Progressive Familial Intrahepatic Cholestasis

Mendelian MONDO:0015762 Pathograph 55 Show in embeddings browser hereditary disease cholestatic liver disease

Progressive familial intrahepatic cholestasis (PFIC) is a genetically heterogeneous group of autosomal recessive disorders of hepatocanalicular bile formation that present in infancy or childhood with intrahepatic cholestasis of hepatocellular origin, intractable pruritus, jaundice, fat and fat-soluble vitamin malabsorption, growth failure, and progression to biliary fibrosis, cirrhosis and end-stage liver disease. The central diagnostic axis is the serum gamma-glutamyltransferase (GGT) split: PFIC1 (ATP8B1, encoding the FIC1 P4-ATPase aminophospholipid flippase) and PFIC2 (ABCB11, encoding the bile salt export pump BSEP) are low/normal-GGT diseases in which injury is confined to the hepatocyte, whereas PFIC3 (ABCB4, encoding the MDR3 phosphatidylcholine floppase) is a high-GGT cholangiopathy because bile salts that are not buffered into mixed micelles by biliary phosphatidylcholine attack the cholangiocyte apical membrane and release GGT. Newer forms include TJP2 (PFIC4), NR1H4/FXR (PFIC5), MYO5B (PFIC10) and the emerging USP53 (PFIC7), KIF12 (PFIC8) and ZFYVE19 (PFIC9) cholestases. Management has been transformed by ileal bile acid transporter (IBAT) inhibitors - odevixibat and maralixibat - which interrupt enterohepatic bile acid recirculation pharmacologically, complementing surgical biliary diversion and liver transplantation.

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Inheritance

Autosomal recessive inheritance HP:0000007

All established PFIC subtypes are caused by biallelic germline loss-of-function variants and segregate as autosomal recessive traits, with a 25% recurrence risk per pregnancy for carrier couples. Consanguinity is over-represented in reported cohorts. Monoallelic (heterozygous) ABCB4, ABCB11 and ATP8B1 variants are not causes of PFIC but predispose to milder adult cholestatic phenotypes such as intrahepatic cholestasis of pregnancy, low-phospholipid-associated cholelithiasis and drug-induced cholestasis.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:23141890 SUPPORT Human Clinical

"Progressive familial intrahepatic cholestasis (PFIC) refers to a heterogeneous group of autosomal-recessive disorders of childhood that disrupt bile formation and present with cholestasis of hepatocellular origin."

Establishes autosomal recessive inheritance for the PFIC group as a whole.

PMID:20301474 SUPPORT Human Clinical

"ATP8B1 deficiency is inherited in an autosomal recessive manner."

GeneReviews confirms autosomal recessive inheritance for the ATP8B1 (PFIC1) subtype.

◆

Subtypes

PFIC1 / ATP8B1 (FIC1) deficiency MONDO:0008892

ATP8B1 hgnc:3706

Biallelic ATP8B1 variants abolish the canalicular FIC1 aminophospholipid flippase. Low/normal-GGT cholestasis presents in the first months of life. Because FIC1 is broadly expressed outside the liver, PFIC1 is distinguished by extrahepatic features - secretory diarrhoea, pancreatic insufficiency, elevated sweat chloride, short stature and sensorineural hearing loss - none of which is corrected by liver transplantation.

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"

Defines the extrahepatic feature set that distinguishes FIC1 (PFIC1) disease.

PFIC2 / ABCB11 (BSEP) deficiency MONDO:0011156

ABCB11 hgnc:42

Biallelic ABCB11 variants abolish or impair the canalicular bile salt export pump. Low/normal-GGT cholestasis with early, severe pruritus and rapid progression; generally the most severe of the classical forms. PFIC2 uniquely carries a substantial risk of hepatobiliary malignancy in early childhood, highest with biallelic protein-truncating genotypes, and can recur functionally after transplant through alloantibodies against the BSEP extracellular loop.

Show evidence (1 reference)

PMID:18395098 SUPPORT Human Clinical

"Patients with severe bile salt export pump (BSEP) deficiency present as infants with progressive cholestatic liver disease."

Defines the PFIC2/BSEP-deficiency clinical entity and its ABCB11 genetic basis in the largest genotype series.

PFIC3 / ABCB4 (MDR3) deficiency MONDO:0011214

ABCB4 hgnc:45

Biallelic ABCB4 variants impair the MDR3 phosphatidylcholine floppase, so bile is phospholipid-poor. This is the one classical PFIC subtype with a HIGH serum GGT, because unbuffered bile salts injure the biliary epithelium. Onset is typically later than PFIC1/PFIC2 - late infancy through young adulthood - with portal fibrosis, bile duct proliferation and cholelithiasis, and it is the subtype most likely to respond to ursodeoxycholic acid.

Show evidence (1 reference)

PMID:20422496 SUPPORT Human Clinical

"Several ABCB4 mutations have been identified in children with PFIC3 and are associated with low level of phospholipids in bile leading to a high biliary cholesterol saturation index."

Links biallelic ABCB4 defects to PFIC3 and to the phospholipid-poor bile that defines the subtype.

PFIC4 / TJP2 (ZO-2) deficiency MONDO:0014381

TJP2 hgnc:11828

Biallelic protein-truncating TJP2 variants abolish the tight junction scaffold ZO-2, so claudin-1 fails to localize and the canalicular tight junction seal is lost, permitting paracellular reflux of detergent bile salts. Low/normal-GGT, often severe neonatal or early-infantile cholestasis with giant-cell transformation; hepatocellular carcinoma has been reported in infancy, so surveillance starts early.

Show evidence (1 reference)

PMID:24614073 SUPPORT Human Clinical

"Protein-truncating mutations in the tight junction protein 2 gene (TJP2) are shown to cause failure of protein localisation, with disruption of tight-junction structure leading to severe cholestatic liver disease."

Establishes biallelic TJP2 truncating variants as a cause of severe cholestatic liver disease through tight-junction failure.

PFIC5 / NR1H4 (FXR) deficiency MONDO:0014884

NR1H4 hgnc:7967

Biallelic NR1H4 variants abolish the nuclear bile acid receptor FXR, removing the transcriptional programme that induces BSEP and represses de novo bile acid synthesis. Extremely rare, low-to-normal GGT, neonatal onset with rapid progression to end-stage liver disease, a characteristic vitamin K-independent coagulopathy, markedly elevated alpha-fetoprotein and undetectable hepatic BSEP.

Show evidence (1 reference)

PMID:26888176 SUPPORT Human Clinical

"Clinical features of severe, persistent NR1H4-related cholestasis include neonatal onset with rapid progression to end-stage liver disease, vitamin K-independent coagulopathy, low-to-normal serum gamma-glutamyl transferase activity, elevated serum alpha-fetoprotein and undetectable liver..."

Defines the PFIC5/FXR-deficiency phenotype including its low-to-normal GGT and vitamin K-independent coagulopathy.

USP53-related low-GGT cholestasis (PFIC7) MONDO:0030503

USP53 hgnc:29255

Biallelic USP53 variants cause low-GGT cholestasis; USP53 co-localizes with the TJP2-associated tight junction complex, placing it mechanistically alongside PFIC4. Cholestasis tends to be biochemically milder and intermittent and to respond to medication, but liver fibrosis and splenomegaly are common on follow-up, so this is not a benign entity. The OMIM/MONDO series numbers this PFIC7 and notes that a subset of patients develop childhood-onset hearing loss - a second route to sensorineural deafness in PFIC distinct from the ATP8B1 mechanism. Subtype numbering for the newer genes is not standardized across the clinical literature, so gene-first naming is used here deliberately with the series number carried in `display_name` and `subtype_term`.

Show evidence (2 references)

PMID:33075013 SUPPORT Human Clinical

"We have now identified biallelic mutation in USP53 in 7 further patients with cholestasis, from 5 families."

Confirms biallelic USP53 mutation as a cause of childhood cholestasis in an independent multi-family series.

PMID:31183005 SUPPORT Human Clinical

"3 members of a family (2 sisters and a cousin) presented with low-ggt cholestasis, liver enzyme elevations, and pruritus"

Places USP53 disease explicitly on the low-GGT side of the diagnostic split, which is why USP53 is included in this entry's low-GGT gene lists and in the GGT triage rule. The USP53 primary report (PMID:33075013) does not itself state the GGT level.

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Pathophysiology

Canalicular Bile Formation Defect

The shared upstream lesion in every PFIC subtype is biallelic loss of a protein required for hepatocanalicular bile formation - a canalicular transporter (BSEP, MDR3), a membrane lipid flippase (FIC1), a tight junction scaffold (ZO-2), the nuclear bile acid receptor (FXR), or an apical trafficking motor (myosin Vb). The result in every case is failure of the hepatocyte to form and export normal bile. USP53, KIF12 and ZFYVE19 are listed here as well: they are established causes of PFIC-spectrum cholestasis but their proximate mechanisms are not yet resolved well enough to warrant separate downstream mechanism nodes, so this umbrella node is the only place they are wired into the pathograph.

hepatocyte CL:0000182

ATP8B1 hgnc:3706 ABCB11 hgnc:42 ABCB4 hgnc:45 TJP2 hgnc:11828 NR1H4 hgnc:7967 MYO5B hgnc:7603 USP53 hgnc:29255 KIF12 hgnc:21495 ZFYVE19 hgnc:20758

bile acid and bile salt transport GO:0015721 ↓ DECREASED

bile canaliculus UBERON:0001283

Downstream

FIC1 Flippase Loss and Canalicular Membrane Destabilization ATP8B1 loss removes the canalicular aminophospholipid flippase.

BSEP-Mediated Bile Salt Export Failure ABCB11 loss removes the canalicular bile salt export pump.

MDR3-Mediated Biliary Phospholipid Secretion Failure ABCB4 loss removes the canalicular phosphatidylcholine floppase.

Canalicular Tight Junction Failure and Paracellular Bile Reflux TJP2 loss destabilizes the tight junction seal around the canaliculus.

FXR Bile Acid Sensing and Transcriptional Failure NR1H4 loss removes the nuclear bile acid sensor governing BSEP expression.

Apical Trafficking Failure of Canalicular Transporters MYO5B loss prevents BSEP and MDR3 from reaching the canalicular membrane.

Show evidence (1 reference)

PMID:23141890 SUPPORT Human Clinical

"Three types of PFIC have been identified and associated with mutations in hepatocellular transport-system genes involved in bile formation."

Establishes defective hepatocellular bile-formation transport machinery as the shared upstream lesion.

FIC1 Flippase Loss and Canalicular Membrane Destabilization

ATP8B1 encodes FIC1, a P4-type ATPase that flips phosphatidylserine from the outer to the inner leaflet of the canalicular membrane. Loss of this inward translocation destroys membrane lipid asymmetry and leaves the canalicular membrane abnormally susceptible to the detergent action of luminal bile salts, impairing bile formation. Because FIC1 is also expressed in intestine, pancreas and cochlea, its loss produces extrahepatic disease that liver replacement cannot correct.

hepatocyte CL:0000182

ATP8B1 hgnc:3706

aminophospholipid translocation GO:0140331 ↓ DECREASED

Downstream

Hepatocellular Bile Salt Retention Destabilized canalicular membrane and impaired bile formation lead to intracellular bile salt retention without primary cholangiocyte injury, preserving a low/normal GGT.

Extrahepatic FIC1 Deficiency The same flippase loss in intestine, pancreas and inner ear produces disease outside the liver.

Show evidence (2 references)

PMID:19731236 SUPPORT In Vitro

"ATP8B1 localizes to the canalicular membrane of hepatocytes where it mediates the inward translocation of phosphatidylserine."

Establishes the molecular function of FIC1 as an inward-directed canalicular phosphatidylserine flippase.

PMID:23141890 SUPPORT Human Clinical

"Both PFIC1 and PFIC2 are caused by impaired bile salt secretion due to defects in ATP8B1 encoding the FIC1 protein and in ABCB11 encoding bile salt export pump (BSEP) protein, respectively."

Attributes impaired bile salt secretion in PFIC1 to ATP8B1/FIC1 loss.

BSEP-Mediated Bile Salt Export Failure

ABCB11 encodes BSEP, the ATP-dependent canalicular pump that performs the rate-limiting step of bile salt secretion into the canaliculus. Biallelic loss blocks bile salt export at the apical hepatocyte membrane. Severity tracks residual protein: the recurrent p.Glu297Gly and p.Asp482Gly alleles retain detectable BSEP in a substantial minority of patients, while biallelic protein-truncating genotypes leave none and are the most severe. Because the cholangiocyte is not the primary target, serum GGT remains low or normal.

hepatocyte CL:0000182

ABCB11 hgnc:42

canalicular bile acid transport GO:0015722 ↓ DECREASED

canalicular bile acid transmembrane transporter activity GO:0015126 ↓ DECREASED

Downstream

Hepatocellular Bile Salt Retention Blocked canalicular export traps bile salts inside the hepatocyte.

Hepatocarcinogenesis in BSEP and TJP2 Deficiency Sustained hepatocyte bile salt exposure and regenerative pressure confer an early hepatobiliary malignancy risk that is specific to severe BSEP deficiency.

Show evidence (2 references)

PMID:18395098 SUPPORT Human Clinical

"Expression varied most for E297G and D482G, with some BSEP detected in 45% of patients (19/42) with these mutations."

Documents the residual-protein gradient across ABCB11 genotypes that underlies the severity spectrum.

PMID:31183005 SUPPORT Human Clinical

"This defect results in a severe hepatobiliary phenotype due to impairment of bile salt handling and subsequent damage to hepatocytes"

Links BSEP loss to impaired bile salt handling and hepatocyte damage.

MDR3-Mediated Biliary Phospholipid Secretion Failure

ABCB4 encodes MDR3, the canalicular floppase that translocates phosphatidylcholine into the outer leaflet of the canalicular membrane for extraction into bile. Biallelic loss makes bile phospholipid-poor. Because phosphatidylcholine is what sequesters bile salts into mixed micelles, its absence leaves free, monomeric bile salts at detergent concentrations in the biliary tree - the mechanistic reason PFIC3 behaves as a cholangiopathy rather than a purely hepatocellular disease, and consequently the reason its serum GGT is high.

hepatocyte CL:0000182

ABCB4 hgnc:45

phospholipid translocation GO:0045332 ↓ DECREASED

phosphatidylcholine floppase activity GO:0090554 ↓ DECREASED

Downstream

Unbuffered Bile Salt Injury to the Cholangiocyte Phospholipid-poor bile cannot form protective mixed micelles, exposing the biliary epithelium to free detergent bile salts.

Biliary Cholesterol Supersaturation Loss of the phospholipid component raises the biliary cholesterol saturation index and promotes intraductal stone formation.

Show evidence (2 references)

PMID:20422496 SUPPORT Human Clinical

"Class III multidrug resistance P-glycoproteins, Mdr2 in mice and MDR3 in human, are canalicular phospholipid translocators involved in biliary phospholipid (phosphatidylcholine) excretion."

Establishes MDR3 as the canalicular phosphatidylcholine translocator whose loss causes PFIC3.

PMID:23141890 SUPPORT Human Clinical

"Defects in ABCB4, encoding multidrug resistance 3 protein (MDR3), impair biliary phospholipid secretion, resulting in PFIC3."

Directly attributes impaired biliary phospholipid secretion to ABCB4/MDR3 loss in PFIC3.

Unbuffered Bile Salt Injury to the Cholangiocyte

This node is the mechanistic pivot of the GGT split. In health, biliary phosphatidylcholine sequesters bile salts into mixed micelles that are non-toxic to the biliary epithelium. When MDR3 is absent (and in the newer high-GGT forms KIF12 and ZFYVE19), free bile salts strip the cholangiocyte apical membrane, on which gamma-glutamyltransferase is a GPI-anchored ectoenzyme; membrane damage releases GGT into bile and serum. In the low-GGT subtypes (ATP8B1, ABCB11, TJP2, NR1H4, USP53, MYO5B) the cholangiocyte is not the primary target, biliary GGT is not shed, and serum GGT stays low or normal despite profound cholestasis. Cholangiocyte injury also drives the ductular reaction, portal fibrosis and bile duct proliferation seen on PFIC3 biopsy.

intrahepatic cholangiocyte CL:0002538

Downstream

Elevated serum gamma-glutamyltransferase Cholangiocyte apical membrane damage releases the GPI-anchored ectoenzyme GGT, producing the high-GGT biochemical signature of ABCB4 disease.

Hepatic Stellate Cell Activation and Biliary Fibrosis Cholangiocyte injury drives a ductular reaction and periportal fibrogenesis.

Show evidence (2 references)

PMID:31183005 SUPPORT Human Clinical

"Without phosphatidylcholine to neutralize bile acids, the imbalance of free bile acids damages cholangiocytes, and cholesterol crystallizes into liver-damaging stones"

States the mechanism by which loss of biliary phosphatidylcholine converts PFIC3 into a cholangiocyte-injuring cholangiopathy.

PMID:23141890 SUPPORT Human Clinical

"Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and PFIC2 patients, but is elevated in PFIC3 patients."

The clinical read-out of this node - the GGT split that separates PFIC3 from PFIC1/PFIC2.

Canalicular Tight Junction Failure and Paracellular Bile Reflux

TJP2 (ZO-2) is a cytosolic scaffold that anchors claudins at the tight junctions sealing the bile canaliculus. Biallelic protein-truncating TJP2 variants abolish the protein; claudin-1 is expressed at normal levels but fails to localize to the junction, and tight junctions appear elongated and lose their densest zonula occludens material. The seal that normally confines detergent bile salts to the canalicular lumen is lost, permitting paracellular reflux of toxic bile constituents into the hepatocyte and the space of Disse.

hepatocyte CL:0000182

TJP2 hgnc:11828

tight junction assembly GO:0120192 ↓ DECREASED

bicellular tight junction GO:0005923

Downstream

Hepatocellular Bile Salt Retention Paracellular reflux returns secreted bile salts to the hepatocyte compartment.

Hepatocarcinogenesis in BSEP and TJP2 Deficiency TJP2 deficiency carries a reported hepatocellular carcinoma risk presenting as early as infancy.

Show evidence (2 references)

PMID:24614073 SUPPORT Human Clinical

"In the unusually hostile environment of the canalicular and cholangiocytic membranes, exposed as these are to high concentrations of detergent bile acids, expression of TJP2 may be essential for hepatobiliary integrity"

Articulates why loss of TJP2 is tolerated outside the liver but catastrophic at the bile-salt-exposed canalicular junction.

PMID:31183005 SUPPORT Human Clinical

"The mechanism of injury is thought to relate to TJP2’s function maintaining junction integrity, the disturbance of which enables toxic molecules to reflux into the paracellular space"

States the paracellular-reflux mechanism, explicitly flagged in the source as not yet clearly established - hence PARTIAL.

FXR Bile Acid Sensing and Transcriptional Failure

NR1H4 encodes the farnesoid X receptor, the bile-acid-activated nuclear receptor that senses the hepatocyte bile acid load and responds by inducing ABCB11/BSEP and repressing de novo bile acid synthesis. Biallelic NR1H4 loss removes both arms of this feedback loop, producing an unregulated bile acid burden together with undetectable hepatic BSEP - a transcriptional phenocopy of BSEP deficiency layered on failure to restrain bile acid synthesis.

hepatocyte CL:0000182

NR1H4 hgnc:7967

nuclear receptor-mediated bile acid signaling pathway GO:0038185 ∅ ABSENT negative regulation of bile acid biosynthetic process GO:0070858 ↓ DECREASED

Downstream

Hepatocellular Bile Salt Retention Loss of BSEP induction plus loss of synthesis repression drives an unopposed hepatocyte bile salt load.

Elevated circulating alpha-fetoprotein concentration FXR deficiency is accompanied by markedly raised serum alpha-fetoprotein, reported as a characteristic feature of the NR1H4 phenotype; the mechanism linking loss of the receptor to AFP derepression is not established.

Show evidence (2 references)

PMID:26888176 SUPPORT Human Clinical

"mutations in NR1H4, which encodes the farnesoid X receptor (FXR), a bile acid-activated nuclear hormone receptor that regulates bile acid metabolism"

Identifies FXR as the bile-acid-activated nuclear receptor whose biallelic loss causes PFIC5.

PMID:31183005 SUPPORT Human Clinical

"the FXR, the nuclear receptor transcription factor which regulates BSEP expression via negative feedback loop and induces FGF19 to repress bile acid synthesis"

Specifies the two transcriptional arms - BSEP induction and bile acid synthesis repression - lost in FXR deficiency.

Apical Trafficking Failure of Canalicular Transporters

MYO5B (myosin Vb) drives Rab11-dependent recycling-endosome delivery of apical cargo. Biallelic loss leaves BSEP and MDR3 synthesized but mislocalized away from the canalicular membrane - immunostaining shows the transporters are present but abnormally distributed. The functional consequence is the same low-GGT bile salt export failure as in PFIC2, reached by a trafficking rather than a transporter lesion. Because MYO5B governs polarity in all epithelia, the same defect can produce microvillus inclusion disease in the gut.

hepatocyte CL:0000182

MYO5B hgnc:7603

establishment of epithelial cell polarity GO:0090162 ⚠ ABNORMAL

recycling endosome GO:0055037

Downstream

Hepatocellular Bile Salt Retention Mislocalized BSEP cannot export bile salts, reproducing the PFIC2 biochemical phenotype.

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Present but abnormal BSEP and MDR3 staining suggest that these transporters are made but can’t appropriately migrate to the canalicular membrane"

Direct histological evidence that the MYO5B lesion is one of transporter trafficking rather than transporter absence.

Hepatocellular Bile Salt Retention

The convergent node of the low-GGT PFIC subtypes. Whatever the upstream lesion, detergent bile salts accumulate inside the hepatocyte and spill into the systemic circulation. Intracellular bile salts are membrane-active and mitochondriotoxic, driving oxidative stress, hepatocyte apoptosis and necrosis and an inflammatory response; the circulating fraction produces pruritus and the raised serum bile acid concentration that is the field's principal pharmacodynamic and prognostic biomarker.

hepatocyte CL:0000182

bile acid secretion GO:0032782 ↓ DECREASED

Downstream

Intrahepatic cholestasis Failure of bile salt secretion is intrahepatic cholestasis at the clinical level.

Increased serum bile acid concentration Retained bile salts spill into the systemic circulation.

Systemic Bile Acid Load and Pruritogenesis Circulating bile salts and co-retained pruritogens drive itch.

Hepatic Stellate Cell Activation and Biliary Fibrosis Chronic bile-salt-mediated hepatocyte injury and inflammation activate the hepatic fibrogenic programme.

Reduced Intestinal Bile Acid Delivery and Fat Malabsorption Bile salts retained in the hepatocyte never reach the intestinal lumen, so micellar fat solubilization fails.

Conjugated hyperbilirubinemia Failure of canalicular secretion retains already-conjugated bilirubin in the hepatocyte and refluxes it into plasma, raising the direct fraction.

Jaundice Cholestasis retains conjugated bilirubin alongside bile salts.

Hepatomegaly Cholestatic hepatocyte swelling and hepatocellular disarray enlarge the liver.

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Without appropriate BSEP localization, secretion of bile acids is impaired and causes hepatocellular toxicity"

States that impaired bile acid secretion is directly hepatotoxic to the hepatocyte.

Enterohepatic Bile Acid Recirculation

Roughly 95% of secreted bile acids are reclaimed from the terminal ileum by the apical sodium-dependent ileal bile acid transporter (IBAT/ASBT, SLC10A2) and returned to the liver in the portal blood. In PFIC this recycling loop continuously re-delivers a bile acid load that the diseased hepatocyte cannot handle, sustaining hepatocellular bile salt retention - so within the pathograph it acts as an amplifier of the central effector node. That also makes it the single most exploitable therapeutic node in PFIC: interrupting it - surgically by partial external or internal biliary diversion or ileal exclusion, or pharmacologically by IBAT inhibition with odevixibat or maralixibat - diverts bile acids into the faeces, lowers serum bile acids, and relieves pruritus. Response is genotype-dependent: reducing enterohepatic return cannot help when canalicular export is completely absent, so patients with complete BSEP loss respond poorly.

enterocyte CL:0000584

SLC10A2 hgnc:10906

bile acid and bile salt transport GO:0015721 ↑ INCREASED

ileum UBERON:0002116

Downstream

Hepatocellular Bile Salt Retention Portal re-delivery of reclaimed bile acids perpetuates the hepatocyte bile salt burden.

Show evidence (2 references)

PMID:35780807 SUPPORT Human Clinical

"Odevixibat, administered as once a day oral capsules, is a non-surgical, pharmacological option to interrupt the enterohepatic circulation in patients with PFIC."

Identifies interruption of enterohepatic bile acid circulation as the therapeutic target exploited by IBAT inhibition.

PMID:20301474 SUPPORT Human Clinical

"the primary surgical therapy is interruption of the enterohepatic circulation which can reduce pruritus and slow or reverse the progression to hepatic fibrosis"

Confirms that interrupting this loop is disease-modifying, not merely symptomatic.

Systemic Bile Acid Load and Pruritogenesis

Cholestasis raises circulating bile acids and other retained pruritogens, producing the intractable itch that is the dominant symptom burden of PFIC. Pruritus in PFIC is severe enough to cause skin mutilation and profound sleep disruption and is a stand-alone indication for biliary diversion or transplantation independent of liver synthetic function. Serum bile acid concentration serves as the pharmacodynamic surrogate for this node in trials.

Downstream

Pruritus Circulating pruritogens produce the clinical symptom.

Show evidence (1 reference)

PMID:38723644 SUPPORT Human Clinical

"Progressive familial intrahepatic cholestasis (PFIC) is a group of autosomal recessive disorders, the most prevalent being BSEP deficiency, resulting in disrupted bile formation, cholestasis, and pruritus."

Places pruritus as a direct consequence of disrupted bile formation and cholestasis.

Reduced Intestinal Bile Acid Delivery and Fat Malabsorption

Bile that never reaches the duodenum cannot form the mixed micelles needed to solubilize dietary long-chain triglyceride and the fat-soluble vitamins A, D, E and K. The result is steatorrhoea, energy deficit despite adequate intake, growth failure and short stature, and fat-soluble vitamin deficiency with rickets and coagulopathy. This is why nutritional management uses medium-chain triglyceride formulas, which are absorbed without micellar solubilization, alongside aggressive fat-soluble vitamin replacement.

small intestine UBERON:0002108

Downstream

Failure to thrive Energy and fat malabsorption produce growth failure.

Steatorrhea Unabsorbed dietary fat is passed in the stool.

Short stature Chronic malnutrition and chronic liver disease limit linear growth.

Vitamin K-responsive coagulopathy Fat-soluble vitamin K malabsorption impairs synthesis of the vitamin K-dependent clotting factors.

Show evidence (2 references)

PMID:20301474 SUPPORT Human Clinical

"Poor growth may require medium-chain triglyceride-based formulas; fat-soluble vitamin deficiencies are treated symptomatically."

GeneReviews links poor growth and fat-soluble vitamin deficiency to the malabsorptive consequence of cholestasis and specifies MCT-based management.

PMID:31183005 SUPPORT Human Clinical

"poor growth due to fat malabsorption and fat-soluble vitamin deficiency"

Explicitly attributes growth failure in PFIC to fat malabsorption and fat-soluble vitamin deficiency.

Hepatic Stellate Cell Activation and Biliary Fibrosis

Sustained bile-salt-mediated hepatocyte injury (low-GGT subtypes) and cholangiocyte injury with ductular reaction (high-GGT subtypes) both converge on activation of hepatic stellate cells into collagen-secreting myofibroblasts. Progressive portal and lobular fibrosis becomes biliary cirrhosis with portal hypertension and synthetic failure, typically before adulthood in untreated disease. Fibrosis may be present early even in phenotypically mild ATP8B1 disease, which is why the historical assumption that intermittent cholestasis is non-fibrotic has been abandoned.

hepatic stellate cell CL:0000632

extracellular matrix organization GO:0030198 ↑ INCREASED

Downstream

Cirrhosis Progressive matrix deposition produces biliary cirrhosis.

Portal hypertension Architectural distortion raises portal pressure.

Splenomegaly Portal hypertension produces congestive splenomegaly.

Hepatic failure Loss of functioning parenchyma produces synthetic failure.

Show evidence (2 references)

PMID:23141890 SUPPORT Human Clinical

"PFIC patients usually develop fibrosis and end-stage liver disease before adulthood."

Establishes progressive fibrosis to end-stage liver disease as the natural history of untreated PFIC.

PMID:20301474 SUPPORT Human Clinical

"Although mild-to-moderate ATP8B1 deficiency initially was thought to involve intermittent symptomatic cholestasis with a lack of hepatic fibrosis, it is now known that hepatic fibrosis may be present early in the disease course."

Documents that fibrosis occurs even at the mild end of the ATP8B1 spectrum, refuting the older non-fibrotic assumption.

Hepatocarcinogenesis in BSEP and TJP2 Deficiency

Severe BSEP deficiency and TJP2 deficiency carry a subtype-specific risk of hepatobiliary malignancy - hepatocellular carcinoma and cholangiocarcinoma - presenting in early childhood, in some cases before age two. Risk is genotype-stratified in ABCB11 disease: biallelic protein-truncating genotypes carry roughly a fourfold higher malignancy risk than potentially less severe genotypes. This is a genuine mechanistic distinction from PFIC1, in which tumour development is not a recognised association, and it drives the recommendation for tumour surveillance from the first year of life.

hepatocyte CL:0000182

Downstream

Hepatocellular carcinoma Malignant transformation of the chronically injured hepatocyte.

Show evidence (2 references)

PMID:16871584 SUPPORT Human Clinical

"PFIC associated with BSEP deficiency represents a previously unrecognized risk for HCC in young children."

The landmark series establishing hepatocellular carcinoma risk in early childhood BSEP deficiency.

PMID:18395098 SUPPORT Human Clinical

"Two protein-truncating mutations conferred particular risk; 38% (8/21) of such patients developed malignancy versus 10% (11/107) with potentially less severe genotypes"

Quantifies the genotype stratification of malignancy risk within ABCB11 disease.

Biliary Cholesterol Supersaturation

In ABCB4/MDR3 disease the phospholipid-poor bile has a high cholesterol saturation index, so cholesterol crystallizes and forms intraductal and gallbladder stones. This underlies the low-phospholipid-associated cholelithiasis phenotype seen in biallelic PFIC3 and in monoallelic ABCB4 carriers.

Downstream

Cholelithiasis Cholesterol crystallization in phospholipid-poor bile produces stones.

Show evidence (1 reference)

PMID:20422496 SUPPORT Human Clinical

"There is evidence that a biallelic or monoallelic ABCB4 defect causes or predisposes to several human liver diseases (PFIC3, low phospholipid associated cholelithiasis syndrome, intrahepatic cholestasis of pregnancy, drug-induced liver injury, transient neonatal cholestasis, adult biliary..."

Establishes low-phospholipid-associated cholelithiasis as part of the ABCB4 disease spectrum.

Extrahepatic FIC1 Deficiency

ATP8B1 is expressed well beyond the hepatocyte, so PFIC1 alone among the classical subtypes has an extrahepatic disease burden: secretory diarrhoea, exocrine pancreatic insufficiency, elevated sweat chloride, short stature and sensorineural hearing loss. This is clinically decisive because liver transplantation replaces only the hepatic compartment: the diarrhoea persists or worsens after transplant and is associated with allograft steatosis and fibrosis that can require re-transplantation, and audiological surveillance must continue lifelong regardless of hepatic outcome.

Downstream

Chronic diarrhea Loss of FIC1 in the intestinal epithelium produces secretory diarrhoea.

Sensorineural hearing impairment Loss of FIC1 in the cochlea produces sensorineural hearing loss.

Exocrine pancreatic insufficiency Loss of FIC1 in the pancreas impairs exocrine secretion.

Show evidence (2 references)

PMID:31183005 SUPPORT Human Clinical

"Extrahepatic disease is also notable due to the broad distribution of FIC1, which can clinically distinguish FIC1 deficiency from other forms of intrahepatic cholestasis."

Attributes the extrahepatic burden of PFIC1 to the wide tissue distribution of FIC1.

PMID:20301474 SUPPORT Human Clinical

"Notably for some, secretory diarrhea can continue or worsen following liver transplantation."

GeneReviews documents that transplantation does not correct - and may worsen - the extrahepatic diarrhoea of ATP8B1 deficiency.

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Histopathology

Canalicular cholestasis with coarse granular Byler bile

In ATP8B1 deficiency, canalicular cholestasis with biliary plugs, giant cell transformation, ductular paucity and lobular disarray; the canalicular bile has a characteristic coarse, granular appearance historically termed Byler bile. In ABCB11 disease the pattern is canalicular cholestasis with hepatocellular disarray and lobular and portal fibrosis. TJP2 and NR1H4 disease show intracellular cholestasis with giant cell transformation.

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Histopathology demonstrates canalicular cholestasis with biliary plugs, giant cell transformation, ductular paucity, and lobular disarray"

Describes the histological pattern of FIC1 deficiency including the Byler bile appearance.

