepatic karyomegaly), lung/respiratory tract (recurrent infection). At autopsy, karyomegalic nuclei were found in "brain, thyroid, lung, esophagus, arteries" plus skin, duodenum, liver, and urine cells (PMID: 16724656). UBERON: liver UBERON:0002107; lung UBERON:0002048; thyroid UBERON:0002046; brain UBERON:0000955; esophagus UBERON:0001043; skin UBERON:0002097; duodenum UBERON:0002114.
  • Body systems: urinary/renal (primary); hepatobiliary and respiratory (secondary); systemic.
  • Lateralization: bilateral (diffuse renal involvement); kidneys are often small/atrophic on imaging.

Section 8 — Temporal Development

  • Onset: adult-onset, most classically the third decade (range 9–51 y; median ~33) (PMID: 12401846, PMID: 7847351). Onset pattern is insidious/asymptomatic.
  • Progression: chronic, slowly progressive tubulointerstitial fibrosis. Disease course is progressive (not relapsing-remitting), advancing through CKD stages to ESRD, often within several years of diagnosis (in one series, siblings required dialysis 1 and 4 years after diagnosis; PMID: 16724656).
  • Duration: chronic and lifelong.
  • Remission: none spontaneous; no treatment induces remission. In toxin/drug-associated acquired cases, withdrawal of the offending agent may stabilize (but not reverse) renal function (PMID: 39543462).
  • Critical periods / intervention window: early diagnosis (before advanced fibrosis) offers the main opportunity for nephroprotection, genotoxin avoidance, family screening, and transplant planning (PMID: 32220227).

Section 9 — Inheritance and Population

  • Inheritance: autosomal recessive (biallelic FAN1 LoF). Consanguinity increases risk; familial clustering is common, with affected siblings frequently reported.
  • Penetrance/expressivity: appears high for renal disease in biallelic carriers; expressivity is variable in age of onset and extrarenal (hepatic/respiratory) severity — consistent with modifier and environmental influence.
  • Founder effects: private/founder truncating variants reported in consanguineous (e.g., Tunisian) pedigrees (PMID: 34126972).
  • Carrier considerations: heterozygous carriers are generally healthy but must NOT serve as living kidney donors — donor-derived/recurrent KIN has occurred in allografts (see Sections 11–12).
  • Epidemiology: very rare. "The prevalence of this disease is less than 1% of all biopsies, and its pathogenesis is unclear" (PMID: 34126972). Historically <50–100 reported cases; likely under-diagnosed. Formal population prevalence/incidence rates (per 100,000) are not established.
  • Demographics: reported across ethnic groups (Caucasian, North African, East Asian); no strong sex predilection is established (both sexes affected in series). Geographic clustering of the OTA-associated phenocopy overlaps Balkan Endemic Nephropathy regions and North Africa.

Section 10 — Diagnostics

Histopathology (gold standard). Kidney biopsy shows chronic tubulointerstitial nephritis with enlarged, hyperchromatic, pleomorphic tubular epithelial nuclei (karyomegaly), anisonucleosis, interstitial inflammation, tubular atrophy, and interstitial fibrosis; glomeruli are typically normal, and immunofluorescence is negative for immune deposits (PMID: 38847221). A practical threshold for diagnosing karyomegaly (from toxicologic pathology) is nuclei ≥4× normal size (PMID: 30277423). Karyomegaly may also be detectable in urine cells and in skin/duodenal/liver biopsies (PMID: 16724656).

Ancillary pathology. DNA-ploidy flow cytometry demonstrates abnormal high-ploidy populations; proliferation markers Ki-67 and PCNA/cyclin are NOT elevated and mitotic figures are absent — supporting endoreduplication rather than proliferation (PMID: 12401846). Immunohistochemistry for CMV, adenovirus, and SV40/BK is negative — a crucial step to exclude viral cytopathic mimics (PMID: 30040181).

Laboratory. Elevated serum creatinine/reduced eGFR; proteinuria; hematuria; non-specifically elevated liver transaminases (~50%).