Portal fibrosis with bile duct proliferation

In ABCB4/MDR3 deficiency the histology is that of a cholangiopathy rather than a purely hepatocellular disease - portal fibrosis and bile duct proliferation with mild giant cell hepatitis at onset, and occasional intraductal cholelithiasis. This ductular pattern is the tissue counterpart of the high serum GGT.

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Histology typically demonstrates portal fibrosis and bile duct proliferation with mild giant cell hepatitis at disease onset with occasional intraductal cholelithiasis"

Documents the biliary/ductular histological pattern that distinguishes PFIC3 from the hepatocellular subtypes.

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Pathograph

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Phenotypes

Cardiovascular 2

Splenomegaly FREQUENT HP:0001744

Show evidence (1 reference)

PMID:33075013 SUPPORT Human Clinical

"splenomegaly was apparent in 5 of 7 at last ultrasound"

A directly quantitative count (5/7, 71%) in the USP53 series maps to the FREQUENT band (30-79%).

Portal hypertension FREQUENT HP:0001409

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"A retrospective review of 38 patients found that those diagnosed in childhood presented with pruritis around 1 year of age and most had hepatosplenomegaly, portal hypertension, and jaundice at the time of presentation"

The statement that most of a 38-patient series had portal hypertension at presentation maps to the FREQUENT band.

Digestive 9

Jaundice VERY_FREQUENT HP:0000952

Show evidence (2 references)

PMID:23141890 SUPPORT Human Clinical

"The main clinical manifestations include cholestasis, pruritus and jaundice."

Lists jaundice as one of the three main clinical manifestations of PFIC.

PMID:31183005 SUPPORT Human Clinical

"Infants often present jaundiced, with pruritis and hepatosplenomegaly developing over the first months of life."

Supports jaundice as the usual presenting sign, consistent with the VERY_FREQUENT band.

Hepatomegaly FREQUENT HP:0002240

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Scleral icterus, hepatomegaly, excoriation of skin, and poor growth due to fat malabsorption and fat-soluble vitamin deficiency may also be apparent due to cholestasis"

Lists hepatomegaly among the manifestations apparent in BSEP deficiency; the qualitative phrasing maps to the FREQUENT band.

Cirrhosis FREQUENT HP:0001394

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:20301474 SUPPORT Human Clinical

"Severe ATP8B1 deficiency is characterized by infantile-onset cholestasis that progresses to cirrhosis, hepatic failure, and early death."

GeneReviews states progression to cirrhosis as characteristic of severe ATP8B1 disease.

Hepatic failure FREQUENT HP:0001399

Show evidence (2 references)

PMID:20301474 SUPPORT Human Clinical

"Severe ATP8B1 deficiency is characterized by infantile-onset cholestasis that progresses to cirrhosis, hepatic failure, and early death."

GeneReviews lists hepatic failure as a characteristic outcome of severe ATP8B1 deficiency.

PMID:26888176 SUPPORT Human Clinical

"neonatal onset with rapid progression to end-stage liver disease"

Documents rapid progression to end-stage liver disease in the NR1H4/PFIC5 subtype.

Steatorrhea HP:0002570

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"poor growth due to fat malabsorption and fat-soluble vitamin deficiency"

Documents fat malabsorption, of which steatorrhoea is the direct clinical expression; PARTIAL because the source names fat malabsorption rather than steatorrhoea explicitly. Frequency deliberately omitted.

Chronic diarrhea FREQUENT HP:0002028

Show evidence (2 references)

PMID:31183005 SUPPORT Human Clinical

"Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"

The phrase "frequently exhibit profound diarrhea" in FIC1 deficiency maps to the FREQUENT band.

PMID:20301474 SUPPORT Human Clinical

"Notably for some, secretory diarrhea can continue or worsen following liver transplantation."

Confirms the secretory character of the diarrhoea and its persistence after transplant.

Exocrine pancreatic insufficiency FREQUENT HP:0001738

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"

The phrase "frequently exhibit" applied to pancreatic insufficiency in FIC1 deficiency maps to the FREQUENT band.

Hepatocellular carcinoma OCCASIONAL HP:0001402

Show evidence (2 references)

PMID:18395098 SUPPORT Human Clinical

"Hepatocellular carcinoma or cholangiocarcinoma developed in 15% of patients (19/128)."

A directly quantitative 15% (19/128) in BSEP deficiency maps to the OCCASIONAL band (5-29%).

PMID:16871584 SUPPORT Human Clinical

"Among the 11 nonrelated children studied aged 13-52 months at diagnosis of HCC"

Documents the strikingly early age at HCC diagnosis (13-52 months) in BSEP deficiency.

Cholelithiasis HP:0001081

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Histology typically demonstrates portal fibrosis and bile duct proliferation with mild giant cell hepatitis at disease onset with occasional intraductal cholelithiasis"

Documents intraductal cholelithiasis in ABCB4 disease. Frequency deliberately omitted because the source qualifier describes histological findings rather than a cohort proportion.

Ear 1

Sensorineural hearing impairment FREQUENT HP:0000407

Show evidence (1 reference)

PMID:20301474 SUPPORT Human Clinical

"Sensorineural hearing loss (SNHL) is common across the phenotypic spectrum."

GeneReviews describes SNHL as common in ATP8B1 deficiency, which maps to the FREQUENT band (30-79%).

Integument 1

Pruritus VERY_FREQUENT HP:0000989

Show evidence (2 references)

PMID:23141890 SUPPORT Human Clinical

"The main clinical manifestations include cholestasis, pruritus and jaundice."

Lists pruritus as one of the three main clinical manifestations of PFIC.

PMID:38723644 SUPPORT Human Clinical

"We recruited participants aged 1-17 years with PFIC with persistent pruritus"

A phase 3 trial that recruited 93 children on the basis of persistent pruritus of more than 6 months' duration supports the VERY_FREQUENT and SEVERE qualifiers.

Metabolism 1

Elevated circulating alpha-fetoprotein concentration HP:0006254

Show evidence (1 reference)

PMID:26888176 SUPPORT Human Clinical

"elevated serum alpha-fetoprotein and undetectable liver bile salt export pump (ABCB11) expression"

Establishes elevated serum AFP as a defining feature of NR1H4-related cholestasis.

Growth 2

Failure to thrive FREQUENT HP:0001508

Show evidence (2 references)

PMID:20301474 SUPPORT Human Clinical

"Poor growth may require medium-chain triglyceride-based formulas"

GeneReviews documents poor growth as a routine management problem in ATP8B1 deficiency.

PMID:31183005 SUPPORT Human Clinical

"Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"

The phrase "frequently exhibit" applied to poor growth maps to the FREQUENT band.

Short stature OCCASIONAL HP:0004322

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Similarly, some patients also suffer short stature, though others have normal growth."

The qualifier "some patients" maps to the OCCASIONAL band (5-29%).

Other 5

Intrahepatic cholestasis OBLIGATE HP:0001406

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:23141890 SUPPORT Human Clinical

Defines cholestasis of hepatocellular origin as the obligate manifestation of the PFIC group. The OBLIGATE frequency band follows directly from this definitional statement.

Conjugated hyperbilirubinemia VERY_FREQUENT HP:0002908

Show evidence (2 references)

PMID:31183005 SUPPORT Human Clinical

"Affected individuals have hyperbilirubinemia, mildly elevated transaminases, and elevated serum bile acids."

PFIC-specific documentation of hyperbilirubinaemia; PARTIAL because the source does not itself specify the conjugated fraction, which the companion evidence item supplies.

PMID:32861449 SUPPORT Human Clinical

"Neonatal cholestasis is characterized by conjugated hyperbilirubinemia in the newborn and young infant"

Establishes that the hyperbilirubinaemia of neonatal/infantile cholestasis, of which PFIC is one cause, is specifically conjugated.

Increased serum bile acid concentration VERY_FREQUENT HP:0012202

Show evidence (1 reference)

PMID:38723644 SUPPORT Human Clinical

"Least-squares mean change from baseline in total serum bile acids was -176 μmol/L (95% CI -257 to -94) for maralixibat versus 11 μmol/L (-58 to 80) for placebo"

A treatment-induced fall of 176 micromol/L implies markedly elevated baseline serum bile acids across the trial population, supporting the VERY_FREQUENT band.

Elevated serum gamma-glutamyltransferase Elevated gamma-glutamyltransferase level HP:0030948

Show evidence (2 references)

PMID:23141890 SUPPORT Human Clinical

"Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and PFIC2 patients, but is elevated in PFIC3 patients."

The definitive statement of the GGT split across the classical PFIC subtypes.

PMID:31183005 SUPPORT Human Clinical

"GGT is typically elevated at presentation, with relatively milder elevation of transaminases and bilirubin"

Confirms that elevated GGT is the typical presenting biochemistry of ABCB4/PFIC3 disease.

Vitamin K-responsive coagulopathy Prolonged prothrombin time HP:0008151

Show evidence (2 references)

PMID:20301474 SUPPORT Human Clinical

"fat-soluble vitamin deficiencies are treated symptomatically."

GeneReviews documents fat-soluble vitamin deficiency requiring treatment; vitamin K deficiency is its coagulation manifestation. PARTIAL because the source does not name prothrombin time. Frequency deliberately omitted.

PMID:26888176 SUPPORT Human Clinical

Establishes the contrasting vitamin K-INDEPENDENT coagulopathy specific to PFIC5, the distinction drawn in this entry's description.

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Genetic Associations

ATP8B1

Gene: ATP8B1 hgnc:3706 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:19731236 SUPPORT In Vitro

"Our data indicate that PFIC1 mutations lead to the complete absence of canalicular expression, whereas in BRIC1/ICP residual protein is expressed in the canalicular membrane."

Provides the molecular basis for the PFIC1-versus-BRIC1 severity distinction within the same gene.

ABCB11

Gene: ABCB11 hgnc:42 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:18395098 SUPPORT Human Clinical

"Thirty-two percent of mutations occurred in >1 family, with E297G and/or D482G present in 58% of European families (52/89)."

Quantifies the recurrent-allele structure of ABCB11 disease in European families.

ABCB4

Gene: ABCB4 hgnc:45 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Of the described defects in MDR3, the majority are missense mutations that result in defective processing or intracellular transport; while the minority have completely absent MDR3 expression secondary to early truncation or destruction of the protein"

Characterizes the variant class distribution in ABCB4 disease.

TJP2

Gene: TJP2 hgnc:11828 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:24614073 SUPPORT Human Clinical

"In contrast, the mutations identified in the patients presented here are predicted to abolish translation of both isoforms ofTJP2."

Establishes that PFIC4 requires complete loss of both TJP2 isoforms, distinguishing it from the milder Amish missense allele.

NR1H4

Gene: NR1H4 hgnc:7967 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:26888176 SUPPORT Human Clinical

"Here we report four individuals from two unrelated families with neonatal cholestasis and mutations in NR1H4"

The original report establishing NR1H4 as a PFIC gene and documenting its extreme rarity.

MYO5B

Gene: MYO5B hgnc:7603 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:27532546 SUPPORT Human Clinical

"Using a new-generation sequencing approach, we identified MYO5B mutations in five patients with progressive familial intrahepatic cholestasis-like phenotype with normal serum gamma-glutamyl transferase activity without intestinal disease."

Establishes isolated hepatic MYO5B disease without intestinal involvement.

USP53

Gene: USP53 hgnc:29255 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Defects in the USP53 protein, thought to colocalize with TJP2 and be part of the tight junction complex"

Places USP53 within the TJP2 tight junction complex, explaining its low-GGT phenotype.

KIF12

Gene: KIF12 hgnc:21495 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:30976738 SUPPORT Human Clinical

"Both children had a rare homozygous damaging mutation (p.Arg219* and p.Val204Met) in kinesin family member 12 (KIF12)."

Documents the specific homozygous KIF12 variants causing high-GGT cholestasis.

ZFYVE19

Gene: ZFYVE19 hgnc:20758 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:33853651 SUPPORT Human Clinical

"Further sequencing investigation revealed a homozygous non-sense mutation (p.Arg223Ter) in ZFYVE19 leading to a 222 aa truncated protein and present in both heterozygous parents."

Documents the specific homozygous ZFYVE19 variant with parental segregation.

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Medical Actions

Odevixibat

Action: Pharmacotherapy NCIT:C15986

Agent: odevixibat NCIT:C166598

Once-daily oral inhibitor of the ileal bile acid transporter (IBAT/ASBT, SLC10A2) that blocks reabsorption of bile acids in the terminal ileum, diverting them into the faeces and lowering the bile acid load returned to the liver - a pharmacological equivalent of surgical biliary diversion. In the PEDFIC 1 phase 3 trial in PFIC1 and PFIC2, odevixibat significantly improved pruritus (55% vs 30% positive pruritus assessments) and serum bile acid response (33% vs 0%). Approved in 2021 in the EU for PFIC and in the US for PFIC-associated pruritus. Response is genotype-dependent - patients with complete loss of BSEP protein do not respond consistently, because reducing enterohepatic return cannot compensate for absent canalicular export. Diarrhoea and frequent bowel movements are the characteristic class effect, reported in 31% of odevixibat-treated versus 10% of placebo-treated patients in PEDFIC 1.

Mechanism Target:

INHIBITS Enterohepatic Bile Acid Recirculation — Blocks IBAT-mediated ileal reclamation of bile acids, interrupting the loop that re-delivers the bile acid load to the diseased liver.

Show evidence (1 reference)

PMID:35780807 SUPPORT Human Clinical

"Odevixibat, administered as once a day oral capsules, is a non-surgical, pharmacological option to interrupt the enterohepatic circulation in patients with PFIC."

States the mechanism of action as interruption of the enterohepatic circulation.

Target Phenotypes: Pruritus HP:0000989 Increased serum bile acid concentration HP:0012202

Show evidence (3 references)

PMID:35780807 SUPPORT Human Clinical

"In children with PFIC, odevixibat effectively reduced pruritus and serum bile acids versus placebo and was generally well tolerated."

Randomised placebo-controlled phase 3 evidence of efficacy on both co-primary endpoints.

PMID:35780807 SUPPORT Human Clinical

"The most common treatment-emergent adverse events (TEAEs) were diarrhoea or frequent bowel movements"

Identifies the characteristic diarrhoeal class effect of IBAT inhibition; the trial reported it in 13 of 42 odevixibat-treated versus 2 of 20 placebo-treated patients.

PMID:39768432 SUPPORT Human Clinical

"Two siblings with complete loss of bile salt export pump (BSEP) protein did not respond to treatment; both underwent liver transplantation"

Real-world evidence of the genotype limit on IBAT inhibitor efficacy - complete BSEP loss predicts non-response. PARTIAL because it qualifies rather than supports the efficacy claim.

Maralixibat

Action: Pharmacotherapy NCIT:C15986

Agent: maralixibat NCIT:C170148

Second oral IBAT inhibitor, evaluated in MARCH-PFIC across all PFIC types. In the biallelic non-truncated BSEP cohort it significantly improved pruritus (least-squares mean between-group difference -1.1 on morning ItchRO(Obs)) and reduced total serum bile acids by 187 micromol/L relative to placebo. Diarrhoea was the most common adverse event, reported in 57% of maralixibat-treated versus 20% of placebo-treated participants and generally mild-to-moderate and transient. The trial design itself encodes the genotype dependency: the primary cohort deliberately excluded biallelic truncated BSEP deficiency.

Mechanism Target:

INHIBITS Enterohepatic Bile Acid Recirculation — Inhibits the ileal bile acid transporter, interrupting enterohepatic recirculation.

Show evidence (1 reference)

PMID:38723644 SUPPORT Human Clinical

"Maralixibat represents a non-surgical, pharmacological option to interrupt the enterohepatic circulation and improve the standard of care in patients with PFIC."

States the mechanism of action as interruption of the enterohepatic circulation.

Target Phenotypes: Pruritus HP:0000989 Increased serum bile acid concentration HP:0012202

Show evidence (2 references)

PMID:38723644 SUPPORT Human Clinical

"Maralixibat improved pruritus and predictors of native liver survival in PFIC (eg, serum bile acids)."

Randomised phase 3 evidence of efficacy on pruritus and serum bile acids.

PMID:38723644 SUPPORT Human Clinical

"The most common adverse event was diarrhoea"

Identifies the diarrhoeal class effect of IBAT inhibition with maralixibat; the trial reported it in 27 of 47 maralixibat versus 9 of 46 placebo participants, all mild or moderate and mostly transient.

Surgical biliary diversion

Action: Surgical Procedure NCIT:C15329

Partial external biliary diversion (a cholecystojejunal cutaneous stoma), partial internal biliary diversion (a gallbladder-to-colon neo-conduit) or ileal exclusion, all of which interrupt the enterohepatic circulation surgically. The oldest disease-modifying therapy in PFIC: it reduces pruritus and serum bile acids and can slow or even reverse fibrosis, allowing many patients to keep their native liver. Response is genotype-dependent in the same way as IBAT inhibition - patients retaining residual transporter function do better - and complications include stoma problems, diarrhoea, malabsorption and recurrent pruritus. In PFIC1 patients coming to transplant, ileal diversion is sometimes performed at the same operation to protect the graft from steatosis.

Mechanism Target:

INHIBITS Enterohepatic Bile Acid Recirculation — Physically diverts bile away from the terminal ileum, or bypasses the ileum, so bile acids are not reclaimed into the portal circulation.

Show evidence (1 reference)

PMID:20301474 SUPPORT Human Clinical

"the primary surgical therapy is interruption of the enterohepatic circulation which can reduce pruritus and slow or reverse the progression to hepatic fibrosis"

States the mechanism and the disease-modifying (not merely symptomatic) effect.

Target Phenotypes: Pruritus HP:0000989

Show evidence (2 references)

PMID:23141890 SUPPORT Human Clinical

"In some PFIC1 and PFIC2 patients, biliary diversion may also relieve pruritus and slow disease progression."

Establishes biliary diversion as a pruritus-relieving and disease-slowing intervention in PFIC1 and PFIC2.

PMID:34082807 SUPPORT Human Clinical

"an SBA concentration below 102 µmol/L or a decrease of at least 75% shortly after SBD reliably predicted NLS of ≥ 15 years following SBD (each p < 0.001)"

Quantifies the prognostic value of the biochemical response to surgical biliary diversion.

Ursodeoxycholic acid

Action: Pharmacotherapy NCIT:C15986

Agent: ursodeoxycholic acid CHEBI:9907

A hydrophilic bile acid that displaces hydrophobic, cytotoxic bile salts from the circulating pool and may also induce BSEP and MDR3 expression. Conventionally started in all PFIC patients, but the benefit is strongly subtype-dependent: most patients with MDR3/ABCB4 deficiency have a favourable outcome on UDCA, whereas sustained benefit in severe PFIC1 and PFIC2 is limited and pharmacotherapy for cholestasis in severe ATP8B1 disease is explicitly described as ineffective.

Show evidence (3 references)

PMID:23141890 SUPPORT Human Clinical

"Ursodeoxycholic acid (UDCA) therapy should be initiated in all patients to prevent liver damage."

The conventional recommendation to initiate UDCA in all PFIC patients.

PMID:20422496 SUPPORT Human Clinical

"Most patients with MDR3 deficiency have a favorable outcome with ursodeoxycholic acid (UDCA) therapy"

Documents the favourable UDCA response specific to ABCB4/MDR3 disease.

PMID:20301474 REFUTE Human Clinical

"Cholestasis: pharmacotherapy is ineffective regardless of disease severity."

GeneReviews explicitly refutes a cholestasis benefit from pharmacotherapy in ATP8B1 deficiency, which is why UDCA benefit is curated here as subtype-dependent rather than general.

Antipruritic pharmacotherapy

Action: Pharmacotherapy NCIT:C15986

Agent: cholestyramine NCIT:C28929 rifampin NCIT:C811

Off-label symptomatic options for cholestatic itch - the bile acid sequestrant cholestyramine, the PXR agonist rifampicin, naltrexone and sertraline - used before or alongside IBAT inhibition. Efficacy is variable and generally poorer in FIC1 deficiency than in other cholestatic disease, and rifampicin is notable for shortening cholestatic exacerbations in the allelic BRIC phenotype.

Target Phenotypes: Pruritus HP:0000989

Show evidence (1 reference)

PMID:31183005 SUPPORT Human Clinical

"Other antipruritic agents (Table 1) such as rifampin and cholestyramine may also be utilized but are often less helpful in FIC1 deficiency"

Documents these agents as antipruritic options while qualifying their limited efficacy in FIC1 deficiency - hence PARTIAL.

AAV-ABCB11 Gene Therapy

Action: Gene Therapy NCIT:C15238

Liver-directed adeno-associated virus (AAV) vector delivery of the ABCB11 gene encoding the bile salt export pump (BSEP). VTX-802, which uses a constitutive promoter for ABCB11 expression, was evaluated in a PFIC2 mouse model and showed sustained, dose-dependent improvement: treated mice displayed significant correction of serum transaminase elevation and significant, but partial, correction of hepatomegaly, with increased bile acid levels in bile and small intestine. This represents an emerging gene-therapy approach that directly restores the deficient transporter function in monogenic BSEP-deficiency disease. As a preclinical proof-of-concept, the work provides mechanistic evidence for in vivo BSEP restoration and primes the platform for clinical translation.

Mechanism Target:

RESTORES BSEP-Mediated Bile Salt Export Failure — AAV-mediated ABCB11 gene delivery restores expression of functional BSEP protein in hepatocytes, permitting resumption of canalicular bile salt export and interruption of the intrahepatic bile acid accumulation that drives cholestatic injury.

Show evidence (1 reference)

PMID:42579774 SUPPORT Model Organism

"The AAV vector containing the constitutive promoter, named VTX-802, showed higher BSEP expression, resulting in better restoration of BA secretion"

Documents VTX-802-mediated restoration of BSEP expression and function in the PFIC2 mouse model.

Target Phenotypes: Elevated circulating hepatic transaminase concentration HP:0002910 Hepatomegaly HP:0002240

Show evidence (1 reference)

PMID:42579774 SUPPORT Model Organism

"Treated mice showed a sustained dose-dependent improvement in serum transaminase levels. These mice also exhibited significant, but partial, correction of hepatomegaly, and increased BA levels in bile and small intestine"

Preclinical evidence that AAV-ABCB11 gene therapy ameliorates the cardinal biochemical and hepatic pathology phenotypes of PFIC2 in mice.

Nutritional and fat-soluble vitamin support

Action: Nutritional Support NCIT:C15433

Hypercaloric feeding with medium-chain triglycerides, which do not require micellar solubilization, plus aggressive replacement of vitamins A, D, E and K with monitoring of INR, vitamin levels, bone health and growth. This is universal supportive care in all PFIC subtypes and becomes more important, not less, on IBAT inhibitor therapy, because reducing intraluminal bile acid delivery can further impair fat-soluble vitamin absorption.

Target Phenotypes: Failure to thrive HP:0001508

Show evidence (2 references)

PMID:20301474 SUPPORT Human Clinical

"Poor growth may require medium-chain triglyceride-based formulas; fat-soluble vitamin deficiencies are treated symptomatically."

GeneReviews specifies MCT-based formula and fat-soluble vitamin replacement as standard management.

PMID:31183005 SUPPORT Human Clinical

"Patients should be treated with caloric, fat, and vitamin supplementation, with the majority of fat being medium chain triglycerides"

Specifies the composition of nutritional support in PFIC.

Liver transplantation

Action: Liver Transplantation NCIT:C15271

Definitive therapy for end-stage liver disease, unresectable hepatocellular carcinoma, severe portal hypertension, or pruritus and growth failure refractory to diversion and IBAT inhibition. Two subtype-specific caveats matter. In ATP8B1 disease, transplantation replaces only the hepatic compartment: secretory diarrhoea persists or worsens and is associated with allograft steatosis and fibrosis that can require re-transplantation, and hearing loss is unaffected - so PFIC1 is the one subtype where transplantation can make an extrahepatic manifestation worse. In ABCB11 disease, alloantibodies against the BSEP extracellular loop can produce an immune-mediated functional recurrence of BSEP deficiency in the graft. In MYO5B disease with microvillus inclusion disease, combined liver-intestinal transplantation or intestinal transplantation with biliary diversion is preferred.

Show evidence (4 references)

PMID:23141890 SUPPORT Human Clinical

"However, most PFIC patients are ultimately candidates for liver transplantation."

Establishes liver transplantation as the eventual endpoint for most patients with untreated progressive disease.

PMID:20301474 SUPPORT Human Clinical

"Notably for some, secretory diarrhea can continue or worsen following liver transplantation."

GeneReviews caveat that transplantation does not correct - and may worsen - the extrahepatic diarrhoea of ATP8B1 deficiency.

PMID:31183005 SUPPORT Human Clinical

"patients can develop allo-reactive antibodies specific to the extracellular loop of the BSEP protein resulting in an immune mediated recurrence of their BSEP disease in the allograft"

Documents antibody-mediated post-transplant recurrence of BSEP deficiency, the PFIC2-specific transplant caveat.

+ 1 more reference

Avoidance of ototoxic agents and oestrogen-containing contraceptives

Action: Supportive Care NCIT:C15747

A GeneReviews agents-and-circumstances-to-avoid recommendation specific to ATP8B1 deficiency. Potentially ototoxic drugs must be avoided because sensorineural hearing loss is already common across the ATP8B1 spectrum and further insult is additive. Oral contraceptive agents can induce or exacerbate cholestatic episodes, which is mechanistically coherent given that oestradiol interferes with FXR-mediated BSEP regulation. Routine audiograms are recommended for all individuals with ATP8B1 deficiency, symptomatic or not.

Show evidence (2 references)

PMID:20301474 SUPPORT Human Clinical

"Agents/circumstances to avoid: Potentially ototoxic agents; oral contraceptive agent therapies can induce and/or exacerbate episodes of cholestasis."

The GeneReviews agents-to-avoid recommendation verbatim.

PMID:20301474 SUPPORT Human Clinical

"routine audiograms for all individuals with ATP8B1 deficiency whether known to be symptomatic or not."

The accompanying GeneReviews surveillance recommendation.

Genetic counselling and family testing

Action: Genetic Counseling NCIT:C15240

Autosomal recessive counselling with a 25% recurrence risk for carrier couples. Once the familial variants are known, carrier testing, prenatal diagnosis and preimplantation genetic testing are available, and at-risk siblings should be tested presymptomatically so that treatment and surveillance can start early.

Show evidence (2 references)

PMID:20301474 SUPPORT Human Clinical

"Once the ATP8B1 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal and preimplantation genetic testing are possible."

GeneReviews statement of the available family testing options.

PMID:20301474 SUPPORT Human Clinical

"It is appropriate to clarify the genetic status of apparently asymptomatic older and younger at-risk relatives of an affected individual in order to identify as early as possible those who would benefit from prompt initiation of treatment, surveillance, and awareness of agents and..."

GeneReviews recommendation for presymptomatic testing of at-risk relatives.

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Biochemical Markers

Serum gamma-glutamyltransferase (Variable by subtype - low or normal in ATP8B1, ABCB11, TJP2, NR1H4, USP53 and MYO5B disease, elevated in ABCB4 disease and in KIF12- and ZFYVE19-related disease)

Context: The central diagnostic axis of PFIC. GGT is a GPI-anchored ectoenzyme of the cholangiocyte apical membrane and of the hepatocyte canalicular membrane; its appearance in serum during cholestasis requires bile-salt-mediated solubilization of that membrane. In ABCB4/MDR3 deficiency, bile lacks the phosphatidylcholine needed to sequester bile salts into mixed micelles, so free detergent bile salts strip the biliary epithelium and GGT rises. In the canalicular transport, tight junction, nuclear receptor and trafficking defects the biliary epithelium is not the primary target and GGT stays low or normal despite profound cholestasis. A low or normal GGT in a cholestatic infant is therefore a strongly informative positive finding, not a reassuring one.

Pathograph Readouts

Readout Of Unbuffered Bile Salt Injury to the Cholangiocyte Diagnostic

Serum GGT reports on whether the biliary epithelium is being attacked by unbuffered bile salts, which is exactly what separates ABCB4 disease from the hepatocyte-restricted subtypes.

Reference Ranges

Gamma glutamyl transferase [Enzymatic activity/volume] in Serum or Plasma –50.0 U/L (children beyond the neonatal period)

Low/normal-GGT cholestasis pattern (–100.0 U/L) High-GGT cholestasis pattern (100.0– U/L) → Elevated gamma-glutamyltransferase level

Low/normal-GGT cholestasis pattern: A GGT below roughly 100 U/L in a cholestatic child directs testing to ATP8B1, ABCB11, TJP2, NR1H4, USP53 and MYO5B (and to bile acid synthesis defects as the main non-PFIC alternative).

High-GGT cholestasis pattern: A GGT above roughly 100 U/L in a cholestatic child directs testing to ABCB4, and to the newer KIF12 and ZFYVE19 cholestases, after biliary obstruction and biliary atresia have been excluded.

Provenance: general clinical laboratory convention for paediatric serum GGT beyond the neonatal period, not a PFIC-specific published interval; no citable numeric interval was available in the sources used for this entry, so no evidence item is attached. Neonatal GGT is physiologically higher. The bands below encode the pragmatic cholestasis-clinic split rather than an assay reference interval.

Show evidence (3 references)

PMID:23141890 SUPPORT Human Clinical

"Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and PFIC2 patients, but is elevated in PFIC3 patients."

The definitive statement of the GGT split across the three classical subtypes.

PMID:26888176 SUPPORT Human Clinical

"low-to-normal serum gamma-glutamyl transferase activity"

Places NR1H4/PFIC5 on the low-GGT side of the split.

PMID:30976738 SUPPORT Human Clinical

"cholestatic liver disease with high GGT in 3 previously undiagnosed children"

Places KIF12-related disease on the high-GGT side of the split.

Serum conjugated (direct) bilirubin (Elevated)

Context: The laboratory definition of cholestasis and the gateway test for the whole PFIC differential. Unlike the GGT reference range, this one has a genuinely citable consensus threshold: cholestasis in infancy is defined as a conjugated/direct bilirubin above 1 mg/dL and more than 20% of total bilirubin, a threshold recently lowered from the historical arbitrary 2 mg/dL. In the first days of life even lower values (>0.3-0.5 mg/dL, or >10% of total) are treated as abnormal.

Pathograph Readouts

Readout Of Hepatocellular Bile Salt Retention Diagnostic

Conjugated bilirubin retention is the routinely measured proxy for failure of canalicular secretion, and is the test that opens the PFIC differential.

Reference Ranges

Bilirubin.direct [Mass/volume] in Serum or Plasma –1.0 mg/dL (infants beyond the first days of life)

Not cholestatic (–1.0 mg/dL) Cholestatic range (1.0– mg/dL) → Conjugated hyperbilirubinemia

Not cholestatic: Below the consensus threshold; in a jaundiced infant this points to unconjugated (breast-milk or physiological) hyperbilirubinaemia rather than cholestasis.

Cholestatic range: At or above the consensus threshold and more than 20% of total bilirubin defines cholestasis, mandating immediate hepatobiliary evaluation including urgent exclusion of biliary atresia.

The threshold is a consensus case definition of cholestasis rather than an assay reference interval, and it is paired with a percentage criterion (>20% of total bilirubin) that a single-analyte range cannot express - so the bands below should be read together with the total bilirubin.

Show evidence (1 reference)

PMID:32861449 SUPPORT Human Clinical

"Cholestasis in infancy is defined as serum conjugated/direct bilirubin level >1 mg/dL and > 20% of the total bilirubin"

Source of the 1 mg/dL consensus cholestasis threshold used as the upper bound of the normal interval.

Show evidence (2 references)

PMID:32861449 SUPPORT Human Clinical

"Neonatal cholestasis is characterized by conjugated hyperbilirubinemia in the newborn and young infant"

Establishes conjugated hyperbilirubinaemia as the defining biochemical signature of neonatal cholestasis.

PMID:31183005 SUPPORT Human Clinical

"Affected individuals have hyperbilirubinemia, mildly elevated transaminases, and elevated serum bile acids."

Documents hyperbilirubinaemia as part of the PFIC biochemical picture.

Total serum bile acids (Elevated)

Context: Markedly raised in all PFIC subtypes and the principal quantitative marker of disease activity. It is the key secondary endpoint of both phase 3 IBAT inhibitor trials, and the post-diversion value is prognostic for native liver survival.

Pathograph Readouts

Readout Of Hepatocellular Bile Salt Retention Monitoring

Circulating total bile acids are the systemic spillover of the hepatocyte bile salt burden and serve as its quantitative readout.

Pharmacodynamic Marker Of Enterohepatic Bile Acid Recirculation Pharmacodynamic

Serum bile acids are the pharmacodynamic readout of IBAT inhibition and biliary diversion, both of which act by interrupting this loop.