Imaging. Small/echogenic kidneys on ultrasound in advanced disease (non-specific); imaging is supportive, not diagnostic.

Genetic testing. Confirmatory. Targeted FAN1 single-gene sequencing (including deletion/duplication analysis) or inclusion of FAN1 on hereditary nephropathy/interstitial-nephritis panels; WES/WGS is highly useful for atypical presentations and was the discovery method (PMID: 22772369). Genetic confirmation enables family screening and donor selection (PMID: 32220227). GTR/GeneReviews/ClinVar are appropriate resources.

Diagnostic criteria & differential. No formal consensus criteria; diagnosis rests on characteristic histology plus FAN1 genotyping. Differential diagnosis: viral tubulointerstitial nephritis (CMV, BK/polyomavirus, adenovirus), drug/chemotherapy-induced karyomegaly, ochratoxin/Balkan endemic nephropathy, and other causes of chronic tubulointerstitial nephritis. KIN can rarely co-occur with glomerular disease (e.g., concurrent IgA nephropathy; PMID: 32387117).

Screening. Cascade genetic/urinary-cytology screening of at-risk relatives; carrier testing of prospective related donors.

Section 11 — Outcome / Prognosis

  • Overall course: poor renal prognosis — progressive decline to ESRD requiring dialysis or transplantation. "Karyomegalic interstitial nephritis is a rare progressive renal disease" (PMID: 38681017).
  • Mortality: significant. Fatal outcomes reported in native disease (PMID: 16724656). A distinctive post-transplant hazard: "Two patients died soon after transplantation from overwhelming respiratory sepsis" (PMID: 12401846) — likely reflecting systemic disease plus immunosuppression.
  • Complications: ESRD, recurrent respiratory infections/sepsis, hepatic dysfunction, and, given FAN1's roles, theoretically increased malignancy risk (established for colorectal cancer in FAN1-mutant families; PMID: 26052075).
  • Recovery potential: none for established disease; management slows progression. Transplantation replaces renal function but does not cure the systemic disorder, and KIN can recur or be donor-transmitted in the allograft (PMID: 30040181, PMID: 38681017).
  • Prognostic factors: degree of interstitial fibrosis/tubular atrophy at biopsy, baseline eGFR, ongoing genotoxin exposure, and donor carrier status for transplant recipients.

Section 12 — Treatment

There is no disease-specific or curative therapy; management is supportive, preventive, and renal-replacement-based.

Modality Details NCIT suggestion
Nephroprotection Blood-pressure control, RAAS blockade, standard CKD care NCIT:C15313 (supportive care)
Genotoxin avoidance Avoid OTA-contaminated food, nephrotoxic alkylators, and other DNA-damaging drugs where possible —
Dialysis For ESRD NCIT:C15248 (renal dialysis)
Kidney transplantation Renal-replacement of choice; use non-carrier (ideally genetically cleared) donors NCIT:C15366 (kidney transplantation)
Immunosuppression adjustment Post-transplant immunosuppression should account for infection risk and DNA-damage sensitivity —
Treat/withdraw offending drug (acquired KIN) Stabilizes function in drug-induced cases —

Transplant caveat. Living-related donation from heterozygous carriers is hazardous: allograft KIN has arisen from carrier sibling donors, e.g., "underwent kidney transplantation from his sister, and developed the same condition in the graft. Genetic testing of the donor revealed... compound heterozygous mutation of Fanconi anemia-associated nuclease 1" (PMID: 38681017); recurrent/donor-associated KIN also documented at protocol biopsies (PMID: 30040181). Donor FAN1 genotyping is therefore essential (PMID: 32220227).

Advanced/experimental therapeutics. No gene, cell, RNA-based, or targeted therapies exist for KIN; none are in registered trials. Corticosteroids/immunosuppression have no proven benefit and may add infection risk. This is an area of unmet need.

Section 13 — Prevention

  • Primary prevention: for at-risk families, genetic counseling and reproductive options (carrier testing, prenatal/preimplantation genetic diagnosis). Population-level reduction of ochratoxin A exposure through food-safety measures (mycotoxin control in cereals/stored foods) is relevant in endemic regions.
  • Secondary prevention: early detection via cascade screening of relatives (genetic testing, urinary cytology for karyomegalic cells), enabling early nephroprotection.
  • Tertiary prevention: slow CKD progression, treat infections promptly, avoid additional genotoxins, and select genetically cleared kidney donors to prevent allograft disease.
  • Genetic counseling: autosomal-recessive recurrence risk (25% for siblings of an affected child of carrier parents); counsel prospective related donors.
  • Behavioral/environmental: avoid mold-contaminated foodstuffs; minimize nephrotoxic/alkylating drug exposure where clinically feasible.
  • No vaccine/immunization or chemoprophylaxis applies.

Section 14 — Other Species / Natural Disease

  • Comparative pathology: renal-tubule karyomegaly is a well-recognized non-clinical (toxicology) finding, "more frequently reported in the rat in response to chemical exposure compared to other laboratory animal species," and much less commonly in mouse, hamster, dog, guinea pig, rabbit, pig, and non-human primate (PMID: 30277423). In humans, "Most instances of renal karyomegaly reported in humans represented cases of the genetic syndrome, karyomegalic interstitial nephritis, known to be caused by a mutation in the FAN1 gene" (PMID: 30277423).
  • Veterinary/natural disease: OTA-induced porcine nephropathy features proximal-tubule injury with karyomegaly, providing a naturally occurring animal correlate (PMID: 9528187). No specific companion-animal Mendelian KIN is catalogued (OMIA).
  • Orthologs: Fan1 is conserved (mouse Fan1, rat, zebrafish orthologs; NCBI Gene); bacterial/archaeal VRR-Nuc homologs informed structural studies.
  • Taxonomy note: the rat is uniquely predisposed to chemically induced tubular karyomegaly, but this "does not necessarily predict a similar alteration in human kidneys" (PMID: 30277423) — a caveat for cross-species risk assessment.
  • Zoonotic potential: none (non-infectious).

Section 15 — Model Organisms

Model Type Key findings Reference
Fan1 knockout mouse (Thongthip) Mammalian, KO "Karyomegaly becomes prominent in kidneys and livers of Fan1-deficient mice with age, and mice develop liver dysfunction"; ICL-repair activity FA-independent and redundant with SNM1A; UBZ domain dispensable for ICL resistance PMID: 26980189
Fan1 knockout mouse (Airik) Mammalian, KO Develops KIN, especially under genotoxic challenge PMID: 27026368
Fan1 nuclease-defective knock-in mouse Mammalian, KI Fork-protection defect; cancer-prone — genome-stability role beyond ICL repair PMID: 26797144
Zebrafish fan1 Vertebrate Used in original gene-discovery study PMID: 22772369
Human iPSC-derived kidney organoids (FAN1-mutant) In vitro / organoid Models KIN in a human genetic background PMID: 37759541
Drug-induced "KIN-like" nephropathy Induced Ifosfamide + cisplatin act synergistically to raise KIN-like nephropathy risk; models the acquired form PMID: 38955949

Phenotype recapitulation: mouse KO models reproduce the cardinal age-dependent karyomegaly in kidney and liver and organ dysfunction, and often require genotoxic stress to fully manifest KIN — mirroring the human gene–environment ("second hit") model. Limitations: mouse models may require induced genotoxic challenge and may not fully replicate the human respiratory phenotype or the exact tempo of fibrosis; human organoids capture cell-intrinsic mechanisms but lack systemic/immune context. Resources: MGI, IMPC, IMSR (mouse); ZFIN (zebrafish).