Reference Ranges

Bile acid [Moles/volume] in Serum or Plasma –10.0 umol/L (children, fasting)

Normal (–10.0 umol/L) Elevated, at or below the odevixibat trial response threshold (10.0–70.0 umol/L) → Increased serum bile acid concentration Markedly elevated (70.0– umol/L) → Increased serum bile acid concentration

Elevated, at or below the odevixibat trial response threshold: A concentration at or below 70 micromol/L was one of the two definitions of serum bile acid response in the PEDFIC 1 odevixibat trial.

Markedly elevated: Typical of untreated severe PFIC. In the NAPPED cohort a post-diversion concentration below 102 micromol/L predicted long native liver survival, so values well above that range mark a poor-prognosis group.

Provenance: standard clinical laboratory convention for fasting total serum bile acids; not a PFIC-specific published interval, so no evidence item is attached to the interval itself. The band thresholds below are taken from the PFIC treatment literature and are cited on the parent record.

Show evidence (2 references)

PMID:35780807 SUPPORT Human Clinical

"proportion of patients with serum bile acid response (ie, serum bile acids reduced by ≥70% from baseline or concentrations of ≤70 μmol/L) at week 24"

Source of the 70 micromol/L response threshold used in the interpretation bands.

PMID:34082807 SUPPORT Human Clinical

"an SBA concentration below 102 µmol/L or a decrease of at least 75% shortly after SBD reliably predicted NLS of ≥ 15 years following SBD (each p < 0.001)"

Source of the 102 micromol/L post-diversion prognostic threshold cited in the severe band.

🔬

Diagnosis

Serum GGT-based subtype triage in cholestatic infants

In an infant with confirmed cholestasis and no biliary obstruction, the serum GGT partitions the differential and directs genetic testing. A low or normal GGT despite marked cholestasis points to ATP8B1, ABCB11, TJP2, NR1H4, USP53 or MYO5B; a high GGT points to ABCB4 and to the newer KIF12 and ZFYVE19 cholestases, once biliary atresia, choledochal cyst and other obstructive cholangiopathies have been excluded by ultrasound and, where indicated, cholangiography.

Show evidence (1 reference)

PMID:23141890 SUPPORT Human Clinical

"Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and PFIC2 patients, but is elevated in PFIC3 patients."

The biochemical basis of the triage rule.

Molecular genetic confirmation

Genetic testing is the etiologic gold standard. A comprehensive cholestasis NGS panel including deletion/duplication analysis is first-line, escalating to trio exome or genome sequencing with periodic reanalysis when negative. Expert consensus recommends initiating treatment for severe pruritus in parallel with, rather than after, genetic confirmation.

Show evidence (2 references)

PMID:38192535 SUPPORT Human Clinical

"suggests that genetic testing be used to confirm genotype whilst treatment is initiated in patients in whom PFIC is suspected"

Expert consensus that genotyping should run in parallel with, not gate, treatment initiation.

PMID:20301474 SUPPORT Human Clinical

"The diagnosis of ATP8B1 deficiency is established in a proband with suggestive clinical and laboratory findings and biallelic pathogenic variants in ATP8B1 identified by molecular genetic testing."

The GeneReviews Diagnosis/Testing statement, establishing biallelic molecular genetic testing as the confirmatory diagnostic step for the ATP8B1 subtype.

Hepatic transporter immunostaining

BSEP and MDR3 immunohistochemistry on liver biopsy supports but does not replace genetic diagnosis. Immunohistochemically detectable BSEP is typically absent or much reduced in severe ABCB11 disease; MDR3 staining is absent, decreased or - where the defect is functional rather than expressive - normal in ABCB4 disease; in MYO5B disease BSEP and MDR3 are present but abnormally localized, which is the diagnostic signature of a trafficking rather than a transporter lesion.

Show evidence (1 reference)

PMID:18395098 SUPPORT Human Clinical

"Immunohistochemically detectable BSEP is typically absent, or much reduced, in severe disease."

Establishes the immunostaining pattern in severe BSEP deficiency and its diagnostic value.

Hepatobiliary malignancy surveillance

Because hepatocellular carcinoma and cholangiocarcinoma occur in early childhood in severe BSEP deficiency and in TJP2 deficiency, alpha-fetoprotein measurement and abdominal ultrasound every 6-12 months are recommended from the first year of life in these subtypes, and should continue in patients who retain their native liver.

Show evidence (2 references)

PMID:23141890 SUPPORT Human Clinical

"Monitoring of liver tumors, especially in PFIC2 patients, should be offered from the first year of life."

States the surveillance recommendation and its subtype focus.

PMID:18395098 SUPPORT Human Clinical

"Close surveillance of BSEP-deficient patients retaining their native liver, particularly those carrying 2 null mutations, is essential."

Specifies that surveillance targets native-liver BSEP-deficient patients, especially null/null genotypes.

📊

Prevalence

Worldwide

Birth Prevalence 1.5 per 100,000 (1.0–2.0) 1–9 per 1,000,000

Reported as an estimated incidence of 1/50,000 to 1/100,000 births, i.e. 1-2 per 100,000 births; converted to the normalized per-100,000 scale. The exact population prevalence remains unknown.

Show evidence (1 reference)

PMID:23141890 SUPPORT Human Clinical

"The exact prevalence remains unknown, but the estimated incidence varies between 1/50,000 and 1/100,000 births."

Source of the 1/50,000-1/100,000 birth incidence estimate and the explicit statement that true prevalence is unknown.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from Progressive Familial Intrahepatic Cholestasis:

Alagille syndrome MONDO:0007318

Overlapping Features The principal syndromic cholestatic differential. Alagille syndrome shares early-onset cholestasis, intractable pruritus and IBAT-inhibitor responsiveness with PFIC, and the dismech Alagille entry already lists PFIC as a differential in the reciprocal direction.

Distinguishing Features

Autosomal dominant (JAG1, less often NOTCH2) versus autosomal recessive in PFIC.
A multisystem Notch developmental disorder in which cholestasis arises from paucity of interlobular bile ducts, accompanied by peripheral pulmonary artery stenosis or other congenital heart disease, posterior embryotoxon, butterfly vertebrae, characteristic facies and renal anomalies.
PFIC is a hepatocellular bile-formation disorder with a normal biliary tree and no developmental extrahepatic syndrome; the extrahepatic features of PFIC1 are functional consequences of FIC1 loss in other tissues, not malformations.
Serum GGT is characteristically elevated in Alagille syndrome, which separates it from the low-GGT PFIC subtypes though not from PFIC3.

Show evidence (1 reference)

PMID:23141890 SUPPORT Human Clinical

"Diagnosis is based on clinical manifestations, liver ultrasonography, cholangiography and liver histology, as well as on specific tests to exclude other causes of childhood cholestasis."

Establishes that PFIC diagnosis explicitly requires excluding other causes of childhood cholestasis, of which Alagille syndrome is the leading syndromic one.

Biliary atresia MONDO:0008867

Overlapping Features The most urgent differential in a cholestatic neonate, because the Kasai portoenterostomy is time-critical.

Distinguishing Features

An acquired obliterative extrahepatic cholangiopathy with a high GGT, acholic stools, an absent or abnormal gallbladder on ultrasound and an abnormal intraoperative cholangiogram.
PFIC has a patent biliary tree with a normal cholangiogram, and the low-GGT PFIC subtypes are separated biochemically at the bedside.
A normal cholangiogram was precisely what excluded biliary atresia in the reported ZFYVE19 high-GGT case, showing that GGT alone cannot make this distinction.

Show evidence (1 reference)

PMID:33853651 SUPPORT Human Clinical

"Despite fibrosis/cirrhosis and biliary ducts proliferation on liver biopsy suggested an extrahepatic biliary obstacle, normal intra-operatory cholangiography excluded biliary atresia."

A worked example of how biliary atresia is excluded in a high-GGT PFIC-spectrum infant, and of why GGT alone is insufficient.

Benign recurrent intrahepatic cholestasis Not Yet Curated MONDO:0019008

Overlapping Features The allelic neighbour, not merely a look-alike. BRIC1 and BRIC2 are caused by variants in the SAME genes as PFIC1 and PFIC2 (ATP8B1 and ABCB11), so a genetic result alone does not distinguish them. They sit at opposite ends of one continuum, and the distinction is made phenotypically and mechanistically rather than by gene.

Distinguishing Features

BRIC causes episodic, self-limiting attacks of cholestasis with complete symptomatic resolution between episodes, whereas PFIC is persistent and progresses to end-stage liver disease.
The molecular basis of the split is residual canalicular protein - PFIC1 missense mutants are entirely absent from the canalicular membrane, whereas BRIC1 and ICP mutants retain canalicular expression.
The boundary is permeable in both directions; some BRIC cases transition to persistent progressive disease, and individuals with ATP8B1 deficiency can shift over time from the episodic to the persistent end of the spectrum, so the label "benign" is not a guarantee.
Hepatic fibrosis can be present early even at the mild end of the ATP8B1 spectrum.

Show evidence (3 references)

PMID:19731236 SUPPORT In Vitro

"Mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign recurrent intrahepatic cholestasis type 1 (BRIC1), forming a spectrum of cholestatic disease."

Establishes the allelic relationship - the same gene causes both entities.

PMID:19731236 SUPPORT In Vitro

"Whereas PFIC1 is a progressive, endstage liver disease, BRIC1 patients suffer from episodic periods of cholestasis that resolve spontaneously."

States the clinical distinction between the two allelic phenotypes.

PMID:20301474 SUPPORT Human Clinical

"in some persons with ATP8B1 deficiency the clinical findings can span the phenotypic spectrum, shifting over time from the mild end of the spectrum (episodic cholestasis) to the severe end of the spectrum (persistent cholestasis)."

GeneReviews evidence that the PFIC1/BRIC1 boundary is permeable within a single individual over time.

Inborn errors of bile acid synthesis MONDO:0019218

Overlapping Features The other major cause of LOW-GGT neonatal cholestasis, and therefore the differential that the GGT split cannot resolve.

Distinguishing Features

Bile acid synthesis defects produce low-GGT cholestasis with characteristically low or normal serum bile acids, because the defect is in making bile acids rather than in exporting them - the opposite of the markedly elevated serum bile acids of PFIC.
Urinary bile acid mass spectrometry identifies the accumulating atypical intermediates and is the discriminating test.
The distinction is therapeutically decisive because bile acid synthesis defects respond to primary bile acid replacement.

Show evidence (1 reference)

PMID:23141890 SUPPORT Human Clinical

"MDR3 and BSEP liver immunostaining, and analysis of biliary lipid composition should help to select PFIC candidates for whom genotyping could be proposed to confirm the diagnosis."

Supports the use of biliary lipid and transporter analysis to select true PFIC candidates from among other low-GGT cholestatic causes.

Alpha-1-antitrypsin deficiency MONDO:0013282

Overlapping Features A routine part of the neonatal cholestasis work-up and one of the commonest genetic causes of childhood liver disease.

Distinguishing Features

SERPINA1 Pi*ZZ disease with a low serum alpha-1-antitrypsin level and a characteristic Pi phenotype on protease inhibitor typing.
PAS-positive diastase-resistant hepatocyte inclusions on liver biopsy.
An associated adult pulmonary emphysema risk that is absent from PFIC.
The liver injury mechanism is retained-polymer proteotoxicity in the hepatocyte endoplasmic reticulum rather than a bile transport defect, and pruritus is not the dominant symptom.

Show evidence (1 reference)

PMID:23141890 SUPPORT Human Clinical

"as well as on specific tests to exclude other causes of childhood cholestasis"

Supports the requirement to exclude other genetic causes of childhood cholestasis before diagnosing PFIC.

Cystic fibrosis liver disease MONDO:0009061

Overlapping Features A particularly instructive differential for PFIC1, because ATP8B1 deficiency itself causes an elevated sweat chloride - the classic cystic fibrosis diagnostic test - and can therefore be mistaken for it.

Distinguishing Features

Caused by biallelic CFTR variants and dominated by sinopulmonary disease with chronic infection; the hepatobiliary manifestation is focal biliary cirrhosis with a high GGT.
PFIC1 has an elevated sweat chloride and pancreatic insufficiency but no bronchiectatic lung disease, and its cholestasis is low-GGT.
CFTR genotyping resolves the ambiguity.
Mechanistic overlap is real rather than coincidental - certain CFTR folding correctors improve defective FIC1 trafficking in cell culture.

Show evidence (2 references)

PMID:31183005 SUPPORT Human Clinical

"Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"

Documents the elevated sweat chloride and pancreatic insufficiency of FIC1 deficiency that create the overlap with cystic fibrosis.

PMID:31183005 SUPPORT In Vitro

"Certain CFTR folding correctors have been shown to improve defective trafficking of FIC1 in cell culture"

In vitro evidence of a shared trafficking-correction mechanism between CFTR and FIC1; PARTIAL because human data are explicitly lacking.

🔬

Clinical Trials

NCT03566238 PHASE_III COMPLETED

PEDFIC 1 - the pivotal 24-week randomised, double-blind, placebo-controlled phase 3 trial of the ileal bile acid transporter inhibitor odevixibat (A4250) at 40 and 120 micrograms/kg/day in 62 children with PFIC1 and PFIC2. Both co-primary endpoints (proportion of positive pruritus assessments and serum bile acid response) were met, and the trial is the registrational basis for odevixibat in PFIC.

Target Phenotypes: Pruritus HP:0000989 Increased serum bile acid concentration HP:0012202

Show evidence (1 reference)

clinicaltrials:NCT03566238 SUPPORT Human Clinical

"Double blind, randomized, placebo controlled, Phase 3 study to investigate the efficacy and safety of low doses and high doses of A4250 compared to placebo in children with progressive familial intrahepatic cholestasis (PFIC) types 1 and 2."

The registered trial record for PEDFIC 1, the phase 3 study of odevixibat in PFIC1 and PFIC2.

NCT03659916 PHASE_III COMPLETED

PEDFIC 2 - the open-label extension of PEDFIC 1, designed to evaluate the long-term safety of odevixibat and the persistence of its effect in children with PFIC. It is the durability arm of the odevixibat programme. Enrolment, duration and outcome figures are deliberately omitted here: the cached registry record states only the study's design and objective, and the PEDFIC 2 results publication is not among this entry's verified references.

Target Phenotypes: Pruritus HP:0000989 Increased serum bile acid concentration HP:0012202

Show evidence (1 reference)

clinicaltrials:NCT03659916 SUPPORT Human Clinical

"Open Label Extension Study to evaluate long term safety and persistence of effect of A4250 in children with PFIC."

The registered trial record for PEDFIC 2, establishing it as the long-term durability study for odevixibat in PFIC.

NCT03905330 PHASE_III COMPLETED

MARCH-PFIC - a 26-week multicentre randomised, double-blind, placebo-controlled phase 3 trial of the IBAT inhibitor maralixibat in 93 children aged 1-17 years across all PFIC types, with a primary cohort restricted to biallelic non-truncated BSEP deficiency. Both the pruritus primary endpoint and the serum bile acid key secondary endpoint were met in that cohort.

Target Phenotypes: Pruritus HP:0000989 Increased serum bile acid concentration HP:0012202

Show evidence (1 reference)

clinicaltrials:NCT03905330 SUPPORT Human Clinical

"The purpose of this study is to determine whether the investigational treatment (maralixibat) is safe and effective in pediatric participants with Progressive Familial Intrahepatic Cholestasis (PFIC)."

The registered trial record for MARCH-PFIC, the phase 3 study of maralixibat in PFIC.

NCT04185363 PHASE_III ACTIVE_NOT_RECRUITING

MARCH-ON - the open-label extension of MARCH-PFIC, evaluating long-term safety and tolerability of maralixibat in PFIC. It is the maralixibat counterpart of PEDFIC 2, so both IBAT-inhibitor programmes are represented here by a pivotal trial plus its durability extension. As with PEDFIC 2, enrolment and outcome figures are omitted because the cached registry record does not contain them.

Target Phenotypes: Pruritus HP:0000989 Increased serum bile acid concentration HP:0012202

Show evidence (1 reference)

clinicaltrials:NCT04185363 SUPPORT Human Clinical

"The primary objective of this open label extension study is to evaluate the long-term safety and tolerability of maralixibat."

The registered trial record for MARCH-ON, the maralixibat open-label extension.

{ }

Source YAML

click to show

name: Progressive Familial Intrahepatic Cholestasis
creation_date: '2026-08-01T05:30:00Z'
description: >-
  Progressive familial intrahepatic cholestasis (PFIC) is a genetically heterogeneous
  group of autosomal recessive disorders of hepatocanalicular bile formation that
  present in infancy or childhood with intrahepatic cholestasis of hepatocellular
  origin, intractable pruritus, jaundice, fat and fat-soluble vitamin malabsorption,
  growth failure, and progression to biliary fibrosis, cirrhosis and end-stage liver
  disease. The central diagnostic axis is the serum gamma-glutamyltransferase (GGT)
  split: PFIC1 (ATP8B1, encoding the FIC1 P4-ATPase aminophospholipid flippase) and
  PFIC2 (ABCB11, encoding the bile salt export pump BSEP) are low/normal-GGT diseases
  in which injury is confined to the hepatocyte, whereas PFIC3 (ABCB4, encoding the
  MDR3 phosphatidylcholine floppase) is a high-GGT cholangiopathy because bile salts
  that are not buffered into mixed micelles by biliary phosphatidylcholine attack the
  cholangiocyte apical membrane and release GGT. Newer forms include TJP2 (PFIC4),
  NR1H4/FXR (PFIC5), MYO5B (PFIC10) and the emerging USP53 (PFIC7), KIF12 (PFIC8) and
  ZFYVE19 (PFIC9) cholestases. Management has been transformed by ileal bile acid transporter (IBAT)
  inhibitors - odevixibat and maralixibat - which interrupt enterohepatic bile acid
  recirculation pharmacologically, complementing surgical biliary diversion and liver
  transplantation.
category: Mendelian
parents:
- hereditary disease
- cholestatic liver disease
synonyms:
- PFIC
- familial intrahepatic cholestasis
- Byler disease
- FIC1 deficiency
- BSEP deficiency
- MDR3 deficiency
- low-GGT familial cholestasis
disease_term:
  preferred_term: progressive familial intrahepatic cholestasis
  term:
    id: MONDO:0015762
    label: progressive familial intrahepatic cholestasis
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    All established PFIC subtypes are caused by biallelic germline loss-of-function
    variants and segregate as autosomal recessive traits, with a 25% recurrence risk
    per pregnancy for carrier couples. Consanguinity is over-represented in reported
    cohorts. Monoallelic (heterozygous) ABCB4, ABCB11 and ATP8B1 variants are not
    causes of PFIC but predispose to milder adult cholestatic phenotypes such as
    intrahepatic cholestasis of pregnancy, low-phospholipid-associated cholelithiasis
    and drug-induced cholestasis.
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Progressive familial intrahepatic cholestasis (PFIC) refers to a heterogeneous \ngroup of autosomal-recessive disorders of childhood that disrupt bile formation \nand present with cholestasis of hepatocellular origin."
    explanation: Establishes autosomal recessive inheritance for the PFIC group as a whole.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ATP8B1 deficiency is inherited in an autosomal recessive \nmanner."
    explanation: GeneReviews confirms autosomal recessive inheritance for the ATP8B1 (PFIC1) subtype.

prevalence:
- population: Worldwide
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_per_100000: 1.5
  rate_low: 1.0
  rate_high: 2.0
  notes: >-
    Reported as an estimated incidence of 1/50,000 to 1/100,000 births, i.e. 1-2 per
    100,000 births; converted to the normalized per-100,000 scale. The exact
    population prevalence remains unknown.
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The exact prevalence \nremains unknown, but the estimated incidence varies between 1/50,000 and \n1/100,000 births."
    explanation: Source of the 1/50,000-1/100,000 birth incidence estimate and the explicit statement that true prevalence is unknown.

has_subtypes:
- name: PFIC1
  display_name: PFIC1 / ATP8B1 (FIC1) deficiency
  subtype_term:
    preferred_term: progressive familial intrahepatic cholestasis type 1
    term:
      id: MONDO:0008892
      label: progressive familial intrahepatic cholestasis type 1
  description: >-
    Biallelic ATP8B1 variants abolish the canalicular FIC1 aminophospholipid flippase.
    Low/normal-GGT cholestasis presents in the first months of life. Because FIC1 is
    broadly expressed outside the liver, PFIC1 is distinguished by extrahepatic
    features - secretory diarrhoea, pancreatic insufficiency, elevated sweat chloride,
    short stature and sensorineural hearing loss - none of which is corrected by liver
    transplantation.
  genes:
  - preferred_term: ATP8B1
    term:
      id: hgnc:3706
      label: ATP8B1
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"
    explanation: Defines the extrahepatic feature set that distinguishes FIC1 (PFIC1) disease.
- name: PFIC2
  display_name: PFIC2 / ABCB11 (BSEP) deficiency
  subtype_term:
    preferred_term: progressive familial intrahepatic cholestasis type 2
    term:
      id: MONDO:0011156
      label: progressive familial intrahepatic cholestasis type 2
  description: >-
    Biallelic ABCB11 variants abolish or impair the canalicular bile salt export pump.
    Low/normal-GGT cholestasis with early, severe pruritus and rapid progression;
    generally the most severe of the classical forms. PFIC2 uniquely carries a
    substantial risk of hepatobiliary malignancy in early childhood, highest with
    biallelic protein-truncating genotypes, and can recur functionally after transplant
    through alloantibodies against the BSEP extracellular loop.
  genes:
  - preferred_term: ABCB11
    term:
      id: hgnc:42
      label: ABCB11
  evidence:
  - reference: PMID:18395098
    reference_title: 'Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with severe bile salt export pump (BSEP) deficiency \npresent as infants with progressive cholestatic liver disease."
    explanation: Defines the PFIC2/BSEP-deficiency clinical entity and its ABCB11 genetic basis in the largest genotype series.
- name: PFIC3
  display_name: PFIC3 / ABCB4 (MDR3) deficiency
  subtype_term:
    preferred_term: progressive familial intrahepatic cholestasis type 3
    term:
      id: MONDO:0011214
      label: progressive familial intrahepatic cholestasis type 3
  description: >-
    Biallelic ABCB4 variants impair the MDR3 phosphatidylcholine floppase, so bile is
    phospholipid-poor. This is the one classical PFIC subtype with a HIGH serum GGT,
    because unbuffered bile salts injure the biliary epithelium. Onset is typically
    later than PFIC1/PFIC2 - late infancy through young adulthood - with portal
    fibrosis, bile duct proliferation and cholelithiasis, and it is the subtype most
    likely to respond to ursodeoxycholic acid.
  genes:
  - preferred_term: ABCB4
    term:
      id: hgnc:45
      label: ABCB4
  evidence:
  - reference: PMID:20422496
    reference_title: 'The spectrum of liver diseases related to ABCB4 gene mutations: pathophysiology and clinical aspects.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Several ABCB4 mutations have been identified in \nchildren with PFIC3 and are associated with low level of phospholipids in bile \nleading to a high biliary cholesterol saturation index."
    explanation: Links biallelic ABCB4 defects to PFIC3 and to the phospholipid-poor bile that defines the subtype.
- name: PFIC4
  display_name: PFIC4 / TJP2 (ZO-2) deficiency
  subtype_term:
    preferred_term: 'cholestasis, progressive familial intrahepatic, 4'
    term:
      id: MONDO:0014381
      label: 'cholestasis, progressive familial intrahepatic, 4'
  description: >-
    Biallelic protein-truncating TJP2 variants abolish the tight junction scaffold ZO-2,
    so claudin-1 fails to localize and the canalicular tight junction seal is lost,
    permitting paracellular reflux of detergent bile salts. Low/normal-GGT, often
    severe neonatal or early-infantile cholestasis with giant-cell transformation;
    hepatocellular carcinoma has been reported in infancy, so surveillance starts early.
  genes:
  - preferred_term: TJP2
    term:
      id: hgnc:11828
      label: TJP2
  evidence:
  - reference: PMID:24614073
    reference_title: Mutations in TJP2 cause progressive cholestatic liver disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Protein-truncating mutations in the tight junction protein 2 gene (TJP2) are shown to cause failure of protein localisation, with disruption of tight-junction structure leading to severe cholestatic liver disease."
    explanation: Establishes biallelic TJP2 truncating variants as a cause of severe cholestatic liver disease through tight-junction failure.
- name: PFIC5
  display_name: PFIC5 / NR1H4 (FXR) deficiency
  subtype_term:
    preferred_term: 'cholestasis, progressive familial intrahepatic, 5'
    term:
      id: MONDO:0014884
      label: 'cholestasis, progressive familial intrahepatic, 5'
  description: >-
    Biallelic NR1H4 variants abolish the nuclear bile acid receptor FXR, removing the
    transcriptional programme that induces BSEP and represses de novo bile acid
    synthesis. Extremely rare, low-to-normal GGT, neonatal onset with rapid progression
    to end-stage liver disease, a characteristic vitamin K-independent coagulopathy,
    markedly elevated alpha-fetoprotein and undetectable hepatic BSEP.
  genes:
  - preferred_term: NR1H4
    term:
      id: hgnc:7967
      label: NR1H4
  evidence:
  - reference: PMID:26888176
    reference_title: Mutations in the nuclear bile acid receptor FXR cause progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical features of severe, persistent NR1H4-related cholestasis include \nneonatal onset with rapid progression to end-stage liver disease, vitamin K-independent \ncoagulopathy, low-to-normal serum gamma-glutamyl \ntransferase activity, elevated serum alpha-fetoprotein and undetectable liver \nbile salt export pump (ABCB11) expression."
    explanation: Defines the PFIC5/FXR-deficiency phenotype including its low-to-normal GGT and vitamin K-independent coagulopathy.
- name: MYO5B-related cholestasis
  display_name: MYO5B-related cholestasis (PFIC10; called PFIC6 in some older sources)
  subtype_term:
    preferred_term: MYO5B-related progressive familial intrahepatic cholestasis
    term:
      id: MONDO:0018804
      label: MYO5B-related progressive familial intrahepatic cholestasis
  description: >-
    Biallelic MYO5B variants disrupt Rab11-dependent apical recycling, so BSEP and MDR3
    are synthesized but fail to reach the canalicular membrane. Low/normal-GGT
    cholestasis that may occur with microvillus inclusion disease (intractable
    diarrhoea) or in isolation without intestinal disease. Children transplanted for
    intestinal failure may develop worsening cholestasis, so combined liver-intestinal
    transplantation or intestinal transplantation with biliary diversion is preferred.
  genes:
  - preferred_term: MYO5B
    term:
      id: hgnc:7603
      label: MYO5B
  evidence:
  - reference: PMID:27532546
    reference_title: MYO5B mutations cause cholestasis with normal serum gamma-glutamyl transferase activity in children without microvillous inclusion disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These data show that MYO5B deficiency may lead to isolated \ncholestasis and that MYO5B should be considered as an additional progressive \nfamilial intrahepatic cholestasis gene."
    explanation: Establishes MYO5B as a PFIC gene causing normal-GGT cholestasis even without intestinal disease.
- name: USP53-related cholestasis
  display_name: USP53-related low-GGT cholestasis (PFIC7)
  subtype_term:
    preferred_term: 'cholestasis, progressive familial intrahepatic, 7, with or without hearing loss'
    term:
      id: MONDO:0030503
      label: 'cholestasis, progressive familial intrahepatic, 7, with or without hearing loss'
  description: >-
    Biallelic USP53 variants cause low-GGT cholestasis; USP53 co-localizes with the
    TJP2-associated tight junction complex, placing it mechanistically alongside PFIC4.
    Cholestasis tends to be biochemically milder and intermittent and to respond to
    medication, but liver fibrosis and splenomegaly are common on follow-up, so this is
    not a benign entity. The OMIM/MONDO series numbers this PFIC7 and notes that a
    subset of patients develop childhood-onset hearing loss - a second route to
    sensorineural deafness in PFIC distinct from the ATP8B1 mechanism. Subtype numbering
    for the newer genes is not standardized across the clinical literature, so gene-first
    naming is used here deliberately with the series number carried in `display_name` and
    `subtype_term`.
  genes:
  - preferred_term: USP53
    term:
      id: hgnc:29255
      label: USP53
  evidence:
  - reference: PMID:33075013
    reference_title: Cholestasis Due to USP53 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We have now identified biallelic mutation in USP53 in 7 \nfurther patients with cholestasis, from 5 families."
    explanation: Confirms biallelic USP53 mutation as a cause of childhood cholestasis in an independent multi-family series.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "3 members of a family (2 sisters and a cousin) presented with low-ggt cholestasis, liver enzyme elevations, and pruritus"
    explanation: Places USP53 disease explicitly on the low-GGT side of the diagnostic split, which is why USP53 is included in this entry's low-GGT gene lists and in the GGT triage rule. The USP53 primary report (PMID:33075013) does not itself state the GGT level.
- name: KIF12-related cholestasis
  display_name: KIF12-related high-GGT cholestasis (PFIC8)
  subtype_term:
    preferred_term: 'cholestasis, progressive familial intrahepatic, 8'
    term:
      id: MONDO:0030505
      label: 'cholestasis, progressive familial intrahepatic, 8'
  description: >-
    Biallelic KIF12 variants cause cholestatic liver disease with a HIGH GGT, placing
    this newer gene on the same side of the GGT split as ABCB4 rather than with the
    low-GGT canalicular transport defects.
  genes:
  - preferred_term: KIF12
    term:
      id: hgnc:21495
      label: KIF12
  evidence:
  - reference: PMID:30976738
    reference_title: Recessive Mutations in KIF12 Cause High Gamma-Glutamyltransferase Cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings \nimplicate rare homozygous mutations in KIF12 in the pathogenesis of cholestatic \nliver disease with high GGT in 3 previously undiagnosed children."
    explanation: Establishes KIF12 as a cause of high-GGT cholestasis by whole-exome sequencing in consanguineous families.
- name: ZFYVE19-related cholestasis
  display_name: ZFYVE19-related high-GGT cholestasis (PFIC9)
  subtype_term:
    preferred_term: 'cholestasis, progressive familial intrahepatic, 9'
    term:
      id: MONDO:0030800
      label: 'cholestasis, progressive familial intrahepatic, 9'
  description: >-
    Biallelic ZFYVE19 variants cause neonatal-onset, non-syndromic, HIGH-GGT chronic
    intrahepatic cholestasis with fibrosis and bile duct proliferation, apparently
    through a ciliary/centriolar mechanism - a further high-GGT member of the expanded
    PFIC spectrum.
  genes:
  - preferred_term: ZFYVE19
    term:
      id: hgnc:20758
      label: ZFYVE19
  evidence:
  - reference: PMID:33853651
    reference_title: 'A ZFYVE19 gene mutation associated with neonatal cholestasis and cilia dysfunction: case report with a novel pathogenic variant.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings are consistent with and expands the recent evidence \nlinking ZFYVE19 to a novel, likely non-syndromic, high GGT-PFIC phenotype with \nneonatal onset."
    explanation: Supports ZFYVE19 as a high-GGT PFIC gene with a candidate ciliary mechanism.

pathophysiology:
- name: Canalicular Bile Formation Defect
  conforms_to: "cholestatic_liver_injury#Impaired Bile Formation and Secretion"
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    The shared upstream lesion in every PFIC subtype is biallelic loss of a protein
    required for hepatocanalicular bile formation - a canalicular transporter (BSEP,
    MDR3), a membrane lipid flippase (FIC1), a tight junction scaffold (ZO-2), the
    nuclear bile acid receptor (FXR), or an apical trafficking motor (myosin Vb). The
    result in every case is failure of the hepatocyte to form and export normal bile.
    USP53, KIF12 and ZFYVE19 are listed here as well: they are established causes of
    PFIC-spectrum cholestasis but their proximate mechanisms are not yet resolved well
    enough to warrant separate downstream mechanism nodes, so this umbrella node is the
    only place they are wired into the pathograph.
  genes:
  - preferred_term: ATP8B1
    term:
      id: hgnc:3706
      label: ATP8B1
  - preferred_term: ABCB11
    term:
      id: hgnc:42
      label: ABCB11
  - preferred_term: ABCB4
    term:
      id: hgnc:45
      label: ABCB4
  - preferred_term: TJP2
    term:
      id: hgnc:11828
      label: TJP2
  - preferred_term: NR1H4
    term:
      id: hgnc:7967
      label: NR1H4
  - preferred_term: MYO5B
    term:
      id: hgnc:7603
      label: MYO5B
  - preferred_term: USP53
    term:
      id: hgnc:29255
      label: USP53
  - preferred_term: KIF12
    term:
      id: hgnc:21495
      label: KIF12
  - preferred_term: ZFYVE19
    term:
      id: hgnc:20758
      label: ZFYVE19
  biological_processes:
  - preferred_term: bile acid and bile salt transport
    term:
      id: GO:0015721
      label: bile acid and bile salt transport
    modifier: DECREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: bile canaliculus
    term:
      id: UBERON:0001283
      label: bile canaliculus
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three types of PFIC have been identified and associated with \nmutations in hepatocellular transport-system genes involved in bile formation."
    explanation: Establishes defective hepatocellular bile-formation transport machinery as the shared upstream lesion.
  downstream:
  - target: FIC1 Flippase Loss and Canalicular Membrane Destabilization
    description: ATP8B1 loss removes the canalicular aminophospholipid flippase.
    causal_link_type: DIRECT
  - target: BSEP-Mediated Bile Salt Export Failure
    description: ABCB11 loss removes the canalicular bile salt export pump.
    causal_link_type: DIRECT
  - target: MDR3-Mediated Biliary Phospholipid Secretion Failure
    description: ABCB4 loss removes the canalicular phosphatidylcholine floppase.
    causal_link_type: DIRECT
  - target: Canalicular Tight Junction Failure and Paracellular Bile Reflux
    description: TJP2 loss destabilizes the tight junction seal around the canaliculus.
    causal_link_type: DIRECT
  - target: FXR Bile Acid Sensing and Transcriptional Failure
    description: NR1H4 loss removes the nuclear bile acid sensor governing BSEP expression.
    causal_link_type: DIRECT
  - target: Apical Trafficking Failure of Canalicular Transporters
    description: MYO5B loss prevents BSEP and MDR3 from reaching the canalicular membrane.
    causal_link_type: DIRECT

- name: FIC1 Flippase Loss and Canalicular Membrane Destabilization
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    ATP8B1 encodes FIC1, a P4-type ATPase that flips phosphatidylserine from the outer
    to the inner leaflet of the canalicular membrane. Loss of this inward translocation
    destroys membrane lipid asymmetry and leaves the canalicular membrane abnormally
    susceptible to the detergent action of luminal bile salts, impairing bile
    formation. Because FIC1 is also expressed in intestine, pancreas and cochlea, its
    loss produces extrahepatic disease that liver replacement cannot correct.
  genes:
  - preferred_term: ATP8B1
    term:
      id: hgnc:3706
      label: ATP8B1
  biological_processes:
  - preferred_term: aminophospholipid translocation
    term:
      id: GO:0140331
      label: aminophospholipid translocation
    modifier: DECREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  subtypes:
  - PFIC1
  evidence:
  - reference: PMID:19731236
    reference_title: Differential effects of progressive familial intrahepatic cholestasis type 1 and benign recurrent intrahepatic cholestasis type 1 mutations on canalicular localization of ATP8B1.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "ATP8B1 localizes to the canalicular membrane of hepatocytes where it mediates the \ninward translocation of phosphatidylserine."
    explanation: Establishes the molecular function of FIC1 as an inward-directed canalicular phosphatidylserine flippase.
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both PFIC1 and PFIC2 are \ncaused by impaired bile salt secretion due to defects in ATP8B1 encoding the \nFIC1 protein and in ABCB11 encoding bile salt export pump (BSEP) protein, \nrespectively."
    explanation: Attributes impaired bile salt secretion in PFIC1 to ATP8B1/FIC1 loss.
  downstream:
  - target: Hepatocellular Bile Salt Retention
    description: >-
      Destabilized canalicular membrane and impaired bile formation lead to intracellular
      bile salt retention without primary cholangiocyte injury, preserving a low/normal GGT.
    causal_link_type: DIRECT
  - target: Extrahepatic FIC1 Deficiency
    description: >-
      The same flippase loss in intestine, pancreas and inner ear produces disease outside
      the liver.
    causal_link_type: DIRECT

- name: BSEP-Mediated Bile Salt Export Failure
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    ABCB11 encodes BSEP, the ATP-dependent canalicular pump that performs the
    rate-limiting step of bile salt secretion into the canaliculus. Biallelic loss
    blocks bile salt export at the apical hepatocyte membrane. Severity tracks residual
    protein: the recurrent p.Glu297Gly and p.Asp482Gly alleles retain detectable BSEP in
    a substantial minority of patients, while biallelic protein-truncating genotypes
    leave none and are the most severe. Because the cholangiocyte is not the primary
    target, serum GGT remains low or normal.
  genes:
  - preferred_term: ABCB11
    term:
      id: hgnc:42
      label: ABCB11
  molecular_functions:
  - preferred_term: canalicular bile acid transmembrane transporter activity
    term:
      id: GO:0015126
      label: canalicular bile acid transmembrane transporter activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: canalicular bile acid transport
    term:
      id: GO:0015722
      label: canalicular bile acid transport
    modifier: DECREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  subtypes:
  - PFIC2
  evidence:
  - reference: PMID:18395098
    reference_title: 'Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Expression varied most for E297G and D482G, with some BSEP detected in \n45% of patients (19/42) with these mutations."
    explanation: Documents the residual-protein gradient across ABCB11 genotypes that underlies the severity spectrum.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This defect results in a severe hepatobiliary phenotype due to impairment of bile salt handling and subsequent damage to hepatocytes"
    explanation: Links BSEP loss to impaired bile salt handling and hepatocyte damage.
  downstream:
  - target: Hepatocellular Bile Salt Retention
    description: Blocked canalicular export traps bile salts inside the hepatocyte.
    causal_link_type: DIRECT
  - target: Hepatocarcinogenesis in BSEP and TJP2 Deficiency
    description: >-
      Sustained hepatocyte bile salt exposure and regenerative pressure confer an early
      hepatobiliary malignancy risk that is specific to severe BSEP deficiency.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Chronic bile-salt-induced hepatocyte DNA damage and compensatory regeneration

- name: MDR3-Mediated Biliary Phospholipid Secretion Failure
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    ABCB4 encodes MDR3, the canalicular floppase that translocates phosphatidylcholine
    into the outer leaflet of the canalicular membrane for extraction into bile.
    Biallelic loss makes bile phospholipid-poor. Because phosphatidylcholine is what
    sequesters bile salts into mixed micelles, its absence leaves free, monomeric bile
    salts at detergent concentrations in the biliary tree - the mechanistic reason PFIC3
    behaves as a cholangiopathy rather than a purely hepatocellular disease, and
    consequently the reason its serum GGT is high.
  genes:
  - preferred_term: ABCB4
    term:
      id: hgnc:45
      label: ABCB4
  molecular_functions:
  - preferred_term: phosphatidylcholine floppase activity
    term:
      id: GO:0090554
      label: phosphatidylcholine floppase activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: phospholipid translocation
    term:
      id: GO:0045332
      label: phospholipid translocation
    modifier: DECREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  subtypes:
  - PFIC3
  evidence:
  - reference: PMID:20422496
    reference_title: 'The spectrum of liver diseases related to ABCB4 gene mutations: pathophysiology and clinical aspects.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Class III multidrug resistance P-glycoproteins, Mdr2 in mice and MDR3 in human, \nare canalicular phospholipid translocators involved in biliary phospholipid \n(phosphatidylcholine) excretion."
    explanation: Establishes MDR3 as the canalicular phosphatidylcholine translocator whose loss causes PFIC3.
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Defects in ABCB4, encoding multidrug resistance 3 protein (MDR3), \nimpair biliary phospholipid secretion, resulting in PFIC3."
    explanation: Directly attributes impaired biliary phospholipid secretion to ABCB4/MDR3 loss in PFIC3.
  downstream:
  - target: Unbuffered Bile Salt Injury to the Cholangiocyte
    description: >-
      Phospholipid-poor bile cannot form protective mixed micelles, exposing the biliary
      epithelium to free detergent bile salts.
    causal_link_type: DIRECT
  - target: Biliary Cholesterol Supersaturation
    description: >-
      Loss of the phospholipid component raises the biliary cholesterol saturation index
      and promotes intraductal stone formation.
    causal_link_type: DIRECT

- name: Unbuffered Bile Salt Injury to the Cholangiocyte
  conforms_to: "cholestatic_liver_injury#Bile Acid-Mediated Hepatocyte and Cholangiocyte Injury"
  biological_scale: CELLULAR
  role: effector
  description: >-
    This node is the mechanistic pivot of the GGT split. In health, biliary
    phosphatidylcholine sequesters bile salts into mixed micelles that are non-toxic to
    the biliary epithelium. When MDR3 is absent (and in the newer high-GGT forms KIF12
    and ZFYVE19), free bile salts strip the cholangiocyte apical membrane, on which
    gamma-glutamyltransferase is a GPI-anchored ectoenzyme; membrane damage releases
    GGT into bile and serum. In the low-GGT subtypes (ATP8B1, ABCB11, TJP2, NR1H4,
    USP53, MYO5B) the cholangiocyte is not the primary target, biliary GGT is not shed, and
    serum GGT stays low or normal despite profound cholestasis. Cholangiocyte injury
    also drives the ductular reaction, portal fibrosis and bile duct proliferation seen
    on PFIC3 biopsy.
  cell_types:
  - preferred_term: intrahepatic cholangiocyte
    term:
      id: CL:0002538
      label: intrahepatic cholangiocyte
  chemical_entities:
  - preferred_term: bile salt
    term:
      id: CHEBI:22868
      label: bile salt
    modifier: INCREASED
  subtypes:
  - PFIC3
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Without phosphatidylcholine to neutralize bile acids, the imbalance of free bile acids damages cholangiocytes, and cholesterol crystallizes into liver-damaging stones"
    explanation: States the mechanism by which loss of biliary phosphatidylcholine converts PFIC3 into a cholangiocyte-injuring cholangiopathy.
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and \nPFIC2 patients, but is elevated in PFIC3 patients."
    explanation: The clinical read-out of this node - the GGT split that separates PFIC3 from PFIC1/PFIC2.
  downstream:
  - target: Elevated serum gamma-glutamyltransferase
    description: >-
      Cholangiocyte apical membrane damage releases the GPI-anchored ectoenzyme GGT,
      producing the high-GGT biochemical signature of ABCB4 disease.
    causal_link_type: DIRECT
  - target: Hepatic Stellate Cell Activation and Biliary Fibrosis
    description: >-
      Cholangiocyte injury drives a ductular reaction and periportal fibrogenesis.
    causal_link_type: DIRECT

- name: Canalicular Tight Junction Failure and Paracellular Bile Reflux
  biological_scale: CELLULAR
  role: trigger
  description: >-
    TJP2 (ZO-2) is a cytosolic scaffold that anchors claudins at the tight junctions
    sealing the bile canaliculus. Biallelic protein-truncating TJP2 variants abolish the
    protein; claudin-1 is expressed at normal levels but fails to localize to the
    junction, and tight junctions appear elongated and lose their densest zonula
    occludens material. The seal that normally confines detergent bile salts to the
    canalicular lumen is lost, permitting paracellular reflux of toxic bile constituents
    into the hepatocyte and the space of Disse.
  genes:
  - preferred_term: TJP2
    term:
      id: hgnc:11828
      label: TJP2
  biological_processes:
  - preferred_term: tight junction assembly
    term:
      id: GO:0120192
      label: tight junction assembly
    modifier: DECREASED
  cellular_components:
  - preferred_term: bicellular tight junction
    term:
      id: GO:0005923
      label: bicellular tight junction
    modifier: ABNORMAL
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  subtypes:
  - PFIC4
  evidence:
  - reference: PMID:24614073
    reference_title: Mutations in TJP2 cause progressive cholestatic liver disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In the unusually hostile environment of the canalicular and cholangiocytic membranes, exposed as these are to high concentrations of detergent bile acids, expression of TJP2 may be essential for hepatobiliary integrity"
    explanation: Articulates why loss of TJP2 is tolerated outside the liver but catastrophic at the bile-salt-exposed canalicular junction.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mechanism of injury is thought to relate to TJP2’s function maintaining junction integrity, the disturbance of which enables toxic molecules to reflux into the paracellular space"
    explanation: States the paracellular-reflux mechanism, explicitly flagged in the source as not yet clearly established - hence PARTIAL.
  downstream:
  - target: Hepatocellular Bile Salt Retention
    description: Paracellular reflux returns secreted bile salts to the hepatocyte compartment.
    causal_link_type: DIRECT
  - target: Hepatocarcinogenesis in BSEP and TJP2 Deficiency
    description: >-
      TJP2 deficiency carries a reported hepatocellular carcinoma risk presenting as early
      as infancy.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES

- name: FXR Bile Acid Sensing and Transcriptional Failure
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    NR1H4 encodes the farnesoid X receptor, the bile-acid-activated nuclear receptor
    that senses the hepatocyte bile acid load and responds by inducing ABCB11/BSEP and
    repressing de novo bile acid synthesis. Biallelic NR1H4 loss removes both arms of
    this feedback loop, producing an unregulated bile acid burden together with
    undetectable hepatic BSEP - a transcriptional phenocopy of BSEP deficiency layered
    on failure to restrain bile acid synthesis.
  genes:
  - preferred_term: NR1H4
    term:
      id: hgnc:7967
      label: NR1H4
  biological_processes:
  - preferred_term: nuclear receptor-mediated bile acid signaling pathway
    term:
      id: GO:0038185
      label: nuclear receptor-mediated bile acid signaling pathway
    modifier: ABSENT
  - preferred_term: negative regulation of bile acid biosynthetic process
    term:
      id: GO:0070858
      label: negative regulation of bile acid biosynthetic process
    modifier: DECREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  subtypes:
  - PFIC5
  evidence:
  - reference: PMID:26888176
    reference_title: Mutations in the nuclear bile acid receptor FXR cause progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "mutations in NR1H4, which encodes the\nfarnesoid X receptor (FXR), a bile acid-activated nuclear hormone receptor that regulates bile\nacid metabolism"
    explanation: Identifies FXR as the bile-acid-activated nuclear receptor whose biallelic loss causes PFIC5.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the FXR, the nuclear receptor transcription factor which regulates BSEP expression via negative feedback loop and induces FGF19 to repress bile acid synthesis"
    explanation: Specifies the two transcriptional arms - BSEP induction and bile acid synthesis repression - lost in FXR deficiency.
  downstream:
  - target: Hepatocellular Bile Salt Retention
    description: >-
      Loss of BSEP induction plus loss of synthesis repression drives an unopposed
      hepatocyte bile salt load.
    causal_link_type: DIRECT
  - target: Elevated circulating alpha-fetoprotein concentration
    description: >-
      FXR deficiency is accompanied by markedly raised serum alpha-fetoprotein, reported
      as a characteristic feature of the NR1H4 phenotype; the mechanism linking loss of
      the receptor to AFP derepression is not established.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES

- name: Apical Trafficking Failure of Canalicular Transporters
  biological_scale: CELLULAR
  role: trigger
  description: >-
    MYO5B (myosin Vb) drives Rab11-dependent recycling-endosome delivery of apical
    cargo. Biallelic loss leaves BSEP and MDR3 synthesized but mislocalized away from
    the canalicular membrane - immunostaining shows the transporters are present but
    abnormally distributed. The functional consequence is the same low-GGT bile salt
    export failure as in PFIC2, reached by a trafficking rather than a transporter
    lesion. Because MYO5B governs polarity in all epithelia, the same defect can produce
    microvillus inclusion disease in the gut.
  genes:
  - preferred_term: MYO5B
    term:
      id: hgnc:7603
      label: MYO5B
  biological_processes:
  - preferred_term: establishment of epithelial cell polarity
    term:
      id: GO:0090162
      label: establishment of epithelial cell polarity
    modifier: ABNORMAL
  cellular_components:
  - preferred_term: recycling endosome
    term:
      id: GO:0055037
      label: recycling endosome
    modifier: ABNORMAL
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  subtypes:
  - MYO5B-related cholestasis
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Present but abnormal BSEP and MDR3 staining suggest that these transporters are made but can’t appropriately migrate to the canalicular membrane"
    explanation: Direct histological evidence that the MYO5B lesion is one of transporter trafficking rather than transporter absence.
  downstream:
  - target: Hepatocellular Bile Salt Retention
    description: >-
      Mislocalized BSEP cannot export bile salts, reproducing the PFIC2 biochemical
      phenotype.
    causal_link_type: DIRECT

- name: Hepatocellular Bile Salt Retention
  conforms_to: "cholestatic_liver_injury#Hepatocellular and Biliary Bile Acid Retention"
  biological_scale: CELLULAR
  role: central_effector
  description: >-
    The convergent node of the low-GGT PFIC subtypes. Whatever the upstream lesion,
    detergent bile salts accumulate inside the hepatocyte and spill into the systemic
    circulation. Intracellular bile salts are membrane-active and mitochondriotoxic,
    driving oxidative stress, hepatocyte apoptosis and necrosis and an inflammatory
    response; the circulating fraction produces pruritus and the raised serum bile acid
    concentration that is the field's principal pharmacodynamic and prognostic
    biomarker.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  chemical_entities:
  - preferred_term: bile salt
    term:
      id: CHEBI:22868
      label: bile salt
    modifier: INCREASED
  biological_processes:
  - preferred_term: bile acid secretion
    term:
      id: GO:0032782
      label: bile acid secretion
    modifier: DECREASED
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Without appropriate BSEP localization, secretion of bile acids is impaired and causes hepatocellular toxicity"
    explanation: States that impaired bile acid secretion is directly hepatotoxic to the hepatocyte.
  downstream:
  - target: Intrahepatic cholestasis
    description: Failure of bile salt secretion is intrahepatic cholestasis at the clinical level.
    causal_link_type: DIRECT
  - target: Increased serum bile acid concentration
    description: Retained bile salts spill into the systemic circulation.
    causal_link_type: DIRECT
  - target: Systemic Bile Acid Load and Pruritogenesis
    description: Circulating bile salts and co-retained pruritogens drive itch.
    causal_link_type: DIRECT
  - target: Hepatic Stellate Cell Activation and Biliary Fibrosis
    description: >-
      Chronic bile-salt-mediated hepatocyte injury and inflammation activate the hepatic
      fibrogenic programme.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Bile-salt-induced hepatocyte apoptosis and necrosis
    - Sterile inflammatory signalling
  - target: Reduced Intestinal Bile Acid Delivery and Fat Malabsorption
    description: >-
      Bile salts retained in the hepatocyte never reach the intestinal lumen, so
      micellar fat solubilization fails.
    causal_link_type: DIRECT
  - target: Conjugated hyperbilirubinemia
    description: >-
      Failure of canalicular secretion retains already-conjugated bilirubin in the
      hepatocyte and refluxes it into plasma, raising the direct fraction.
    causal_link_type: DIRECT
  - target: Jaundice
    description: Cholestasis retains conjugated bilirubin alongside bile salts.
    causal_link_type: DIRECT
  - target: Hepatomegaly
    description: Cholestatic hepatocyte swelling and hepatocellular disarray enlarge the liver.
    causal_link_type: DIRECT

- name: Enterohepatic Bile Acid Recirculation
  biological_scale: ORGANISM
  role: therapeutic_vulnerability
  description: >-
    Roughly 95% of secreted bile acids are reclaimed from the terminal ileum by the
    apical sodium-dependent ileal bile acid transporter (IBAT/ASBT, SLC10A2) and
    returned to the liver in the portal blood. In PFIC this recycling loop continuously
    re-delivers a bile acid load that the diseased hepatocyte cannot handle, sustaining
    hepatocellular bile salt retention - so within the pathograph it acts as an
    amplifier of the central effector node. That also makes it the single most
    exploitable therapeutic node in PFIC: interrupting it - surgically by partial
    external or internal biliary diversion or ileal exclusion, or pharmacologically by
    IBAT inhibition with odevixibat or maralixibat - diverts bile acids into the faeces,
    lowers serum bile acids, and relieves pruritus. Response is genotype-dependent:
    reducing enterohepatic return cannot help when canalicular export is completely
    absent, so patients with complete BSEP loss respond poorly.
  biological_processes:
  - preferred_term: bile acid and bile salt transport
    term:
      id: GO:0015721
      label: bile acid and bile salt transport
    modifier: INCREASED
  gene:
    preferred_term: SLC10A2
    term:
      id: hgnc:10906
      label: SLC10A2
  cell_types:
  - preferred_term: enterocyte
    term:
      id: CL:0000584
      label: enterocyte
  locations:
  - preferred_term: ileum
    term:
      id: UBERON:0002116
      label: ileum
  evidence:
  - reference: PMID:35780807
    reference_title: 'Odevixibat treatment in progressive familial intrahepatic cholestasis: a randomised, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Odevixibat, administered as once a day oral capsules, is a non-surgical, \npharmacological option to interrupt the enterohepatic circulation in patients \nwith PFIC."
    explanation: Identifies interruption of enterohepatic bile acid circulation as the therapeutic target exploited by IBAT inhibition.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the primary \nsurgical therapy is interruption of the enterohepatic circulation which can \nreduce pruritus and slow or reverse the progression to hepatic fibrosis"
    explanation: Confirms that interrupting this loop is disease-modifying, not merely symptomatic.
  downstream:
  - target: Hepatocellular Bile Salt Retention
    description: >-
      Portal re-delivery of reclaimed bile acids perpetuates the hepatocyte bile salt
      burden.
    causal_link_type: DIRECT

- name: Systemic Bile Acid Load and Pruritogenesis
  biological_scale: ORGANISM
  role: consequence
  description: >-
    Cholestasis raises circulating bile acids and other retained pruritogens, producing
    the intractable itch that is the dominant symptom burden of PFIC. Pruritus in PFIC
    is severe enough to cause skin mutilation and profound sleep disruption and is a
    stand-alone indication for biliary diversion or transplantation independent of liver
    synthetic function. Serum bile acid concentration serves as the pharmacodynamic
    surrogate for this node in trials.
  chemical_entities:
  - preferred_term: bile salt
    term:
      id: CHEBI:22868
      label: bile salt
    modifier: INCREASED
  evidence:
  - reference: PMID:38723644
    reference_title: 'Maralixibat in progressive familial intrahepatic cholestasis (MARCH-PFIC): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Progressive familial intrahepatic cholestasis (PFIC) is a group of \nautosomal recessive disorders, the most prevalent being BSEP deficiency, \nresulting in disrupted bile formation, cholestasis, and pruritus."
    explanation: Places pruritus as a direct consequence of disrupted bile formation and cholestasis.
  downstream:
  - target: Pruritus
    description: Circulating pruritogens produce the clinical symptom.
    causal_link_type: DIRECT

- name: Reduced Intestinal Bile Acid Delivery and Fat Malabsorption
  biological_scale: ORGANISM
  role: consequence
  description: >-
    Bile that never reaches the duodenum cannot form the mixed micelles needed to
    solubilize dietary long-chain triglyceride and the fat-soluble vitamins A, D, E and
    K. The result is steatorrhoea, energy deficit despite adequate intake, growth
    failure and short stature, and fat-soluble vitamin deficiency with rickets and
    coagulopathy. This is why nutritional management uses medium-chain triglyceride
    formulas, which are absorbed without micellar solubilization, alongside aggressive
    fat-soluble vitamin replacement.
  locations:
  - preferred_term: small intestine
    term:
      id: UBERON:0002108
      label: small intestine
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Poor \ngrowth may require medium-chain triglyceride-based formulas; fat-soluble vitamin \ndeficiencies are treated symptomatically."
    explanation: GeneReviews links poor growth and fat-soluble vitamin deficiency to the malabsorptive consequence of cholestasis and specifies MCT-based management.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "poor growth due to fat malabsorption and fat-soluble vitamin deficiency"
    explanation: Explicitly attributes growth failure in PFIC to fat malabsorption and fat-soluble vitamin deficiency.
  downstream:
  - target: Failure to thrive
    description: Energy and fat malabsorption produce growth failure.
    causal_link_type: DIRECT
  - target: Steatorrhea
    description: Unabsorbed dietary fat is passed in the stool.
    causal_link_type: DIRECT
  - target: Short stature
    description: Chronic malnutrition and chronic liver disease limit linear growth.
    causal_link_type: DIRECT
  - target: Vitamin K-responsive coagulopathy
    description: >-
      Fat-soluble vitamin K malabsorption impairs synthesis of the vitamin
      K-dependent clotting factors.
    causal_link_type: DIRECT

- name: Hepatic Stellate Cell Activation and Biliary Fibrosis
  biological_scale: TISSUE
  role: consequence
  conforms_to: fibrotic_response#Mesenchymal Cell Activation
  description: >-
    Sustained bile-salt-mediated hepatocyte injury (low-GGT subtypes) and cholangiocyte
    injury with ductular reaction (high-GGT subtypes) both converge on activation of
    hepatic stellate cells into collagen-secreting myofibroblasts. Progressive portal
    and lobular fibrosis becomes biliary cirrhosis with portal hypertension and
    synthetic failure, typically before adulthood in untreated disease. Fibrosis may be
    present early even in phenotypically mild ATP8B1 disease, which is why the historical
    assumption that intermittent cholestasis is non-fibrotic has been abandoned.
  cell_types:
  - preferred_term: hepatic stellate cell
    term:
      id: CL:0000632
      label: hepatic stellate cell
  biological_processes:
  - preferred_term: extracellular matrix organization
    term:
      id: GO:0030198
      label: extracellular matrix organization
    modifier: INCREASED
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PFIC patients usually develop fibrosis and end-stage liver disease before \nadulthood."
    explanation: Establishes progressive fibrosis to end-stage liver disease as the natural history of untreated PFIC.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although mild-to-moderate ATP8B1 deficiency initially was \nthought to involve intermittent symptomatic cholestasis with a lack of hepatic \nfibrosis, it is now known that hepatic fibrosis may be present early in the \ndisease course."
    explanation: Documents that fibrosis occurs even at the mild end of the ATP8B1 spectrum, refuting the older non-fibrotic assumption.
  downstream:
  - target: Cirrhosis
    description: Progressive matrix deposition produces biliary cirrhosis.
    causal_link_type: DIRECT
  - target: Portal hypertension
    description: Architectural distortion raises portal pressure.
    causal_link_type: DIRECT
  - target: Splenomegaly
    description: Portal hypertension produces congestive splenomegaly.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Portal hypertension with splenic venous congestion
  - target: Hepatic failure
    description: Loss of functioning parenchyma produces synthetic failure.
    causal_link_type: DIRECT

- name: Hepatocarcinogenesis in BSEP and TJP2 Deficiency
  biological_scale: CELLULAR
  role: consequence
  description: >-
    Severe BSEP deficiency and TJP2 deficiency carry a subtype-specific risk of
    hepatobiliary malignancy - hepatocellular carcinoma and cholangiocarcinoma -
    presenting in early childhood, in some cases before age two. Risk is
    genotype-stratified in ABCB11 disease: biallelic protein-truncating genotypes carry
    roughly a fourfold higher malignancy risk than potentially less severe genotypes.
    This is a genuine mechanistic distinction from PFIC1, in which tumour development is
    not a recognised association, and it drives the recommendation for tumour
    surveillance from the first year of life.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  subtypes:
  - PFIC2
  - PFIC4
  evidence:
  - reference: PMID:16871584
    reference_title: Hepatocellular carcinoma in ten children under five years of age with bile salt export pump deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PFIC associated with BSEP deficiency represents a previously \nunrecognized risk for HCC in young children."
    explanation: The landmark series establishing hepatocellular carcinoma risk in early childhood BSEP deficiency.
  - reference: PMID:18395098
    reference_title: 'Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two protein-truncating \nmutations conferred particular risk; 38% (8/21) of such patients developed \nmalignancy versus 10% (11/107) with potentially less severe genotypes"
    explanation: Quantifies the genotype stratification of malignancy risk within ABCB11 disease.
  downstream:
  - target: Hepatocellular carcinoma
    description: Malignant transformation of the chronically injured hepatocyte.
    causal_link_type: DIRECT

- name: Biliary Cholesterol Supersaturation
  biological_scale: ORGANISM
  role: consequence
  description: >-
    In ABCB4/MDR3 disease the phospholipid-poor bile has a high cholesterol saturation
    index, so cholesterol crystallizes and forms intraductal and gallbladder stones.
    This underlies the low-phospholipid-associated cholelithiasis phenotype seen in
    biallelic PFIC3 and in monoallelic ABCB4 carriers.
  subtypes:
  - PFIC3
  evidence:
  - reference: PMID:20422496
    reference_title: 'The spectrum of liver diseases related to ABCB4 gene mutations: pathophysiology and clinical aspects.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There is evidence that a biallelic or monoallelic ABCB4 defect causes \nor predisposes to several human liver diseases (PFIC3, low phospholipid \nassociated cholelithiasis syndrome, intrahepatic cholestasis of pregnancy, \ndrug-induced liver injury, transient neonatal cholestasis, adult biliary \nfibrosis, or cirrhosis)."
    explanation: Establishes low-phospholipid-associated cholelithiasis as part of the ABCB4 disease spectrum.
  downstream:
  - target: Cholelithiasis
    description: Cholesterol crystallization in phospholipid-poor bile produces stones.
    causal_link_type: DIRECT