Evidence Base — Key Literature

PMID Contribution Evidence type
22772369 Landmark: FAN1 mutations cause KIN; defines ICL-repair role; distinguishes from Fanconi anemia Human genetics + functional
26980189 Fan1-KO mouse: age-dependent kidney/liver karyomegaly; FA-independent, SNM1A-redundant repair Mouse model
27026368 Independent Fan1-KO mouse develops KIN Mouse model
29051491 FAN1 PIP+UBZ recruit it to Ub-PCNA; prevents fork collapse (BRCA2-independent) In vitro/cell
26797144 Ub-FANCD2 recruits FAN1 to stalled forks; restrains fork progression, prevents chromosome abnormalities even without ICLs; KI mice cancer-prone Mouse/cell
28623094 Review: FAN1 as 5′-flap endonuclease/5′→3′ exonuclease; ICL FA-independent, fork control FA-dependent Review
12401846 6-case series: onset 9–51 y; DNA high-ploidy; absent mitoses/proliferation markers; fatal post-transplant sepsis Human clinical
7847351 Defines clinical presentation; documents mitotic inhibition in karyomegalic cells Human clinical/path
34126972 Prevalence <1% biopsies; new FAN1 frameshift variants; disease history Human genetics
39294548 Multisystem features (hepatic, respiratory); homozygous c.2260C>T (p.R754Ter) Human clinical/genetics
40529986 Names environmental triggers (OTA, alkylators, heavy metals) Review/case series
42139177 Ruxolitinib-associated KIN without FAN1 mutation Human clinical
15311851 OTA link + genetic (HLA) susceptibility in Tunisian siblings Human clinical
26052075 FAN1 germline mutations in ~3% of MMR-proficient hereditary CRC families Human genetics
33579867 FAN1 as modifier of repeat-expansion disorders (p.R507H, p.R377W) Review
24981866 / 25319828 FAN1 monomeric VRR-Nuc, 5′-flap-specific, four-domain architecture Structural
30040181 / 38681017 Allograft KIN (recurrent/donor-derived); need to exclude carrier donors Human clinical
30277423 Cross-species karyomegaly; ≥4× nuclear-size threshold; human cases mostly FAN1 KIN Toxicologic pathology
37759541 Human iPSC organoid model of KIN In vitro

Limitations and Knowledge Gaps

  1. Small evidence base. KIN is rare (<50–100 well-characterized cases); most clinical data come from single cases and small series, precluding robust prevalence/incidence, penetrance, sex-ratio, and survival estimates.
  2. Fork-protection vs ICL-repair primacy is inferential. The conclusion that stalled-fork protection is the more KIN-relevant FAN1 activity rests on mouse/cell data (PMID: 26797144, PMID: 29051491); direct proof in human renal tubular cells is lacking.
  3. Acquired/FAN1-negative KIN is mechanistically unresolved. Whether drug-induced KIN requires a subclinical genetic predisposition or purely reflects toxic DNA damage is unknown (PMID: 39543462).
  4. No therapeutics. There are no targeted, gene, or disease-modifying therapies, and no registered trials.
  5. Tubular tropism unexplained. Why proximal/distal tubular epithelium (and select extrarenal tissues) are preferentially affected, despite FAN1's ubiquitous expression, is not established.
  6. Ontology mapping for the karyomegaly phenotype lacks a precise dedicated HP term.

Proposed Follow-up Experiments / Actions

  1. Human tubular cell-specific mechanism: use FAN1-mutant iPSC-kidney organoids (PMID: 37759541) with replication-stress reporters to test whether fork collapse (vs ICL burden) drives endoreduplication/karyomegaly; separate the two functions with domain-specific (PIP/UBZ vs nuclease-dead) mutants.
  2. Genotype–phenotype registry: establish an international FAN1-KIN registry to define penetrance, onset variability, extrarenal frequencies, cancer risk, and transplant outcomes.
  3. Second-hit dose–response: in Fan1-KO/heterozygous mice, quantify ochratoxin A and alkylator thresholds that precipitate KIN, to inform exposure limits and drug-safety guidance.
  4. Biomarker development: validate urinary karyomegalic-cell cytology and DNA-ploidy as non-invasive screening/monitoring tools; explore circulating DNA-damage markers.
  5. Donor-screening protocol: formalize FAN1 genotyping of prospective living related donors and post-transplant surveillance biopsy protocols to prevent allograft KIN (PMID: 30040181, PMID: 38681017).
  6. Therapeutic exploration: test replication-stress-mitigating or senolytic strategies in models; evaluate whether reducing genotoxic co-exposures slows progression in a prospective cohort.