- name: Extrahepatic FIC1 Deficiency
  biological_scale: ORGANISM
  role: consequence
  description: >-
    ATP8B1 is expressed well beyond the hepatocyte, so PFIC1 alone among the classical
    subtypes has an extrahepatic disease burden: secretory diarrhoea, exocrine pancreatic
    insufficiency, elevated sweat chloride, short stature and sensorineural hearing loss.
    This is clinically decisive because liver transplantation replaces only the hepatic
    compartment: the diarrhoea persists or worsens after transplant and is associated
    with allograft steatosis and fibrosis that can require re-transplantation, and
    audiological surveillance must continue lifelong regardless of hepatic outcome.
  subtypes:
  - PFIC1
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Extrahepatic disease is also notable due to the broad distribution of FIC1, which can clinically distinguish FIC1 deficiency from other forms of intrahepatic cholestasis."
    explanation: Attributes the extrahepatic burden of PFIC1 to the wide tissue distribution of FIC1.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably for some, secretory diarrhea can continue or worsen following liver \ntransplantation."
    explanation: GeneReviews documents that transplantation does not correct - and may worsen - the extrahepatic diarrhoea of ATP8B1 deficiency.
  downstream:
  - target: Chronic diarrhea
    description: Loss of FIC1 in the intestinal epithelium produces secretory diarrhoea.
    causal_link_type: DIRECT
  - target: Sensorineural hearing impairment
    description: Loss of FIC1 in the cochlea produces sensorineural hearing loss.
    causal_link_type: DIRECT
  - target: Exocrine pancreatic insufficiency
    description: Loss of FIC1 in the pancreas impairs exocrine secretion.
    causal_link_type: DIRECT

phenotypes:
- category: Hepatobiliary
  name: Intrahepatic cholestasis
  description: >-
    Impairment of bile flow arising within the liver, of hepatocellular rather than
    obstructive origin. This is the defining manifestation of PFIC and is present in all
    subtypes, typically from the first months of life in PFIC1, PFIC2, PFIC4, PFIC5 and
    MYO5B-related disease, and later in PFIC3.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Intrahepatic cholestasis
    term:
      id: HP:0001406
      label: Intrahepatic cholestasis
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Progressive familial intrahepatic cholestasis (PFIC) refers to a heterogeneous \ngroup of autosomal-recessive disorders of childhood that disrupt bile formation \nand present with cholestasis of hepatocellular origin."
    explanation: Defines cholestasis of hepatocellular origin as the obligate manifestation of the PFIC group. The OBLIGATE frequency band follows directly from this definitional statement.
- category: Dermatological
  name: Pruritus
  description: >-
    Intractable itch, typically severe and often the dominant symptom burden. Pruritus in
    PFIC causes skin excoriation and mutilation and profound sleep disruption, and is a
    stand-alone indication for biliary diversion, IBAT inhibition or transplantation.
  frequency: VERY_FREQUENT
  severity: SEVERE
  phenotype_term:
    preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main clinical manifestations include cholestasis, pruritus and jaundice."
    explanation: Lists pruritus as one of the three main clinical manifestations of PFIC.
  - reference: PMID:38723644
    reference_title: 'Maralixibat in progressive familial intrahepatic cholestasis (MARCH-PFIC): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We recruited participants \naged 1-17 years with PFIC with persistent pruritus"
    explanation: A phase 3 trial that recruited 93 children on the basis of persistent pruritus of more than 6 months' duration supports the VERY_FREQUENT and SEVERE qualifiers.
- category: Hepatobiliary
  name: Jaundice
  description: Yellow discoloration of skin and sclerae from retained conjugated bilirubin.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Jaundice
    term:
      id: HP:0000952
      label: Jaundice
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main clinical manifestations include cholestasis, pruritus and jaundice."
    explanation: Lists jaundice as one of the three main clinical manifestations of PFIC.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Infants often present jaundiced, with pruritis and hepatosplenomegaly developing over the first months of life."
    explanation: Supports jaundice as the usual presenting sign, consistent with the VERY_FREQUENT band.
- category: Laboratory
  name: Conjugated hyperbilirubinemia
  description: >-
    Raised serum conjugated (direct) bilirubin, the laboratory definition of cholestasis
    and the finding that separates true cholestatic jaundice from the far commoner
    unconjugated (breast-milk, physiological) hyperbilirubinaemia of infancy. In a
    jaundiced infant, fractionating the bilirubin is the step that puts PFIC on the
    differential at all.
  frequency: VERY_FREQUENT
  diagnostic: true
  phenotype_term:
    preferred_term: Conjugated hyperbilirubinemia
    term:
      id: HP:0002908
      label: Conjugated hyperbilirubinemia
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals have hyperbilirubinemia, mildly elevated transaminases, and elevated serum bile acids."
    explanation: PFIC-specific documentation of hyperbilirubinaemia; PARTIAL because the source does not itself specify the conjugated fraction, which the companion evidence item supplies.
  - reference: PMID:32861449
    reference_title: Recent developments in diagnostics and treatment of neonatal cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neonatal cholestasis is characterized by conjugated hyperbilirubinemia in the \nnewborn and young infant"
    explanation: Establishes that the hyperbilirubinaemia of neonatal/infantile cholestasis, of which PFIC is one cause, is specifically conjugated.
- category: Laboratory
  name: Increased serum bile acid concentration
  description: >-
    Markedly elevated circulating total bile acids, often above 200 micromol/L. This is
    the principal biochemical marker of disease activity in PFIC, the pharmacodynamic
    endpoint of IBAT inhibitor trials, and a prognostic marker for native liver survival
    after biliary diversion.
  frequency: VERY_FREQUENT
  diagnostic: true
  phenotype_term:
    preferred_term: Increased serum bile acid concentration
    term:
      id: HP:0012202
      label: Increased serum bile acid concentration
  evidence:
  - reference: PMID:38723644
    reference_title: 'Maralixibat in progressive familial intrahepatic cholestasis (MARCH-PFIC): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Least-squares mean change from baseline in \ntotal serum bile acids was -176 μmol/L (95% CI -257 to -94) for maralixibat \nversus 11 μmol/L (-58 to 80) for placebo"
    explanation: A treatment-induced fall of 176 micromol/L implies markedly elevated baseline serum bile acids across the trial population, supporting the VERY_FREQUENT band.
- category: Laboratory
  name: Elevated serum gamma-glutamyltransferase
  description: >-
    High serum GGT despite cholestasis. This is the single most useful bedside
    discriminator within PFIC: it is characteristic of ABCB4/MDR3 disease (PFIC3) and of
    the newer KIF12 and ZFYVE19 cholestases, and its ABSENCE - a low or normal GGT in the
    face of profound cholestasis - points to ATP8B1, ABCB11, TJP2, NR1H4, USP53 or
    MYO5B. Note
    that low/normal GGT is not curated here as a separate HPO-coded phenotype because it
    denotes a normal value, not an abnormality; it is captured in the biochemical section
    and the pathophysiology.
  subtype: PFIC3
  diagnostic: true
  phenotype_term:
    preferred_term: Elevated gamma-glutamyltransferase level
    term:
      id: HP:0030948
      label: Elevated gamma-glutamyltransferase level
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and \nPFIC2 patients, but is elevated in PFIC3 patients."
    explanation: The definitive statement of the GGT split across the classical PFIC subtypes.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GGT is typically elevated at presentation, with relatively milder elevation of transaminases and bilirubin"
    explanation: Confirms that elevated GGT is the typical presenting biochemistry of ABCB4/PFIC3 disease.
- category: Hepatobiliary
  name: Hepatomegaly
  description: Enlarged liver, usually present from infancy in the severe subtypes.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Scleral icterus, hepatomegaly, excoriation of skin, and poor growth due to fat malabsorption and fat-soluble vitamin deficiency may also be apparent due to cholestasis"
    explanation: Lists hepatomegaly among the manifestations apparent in BSEP deficiency; the qualitative phrasing maps to the FREQUENT band.
- category: Hepatobiliary
  name: Splenomegaly
  description: >-
    Enlarged spleen, usually reflecting congestive splenomegaly from portal hypertension
    rather than a primary splenic process.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Splenomegaly
    term:
      id: HP:0001744
      label: Splenomegaly
  evidence:
  - reference: PMID:33075013
    reference_title: Cholestasis Due to USP53 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "splenomegaly was apparent in 5 of 7 at last ultrasound"
    explanation: A directly quantitative count (5/7, 71%) in the USP53 series maps to the FREQUENT band (30-79%).
- category: Hepatobiliary
  name: Portal hypertension
  description: >-
    Raised portal venous pressure from progressive biliary fibrosis. In ABCB4 disease it
    may be the presenting problem, with variceal bleeding as the first symptom.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Portal hypertension
    term:
      id: HP:0001409
      label: Portal hypertension
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A retrospective review of 38 patients found that those diagnosed in childhood presented with pruritis around 1 year of age and most had hepatosplenomegaly, portal hypertension, and jaundice at the time of presentation"
    explanation: The statement that most of a 38-patient series had portal hypertension at presentation maps to the FREQUENT band.
- category: Hepatobiliary
  name: Cirrhosis
  description: >-
    Biliary cirrhosis is the expected endpoint of untreated progressive disease, usually
    reached before adulthood.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Cirrhosis
    term:
      id: HP:0001394
      label: Cirrhosis
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Severe ATP8B1 deficiency is characterized \nby infantile-onset cholestasis that progresses to cirrhosis, hepatic failure, \nand early death."
    explanation: GeneReviews states progression to cirrhosis as characteristic of severe ATP8B1 disease.
- category: Hepatobiliary
  name: Hepatic failure
  description: >-
    Synthetic liver failure, reached rapidly in PFIC5 and after longer progression in the
    other subtypes; the usual indication for liver transplantation.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hepatic failure
    term:
      id: HP:0001399
      label: Hepatic failure
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Severe ATP8B1 deficiency is characterized \nby infantile-onset cholestasis that progresses to cirrhosis, hepatic failure, \nand early death."
    explanation: GeneReviews lists hepatic failure as a characteristic outcome of severe ATP8B1 deficiency.
  - reference: PMID:26888176
    reference_title: Mutations in the nuclear bile acid receptor FXR cause progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "neonatal onset with rapid progression to end-stage liver disease"
    explanation: Documents rapid progression to end-stage liver disease in the NR1H4/PFIC5 subtype.
- category: Growth
  name: Failure to thrive
  description: >-
    Growth failure from fat and fat-soluble vitamin malabsorption combined with the
    energy cost of chronic liver disease; managed with hypercaloric, medium-chain
    triglyceride-based feeding.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Poor \ngrowth may require medium-chain triglyceride-based formulas"
    explanation: GeneReviews documents poor growth as a routine management problem in ATP8B1 deficiency.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"
    explanation: The phrase "frequently exhibit" applied to poor growth maps to the FREQUENT band.
- category: Growth
  name: Short stature
  description: Reduced linear growth from chronic malnutrition and chronic liver disease.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Similarly, some patients also suffer short stature, though others have normal growth."
    explanation: The qualifier "some patients" maps to the OCCASIONAL band (5-29%).
- category: Gastrointestinal
  name: Steatorrhea
  description: >-
    Fatty stool from failure of micellar solubilization of dietary long-chain
    triglyceride in the bile-acid-deficient intestinal lumen.
  phenotype_term:
    preferred_term: Steatorrhea
    term:
      id: HP:0002570
      label: Steatorrhea
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "poor growth due to fat malabsorption and fat-soluble vitamin deficiency"
    explanation: Documents fat malabsorption, of which steatorrhoea is the direct clinical expression; PARTIAL because the source names fat malabsorption rather than steatorrhoea explicitly. Frequency deliberately omitted.
- category: Hematological
  name: Vitamin K-responsive coagulopathy
  description: >-
    Prolonged prothrombin time from malabsorption of fat-soluble vitamin K, correctable
    with vitamin K replacement. This must be distinguished from the vitamin
    K-INDEPENDENT coagulopathy that is characteristic of NR1H4/PFIC5 and reflects
    hepatic synthetic failure rather than malabsorption.
  phenotype_term:
    preferred_term: Prolonged prothrombin time
    term:
      id: HP:0008151
      label: Prolonged prothrombin time
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "fat-soluble vitamin \ndeficiencies are treated symptomatically."
    explanation: GeneReviews documents fat-soluble vitamin deficiency requiring treatment; vitamin K deficiency is its coagulation manifestation. PARTIAL because the source does not name prothrombin time. Frequency deliberately omitted.
  - reference: PMID:26888176
    reference_title: Mutations in the nuclear bile acid receptor FXR cause progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical features of severe, persistent NR1H4-related cholestasis include \nneonatal onset with rapid progression to end-stage liver disease, vitamin K-independent \ncoagulopathy, low-to-normal serum gamma-glutamyl \ntransferase activity, elevated serum alpha-fetoprotein and undetectable liver \nbile salt export pump (ABCB11) expression."
    explanation: Establishes the contrasting vitamin K-INDEPENDENT coagulopathy specific to PFIC5, the distinction drawn in this entry's description.
- category: Auditory
  name: Sensorineural hearing impairment
  description: >-
    Sensorineural hearing loss from loss of FIC1 in the cochlea. Common across the whole
    ATP8B1 phenotypic spectrum including mild disease, and not corrected by liver
    transplantation, so routine audiograms are recommended for every individual with
    ATP8B1 deficiency whether or not they are symptomatic.
  subtype: PFIC1
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sensorineural hearing loss (SNHL) is common across the \nphenotypic spectrum."
    explanation: GeneReviews describes SNHL as common in ATP8B1 deficiency, which maps to the FREQUENT band (30-79%).
- category: Gastrointestinal
  name: Chronic diarrhea
  description: >-
    Secretory diarrhoea from loss of FIC1 in the intestinal epithelium. Clinically
    decisive because it is extrahepatic: it persists or even worsens after liver
    transplantation and is associated with allograft steatosis.
  subtype: PFIC1
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Chronic diarrhea
    term:
      id: HP:0002028
      label: Chronic diarrhea
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"
    explanation: The phrase "frequently exhibit profound diarrhea" in FIC1 deficiency maps to the FREQUENT band.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably for some, secretory diarrhea can continue or worsen following liver \ntransplantation."
    explanation: Confirms the secretory character of the diarrhoea and its persistence after transplant.
- category: Gastrointestinal
  name: Exocrine pancreatic insufficiency
  description: >-
    Reduced pancreatic exocrine secretion in ATP8B1 deficiency, compounding the
    malabsorption already caused by intraluminal bile acid deficiency.
  subtype: PFIC1
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Exocrine pancreatic insufficiency
    term:
      id: HP:0001738
      label: Exocrine pancreatic insufficiency
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"
    explanation: The phrase "frequently exhibit" applied to pancreatic insufficiency in FIC1 deficiency maps to the FREQUENT band.
- category: Neoplastic
  name: Hepatocellular carcinoma
  description: >-
    Hepatocellular carcinoma (and cholangiocarcinoma) arising in early childhood,
    sometimes before age two. This risk is specific to severe BSEP deficiency and to TJP2
    deficiency; it is not a recognised feature of ATP8B1 disease. Surveillance with
    alpha-fetoprotein and abdominal ultrasound is recommended from the first year of life
    in these subtypes.
  subtype: PFIC2
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Hepatocellular carcinoma
    term:
      id: HP:0001402
      label: Hepatocellular carcinoma
  evidence:
  - reference: PMID:18395098
    reference_title: 'Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hepatocellular carcinoma or \ncholangiocarcinoma developed in 15% of patients (19/128)."
    explanation: A directly quantitative 15% (19/128) in BSEP deficiency maps to the OCCASIONAL band (5-29%).
  - reference: PMID:16871584
    reference_title: Hepatocellular carcinoma in ten children under five years of age with bile salt export pump deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among the 11 \nnonrelated children studied aged 13-52 months at diagnosis of HCC"
    explanation: Documents the strikingly early age at HCC diagnosis (13-52 months) in BSEP deficiency.
- category: Hepatobiliary
  name: Cholelithiasis
  description: >-
    Cholesterol gallstones and intraductal stones arising from the high cholesterol
    saturation index of phospholipid-poor bile in ABCB4/MDR3 disease.
  subtype: PFIC3
  phenotype_term:
    preferred_term: Cholelithiasis
    term:
      id: HP:0001081
      label: Cholelithiasis
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histology typically demonstrates portal fibrosis and bile duct proliferation with mild giant cell hepatitis at disease onset with occasional intraductal cholelithiasis"
    explanation: Documents intraductal cholelithiasis in ABCB4 disease. Frequency deliberately omitted because the source qualifier describes histological findings rather than a cohort proportion.
- category: Laboratory
  name: Elevated circulating alpha-fetoprotein concentration
  description: >-
    Markedly raised serum alpha-fetoprotein, a characteristic feature of NR1H4/PFIC5.
    AFP is also used as a hepatocellular carcinoma surveillance marker in PFIC2 and
    PFIC4, so its interpretation is subtype-dependent.
  subtype: PFIC5
  phenotype_term:
    preferred_term: Elevated circulating alpha-fetoprotein concentration
    term:
      id: HP:0006254
      label: Elevated circulating alpha-fetoprotein concentration
  evidence:
  - reference: PMID:26888176
    reference_title: Mutations in the nuclear bile acid receptor FXR cause progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "elevated serum \nalpha-fetoprotein and undetectable liver \nbile salt export pump (ABCB11) expression"
    explanation: Establishes elevated serum AFP as a defining feature of NR1H4-related cholestasis.

biochemical:
- name: Serum gamma-glutamyltransferase
  presence: Variable by subtype - low or normal in ATP8B1, ABCB11, TJP2, NR1H4, USP53 and MYO5B disease, elevated in ABCB4 disease and in KIF12- and ZFYVE19-related disease
  context: >-
    The central diagnostic axis of PFIC. GGT is a GPI-anchored ectoenzyme of the
    cholangiocyte apical membrane and of the hepatocyte canalicular membrane; its
    appearance in serum during cholestasis requires bile-salt-mediated solubilization of
    that membrane. In ABCB4/MDR3 deficiency, bile lacks the phosphatidylcholine needed to
    sequester bile salts into mixed micelles, so free detergent bile salts strip the
    biliary epithelium and GGT rises. In the canalicular transport, tight junction,
    nuclear receptor and trafficking defects the biliary epithelium is not the primary
    target and GGT stays low or normal despite profound cholestasis. A low or normal GGT
    in a cholestatic infant is therefore a strongly informative positive finding, not a
    reassuring one.
  specificity: >-
    High for subtype triage within genetic cholestasis, but not for PFIC versus other
    causes - biliary atresia and other obstructive cholangiopathies are also high-GGT,
    and bile acid synthesis defects are also low-GGT.
  biomarker_term:
    preferred_term: Gamma-Glutamyl Transpeptidase
    term:
      id: NCIT:C37959
      label: Gamma-Glutamyl Transpeptidase
  mappings_list:
  - preferred_term: Gamma glutamyl transferase [Enzymatic activity/volume] in Serum or Plasma
    term:
      id: LOINC:2324-2
      label: Gamma glutamyl transferase [Enzymatic activity/volume] in Serum or Plasma
  reference_ranges:
  - loinc_term:
      id: LOINC:2324-2
      label: Gamma glutamyl transferase [Enzymatic activity/volume] in Serum or Plasma
    upper_bound: 50.0
    unit: U/L
    population: children beyond the neonatal period
    notes: >-
      Provenance: general clinical laboratory convention for paediatric serum GGT beyond
      the neonatal period, not a PFIC-specific published interval; no citable numeric
      interval was available in the sources used for this entry, so no evidence item is
      attached. Neonatal GGT is physiologically higher. The bands below encode the
      pragmatic cholestasis-clinic split rather than an assay reference interval.
    interpretation_bands:
    - name: Low/normal-GGT cholestasis pattern
      upper_bound: 100.0
      unit: U/L
      abnormal_flag: NORMAL
      interpretation: >-
        A GGT below roughly 100 U/L in a cholestatic child directs testing to ATP8B1,
        ABCB11, TJP2, NR1H4, USP53 and MYO5B (and to bile acid synthesis defects as the
        main non-PFIC alternative).
    - name: High-GGT cholestasis pattern
      lower_bound: 100.0
      unit: U/L
      abnormal_flag: HIGH
      phenotype_term:
        preferred_term: Elevated gamma-glutamyltransferase level
        term:
          id: HP:0030948
          label: Elevated gamma-glutamyltransferase level
      interpretation: >-
        A GGT above roughly 100 U/L in a cholestatic child directs testing to ABCB4, and
        to the newer KIF12 and ZFYVE19 cholestases, after biliary obstruction and biliary
        atresia have been excluded.
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and \nPFIC2 patients, but is elevated in PFIC3 patients."
    explanation: The definitive statement of the GGT split across the three classical subtypes.
  - reference: PMID:26888176
    reference_title: Mutations in the nuclear bile acid receptor FXR cause progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "low-to-normal serum gamma-glutamyl \ntransferase activity"
    explanation: Places NR1H4/PFIC5 on the low-GGT side of the split.
  - reference: PMID:30976738
    reference_title: Recessive Mutations in KIF12 Cause High Gamma-Glutamyltransferase Cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "cholestatic \nliver disease with high GGT in 3 previously undiagnosed children"
    explanation: Places KIF12-related disease on the high-GGT side of the split.
  readouts:
  - target: Unbuffered Bile Salt Injury to the Cholangiocyte
    relationship: READOUT_OF
    endpoint_context: DIAGNOSTIC
    description: >-
      Serum GGT reports on whether the biliary epithelium is being attacked by
      unbuffered bile salts, which is exactly what separates ABCB4 disease from the
      hepatocyte-restricted subtypes.
- name: Serum conjugated (direct) bilirubin
  presence: Elevated
  context: >-
    The laboratory definition of cholestasis and the gateway test for the whole PFIC
    differential. Unlike the GGT reference range, this one has a genuinely citable
    consensus threshold: cholestasis in infancy is defined as a conjugated/direct
    bilirubin above 1 mg/dL and more than 20% of total bilirubin, a threshold recently
    lowered from the historical arbitrary 2 mg/dL. In the first days of life even lower
    values (>0.3-0.5 mg/dL, or >10% of total) are treated as abnormal.
  specificity: >-
    Sensitive for cholestasis but not specific for PFIC - it is shared with biliary
    atresia and the whole neonatal cholestasis differential. Its role here is to trigger
    the work-up, after which serum GGT performs the subtype triage.
  biomarker_term:
    preferred_term: Direct Bilirubin Measurement
    term:
      id: NCIT:C64481
      label: Direct Bilirubin Measurement
  mappings_list:
  - preferred_term: Bilirubin.direct [Mass/volume] in Serum or Plasma
    term:
      id: LOINC:1968-7
      label: Bilirubin.direct [Mass/volume] in Serum or Plasma
  reference_ranges:
  - loinc_term:
      id: LOINC:1968-7
      label: Bilirubin.direct [Mass/volume] in Serum or Plasma
    upper_bound: 1.0
    unit: mg/dL
    population: infants beyond the first days of life
    evidence:
    - reference: PMID:32861449
      reference_title: Recent developments in diagnostics and treatment of neonatal cholestasis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Cholestasis in infancy is defined as serum conjugated/direct bilirubin level >1 mg/dL and > 20% of the total bilirubin"
      explanation: Source of the 1 mg/dL consensus cholestasis threshold used as the upper bound of the normal interval.
    notes: >-
      The threshold is a consensus case definition of cholestasis rather than an assay
      reference interval, and it is paired with a percentage criterion (>20% of total
      bilirubin) that a single-analyte range cannot express - so the bands below should
      be read together with the total bilirubin.
    interpretation_bands:
    - name: Not cholestatic
      upper_bound: 1.0
      unit: mg/dL
      abnormal_flag: NORMAL
      interpretation: >-
        Below the consensus threshold; in a jaundiced infant this points to unconjugated
        (breast-milk or physiological) hyperbilirubinaemia rather than cholestasis.
    - name: Cholestatic range
      lower_bound: 1.0
      unit: mg/dL
      abnormal_flag: HIGH
      phenotype_term:
        preferred_term: Conjugated hyperbilirubinemia
        term:
          id: HP:0002908
          label: Conjugated hyperbilirubinemia
      interpretation: >-
        At or above the consensus threshold and more than 20% of total bilirubin defines
        cholestasis, mandating immediate hepatobiliary evaluation including urgent
        exclusion of biliary atresia.
  evidence:
  - reference: PMID:32861449
    reference_title: Recent developments in diagnostics and treatment of neonatal cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neonatal cholestasis is characterized by conjugated hyperbilirubinemia in the \nnewborn and young infant"
    explanation: Establishes conjugated hyperbilirubinaemia as the defining biochemical signature of neonatal cholestasis.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals have hyperbilirubinemia, mildly elevated transaminases, and elevated serum bile acids."
    explanation: Documents hyperbilirubinaemia as part of the PFIC biochemical picture.
  readouts:
  - target: Hepatocellular Bile Salt Retention
    relationship: READOUT_OF
    endpoint_context: DIAGNOSTIC
    description: >-
      Conjugated bilirubin retention is the routinely measured proxy for failure of
      canalicular secretion, and is the test that opens the PFIC differential.
- name: Total serum bile acids
  presence: Elevated
  context: >-
    Markedly raised in all PFIC subtypes and the principal quantitative marker of disease
    activity. It is the key secondary endpoint of both phase 3 IBAT inhibitor trials, and
    the post-diversion value is prognostic for native liver survival.
  biomarker_term:
    preferred_term: Bile Acid Measurement
    term:
      id: NCIT:C74800
      label: Bile Acid Measurement
  mappings_list:
  - preferred_term: Bile acid [Moles/volume] in Serum or Plasma
    term:
      id: LOINC:14628-2
      label: Bile acid [Moles/volume] in Serum or Plasma
  - preferred_term: bile salt
    term:
      id: CHEBI:22868
      label: bile salt
  reference_ranges:
  - loinc_term:
      id: LOINC:14628-2
      label: Bile acid [Moles/volume] in Serum or Plasma
    upper_bound: 10.0
    unit: umol/L
    population: children, fasting
    notes: >-
      Provenance: standard clinical laboratory convention for fasting total serum bile
      acids; not a PFIC-specific published interval, so no evidence item is attached to
      the interval itself. The band thresholds below are taken from the PFIC treatment
      literature and are cited on the parent record.
    interpretation_bands:
    - name: Normal
      upper_bound: 10.0
      unit: umol/L
      abnormal_flag: NORMAL
    - name: Elevated, at or below the odevixibat trial response threshold
      lower_bound: 10.0
      upper_bound: 70.0
      unit: umol/L
      abnormal_flag: HIGH
      severity: MILD
      phenotype_term:
        preferred_term: Increased serum bile acid concentration
        term:
          id: HP:0012202
          label: Increased serum bile acid concentration
      interpretation: >-
        A concentration at or below 70 micromol/L was one of the two definitions of
        serum bile acid response in the PEDFIC 1 odevixibat trial.
    - name: Markedly elevated
      lower_bound: 70.0
      unit: umol/L
      abnormal_flag: CRITICAL_HIGH
      severity: SEVERE
      phenotype_term:
        preferred_term: Increased serum bile acid concentration
        term:
          id: HP:0012202
          label: Increased serum bile acid concentration
      interpretation: >-
        Typical of untreated severe PFIC. In the NAPPED cohort a post-diversion
        concentration below 102 micromol/L predicted long native liver survival, so
        values well above that range mark a poor-prognosis group.
  evidence:
  - reference: PMID:35780807
    reference_title: 'Odevixibat treatment in progressive familial intrahepatic cholestasis: a randomised, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "proportion of patients with serum bile acid response (ie, serum bile acids \nreduced by ≥70% from baseline or concentrations of ≤70 μmol/L) at week 24"
    explanation: Source of the 70 micromol/L response threshold used in the interpretation bands.
  - reference: PMID:34082807
    reference_title: 'Epidemiology and burden of progressive familial intrahepatic cholestasis: a systematic review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "an SBA concentration below 102 µmol/L or a decrease of at least 75% shortly after SBD reliably predicted NLS of ≥ 15 years following SBD (each p < 0.001)"
    explanation: Source of the 102 micromol/L post-diversion prognostic threshold cited in the severe band.
  readouts:
  - target: Hepatocellular Bile Salt Retention
    relationship: READOUT_OF
    endpoint_context: MONITORING
    description: >-
      Circulating total bile acids are the systemic spillover of the hepatocyte bile
      salt burden and serve as its quantitative readout.
  - target: Enterohepatic Bile Acid Recirculation
    relationship: PHARMACODYNAMIC_MARKER_OF
    endpoint_context: PHARMACODYNAMIC
    description: >-
      Serum bile acids are the pharmacodynamic readout of IBAT inhibition and biliary
      diversion, both of which act by interrupting this loop.

genetic:
- name: ATP8B1
  gene_term:
    preferred_term: ATP8B1
    term:
      id: hgnc:3706
      label: ATP8B1
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: PFIC1
  presence: Biallelic loss-of-function
  features: >-
    Encodes FIC1, a P4-type ATPase aminophospholipid flippase of the canalicular
    membrane. Missense variants are relatively more common in the milder BRIC1 end of the
    spectrum and nonsense variants or large deletions in severe PFIC1, and the two
    classes differ functionally: PFIC1 missense mutants fail entirely to reach the
    canalicular membrane, whereas BRIC1 mutants retain residual canalicular expression.
  evidence:
  - reference: PMID:19731236
    reference_title: Differential effects of progressive familial intrahepatic cholestasis type 1 and benign recurrent intrahepatic cholestasis type 1 mutations on canalicular localization of ATP8B1.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Our data indicate that \nPFIC1 mutations lead to the complete absence of canalicular expression, whereas \nin BRIC1/ICP residual protein is expressed in the canalicular membrane."
    explanation: Provides the molecular basis for the PFIC1-versus-BRIC1 severity distinction within the same gene.
- name: ABCB11
  gene_term:
    preferred_term: ABCB11
    term:
      id: hgnc:42
      label: ABCB11
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: PFIC2
  presence: Biallelic loss-of-function
  features: >-
    Encodes BSEP. Highly allelically heterogeneous - 82 different mutations across 109
    families in the largest series, spanning nonsense, frameshift, splice, whole-gene
    deletion and missense classes. Two recurrent missense alleles, p.Glu297Gly and
    p.Asp482Gly, together account for 58% of European families and are associated with
    detectable residual BSEP; biallelic protein-truncating genotypes have none and carry
    the worst native liver survival and the highest malignancy risk.
  evidence:
  - reference: PMID:18395098
    reference_title: 'Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty-two percent of mutations occurred in >1 family, with \nE297G and/or D482G present in 58% of European families (52/89)."
    explanation: Quantifies the recurrent-allele structure of ABCB11 disease in European families.
  case_fractions:
  - population: European families with severe BSEP deficiency
    case_fraction_percent: 58.0
    cohort_size: 89
    notes: >-
      Proportion of European families carrying at least one of the two recurrent
      residual-function missense alleles E297G or D482G, not the proportion of PFIC
      caused by ABCB11.
    evidence:
    - reference: PMID:18395098
      reference_title: 'Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "E297G and/or D482G present in 58% of European families (52/89)"
      explanation: Directly quantifies the 58% figure in an 89-family European denominator.
- name: ABCB4
  gene_term:
    preferred_term: ABCB4
    term:
      id: hgnc:45
      label: ABCB4
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: PFIC3
  presence: Biallelic loss-of-function
  features: >-
    Encodes MDR3. Most reported defects are missense variants causing defective
    processing or intracellular transport; a minority abolish expression through early
    truncation. Monoallelic ABCB4 variants are not a cause of PFIC3 but predispose to a
    spectrum of adult and pregnancy-associated cholestatic phenotypes.
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Of the described defects in MDR3, the majority are missense mutations that result in defective processing or intracellular transport; while the minority have completely absent MDR3 expression secondary to early truncation or destruction of the protein"
    explanation: Characterizes the variant class distribution in ABCB4 disease.
- name: TJP2
  gene_term:
    preferred_term: TJP2
    term:
      id: hgnc:11828
      label: TJP2
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: PFIC4
  presence: Biallelic protein-truncating
  features: >-
    Encodes ZO-2. The PFIC4 mechanism specifically requires biallelic protein-truncating
    variants abolishing both isoforms; this is distinct from the single incompletely
    penetrant homozygous TJP2 missense allele previously reported in Amish familial
    hypercholanaemia, which impairs claudin binding but does not cause progressive liver
    disease.
  evidence:
  - reference: PMID:24614073
    reference_title: Mutations in TJP2 cause progressive cholestatic liver disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In contrast, the mutations identified in the patients presented here are predicted to abolish translation of both isoforms ofTJP2."
    explanation: Establishes that PFIC4 requires complete loss of both TJP2 isoforms, distinguishing it from the milder Amish missense allele.
- name: NR1H4
  gene_term:
    preferred_term: NR1H4
    term:
      id: hgnc:7967
      label: NR1H4
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: PFIC5
  presence: Biallelic loss-of-function
  features: >-
    Encodes the farnesoid X receptor. Extremely rare - four individuals from two families
    in the original report. Exon-level and intragenic copy-number variants occur, so
    panel and exome pipelines must include CNV calling.
  evidence:
  - reference: PMID:26888176
    reference_title: Mutations in the nuclear bile acid receptor FXR cause progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we report four individuals from\ntwo unrelated families with neonatal cholestasis and mutations in NR1H4"
    explanation: The original report establishing NR1H4 as a PFIC gene and documenting its extreme rarity.
- name: MYO5B
  gene_term:
    preferred_term: MYO5B
    term:
      id: hgnc:7603
      label: MYO5B
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: MYO5B-related cholestasis
  presence: Biallelic loss-of-function
  features: >-
    Encodes myosin Vb. Historically identified as the microvillus inclusion disease gene;
    biallelic variants can cause isolated low-GGT cholestasis with no intestinal disease
    at all, so MYO5B must be on any cholestasis panel regardless of gut phenotype.
  evidence:
  - reference: PMID:27532546
    reference_title: MYO5B mutations cause cholestasis with normal serum gamma-glutamyl transferase activity in children without microvillous inclusion disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Using a \nnew-generation sequencing approach, we identified MYO5B mutations in five \npatients with progressive familial intrahepatic cholestasis-like phenotype with \nnormal serum gamma-glutamyl transferase activity without intestinal disease."
    explanation: Establishes isolated hepatic MYO5B disease without intestinal involvement.
- name: USP53
  gene_term:
    preferred_term: USP53
    term:
      id: hgnc:29255
      label: USP53
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: USP53-related cholestasis
  presence: Biallelic loss-of-function
  features: >-
    Encodes an inactive ubiquitin-specific peptidase that co-localizes with TJP2 in the
    tight junction complex, placing USP53 disease mechanistically adjacent to PFIC4.
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Defects in the USP53 protein, thought to colocalize with TJP2 and be part of the tight junction complex"
    explanation: Places USP53 within the TJP2 tight junction complex, explaining its low-GGT phenotype.
- name: KIF12
  gene_term:
    preferred_term: KIF12
    term:
      id: hgnc:21495
      label: KIF12
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: KIF12-related cholestasis
  presence: Biallelic loss-of-function
  features: >-
    Encodes a kinesin motor protein. Homozygous damaging variants (p.Arg219* and
    p.Val204Met reported) cause high-GGT cholestasis, identified in offspring of
    consanguineous unions.
  evidence:
  - reference: PMID:30976738
    reference_title: Recessive Mutations in KIF12 Cause High Gamma-Glutamyltransferase Cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both children had a rare homozygous damaging mutation \n(p.Arg219* and p.Val204Met) in kinesin family member 12 (KIF12)."
    explanation: Documents the specific homozygous KIF12 variants causing high-GGT cholestasis.
- name: ZFYVE19
  gene_term:
    preferred_term: ZFYVE19
    term:
      id: hgnc:20758
      label: ZFYVE19
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: ZFYVE19-related cholestasis
  presence: Biallelic loss-of-function
  features: >-
    Encodes a zinc-finger FYVE-domain protein with a probable role in ciliary and
    centriolar function. A homozygous nonsense variant (p.Arg223Ter) has been reported in
    high-GGT neonatal cholestasis with a demonstrable ciliary phenotype on patient
    fibroblasts.
  evidence:
  - reference: PMID:33853651
    reference_title: 'A ZFYVE19 gene mutation associated with neonatal cholestasis and cilia dysfunction: case report with a novel pathogenic variant.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Further sequencing investigation revealed a homozygous non-sense mutation \n(p.Arg223Ter) in ZFYVE19 leading to a 222 aa truncated protein and present in \nboth heterozygous parents."
    explanation: Documents the specific homozygous ZFYVE19 variant with parental segregation.

diagnosis:
- name: Serum GGT-based subtype triage in cholestatic infants
  description: >-
    In an infant with confirmed cholestasis and no biliary obstruction, the serum GGT
    partitions the differential and directs genetic testing. A low or normal GGT despite
    marked cholestasis points to ATP8B1, ABCB11, TJP2, NR1H4, USP53 or MYO5B; a high GGT points
    to ABCB4 and to the newer KIF12 and ZFYVE19 cholestases, once biliary atresia,
    choledochal cyst and other obstructive cholangiopathies have been excluded by
    ultrasound and, where indicated, cholangiography.
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and \nPFIC2 patients, but is elevated in PFIC3 patients."
    explanation: The biochemical basis of the triage rule.
- name: Molecular genetic confirmation
  description: >-
    Genetic testing is the etiologic gold standard. A comprehensive cholestasis NGS panel
    including deletion/duplication analysis is first-line, escalating to trio exome or
    genome sequencing with periodic reanalysis when negative. Expert consensus recommends
    initiating treatment for severe pruritus in parallel with, rather than after, genetic
    confirmation.
  evidence:
  - reference: PMID:38192535
    reference_title: Opinion paper on the diagnosis and treatment of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "suggests that genetic testing be used to confirm genotype whilst treatment \nis initiated in patients in whom PFIC is suspected"
    explanation: Expert consensus that genotyping should run in parallel with, not gate, treatment initiation.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of ATP8B1 deficiency is established in \na proband with suggestive clinical and laboratory findings and biallelic \npathogenic variants in ATP8B1 identified by molecular genetic testing."
    explanation: The GeneReviews Diagnosis/Testing statement, establishing biallelic molecular genetic testing as the confirmatory diagnostic step for the ATP8B1 subtype.
- name: Hepatic transporter immunostaining
  description: >-
    BSEP and MDR3 immunohistochemistry on liver biopsy supports but does not replace
    genetic diagnosis. Immunohistochemically detectable BSEP is typically absent or much
    reduced in severe ABCB11 disease; MDR3 staining is absent, decreased or - where the
    defect is functional rather than expressive - normal in ABCB4 disease; in MYO5B
    disease BSEP and MDR3 are present but abnormally localized, which is the diagnostic
    signature of a trafficking rather than a transporter lesion.
  evidence:
  - reference: PMID:18395098
    reference_title: 'Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Immunohistochemically detectable BSEP is typically absent, or much reduced, in \nsevere disease."
    explanation: Establishes the immunostaining pattern in severe BSEP deficiency and its diagnostic value.
- name: Hepatobiliary malignancy surveillance
  description: >-
    Because hepatocellular carcinoma and cholangiocarcinoma occur in early childhood in
    severe BSEP deficiency and in TJP2 deficiency, alpha-fetoprotein measurement and
    abdominal ultrasound every 6-12 months are recommended from the first year of life in
    these subtypes, and should continue in patients who retain their native liver.
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Monitoring of liver tumors, especially in PFIC2 \npatients, should be offered from the first year of life."
    explanation: States the surveillance recommendation and its subtype focus.
  - reference: PMID:18395098
    reference_title: 'Severe bile salt export pump deficiency: 82 different ABCB11 mutations in 109 families.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Close \nsurveillance of BSEP-deficient patients retaining their native liver, \nparticularly those carrying 2 null mutations, is essential."
    explanation: Specifies that surveillance targets native-liver BSEP-deficient patients, especially null/null genotypes.

histopathology:
- name: Canalicular cholestasis with coarse granular Byler bile
  description: >-
    In ATP8B1 deficiency, canalicular cholestasis with biliary plugs, giant cell
    transformation, ductular paucity and lobular disarray; the canalicular bile has a
    characteristic coarse, granular appearance historically termed Byler bile. In ABCB11
    disease the pattern is canalicular cholestasis with hepatocellular disarray and
    lobular and portal fibrosis. TJP2 and NR1H4 disease show intracellular cholestasis
    with giant cell transformation.
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histopathology demonstrates canalicular cholestasis with biliary plugs, giant cell transformation, ductular paucity, and lobular disarray"
    explanation: Describes the histological pattern of FIC1 deficiency including the Byler bile appearance.
- name: Portal fibrosis with bile duct proliferation
  description: >-
    In ABCB4/MDR3 deficiency the histology is that of a cholangiopathy rather than a
    purely hepatocellular disease - portal fibrosis and bile duct proliferation with mild
    giant cell hepatitis at onset, and occasional intraductal cholelithiasis. This
    ductular pattern is the tissue counterpart of the high serum GGT.
  subtype: PFIC3
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histology typically demonstrates portal fibrosis and bile duct proliferation with mild giant cell hepatitis at disease onset with occasional intraductal cholelithiasis"
    explanation: Documents the biliary/ductular histological pattern that distinguishes PFIC3 from the hepatocellular subtypes.

treatments:
- name: Odevixibat
  description: >-
    Once-daily oral inhibitor of the ileal bile acid transporter (IBAT/ASBT, SLC10A2)
    that blocks reabsorption of bile acids in the terminal ileum, diverting them into the
    faeces and lowering the bile acid load returned to the liver - a pharmacological
    equivalent of surgical biliary diversion. In the PEDFIC 1 phase 3 trial in PFIC1 and
    PFIC2, odevixibat significantly improved pruritus (55% vs 30% positive pruritus
    assessments) and serum bile acid response (33% vs 0%). Approved in 2021 in the EU for
    PFIC and in the US for PFIC-associated pruritus. Response is genotype-dependent -
    patients with complete loss of BSEP protein do not respond consistently, because
    reducing enterohepatic return cannot compensate for absent canalicular export.
    Diarrhoea and frequent bowel movements are the characteristic class effect, reported
    in 31% of odevixibat-treated versus 10% of placebo-treated patients in PEDFIC 1.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: odevixibat
      term:
        id: NCIT:C166598
        label: Odevixibat
  target_mechanisms:
  - target: Enterohepatic Bile Acid Recirculation
    treatment_effect: INHIBITS
    description: >-
      Blocks IBAT-mediated ileal reclamation of bile acids, interrupting the loop that
      re-delivers the bile acid load to the diseased liver.
    evidence:
    - reference: PMID:35780807
      reference_title: 'Odevixibat treatment in progressive familial intrahepatic cholestasis: a randomised, placebo-controlled, phase 3 trial.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Odevixibat, administered as once a day oral capsules, is a non-surgical, \npharmacological option to interrupt the enterohepatic circulation in patients \nwith PFIC."
      explanation: States the mechanism of action as interruption of the enterohepatic circulation.
  target_phenotypes:
  - preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  - preferred_term: Increased serum bile acid concentration
    term:
      id: HP:0012202
      label: Increased serum bile acid concentration
  evidence:
  - reference: PMID:35780807
    reference_title: 'Odevixibat treatment in progressive familial intrahepatic cholestasis: a randomised, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In children with PFIC, odevixibat effectively reduced pruritus \nand serum bile acids versus placebo and was generally well tolerated."
    explanation: Randomised placebo-controlled phase 3 evidence of efficacy on both co-primary endpoints.
  - reference: PMID:35780807
    reference_title: 'Odevixibat treatment in progressive familial intrahepatic cholestasis: a randomised, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common treatment-emergent adverse events (TEAEs) \nwere diarrhoea or frequent bowel movements"
    explanation: Identifies the characteristic diarrhoeal class effect of IBAT inhibition; the trial reported it in 13 of 42 odevixibat-treated versus 2 of 20 placebo-treated patients.
  - reference: PMID:39768432
    reference_title: 'Practical Considerations for Odevixibat Treatment in Patients with Progressive Familial Intrahepatic Cholestasis: A Single-Center Case Series.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two siblings with \ncomplete loss of bile salt export pump (BSEP) protein did not respond to \ntreatment; both underwent liver transplantation"
    explanation: Real-world evidence of the genotype limit on IBAT inhibitor efficacy - complete BSEP loss predicts non-response. PARTIAL because it qualifies rather than supports the efficacy claim.
- name: Maralixibat
  description: >-
    Second oral IBAT inhibitor, evaluated in MARCH-PFIC across all PFIC types.
    In the biallelic non-truncated BSEP cohort it significantly improved pruritus
    (least-squares mean between-group difference -1.1 on morning ItchRO(Obs)) and reduced
    total serum bile acids by 187 micromol/L relative to placebo. Diarrhoea was the most
    common adverse event, reported in 57% of maralixibat-treated versus 20% of
    placebo-treated participants and generally mild-to-moderate and transient. The
    trial design itself encodes the genotype dependency: the primary cohort deliberately
    excluded biallelic truncated BSEP deficiency.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: maralixibat
      term:
        id: NCIT:C170148
        label: Maralixibat
  target_mechanisms:
  - target: Enterohepatic Bile Acid Recirculation
    treatment_effect: INHIBITS
    description: >-
      Inhibits the ileal bile acid transporter, interrupting enterohepatic recirculation.
    evidence:
    - reference: PMID:38723644
      reference_title: 'Maralixibat in progressive familial intrahepatic cholestasis (MARCH-PFIC): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Maralixibat represents a non-surgical, \npharmacological option to interrupt the enterohepatic circulation and improve \nthe standard of care in patients with PFIC."
      explanation: States the mechanism of action as interruption of the enterohepatic circulation.
  target_phenotypes:
  - preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  - preferred_term: Increased serum bile acid concentration
    term:
      id: HP:0012202
      label: Increased serum bile acid concentration
  evidence:
  - reference: PMID:38723644
    reference_title: 'Maralixibat in progressive familial intrahepatic cholestasis (MARCH-PFIC): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Maralixibat improved pruritus and predictors of native liver \nsurvival in PFIC (eg, serum bile acids)."
    explanation: Randomised phase 3 evidence of efficacy on pruritus and serum bile acids.
  - reference: PMID:38723644
    reference_title: 'Maralixibat in progressive familial intrahepatic cholestasis (MARCH-PFIC): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common \nadverse event was diarrhoea"
    explanation: Identifies the diarrhoeal class effect of IBAT inhibition with maralixibat; the trial reported it in 27 of 47 maralixibat versus 9 of 46 placebo participants, all mild or moderate and mostly transient.
- name: Surgical biliary diversion
  description: >-
    Partial external biliary diversion (a cholecystojejunal cutaneous stoma), partial
    internal biliary diversion (a gallbladder-to-colon neo-conduit) or ileal exclusion,
    all of which interrupt the enterohepatic circulation surgically. The oldest
    disease-modifying therapy in PFIC: it reduces pruritus and serum bile acids and can
    slow or even reverse fibrosis, allowing many patients to keep their native liver.
    Response is genotype-dependent in the same way as IBAT inhibition - patients
    retaining residual transporter function do better - and complications include stoma
    problems, diarrhoea, malabsorption and recurrent pruritus. In PFIC1 patients coming to
    transplant, ileal diversion is sometimes performed at the same operation to protect
    the graft from steatosis.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Surgical Procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Enterohepatic Bile Acid Recirculation
    treatment_effect: INHIBITS
    description: >-
      Physically diverts bile away from the terminal ileum, or bypasses the ileum, so
      bile acids are not reclaimed into the portal circulation.
    evidence:
    - reference: PMID:20301474
      reference_title: ATP8B1 Deficiency.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "the primary \nsurgical therapy is interruption of the enterohepatic circulation which can \nreduce pruritus and slow or reverse the progression to hepatic fibrosis"
      explanation: States the mechanism and the disease-modifying (not merely symptomatic) effect.
  target_phenotypes:
  - preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In \nsome PFIC1 and PFIC2 patients, biliary diversion may also relieve pruritus and \nslow disease progression."
    explanation: Establishes biliary diversion as a pruritus-relieving and disease-slowing intervention in PFIC1 and PFIC2.
  - reference: PMID:34082807
    reference_title: 'Epidemiology and burden of progressive familial intrahepatic cholestasis: a systematic review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "an SBA concentration below 102 µmol/L or a decrease of at least 75% shortly after SBD reliably predicted NLS of ≥ 15 years following SBD (each p < 0.001)"
    explanation: Quantifies the prognostic value of the biochemical response to surgical biliary diversion.
- name: Ursodeoxycholic acid
  description: >-
    A hydrophilic bile acid that displaces hydrophobic, cytotoxic bile salts from the
    circulating pool and may also induce BSEP and MDR3 expression. Conventionally started
    in all PFIC patients, but the benefit is strongly subtype-dependent: most patients
    with MDR3/ABCB4 deficiency have a favourable outcome on UDCA, whereas sustained
    benefit in severe PFIC1 and PFIC2 is limited and pharmacotherapy for cholestasis in
    severe ATP8B1 disease is explicitly described as ineffective.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ursodeoxycholic acid
      term:
        id: CHEBI:9907
        label: ursodeoxycholic acid
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ursodeoxycholic acid \n(UDCA) therapy should be initiated in all patients to prevent liver damage."
    explanation: The conventional recommendation to initiate UDCA in all PFIC patients.
  - reference: PMID:20422496
    reference_title: 'The spectrum of liver diseases related to ABCB4 gene mutations: pathophysiology and clinical aspects.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most patients with MDR3 deficiency have a favorable \noutcome with ursodeoxycholic acid (UDCA) therapy"
    explanation: Documents the favourable UDCA response specific to ABCB4/MDR3 disease.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Cholestasis: pharmacotherapy is \nineffective regardless of disease severity."
    explanation: GeneReviews explicitly refutes a cholestasis benefit from pharmacotherapy in ATP8B1 deficiency, which is why UDCA benefit is curated here as subtype-dependent rather than general.
- name: Antipruritic pharmacotherapy
  description: >-
    Off-label symptomatic options for cholestatic itch - the bile acid sequestrant
    cholestyramine, the PXR agonist rifampicin, naltrexone and sertraline - used before
    or alongside IBAT inhibition. Efficacy is variable and generally poorer in FIC1
    deficiency than in other cholestatic disease, and rifampicin is notable for shortening
    cholestatic exacerbations in the allelic BRIC phenotype.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: cholestyramine
      term:
        id: NCIT:C28929
        label: Cholestyramine
    - preferred_term: rifampin
      term:
        id: NCIT:C811
        label: Rifampin
  target_phenotypes:
  - preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other antipruritic agents (Table 1) such as rifampin and cholestyramine may also be utilized but are often less helpful in FIC1 deficiency"
    explanation: Documents these agents as antipruritic options while qualifying their limited efficacy in FIC1 deficiency - hence PARTIAL.
- name: AAV-ABCB11 Gene Therapy
  description: >-
    Liver-directed adeno-associated virus (AAV) vector delivery of the ABCB11 gene encoding
    the bile salt export pump (BSEP). VTX-802, which uses a constitutive promoter for ABCB11
    expression, was evaluated in a PFIC2 mouse model and showed sustained, dose-dependent
    improvement: treated mice displayed significant correction of serum transaminase
    elevation and significant, but partial, correction of hepatomegaly, with increased bile
    acid levels in bile and small intestine. This represents an emerging gene-therapy approach that
    directly restores the deficient transporter function in monogenic BSEP-deficiency
    disease. As a preclinical proof-of-concept, the work provides mechanistic evidence for
    in vivo BSEP restoration and primes the platform for clinical translation.
  therapeutic_modality: GENE_THERAPY
  treatment_term:
    preferred_term: Gene Therapy
    term:
      id: NCIT:C15238
      label: Gene Therapy
  target_mechanisms:
  - target: BSEP-Mediated Bile Salt Export Failure
    treatment_effect: RESTORES
    description: >-
      AAV-mediated ABCB11 gene delivery restores expression of functional BSEP protein
      in hepatocytes, permitting resumption of canalicular bile salt export and
      interruption of the intrahepatic bile acid accumulation that drives cholestatic
      injury.
    evidence:
    - reference: PMID:42579774
      reference_title: Liver-directed gene therapy results in amelioration of progressive familial intrahepatic cholestasis type 2 in mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The AAV vector containing the constitutive promoter, named VTX-802, showed higher BSEP expression, resulting in better restoration of BA secretion"
      explanation: Documents VTX-802-mediated restoration of BSEP expression and function in the PFIC2 mouse model.
  target_phenotypes:
  - preferred_term: Elevated circulating hepatic transaminase concentration
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
  - preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: PMID:42579774
    reference_title: Liver-directed gene therapy results in amelioration of progressive familial intrahepatic cholestasis type 2 in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Treated mice showed a sustained dose-dependent improvement in serum transaminase levels. These mice also exhibited significant, but partial, correction of hepatomegaly, and increased BA levels in bile and small intestine"
    explanation: Preclinical evidence that AAV-ABCB11 gene therapy ameliorates the cardinal biochemical and hepatic pathology phenotypes of PFIC2 in mice.
- name: Nutritional and fat-soluble vitamin support
  description: >-
    Hypercaloric feeding with medium-chain triglycerides, which do not require micellar
    solubilization, plus aggressive replacement of vitamins A, D, E and K with monitoring
    of INR, vitamin levels, bone health and growth. This is universal supportive care in
    all PFIC subtypes and becomes more important, not less, on IBAT inhibitor therapy,
    because reducing intraluminal bile acid delivery can further impair fat-soluble
    vitamin absorption.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Nutritional Support
    term:
      id: NCIT:C15433
      label: Nutritional Support
  target_phenotypes:
  - preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Poor \ngrowth may require medium-chain triglyceride-based formulas; fat-soluble vitamin \ndeficiencies are treated symptomatically."
    explanation: GeneReviews specifies MCT-based formula and fat-soluble vitamin replacement as standard management.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients should be treated with caloric, fat, and vitamin supplementation, with the majority of fat being medium chain triglycerides"
    explanation: Specifies the composition of nutritional support in PFIC.
- name: Liver transplantation
  description: >-
    Definitive therapy for end-stage liver disease, unresectable hepatocellular
    carcinoma, severe portal hypertension, or pruritus and growth failure refractory to
    diversion and IBAT inhibition. Two subtype-specific caveats matter. In ATP8B1
    disease, transplantation replaces only the hepatic compartment: secretory diarrhoea
    persists or worsens and is associated with allograft steatosis and fibrosis that can
    require re-transplantation, and hearing loss is unaffected - so PFIC1 is the one
    subtype where transplantation can make an extrahepatic manifestation worse. In ABCB11
    disease, alloantibodies against the BSEP extracellular loop can produce an
    immune-mediated functional recurrence of BSEP deficiency in the graft. In MYO5B
    disease with microvillus inclusion disease, combined liver-intestinal transplantation
    or intestinal transplantation with biliary diversion is preferred.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Liver Transplantation
    term:
      id: NCIT:C15271
      label: Liver Transplantation
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, most PFIC patients are ultimately candidates \nfor liver transplantation."
    explanation: Establishes liver transplantation as the eventual endpoint for most patients with untreated progressive disease.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably for some, secretory diarrhea can continue or worsen following liver \ntransplantation."
    explanation: GeneReviews caveat that transplantation does not correct - and may worsen - the extrahepatic diarrhoea of ATP8B1 deficiency.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "patients can develop allo-reactive antibodies specific to the extracellular loop of the BSEP protein resulting in an immune mediated recurrence of their BSEP disease in the allograft"
    explanation: Documents antibody-mediated post-transplant recurrence of BSEP deficiency, the PFIC2-specific transplant caveat.
  - reference: PMID:35070006
    reference_title: Newer variants of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These children are at risk of worsening cholestasis \npost intestinal transplant (IT) for MVID, hence combined intestinal and liver \ntransplant or IT with biliary diversion is preferred."
    explanation: Documents the MYO5B-specific transplant strategy.
- name: Avoidance of ototoxic agents and oestrogen-containing contraceptives
  description: >-
    A GeneReviews agents-and-circumstances-to-avoid recommendation specific to ATP8B1
    deficiency. Potentially ototoxic drugs must be avoided because sensorineural hearing
    loss is already common across the ATP8B1 spectrum and further insult is additive.
    Oral contraceptive agents can induce or exacerbate cholestatic episodes, which is
    mechanistically coherent given that oestradiol interferes with FXR-mediated BSEP
    regulation. Routine audiograms are recommended for all individuals with ATP8B1
    deficiency, symptomatic or not.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Agents/circumstances to avoid: Potentially ototoxic agents; oral \ncontraceptive agent therapies can induce and/or exacerbate episodes of \ncholestasis."
    explanation: The GeneReviews agents-to-avoid recommendation verbatim.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "routine audiograms \nfor all individuals with ATP8B1 deficiency whether known to be symptomatic or \nnot."
    explanation: The accompanying GeneReviews surveillance recommendation.
- name: Genetic counselling and family testing
  description: >-
    Autosomal recessive counselling with a 25% recurrence risk for carrier couples. Once
    the familial variants are known, carrier testing, prenatal diagnosis and
    preimplantation genetic testing are available, and at-risk siblings should be tested
    presymptomatically so that treatment and surveillance can start early.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Once the ATP8B1 pathogenic variants \nhave been identified in an affected family member, carrier testing for at-risk \nrelatives and prenatal and preimplantation genetic testing are possible."
    explanation: GeneReviews statement of the available family testing options.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is appropriate to clarify the \ngenetic status of apparently asymptomatic older and younger at-risk relatives of \nan affected individual in order to identify as early as possible those who would \nbenefit from prompt initiation of treatment, surveillance, and awareness of \nagents and circumstances to avoid."
    explanation: GeneReviews recommendation for presymptomatic testing of at-risk relatives.

differential_diagnoses:
- name: Alagille syndrome
  disease_term:
    preferred_term: Alagille syndrome
    term:
      id: MONDO:0007318
      label: Alagille syndrome
  description: >-
    The principal syndromic cholestatic differential. Alagille syndrome shares
    early-onset cholestasis, intractable pruritus and IBAT-inhibitor responsiveness with
    PFIC, and the dismech Alagille entry already lists PFIC as a differential in the
    reciprocal direction.
  distinguishing_features:
  - Autosomal dominant (JAG1, less often NOTCH2) versus autosomal recessive in PFIC.
  - A multisystem Notch developmental disorder in which cholestasis arises from paucity of interlobular bile ducts, accompanied by peripheral pulmonary artery stenosis or other congenital heart disease, posterior embryotoxon, butterfly vertebrae, characteristic facies and renal anomalies.
  - PFIC is a hepatocellular bile-formation disorder with a normal biliary tree and no developmental extrahepatic syndrome; the extrahepatic features of PFIC1 are functional consequences of FIC1 loss in other tissues, not malformations.
  - Serum GGT is characteristically elevated in Alagille syndrome, which separates it from the low-GGT PFIC subtypes though not from PFIC3.
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diagnosis is based on \nclinical manifestations, liver ultrasonography, cholangiography and liver \nhistology, as well as on specific tests to exclude other causes of childhood \ncholestasis."
    explanation: Establishes that PFIC diagnosis explicitly requires excluding other causes of childhood cholestasis, of which Alagille syndrome is the leading syndromic one.
- name: Biliary atresia
  disease_term:
    preferred_term: biliary atresia
    term:
      id: MONDO:0008867
      label: biliary atresia
  description: >-
    The most urgent differential in a cholestatic neonate, because the Kasai
    portoenterostomy is time-critical.
  distinguishing_features:
  - An acquired obliterative extrahepatic cholangiopathy with a high GGT, acholic stools, an absent or abnormal gallbladder on ultrasound and an abnormal intraoperative cholangiogram.
  - PFIC has a patent biliary tree with a normal cholangiogram, and the low-GGT PFIC subtypes are separated biochemically at the bedside.
  - A normal cholangiogram was precisely what excluded biliary atresia in the reported ZFYVE19 high-GGT case, showing that GGT alone cannot make this distinction.
  evidence:
  - reference: PMID:33853651
    reference_title: 'A ZFYVE19 gene mutation associated with neonatal cholestasis and cilia dysfunction: case report with a novel pathogenic variant.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Despite fibrosis/cirrhosis and biliary ducts proliferation \non liver biopsy suggested an extrahepatic biliary obstacle, normal \nintra-operatory cholangiography excluded biliary atresia."
    explanation: A worked example of how biliary atresia is excluded in a high-GGT PFIC-spectrum infant, and of why GGT alone is insufficient.
- name: Benign recurrent intrahepatic cholestasis
  disease_term:
    preferred_term: benign recurrent intrahepatic cholestasis
    term:
      id: MONDO:0019008
      label: benign recurrent intrahepatic cholestasis
  description: >-
    The allelic neighbour, not merely a look-alike. BRIC1 and BRIC2 are caused by
    variants in the SAME genes as PFIC1 and PFIC2 (ATP8B1 and ABCB11), so a genetic
    result alone does not distinguish them. They sit at opposite ends of one continuum,
    and the distinction is made phenotypically and mechanistically rather than by gene.
  distinguishing_features:
  - BRIC causes episodic, self-limiting attacks of cholestasis with complete symptomatic resolution between episodes, whereas PFIC is persistent and progresses to end-stage liver disease.
  - The molecular basis of the split is residual canalicular protein - PFIC1 missense mutants are entirely absent from the canalicular membrane, whereas BRIC1 and ICP mutants retain canalicular expression.
  - The boundary is permeable in both directions; some BRIC cases transition to persistent progressive disease, and individuals with ATP8B1 deficiency can shift over time from the episodic to the persistent end of the spectrum, so the label "benign" is not a guarantee.
  - Hepatic fibrosis can be present early even at the mild end of the ATP8B1 spectrum.
  evidence:
  - reference: PMID:19731236
    reference_title: Differential effects of progressive familial intrahepatic cholestasis type 1 and benign recurrent intrahepatic cholestasis type 1 mutations on canalicular localization of ATP8B1.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type 1 \n(PFIC1) and benign recurrent intrahepatic cholestasis type 1 (BRIC1), forming a \nspectrum of cholestatic disease."
    explanation: Establishes the allelic relationship - the same gene causes both entities.
  - reference: PMID:19731236
    reference_title: Differential effects of progressive familial intrahepatic cholestasis type 1 and benign recurrent intrahepatic cholestasis type 1 mutations on canalicular localization of ATP8B1.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Whereas PFIC1 is a progressive, endstage liver \ndisease, BRIC1 patients suffer from episodic periods of cholestasis that resolve \nspontaneously."
    explanation: States the clinical distinction between the two allelic phenotypes.
  - reference: PMID:20301474
    reference_title: ATP8B1 Deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in some persons with ATP8B1 deficiency the clinical \nfindings can span the phenotypic spectrum, shifting over time from the mild end \nof the spectrum (episodic cholestasis) to the severe end of the spectrum \n(persistent cholestasis)."
    explanation: GeneReviews evidence that the PFIC1/BRIC1 boundary is permeable within a single individual over time.
  notes: >-
    Because BRIC is allelic rather than merely phenotypically similar, a low-GGT
    cholestasis panel result naming ATP8B1 or ABCB11 must be interpreted together with the
    clinical course; the gene alone does not assign the PFIC versus BRIC label.
- name: Inborn errors of bile acid synthesis
  disease_term:
    preferred_term: inborn disorder of bile acid synthesis
    term:
      id: MONDO:0019218
      label: inborn disorder of bile acid synthesis
  description: >-
    The other major cause of LOW-GGT neonatal cholestasis, and therefore the differential
    that the GGT split cannot resolve.
  distinguishing_features:
  - Bile acid synthesis defects produce low-GGT cholestasis with characteristically low or normal serum bile acids, because the defect is in making bile acids rather than in exporting them - the opposite of the markedly elevated serum bile acids of PFIC.
  - Urinary bile acid mass spectrometry identifies the accumulating atypical intermediates and is the discriminating test.
  - The distinction is therapeutically decisive because bile acid synthesis defects respond to primary bile acid replacement.
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MDR3 and BSEP liver immunostaining, and analysis of biliary lipid \ncomposition should help to select PFIC candidates for whom genotyping could be \nproposed to confirm the diagnosis."
    explanation: Supports the use of biliary lipid and transporter analysis to select true PFIC candidates from among other low-GGT cholestatic causes.
- name: Alpha-1-antitrypsin deficiency
  disease_term:
    preferred_term: alpha-1-antitrypsin deficiency
    term:
      id: MONDO:0013282
      label: alpha-1-antitrypsin deficiency
  description: >-
    A routine part of the neonatal cholestasis work-up and one of the commonest genetic
    causes of childhood liver disease.
  distinguishing_features:
  - SERPINA1 Pi*ZZ disease with a low serum alpha-1-antitrypsin level and a characteristic Pi phenotype on protease inhibitor typing.
  - PAS-positive diastase-resistant hepatocyte inclusions on liver biopsy.
  - An associated adult pulmonary emphysema risk that is absent from PFIC.
  - The liver injury mechanism is retained-polymer proteotoxicity in the hepatocyte endoplasmic reticulum rather than a bile transport defect, and pruritus is not the dominant symptom.
  evidence:
  - reference: PMID:23141890
    reference_title: Progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "as well as on specific tests to exclude other causes of childhood \ncholestasis"
    explanation: Supports the requirement to exclude other genetic causes of childhood cholestasis before diagnosing PFIC.
- name: Cystic fibrosis liver disease
  disease_term:
    preferred_term: cystic fibrosis
    term:
      id: MONDO:0009061
      label: cystic fibrosis
  description: >-
    A particularly instructive differential for PFIC1, because ATP8B1 deficiency itself
    causes an elevated sweat chloride - the classic cystic fibrosis diagnostic test - and
    can therefore be mistaken for it.
  distinguishing_features:
  - Caused by biallelic CFTR variants and dominated by sinopulmonary disease with chronic infection; the hepatobiliary manifestation is focal biliary cirrhosis with a high GGT.
  - PFIC1 has an elevated sweat chloride and pancreatic insufficiency but no bronchiectatic lung disease, and its cholestasis is low-GGT.
  - CFTR genotyping resolves the ambiguity.
  - Mechanistic overlap is real rather than coincidental - certain CFTR folding correctors improve defective FIC1 trafficking in cell culture.
  evidence:
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected children frequently exhibit profound diarrhea, poor growth, short stature, pancreatic insufficiency, elevated sweat chloride, and sensorineural deafness"
    explanation: Documents the elevated sweat chloride and pancreatic insufficiency of FIC1 deficiency that create the overlap with cystic fibrosis.
  - reference: PMID:31183005
    reference_title: Expanding etiology of progressive familial intrahepatic cholestasis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Certain CFTR folding correctors have been shown to improve defective trafficking of FIC1 in cell culture"
    explanation: In vitro evidence of a shared trafficking-correction mechanism between CFTR and FIC1; PARTIAL because human data are explicitly lacking.

clinical_trials:
- name: NCT03566238
  phase: PHASE_III
  status: COMPLETED
  description: >-
    PEDFIC 1 - the pivotal 24-week randomised, double-blind, placebo-controlled phase 3
    trial of the ileal bile acid transporter inhibitor odevixibat (A4250) at 40 and 120
    micrograms/kg/day in 62 children with PFIC1 and PFIC2. Both co-primary endpoints
    (proportion of positive pruritus assessments and serum bile acid response) were met,
    and the trial is the registrational basis for odevixibat in PFIC.
  target_phenotypes:
  - preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  - preferred_term: Increased serum bile acid concentration
    term:
      id: HP:0012202
      label: Increased serum bile acid concentration
  evidence:
  - reference: clinicaltrials:NCT03566238
    reference_title: A Double-Blind, Randomized, Placebo-Controlled, Phase 3 Study to Demonstrate Efficacy and Safety of A4250 in Children With Progressive Familial Intrahepatic Cholestasis Types 1 and 2 (PEDFIC 1)
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Double blind, randomized, placebo controlled, Phase 3 study to investigate the efficacy and safety of low doses and high doses of A4250 compared to placebo in children with progressive familial intrahepatic cholestasis (PFIC) types 1 and 2."
    explanation: The registered trial record for PEDFIC 1, the phase 3 study of odevixibat in PFIC1 and PFIC2.
- name: NCT03659916
  phase: PHASE_III
  status: COMPLETED
  description: >-
    PEDFIC 2 - the open-label extension of PEDFIC 1, designed to evaluate the long-term
    safety of odevixibat and the persistence of its effect in children with PFIC. It is
    the durability arm of the odevixibat programme. Enrolment, duration and outcome
    figures are deliberately omitted here: the cached registry record states only the
    study's design and objective, and the PEDFIC 2 results publication is not among this
    entry's verified references.
  target_phenotypes:
  - preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  - preferred_term: Increased serum bile acid concentration
    term:
      id: HP:0012202
      label: Increased serum bile acid concentration
  evidence:
  - reference: clinicaltrials:NCT03659916
    reference_title: An Open-label Extension Study to Evaluate Long-term Efficacy and Safety of A4250 in Children With Progressive Familial Intrahepatic Cholestasis Types 1 and 2 (PEDFIC 2)
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Open Label Extension Study to evaluate long term safety and persistence of effect of A4250 in children with PFIC."
    explanation: The registered trial record for PEDFIC 2, establishing it as the long-term durability study for odevixibat in PFIC.
- name: NCT03905330
  phase: PHASE_III
  status: COMPLETED
  description: >-
    MARCH-PFIC - a 26-week multicentre randomised, double-blind, placebo-controlled phase
    3 trial of the IBAT inhibitor maralixibat in 93 children aged 1-17 years across all
    PFIC types, with a primary cohort restricted to biallelic non-truncated BSEP
    deficiency. Both the pruritus primary endpoint and the serum bile acid key secondary
    endpoint were met in that cohort.
  target_phenotypes:
  - preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  - preferred_term: Increased serum bile acid concentration
    term:
      id: HP:0012202
      label: Increased serum bile acid concentration
  evidence:
  - reference: clinicaltrials:NCT03905330
    reference_title: 'MRX-502: Randomized Double-blind Placebo-controlled Phase 3 Study to Evaluate the Efficacy and Safety of Maralixibat in the Treatment of Subjects With Progressive Familial Intrahepatic Cholestasis (PFIC) - MARCH-PFIC'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The purpose of this study is to determine whether the investigational treatment (maralixibat) is safe and effective in pediatric participants with Progressive Familial Intrahepatic Cholestasis (PFIC)."
    explanation: The registered trial record for MARCH-PFIC, the phase 3 study of maralixibat in PFIC.
- name: NCT04185363
  phase: PHASE_III
  status: ACTIVE_NOT_RECRUITING
  description: >-
    MARCH-ON - the open-label extension of MARCH-PFIC, evaluating long-term safety and
    tolerability of maralixibat in PFIC. It is the maralixibat counterpart of PEDFIC 2,
    so both IBAT-inhibitor programmes are represented here by a pivotal trial plus its
    durability extension. As with PEDFIC 2, enrolment and outcome figures are omitted
    because the cached registry record does not contain them.
  target_phenotypes:
  - preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
  - preferred_term: Increased serum bile acid concentration
    term:
      id: HP:0012202
      label: Increased serum bile acid concentration
  evidence:
  - reference: clinicaltrials:NCT04185363
    reference_title: An Open-label Extension Study to Evaluate the Long-term Safety and Efficacy of Maralixibat in the Treatment of Subjects With Progressive Familial Intrahepatic Cholestasis (PFIC)
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The primary objective of this open label extension study is to evaluate the long-term safety and tolerability of maralixibat."
    explanation: The registered trial record for MARCH-ON, the maralixibat open-label extension.

references:
- reference: PMID:20301474
  title: ATP8B1 Deficiency.
  tags:
  - GeneReviews

notes: >-
  Deep research provider: Edison/FutureHouse "falcon" (report at
  research/Progressive_Familial_Intrahepatic_Cholestasis-deep-research-falcon.md). The DR
  report was used as a lead-generation source only; every PMID was independently fetched
  and every snippet verified against the cached abstract. Several DR-supplied ontology
  identifiers were semantically wrong and were discarded after OAK resolution: HP:0031964
  (offered as "abnormal GGT", actually Elevated circulating alanine aminotransferase
  concentration), HP:0006744 (offered as HCC, actually Adrenocortical carcinoma),
  HP:0001882 (offered for fat-soluble vitamin deficiency, actually Decreased total
  leukocyte count), GO:0044294 (offered as bile canaliculus, actually dendritic growth
  cone - bile canaliculus is UBERON:0001283), and all four suggested NCIT intervention
  terms (C15469 Interferon Therapy, C15221 Dialysis, C15274 Lung Transplantation, C15236
  Gastrectomy, offered as Nutritional Support, Drug Therapy, Liver Transplantation and
  Genetic Counseling respectively). MAXO treatment terms are not reachable from the
  NCIT:C25218 root that the TreatmentActionTerm dynamic enum expands from, so NCIT
  intervention terms are used for the surgical treatments (NCIT:C15329 Surgical Procedure,
  NCIT:C15271 Liver Transplantation); note also that MAXO:0000070 liver transplantation is
  obsolete and MAXO:0001175 is its live replacement.