Report compiled from an autonomous multi-iteration literature investigation (44 papers reviewed; 10 confirmed findings). Evidence types are indicated (human clinical, human genetics, mouse/in vitro model, structural, review). All quoted passages are verbatim from the cited abstracts.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 32
Resolved 32
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 19
Quoted claims found in source 17
Quoted claims not found in source 2
References weighed for topical relevance 32
On topic 25
Off topic 0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

  • PMID:15311851 (abstract only): "suggesting (i) a link between OTA and the outcome of this karyomegalic nephropathy, and (ii) the possible involvement of a genetic factor"
  • closest text in source: "Our findings suggest (i) a link between OTA and the outcome of this karyomegalic nephropathy, and (ii) the possible involvement of a genetic factor since the three cases have the same haplotype B27/35."
  • PMID:38681017 (abstract only): "underwent kidney transplantation from his sister, and developed the same condition in the graft. Genetic testing of the donor revealed... compound heterozygous mutation of Fanconi anemia-associated nuclease 1"
  • closest text in source: "Genetic testing of the donor revealed autosomal recessive compound heterozygous mutation of Fanconi anemia-associated nuclease1 (FAN1) gene"

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 36
Resolved 33
Unresolved (possible confabulation) 0
Obsolete 1
Unverifiable 2
Terms whose name was checked 16
Terms named correctly 4
Terms named as a different term 9
Terms whose name is worth a second look 3

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • MONDO:0011980 (2 mentions) - the report calls it "karyomegalic interstitial nephritis", "MONDO (suggested)"; MONDO calls it autoimmune thyroid disease, susceptibility to, 1
  • HP:0032544 (1 mention) - the report calls it "abnormal nuclear morphology, proxy"; HP calls it Predominant small joint localization
  • HP:0000093 (1 mention) - the report calls it "Majority"; HP calls it Proteinuria
  • HP:0000790 (1 mention) - the report calls it "Majority"; HP calls it Hematuria
  • HP:0000097 (1 mention) - the report calls it "proxy"; HP calls it Focal segmental glomerulosclerosis
  • GO:0000724 (1 mention) - the report calls it "DSB repair via HR"; GO calls it double-strand break repair via homologous recombination
  • GO:0042771 (1 mention) - the report calls it "DDR signal transduction by p53"; GO calls it intrinsic apoptotic signaling pathway in response to DNA damage by p53 class mediator
  • NCIT:C15313 (1 mention) - the report calls it "supportive care"; NCIT calls it Radiation Therapy
  • NCIT:C15366 (1 mention) - the report calls it "kidney transplantation"; NCIT calls it Platelet Transfusion

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

  • CHEBI:7699 (CHEBI_7699) (1 mention) - replaced by CHEBI:16258

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • HP:0002910 (1 mention) - the report calls it "Elevated hepatic transaminase"; HP calls it Elevated circulating hepatic transaminase concentration, and lists "Elevated transaminases" among its other names
  • GO:0007095 (1 mention) - the report calls it "mitotic G2/M checkpoint"; GO calls it mitotic G2 DNA damage checkpoint signaling, and lists "mitotic G2 DNA damage checkpoint" among its other names
  • UBERON:0002113 (1 mention) - the report calls it "Primary organ: kidney"; UBERON calls it kidney**, and lists "reniculate kidney" among its other names

Terms named inconsistently

The report gives these identifiers more than one name of its own:

  • MONDO:0011980 - called "karyomegalic interstitial nephritis", "MONDO (suggested)"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.