  Named Entity Confusion preflight: MONDO:0015762 was confirmed against Orphanet:172 and
  OMIMPS:211600 with the numbered subtype series (MONDO:0008892/0011156/0011214/0014381/
  0014884/0018804) resolved individually. The high-risk confusion here is with benign
  recurrent intrahepatic cholestasis (MONDO:0019008), which is ALLELIC to PFIC1/PFIC2
  rather than merely similar; it is curated as a structured differential rather than
  folded into this entry.

  Subtype numbering (a second, distinct confusion risk): the OMIM/MONDO gene series
  assigns PFIC6 to SLC51A/OSTa (MONDO:0030360), PFIC7 to USP53 (MONDO:0030503), PFIC8 to
  KIF12 (MONDO:0030505), PFIC9 to ZFYVE19 (MONDO:0030800) and PFIC10 to MYO5B
  (MONDO:0030810). Older clinical reviews frequently call the MYO5B form "PFIC6", which
  collides with the SLC51A entity that this entry deliberately excludes. All post-PFIC5
  subtypes therefore use gene-first names, with the series number carried only in
  display_name and subtype_term. MYO5B keeps MONDO:0018804 (MYO5B-related progressive
  familial intrahepatic cholestasis) as its subtype_term - the Orphanet-anchored term for
  the same entity that OMIM numbers PFIC10.

  Deliberate scope decisions: (1) "Low/normal GGT" is not curated as an HPO-coded
  phenotype because it denotes a normal laboratory value rather than an abnormality;
  HP:0034445 Reduced gamma-glutamyltransferase level would be a factual misstatement of
  the PFIC1/PFIC2 biochemistry. The split is carried in the biochemical section and in the
  "Unbuffered Bile Salt Injury to the Cholangiocyte" pathophysiology node. (2) SLC51A/OSTa
  and VPS33B/VIPAS39 (ARC syndrome) appear in some expanded PFIC classifications but are
  omitted here - ARC is a distinct multisystem syndrome better modelled separately, and
  SLC51A evidence remains thin. (3) Reference-range intervals carry provenance in notes
  rather than a citation because no citable numeric interval was found; the interpretation
  band thresholds (70 and 102 micromol/L) are cited on the parent biochemical record.

📚

References & Deep Research

References

PMID:20301474

ATP8B1 Deficiency.

No top-level findings curated for this source.

Deep Research

Falcon ▸

Disease Characteristics Research Template

Edison Scientific Literature 51 citations 2026-08-01T05:13:04.644305

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

Disease Name: Progressive Familial Intrahepatic Cholestasis
MONDO ID: (if available)
Category: Mendelian

Research Objectives

Please provide a comprehensive research report on Progressive Familial Intrahepatic Cholestasis covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

What is the disease? Provide a concise overview.
What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
What are the common synonyms and alternative names?
Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
Risk Factors:

Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases
Genetic risk factors (causal variants, susceptibility loci, modifier genes)
Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
Protective Factors:

Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases
Genetic protective factors (protective variants, modifier alleles)
Environmental protective factors (diet, lifestyle, exposures that reduce risk)
Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene
Pathogenic Variants:
Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
Variant type/class (missense, frameshift, nonsense, splice-site, structural)
Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
Functional consequences (loss of function, gain of function, dominant negative)
Modifier Genes: Genes that modify disease severity or expression
Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth
Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases
Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

Search first: CDC databases, WHO, PubMed, NHANES
Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc
Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

Search first: Gene Ontology (GO), Reactome, KEGG, PubMed
Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold
Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA
Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

Search first: ImmPort, Immunome Database, IEDB, Gene Ontology
Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

Search first: PubMed, Gene Ontology, Reactome
Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

Search first: BRENDA, UniProt, KEGG, OMIM, PubMed
Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth
Molecular Profiling (if available):
Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
Advanced Technologies (if applicable):
Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

Organ Level:
Primary organs directly affected
Secondary organ involvement (complications, secondary effects)
Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT
Tissue and Cell Level:
Specific tissue types affected (epithelial, connective, muscle, nervous)
Specific cell populations targeted (with Cell Ontology terms)

Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB
Subcellular Level:
Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas
Localization:
Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

Onset:
Typical age of onset (congenital, pediatric, adult, geriatric)
Onset pattern (acute, subacute, chronic, insidious)

Search first: OMIM, Orphanet, HPO, PubMed
Progression:
Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
Progression rate (rapid, slow, variable)
Disease course pattern (episodic, relapsing-remitting, progressive, stable)
Disease duration (self-limited, chronic lifelong)

Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM
Patterns:
Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

Epidemiology:
Prevalence (cases per 100,000 at given time)
Incidence (new cases per 100,000 per year)

Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries
For Genetic Etiology:
Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
Population Demographics:
Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
Geographic distribution of specific variants
Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

Clinical Tests:
Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
Genetic Testing:

Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen
Overview of recommended genetic testing approach
Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
FISH > Search first: ClinVar, cytogenetics databases, PubMed
Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
Omics-Based Diagnostics (if applicable):
RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
Clinical Criteria:
Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
Screening:
Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

Survival and Mortality:
Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
Morbidity and Function:
Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
Disease Course:
Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
Prediction:
Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

Pharmacotherapy:
Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
Advanced Therapeutics:
Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
Surgical and Interventional:
Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
Supportive and Rehabilitative:
Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
Experimental:
Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
Treatment Outcomes:
Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
Treatment Strategy:
Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest NCIT (NCI Thesaurus) clinical-intervention terms where applicable.

13. Prevention

Prevention Levels:
Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
Immunization: Vaccine strategies (if applicable)

Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database
Screening and Early Detection:
Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
Behavioral Interventions: Lifestyle modifications to reduce risk

Search first: CDC, WHO, behavioral intervention databases, Cochrane Library
Counseling: Genetic counseling (risk assessment, family planning guidance)

Search first: NSGC resources, ACMG guidelines, GeneReviews
Public Health:
Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
Prophylaxis: Preventive medications or procedures

Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

Taxonomy: Species affected (with NCBI Taxon identifiers)

Search first: NCBI Taxonomy
Breed: Specific breeds affected (with VBO identifiers if applicable)

Search first: VBO (Vertebrate Breed Ontology)
Gene: Orthologous genes in other species (with NCBI Gene IDs)

Search first: NCBI Gene
Natural Disease:
Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
Comparative Biology:
Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
Transmission (if applicable):
Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

Model Types:
Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
Genetic Models:
Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
Model Characteristics:
Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
Applications:
Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
Resources:
Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

Cite primary literature (PMID preferred) for all mechanistic and clinical claims
Prioritize recent reviews and landmark papers
Include direct quotes from abstracts where possible to support key statements
Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, NCIT, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (NCIT terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Progressive Familial Intrahepatic Cholestasis (PFIC): comprehensive disease-characteristics report

Scope and evidence date. This synthesis prioritizes 2023–2024 peer-reviewed evidence, supported by landmark genetics and natural-history studies. Evidence is labeled as human clinical, registry/observational, review/expert opinion, or preclinical. Because PFIC is ultrarare and molecular nomenclature is evolving, precise subtype-level frequencies, penetrance, carrier frequencies, and several newer-gene natural histories remain uncertain.

Executive summary

PFIC is not one disease but a genetically heterogeneous group of predominantly autosomal-recessive disorders in which defective hepatocellular bile formation or export causes intrahepatic cholestasis, often beginning in infancy. Typical manifestations are jaundice, very high serum bile acids, severe pruritus, fat and fat-soluble-vitamin malabsorption, growth failure, progressive fibrosis, portal hypertension, and eventually liver failure. Estimated incidence is approximately 1 per 50,000–100,000 births. PFIC2/BSEP deficiency and TJP2 deficiency confer notable childhood hepatocellular-carcinoma (HCC) risk. (mckiernan2024opinionpaperon pages 1-3, henkel2019expandingetiologyof pages 6-8)

The major recent clinical advance is inhibition of the ileal bile-acid transporter (IBAT/ASBT; SLC10A2) to interrupt enterohepatic bile-acid recycling. In PEDFIC-1, odevixibat produced a pruritus response in 55% versus 30% with placebo and a serum-bile-acid response in 33% versus 0%, while longer-term and real-world studies indicate sustained benefit in many—but not all—patients. Complete BSEP loss predicts poor response, making genotype and residual transporter activity clinically actionable. (mckiernan2024opinionpaperon pages 4-5, marx2024practicalconsiderationsfor pages 1-2, mckiernan2024opinionpaperon pages 5-6, komaniecka2024transporterproteinsas pages 24-26)

1. Disease information

Definition and classification

PFIC comprises Mendelian hepatocellular cholestasis disorders caused by defects in canalicular transporters, membrane lipid organization, tight-junction integrity, bile-acid sensing, or intracellular transporter trafficking. Although “progressive” remains in the name, expression ranges from episodic benign recurrent intrahepatic cholestasis (BRIC) to rapidly progressive neonatal liver failure. (mckiernan2024opinionpaperon pages 1-3, ziccardi2026beyondthepump pages 1-3, ziccardi2026beyondthepump pages 3-4)

Identifiers and synonyms

MONDO: MONDO:0015762, progressive familial intrahepatic cholestasis. Subtype records include PFIC1 MONDO:0008892, PFIC2 MONDO:0011156, PFIC3 MONDO:0011214, and PFIC4 MONDO:0014381. (OpenTargets Search: Progressive familial intrahepatic cholestasis)
Orphanet: commonly represented under ORPHA:43708 (PFIC); subtype records also exist.
OMIM phenotype examples: PFIC1/Byler disease #211600; PFIC2/BSEP deficiency #601847; PFIC3/MDR3 deficiency #602347; PFIC4/TJP2 deficiency #615878; PFIC5/FXR deficiency #617049. Subtype numbering beyond PFIC5 differs among publications; gene-first naming is safer.
MeSH: Cholestasis, Intrahepatic is the principal broad indexing term; PFIC does not consistently have a unique MeSH heading.
ICD: there is no universally used subtype-specific ICD-10 code. Cases are generally coded under K76.89 (other specified diseases of liver), K71.0/K83.1 where locally appropriate, or rare-disease extensions. ICD-11 similarly places inherited cholestatic disorders within hepatobiliary disease; coding should be verified against the deploying jurisdiction/version.
Synonyms: familial intrahepatic cholestasis; Byler disease (historically PFIC1); FIC1 deficiency; BSEP deficiency; MDR3 deficiency; hereditary intrahepatic cholestasis; low-GGT familial cholestasis.

This report aggregates disease-level literature, registries, trials, and expert guidance; it is not derived from an individual EHR.

2. Etiology, risk, protective factors, and gene–environment interaction

Causal factors

PFIC is fundamentally genetic. Classical causal genes are ATP8B1, ABCB11, and ABCB4; firmly established newer causes include TJP2, NR1H4, MYO5B, USP53, and additional PFIC/PFIC-like genes such as KIF12, SLC51A, ZFYVE19, VPS33B/VIPAS39. Open Targets associates 12 targets with the umbrella phenotype, with strongest evidence for ATP8B1, ABCB4, ABCB11, TJP2, and MYO5B. (OpenTargets Search: Progressive familial intrahepatic cholestasis)

Subtype / common name	Causal gene / protein	Core molecular defect	Expected GGT pattern	Typical onset / key phenotype and extrahepatic clues	Prognosis / cancer or treatment-response notes
PFIC1 / FIC1 deficiency	ATP8B1 / FIC1 (aminophospholipid flippase)	Loss of canalicular membrane lipid asymmetry and stability, impairing bile formation and promoting bile-acid toxicity (mckiernan2024opinionpaperon pages 1-3, henkel2019expandingetiologyof pages 2-4)	Usually low/normal (mckiernan2024opinionpaperon pages 1-3, henkel2019expandingetiologyof pages 2-4)	Neonatal or early-infantile cholestasis with jaundice, severe pruritus, hepatosplenomegaly, failure to thrive; extrahepatic clues include diarrhea, pancreatic insufficiency, short stature, elevated sweat chloride, sensorineural hearing loss (mckiernan2024opinionpaperon pages 1-3, henkel2019expandingetiologyof pages 2-4)	Progressive disease; native-liver survival improved when serum bile acids fall after diversion; residual extrahepatic disease may persist after transplant, including diarrhea/steatosis (mckiernan2024opinionpaperon pages 5-6, mckiernan2024opinionpaperon pages 3-4)
PFIC2 / BSEP deficiency	ABCB11 / BSEP	Defective canalicular bile-salt export causing intracellular bile-salt retention and hepatocyte injury (mckiernan2024opinionpaperon pages 1-3, ziccardi2026beyondthepump pages 3-4, henkel2019expandingetiologyof pages 2-4)	Usually low/normal (mckiernan2024opinionpaperon pages 1-3, mckiernan2024opinionpaperon pages 3-4)	Early infancy; severe pruritus, cholestasis, rapid progression; genotype-defined severity spectrum with residual vs absent BSEP expression/function (marx2024practicalconsiderationsfor pages 1-2, ziccardi2026beyondthepump pages 10-12)	Generally the most severe common form; higher HCC risk, especially biallelic truncating / severe BSEP groups; poorer response to biliary diversion and IBAT inhibitors when BSEP is absent; risk of antibody-induced BSEP deficiency after transplant (mckiernan2024opinionpaperon pages 4-5, marx2024practicalconsiderationsfor pages 1-2, mckiernan2024opinionpaperon pages 5-6, mckiernan2024opinionpaperon pages 3-4, ziccardi2026beyondthepump pages 10-12)
PFIC3 / MDR3 deficiency	ABCB4 / MDR3	Impaired phosphatidylcholine secretion into bile, leaving bile acids insufficiently buffered and injuring cholangiocytes/hepatocytes (henkel2019expandingetiologyof pages 6-8, henkel2019expandingetiologyof pages 2-4)	Usually high (henkel2019expandingetiologyof pages 6-8, mckiernan2024opinionpaperon pages 3-4)	Often later infancy, childhood, adolescence, or adulthood; cholestasis with portal fibrosis and bile duct proliferation; heterozygotes may have milder phenotypes such as transient neonatal cholestasis, cholelithiasis, ICP, or drug-induced cholestasis (henkel2019expandingetiologyof pages 6-8)	Variable expressivity; carcinogenesis including cholangiocarcinoma/HCC reported in severe disease; generally not the main low-GGT/IBAT-responsive archetype (henkel2019expandingetiologyof pages 6-8)
PFIC4 / TJP2 deficiency	TJP2 / tight junction protein 2 (ZO-2)	Tight-junction failure with claudin-1 mislocalization and paracellular reflux of toxic bile acids from canaliculi (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 2-4)	Usually low/normal (henkel2019expandingetiologyof pages 6-8, mckiernan2024opinionpaperon pages 3-4)	Often severe neonatal/infantile cholestasis; giant-cell transformation on histology; some patients have respiratory or neurologic features; phenotype can range from self-limited to progressive liver disease (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 2-4)	Increased HCC risk reported even in infancy; close surveillance recommended; severity variable across families (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 10-11)
PFIC5 / FXR deficiency	NR1H4 / FXR	Loss of bile-acid sensing/transcriptional control, with impaired ABCB11/BSEP induction and defective repression of bile-acid synthesis (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 2-4)	Usually low/normal (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 10-11)	Neonatal cholestasis with markedly elevated bile acids; characteristic early coagulopathy that may be vitamin K-unresponsive; often high AFP (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 10-11, vinayagamoorthy2021newervariantsof pages 2-4)	Usually rapidly progressive with early liver failure and need for transplant; very rare (henkel2019expandingetiologyof pages 6-8)
MYO5B-related PFIC / isolated MYO5B cholestasis / “PFIC6” in some sources	MYO5B / myosin Vb	Rab11-dependent apical trafficking defect causing BSEP/MDR3 mislocalization away from the canalicular membrane; epithelial polarity defect (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 2-4, henkel2019expandingetiologyof pages 8-10)	Usually low/normal (vinayagamoorthy2021newervariantsof pages 10-11, vinayagamoorthy2021newervariantsof pages 6-7)	Infancy or early childhood; may present as isolated cholestasis, microvillus inclusion disease, or both; extrahepatic clue is intractable diarrhea/enteropathy when intestinal disease is present (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 10-11, vinayagamoorthy2021newervariantsof pages 6-7)	Post-intestinal-transplant cholestasis can worsen; combined liver-intestinal strategies or diversion may be needed in selected cases; phenotype highly variable (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 10-11, vinayagamoorthy2021newervariantsof pages 6-7)
USP53-related cholestasis (newer nomenclature varies)	USP53 / USP53	Tight-junction–associated defect; protein colocalizes/interacts with TJP2 pathway (henkel2019expandingetiologyof pages 8-10, ziccardi2026beyondthepump pages 4-5)	Usually low/normal (vinayagamoorthy2021newervariantsof pages 10-11)	Low-GGT cholestasis identified by exome sequencing; currently a rarer PFIC-like presentation with limited phenotype definition (vinayagamoorthy2021newervariantsof pages 10-11, ziccardi2026beyondthepump pages 4-5)	Natural history and treatment-response data remain sparse (vinayagamoorthy2021newervariantsof pages 10-11, ziccardi2026beyondthepump pages 4-5)
KIF12-related cholestasis (sometimes mapped to a later-numbered PFIC; nomenclature varies)	KIF12 / kinesin family member 12	Intracellular trafficking / motor-protein defect affecting hepatocellular bile transport pathways (ziccardi2026beyondthepump pages 4-5, ziccardi2026beyondthepump pages 3-4)	Often reported in the low/normal-GGT PFIC-like spectrum, but source conventions vary (ziccardi2026beyondthepump pages 4-5)	Pediatric cholestatic liver disease; detailed extrahepatic pattern remains less established than classical PFIC forms (ziccardi2026beyondthepump pages 4-5)	Evidence base is emerging; numbering and disease boundaries vary across reviews and databases (ziccardi2026beyondthepump pages 4-5)
ZFYVE19-related cholestasis (newer/related PFIC-like gene; numbering varies)	ZFYVE19 / zinc finger FYVE-type containing 19	Ciliary / trafficking-related mechanism proposed in PFIC-like cholestasis; evidence base remains limited in the retrieved sources (OpenTargets Search: Progressive familial intrahepatic cholestasis)	Not firmly established here	Reported as a newer PFIC-related gene in expanded molecular classifications, but detailed phenotype data were not available in the retrieved evidence set (OpenTargets Search: Progressive familial intrahepatic cholestasis)	Important emerging gene; requires confirmation from primary case literature in a full database curation workflow (OpenTargets Search: Progressive familial intrahepatic cholestasis)
SLC51A-related cholestasis / OSTα deficiency (newer/related PFIC-like form; numbering varies)	SLC51A / OSTα	Defect in basolateral bile-acid transport (organic solute transporter α), disturbing enterohepatic bile-acid handling (ziccardi2026beyondthepump pages 4-5)	Often grouped with low/normal-GGT PFIC-like disorders, but conventions vary (ziccardi2026beyondthepump pages 4-5)	Early-onset cholestatic phenotype in expanded classifications; detailed syndrome boundaries were not fully captured in the retrieved sources (ziccardi2026beyondthepump pages 4-5)	Limited outcome and treatment-response data in current retrieved evidence (ziccardi2026beyondthepump pages 4-5)
VPS33B / VIPAS39-related cholestasis (ARC spectrum; PFIC-like, not always numbered as PFIC)	VPS33B / VPS33B; VIPAS39 / VIPAR	Vesicular trafficking / apical membrane biogenesis defect causing multisystem cholestasis syndrome (vinayagamoorthy2021newervariantsof pages 10-11, ziccardi2026beyondthepump pages 4-5)	Often low/normal in ARC-associated cholestasis, though syndrome-based classification is preferred (vinayagamoorthy2021newervariantsof pages 10-11, ziccardi2026beyondthepump pages 4-5)	Neonatal/infantile cholestasis with multisystem clues: arthrogryposis, renal tubular dysfunction, developmental issues; histology may show bile duct paucity, giant cells, bile plugs (vinayagamoorthy2021newervariantsof pages 10-11)	Usually severe syndromic disease; better viewed as a PFIC-like cholestatic disorder rather than classical isolated PFIC (vinayagamoorthy2021newervariantsof pages 10-11, ziccardi2026beyondthepump pages 4-5)
Nomenclature note for newer forms	—	Expanded PFIC numbering beyond PFIC1-5 is not standardized across sources; some reviews now include many later-numbered forms, whereas others prefer “PFIC-like” or gene-specific cholestasis terminology (ziccardi2026beyondthepump pages 3-4, ziccardi2026beyondthepump pages 4-5)	—	Gene-first reporting is often clearer than subtype numbering for USP53, KIF12, ZFYVE19, SLC51A, and VPS33B/VIPAS39 (ziccardi2026beyondthepump pages 3-4, ziccardi2026beyondthepump pages 4-5)	Use explicit gene/protein names in knowledge-base entries to avoid cross-source ambiguity (ziccardi2026beyondthepump pages 3-4, ziccardi2026beyondthepump pages 4-5)

Table: This table summarizes major classical and newer PFIC-associated genotypes, their core molecular defects, expected GGT patterns, hallmark phenotypes, and key prognostic or treatment-response notes. It is useful for rapid subtype comparison and highlights that nomenclature for newer numbered forms is not standardized across sources.

Genetic risk

Most severe PFIC is caused by biallelic germline pathogenic variants and follows autosomal-recessive inheritance. Missense, nonsense, frameshift, canonical splice, exon-level deletion, and larger intragenic deletion variants are documented. For example, a 2024 Pakistani PFIC2 cohort of 66 unrelated children identified 20 ABCB11 variants—11 missense, two frameshift, two nonsense, and five splice variants—illustrating marked allelic heterogeneity and enrichment in consanguineous populations. Variants absent or extremely rare in ancestry-matched controls and gnomAD, together with segregation, phenotype, protein staining, RNA-splicing, or transport assays, support ACMG/AMP classification; frequency must be recorded per exact HGVS allele rather than generalized by gene.

In ABCB11 disease, residual-function missense alleles are generally milder than biallelic protein-truncating variants. The NAPPED risk groups classify p.Asp482Gly/p.Glu297Gly as BSEP1, other missense genotypes as BSEP2, and biallelic truncating genotypes as BSEP3; median native-liver survival falls from 20.4 years in BSEP1 to 3.5 years in BSEP3. (ziccardi2026beyondthepump pages 10-12)

Heterozygous ABCB4, ABCB11, or ATP8B1 variants can predispose to intrahepatic cholestasis of pregnancy, contraceptive/drug-induced cholestasis, gallstones, or adult cryptogenic cholestasis, usually with incomplete penetrance. ABCB11 p.Val444Ala/1331T>C is a susceptibility allele rather than a fully penetrant PFIC cause. (henkel2019expandingetiologyof pages 10-11, mattiaccio2020molecularcharacterizationof pages 109-113, henkel2019expandingetiologyof pages 6-8)

Environmental, lifestyle, infectious, and protective factors

No environmental exposure, lifestyle behavior, or infectious agent is a primary cause of Mendelian PFIC, and PFIC is not contagious or zoonotic. Hormones and drugs can reveal or worsen partial transporter deficiency: estradiol can interfere with FXR-mediated BSEP regulation, while selected medicines may provoke cholestasis in genetically susceptible carriers. Intercurrent illness, fasting, pregnancy, and hormonal contraception may similarly trigger episodic phenotypes. (mattiaccio2020molecularcharacterizationof pages 109-113, ziccardi2026beyondthepump pages 10-12, henkel2019expandingetiologyof pages 6-8)

No validated genetic “protective allele” prevents PFIC. Functionally protective factors are residual protein expression/activity and effective lowering of the circulating bile-acid pool. Post-diversion serum bile acids are strongly prognostic, but this is treatment response rather than primary genetic protection. Modifier genes, polygenic haplotypes, and environment likely explain intrafamilial variability, but none is ready for routine risk prediction. PFIC-specific epigenetic protective/risk signatures have not been validated. (mckiernan2024opinionpaperon pages 5-6, mattiaccio2020molecularcharacterizationof pages 109-113)

3. Phenotypes

Phenotype	Type, timing, course, and frequency	Quality-of-life effect	Suggested HPO term
Intrahepatic cholestasis	Laboratory/clinical sign; usually neonatal or infantile in PFIC1/2/4/5, later and more variable in PFIC3; chronic or episodic	Drives all downstream morbidity	HP:0001406
Pruritus	Symptom; usually severe, progressive or fluctuating; hallmark of low-GGT PFIC	Sleep loss, irritability, skin mutilation, poor attention and school performance	HP:0000989
Jaundice/conjugated hyperbilirubinemia	Sign/laboratory abnormality; neonatal to childhood, variable	Stigma and marker of active disease	HP:0000952, HP:0002904
Elevated serum bile acids	Laboratory abnormality; common and often marked	Correlates with itch and native-liver prognosis	HP:0012202
Low/normal GGT despite cholestasis	Laboratory discriminator in PFIC1/2/4/5 and several newer forms	Diagnostic rather than directly symptomatic	HP:0031964 (abnormal GGT; annotate direction locally)
Elevated GGT	Typical of ABCB4/PFIC3 and selected newer forms	Helps subtype disease	HP:0031964
Hepatomegaly/splenomegaly	Physical sign; develops with chronic disease/portal hypertension	Abdominal discomfort and activity limitation	HP:0002240, HP:0001744
Failure to thrive/short stature	Physical manifestation; frequent in severe pediatric disease from malabsorption and chronic illness	Major developmental and family burden	HP:0001508, HP:0004322
Fat-soluble-vitamin deficiency	Laboratory/clinical; chronic cholestasis	Bleeding, rickets, visual or neurologic complications	HP:0001882, HP:0002748 as applicable
Diarrhea	Symptom; particularly ATP8B1 and MYO5B disease; may worsen after PFIC1 transplant	Nutrition, continence, school/social burden	HP:0002014
Portal hypertension/cirrhosis	Progressive sign/pathology	Variceal bleeding, ascites, transplant need	HP:0001409, HP:0001394
Sensorineural hearing impairment	Extrahepatic sign in ATP8B1 deficiency; not universal	Communication/development	HP:0000407
Pancreatic insufficiency	Extrahepatic sign in ATP8B1 deficiency	Malabsorption and growth failure	HP:0001738
HCC	Complication, particularly severe ABCB11 and TJP2 disease; can occur in childhood	Life-threatening; mandates surveillance	HP:0006744

Published studies seldom provide robust phenotype percentages by genotype. A systematic review found only two usable health-related-quality-of-life studies and substantial heterogeneity. Its abstract states that pruritus “may affect many activities of daily living through loss of sleep, irritability, poor attention, and impaired school performance.” (Human systematic review, published June 2021; DOI: 10.1186/s13023-021-01884-4). (joneshughes2021epidemiologyandburden pages 11-12)

4. Genetic and molecular information

Variant interpretation

Origin: constitutional/germline. Somatic variants are not an established cause of PFIC, although somatic oncogenic changes may occur secondarily in HCC.
Pathogenic mechanism: predominantly loss of function, impaired folding/processing, reduced transport, defective membrane targeting, or loss of transcriptional regulation. Dominant-negative mechanisms are not the usual basis of classical severe PFIC.
Classification: use ACMG/AMP criteria with ClinVar review status, segregation, ancestry-specific population frequency, immunohistochemistry, RNA assays, and functional transport/localization evidence. A VUS alone should not establish PFIC. Reanalysis is appropriate as gene–disease validity and variant databases evolve. (ziccardi2026beyondthepump pages 9-10, ziccardi2026beyondthepump pages 10-12)
Chromosomal abnormalities: PFIC is not ordinarily an aneuploidy/translocation syndrome. Exon or intragenic copy-number variants can occur—for example a reported 31.7-kb NR1H4 deletion—and therefore panel/WES pipelines should include CNV calling. (vinayagamoorthy2021newervariantsof pages 2-4)
Epigenetics: no reproducible PFIC-specific DNA-methylation, histone, or chromatin biomarker has entered clinical use.

5. Environmental information

Toxins, radiation, pollution, smoking, alcohol, occupation, diet, and infection are not established initiating causes. Drugs and sex hormones can act as phenotypic stressors in people with partial transporter function; potentially cholestatic medicines should therefore be reviewed carefully. Adequate energy intake, medium-chain triglycerides, and replacement of vitamins A, D, E, and K mitigate consequences but do not prevent the genotype. (vinayagamoorthy2021newervariantsof pages 10-11, mattiaccio2020molecularcharacterizationof pages 109-113, henkel2019expandingetiologyof pages 6-8)

6. Mechanism and pathophysiology

Causal chain

Upstream germline defect. A canalicular transporter, phospholipid flippase/floppase, tight-junction component, nuclear bile-acid receptor, or trafficking motor is absent or dysfunctional.
Canalicular failure. Bile salts cannot exit through BSEP; phosphatidylcholine cannot protect membranes in MDR3 deficiency; canalicular lipid asymmetry becomes unstable in FIC1 deficiency; bile leaks paracellularly in TJP2 deficiency; or BSEP/MDR3 fail to reach the apical membrane in MYO5B disease. FXR deficiency reduces BSEP transcription and physiological suppression of bile-acid synthesis. (henkel2019expandingetiologyof pages 6-8, vinayagamoorthy2021newervariantsof pages 2-4, ziccardi2026beyondthepump pages 3-4, henkel2019expandingetiologyof pages 2-4)
Bile-acid retention and altered bile composition. Toxic, detergent-like bile acids accumulate in hepatocytes and blood; in ABCB4 deficiency, poorly phospholipid-buffered bile also damages cholangiocytes.
Cellular injury. Bile acids disrupt mitochondria, increase oxidative stress and permeability transition, and promote hepatocyte apoptosis/necrosis and inflammatory signaling. (ziccardi2026beyondthepump pages 1-3)
Tissue response. Hepatocyte injury, ductular reaction, stellate-cell activation and extracellular-matrix deposition generate fibrosis, cirrhosis, portal hypertension and regenerative pressure that contributes to HCC.
Clinical output. Systemic bile acids produce pruritus; reduced intestinal bile causes fat/vitamin malabsorption and growth failure; advanced fibrosis causes synthetic failure and portal-hypertensive complications.

Cell Ontology suggestions: hepatocyte CL:0000182; cholangiocyte CL:0002538; hepatic stellate cell CL:0000632; liver-resident macrophage/Kupffer cell CL:0000091; ileal enterocyte CL:0000584. GO biological-process suggestions: bile-acid transport GO:0015721; bile-acid biosynthetic process GO:0006699; phospholipid translocation GO:0045332; epithelial-cell polarity GO:0090162; tight-junction assembly GO:0120192; response to oxidative stress GO:0006979; apoptotic process GO:0006915; extracellular-matrix organization GO:0030198. GO cellular components: bile canaliculus GO:0044294; apical plasma membrane GO:0016324; tight junction GO:0070160; recycling endosome GO:0055037; mitochondrion GO:0005739; nucleus GO:0005634.

Molecular profiling and advanced technologies

Serum bile-acid concentration is the best-established molecular biomarker. Routine PFIC-specific transcriptomic, proteomic, lipidomic, single-cell, spatial-transcriptomic, or clinical multi-omic classifiers are not yet validated. Patient-derived hepatocyte organoids and iPSC systems are promising for testing trafficking defects and personalized rescue, but current organoid reviews emphasize incomplete maturation, absence of whole-organ enterohepatic physiology, and matrix/standardization limitations. The 2024 organoid review describes these systems as enabling “better model liver disease, improve (personalized) drug testing, and advance bioengineering options” (DOI: 10.1097/HEP.0000000000000343).

7. Anatomical structures affected

Primary organ: liver UBERON:0002107, especially hepatic lobule UBERON:0004647 and bile canaliculi. The principal cells are hepatocytes; cholangiocytes are particularly injured in ABCB4 deficiency.
Secondary sites: ileum UBERON:0002116 (enterohepatic recycling and IBAT target); small-intestinal epithelium in MYO5B disease; pancreas and inner ear in ATP8B1 deficiency; spleen through portal hypertension; bone through vitamin-D deficiency.
Systems: digestive/hepatobiliary primarily, with nutritional, skeletal, hematologic and occasional auditory/neurologic effects.
Subcellular sites: apical/canalicular membrane, tight junction, recycling endosome, nucleus/FXR transcriptional machinery, and mitochondria.
Lateralization: not applicable; liver disease is diffuse rather than unilateral.

8. Temporal development

PFIC1/2/4/5 commonly begins in the neonatal period or first year, while PFIC3 may begin later in childhood, adolescence, or adulthood. The untreated course is chronic and usually progressive, although residual-function alleles may produce episodic BRIC or stable adult disease. Early disease consists of biochemical cholestasis, jaundice and itch; intermediate disease adds growth failure, hepatosplenomegaly and fibrosis; advanced disease includes portal hypertension and synthetic dysfunction; end-stage disease requires transplantation. (henkel2019expandingetiologyof pages 6-8, henkel2019expandingetiologyof pages 2-4, ziccardi2026beyondthepump pages 1-3)

Critical intervention windows are before irreversible fibrosis, severe growth compromise, or malignancy. Treatment-induced biochemical remission can occur after effective IBAT inhibition or biliary diversion; spontaneous durable remission is atypical in severe PFIC. Genotype and post-treatment bile-acid reduction should guide whether to continue medical therapy, perform diversion, or proceed to transplant. (mckiernan2024opinionpaperon pages 5-6, joneshughes2021epidemiologyandburden pages 11-12)

9. Inheritance and population

Incidence: approximately 1:50,000–100,000 births; reliable population prevalence and annual incidence are unavailable. (mckiernan2024opinionpaperon pages 1-3)
Hospital-based proportion: three studies reported PFIC in 9–12% of selected children admitted with cholestasis, acute liver failure, or splenomegaly; this is not population prevalence. The systematic review included 22 studies and 2,603 patients. (joneshughes2021epidemiologyandburden pages 11-12)
Inheritance: predominantly autosomal recessive; recurrence risk is 25% per pregnancy when both parents carry pathogenic variants in the same gene.
Penetrance/expressivity: severe biallelic loss is often highly penetrant, but expression is allele- and gene-dependent. Heterozygous susceptibility phenotypes have incomplete penetrance. No genetic anticipation is known.
Consanguinity/founder effects: consanguinity increases homozygosity and disease frequency; population-specific founder variants occur, but no single global founder allele exists. (henkel2019expandingetiologyof pages 6-8)
Germline mosaicism: biologically possible but not a characteristic documented mechanism; standard counseling should mention a small residual recurrence risk after apparently de novo findings.
Carrier frequency: not reliably established across ancestries because of extreme allelic heterogeneity.
Demographics: all sexes are affected approximately equally; geographic clustering reflects ancestry, founder effects, testing access, and consanguinity rather than endemic exposure.

10. Diagnostics

Recommended work-up

Confirm cholestasis and severity: fractionated bilirubin, serum bile acids, ALT, AST, ALP, GGT, albumin, glucose, PT/INR, CBC, fat-soluble vitamins, AFP, and renal/electrolyte tests. Low/normal GGT despite marked cholestasis strongly suggests ATP8B1, ABCB11, TJP2, NR1H4, MYO5B and selected newer forms; high GGT favors ABCB4 and structural/ductal disease. (ziccardi2026beyondthepump pages 9-10, ziccardi2026beyondthepump pages 7-9, henkel2019expandingetiologyof pages 2-4)
Exclude urgent obstruction: abdominal ultrasound with Doppler; in neonates, rapidly exclude biliary atresia and choledochal cyst. MRCP is selective, particularly with high GGT or ductal suspicion. (ziccardi2026beyondthepump pages 7-9, vinayagamoorthy2021newervariantsof pages 6-7)
Genetic confirmation: use a comprehensive cholestasis NGS panel with deletion/duplication analysis, followed by trio WES/WGS and periodic reanalysis if negative. Gene sequencing is the etiologic gold standard; reported targeted-panel diagnostic yield is 28.1–68%, depending on selection and panel composition. (mckiernan2024opinionpaperon pages 3-4)
Biopsy when needed: stage fibrosis, resolve an inconclusive genetic result, or assess competing disease. Findings include bland canalicular/“Byler” bile and giant-cell change in PFIC1; paucity or reduced BSEP staining in ABCB11 disease; portal fibrosis/ductular proliferation and absent/reduced MDR3 in PFIC3; giant-cell transformation in TJP2/FXR disease. Immunostaining can support but not replace genetic interpretation. (henkel2019expandingetiologyof pages 6-8, henkel2019expandingetiologyof pages 2-4)
Monitoring: serial growth, itch/sleep scores, serum bile acids, liver synthetic function, ultrasound/elastography, and AFP/ultrasound HCC surveillance in high-risk ABCB11 and TJP2 disease.

Differential diagnosis

Urgently exclude biliary atresia; also consider Alagille syndrome, alpha-1-antitrypsin deficiency, cystic fibrosis, neonatal sclerosing cholangitis, congenital infection, sepsis/TPN cholestasis, bile-acid synthesis defects, mitochondrial disease, galactosemia/tyrosinemia, ARC syndrome, citrin deficiency, endocrine disease, drug-induced injury and mechanical obstruction. Urinary bile-acid mass spectrometry is valuable when a primary bile-acid-synthesis defect is suspected. (vinayagamoorthy2021newervariantsof pages 10-11, ziccardi2026beyondthepump pages 7-9)

CMA, karyotype, FISH, mitochondrial DNA testing, and repeat-expansion assays are not routine PFIC tests unless syndromic findings suggest another diagnosis. RNA sequencing can resolve selected splice variants, but proteomics, metabolomics, epigenomics, and liquid biopsy remain investigational.

Screening

PFIC is not included in routine population newborn screening. Test symptomatic infants promptly; offer cascade testing to relatives and targeted testing to siblings from birth. Carrier, prenatal, and preimplantation testing require prior identification of familial pathogenic variants.

11. Outcome and prognosis

Only about one-third of severe BSEP-deficient patients in historical cohorts reached adulthood with their native liver. BSEP native-liver survival varies sharply by genotype—median 20.4 years for BSEP1 versus 3.5 years for BSEP3—and biallelic truncating disease has reported HCC risk up to 34% by age 15. Less than half of historical PFIC1/2 cohorts retained native liver into adulthood. (marx2024practicalconsiderationsfor pages 1-2, joneshughes2021epidemiologyandburden pages 11-12, ziccardi2026beyondthepump pages 10-12)

Serum bile acids are both pharmacodynamic and prognostic. Values below 194 μmol/L were associated with approximately threefold better 15-year native-liver survival; after diversion, a threshold near 102 μmol/L identified particularly favorable BSEP outcomes. These are cohort associations, not universally validated individual cutoffs. (mckiernan2024opinionpaperon pages 5-6, joneshughes2021epidemiologyandburden pages 11-12)

Complications include malnutrition, rickets, bleeding, growth and developmental impairment, severe sleep disruption, portal hypertension, varices, ascites, liver failure, HCC and—in ABCB4 disease—possible cholangiocarcinoma. After transplant, PFIC2 can recur functionally through anti-BSEP antibodies; PFIC1 may develop persistent diarrhea and graft steatosis because extrahepatic ATP8B1 deficiency remains. (henkel2019expandingetiologyof pages 6-8, mckiernan2024opinionpaperon pages 3-4)

Standardized 5- and 10-year overall-survival estimates across all PFIC genotypes are unavailable. Prognosis is determined more meaningfully by genotype, residual protein function, fibrosis/portal hypertension, HCC, growth, and biochemical response to bile-acid-lowering therapy.

12. Treatment and current implementation

Supportive and pharmacological care

Nutrition: approximately 125–140% of age-based recommended calories, protein 2–3 g/kg/day, medium-chain triglycerides, and aggressive vitamins A/D/E/K replacement; monitor INR, vitamin levels, bone health and growth. (vinayagamoorthy2021newervariantsof pages 10-11)
UDCA (CHEBI:9907) is often tried, especially in ABCB4 disease with residual MDR3 activity, but sustained benefit in severe PFIC1/2 is limited. Cholestyramine, rifampicin, naltrexone and sertraline are off-label antipruritic options with variable efficacy and safety burdens. (mckiernan2024opinionpaperon pages 4-5)
NCIt intervention suggestions: Nutritional Support C15469; Drug Therapy C15221; Biliary Diversion Procedure (map to the nearest local NCIt surgical concept); Liver Transplantation C15274; Genetic Counseling C15236.

IBAT inhibition: leading targeted therapy

Odevixibat inhibits ileal SLC10A2/IBAT, increases fecal bile-acid loss and lowers the returning hepatic bile-acid load. It was approved in the EU and US in July 2021—for PFIC treatment in the EU and PFIC-associated pruritus in the US, with exact age and label wording jurisdiction-dependent. (mckiernan2024opinionpaperon pages 4-5, marx2024practicalconsiderationsfor pages 2-3)

PEDFIC-1, NCT03566238: 62 patients aged 0.5–18 years with PFIC1/2 received 40 or 120 µg/kg/day or placebo for 24 weeks. Overall pruritus response was 55% versus 30% with placebo (p=0.0038), and serum-bile-acid response was 33% versus 0% (p=0.003). A secondary summary reported ≥70% bile-salt reduction in 71.4% and 28.6% of monitored patients in the two dose groups versus 0% placebo. (mckiernan2024opinionpaperon pages 4-5, komaniecka2024transporterproteinsas pages 24-26)

PEDFIC-2, NCT03659916: completed phase 3 open-label extension; 116 participants, 40 or 120 µg/kg/day, planned 72 weeks. Evaluated patients maintained reductions in bile acids, ALT, AST and bilirubin with generally acceptable long-term tolerability. (komaniecka2024transporterproteinsas pages 24-26, NCT03659916 chunk 1)

Real-world 2024 evidence: in a German single-center series of nine patients (PFIC1 n=2; PFIC2 n=7), five improved in bile acids, itch, liver tests and sleep. Two siblings with complete BSEP loss did not respond and underwent transplantation; four reported transient abdominal symptoms or symptoms managed by dose reduction. The abstract concludes that “clinical benefits were observed in most patients,” while emphasizing monitoring in complete BSEP deficiency. Published December 2024; DOI: 10.3390/jcm13247508. (marx2024practicalconsiderationsfor pages 1-2)

Maralixibat is another IBAT inhibitor. MARCH-PFIC (NCT03905330) was a multicenter randomized phase 3 study published in July 2024 (DOI: 10.1016/S2468-1253(24)00080-3); its extension is NCT04185363 with 84 participants. Genotype matters: biallelic ABCB11 truncating variants predict non-response because reducing enterohepatic return cannot restore absent canalicular export. (mckiernan2024opinionpaperon pages 5-6, mckiernan2024opinionpaperon pages 9-9)

Common class concerns are diarrhea, abdominal pain, altered bowel habits, and reduced absorption of fat-soluble vitamins. Monitor growth, vitamins, INR, liver tests, serum bile acids, itch and sleep. No established CPIC/PharmGKB pharmacogenomic dosing rule exists, but disease genotype itself functions as a response biomarker.

Surgery and transplantation

Partial external/internal biliary diversion or ileal exclusion reduces enterohepatic recycling. Across 17 surgical series totaling 536 patients, diversion reduced pruritus and bile acids, but response varied by genotype. A synthesis reported complete itch resolution in 59.5%, while 27% later required transplant; 10-year native-liver survival after diversion ranged 22–75% by genotype. Stoma complications, diarrhea, malabsorption and recurrent itch occur. (mckiernan2024opinionpaperon pages 3-4, hupper2023surgicalversusmedical pages 10-12)

Liver transplantation is definitive for end-stage liver disease, unresectable HCC, severe portal hypertension, or refractory pruritus/growth failure. It corrects hepatocyte-specific transporter deficiency but not systemic ATP8B1 or intestinal MYO5B disease. Combined liver–intestinal transplantation may be required in severe MYO5B microvillus-inclusion disease. (henkel2019expandingetiologyof pages 6-8, mckiernan2024opinionpaperon pages 3-4)

Practical treatment algorithm

Correct nutrition/vitamins and treat complications.
Obtain genotype while promptly treating severe itch.
Start a licensed IBAT inhibitor early when appropriate; one 2024 expert algorithm suggests odevixibat 40 µg/kg/day for 12 weeks, then assess itch and serum-bile-acid response. (mckiernan2024opinionpaperon pages 5-6, mckiernan2024opinionpaperon pages 1-3)
Escalate dose/adjuncts according to label and response.
If inadequate response—especially complete BSEP loss—discuss diversion or transplant in a specialist multidisciplinary center.
Maintain HCC surveillance and monitor fibrosis irrespective of itch improvement.

Experimental and ongoing research

Gene replacement, RNA therapy, CRISPR correction, and chemical chaperones for trafficking-defective missense variants remain preclinical. No approved PFIC gene, cell, or RNA therapy exists. Key research programs include NAPPED NCT03930810 (planned 1,500 participants), TreatFIC NCT06778174 (200), Indian PFIC Registry NCT05704517 (200), and the odevixibat-versus-NAPPED external-control study NCT07497724 (200). Some registry identifiers beginning NCT07 were initiated after 2024 and are included only as forward-looking developments, not as 2024 evidence. (NCT07497724 chunk 1, NCT07191704 chunk 1, NCT07497724 chunk 2)

13. Prevention

Primary prevention: no lifestyle or vaccine prevents a biallelic PFIC genotype. Genetic counseling, carrier testing in relatives or high-risk consanguineous families, preimplantation genetic testing, chorionic-villus/amniotic testing, and informed reproductive planning can prevent recurrence or enable early diagnosis.

Secondary prevention: rapid evaluation of neonatal cholestasis, cascade testing, presymptomatic sibling testing, early nutrition and early bile-acid-lowering therapy may prevent irreversible fibrosis and developmental harm.

Tertiary prevention: maintain vitamin and nutritional status; avoid unnecessary cholestatic medicines; vaccinate according to routine and chronic-liver-disease schedules, including hepatitis A/B where nonimmune; screen for varices, fibrosis and HCC; and refer before decompensation. Vaccination prevents superimposed infection, not PFIC itself.

14. Other species and natural disease

PFIC is not infectious and has no transmission or zoonotic potential. Orthologous bile-transport genes are evolutionarily conserved across vertebrates. Naturally occurring ABCB4/MDR3-like hepatobiliary disease has been described in veterinary species, but a standardized breed-specific PFIC counterpart was not established in the retrieved evidence; VBO annotation is therefore premature. Relevant taxonomy terms for experimental comparison are Mus musculus NCBI Taxon 10090, Danio rerio 7955, and Rattus norvegicus 10116.

15. Model organisms and experimental systems

Atp8b1-deficient mice: model canalicular membrane instability and bile-acid susceptibility, but mouse bile-acid composition is more hydrophilic than humans and disease can be milder. (henkel2019expandingetiologyof pages 2-4)
Abcb11 knockout/edited mice: reproduce impaired bile-salt export but often lack the severe human injury phenotype. A 2024 liver-specific CRISPR/AAV8 system simultaneously disrupted Abcb11 and Cyp2c70, humanizing the bile-acid pool and producing higher transaminases and parenchymal necrosis. The abstract states that Abcb11 targeting alone caused “hepatomegaly and cholestasis without histological evidence of liver injury,” whereas bile-acid humanization better resembled human ABCB11 deficiency. Published March 2024; DOI: 10.1097/HC9.0000000000000382.
Abcb4/Mdr2-null mice: useful for phospholipid-deficient bile, cholangiocyte injury and fibrosis, although often used as a PSC-like model rather than a complete PFIC3 phenocopy.
Zebrafish: transparent larvae enable bile-flow and canalicular-trafficking imaging; bsep and trafficking models are useful for rapid functional screens, but hepatic maturation and bile-acid physiology differ from humans.
Cellular systems: polarized hepatocyte lines, primary hepatocytes, patient fibroblast/iPSC-derived hepatocyte-like cells and liver organoids permit localization, splicing, transport and rescue assays. They do not fully reproduce enterohepatic circulation, immune–stromal interaction, portal flow, or long-term carcinogenesis.

Expert interpretation and evidence gaps

The strongest contemporary expert position is that PFIC management should be gene-informed but response-driven: sequence early, use serum bile acids and validated itch instruments serially, introduce licensed IBAT inhibition early, and avoid delaying diversion or transplantation in biochemical nonresponders or complete BSEP deficiency. The 2024 opinion paper recommends referral to experienced centers and concurrent genetic testing rather than waiting for molecular confirmation before addressing severe symptoms. (mckiernan2024opinionpaperon pages 5-6, mckiernan2024opinionpaperon pages 1-3)

Major gaps are: reliable population prevalence; phenotype frequencies for newer genes; ancestry-specific carrier frequencies; validated modifier/protective alleles; PFIC-specific epigenetic, single-cell and spatial maps; randomized comparisons of IBAT inhibition versus diversion; and proof that itch/serum-bile-acid improvement translates into long-term transplant-free and cancer-free survival. Ongoing registry and external-control studies are designed to address the last question. (joneshughes2021epidemiologyandburden pages 11-12, NCT07497724 chunk 1)

Selected source index

McKiernan P, et al. Opinion paper on diagnosis and treatment of PFIC. JHEP Reports. Published January 2024; DOI: 10.1016/j.jhepr.2023.100949. (mckiernan2024opinionpaperon pages 3-4)
Marx M, et al. Real-world odevixibat case series. J Clin Med. Published December 2024; DOI: 10.3390/jcm13247508. (marx2024practicalconsiderationsfor pages 1-2)
Hüpper MN, et al. Surgical versus medical management. Children. Published May 2023; DOI: 10.3390/children10060949. (hupper2023surgicalversusmedical pages 10-12)
Jones-Hughes T, et al. Epidemiology and burden systematic review. Orphanet J Rare Dis. Published June 2021; DOI: 10.1186/s13023-021-01884-4. (joneshughes2021epidemiologyandburden pages 11-12)
van Wessel DBE, et al. BSEP genotype/natural history. J Hepatol. Published July 2020; DOI: 10.1016/j.jhep.2020.02.007.
van Wessel DBE, et al. FIC1 genotype, bile acids and diversion. Hepatology. Published July 2021; DOI: 10.1002/hep.31787.
Landmark gene-association PMIDs available in Open Targets include ATP8B1 PMID:9500542, ABCB11 PMID:9806540, TJP2 PMID:24614073, NR1H4 PMID:26888176, and MYO5B PMID:27532546. (OpenTargets Search: Progressive familial intrahepatic cholestasis)

References

(mckiernan2024opinionpaperon pages 1-3): Patrick McKiernan, Jesus Quintero Bernabeu, Muriel Girard, Giuseppe Indolfi, Eberhard Lurz, and Palak Trivedi. Opinion paper on the diagnosis and treatment of progressive familial intrahepatic cholestasis. Jan 2024. URL: https://doi.org/10.1016/j.jhepr.2023.100949, doi:10.1016/j.jhepr.2023.100949. This article has 36 citations and is from a peer-reviewed journal.
(henkel2019expandingetiologyof pages 6-8): Sarah AF Henkel, Judy H Squires, Mary Ayers, Armando Ganoza, Patrick Mckiernan, and James E Squires. Expanding etiology of progressive familial intrahepatic cholestasis. World Journal of Hepatology, 11:450-463, May 2019. URL: https://doi.org/10.4254/wjh.v11.i5.450, doi:10.4254/wjh.v11.i5.450. This article has 101 citations.
(mckiernan2024opinionpaperon pages 4-5): Patrick McKiernan, Jesus Quintero Bernabeu, Muriel Girard, Giuseppe Indolfi, Eberhard Lurz, and Palak Trivedi. Opinion paper on the diagnosis and treatment of progressive familial intrahepatic cholestasis. Jan 2024. URL: https://doi.org/10.1016/j.jhepr.2023.100949, doi:10.1016/j.jhepr.2023.100949. This article has 36 citations and is from a peer-reviewed journal.
(marx2024practicalconsiderationsfor pages 1-2): Milena Marx, Steffen Hartleif, Johannes Hilberath, Christoph P. Berg, Ilias Tsiflikas, Stephan Singer, and Ekkehard Sturm. Practical considerations for odevixibat treatment in patients with progressive familial intrahepatic cholestasis: a single-center case series. Journal of Clinical Medicine, 13:7508, Dec 2024. URL: https://doi.org/10.3390/jcm13247508, doi:10.3390/jcm13247508. This article has 8 citations.
(mckiernan2024opinionpaperon pages 5-6): Patrick McKiernan, Jesus Quintero Bernabeu, Muriel Girard, Giuseppe Indolfi, Eberhard Lurz, and Palak Trivedi. Opinion paper on the diagnosis and treatment of progressive familial intrahepatic cholestasis. Jan 2024. URL: https://doi.org/10.1016/j.jhepr.2023.100949, doi:10.1016/j.jhepr.2023.100949. This article has 36 citations and is from a peer-reviewed journal.
(komaniecka2024transporterproteinsas pages 24-26): Nina Komaniecka, Sonia Maroszek, Maria Drozdzik, Stefan Oswald, and Marek Drozdzik. Transporter proteins as therapeutic drug targets—with a focus on sglt2 inhibitors. International Journal of Molecular Sciences, 25:6926, Jun 2024. URL: https://doi.org/10.3390/ijms25136926, doi:10.3390/ijms25136926. This article has 16 citations.
(ziccardi2026beyondthepump pages 1-3): Ilaria Ziccardi, Michela Zorzi, and Adamo Pio d’Adamo. Beyond the pump: the evolving molecular landscape of intrahepatic cholestasis. Diagnostics, 16:726, Feb 2026. URL: https://doi.org/10.3390/diagnostics16050726, doi:10.3390/diagnostics16050726. This article has 1 citations.
(ziccardi2026beyondthepump pages 3-4): Ilaria Ziccardi, Michela Zorzi, and Adamo Pio d’Adamo. Beyond the pump: the evolving molecular landscape of intrahepatic cholestasis. Diagnostics, 16:726, Feb 2026. URL: https://doi.org/10.3390/diagnostics16050726, doi:10.3390/diagnostics16050726. This article has 1 citations.
(OpenTargets Search: Progressive familial intrahepatic cholestasis): Open Targets Query (Progressive familial intrahepatic cholestasis, 21 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(henkel2019expandingetiologyof pages 2-4): Sarah AF Henkel, Judy H Squires, Mary Ayers, Armando Ganoza, Patrick Mckiernan, and James E Squires. Expanding etiology of progressive familial intrahepatic cholestasis. World Journal of Hepatology, 11:450-463, May 2019. URL: https://doi.org/10.4254/wjh.v11.i5.450, doi:10.4254/wjh.v11.i5.450. This article has 101 citations.
(mckiernan2024opinionpaperon pages 3-4): Patrick McKiernan, Jesus Quintero Bernabeu, Muriel Girard, Giuseppe Indolfi, Eberhard Lurz, and Palak Trivedi. Opinion paper on the diagnosis and treatment of progressive familial intrahepatic cholestasis. Jan 2024. URL: https://doi.org/10.1016/j.jhepr.2023.100949, doi:10.1016/j.jhepr.2023.100949. This article has 36 citations and is from a peer-reviewed journal.
(ziccardi2026beyondthepump pages 10-12): Ilaria Ziccardi, Michela Zorzi, and Adamo Pio d’Adamo. Beyond the pump: the evolving molecular landscape of intrahepatic cholestasis. Diagnostics, 16:726, Feb 2026. URL: https://doi.org/10.3390/diagnostics16050726, doi:10.3390/diagnostics16050726. This article has 1 citations.
(vinayagamoorthy2021newervariantsof pages 2-4): Vignesh Vinayagamoorthy, Anshu Srivastava, and Moinak Sen Sarma. Newer variants of progressive familial intrahepatic cholestasis. World Journal of Hepatology, 13:2024-2038, Dec 2021. URL: https://doi.org/10.4254/wjh.v13.i12.2024, doi:10.4254/wjh.v13.i12.2024. This article has 67 citations.
(vinayagamoorthy2021newervariantsof pages 10-11): Vignesh Vinayagamoorthy, Anshu Srivastava, and Moinak Sen Sarma. Newer variants of progressive familial intrahepatic cholestasis. World Journal of Hepatology, 13:2024-2038, Dec 2021. URL: https://doi.org/10.4254/wjh.v13.i12.2024, doi:10.4254/wjh.v13.i12.2024. This article has 67 citations.
(henkel2019expandingetiologyof pages 8-10): Sarah AF Henkel, Judy H Squires, Mary Ayers, Armando Ganoza, Patrick Mckiernan, and James E Squires. Expanding etiology of progressive familial intrahepatic cholestasis. World Journal of Hepatology, 11:450-463, May 2019. URL: https://doi.org/10.4254/wjh.v11.i5.450, doi:10.4254/wjh.v11.i5.450. This article has 101 citations.
(vinayagamoorthy2021newervariantsof pages 6-7): Vignesh Vinayagamoorthy, Anshu Srivastava, and Moinak Sen Sarma. Newer variants of progressive familial intrahepatic cholestasis. World Journal of Hepatology, 13:2024-2038, Dec 2021. URL: https://doi.org/10.4254/wjh.v13.i12.2024, doi:10.4254/wjh.v13.i12.2024. This article has 67 citations.
(ziccardi2026beyondthepump pages 4-5): Ilaria Ziccardi, Michela Zorzi, and Adamo Pio d’Adamo. Beyond the pump: the evolving molecular landscape of intrahepatic cholestasis. Diagnostics, 16:726, Feb 2026. URL: https://doi.org/10.3390/diagnostics16050726, doi:10.3390/diagnostics16050726. This article has 1 citations.
(henkel2019expandingetiologyof pages 10-11): Sarah AF Henkel, Judy H Squires, Mary Ayers, Armando Ganoza, Patrick Mckiernan, and James E Squires. Expanding etiology of progressive familial intrahepatic cholestasis. World Journal of Hepatology, 11:450-463, May 2019. URL: https://doi.org/10.4254/wjh.v11.i5.450, doi:10.4254/wjh.v11.i5.450. This article has 101 citations.
(mattiaccio2020molecularcharacterizationof pages 109-113): Alessandro Mattiaccio. Molecular characterization of gene defects associated with progressive familial intrahepatic cholestasis by next generation sequencing. ArXiv, Apr 2020. URL: https://doi.org/10.6092/unibo/amsdottorato/9386, doi:10.6092/unibo/amsdottorato/9386. This article has 0 citations.
(joneshughes2021epidemiologyandburden pages 11-12): Tracey Jones-Hughes, Jo Campbell, and Louise Crathorne. Epidemiology and burden of progressive familial intrahepatic cholestasis: a systematic review. Orphanet Journal of Rare Diseases, Jun 2021. URL: https://doi.org/10.1186/s13023-021-01884-4, doi:10.1186/s13023-021-01884-4. This article has 48 citations and is from a peer-reviewed journal.
(ziccardi2026beyondthepump pages 9-10): Ilaria Ziccardi, Michela Zorzi, and Adamo Pio d’Adamo. Beyond the pump: the evolving molecular landscape of intrahepatic cholestasis. Diagnostics, 16:726, Feb 2026. URL: https://doi.org/10.3390/diagnostics16050726, doi:10.3390/diagnostics16050726. This article has 1 citations.
(ziccardi2026beyondthepump pages 7-9): Ilaria Ziccardi, Michela Zorzi, and Adamo Pio d’Adamo. Beyond the pump: the evolving molecular landscape of intrahepatic cholestasis. Diagnostics, 16:726, Feb 2026. URL: https://doi.org/10.3390/diagnostics16050726, doi:10.3390/diagnostics16050726. This article has 1 citations.
(marx2024practicalconsiderationsfor pages 2-3): Milena Marx, Steffen Hartleif, Johannes Hilberath, Christoph P. Berg, Ilias Tsiflikas, Stephan Singer, and Ekkehard Sturm. Practical considerations for odevixibat treatment in patients with progressive familial intrahepatic cholestasis: a single-center case series. Journal of Clinical Medicine, 13:7508, Dec 2024. URL: https://doi.org/10.3390/jcm13247508, doi:10.3390/jcm13247508. This article has 8 citations.
(NCT03659916 chunk 1): Long Term Safety & Efficacy Study Evaluating The Effect of A4250 in Children With PFIC. Albireo, an Ipsen Company. 2018. ClinicalTrials.gov Identifier: NCT03659916
(mckiernan2024opinionpaperon pages 9-9): Patrick McKiernan, Jesus Quintero Bernabeu, Muriel Girard, Giuseppe Indolfi, Eberhard Lurz, and Palak Trivedi. Opinion paper on the diagnosis and treatment of progressive familial intrahepatic cholestasis. Jan 2024. URL: https://doi.org/10.1016/j.jhepr.2023.100949, doi:10.1016/j.jhepr.2023.100949. This article has 36 citations and is from a peer-reviewed journal.
(hupper2023surgicalversusmedical pages 10-12): Maria Noelle Hüpper, Judith Pichler, Wolf-Dietrich Huber, Andreas Heilos, Rebecca Schaup, Martin Metzelder, and Sophie Langer. Surgical versus medical management of progressive familial intrahepatic cholestasis—case compilation and review of the literature. Children, 10:949, May 2023. URL: https://doi.org/10.3390/children10060949, doi:10.3390/children10060949. This article has 9 citations.
(NCT07497724 chunk 1): Odevixibat Outcomes in Patients With PFIC Versus an External Control Cohort (OvEC-PFIC). Ipsen. 2026. ClinicalTrials.gov Identifier: NCT07497724
(NCT07191704 chunk 1): A Study to Assess the Genetic Variations in Bile Flow Disorders: Linking Progressive Familial Intrahepatic Cholestasis (PFIC)-Related Genes to Symptoms in Adults With Recurrent Cholestasis in Spain. Ipsen. 2025. ClinicalTrials.gov Identifier: NCT07191704
(NCT07497724 chunk 2): Odevixibat Outcomes in Patients With PFIC Versus an External Control Cohort (OvEC-PFIC). Ipsen. 2026. ClinicalTrials.gov Identifier: NCT07497724

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Inheritance

Subtypes

Pathophysiology

Histopathology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Biochemical Markers

Diagnosis

Prevalence

Differential Diagnoses

Clinical Trials

Source YAML

References & Deep Research

References

Deep Research

Disease Characteristics Research Template

Target Disease

Research Objectives

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Citation Requirements

Output Format

Progressive Familial Intrahepatic Cholestasis (PFIC): comprehensive disease-characteristics report

Executive summary

1. Disease information

Definition and classification

2. Etiology, risk, protective factors, and gene–environment interaction

Causal factors

Genetic risk

Environmental, lifestyle, infectious, and protective factors

3. Phenotypes

4. Genetic and molecular information

Variant interpretation

5. Environmental information

6. Mechanism and pathophysiology

Causal chain

Molecular profiling and advanced technologies

7. Anatomical structures affected

8. Temporal development

9. Inheritance and population

10. Diagnostics

Recommended work-up

Differential diagnosis

Screening

11. Outcome and prognosis

12. Treatment and current implementation

Supportive and pharmacological care

IBAT inhibition: leading targeted therapy

Surgery and transplantation

Practical treatment algorithm

Experimental and ongoing research

13. Prevention

14. Other species and natural disease

15. Model organisms and experimental systems

Expert interpretation and evidence gaps

Selected source index

Artifacts